No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Elastic behavior of plain and fiber-reinforced syntactic foams under compression
Abstract
Syntactic foams (SF) with 0, 0.9, 1.76, 2.54, 3.54 and 4.5 vol.% of E-glass fibres in the form of chopped strands were processed and subjected to compressive loading. It was found that introduction of chopped strand fibres into the syntactic foam system increases compressive modulus values. The values increased with the content of fibres in the system except for the one containing 3.54% of fibres, which showed a lower value than other fibre-reinforced systems, thus deviating from the trend. This exception was attributed to the difference in processing route adopted for this particular fibre-bearing foam. However, in general, the incorporation of chopped strand fibres improved the elastic property of the syntactic foam system without much variation in density as it is evident from the specific modulus values reported in this work.
... One study has reported significantly high void contents in glass fibers reinforced syntactic foam and resulted in lower composite's modulus [20]. Clustering of fibers in syntactic foams is the main reason, where the fibers failed to disperse uniformly in matrix which hindered by microspheres ( Figure 1). ...
... Clustering of fibers in epoxy syntactic foams[20]. ...
Syntactic foam is a low density but high compressive strength material. Insertion of fiber reinforcements had increases density of the syntactic foam. However, it has widened its application by the ability of properties tailoring with natural fibers. Influences of fiber length, fiber contents, types of fiber and slab orientation on properties have been reviewed in this paper. On the other hand, to reduce the dependence of high-cost microsphere, fiber reinforced macrosphere has introduced recently. “Rolling ball” and “electrostatic fiber flocking” methods found effectively to lower density and the latter method has better performance reserved. Yet no further information can be revealed currently. On the other hand, uneven properties of natural fibers were unflavored from the material selection. Nonetheless, it will be a “requirement” in future of composite materials innovation. This review paper served as a bird’s eye view for researchers to review the effect of fiber reinforcements in syntactic foams.
... Thus, the latter method was found to be more effective, as evident from the lower void content and good mechanical properties [123,124]. The compressive modulus also increased with the content of fibers in the system, except for the one containing 3.54% of fibers, which showed a lower value than other fiber-reinforced systems [125]. ...
... Karthikeyan et al. found that compressive modulus and specific compressive modulus increased with an increase in fiber concentration despite the presence of voids [125]. In another study, Karthikeyan et al. observed that fiber-free syntactic foams had a higher compressive strength than the fiber-bearing ones, whereas the moduli values did not differ much. ...
Syntactic foams are particulate polymer matrix composite materials consisting of hollow microspheres dispersed in a matrix. The matrix used in syntactic foams can be polymer, metal, or ceramic. Polymer matrices, particularly the thermosetting polymers, have been the most widely accepted matrices in syntactic foams. From the processing and application point of view, thermosetting syntactic foams have many advantages compared to thermoplastic ones. This chapter deals with syntactic foams based on various thermosetting resins and the chemistry of the resin systems. The resin systems are mainly phenolic, epoxy, cyanate ester, siloxane, polybenzoxazine, bismaleimide, and their blends. Apart from a brief chemistry of the parent resin systems, their syntactic foams have been described in detail. The aspects discussed are their processing, physical, thermal, and mechanical properties, applications, and degradation. Their properties can be engineered by a choice of matrix, microcell structure and its concentration, reinforcement, toughners, etc. While the thermal and thermo-physical characteristics are dictated by resin, mechanical and fracture characteristics are decided by both components. While epoxy, cyanate ester, and other such compounds provide structural syntactic foams, phenolics and their new generation versions provide thermo-structural materials. Syntactic foam ablators have made possible interplanetary space missions. Novel engineering concepts like lightweight self-healing give scope for extended applications of these systems. The recent advances in these areas are also discussed. These special materials with high specific strength are slated to replace conventional structural and thermo-structural materials in related engineering applications ranging from domestic to aerospace and defense.
... Một số lượng lớn các nghiên cứu đã được công bố về tính chất cơlý của loại vật liệu này. Các đặc tính nén được nghiên cứu rất chi tiết bởi vì hầu hết các ứng dụng của bọt thủy tinh nằm trong cấu trúc của vật liệu hàng hải, nơi nén thủy tĩnh là lực phổ biến nhất tác dụng lên vật liệu [1][2][3][4]. Bọt thủy tinh còn được sử dụng làm vật liệu cách nhiệt trong việc phục hồi dầu từ các giếng dầu siêu sâu và sử dụng trong các hệ thống bảo vệ nhiệt. Các nghiên cứu về tính dẫn nhiệt có thể kể đến trong [5][6][7]. ...
Vật liệu Composite có cốt liệu là vi cầu thủy tinh rỗng nền epoxy rất được quan tâm nghiên cứu trong thời gian gần đây do ngoài những ứng dụng làm vật liểu nổi của hàng hải, nó còn được ứng dụng làm vật liệu mật độ thấp trong điện tử. Bài báo nghiên cứu xây dựng mô hình số PTHH để tính toán hằng số điện môi của vật liệu Composite có cốt liệu là vi cầu thủy tinh rỗng đặt trong nền epoxy (vật liệu bọt thủy tinh), khi tỉ lệ thể tích vi cầu thủy tinh biến đổi từ 0 tới 60%, độ dày thành thủy tinh và bán kính ngoài thay đổi. Mô hình số xây dựng với vật liệu tuần hoàn có nhân tử tuần hoàn là lập phương đơn giản, lập phương tâm khối, lập phương tâm mặt với sự hỗ trợ của phần mềm có mã nguồn mở Cast3m. Trên nhân tuần hoàn, các điều kiện tuần hoàn cho cảm ứng điện trường và trường điện thế vi mô được thỏa mãn. Sau đó, áp dụng tính toán cho bốn dạng hạt của vi cầu thủy tinh là K1, K20, S38HS và S60HS sản xuất tại công ty 3M China. Kết quả số đạt được so sánh với kết quả của đường bao Hashin-Strikman, với kết quả theo công thức giải tích, kết quả thực nghiệm của các nghiên cứu trước để kiểm tra độ tin cậy. Kết quả của nghiên cứu này bổ sung thêm lý thuyết tính toán, dự báo hằng số điện môi hiệu dụng của vật liệu bọt thủy tinh
... [4] Most published research on syntactic foams focused on those without fiber reinforcements. [5,[11][12][13][14][15][16] Studies reported on hybrid composites with densities below 1.0 g/cm 3 , but these were achieved with GF loadings less than 4.51 vol% [9,10,[17][18][19][20][21][22] which means the composites have low mechanical properties. Ferreira, et al. examined the flexural stiffness of nonreinforced as well as glass and carbon fiber reinforced syntactic foams. ...
Sheet molding compounds (SMC) are commonly used in automotive applications as they lead to increased fuel efficiency of vehicles due to their high strength to weight ratios. This study focuses on understanding the effect of replacing calcium carbonate (CaCO3) with hollow glass spheres (HGS) in an unsaturated polyester resin matrix SMC composite with the ultimate goal to further reduce density without compromising performance. The resulting glass fiber (GF)‐reinforced syntactic foam laminate composites with GF content ranging from 10 to 15 vol% have densities of 1.2 and 1 g/cm³, respectively. This is significantly lower than the industry standard SMC density of 1.9 g/cm³. The HGS parameters of interest are primarily HGS type (S28HS and S32HS), loading level (33–44 vol%), and surface functionalization (methacrylsilane). The syntactic foam composites were characterized in terms of tensile, flexural, and impact properties, and their properties were compared to those of standard density SMC. As expected, the flexural, tensile, and impact properties were compromised with a decrease of density. However, they were higher than the corresponding properties of low‐ and ultra‐low density composites reported in the literature, as we were able to add higher GF content in these low‐density SMC formulations. It was also concluded that methacrylsilanized surface treated HGS showed promise in maintaining the mechanical properties, especially at high sphere loadings. The impact energy of the low‐density formulations was relatively unaffected by HGS type or loading.
... These materials were combined together using a simple casting technique. It would provide different approaches in the production of syntactic foam compared to previously studied foams [80][81][82]. The ''rolling ball method'' in the previous papers can prepare GFR-HEMS, GR-HEMS or CR-HEMS automatically using a rolling ball machine, and graphite, glass fiber or carbon fiber was added into the epoxy hollow sphere to improve the compressive strength of hollow epoxy macrosphere. ...
Epoxy syntactic foam (ESF) materials are widely used in marine detection systems, deep sea diving equipment, offshore oil exploration and other deep sea development and exploration equipment due to their superior properties such as low density, high compressive strength and low water absorption. The composition and preparation process of the ESF material determine the structure of the ESF material, the structure determines the performance, and the performance determines the application of the ESF material. The review describes the epoxy-based syntactic foams from the following aspects: definition and classification, preparation methods, properties and influencing factors, application, problems and development trend. The forming methods of hollow glass microspheres (solid-state powder processing method and liquid atomization method), hollow polymer microspheres (spray drying method) and centimeter-sized hollow spheres (rolling ball method and electrostatic fiber flocking method) are introduced in detail, as well as the casting molding method, vacuum molding method and pressure molding method of the syntactic foams. The main objective of this paper is focusing on the influence of various factors including filler content, graded structure, clay material, carbon material, fiber-reinforced material, molding process, material structure (sandwich structure) on the compressive strength and the density of the syntactic foam in detail. The paper may also provide some guidance to the preparation of ESF used in deep sea development and exploration equipment.
... In epoxy-resin syntactic foams, carbon fiber has been shown to increase the mechanical strength of the composite material, particularly in tension [4,[15][16][17][18][19]. These systems often add 1-5% of carbon fiber or carbon nanofibers to the existing foam, and the addition of the fibers strengthens the material through crack bridging, crack blunting, and the transfer of load from the matrix to the fibers [15,[19][20][21][22][23]. While adding carbon or silica (SiO 2 ) fibers has consistently been shown to improve the mechanical properties of epoxy-resin syntactic foams [15], the mechanisms that allow for this phenomenon would not be present in a syntactic foam where the matrix is a coating on the reinforcement rather than a bulk material. ...
Glass microballoons (GMBs) are commonly used to reduce the density of epoxy-resin syntactic foams, but they can also be applied as a low-cost and lightweight catalyst support. In order to create a practical structure that can be utilized for such an application, a ceramic syntactic foam consisting of glass microballoons (GMBs) and silica nanofibers (NFs) with or without TiO2 binder was synthesized. The mechanical strength, phase composition, high-temperature deformation behavior, and microstructure of the composite material were analyzed using bending and compression tests, X-ray diffraction, and scanning electron microscopy, respectively. It was determined that the addition of nanofibers improves the thermal behavior and mechanical strength of the composite material during and after processing. The composite materials maintained up to 70% anatase titania at as high as 700 °C, and this indicates that they can be of interest for high-temperature catalysis. No high-temperature deformation of GMBs was observed at 800 °C or 1000 °C, whereas XRD of samples coated with TiO2 using a titanium oxysulfate solution indicated the formation of cristobalite above 800 °C. Preliminary methane-reforming experiments were performed with NiO-seeded titania-coated GMBs, uncoated GMBs, and an uncoated silica fibers/GMBs composite. Uncoated GMBs and titania-coated GMBs had a low conversion ratio of methane to products, but the uncoated composite structure showed high conversion of the reactants at high temperatures, indicating that it may be suitable catalyst support in this reaction.
... Glass fiber is one of the most studied reinforcement material that was used for enhancement of epoxy syntactic foams. Studies showed that various mechanical properties were improved including compressive strength, 17,18 compressive modulus, 19 flexural strength, 20,21 flexural modulus, 22,23 and impact strength 24 with the incorporation of glass fiber into the epoxy syntactic foams. Using fiberglass mesh in epoxy syntactic foams also improved the flexural properties. ...
The study aims to produce poly(methyl methacrylate) (PMMA)‐based lower density syntactic foams with hollow glass microspheres (HGMs) and to improve their mechanical properties by the addition of polyhedral oligomeric silsesquioxanes (POSSs) while maintaining the thermal properties of the neat polymer. First to understand the effect of POSS addition, PMMA–POSS composites with octaisobutyl and octaphenyl POSS were produced through extrusion. Higher relative flexural and impact strengths were obtained with POSS addition to PMMA. Obtaining more enhanced properties with octaphenyl POSS, PMMA‐HGM‐POSS hybrid syntactic foams were prepared with this additive. In general, the specific flexural strength and modulus of the PMMA syntactic foams were improved with the POSS loading, while the lower density and thermal properties of the PMMA syntactic foams were maintained. PMMA hybrid syntactic foams with 15 wt % HGMs and 0.25 wt % POSS exhibited 37.6% improvement in the specific flexural modulus with respect to the neat PMMA. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48368.
... By altering a great variety of parameters like the microballoon and matrix materials, microballoon density, microballoon size, wall thickness, size distribution and volume fraction, it is possible to characterize the properties of syntactic foams [4][5][6]. ...
The aim of this study was to research the effect of carbon nanofiber (CNF), the microballoon (MB) volume fraction and its density on both the vibration properties and impact behavior of carbon nanofiber – reinforced syntactic foam. Twelve different types of syntactic foam were produced with two different CNF contents, two different MB densities and two different MB volume fractions. Neat epoxy, syntactic foams with and without carbon nanofiber were manufactured for characterization by comparing each other in terms of mechanical and dynamic properties. With the free vibration tests, natural frequencies and damping ratios were investigated. Besides vibrations tests, low-velocity impact and tensile tests were conducted on the syntactic foams. Analyses of the results were performed on the effect of the volume fraction of additives and MB density on the vibration, impact and tensile behavior of the syntactic foams. In addition, SEM was used to understand the microstructure of the samples tested. Vibration results presented that the presence of carbon nanofiber enhanced strength but was not effective on damping, while low-velocity impact, and tensile test results also demonstrated the same trend.
... Amongst hollow fillers, glass microballoons (HGM) are most extensively used [11][12][13][14], due to their low coefficient of thermal expansion and chemical inertness. Amongst all polymeric matrices, epoxy has been extensively studied [15][16][17][18][19][20], in view of its excellent mechanical properties and low shrinkage [21,22]. ...
In this paper, we discuss the chemorheology of epoxy based syntactic foams containing glass microballoons of varying density, with an aim of establishing the effect of microballoon loading on its processability. The primary objective is to determine the maximum microballoon loading that disperses uniformly in the resin without the aid of any diluent. The viscosity and dynamic mechanical properties of epoxy formulations containing varying amounts of glass microballoons were established by parallel plate rheometry. Our studies reveal that solventless processing of formulations with microballoon loading > 60% poses practical difficulties due to prohibitively high viscosities, although a packing efficiency of 74% is theoretically allowed in the case of hexagonal close packing. The presence of microballoons does not alter the curing mechanism. The mechanical properties of syntactic foams were inversely proportional to the loading and type of glass microballoons.
... As a result, the diameter of the microsphere can increase by several dozen times after the expansion process [19][20][21]. Since the pore expansion during foaming process is not such integrated with the curing reaction, employing expandable microsphere as the foaming agent provides wide latitude in matrix choices and great flexibility of formulation [22]. ...
Herein, the acoustically and thermally insulating epoxy foams were prepared using non‐traditional expandable microspheres. The effect of foaming temperature and microsphere content on the morphology, the mechanical strength, the thermal insulation and acoustical properties of the epoxy foams was investigated in detail. It can be found that the closed pores can be partially opened by adjusting the preparation parameters, which is also accompanied by obvious changes in acoustic and thermal insulation properties. By giving high‐content expandable microspheres above 2 wt%, the epoxy foams exhibit highly thermal insulation, and meanwhile achieving an acceptable mechanical property. The results convince us that such light‐weight epoxy foams will outshine as the promising structural, soundproof and heat‐insulated material in many multifunctional systems, such as buildings, vehicles and aircrafts. POLYM. ENG. SCI., 2018.
... In order to improve the properties of the foams, various types of short fibers have been used to reinforce the syntactic foam matrices. For example, glass and aramid fiber bearing syntactic foams have been used to improve compressive strength and modulus properties of syntactic foams [4][5][6]. The addition of short glass fibers has also significantly increased the flexural strength and modulus of syntactic foams [7,8]. ...
Benefits of employing graphene nanopletlates (GNPLs) in composite structures include mechanical as well as multifunctional properties. Understanding the impedance behavior of GNPLs reinforced syntactic foams may open new applications for syntactic foam composites. In this work, GNPLs reinforced syntactic foams were fabricated and tested for DC and AC electrical properties. Four sets of syntactic foam samples containing 0, 0.1, 0.3, and 0.5 vol% of GNPLs were fabricated and tested. Significant increase in conductivity of syntactic foams due to the addition of GNPLs was noted. AC impedance measurements indicated that the GNPLs syntactic foams become frequency dependent as the volume fraction of GNPLs increases. With addition of GNPLs, the characteristic of the syntactic foams are also observed to transition from dominant capacitive to dominant resistive behavior.
... These materials were combined together using a simple "molding method". Thus it would provide different approach in the production of syntactic foam compared to previously studied foams [49][50][51]. Centimeter-sized GR-HEMS could further reduce the density of the syntactic foam on the basis of epoxy/HGMS composite. "Rolling ball method" in this paper can prepare GR-HEMS automatically using a rolling ball machine. ...
Graphite reinforced hollow epoxy macrospheres (GR-HEMS) and hollow glass microspheres (HGMS) were used to prepare three phase epoxy syntactic foam (ESF) using “molding method”, and the physical and mechanical properties of ESF were also studied and investigated. An innovative “rolling ball method” was implemented in the GR-HEMS preparation process. The performance tests show that higher GR-HEMS stacking volume fraction, lower GR-HEMS thickness, higher GR-HEMS diameter, higher HGMS volume fraction, lower HGMS density are beneficial to reducing the density of ESF, but the effects of the five factors on the strength of ESF are the opposite. Therefore, in order to obtain “high strength and low density” ESF composites, the various factors should be considered to achieve a balance of the strength and the density. Scanning electron microscope (SEM) shows that the “rolling ball method” can make graphite form a graphite spherical x-y network throughout the macrosphere wall, which can make GR-HEMS and ESF have great compressive strength. The ESF (450 kg/m³, 20.75 MPa) can withstand the 2075 meters water pressure and provide 550 kg/m³ buoyancy, which can give some advice to the preparation of buoyancy material used in deepwater oil exploration.
... Epoxy foams have attracted much attention due to their excellent properties, including lightweight, low moisture absorption, good thermal and chemical stability, and high mechanical properties [1,2]. generation occurs simultaneously with the formation of three-dimensional cross-linking networks in the epoxy foaming process. ...
The foaming behavior of a diglycidyl ether of bisphenol-A (DGEBA) epoxy resin–anhydride hardener system at varying accelerator (tertiary amine) concentration, using chemical foaming agent (CFA), was investigated. The microstructure of foams revealed a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher curing rate by varying accelerator contents, whereas not the same by varying foaming temperatures. The curing of epoxy system was studied by a differential scanning calorimetry, while the decomposition process of CFA was investigated by the foaming pressure measurement. Kinetics data showed that the addition of CFA in epoxy system produced obvious influence on the curing process of epoxy mixture; meanwhile, the decomposition reaction of CFA in epoxy system showed an autocatalytic behavior, which can be well predicted by Šesták–Berggren equation. Reaction rate constants of the curing of epoxy foaming system (kt) and the degradation of CFA (kd) were calculated, and the competition between these two simultaneously occurring reactions was expressed by the kinetic parameter kt/kd. The high specific value of kt/kd, which can be tuned by both accelerator concentration and foaming temperature, indicated that the curing rate was much higher than degradation rate of CFA. By further accelerating the curing rate in the foaming stage, a new two-step method was introduced to fabricate microcellular epoxy foam at relatively low viscosity.
... [6][7][8][9][10][11] Furthermore, the mechanical and fracture properties of the epoxy foam were investigated under compressive, tensile, and thermal degradation. 3,4,[12][13][14][15][16][17][18] In particular, Takiguche et al. (2008) produced epoxy foams using an azodicarbonamide (ADCA) chemical blowing agent. They reported that the mean diameter of the bubbles decreased with increasing precuring time. ...
The effects of the curing and blowing agent concentration in an epoxy resin were investigated using rheological, mechanical, and optical methods. The curing time from the time sweep test decreased with increasing amount of curing agent at the fixed blowing agent concentration. On the other hand, with increasing blowing agent at a fixed curing agent concentration, the curing time showed a local minimum value. Minimization of the curing time is very useful for reducing the processing time. Axial normal forces as a function of time showed a relationship between the contraction force by the curing process and the expansion force by foaming process. From the axial normal force measurements, it could be categorized quantitatively into three parts: the curing dominant region (negative axial normal force development), transition region, and the foaming dominant region (positive axial normal force development). At the transition region, the axial normal force development was delayed because the foaming process was disturbed by the contraction. Mechanical and structural analysis were conducted for the fully cured and foamed epoxy resin. The completely developed epoxy foams with the high curing agent concentration become brittle. On the other hand, they contained well-distributed unit cell foams inside. This is because the fast curing process interrupts the coalescence of the closed foams. Overall, the optimal curing and blowing agent concentration for the epoxy resin could be determined from rheological analysis during the process and mechanical and structural analysis for fully cured and foamed epoxy resin.
... Numerous studies and research activities on the mechanical properties of fiberreinforced syntactic foams have mainly focused on quasi-static properties, such as tension, compression, and flexural properties, as well as their associated fracture mode behavior [Alonso et al., 2006;Huang et al., 2006;Karthikeyan et al., 2004;Nguyen and Gupta, 2010;Poveda and Gupta, 2014;Poveda et al., 2013]. To use syntactic foams in advanced applications such as crash or impact protection, blast resistance, and aeronautical and space structures, understanding their behavior under high loading rates is crucial. ...
The quasi-static and dynamic compression responses and failure of fiber-reinforced syntactic foams were investigated. The role of fiber volume fraction on the compression response of syntactic foams was examined in terms of mechanical behavior and energy absorption under both quasi-static and dynamic conditions. Results showed that the mechanical behavior and energy absorption of the reinforced specimens increased with increasing fiber volume fraction. The syntactic foams exhibited distinct strain rate sensitivity; and their yield strength and elastic modulus increased by 41.1% and 85.1%, respectively, as strain rate increased from 0.0011 s(Formula presented.) to 1070 s(Formula presented.). The deformation and failure processes of the syntactic foams were also examined, and the underlying mechanisms were discussed.
... Flexural and tensile strength of foams can be enhanced by incorporation of randomly dispersed short macro fibres. The effect of such reinforcement on both static and dynamic properties was investigated [9][10][11]. The effect of the addition of short fibre reinforcements on the flexural stiffness, compressive strength, fracture toughness and absorbed impact energy were studied on foam with a microsphere content of up to 50% and with fibre reinforcement up to 1.2 vol.% by Ferreira at all [11]. ...
Due to explosion, and insufficient energy absorbing capabilities of civil building structures, many structures collapsed, which can be connected with losses of human lives and properties. One way how to improve the blast resistance of the structure is using of sacrificial cladding structures with the core made of high blast absorbing material. Foams based on lightweight porous particles and resins are materials with high potential of impact energy absorption. This article describes the mechanical properties of the foams reinforced with carbon nanofibers and nanotubes. Specific porous lightweight foam with high volume fraction of microspheres (70 vol.%) was prepared and modified by 1–5 vol.% of multi-wall carbon nanotubes and nanofibers (separately). The compressive and flexural strength tests were conducted at quasi-static load. Split Hopkinson Pressure Bar apparatus was used to obtain high velocity characteristics of the materials. The relative absorbed energy was calculated to assess the relation between the composition of the material and its shock wave attenuation capacity. The mixtures containing carbon nanofibers exhibited an increasing trend in the energy absorption capacity with increasing nanoparticle content up to 4 vol.%. The addition of carbon nanotubes also increased absorbed energy (again up to 4 vol.%, crossing this concentration, the significant drop was observed). Comparing the values of the relative absorbed energy, the carbon nanofibers composites prevail over the nanotubes modified ones.
... Flexural and tensile strength of foams can be enhanced by incorporation of randomly dispersed short macro fibres. The effect of such reinforcement on both static and dynamic properties was investigated [11][12][13]. ...
The effect of multi-wall carbon nanotubes and nanosilica (nano SiO2) content on physico-mechanical properties of glass microspheres-epoxy resin composite, designed for blast energy absorbing applications, was evaluated experimentally. Specific porous lightweight foam with high volume fraction of microspheres (70 vol.%) was prepared and modified by 1 to 5 vol.% of multi-wall carbon nanotubes and nanosilica. Compressive and flexural strength tests were conducted at quasi-static load. Split Hopkinson Pressure Bar apparatus was used to obtain high velocity characteristics of the materials. The relative absorbed energy was calculated to assess the relation between the composition of the material and its shock wave attenuation capacity. The mixtures containing nanosilica exhibited an increasing trend in the energy absorption capacity with increasing nanoparticle content up to 4 vol.%. The addition of carbon nanotubes also increased absorbed energy (again up to 4 vol.%, a significant drop was observed at higher concentrations). Comparing the values of the relative absorbed energy, the carbon nanotubes composites prevail over the nanosilica modified ones.
... Addition of the short and long carbon and glass fibers have shown to improve the tensile, compressive, flexural strength, fracture toughness, and thermal properties of syntactic foams. [17][18][19][20] The tensile strength, Young's modulus, and plane strain fracture toughness of syntactic was increased by 40, 115, and 95%, respectively, in presence of 3 wt% of carbon fiber. 18 Natural fibers are another alternative to be considered for reinforcement of syntactic foams. ...
Syntactic foams are light-weight, energy absorbing structural composites consisting of hollow microparticles (glass microballons in this study) embedded in a resin matrix. The effect of different fillers has been studied to improve the mechanical properties of syntactic foams. In this study, short sisal fiber was selected as filler to investigate its effect on viscoelastic properties of syntactic foams. Samples were prepared using four different volume fractions of sisal fibers (0%, 1.5%, 2.5%, and 3.5%), while the volume fraction of glass microballoons was kept constant. Samples were then characterized using dynamic mechanical analyzer (DMA). Storage and loss modulus, complex viscosity, and tan-delta were recorded as function of temperature. Glass transition temperature (Tg) of the samples was determined based on the loss modulus curve as well as tan-delta following ASTM E1640-04 standard. Results showed improvement in storage and loss moduli in glassy region (30°C) up to 12% and 300%, respectively. In rubbery region (150°C), the storage modulus of sisal fiber syntactic foam was three orders of magnitude higher than plain ones. Decrease in the tan-delta peak also indicated improved interfacial bonding by addition and increase in the content of sisal fibers.
... Reinforcing fibres and other inorganic fillers must be therefore included in the ablative formulation to improve the char stability [9]. Also, the incorporation of fibrous reinforcements is a known method for strengthening syntactic foams [10][11][12][13]. In view of this, silica fibre reinforced, phenolic syntactic foams are considered as appropriate candidates for atmospheric re-entry TPS applications. ...
Medium-density foam composites based on silica fibre-filled phenolic syntactic foams were processed and characterised for mechanical, dynamic mechanical and thermophysical properties, and they were evaluated as Thermal Protection Systems (TPSs) materials by way of experiment and simulated thermal response studies under atmospheric re-entry conditions. Ablative composites with different specific gravities were processed by varying the volume fraction of the constituents. Tensile strength increased with fibre concentration and showed a maximum corresponding to 15% by volume of silica fibre and decreased on further addition, whereas flexural and compressive strength increased with increase in volume percentage of silica fibre. The mechanical properties of the fibre reinforced system were superior compared to those of bare phenolic syntactic foams. Storage modulus was considerably improved by the addition of fibre whilst the glass transition temperature was unaffected. The compositional dependency of the ablative composites on their thermophysical properties and thermal degradation behaviour was also examined. The thermal response of the ablatives was studied by simulating a moderate atmospheric re-entry heat flux history on the specimen with a maximum heat flux of about 15–18% of the stagnation heating. The thermal response was measured, and the material surface behaviour, mass loss and flammability were studied. For fibre fractions corresponding to various specific gravities, the thermal simulation experiments were studied, and it was observed that the char strength and its structural integrity were satisfactory for a specific gravity of 0.5. The maximum backwall temperature measured was 110 °C for a test duration of 500 s, and this meets the structural temperature constraint of 150 °C at the interface. The thermal response was numerically modelled, and fairly good comparison was obtained with the experimental results. This validated the accuracy of the measurement of the thermophysical properties and delivered the medium-density ablative TPS system qualified for application in atmospheric re-entry.
Journal of Materials ScienceJournal of Materials Science Look
Inside
Article Metrics
Citations 7
Reference tools
Export citation
Add to Papers
Other actions
Register for Journal Updates
About This Journal
Reprints and Permissions
Share
Share this content on Facebook Share this content on Twitter Share this content on LinkedIn
Related Content
... An extensive variety of polymer, metal and ceramic matrix syntactic foams has been studied in the previous published literature. In polymer matrix syntactic foams, epoxy resins are most commonly used as matrix resin, due to the widespread use of these resins in aerospace applications [9][10][11][12][13][14][15][16][17][18]. ...
... Thus it provides a different approach in the production of a syntactic foam compared to previously studied foams. [34][35][36] Centimetersized GFR-HEMS could further reduce the density of the syntactic foam on the basis of the epoxy/HGMS composite. The macrosphere preparation method oen is the secret of the marine equipment production company. ...
Glass fiber reinforced hollow epoxy macrospheres (GFR-HEMS) and hollow glass microspheres (HGMS) were used to prepare a three phase epoxy syntactic foam (ESF) in this study. An innovative “rolling ball method” was implemented in the preparation of GFR-HEMS where expanded polystyrene (EPS) beads were used as an initiation template. The EPS beads were coated with the epoxy resin and glass fiber using the “rolling ball method”, and these coated EPS beads were later cured and post-cured at high temperature which caused the EPS beads to shrink thus producing a hollow macrosphere structure. The effects of the volume fraction of the GFR-HMES, the wall thickness of the GFR-HEMS and the volume fraction of the HGMS on the compressive properties were discussed to find a comprehensive understanding of the structure–property relationship between the epoxy matrix and sphere fillers. Scanning electron microscopy (SEM) shows that the “rolling ball method” can make glass fibers form a fiber spherical x–y network throughout the macrosphere wall, which can make the GFR-HEMS and three phase ESF have great compressive strength. The ESF (570 kg m−3, 27.3 MPa) can withstand 2730 meters water pressure and provide 430 kg m−3 buoyancy, which can give some advice to the preparation of buoyancy material used in deepwater oil exploration.
... It has been confirmed that MMSF possesses excellent mechanical properties compared with traditional metal foams, e.g. high specific strength and stiffness, good energy absorption capacity, etc. [1][2][3][4]. For these reasons, MMSF has been widely used in automotive, aerospace, military vehicles and other industrial fields [5]. ...
Closed-cell AZ31 magnesium alloy foams with different percentages of hollow ceramic microspheres (CMs) are synthesized using modified melt foaming method. The distribution of CMs is investigated and also the effect of CMs on the foaming behaviors (specifically for porosity and pore size) and quasi-static compressive behaviors of Mg-based composite foams are characterized. The results show that CMs distribute in cell walls homogeneously and most of them are penetrated by magnesium alloy melt. In addition, the mean pore size declines with the increase of CMs percentage. Moreover, the overall porosity of the foams increases first and then decreases with the increase of CMs content, and the variation tendency is more obvious when the foaming temperature is lower (namely 680 °C). Besides, proper percentage of CMs changes the compression fracture mode of the foams from brittleness to ductility. OM/SEM/EDS/XRD detections and finite element analysis are applied to explain the reasons.
... These materials were combined together using a simple casting technique. Thus it would provide different approach in the production of syntactic foam compared to previously studied foams [21][22][23]. ...
The present study focuses on the preparation and characterization of three phase epoxy syntactic foam (ESF) filled with carbon fiber reinforced hollow epoxy macrospheres (CFR-HEMS) and hollow glass microspheres (HGMS). The ESF was produced by embedding CFR-HEMS into a mixture of epoxy-hardener and 30 wt% HGMS. An innovative approach and simple procedure was implemented in the preparation of CFR-HEMS where expanded polystyrene (EPS) beads were used as initiation template. The EPS beads were coated with epoxy resin and carbon fiber using “rolling ball method,” and these coated EPS beads were later cured and post-cured at high temperature which will shrink the EPS beads thus producing a hollow macrosphere structure. The compressive property of ESF was characterized and the mechanical model was issued. The ESF (450 kg/m3, 30.74 MPa) can withstand 2049 m water pressure and provide 550 kg/m3 buoyancy, the higher strength are due to the fiber spherical x–y network throughout the macrosphere epoxy matrix, which can give some support to the preparation of buoyancy material used in deepwater oil exploration. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
... An extensive variety of polymer, metal and ceramic matrix syntactic foams has been studied in the previous published literature. In polymer matrix syntactic foams, epoxy resins are most commonly used as matrix resin, due to the widespread use of these resins in aerospace applications [9][10][11][12][13][14][15][16][17][18]. ...
This paper focuses on the comparison of various types of matrix
materials and their mechanical properties for development of syntactic
foams for marine applications. Generally, syntactic foams are close pore
foams fabricated by the mechanical mixing of hollow microsphere
particles in a polymeric matrix resin. From the literature review, it
was found that there are several polymeric resins that have been used
for development of syntactic foams such as epoxy, cyanate ester,
polypropylene, polysialate and vinyl ester. In this paper, a comparative
discussion is presented on the mechanical properties of hollow glass
particles mixing with polymeric resins for development of syntactic
foams for the use of these composites in bulk applications such as
marine structures.
An expandable and Fire, Smoke, and Toxicity (FST) compliant epoxy foam is proposed as an interesting alternative to Nomex® honeycomb cores for the development of Multi‐Functional Structures (MFS). The paper first analyzes the processing conditions using several experimental techniques as differential scanning calorimetry (DSC), rheology, and expansion in a closed volume in order to evaluate the reaction kinetics, the chemorheological behavior, and the expansion kinetics of the material. The experimental data are used to identify several empirical models describing the material processing behavior and finally plotting the isothermal time–temperature transformation (TTT) diagram. A typical curing cycle for the foam is used to describe the evolution of the material parameters during the curing process. The fully cured foam is then characterized using optical and laser microscopy in order to identify its cell size distribution and density. Quasi‐static and dynamic machines are used to evaluate its mechanical and dynamical properties. The time–temperature equivalence is finally used to plot the master's curves of the material, representing the evolution of the material viscoelastic properties as a function of the frequency.
Generally, foamed epoxy resin prepared by chemical method has relatively large average cell size and low cell density, resulting in low mechanical properties and poor heat resistance. In this work, a new type of composite foaming agent (CFA) was prepared by filling the chemical foaming agent 4,4′‐bisoxybenzenesulfonyl hydrazide (OBSH) into microporous silica microspheres (MSMs), and then used for epoxy resin foaming research. The effects of curing agent diethylenetriamine (DETA) and CFA contents on cell density and size were also discussed. The best epoxy resin foaming sample has a cell density of 10⁶ cells cm⁻³ with an average cell diameter of 65 μm, and a high compressive strength of 34 MPa as well as a good heat resistance. These results indicate the potential application of CFA in epoxy resin foaming area.
In this chapter, we first reviewed the various crack self-healing strategies. We then focused on self-healing of thermosetting shape memory polymer (SMP) composite according to the close-then-heal (CTH) healing strategy. Three types of composite structures were prepared, including thermosetting SMP-based syntactic foam cored sandwich, grid stiffened thermosetting SMP-based syntactic foam cored sandwich, and 3D woven fabric reinforced thermosetting SMP based syntactic foam composite. The prepared fiber-reinforced composite panels were repeatedly impact damaged and healed according to the CTH scheme. The healing efficiency was evaluated per relevant mechanical strength tests. Damage sensing by percolated carbon nanotube network was also investigated hereby. The comprehensive experimental program confirms that the CTH scheme can heal structural-length scale cracks repeatedly, efficiently, timely, molecularly, and have a potential to heal autonomously.
Syntactic foams are particulate-filled composite materials consisting of hollow microspheres dispersed in a matrix. The matrix used in syntactic foams can be polymer, metal, or ceramic. Polymer matrices, particularly the thermosetting polymers, have been the most widely used matrices in syntactic foams. This chapter deals with syntactic foams based on various thermosetting resins. The resin systems mainly employed in syntactic foams are epoxy, phenolic, cyanate ester, silicone, etc. The properties of syntactic foams can be engineered by proper choice of matrix, microsphere structure and its concentration, reinforcement, tougheners, etc. While the thermal and thermophysical characteristics are dictated by resin, mechanical, and fracture characteristics are decided by both components. While epoxy, cyanate ester, etc. provide structural syntactic foams, phenolics, and their new generation versions provide thermostructural materials. Novel engineering concepts like lightweight self-healing give scope for extended applications of these systems. Syntactic foams with high specific strength are slated to replace conventional structural and thermostructural materials in related engineering applications ranging from domestic to aerospace and defense.
Traffic density, the number of vehicles per unit length of the road, is one of the basic properties of a traffic stream. One way to detect traffic congestion before it happens is to predict near future traffic density. Traffic density data is a time series by nature, and as it is known, various statistical methods or machine learning methods can be used in the forecasting of time series. In this study, for traffic density forecasting, a forecasting model is generated based on a hybrid artificial neural network approach, which was proposed in one of our previous studies. In this approach, the parameters of the artificial neural network are optimized using a biased random key genetic algorithm. To test the proposed forecasting model, the hourly traffic density data of Istanbul is used. In addition, the proposed approach
is compared with the forecasting models based on the most used machine learning models
Polymer syntactic foams are a class of polymer composites prepared by incorporation of hollow microballoons in a polymer matrix. The advantageous feature of this class of foams is their tailor-made properties by changing the volume fraction of hollow fillers and matrix. The present study deals with the preparation and properties of epoxy-glass microballoon syntactic foams containing 40–60% (v/v) of glass microballoons. Halloysite nanotubes (HNTs) (0.1–0.5% v/v) have been used as reinforcement to enhance the mechanical properties while maintaining a constant filler percentage (40% v/v) for all compositions. Results indicate significant improvement in quasi-static mechanical properties at 0.3% v/v HNTs. Compressive toughness, indicated by the area under stress-strain curve increases by ∼60% signifying higher energy absorption due to incorporation of HNTs. The present study highlights the efficacy of HNTs in reinforcing epoxy-glass microballoons syntactic foams.
It is generally accepted that matrix pores in the hollow glass microspheres (HGMs)/resin-based composites prepared using stir-casting method (SCM) seriously affect its performance. In this paper, HGMs preforms were prepared using sintering method, and co-continuous HGMs/epoxy resin syntactic foams were prepared using vacuum resin transfer molding (VARTM) method. In order to compare how preparation method affects properties of the composites, the same volume fraction of HGMs filled epoxy resin composites was prepared by SCM. The effects of preparation methods on microstructure, density, compression properties and water absorption of composites were investigated. Compression deformation mechanism of the composites prepared by two methods is discussed. Syntactic foam with the same HGMs volume fraction contained different porosity depending on the preparation method. Porosity of the matrix in the composite prepared using SCM was ∼10 vol.%, while the densities of composites prepared by VARTM were close to the theoretical density, indicating no matrix pores. Co-continuous HGMs/epoxy resin syntactic foams prepared using VARTM showed properties superior to syntactic foams prepared by SCM: compressive strength increase by 45.31%, compressive modulus increase by 37.63%, and water absorption decrease by 69.91%. All these properties improved mainly because of the elimination of the matrix pores.
Carbon nanofibers (CNFs) and halloysite nanotubes (HNTs) were incorporated in syntactic foams containing a 90% by volume homogeneous mixture of (20/80 wt%) glass/thermoplastic microballoons to enhance the mechanical and impact response properties. Tensile, compressive, and impact tests were employed to comparatively characterize the effect of nano-additive reinforcement on mechanical response properties. Compressive strength and modulus enhancements as large as 39% and 18%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 61% and 7%, respectively, were achieved with a 0.125 wt% addition of HNT. Tensile strength and modulus enhancements as large as 107% and 68%, respectively, were achieved with a 0.125 wt% addition of CNF and increases of 104% and 70%, respectively, were achieved with a 0.125 wt% addition of HNT. Impact analysis data were used to show that measured peak force increased and build-up time to peak force decreased with increasing CNF or HNT weight percentage due to stiffening of the matrix. The smallest increase observed in peak force was 20% for a 0.125 wt% addition of CNF and 17% for a 0.125 wt% addition of HNT.
Syntactic foam composites are widely used as aviation, construction and marine materials because of their high specific strength, specific modulus, damage tolerance and low moisture absorption. The present work aimed to investigate the compression behaviours of syntactic foam reinforced by warp knitted spacer fabric (SF-WKSF). Eight kinds of SF-WKSF samples were produced with warp knitted spacer fabrics of various surface layer structures and parameters including inclination-angle, fineness of spacer yarns, different microballoons types as well as contents. The compression tests were carried out on aMTS material testing system and the compression properties of SF-WKSF were analyzed based on the experimental compressive stress-strain curves and modulus values. It was indicated that the SF-WKSF made with preferable spacer fabric showed higher compressive modulus and yield strength values compared to neat syntactic foam (NSF). The results also demonstrated that all the parameters had significant effects on the compression performances of SF-WKSF. The composites could gain better anti-compression capacities by selecting larger inclination-angle, coarser spacer yarn, denser surface layer structure, higher microballoon density and higher S60HS microballoon contents.
Syntactic foams comprising glass microballoons have gained considerable attention over the past several years due to mechanical and thermal properties that are advantageous for use as a core material in naval and aerospace applications. Recent advancements in the production of thermoplastic microballoon syntactic foams have allowed for an increase in microballoon volume fraction (up to 0.9 volume fraction), with correspondingly lower densities but reduced mechanical properties. In this work, carbon nanofibers and halloysite nanotubes were incorporated in thermoplastic microballoon-based syntactic foam to enhance the mechanical properties and the relative effects of these two nanoscale reinforcements were compared. X-ray micro-computed tomography was employed to analyze the microstructure of the materials produced, and scanning electron microscopy was used to assess the dispersion of nano-additives within the resin. Compressive strength and modulus enhancements as large as 180% and 250% respectively were achieved with a 0.25 wt% addition of carbon nanofiber and increases of 165% and 244% respectively were achieved with a 0.5 wt% addition of halloysite nanotube. Tensile strength and modulus enhancements as large as 110% and 165% respectively were achieved with a 0.125 wt% addition of carbon nanofiber and increases of 133% and 173% respectively were achieved with a 0.125 wt% addition of halloysite nanotube.
Glass microballoon syntactic foams consisting of 60–70 vol% hollow glass microballoons and epoxy resin matrix have gained considerable attention in recent years due to their unique combination of mechanical properties and low density, with applications in the naval and aerospace industries. An important limitation of these materials is the volume fraction ceiling (∼0.74) and subsequent density limit (0.36 g/cm³). Utilizing thermoplastic microballoons, syntactic foams were produced with densities as low as 0.067 g/cm³, achieved by developing a method that produces epoxy/microballoon compositions comprising an unusually high volume fraction of microballoons (0.75–0.95). The resulting morphology features microballoons which, having expanded in a restricted volume, are deformed into irregular shapes that efficiently pack together and are encapsulated by a thin coating of epoxy. The compressive yield strength, tensile strength and initial modulus of these highly loaded syntactic foams exhibit a non-linear decrease with increasing microballoon volume fraction to values typical of highly porous polymers, but display a high degree of recovery, or rebound, from large compressive strain compared with glass microballoon syntactic foams.
Syntactic foams
comprised of glass microballoons have gained considerable attention over the past several years due to mechanical and thermal properties that are advantageous for use as a core material in naval and aerospace applications. Recently, advancements in the production of thermoplastic microballoon syntactic foams have allowed for an increase in microballoon volume fraction (up to 90 volume fraction), with corresponding lower densities but reduced mechanical properties. In this work, carbon nanofibers
and halloysite nanotubes were incorporated in thermoplastic microballoon-based syntactic foam to enhances its mechanical properties, and the effects of these two nanoscale reinforcements
are compared. X-Ray micro-computed tomography (MCT) was employed to analyze the microstructure of the materials produced, and scanning electron microscopy was used to assess the dispersion of nano-additives within the resin. Through characterization of the tensile and compressive strength properties of these materials, it was observed that dramatic mechanical property enhancements can be engineered through additions of either nano-additive at specific loading levels.
Owing to their lightweight and high strength characteristics and tailorable end-use properties, rigid syntactic foams fabricated from polymeric binders, hollow micro-spheres, and other fillers, and their variants have assumed great importance in material design. The highly ordered syntactic foams have potential to be utilized in designs involving multifunctional requirements, viz., aerospace structures, radar transparency, microwave electronics, EMI shielding, etc. This overview article introduces syntactic foams and gives an insight into establishing multifunctional characteristics in them to meet the end applications and presents a collection of related literature on techniques and uses.
Representative volume elements of syntactic foams with a random filling of short glass fibers and hollow glass microspheres in epoxy resin were established by a random sequential adsorption method. The fiber volume fraction was set at 4%, and the microsphere volume fraction range was from 5 to 30%. This numerical simulation was studied with ANSYS software. The influence on the elastic and plastic mechanical properties of syntactic foams of the microsphere volume fraction and relative wall thickness were investigated, and the plastic strain evolution process in the composites was analyzed. The results show that the compressive yield limit and Young's modulus values of the syntactic foams decreased with increasing microsphere volume fraction when the microsphere relative wall thickness was 0.02, but these properties were enhanced with increasing microsphere volume fraction when the relative wall thickness exceeded 0.04. The specific strength and tangent modulus values of the composites increased with increasing microsphere volume fraction. In addition, we observed that the yield stress, Young's modulus, and tangent modulus values of the syntactic foams were obviously enhanced by the addition of glass fibers. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44188.
Syntactic foam with low density polyethylene as matrix and varying w/w% of polymer micro balloon were prepared and the compressive behavior is analysed. There was uniform reduction in the compression strength with increase in the w/w% of polymer micro-balloons. The preferable cushion property of extended strain rate during compression was observed. The structural stability and uniform dispersion of the polymer micro-balloons in the LDPE matrix is quantified by the microscopic images.
The mechanical properties of hollow glass microsphere/epoxy resin syntactic foams reinforced by short glass fibers are studied using representative volume elements. Both the glass fibers and the hollow glass microspheres exhibit random arrangement in the epoxy resin. The volume fraction and wall thickness of hollow glass microspheres and the volume fraction of glass fibers are considered as parameters. It is observed that the elastic modulus values of syntactic foams decrease with the increase of microsphere volume fraction when the microsphere relative wall thickness is lower. However, it increases with the increase of microsphere volume fraction when the relative wall thickness exceeds a critical value. The elastic modulus value goes through a maximum when the relative wall thickness is around 0.06 at 25 % volume fraction of microspheres. The addition of glass fibers reduces the critical wall thickness values of the microspheres and increases the mechanical properties of the composites. The highest stress lies on the equatorial plane perpendicular to the loading direction. Adding fibers reduces the large stress distribution areas on the microspheres, and the fibers aligned with the loading direction play an important load-bearing role.
The effect of multi-wall carbon nanotubes and nanoSiO2 content on physico-mechanical properties of glass microspheres-epoxy resin composite, designed for blast energy absorbing applications, was evaluated experimentally. Specific porous lightweight foam with high volume fraction of microspheres (70 vol.%) was prepared and modified by 1 to 5 vol.% of multi-wall carbon nanotubes and nanosilica (nanoSiO2). Two types of microsperes with different wall thickness and strength were used. The quality of dispersion of nanoparticles was evaluated in relation to the mixing procedure using scanning electron microscope observation. The compressive and flexural strength tests were conducted at quasi-static load. The mixtures containing nanosilica exhibited an increasing trend in both flexural and compressive strength with increasing nanoparticle content up to 4 vol.%. The addition of carbon nanotubes also increased flexural strength (again up to 4 vol%, crossing this concentration, the significant drop was observed), whereas the compressive strength was affected at lower level. Nanoparticle modification is more effective in the foams with higher thickness and thus strength. The evaluation of test results showed that the properties of glass/epoxy foams can be tailored by adding nanoscale fillers.
In this chapter, we first review the various crack self-healing strategies. We then focus on self-healing of thermosetting shape memory polymer (SMP) composites per the close-then-heal (CTH) healing strategy. Three types of composite structures are prepared, including a thermosetting SMP-based syntactic foam-cored sandwich, a grid-stiffened thermosetting SMP-based syntactic foam-cored sandwich, and a 3-D woven fabric-reinforced thermosetting SMP-based syntactic foam composite. The prepared fiber-reinforced composite panels are repeatedly impact damaged and healed per the CTH scheme. The healing efficiency is evaluated per relevant mechanical strength tests. Damage sensing by a percolated carbon nanotube network is also investigated. The comprehensive experimental program confirms that the CTH scheme can heal structural-length scale cracks repeatedly, efficiently, timely, molecularly, and it has the potential to heal autonomously.
Syntactic foam composites are widely used as aviation, construction and marine materials because of their high specific strength, specific modulus, damage tolerance and low moisture absorption. The present work aimed to investigate the compression behaviours of syntactic foam reinforced by warp knitted spacer fabric (SF-WKSF). Eight kinds of SF-WKSF samples were produced with warp knitted spacer fabrics of various surface layer structures and parameters including inclination-angle, fineness of spacer yarns, different microballoons types as well as contents. The compression tests were carried out on aMTS material testing system and the compression properties of SF-WKSF were analyzed based on the experimental compressive stress-strain curves and modulus values. It was indicated that the SF-WKSF made with preferable spacer fabric showed higher compressive modulus and yield strength values compared to neat syntactic foam (NSF). The results also demonstrated that all the parameters had significant effects on the compression performances of SF-WKSF. The composites could gain better anti-compression capacities by selecting larger inclination-angle, coarser spacer yarn, denser surface layer structure, higher microballoon density and higher S60HS microballoon contents.
Application of natural fibers has attracted a great deal of attention among the composite research community in the past couple of decades. In this study, sisal fiber was utilized in fabrication of syntactic foam to improve the mechanical properties. Four sets of samples with different volume fractions of sisal fibers (0%, 1.5%, 2.5%, and 3.5%) were prepared. Viscoelastic properties of the samples were characterized with dynamic mechanical analysis. Storage and loss moduli, complex viscosity, and damping factor (tan ) of syntactic foam samples were recorded. Dynamic mechanical analysis results showed improvement in storage and loss moduli in glassy region (30?) up to 12% and 300%, respectively. In rubbery region (150?), the storage modulus of sisal fiber syntactic foam was three orders of magnitude higher than plain ones. Decrease in the tan peak also indicated improved interfacial bonding by addition and increase in the content of sisal fibers. All these improvements in viscoelastic properties were achieved without any significant change in the density of syntactic foam.
This article provides information on the typology, the preparation methods, and the potential applications of microspheres and microcapsules in the field of composites. A wide range of reported protocols for fabrication of these microstructured materials have been presented. The effect of these fillers on the properties of composites has also been discussed.Keywords:microparticles;hollow microspheres;solid microspheres;microcapsules;self-healing composites;phase change materials
Expandable microspheres/epoxy foams with different densities and microstructures were prepared by changing the foaming temperature and the precuring extent. The microstructure of foams reveals a homogeneous distribution of cells at high precuring extent and high foaming temperature, while small cells size at high precuring extent and low foaming temperature. Furthermore, the compressive properties of epoxy foams were investigated. The compressive strength and modulus of the foam exhibited a power-law dependence with respect to density. By optimizing the foaming temperature and the precuring extent, epoxy foams with homogeneous cells and stable compressive property can be obtained. Fracture surface showed that deformed microspheres and less debris were observed at relatively high-density foams.
The short glass fiber (SGF)/polypropylene (PP) and ethylene-1-octene copolymer (POE)/SGF/PP foam composites were prepared by extrusion and subsequent post-foaming process in designed dies. The compatilizers, maleic anhydride grafted PP (PP-g-MAH) and maleic anhydride grafted POE (POE-g-MAH), were employed to improve the performance of the foam composites, respectively, and their influences on the cellular structures, interfacial morphologies and mechanical properties of PP foam composites were investigated. It was found that the compatilizers resulted in modified PP foam composites characterized by uniform cell size distribution, reduced cell size and increased cell density except POE/SGF/PP with POE-g-MAH. The obvious enhanced SGF-matrix interfacial bonding was observed from the SEM examination, and POE-g-MAH also facilitated the compatibility between elastomeric particles and matrix. Testing results indicated that, by the introduction of PP-g-MAH or POE-g-MAH, the mechanical properties of PP foam composites were significantly improved, and it seemed that the PP-g-MAH was more effective in strengthening the flexural and compressive strength while POE-g-MAH greatly increased the impact toughness.
Full paper available for free: http://annuaire.ifremer.fr/cv/17113/
Syntactic foams, used in submersibles and in pipelines for deep sea oil wells, must be resistant to the severe conditions of the deep sea environment. As these foams will be in service for at least 20 years, their qualification testing is crucial. However, their mechanical characterization under real conditions of use is a challenge. In deep sea, the main loading is hydrostatic compression, however there is no standard procedure for testing material under pure hydrostatic pressure. The aim of this paper is to present a new characterization technique based on buoyancy loss measurement under hydrostatic pressure. To validate the method, two different syntactic foams (one brittle and one ductile) have been tested. Their behaviours under hydrostatic pressure have been followed by the proposed technique. The results from this innovative characterization technique have been compared to those of traditional uniaxial compression tests performed on the same materials.
Epoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non-uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non-uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power-law dependence with respect to the relative density. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41175.
Word syntactic derived from Greek syntax, meaning orderly arrangement as a group of words or structure. In the context of microcellular materials, they differ significantlyfrom other foams, which rely on blowing or foaming agents to achieve a cellular structure, by bonding lightweight particles with usually a thermosetting resin matrix, so achieving a predetermined structures. Such foams, when combined with suitable inorganic microspheres and Polyester or epoxy resins, can provide low densities with a very high resistance to hydrostatic pressure.
Sandwich structures, especially those with honeycomb and grid structures as the core material, are very commonly employed in aircraft structures. There is an increasing use of closed-pore rigid syntactic foams as core materials in sandwich constructions because they possess a number of favourable properties. The syntactic foams, owing to their structure and formation, behave differently under compression compared to other traditionally used core materials. In the present study, therefore, syntactic foam core sandwich constructions are evaluated for their behaviour under compression in both edgewise and flatwise orientations. Further, the work characterises the relative performance of two sets of sandwich materials, one containing glass-epoxy and the other, glass/carbon hybrid-epoxy skins. As non-standard geometry test specimens were involved, only a comparative evaluation was contemplated in this approach. The experiments indicate that the nature of the reinforcement fabric in the skin has a bearing on the test results in edgewise orientation. Thus, the tendency towards initiation of vertical crack in the central plane of the core material, which is a typical fracture event in this kind of material, was found to occur after a delay for the specimens containing the glass fabric in the skin. Attempts are made to establish the correlation between observations made on the test specimen visually during the course of testing and the post-compression microscopic examinations of the fracture features.
An account is given of an inspection method that has been successfully used to assess the postimpact damage and residual strength of syntactic (glass microspheres in epoxy matrix) foam-core sandwich panels with hybrid (carbon and glass fiber-reinforced) composite skins, which inherently possess high damage tolerance. SEM establishes that the crushing of the microspheres is responsible for the absorption of most of the impact energy. Damage tolerance is a function of the localization of damage by that high impact energy absorption.
Syntactic foams are composite materials in which hollow microspheres are dispersed. Such foams are characterized by low compressibility due to the spherical shape of the rigid hollow particles. Syntactic systems usually consist of organic, carbon or glass microspheres imbedded in epoxy, polyester, polyimide or polysilicone thermosetting resins. Production techniques vary from simple blending of the components to novel coating methods of the resin on the spheres surface. Three-phase syntactic foams comprise hollow spheres and resin containing dispersed air bubbles. The theoretical minimal density in this case is given in a system of a self-supporting bed of spheres (volume fraction 0. 53 for cubic packing) filled with air (maximum volume fraction of the lighter component). The physical and mechanical properties of syntactic foams thus depend upon their component type and proportions and their structure.
Four types of syntactic foams were fabricated from a phenolic resin and inorganic hollow microspheres, and the mechanical and thermal properties were compared with those of similarly prepared polyester resin syntactic foams. Phenolic resin syntactic foams can be prepared over a density range from 0. 75 to 1. 30 g/cm**3. The mechanical properties of these syntactic foams are considerably better than those of simple phenolic resin foams and are comparable to polyester resin syntactic foams. Phenolic resin syntactic foams also possess better thermal stability and resistance to burning. Good agreement was found between the theoretically derived expressions for modulus of the syntactic foam and the experimental results. For strength determinations, good agreement with the experimental values could be obtained by proper choice of a value for the stress concentration factor.
The comparative compressive properties of syntactic foam with and without the inclusion of E-glass fibers in the form of chopped strands are reported. The effort pointed to the fact that the fiber-free syntactic foam had a higher compressive strength than the fiber-bearing one whereas as regards the moduli values they did not differ much. The difference in strength is correlated with the amount of voids present in two foams. The scope of the work was further expanded by including scanning electron microscopy for examining the surface features of samples prior to and after compression test.
A study has been made of the processability, bulk density, and uniaxial compression properties of a syntactic foam system with varying volume fractions of phenolic microballoons. Short-term compression tests showed that the compression yield strength and initial tangent modulus of elasticity were linearly dependent on the bulk density (and the volume fraction of microballoons). The microballoon concentration and resin binder composition was found to be crucial to the ease of manufacturing syntactic foams.
The comparative performance in a three point bending test of syntactic foam comprising epoxy resin and glass microballoons with and without the inclusion of glass fibre in the form of chopped strands is reported. Test samples having a span-to-depth ratio of 16:1 were used. The data show that the glass fibre reinforced foam system had a higher strength compared to the unreinforced system. Resorting to light macroscopic and scanning electron microscopic examinations on mechanically tested samples expanded the scope of the work for a structure–property correlation to emerge.© 2000 Society of Chemical Industry
Syntactic foam composites containing 0, 0.9, 1.76, 2.54, 3.54, and 4.5 vol % of E-glass fibers in the form of chopped strands were fabricated and subjected to compression testing. It was found that the compressive strength values generally increased with fiber content except for the 3.54% fiber-bearing cast slab, which recorded lower values. This lone exception was due to the difference in processing route adopted in fabricating this particular fiber-bearing foam. Also noticed was the fact that the compressive strength of the 0.9 vol % fiber-bearing system was lower compared to the fiber-free system. This was correlated to the higher level of void content noticed with this fiber-bearing foam compared to that seen in the unreinforced foam. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 405–411, 2001
The effect of processing on the entrapment of voids in both fiber-free and fiber-bearing syntactic foam systems is studied. The process modifications for reinforced foam systems decreased the amount of voids. Foams with different void contents were later on tested for evaluating the compressive strengths. Also recorded were the strengths in two mutually perpendicular axes of the cast reinforced system. It was found that strength of syntactic foams increased as void content decreased, emphasizing that a good correlation between the two parameters exists.
The objective of this article is to highlight the existence of a specific geometrical configuration of syntactic foams (solid or hollow microballs soaked in a resin), which enables the design of a composite material possessing good thermal insulation properties while ensuring optimal mechanical behavior in compression and a significant weight gain. To carry this out, an economical approximated homogenization technique, adapted to the composites being studied herein, is first of all proposed. The results yielded turn out to be in good agreement with those obtained by the application of classical methods which have already demonstrated their effectiveness. In order to highlight the desired geometrical configuration, a minimization problem is then developed and solved. The value of this approach lies in the fact that all the computations necessary can be performed in a quasi-analytical manner, thereby avoiding reliance upon heavy computing resources. The resultant design tool proves to be most costeffective and simple to use.
This work concerns composite materials called “syntactic foams”, i.e., materials made by a polymeric matrix filled with hollow solid inclusions. Explicit formulae for the homogenized values of the elastic moduli of these materials are derived, by means of the physical model and the corresponding elastic solution used by Hervé and Pellegrini [Hervé, E., Pellegrini, O., 1995. Archives Mechanics. 47 (2), 223–246.]. The morphologically representative patterns theory of Bornert et al. [Bornert, M., Stolz, C., Zaoui, A., 1996. Journal of the Mechanics and Physics of Solids 44, 307–331.] is used to take into account both the influence of the filler gradation and the presence of “unwanted” voids in the matrix, factors that are shown to be important in characterizing the mechanical behavior of syntactic foams. Comparisons with both experimental and numerical results show that the techniques used are capable of predicting, with good accuracy, the elastic moduli of real syntactic foams, i.e., those arising from an actual production process.
Non-destructive evaluation of defects like voids in syntactic foam reinforced with epoxy compatible chopped strand glass fibres,
employing ultrasonic C-scan immersion through transmission method, was under-taken. The results showed that in four of the
five similarly processed foam samples, the voids were uniformly spread while in the fifth, which was processed by a different
route, a large spread of low dense area was noticed emphasizing the influence that processing technique has on the amount
of voids present in the composites.
This paper reports the results of a research activity concerning the mechanical behavior of a syntactic foam employed as core material for sandwich composite panels. Following a purely phenomenological approach, experimental and numerical results are presented and compared at the macroscopic scale. The main features observed in the uniaxial, biaxial and Three Point Bending (TPB) tests are highlighted. A bimodulus constitutive model of the Drucker–Prager type is chosen for modeling biaxial stress states with diffused damage. An alternative discrete crack approach is devised for the computer simulation of the (TPB) three point bending tests: the best matching is achieved for a rectangular Dugdale-type cohesive law. Though not proposing novel experimental or numerical methodologies, the present engineering approach should interest readers generally involved in computational composite mechanics and, specifically, in modeling particulate composites of the type considered here.
The paper shows the relationship among polymer, particles, and voids in a three-phase composite and how some of the properties of a composite may be changed by changing the proportions of the phases. The three-phase composite is an aggregate of microspheres bonded together with a small amount of polymer which may not form a continuous matrix. The void space (third phase) is obtained by limiting the amount of polymer which is mixed with the microspheres. A ternary phase diagram is used to show the proportional relationship among the three phases, with each apex representing a volume fraction of unity for a constituent while the side opposite the apex represents a volume fraction of zero for that constituent. The vertical dimension represents some composite property such as density or strength. The effect of composition on composite properties is shown by plotting them on a binary phase diagram which represents a perpendicular plane coincident with the 0.60 volume fraction microsphere line.