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Impactor Diameter and Ply Number Effects on the Impact Behavior of Carbon Fiber Composite Laminates
Abstract
As it is known, impact damage is a major mechanical phenomena for composite materials especially used in the aerospace structures. The factors affecting the impact behaviour of the composites depend on the impactor systems as well as the target material. In this study ply number and impactor geometry effects of carbon fiber reinforced epoxy composites were investigated by impact tests. In this context, drop weight impact tests were carried out at 6J, 12J and 24J energy levels by using hemispherical impactors with 10 mm and 20 mm diameters. Laminated composites were manufactured in 6, 10 and 14 plies with vacuum infusion method. The effects of laminate thickness, impactor diameter and impact energy effects on the force, velocity, absorbed energy and damage surfaces were investigated. It is observed that impactor geometries and velocities caused the different damage mechanisms in composites and impactors played an important role in determining the penetration and perforation behaviours of composites.
Barely visible impact damage (BVID) on carbon fibre reinforced polymer (CFRP) aerospace components can create interlaminar defects that may deteriorate during operation with potential failure as a result. Especially damage-prone regions such as the feet of a stiffener must therefore be inspected for BVIDs frequently, which is an effort that increases downtimes and operational costs. The potential of optical fibre sensors as part of a permanently installed structural health monitoring network is well-known. Individual FBG-based strain sensors have shown their capability to detect BVIDs. In this work we introduce a global damage index (GDI) as a figure of merit for the combined response of 60 FBG sensors mounted on several aerospace-grade CFRP flat stiffened panels. We first obtain a detection threshold for the GDI and then demonstrate its use for BVID detection. The proposed methodology is the first of its kind for the representation of the health of a component in a single parameter.
This study experimentally investigated the flexural fatigue behaviors of honeycomb sandwich composites subjected to low velocity impact damage by considering the type and thickness of the face sheet material, the cell size and the core height parameters. Carbon-fiber reinforced composite and the aluminum alloy was used as the face sheet material. First, the static strength of undamaged and damaged specimens was determined by three-point bending loads. Secondly, the fatigue behaviors of the damaged and undamaged specimens were determined. Low velocity impact damage decreased the flexural strength and fatigue lives but increased the damping ratio for all specimens. Maximum damping ratio values were observed on specimens with a aluminum face sheet.
One of the problems with composites is their weak impact damage resistance and post-impact mechanical properties. Composites are prone to delamination damage when impacted by low-speed projectiles because of the weak through-thickness strength. To combat the problem of delamination damage, composite parts are often over-designed with extra layers. However, this increases the cost, weight, and volume of the composite and, in some cases, may only provide moderate improvements to impact damage resistance. The selection of the optimal parameters for composite plates that give high impact resistance under low-velocity impact loads should consider several factors related to the properties of the materials as well as to how the composite product is manufactured. To obtain the desired impact resistance, it is essential to know the interrelationships between these parameters and the energy absorbed by the composite. Knowing which parameters affect the improvement of the composite impact resistance and which parameters give the most significant effect are the main issues in the composite industry. In this work, the impact response of composite laminates with various stacking sequences and resins was studied with the Instron 9250G drop-tower to determine the energy absorption. Three types of composites were used: carbon-fiber, glass-fiber, and mixed-fiber composite laminates. Also, these composites were characterized by different stacking sequences and resin types. The effect of several composite structural parameters on the absorbed energy of composite plates is studied. A finite element model was then used to find an optimized design with improved impact resistance based on the best attributes found from the experimental testing.
The present study delved into the effect of impactor diameter on low velocity impact response and damage characteristics of CFRP. Moreover, the phased array ultrasonic technique (PAUT) was adopted to identify the impact damages based on double-sided scanning. Low-velocity impact tests were carried out using three hemispherical impactors with different diameters. The relationship of impact response and impactor diameters was analyzed by ultrasonic C-scans and S-scans, combined with impact response parameters. Subsequently, the damage characteristics were assessed in terms of dent depth, delamination area and extension shape via the thickness, and the relationships between absorbed energy, impactor displacement, dent depth and delamination area were elucidated. As revealed from experiment results, double-sided PAUT is capable of representing the internal damage characteristics more accurately. Moreover, the impactor diameter slightly affects the impact response under small impact energy, whereas it significantly affects the impact response under large impact energy.
Carbon-fibre/epoxy-matrix composites used in aerospace and vehicle applications are often susceptible to critical loading conditions and one example is impact loading. The present paper describes a detailed experimental and numerical investigation on the relatively low-velocity (i.e. <10 m/s) impact behaviour of such composite laminates. In particular, the effects of the geometry of the impactor have been studied and two types of impactor were investigated: (a) a steel impactor with a hemispherical head and (b) a flat-ended steel impactor. They were employed to strike the composite specimens with an impact energy level of 15 J. After the impact experiments, all the composite laminates were inspected using ultrasonic C-scan tests to assess the damage that was induced by the two different types of impactor. A three-dimensional finite-element (FE) model, incorporating a newly developed elastic-plastic damage model which was implemented as a VUMAT subroutine, was employed to simulate the impact event and to investigate the effects of the geometry of the impactor. The numerical predictions, including those for the loading response and the damage maps, gave good agreement with the experimental results.
Composites have been found to be the most promising and discerning material available in this century. Presently, composites reinforced with fibers of synthetic or natural materials are gaining more importance as demands for lightweight materials with high strength for specific applications are growing in the market. Fiber-reinforced polymer composite offers not only high strength to weight ratio, but also reveals exceptional properties such as high durability; stiffness; damping property; flexural strength; and resistance to corrosion, wear, impact, and fire. These wide ranges of diverse features have led composite materials to find applications in mechanical, construction, aerospace, automobile, biomedical, marine, and many other manufacturing industries. Performance of composite materials predominantly depends on their constituent elements and manufacturing techniques, therefore, functional properties of various fibers available worldwide, their classifications, and the manufacturing techniques used to fabricate the composite materials need to be studied in order to figure out the optimized characteristic of the material for the desired application. An overview of a diverse range of fibers, their properties, functionality, classification, and various fiber composite manufacturing techniques is presented to discover the optimized fiber-reinforced composite material for significant applications. Their exceptional performance in the numerous fields of applications have made fiber-reinforced composite materials a promising alternative over solitary metals or alloys.
Fibre-reinforced composite materials have remarkable potential for use in automobile, aerospace and defence applications due to their high specific properties and stiffness. E-glass fiber reinforced composite laminates are found to be more promising for various defence applications due to their low cost, easy availability, flexibility in design and processing. In the present study, E-glass/epoxy composite laminates were subjected to low velocity impact using 16 mm hemispherical impactor with the impact energy range of 50-150 J. Effect of laminate thickness on impact parameters like peak force, maximum displacement and damage area was experimentally evaluated. It was found that peak force is increased with increase in impact energy up to complete perforation and then became constant. Peak force is found to be increased linearly with the increase in thickness at all impact energies. Maximum displacement has decreased 50% as the thickness of the laminate is doubled. Interaction time/contact duration also decreased due to increased resistance with thickness. Visual inspection of impacted laminates indicates two types of damage regions namely fibre breakage area and delamination area. However, the extent of damage regions and their ratio are found to be thickness dependent. Dominant failure mode gradually changes from fibre breakage to delamination as the thickness is increased.
An efficient numerical approach for the prediction of the Compression After Impact (CAI) strength of aerospace-grade CFRP laminates when exposed to Barely Visible Impact Damage (BVID) is proposed. The approach is based on mapping relevant BVID features, i.e. delaminations, onto an efficient CAI finite element model based on continuum shell discretization, and can be used on Low-Velocity Impact (LVI) results obtained experimentally or by means of high-fidelity virtual tests. It is proposed that delaminations may be represented by simplified shapes, and only the ones at critical through-thickness locations need to be mapped, allowing the clustering of several plies in a single shell layer. General guidelines, that are potentially valid for a wide range of unidirectional CFRP laminates, are proposed to identify relevant and critical BVID features to be mapped onto the efficient CAI modelling. The approach was validated for five laminates of AS4/8552 material, covering a range of different thicknesses, overall achieving CAI strength predictions within 5\% of the experimental results. In comparison with the alternative high-fidelity CAI virtual testing approach, this method leads to computational efficiency gains of an order of magnitude. Moreover, the full simulation of the sequence LVI plus CAI steps can be accelerated by a factor of four.
Composite structures are particularly vulnerable to impact, which drastically reduces their residual strength, in particular, at high temperatures. The glass-transition temperature (Tg) of a polymer is a critical factor that can modify the mechanical properties of the material, affecting its density, hardness and rigidity. In this work, the influence of thermal ageing on the low-velocity impact resistance and tolerance of composites is investigated by means of compression after impact (CAI) tests. Carbon-fibre-reinforced polymer (CFRP) laminates with a Tg of 195 °C were manufactured and subjected to thermal ageing treatments at 190 and 210 °C for 10 and 20 days. Drop-weight impact tests were carried out to determine the impact response of the different composite laminates. Compression after impact tests were performed in a non-standard CAI device in order to obtain the compression residual strength. Ultrasonic C-scanning of impacted samples were examined to assess the failure mechanisms of the different configurations as a function of temperature. It was observed that damage tolerance decreases as temperature increases. Nevertheless, a post-curing process was found at temperatures below the Tg that enhances the adhesion between matrix and fibres and improves the impact resistance. Finally, the results obtained demonstrate that temperature can cause significant changes to the impact behaviour of composites and must be taken to account when designing for structural applications.
This study investigated the damage and failure mechanism of composite laminates under low-velocity impact and compression-after-impact (CAI) loading conditions by numerical and experimental methods. Ultrasonic C-scan, DIC and SEM methods were combined to give a new and deep insight of damage evolution and failure mechanisms in composite laminates. A novel three-dimensional damage model based on continuum damage mechanics was developed to investigate the impact and CAI behavior with consideration of both interlaminar delamination damage and intralaminar damage. The maximum-strain failure criterion and an improved three-dimensional Puck criterion, which was physically-based, were employed to capture the initiation of fiber and matrix damage respectively and a bi-linear damage constitutive relation was used for characterization of damage evolution. The interlaminar delamination damage was simulated by the interfacial cohesive behavior. Good correlation between numerical and experimental results demonstrated the effectiveness and rationality of the proposed numerical model. The effects of impact energy level and multiple impacts were discussed.
Honeycomb sandwich composites are used as significant structural members in advanced engineering applications. Thus, it is critical to determine how they behave under impact loading, in addition to other loads. In this study, low velocity impact loading behaviors of honeycomb sandwich composites were experimentally investigated. Almost all of the design parameters of honeycomb sandwich composites were investigated. The results indicated that the core thickness of honeycomb had no effect on the strength of the composite, and the parameter influencing the impact behavior of the specimen the most was the face sheet thickness. When the face sheet thickness of the specimen was increased, the most apparent strength increase was observed in the models using carbon fiber-reinforced composite face sheets. For all face sheet types subject to impact energy of 10 Joules, the upper face sheets of 0.5 mm-thick specimens were perforated.
Despite the key advantages of Fiber Reinforced Polymer (FRP) composites, they are susceptible to Barely Visible Impact Damage (BVID) under transverse loadings. This study investigates BVID in two quasi-isotropic carbon/epoxy laminates under quasi-static indentation and Low-Velocity Impact (LVI) loadings using Acoustic Emission (AE). First, the evolution of interlaminar and intralaminar damages is studied by analyzing the AE signals of the indentation test using b-value and sentry function methods. Then, the specimens are subjected to the LVI loading and the induced damages are compared with the indentation test and the percentage of each damage mechanism is calculated using Wavelet Packet Transform (WPT). In consistent with the mechanical data, ultrasonic C-scan and digital camera images of the specimens, the AE results show a considerable similarity between the induced BVID under quasi-static indentation and LVI tests. Finally, the obtained results show that AE is a powerful tool to study BVID in laminated composites under quasi-static and dynamic transverse loadings.
Kompozit malzemeler kullanım yerlerine bağlı olarak çeşitli darbelere maruz kalabilirler. Darbe nedeniyle malzemede oluşan hasar artan darbe enerjisine bağlı olarak artmaktadır. Fiberlerin kırılması, matris çatlağı, fiber matris arayüzey hasarı, delinme ve delaminasyon genel olarak darbe sonrası kompozit malzemede oluşan hasar türleridir. Bu çalışmada, iki farklı kalınlık ve darbe enerjisi için cam elyaf takviyeli epoksi kompozit plakaların darbe davranışları deneysel olarak incelenmiştir. Bu amaçla, 100x100 mm boyutlarında; iki farklı kalınlıkta (2 ve 4 mm), 8 ve 16 tabakalı kompozit numuneler vakum infüzyon yöntemi kullanılarak üretilmiştir. Üretilen numuneler 20J ve 60J’ luk iki farklı darbe enerjisi altında test edilmiştir. Kuvvet çökme eğrileri, darbe enerjisi- maksimum kuvvet enerji eğrileri, darbe enerjisi -çökme eğrileri, hız zaman eğrileri, kuvvet zaman eğrileri ve absorbe edilen enerji-zaman eğrileri çizilmiştir. Deneysel çalışma sonucunda 20J darbe enerjisine maruz kalan 8 tabakalı numunelerde delinme hasarı oluşmazken, 60J darbe enerjisine maruz kalan numunelerde delinme hasarı oluşmuştur. 16 tabakalı kompozit numunelerde ise her iki darbe enerjisi için de delinme hasarı oluşmamıştır.
Low-velocity impact response of interply hybrid composites based on glass and carbon woven fabrics as reinforcement and polymerized poly (butylene terephthalate) (PCBT) as matrix was presented in this paper. Experiment and finite element method (FEM) were respectively performed to investigate the hybridization effect on the composites under impact velocity of 3 m/s, 5 m/s and 7 m/s. Specimens used in the experiment were made by vacuum assisted prepregs process (VAPP). All the material parameters used in simulation were determined by experimental test. Three-dimensional finite element models were developed in ABAQUS/Explicit to analyze the damage behavior of interply hybrid composite laminates, and a user subroutine VUMAT was compiled for the woven fabrics reinforced PCBT composites. Experimental results show that hybrid composites at hybrid mass ratio of 37:63 could absorb more energy in the impact event compared with pure composites, and the perforation thresholds enhance significantly. The simulation results are well agreed with experimental results. The damage mode of the interply hybrid composites under low-velocity impact is further discussed.
Energy absorption of two different types of composite laminates i.e. glass composite (E-glass/epoxy) and ultra high molecular weight polyethylene (UHMWPE) (Dyneema®) laminates were studied under low and high velocity impact. Instrumented drop weight impact tester was used for low velocities and sub machine carbine (SMC) gun was used for high velocity impact. Failure behaviour of both E-glass/epoxy and dyneema laminates during impact was studied and results of the energy absorption of the tested composite laminates have been presented. Dyneema laminates showed 2 times higher energy absorption than E-glass/epoxy laminate under high velocity impact. However, both the laminates have showed higher energy absorption at high velocity impact as compared to low velocity impact. Failure analysis on impacted laminates reveals that the E-glass/epoxy laminate undergoes elastic deformation, delamination and brittle failure of fibres, whereas dyneema laminates undergo plastic deformation and associated tensile stretching of fibres. The results obtained from this study bear significance in the development of light weight add-on and structural composite armours for the real time applications.
This work is concerned with the prediction of low velocity impact damage resistance of carbon fibre-reinforced laminated composite laminates. Pre-assumed damage induced laminates were simulated to correlate damage corresponding to impactor nose profiles. Majority of the existing studies conducted on the topic are experimental, based on three-dimensional stresses and failure theories that cannot readily predict ply level impact damage. Hence efficient computational models are required. The present study was conducted to efficiently predict ply level impact response of composite laminates. Static load-deflection based computational model was developed in the commercial software ABAQUSTM. Eight, 16, and 24 ply laminates impacted by point, small, medium, and flat nose impactors were considered with emphasis on flat nose impacts. Loading areas under the impactor nose profiles were partitioned to investigate effects from variations in applied loading. Pre-assumed damage zones consisting of degraded material properties equivalent to the impactor nose profiles were inserted across thickness of the laminates to predict ply-by-ply damage. Impactor nose profiles and pre-assumed damage zones (size, type, and location) were correlated to the simulation produced deflection quantities to predict the ply level damage. Selected results were compared against the data available in the literature and also against the intra-simulation results and found in good agreement.
In this work, the analysis of the impactor mass effect on the behaviour of carbon/epoxy woven laminates under low velocity impact is carried out. To this end experimental test were performed by means of a drop weigh tower in a range of energies varying from 10 to 110. J, and using three different impactor masses. Two different laminate thicknesses were considered in order to take into account its possible influence. An analysis of the impact tests is performed using the Composite Structure Impact Performance Assessment Program, in order to observe the influence of impactor mass. Once impacted, the laminates were inspected by means of a C-Scan (to quantify the delamination extension) and a phased array ultrasonic system (to analyse the failure through the thickness); this non-destructive analysis will determine the influence of the impactor mass on the laminate failure.
In this paper, the effects of the stacking sequence on the mechanical behavior of composite laminates subjected to low velocity impacts is investigated, taking into account inter-laminar and intra-laminar damage onset and evolution. The response of the composite laminate configurations characterized by different stacking sequences subjected to low velocity impacts with different impact energies have been studied to estimate the influence on the load-time, displacement-time and energy-time histories. A Finite element (FE) model has been used to numerically simulate the behavior of the composite plates. ABAQUS/EXPLICT FE environment has been considered for the implementation and the analyses and cohesive elements have been adopted to model the inter-laminar damage formation and evolution in the analyzed composite plate.
The effects of hygrothermal conditioning and moisture on the impact resistance of carbon fiber/epoxy composite laminates were investigated. Specimens were fabricated from carbon fiber/epoxy woven prepreg materials. The fabricated specimens were either immersed in water at 80°C or subjected to hot/wet (at 80°C in water for 12 h) to cold/dry (at -30°C in a freezer for 12 h) cyclic hygrothermal conditions, which resulted in different moisture contents inside the laminates. It was found that the absorbed moisture did not migrate out from composite materials at -30°C. Neither of the hygrothermal conditions in this study had detrimental effects on the microstructure of the laminates. Low-velocity impact testing was subsequently conducted on the conditioned specimens. When attacked by the same level of impact energy, laminates with different moisture levels experienced different levels of impact damage. Moisture significantly alleviated the extent of damage in carbon fiber/epoxy woven laminates. The elastic response of the laminate under impact was improved after hygrothermal conditioning. The mechanism behind the improved impact resistance after absorbing moisture was proposed and deliberated.
In this paper validation of experimental and numerical results of low-velocity impact tests of unsaturated polyester/glass fibre composite laminate has been carried out. Impact response of composite laminates was experimentally studied with drop-tower Instron 9250HV determining impact force, energy absorption and deflection. In addition, quasi-static testing equipment Zwick Z100 has been used to determine material mechanical properties to ensure good input data for numerical predictions. Numerical model has been created with the finite element commercial code ANSYS/LS-DYNA to simulate impact response of composite laminate. Also non-destructive ultrasonic B-and C-scan imagining with USPC 3010 system has been used to identify the deformation regions in the specimens and compare to simulation results. During the impact test all samples were perforated, showing brittle response followed by matrix cracking and delamination. Overall good agreement between experimental and simulation results was achieved, comparing impact characterizing parameters as load, energy and deflection. Discrepancy has been observed between ultrasonic scanning and simulation code ANSYS/LS-DYNA results of rupture and delamination. Simulation shows less uniform and larger deformation than it was experimentally observed.
The impact responses of typical laminates are investigated numerically in this research. Delamination responses among plies and fibre and/or matrix damage responses within plies are simulated to understand
the behaviours of laminates under different impaction conditions. Damage resistance of a laminate is highly dependent upon several factors including geometry, thickness, stiffness, mass, and impact energies (impact velocities), which are here considered by the finite element (FE) method. Three groups of composite laminates are simulated and the numerical results in general are in good agreement with corresponding experiments. Models containing different stacking sequences and impact energies are built to study their influence on impact responses and demonstrate that clustered (or nearly clustered) plies in the laminate can effectively reduce the degree of interface damage. Models containing different indenters and plate shapes are also built to systematically study their influence on the low-speed drop-weight behaviour of composite laminates. Suggestions are proposed for designing impact tests for particular purposes.
This study addresses the effects of basalt fibre hybridization on quasi-static mechanical properties and low velocity impact behaviour of carbon/epoxy laminates. Interply hybrid specimens with two different stacking sequences (sandwich-like and intercalated) are tested at three different energies, namely 5, 12.5 and 25 J. Residual post-impact properties of the different configurations of carbon/basalt hybrid laminates are characterized by quasi static four point bending tests. Post-impact flexural tests and interlaminar shear tests are used for the mechanical characterization along with two non-destructive methods, namely acoustic emission and ultrasonic phased array, in order to get further information on both the extent of damage and failure mechanisms. Results indicate that hybrid laminates with intercalated configuration (alternating sequence of basalt and carbon fabrics) have better impact energy absorption capability and enhanced damage tolerance with respect to the all-carbon laminates, while hybrid laminates with sandwich-like configuration (seven carbon fabric layers at the centre of the laminate as core and three basalt fabric layers for each side of the composite as skins) present the most favourable flexural behaviour.
In this study, the effect of impactor diameter on the impact response of woven glass–epoxy laminates has been investigated. Impact tests were performed by using Fractovis Plus test machine with four different impactor nose diameters as 12.7, 20.0, 25.4 and 31.8 mm. Specimens were impacted at various impact energies ranging from 5 J to perforation thresholds of the composite at room temperature. Variation of the impact characteristics such as the maximum contact load, maximum deflection, maximum contact time and absorbed energy versus impact energy are investigated. Results indicated that the projectile diameter highly affects the impact and Compression After Impact (CAI) response of composite materials.
The impact behaviour of composite laminates under low velocity impact load is investigated by considering the influence of stacking sequence and laminate thickness in terms of contact loads, absorbed energy and delamination extent. After a detailed analysis of impact induced damage evolution, a new methodology for the assessment of the energy absorption capability of composite laminates is proposed. The new approach allows the definition of an empirical master curve suitable to summarise the impact data independently of material system, laminate thickness and lay-up.
Experimental results of low-energy drop-weight impact tests on woven-roving E-glass/polyester composites are presented. The effects of specimen thickness, impactor kinetic energy, velocity of impact and laminator are investigated. Damage was observed for all impact energies. The assumption that shear deformation dominates the response gives good agreement with the results. A model assuming a circular delamination area predicts very well the interlaminar shear strength for the 5-ply specimens, but not for the 10 ply specimens.
The Z-pinning technique can enhance the delamination resistance for composite laminates effectively. In this paper, the effect of laminate thickness on the low velocity impact responses of Z-pinned laminates with [02/902]2S, [02/902]4S, and [02/902]6S layup patterns was explored. These laminates had nominal thickness of 2.1 mm, 4.5 mm and 6.9 mm, respectively. The impact energy was set to 5J, 10J, 20J and 30J, and the mechanical curves during the experiment were recorded. Afterwards, ultrasonic C-scanner, scanning electron microscope (SEM) and X-ray micro-computed tomography (μCT) were used to detect the impact-induced damage. The theoretical models for predicting the delamination initiation threshold and related threshold impact energy were consistent with the experimental data. The results showed that Z-pins had almost no effect on the delamination initiation, but Z-pinning became significant for delamination suppression as the impact energy exceeded the threshold impact energy. In addition, due to the improved penetration resistance, the maximum central displacements were suppressed with Z-pin implantation as the noticeable fiber breakage occurred. Due to the fact that the dominant failure mode changed from fiber breakage to delamination with the increase of the laminate thickness, the delamination damage and internal defect suppression for thin laminate was inferior to that for the intermediate-thickness laminate. However, the suppression effectiveness became weak for the thick laminate at the same impact energy due to the smaller bridging force with slight Z-pin pull-out.
Detection of damage due to impact in an isotropic structure like metal, its alloys, etc. is an easy task but in the case of fibre reinforced polymer matrix composite structures, it becomes one of the critical factors which cannot be tolerated to use this structure extensively. Metals are usually ductile in nature as they can absorb more energy but in case of composite it is different; impact in composite reduces the structural strength. Most of the composite are brittle in nature. Composite can absorb energy in elastic deformation but not via plastic deformation. So it becomes important to consider the impact loading and influence of parameters to improve the damage resistance of composite structures in many applications like automobiles, aerospace, defense, etc. This paper presents the pivotal reviews of the previously published literature regarding the influence of parameters, damage mechanisms, enhancement of damage resistance of various composites. Firstly this paper briefly reviews the approach of analysis and the influence of stacking sequence on failure of the composite. Following this, the compendium review of other parameters for improvement of low velocity impact resistance specifically different constituents materials, geometrical factors, self-healing, bio-composites, off-centre loading and angle impact that influences the structural behaviour of different composites under the impact loading is briefly discussed. This review further discusses the different factors to be considered to enhance the impact damage resistance of fibre reinforced polymer matrix composites and concludes with future work discussion.
In this paper, the authors presented a concept of a construction of a parametric model of barely visible impact damage (BVID) in carbon fiber-reinforced composite structures based on a reconstruction of X-ray computed tomography scans, ultrasonic B- and C-Scans as well as numerical simulations of such a type of impact loading. Considering the results of the experimental tests made it possible to model the resulting BVID with a realistic geometry and the location of delaminations, while the results of the numerical simulations allowed confirming and adjusting the damage extent. The original procedure of the BVID reconstruction from non-destructive testing data was developed and presented in the paper for the purpose of preparing the parametric computer-aided design (CAD) models. Using both numerical and experimental results the generic shapes of BVID for the set of various impact energies and various impactors were achieved. The determined dependencies of changing the damage extent with respect to various energies and impactors made it possible to parametrize BVID. The resulting generic models of BVID were validated on the X-ray computed tomography scans.
Today composite structures are widely used in different industries. Since these structures are sometimes experienced impacts of low-velocity objects, evaluating the intensity of the damage due to the impact in these structures seems important and necessary. In this article, the effectiveness of the thermography method with three different thermal excitation sources, including the ultrasonic vibrothermography, infrared thermography with the heating element, and infrared thermography with hot airflow, for damage evaluation in CFRP and GFRP composite plates subjected to low-velocity impacts are investigated. The ultrasonic vibrothermography method is introduced as the most promising technique for damage evaluation in CFRP and GFRP composite plates subjected to low-velocity impacts, and the effect of the excitation power and excitation frequency on the effectiveness of this method is studied. To find the damage location in the thermography images in which the damage is not clear enough to be identified, the wavelet transform is applied while it is not suitable for calculating the damaged area. Finally, finite element (FE) simulations are carried out for the case of an internal defect. The results show the acceptable accuracy of the FE simulation in comparison with the experimental results.
Structural composite materials with good impact resistance are required in several industrial sectors to design parts submitted to crashes or falling objects. This work investigates the impact behaviour of flax fabrics-epoxy and commingled flax-polypropylene (PP) fibres composite plates manufactured using compression moulding process. An instrumented drop tower was used to conduct low velocity impact tests at several energies and high-speed imaging coupled with DIC analysis was used to assess the damage evolution. A crack-tracking algorithm was implemented in ImageJ to identify the initiation and propagation of cracks. A comparison of the force-displacement histories and high-speed camera results for both composites were used to identify the different modes of damage and the critical energy for complete penetration. The proposed method is able to depict the successive events that lead to the breakage of biocomposites and it will be a valuable tool to investigate the impact behaviour of other materials as well.
In this paper, a 3D finite element model is established in ABAQUS/Explicit based on a modified progressive damage model to study the dynamic mechanical response and damage development in cross-ply composite laminates subjected to low-velocity impact. The 3D Hashin criterion and the damage evolution model with the through-thickness normal stress component σ33 are applied to predict the intra-laminar damage initiation and evolution. The cohesive elements with the bilinear traction-separation relationship are inserted between layers to predict the inter-laminar delamination induced by impact loading. A user-material subroutine VUMAT involving the modified progressive damage del of intra-laminar and inter-laminar damage is coded and implemented in the finite element package ABAQUS/Explicit. The numerical results of three different impact energies (7.35, 11.03 and 14.70 J) are analyzed by the impact force–time, force-displacement and energy-time histories curves as well as different damage modes. The respectable relationship between numerical simulation and experimental result indicates that the proposed modified method is more suitable for low-velocity impact on composite laminates under different impact energies than the previous method without σ33. Moreover, the effects of Smt and Smc on global mechanical response and local damage predictions for laminates are discussed in detail. It can be concluded that both of the coefficients should be adopted between 0.93 and 0.96 when using this damage model to simulate composite laminates under low-velocity impact.
The damage of fiber reinforced polymer matrix composite materials induced by impact load is one of the most critical factors that restrict extensive use of these materials. The behavior of composite structures under transient impact loading and the ways to enhance their characteristics to withstand this type of dynamic loading might be of specific significance in the aerospace sector and other applications. This paper critically reviews the important parameters from the published literature influencing the impact resistance and the damage mechanics of fiber-reinforced composite materials. Firstly, the paper reviews the influence of impact velocity on various failure modes. Following this, a comprehensive review on the four key parameters specifically material, geometry, event and the environmental-related conditions that affect the structural behavior of fiber reinforced polymer matrix composites to impact loading is discussed. The review further outlines areas to improve the impact damage characteristics of composites and then conclude with a summary of the discussion on the future work relating to the most influencing parameters.
Aerospace structures are prone to impact which affected their residual strength. The aim of this paper to investigate the impact and after-impact behaviour of multi-walled carbon nanotube (MWCNTs) as nanofiller enhanced flax/carbon fibre composites (FLXC) and flax/glass fibre composites (FLXG) hybrid composites. Wet lay-up method was used to fabricate the hybrid composites. The hybrid composites were impacted with impact energies ranging from 5J to 20J, with different types of surface susceptible to the impactor to compare their response under loading. Compression after impact (CAI) testing were done to evaluate the after-impact properties of the hybrid composites. Obtained results found that FLXG composites impacted at glass surface (G-FLX) showed better impact properties compared to C-FLX composites. In another end, it was found that the compressive strength of FLXG composites is higher compared to FLXC composites due to severe damage occurred on FLXC composites surface compared to FLXG composites. Therefore, from the results, it can be concluded that FLXG hybrid composites shows good behaviour to be applied as the interior and functional surfaces inside an aircraft.
This paper experimentally studies the low-velocity impact behaviors and residual tensile strength of carbon fiber reinforced plastics (CFRP) laminates. Firstly, the effects of four factors, i.e. impact angle, impactor diameter, the proportion of ply orientation and stacking sequence, on the impact responses of laminates are studied. The damage characteristics are evaluated by dent depth, delamination damage projection area (DDPA) and energy dissipation. Secondly, the tensile responses of the laminates after impact are investigated based on residual tensile strength (RTS). Finally, the correlations between the four damage evaluation criteria, i.e. dent depth, DDPA, energy dissipation and RTS, are sorted out. Experimental results demonstrate that the four factors have significant effects on the impact behaviors of laminates in different ways. The DDPA is negatively correlated with the dent depth of laminates, and the dent depth can be treated as an important reference for the RTS. Besides, a fracture phenomenon, i.e. a clear band of fiber fracture around the impact area after impact, has been observed and discussed.
The effect of impact load with low velocity in thin-walled plates and profiles has been investigated. The paper deals with the relation between damage propagation, size and shape as a function of boundary conditions, layer arrangements and impact energy. The structures under consideration were made of eight-layer Glass Fiber Reinforced Polymer (GFRP) laminate with a quasi-isotropic, quasi-orthotropic and angle ply arrangement of layers. The standardised plates predefined to CAI tests and channel section profiles have been subjected to impact load. Based on the performed tests, the impact characteristics have been obtained and compared with the theoretical model (one degree of freedom mass-spring system). Further, despite it not being mentioned in the ASTM 7136 standard, characteristic curves were identified. It was noted that the impacts introducing matrix damages and the partial fracture of the fibres significantly change the course of the Force-Time histories, particularly after the maximum impact force is reached.
The present paper aims to provide further understanding of the low-velocity impact behaviour of glass fabric cloth reinforced epoxy composite panels embedded with wire nets (WN-GF/epoxy). WN-GF/epoxy hybrid panels with six layer modes were manufactured by vacuum-assisted injection process. Low-velocity impact tests with various incident velocities were performed, and the perforation thresholds of the designed specimens were found out. Scanning electron microscope was carried out to study the microstructure of the composites after impact. Experimental results show that perforation threshold velocity of the specimens appears a bi-linear increasing tendency with increase of the embedded wire nets, and the increase ratio has an inflection point. Damage pattern observation results show that the enhanced energy abortion ability is mainly due to the increased delamination area of the specimens during the impact events. 3D finite element models were developed in ABAQUS/Explicit to analyze the damage behavior of WN-GF/epoxy composites, and a user subroutine was compiled. The contact load and change of kinetic energy absorption characteristics have been used to validate the finite element results. The penetration process and damage modes of WN-GF/epoxy interply hybrid composites under low-velocity impact are further discussed with the assistant of numerical results.
Numerical simulations can help in the understanding of the damage sequence of polymer based composite laminates during an impact event, which is a difficult experimental task when dealing with a large number of plies. Low velocity impact and compression after impact in thin ply fabric laminates are studied through numerical simulations in which special attention has been devoted towards the computational efficiency. The impact results show the importance of delamination during the damage initiation, which takes place at few interfaces. After damage initiation, delamination and fiber breakage propagate until a last stage which is mainly governed by fiber breakage. Compression after impact shows a brittle behaviour with almost no damage propagation prior to failure. The numerical models indicate that matrix cracking effects can be assumed negligible for the studied thin ply laminates while delamination and especially the fiber constitutive law shape are important for accurate predictions.
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For the analysis of low-velocity impact damage, many analytical and numerical models were developed by various authors. These models range from simple approaches with a single degree of freedom up to finite element models on micro-scale. The prediction of delamination, fiber failure, and inter-fiber damage, as well as a physically sound kinematic behavior, are usually the objectives of these simulations. However, achieving satisfactory results requires massive computation and modeling efforts. In the present paper, we review the capability to capture impact damage on the coupon and the structural level. For this purpose, a large compendium of analytical and numerical analysis methods from various authors is considered. Based on existing works, six representative modeling approaches of different abstraction scales are derived and considered on a qualitative and quantitative benchmark study. We analyze all models regarding their advantages and deficiencies. With two experimental coupon impacts, all approaches are tested on their predictive capabilities on the coupon level. The applicability of these methods on the structural level is evaluated according to the benchmark results. Modeling approaches included in the benchmark range from high-fidelity models on meso-scale, macro-scale shell models, and analytical estimations. The focus is put on stacked layer models with solid or shell elements and various cohesive zone approaches.
With this paper, we also present guidelines for impact analysis strategies on the structural level. These guidelines aim for a good balance between accuracy and computation effort and involve various
simplifications of impact scenarios. In this regard, the range of low-velocity has to be monitored. The energy distribution over the eigenmodes of the impact system suitably indicates the limit of low-velocity impact.
In order to study the delamination of thick composite laminates under low-energy impact, damage prediction and analysis were presented in this paper. The impact tests were carried out on specimens with three kinds of stacking sequence under three energy levels, and followed by the nondestructive tests to obtain the delamination region. Then numerical models were built to simulate the delamination behavior of composite laminates. The simulation results showed a good correlation to the experimental observations. Furthermore, delamination characteristics in plane and its extension through thickness direction were put forward. The delamination shape was found enclosed by Archimedes spiral and the fiber direction of the layer above and below. The delamination location was limited by the impact zone and the fiber distribution. In the thickness direction, the extension area was found decreased layer by layer. Moreover, the characteristics above were revealed through the analysis of damage mechanism. Finally, the verification of the predicted results was presented based on experiments. The realization of delamination prediction may contribute to evaluating residual strength and optimizing airplane structures.
A major concern affecting the efficient use of composite laminates is the effect of low velocity impact damage on the structural integrity [1–3]. The aim of this study is to characterize and assess the effect of laminate thickness, ply-stacking sequence and scaling technique on the damage resistance of CFRP laminates subjected to low velocity impact. Drop-weight impact tests are carried out to determine impact response. Ultrasonic C-scanning and cross-sectional micrographs are examined to assess failure mechanisms of the different configurations. It is observed that damage resistance decreases as impact energy increases. In addition, thicker laminates show lower absorbed energy but, conversely, a more extensive delamination due to higher bending stiffness. Thinner laminates show higher failure depth. Furthermore, quasi-isotropic laminates show better performance in terms of damage resistance. Finally, the results obtained demonstrate that introducing ply clustering had a negative effect on the damage resistance and on the delamination area.
The investigation of the impact performance of flax-based composites is the key in order to understand which material parameters determine the safety and longevity of flax composite products. In this study, the effect of fibre architectures and matrix type on the absorbed energy after perforation, on the damage resistance as well as on the residual properties after impact were investigated. The matrix choice (epoxy vs MAPP) was found to greatly influence the absorbed energy as well as the damage area. The absorbed energy at perforation for the flax-MAPP composite was more than 50% higher compared to the flax-epoxy composites. Overall, the type of architecture has been found to have a limited effect on the absorbed energy at perforation. Furthermore, the use of a ductile thermoplastic matrix results in a decreased impact damage area by 38% to 59% with little delamination growth. The flax-epoxy composites experienced a stronger decrease in properties after impact, however these quasi-static properties are still much higher than the flax-MAPP composites.
This paper proposes a novel technique for improving the low-velocity impact response of woven composites, which involves synthesizing ZnO nanowires on dry woven carbon fabric layers. ZnO nanowire reinforcements were added to the interlaminar regions that are most susceptible to damage within layered composites, which were determined using finite element method analysis. Upon fabricating the laminates with and without ZnO nanowire interlaminar reinforcements, low-velocity impact responses were investigated next and the degree of damage was experimentally determined. The physical tests reveal that the samples with ZnO nanowires experience a lower degree of damage, up to a maximum of 25% for different impact energies, in comparison to the samples without ZnO nanowires. Therefore, the study presented in this paper shows the potential of using ZnO nanowires as interlaminar reinforcements for woven composites to improve their impact damage resistance.
Impact damage is one of the major concerns that should be taken into account with the new aircraft and spacecraft structures which employ ever-growing use of composite materials. Considering the thermal loads encountered at different altitudes, both low and high temperatures can affect the properties and impact behavior of composite materials. This study aims to investigate the effect of temperature and impactor diameter on the impact behavior and damage development in balanced and symmetrical CFRP laminates which were manufactured by employing vacuum bagging process with autoclave cure. Instrumented drop-weight impact testing system is used to perform the low velocity impact tests in a range of temperatures ranged from 60 down to −50 °C. Impact tests for each temperature level were conducted using three different hemispherical impactor diameters varying from 10 to 20 mm. Energy profile method is employed to determine the impact threshold energies for damage evolution. The level of impact damage is determined from the dent depth on the impacted face and delamination damage detected using ultrasonic C-Scan technique. Test results reveal that the threshold of penetration energy, main failure force and delamination area increase with impactor diameter at all temperature levels. No clear influence of temperature on the critical force thresholds could be derived. However, penetration threshold energy decreased as the temperature was lowered. Drop in the penetration threshold was more obvious with quite low temperatures. Delamination damage area increased while the temperature decreased from +60 °C to −50 °C.
This study reports on the results of an experimental investigation on the impact behaviour of pultruded composites samples subjected to low-velocity impacts with higher impact energies ranging from 16.75 to 67 J. The specimens were placed and supported according to the requirement of ASTM 7136 standard. The results of impact characteristics and performance are demonstrated and compared for different impact energy levels. The damage evaluation is also introduced to compare the failure modes of pultruded composites subjected to different energy levels. The development and propagation of stress during the low-velocity impacts are analysed using the finite element method. The numerical predictions were found to corroborate the experimental results in terms of load-time and central deflection-time curves.
The present experimental investigation is aimed at performing an analysis of mechanical and impact properties of flax and basalt fibres and their hybrids using a vinylester resin to produce reinforced thermosetting composites. Laminates were fabricated by hand lay-up and resin infusion. Cure processes were accelerated and controlled by applying heat and pressure in autoclave. Tensile, flexural and falling weight impact tests were carried out, the latter with energies of up to 40 J. The results indicated that hybrid laminates did not mostly offer properties to the level predicted by an application of the rule-of-mixtures, especially as regards flexural performance. On the other side, advantages provided concerned in particular reducing the brittleness of basalt offering some evidence of plastic behaviour, especially related to the fact of flax fibre reinforced laminated providing a quite long period at quasi constant load during impact tests, therefore resulting in delayed failure, while extensive damage is produced. The results tend to challenge the idea that basalt/flax fibre hybrid laminates would offer a good performance only with the presence of basalt fibres in the outer layers and would suggest the possible adoption in future of more complex stacking sequences, involving intercalation of flax and basalt layers.
This study investigates the low velocity impact properties such as damage thresholds, critical energy thresholds and damage process of laminated composites. Damage thresholds of Hertzian failure and main failure corresponding to woven and unidirectional Glass Fiber Reinforced Polymer laminates in varying thicknesses from 2 mm to 8 mm are determined through impact tests with nominal impact energies of 4, 6, and 8 J/layer. Hertzian failure and main failure thresholds of a composite laminate with a particular thickness remain substantially constant with the nominal and incipient impact energies. Energy profile and normalized energy profile diagrams are used to find out the penetration and perforation thresholds as well as explaining the correlation between the threshold energies and damage process of the laminates. Dissipated energy by a laminate is determined using a second order polynomial regression based on the relationship between energy dissipation and impact energy of data points before penetration. Penetration and perforation energies increase non-linearly with the thickness and thickness dependence is expressed using a power regression. Test results related to damage thresholds, threshold energies and effective damage area reveal that unidirectional laminates possess lower impact damage resistance and hence are more sensitive to impact damage.
The shrinkage of vinyl ester particulate composites has been reduced by curing the resins under microwave conditions. The reduction in the shrinkage of the resins by microwaves will enable the manufacture of large vinyl ester composite items possible [12-15]. This project is to investigate the difference in impact strength between microwave cured vinyl ester particulate composites and those cured under ambient conditions. Drop weight impact test will be used to achieve the aim of the project [7]. The results show that the difference in the impact strength is minimal [5]. The original contribution of this paper is to view the fractured surface of composites cured under different conditions to find out whether they are the same. If they are the same, it can be deduced that the initial expansion of the composite due to microwave irradiation will not affect the final structure of the composite.
The low-velocity impact response of thin carbon woven fabric composites reinforced with functionalized multi-walled carbon nanotubes (MWCNTs) is investigated. Three loadings of MWCNTs by weight of epoxy are examined; 0.5%, 1.0%, and 1.5%. The composite plates are subjected to five levels of energy; 15, 24, 30, 60, and 120 J. The time history response of load, displacement, velocity, and energy are measured and reported. Moreover, the composite damage, associated with each energy level, is quantified and compared between different MWCNTs loadings. It is observed that the functionalized MWCNTs enhanced the impact response and limited the damage size in the woven carbon fiber composite. The addition of 1.5% MWCNTs resulted in 50% increase in energy absorption.