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Failure modes of the metal adherends: (a) locations of different modes; (b) adhesive failure (c) cohesive failure.
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Welded joints are treated as critical sites when constructing and calculating welded structures due to inhomogeneity and anisotropy of materials at the welded joint site. Because of the change in the geometry of the elements, the welded joint is viewed as the location of the stress concentration and therefore as a place that weakens the overall loa...
Citations
... In order to control the adhesive thickness after curing, the calibration gaskets were placed in the fixture. The gap between the thickness of the calibration gaskets and the thickness of the substrate was the thickness of the adhesive layer [41]: ...
This paper investigated the mechanical performance, progressive failure process, and failure modes of riveted joints, bonded joints, and hybrid joints with different adhesive layer thicknesses connecting carbon-fiber-reinforced plastic (CFRP) and aluminum alloy subjected to quasi-static tensile loading. The 2D digital image correlation technique was used to record the deformation and strain of the overlap area. The results show that the thickness of the adhesive layer had a negative effect on the mechanical properties of the hybrid joints, and when the thickness of the adhesive layer was increased from 0.2 to 0.8 mm, the peak load and the energy absorption (EA) values of the hybrid joints were reduced by 14.38 and 23.22%, respectively. Compared with the bonded and riveted joints, hybrid joints showed better performances in peak load and EA values, and rivets were able to continue carrying loads when the adhesive layer failed. The typical failure modes of the hybrid joints included CFRP compressive failure, adhesive failure, fiber-tear failure, and light-fiber-tear failure. It was further found that the adhesive could disperse the stress around the rivet holes and effectively reduce the stress concentration around the rivet holes. Nomenclature D = diameter of rivet header H = height of rivet header h = thicknesses of adhesive layer m 1 , m 2 = thicknesses of calibrated gaskets n 1 = thicknesses of aluminum alloy sheet n 2 = thicknesses of carbon-fiber-reinforced plastic sheet
... Sun et al. [49] pointed out that the bending of joints can be accurately characterized by the displacement in difference ΔU (defined as the difference between the maximum displacement Umax and the minimum displacement Umin in the bonded area). The calculated maximum value of ΔU during the entire loading process of this test is about 0.1 mm, which is very small and can be almost ignored. ...
... The above phenomenon indicates that the presence of peel strain changes the failure mode of the joint and that the steel-adhesive bonded interface is less resistant to peeling. The longitudinal strain ԑXX is small and fluctuates little during loading and has no effect on the failure of the double-lap joint, which is the same as in the case of a single-lap joint [49,50]. ...
The epoxy-bonded interfaces between carbon fiber reinforced polymer (CFRP) and steel usually have insufficient strength and toughness, and the toughening of bonded interface is a key problem for the usage of CFRP in steel structures. In this study, electrospun nanofiber veils were first proposed to enhance the bond performance of CFRP-steel epoxy-bonded interfaces. Firstly, shear tests were conducted on neat epoxy and nano-modified single-lap aluminum-aluminum joints to determine the optimal areal density and number of layers of nanofiber veils, as well as the optimal curing processes. Then, a series of neat epoxy and nano-modified CFRP-steel double-lap joints with different bond lengths were tested to investigate the size effect of the bond behavior. The displacement and strain field evolution of the joints were captured by the digital image correlation (DIC) technique, allowing for visualization of the detailed failure process. The failure modes, load-displacement curves, CFRP strain distributions, and bond-slip relationships of the CFRP-steel joints were obtained. Both the tests on aluminum-aluminum and CFRP-steel joints show that the optimal modification strategy is incorporating 3 layers of nanofiber wels with an areal density of 4.5 g/m2, with 5 h room-temperature and 2 h 80°C high-temperature curing. The primary failure mode of CFRP-steel joints is CFRP delamination accompanied by CFRP-adhesive interface or steel-adhesive interface debonding. The bond strengths of the modified joints with 3 layers of 1.5 g/m2 and 4.5 g/m2 nanofiber veils are increased by 7% and 25% compared to those of un-modified joints, respectively. The 4.5 g/m2 nanofiber veils modified bonded interface has an effective bond length of about 152 mm, with a corresponding ultimate bearing capacity of 117 kN. Different from the triangular (brittle) shape of most neat epoxy interfaces, the nano-modified interfaces have trapezoidal (ductile) bond-slip relationships, providing superior cracking resistance. Moreover, a comparison with the bond strength of SiO2 nano-particles and carbon nanotubes (CNTs) modified joints revealed that nanofiber veil modification comes to higher bond strength in most cases. The proposed electrospun nanofiber veil modification technique provides great insight into the interfacial toughening of CFRP-steel composite structures.
... The findings showed that incorporating aluminum patches in the lower stiffness adherend considerably enhanced the joint strength. Sun et al. [14] investigated the fracture characteristics of adhesive joints with dissimilar materials. It was observed that for joints with the same adherends, the fracture processes and strain evolutions along the bondline were found to be symmetrical; however, for joints with different materials, the maximum strain and crack initially emerged on the lap end of the adherend with lower yield strength. ...
This study investigates the impact of two innovative methods, namely, intermittent metal part reinforcement and countersinking, on the strength of single lap joints (SLJs). In the former method, metal inserts are strategically integrated within the adhesive layer, while the latter involves the application of countersinks on the adherends to create conical depressions for adhesive application. The metal inserts and countersink samples were fabricated using a 5-axis CNC milling machine. Subsequently, the joints were produced by subjecting the samples to 0.15 MPa pressure and 70 °C temperature for 120 min with the aid of a hot press. Tensile tests were conducted on single lap joints (SLJs) featuring five different configurations of intermittent metal part reinforcement joints (IMRJs) with varying sizes and positions of reinforcements, as well as six countersunk reinforced joints (CRJs) with different orientations of countersinks, all while keeping the width and overlap length constant. A two-dimensional finite element (FE) model of the IMRJ was constructed using ABAQUS software, incorporating cohesive zone elements to simulate the behavior of the adhesive layer (DP 460). The model's accuracy was confirmed through experimental verification. Additionally, fractographic analysis of the failure surfaces of both types of joints was carried out. The inclusion of IMRJs and CRJs in the SLJs increased their load-carrying capacity by more than 10 % and 30 %, respectively.
... ( a ) ( b ) Figure 2: Basic stress-strain curve. (a) Aluminium alloy 2024-T3 [31] (b) Araldite 2015[32]. ...
Over the last two decades, piezoelectric actuators have emerged as a promising solution for structural repair. In this work, initially the stress intensity factor (SIF) estimation using the finite element (FE) approach at crack tips in aluminium 2024-T3 plates. Based on Taguchi’s L9 orthogonal array the FE simulation has been conducted. Later, this study uses the optimization method via the design of experiments to systematically evaluate the effect of various dimensions and material qualities, especially under the conditions of Mode-I crack propagation. It also investigated the complex interaction of factors impacting adhesive bonds, piezoelectric actuators, and aluminium plates, The study not only analyses the parameter relationships but also examines their controls, identifying those best aligned with primary objectives. This sensitivity enhances the piezoelectric actuator's efficacy and quality. The research determines an optimal parameter combination, developing active repair performance and establishing an essential SIF benchmark. This research explores the complex world of piezoelectric actuator-assisted repairs, providing a road map for better structural rehabilitation.
... (d) After applying the adhesive evenly on the bonding area of the Al substrate, both substrates were placed on a flat plate. In this step, the rivet body wrapped with a circle of transparent tapes was inserted through the hole of the bonding area to prevent the Note: 'a': referring to Sun et al. [42]. ...
... This feature was somewhat similar to that of a notched composite plate under tension [44]. The substrate would rotate and generate a hinge as a result of the bending effect [42], thereby forming compressive strain at the end of bonding area on the substrate, as shown by the purple stripe in the e yy contour in Fig. 5(a1)-(a4). As the test progressed, cracks in the adhesive layer would initiate and propagate from the overlap end toward the center. ...
... Material properties of CFRP[7,42]. ...
In comparison with an adhesive joint, a hybrid joint often provides a more effective and reliable way to meet heightened safety requirements in engineering like FAA AC 20-107B. Nevertheless, its fatigue failure characterization, life improvement mechanism and engineering design approach have been understudied as compared to the static loading condition. This study aims to characterize the failure mechanisms by use of the digital image correlation (DIC) technique for elucidating the load sharing phenomenon of hybrid joints in the course of fatigue failure. In the study, bonded, riveted and hybrid joints were tested under static and fatigue loading conditions. To explore different mechanical behaviors of hybrid joints, two types of adhesives with an evident difference in modulus were selected to fabricate the joints. The fatigue life of an adhesive layer and that of the hybrid joint were separately studied to explore the means for life improvement. It is shown that the fatigue life of the hybrid joint can be significantly improved as a result of load sharing by rivets. The improvement of the fatigue life could reach 5 to 13 folders for the hybrid joint due to the load sharing, whereas its improvement ratio was only 1–2 times when the adhesive and the rivet were independent. By considering the overlap area as an effective region for design of rivet group, an optimal stiffness can be obtained for the hybrid joint. This study clearly presents two completely different fatigue failure processes for hybrid joints and illustrates the improvement mechanisms of fatigue life, thereby providing useful guidance for optimal design of hybrid joints.
... The joining of multi-materials structures usually requires the use of different joining techniques, such as adhesive and mechanical fasteners [4], each with its advantages and disadvantages. Mechanical fasteners are widely used to joint dissimilar materials and are, from a technological point of view, a more consolidated and known solution, however there exist some apparent disadvantages such as high stress concentration and destruction of structural integrity [5]. On the other hand, adhesive bonding features a more uniform stress distribution along the joint, in addition to corrosion resistance, although issues such as curing time and lack of knowledge about the factors that affect the performance of this type of joint limit its application [2,5]. ...
... Mechanical fasteners are widely used to joint dissimilar materials and are, from a technological point of view, a more consolidated and known solution, however there exist some apparent disadvantages such as high stress concentration and destruction of structural integrity [5]. On the other hand, adhesive bonding features a more uniform stress distribution along the joint, in addition to corrosion resistance, although issues such as curing time and lack of knowledge about the factors that affect the performance of this type of joint limit its application [2,5]. As acknowledged by Kanani, A. Y. et al. [2], when considering the production of multi-material joints in automotive structures, the financial feasibility of the assembling procedure is just as critical as the required mechanical strength of joints. ...
In a world in which vehicles of higher energy efficiency have constantly been pursued, the development of multi-material structures can be extremely interesting as far as structural weight reduction and the mitigation of greenhouse gas emissions are concerned. This paper evaluates basic mechanical properties of vehicular structural joints between commercial grades aluminium alloys and grade steels. These joints were produced by either riveting or adhesive bonding techniques, currently used as standard procedures in the automotive industry. Five types of joints were studied: three were adhesively bonded and two were riveted. For each joint, basic mechanical properties were measured via tensile and fatigue tests.
The tensile tests of the riveted joints have shown that the failure has constantly occurred associated to the fracture at the rivets, whereas for the adhesively bonded joints a cohesive fracture has always occurred regardless of the characteristics of the joint. The data from the fatigue tests could be well fitted to Wöhler S-N curves, so that fatigue limits for all joints could be obtained. Thus, this technology research has shown the feasibility of using adhesive bonding and riveting techniques to successfully join multi-material structures to be used in the automotive industry.
... For as concerns crack monitoring, DIC may be considered as a promising technique in adhesive joints [17] and in coated laminates [18]. ...
Thin rim gears present a complex strain and stress field due to its particular geometry, above all in bending problems. From this point of view, the position of the most stressed point and the corresponding equivalent stress value are useful for an accurate design of thin rim gears. More in detail, in case of bending failure, both crack initiation point and corresponding propagation path are strictly related to the gear’s geometry.
In this work, an experimental analysis was performed to evaluate how light weight gears geometry may influence the strain field close to the tooth root.
To this aim, an experimental activity was carried on by a dedicated equipment for bending tests and the gear deformation was monitored by using the 3D Digital Image Correlation (DIC) technique.
The local strain field in both tooth and web portions was measured for two types of gears ( standard gear and thin-rim gear) in order to identify the stress condition due to the bending loading. A particular attention was devoted to point out the most stressed point for both gears. Results were also compared with XFEM model available in literature.
... Benefits of adhesive bonding include smoother stress distribution, a significant decrease of stress concentration, weight reduction, and higher corrosion resistance. For these reasons, it has emerged as a valid strategy that can complement (or replace) bolting and riveting in joining CFRPs to metals, such as steel [4][5][6][7][8], aluminum [9][10][11][12][13][14][15][16], or titanium alloys [17]. Most research work in adhesive bonding of metals and C. Morano et al. [32]; thin film consisting of alternating stiff and compliant stripes peeled from a rigid substrate with uniform adhesion investigated by Xia et al. [37]; DCB adhesive joints comprising architected nylon substrates inspired to the basal shell of the acorn barnacle analyzed by Morano et al. [38]. ...
As the demand for structural light-weighting continues to rise, so does the interest in bonding with structural adhesives. However, adhesive joints are subjected to the nucleation and growth of crack, and there is a growing need for toughening strategies that can prevent catastrophic failures. This work focuses on secondary bonded composite/metal joints and explores a toughening approach enabled by a snap-through cracking process. A composite flat panel is bonded with a corrugated aluminum substrate with a square-wave profile, whose geometry is defined by grooves’ spacing, depth, and width. These key geometrical parameters provide opportunities to tailor the mechanics of crack growth and were chosen by resorting to finite element simulations with cohesive elements. The computational results are validated by experiments that systematically show the occurrence of snap-through cracking and a significant enhancement of load bearing capacity and dissipated energy (up to 260 %) compared to adhesive joints without corrugation.
... Other important parameters associated with the behavior of adhesive joints that are being studied on different materials, including composite materials, are the mechanical and physical characteristics of the elements that comprise the joint [7][8][9][10][11][12] and the influence in the type and rate of stress of an applied load [13][14][15][16][17]. ...
... The scheme followed in the work is as follows (Scheme 1): Other important parameters associated with the behavior of adhesive joints that are being studied on different materials, including composite materials, are the mechanical and physical characteristics of the elements that comprise the joint [7][8][9][10][11][12] and the influence in the type and rate of stress of an applied load [13][14][15][16][17]. ...
This study analyzes the behavior under the static delamination and mode-I fracture stress of adhesive joints made on the same composite material with an epoxy matrix and unidirectional carbon fiber reinforcement and two types of adhesives, one epoxy and the other acrylic. Standard DCB tests (for mode-I fracture) were used to quantify the influence on the interlaminar fracture toughness of the type of adhesive used. Both materials were subjected to two different degradation processes, one hygrothermal and the other in a salt-fog chamber. After aging, the mode-I fracture has been evaluated for both materials. From the experimental results obtained, it can be deduced for the epoxy adhesive that exposure to the hygrothermal environment used moderately modifies its behavior against delamination, while its exposure to the saline environment produces a significant loss of its resistance to delamination. For the acrylic adhesive, the hygrothermal exposure causes an improvement in its delamination behavior for all the exposure periods considered, while the saline environment slightly modifies its behavior. There is, therefore, a clear influence of the type of aging on the fracture behavior of both adhesives.
... For this application, the mechanical behaviour under fatigue loading and the environmental resistance of adhesive joints needs to be studied in order to guarantee safety and reliability. 15,16 A preliminary assessment of the adhesive joint between the metallic collar and the composite tube of concept 3 was conducted based on local stress analysis, which eventually led to the proposal of an improved joint configuration. The evaluation of the local stresses in the adhesive layer was conducted by finite element (FE) analysis using Abaqus CAE software. ...
Rail vehicle lightweighting using fibre reinforced polymer composite materials is essential for the future of rail. This is recognised as a means of reducing carbon dioxide production through lower energy consumption, as well as reducing the impact on track degradation, thus delivering improved rail capacity and performance. This paper presents an overview of the work conducted within work package three of the NEXTGEAR project focused on the ‘wheelset of the future’. Three concepts for a hybrid metallic-composite railway axle are proposed and their strengths and weaknesses are assessed. A finite element analysis on the selected concept was conducted, including a solution for the bonded joints of the metallic collars which provide the interface to the wheels and bearings. An axle mass reduction of over 63% was shown. An overview is also provided regarding the analysis of manufacturability of the axle, non-destructive methods for axle inspection/structural health monitoring and effects of impacts from ballast stones. Finally, a preliminary evaluation of the benefits arising from the reduction of the unsprung masses is provided, based on multibody simulations of vehicle dynamics.
