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In this research, initiation and propagation of delamination are investigated using finite element analysis and existing theories for isotropic and composite double cantilever beam (DCB) specimens. These theories work based on the well-known traction-separation laws such as linear, bilinear and exponential laws. In addition, the effects of cohesive zone parameters, i.e., critical strain energy release rate and maximum interfacial stress, transverse shear deformations and fiber bridging law are studied. The results show that the introduced theories and finite element analysis based on bilinear cohesive law are not capable to predict initiation and propagation of delamination in unidirectional composite specimen with fiber bridging effect and neglecting this region in CZM cause significant error in prediction of delamination growth. For this purpose, bilinear CZM considering bridging law is modified and implemented in 3D finite element analysis. Comparing numerical results with available experimental data in the literature shows that finite element models based on modified CZM can predict initiation of delamination as well as propagation accurately.

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The main limitation of the use of adhesive joints is weakening the adhesive layer against damaging environmental factors such as humidity. Use of numerical methods for predicting the strength of adhesive joints exposed to moist environment can significantly save time and cost. In this study, first experimental investigation and numerical modeling of the complete process of moisture diffusion into the adhesive layer and its damaging effect on the adhesive joint strength was determined. Then this process was applied for a single lap joint of SBT 9244 pressure sensitive adhesive and AL2024-T3 aluminum alloy substrate with two 12.5 and 50 mm overlap of lengths. As the first step, moisture distribution for 30, 60 and 90 days exposure times in environmental condition of 100% relative humidity was obtained. Then single lap joint tensile test was simulated using cohesive zone model for different exposure times. In this simulation cohesive zone model parameters were determined in such a way that numerical failure load and the existing experimental failure load be in good agreement. The cohesive zone model parameters were determined dependent on the moisture content. The first simulation was done without considering swelling and in the second one swelling was considered. Swelling stress was obtained separately at different exposure time periods. It was found that swelling effect was more considerable in the joints with longer overlap length and shorted exposure time.

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Fracture of femur is considered as one of the most significant causes of disability and death, especially among the elderly. Therefore, there is a global effort towards noninvasive assessment of the femoral fractures. This study was aimed at the investigation of the mechanical behavior of human femur subjected to various loading orientations, under the two categories of high-stiffness (HS) and low-stiffness (LS) loading conditions. The experimental and computational analysis of deformation and fracture patterns were carried out using the QCT images and finite element analysis. The predictions of the force and fracture pattern of the HS and LS specimens were performed using linear and nonlinear finite element analyses, respectively. Also, the cohesive zone model (CZM) was used to simulate the damage initiation and propagation in the finite element analysis of latter specimens. The comparison between the results of the numerical analysis and the experimentation showed successful simulation and prediction of fracture force of human femur under various loading orientations.

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Thermal Barrier Coatings are used as thermal protective of parts using under high temperature circumstance. These coatings usually include three layers respectively: ceramic top coat, grown oxide layer and bond coat. Due to manufacturing process and special structure of thermal barrier coatings, failure mechanisms of these coatings are affected by applied loads on coated part. In this paper failure of these coating under thermal fatigue was studied numerically and experimentally. A specimen of Inconel 617 which were coated by air plasma method and it was tested in a test setup with capability of applying four point bending load, under thermal fatigue experiment with the maximum temperature of 1170 oC in addition to constant bending load with the magnitude of 7500 Nmm. Thermal fatigue test was contined until coating spallation and temperature of specimen surfaces was measured during the test. Finite elements modeling was performed by ABAQUS to simulate the experiments thermal and mechanical loading conditions with using cohesive zone model to model top coat delamination and failure. Finally with a little change in the model, was attempted to adapt the bending magnitude of the specimen from model on experiment result to estimate interfacial cohesive properties for these coatings from finite elements results.

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In this paper, the static stiffness and strength as well as fatigue life of adhesively bonded single lap joint (SLJ) are numerically studied using the cohesive zone model (CZM). In order to simulation of the SLJ using mixed-mode bi-linear CZM, the failure behavior of adhesive in modes II and III is considered the same. Fatigue damage propagation is simulated through scripting USDFLD Subroutine in ABAQUS/Standard. Static stiffness and strength and fatigue life obtained in this study are consistent with experimental results available in literature. Then, the effect of geometric parameters including overlap length, substrate thickness, and tapered substrates are investigated. The obtained results reveal that the increase of the overlap length would lead to increase the static strength and fatigue life prediction. While increasing substrate thickness results improved fatigue life, there are no a known relation between the static strength and substrate thickness due to the changes of the loading modes. Tapered substrates have also positive effect on the strength and fatigue life because of more compatible rotations. Therefore, to improve the strength and fatigue life of a SLJ, authors suggest greater overlap length and thickness along with tapered substrates.

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Sandwich structures are consisted of two thin skins with high mechanical properties and a thick core with lower mechanical properties and weight. Due to high strength/ stiffness to weight ratio, these structures are used extensively in engineering structures such as aerospace structures, ship hulls, turbines blades, etc. Skin/core debonding is one of the major failure modes in these structures. In this paper, debonding resistance of sandwich panels with composite skins and a core consisted of PVC foam and a corrugated composite laminate is investigated both experimentally and numerically. Square geometry is considered for corrugated composite laminate and obtained results are compared with reference specimen with simple core made of PVC foam. The three point bend test with attached ENS fixture is used to perform the standard experimental test. The results have shown that in square specimen with 3 and 6 layer skin before the separation between skin/core, the specimens are failed from the middle of the upper skin, but for 8 layer skin, the skin/core debonding are accured before other modes of failure. The maximum skin/core debonding resistance for square specimen are increased 269.26 percent. Specimens are modeled in Abaqus and results show a reasonable agreement between experimental and numerical result.

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The sandwich panel is a combination of a soft core and two stiff, high-strength facesheets. In many cases, the connection between the facesheet and the core is considered as a critical point that can damages the integrity of the sandwich structure. In this study, the debonding toughness between the facesheet and the core in sandwich beams with grooved cores made of Kevlar 49/polyester facesheets and polyurethane foam core has been measured experimentally. The values ​​of the strain energy release rate obtained at the onset of crack growth for the tested specimens are in the range of 340 (J/Square meters) and increase with the crack growth up to 500 (J/Square meters). One of the innovations of the present study is to investigate the effect of grooving the core of the sandwich panel on the resistance of the structure to the growth of interfacial cracks. The results show that by placing the groove inside the core of the sandwich panel, the interfacial crack stops during growth by hitting each groove and requires higher force to restart its growth. This phenomenon increases the resistance of this type of structure against the growth of cracks in the face/core area. In this research, a model based on cohesive zone theory was used to simulate crack growth in the tested specimens. Comparison of load-displacement curves obtained from the analysis shows that the proposed model has a good ability to predict the behavior of the structure under similar loading conditions.