Investigation of the effect of different variables on strength of adhesive joints

In this article, the tensile strength of different adhesive bonded joints under a tensile load was analyzed numerically. The effects of certain parameters, including the bonding length and bonding ratio, were investigated. For this reason, the epoxy adhesive was used. Joints were prepared with aluminum materials. The stress analyses were employed using the Finite Element Method (FEM). ANSYS (v.14.0.1) FEM tool was utilized to investigate the stress distribution characteristics of aluminum lap joint under tensile loading. Numerical results were found to be quite reasonable. The numerical results show that the influences of variations are very notable when the equivalent stresses are between 18 MPa and 20 MPa.     

基于循环载荷的单搭胶接接头残余强度分析

为研究循环载荷下单搭胶接接头的残余强度及失效机理,以5052铝合金单搭胶接接头为研究对象,先后对其进行静强度测试、疲劳强度测试和残余强度测试,引入威布尔分布对试验数据进行分析,检验其有效性,并采用超声扫描显微镜和扫描电子显微镜对失效胶层进行失效机理分析。结果表明,在疲劳循环载荷作用下,接头刚度基本稳定,而残余强度随着疲劳循环载荷周次的增加,呈现出先增大后减小的变化趋势;疲劳裂纹从接头搭接端部的界面端点处开始萌生,并快速向中间扩展,当疲劳循环达到一定次数时,胶层瞬间断裂,裂纹萌生阶段几乎占据了其全部疲劳寿命,失效后的胶层会出现"凹台"状微观结构。     

Predicting fracture of solder joints with different constraint factors

Double cantilever beam (DCB) specimens of 2.5‐mm‐long SAC305 solder joints were prepared with thickness of copper adherends varying from 8 to 21 mm each. The specimens were tested under mode I loading conditions (ie, pure opening mode with no shear component of loading) with a strain rate of 0.03 second^?1. The measured fracture load was used to calculate the critical strain energy release rate for crack initiation, J_ci, in each case. Fracture behaviour showed a significant dependence on the adherend thickness; the J_ci and plastic deformation of the solder at crack initiation decreased significantly with increase in adherend thickness. This behaviour was attributed to changes in stress distribution along the solder layer when the adherend thickness was varied. The capability of J_ci as a property was then assessed to predict the fracture load of solder joints in specimens with different constraint levels caused by variations in adherend thicknesses. In light of the results obtained, a cohesive zone model (CZM) was developed to predict the fracture load of solder joints as a function of adherend thickness. Finally, a CZM with a single set of parameters was established to predict the fracture loads for all the cases. It was concluded that CZM was a better methodology to account for changes in degree of joint constraint imposed by bonding adherends.     

A study on the strength of adhesively bonded joints with different adherends

In this study, mechanical properties of adhesively bonded single-lap joint (SLJ) geometry with different configurations of lower and upper adherends under tensile loading were investigated experimentally and numerically. The adherends were AA2024-T3 aluminum and carbon/epoxy composite with 16 laminates while, the adhesive was a two-part liquid, structural adhesive DP 460. In experimental studies, four different types of single-lap joints were produced and used namely; composite–composite (Type-I) with lower and upper adherends of the same thicknesses and four different stacking sequences, composite–aluminum (Type-II) with lower and upper adherends of the same thicknesses and four different stacking sequences, composite–aluminum (Type-III) with lower adherend (composite) of the same thickness but upper adherend of three different thicknesses, aluminum–aluminum (Type-IV) with lower adherend of the same thickness but upper adherend of three different thicknesses, composite–composite (Type-V) with [0]₁₆ stacking sequences and three different overlap length, aluminum–aluminum (Type-VI) with three different overlap length. In the numerical analysis, the composite adherends were assumed to behave as linearly elastic materials while the adhesive layer and aluminum adherend were assumed to be nonlinear. The results obtained from experimental and numerical analyses showed that composite adherends with different fiber orientation sequence, different adherend thicknesses and overlap length affected the failure load of the joint and stress distributions in the SLJ.     

A parametric study on the failure of bonded single-lap joints of carbon composite and aluminum

A parametric study on adhesively bonded carbon composite-to-aluminum single-lap joints was experimentally conducted. FM73m, a high strength adhesive produced by Cytec, was used for bonding. The primary objective of this study is to investigate the effects of various parameters, such as bonding pressure, overlap length, adherend thickness, and material type, on the failure load and failure mode of joints with dissimilar materials. While metal bonded joints generally fail at the adhesive, the final failure mode of all the tested bonded joints with dissimilar materials was delamination of the composite adherend. Bonding strengths of the tested joints were lower than the metal-to-metal bonded joint strength. The specimens bonded under pressure of 4 and 6 atm yielded higher failure loads than under pressure of 3 atm, which is within the range of the manufacturer-recommended bonding pressure. Failure loads of the joint increased slightly at an overlap length larger than 30 mm. Increasing adherend thickness resulted in an increase of the failure load, but was not linearly proportional to the failure load.     

Experiment and design methods of composite scarf repair for primary-load bearing structures

A relative thick plate of composite being repaired by scarf bonding was substituted as the scarf joints and studied under tensile load in this paper. The experimental investigation told us the ultimate capability of load and failure mechanism of composite scarf joints. In order to explain failure mechanism for scarf bonding repair of composite structures distinctly, FEM based on continuum damage mechanics (CDM) was carried out. CDM equations were derived by adding the delamination mode and 3D Hashin criteria based on strain into the composite constitutive relation. Furthermore, a modified semi-analytical method (MAM) was developed to obtain shear stress distribution in theory. MAM can improve the accuracy of Harman and Wang method, solve the stress asymmetry, obtain secondary peak of shear stress, and increase the highest peak of stress. In the end, the discussions for the methodologies of MAM, CDM and linear FEM were executed to compare the errors of predicting ultimate load. The discussion revealed that MAM has sufficient accuracy as an analytical methodology which could be utilized to design composite scarf repairs in a short cycle simply.     

Fatigue performance of adhesively bonded single lap joints with non‐flat sinusoid interfaces

The role of a sinusoid interface shape on the load bearing capacity and fatigue life of adhesively bonded single lap joints (SLJs) was investigated numerically and experimentally. Aluminium adherends with wavy interfaces were tested under both quasi‐static and fatigue loading conditions. The experimental results showed that the non‐flat SLJs were indeed much stronger than the conventional flat joints. In order to fully demonstrate the advantage of the non‐flat sinusoid SLJ over the conventional SLJ, comparative fatigue tests with different loading levels were performed to determine the durability performance of the SLJs with non‐flat interfaces. The experimental results revealed that the non‐flat SLJ had considerably higher fatigue life than the conventional lap joint.     

Effects of laminate carbon/epoxy composite patches on the strength of double-strap adhesive joints: Experimental and numerical analysis

In this study, mechanical properties of double-strap joints with aluminum or composite patches of different orientation angles at their overlap area were investigated under tensile loading. For this purpose, AA2024-T3 aluminum was used as adherend, while patches were either AA2024-T3 aluminum or 16-ply laminate of carbon/epoxy composite with five different orientation angles ([0]₁₆, [90]₁₆, [0/90]₈, [45/−45]₈, [0/45/−45/90]₄). A two-part paste adhesive (DP 460) was used to bond adherend and patches. Six different types of joint samples were subjected to tensile loading. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. As a result, it was concluded that the data obtained from 3-D finite element analysis were coherent with experimental results and additional to that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.     

Finite element simulation of the dynamic response of human joints: application of the PAM-SAFE™ explicit code

Models of prosthetic joint implants can provide biomechanical engineers with the analytical tools to improve the lifespan of implants and increase patient comfort. This paper reports the results of three studies using finite element models (FEM) of human joints wherein useful data can be acquired from observing the kinematics, as well as the strain and stress distributions, in different configurations of load impact.     

A mechanically fastened composite laminate joint and progressive failure analysis

A comprehensive procedure for a mechanically fastened composite laminate joint (ASTM D5961 Proc. A, B) is demonstrated from fixture design to analysis of test results. The ASTM tests are applied to evaluate the standard laminate properties and the composite joints. Composite laminate mechanical joints were analyzed using the finite element method (FEM), and the results were compared to test results. A progressive failure analysis (PFA) was applied to the FEM to predict the overall failure behavior of the test specimens. Three laminate failure theories – maximum stress, maximum strain, and Tsai–Wu – were applied to the PFA to predict the test failure load, displacement and strength. The PFA method was suitable to predict the initial test range of test and maximum test load except for the excessive failure area.     

Elastoplastic response and failure assessment of steel alloys: Empirical and computational analyses

This work aims to study material nonlinearity related to a dual‐phase Steel (DP600) specimen loaded under a tension. Experiment is performed, and then captured data are processed by 3D digital image correlation (DIC). It deals with two analyses; firstly, elastoplastic response of material due to tension up to material plastification. Then, the problem is modelled using FEM, considering an isotropic von Mises criterion/hardening behaviour. To obtain comparable numerical results, model is solved using meshless methods. Besides strain fields, load/displacement response is evaluated, and numerical formulations are validated with experimental solution. Second, failure phenomenon due to plasticity is studied since material undergoes its failure. The empirical results rely on DIC, and then, damage model is resolved using Gurson‐Tvergaard‐Needleman (GTN) criterion. As a result, the engineering stress/strain curves are reported. Comparisons are made between DIC and GTN damage model. Promising computational results are verified by DIC results implying that supportive strategy is proficient.     

The Effect of Composite Patches on the Failure of Adhesively-Bonded Joints Under Bending Moment

In this study, it was aimed to compare mechanical behavior of double-strap joints with aluminum (AA2024-T3) or 16-ply laminate of carbon/epoxy composite (T300/934) patches of different orientation angles at their overlap area subjected to bending moment. For this purpose, AA2024-T3 aluminum was used as adherend, while the adhesive was a two-part paste (DP 460). Six different types of joint samples were subjected to bending moment. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. In the numerical analysis, the composite patches were assumed to behave linearly elastic, while adherend and adhesive layers were assumed to be nonlinear. It was found that the data obtained from 3-D finite element analysis were coherent with experimental results. Meanwhile, experiments showed that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.     

改进的复合材料斜接结构胶层应力半解析法

引入微分概念和复合材料铺层刚度分配原则,形成一种改进的求解复合材料斜面对接结构胶层应力的半解析方法 MAM(Modified semi-Analytical Method)。首先,针对铺层角度及铺层数不一致的情况,采用有限元法(FEM)平面应变模型对MAM进行验证;然后,分别用平均剪应力法、FEM及MAM预测了复合材料斜接结构的承载能力并与试验值进行对比;最后,利用MAM分析工程应用问题,考虑了被粘结体刚度不匹配及胶层厚度的变化。研究结果表明:MAM适于设计复合材料斜接结构;采用MAM能得到胶层应力的尖峰值,且应力分布与FEM计算一致。     

液体垫片对复合材料单搭接螺栓接头力学性能的影响

复合材料构件由于存在制造误差,装配时常常产生间隙,消除间隙的一种基本手段是向其中填充液体垫片。以复合材料单搭接螺栓连接接头为研究对象,设计了拉伸实验,选取一种改进的失效准则与对应的材料退化准则建立了渐进损伤有限元分析（FEA）模型,在此基础上研究了液体垫片对复合材料单搭接接头强度、刚度等力学性能的影响及复合材料孔内损伤演化的过程,此外还研究了液体垫片孔边的应力-应变状态。由实验与有限元结果可以得出：随着液体垫片厚度的增加,接头的拉伸刚度与峰值载荷均有所降低;相同载荷下复合材料孔内损伤加剧,孔内单元产生初始损伤时对应的载荷降低;但液体垫片厚度的增加可以降低垫片孔边的应力与塑性应变峰值,并使其分布更加均匀化,改善液体垫片孔边受力状态。     

Fracture load prediction of lead-free solder joints

Continuous and discrete SAC305 solder joints of different lengths were made between copper bars under standard surface mount (SMT) processing conditions, and then fractured under mode-I loading. The load-displacement behavior corresponding to crack initiation and the subsequent toughening before ultimate failure were recorded and used to calculate the critical strain energy release rates. The fracture of the discrete solder joints was then simulated using finite elements with two different failure criteria: one in terms of the critical strain energy release rate at initiation, G_ci, and another based on a cohesive zone model at the crack tip (CZM). Both criteria predicted the fracture loads reasonably well. In addition, the CZM was able to predict accurately the overall load-displacement behavior of the discrete joint specimen. It could also predict the load sharing that occurred between neighboring solder joints as a function of joint pitch and adherend stiffness. This has application in the modeling of the strength of solder joint arrays such as those found in ball grid array packages.     

金属胶接接头残余应力计算及数值分析

利用Baker模型和弹塑性有限元方法研究了胶接接头搭接区残余应力的分布.结果表明,因胶粘荆的线膨胀系数比被粘物高得多,胶层固化时被粘物阻碍了胶层的收缩,故胶层中为残余拉伸应力,被粘物中为残余压缩应力,胶层中的残余应力远大于被粘物中的残余应力.利用Baker模型和有限元计算远离自由端的胶层中的残余应力,两者吻合.被粘物中的残余应力呈中心对称,等效应力经多项式拟合后呈抛物线分布.     

复合材料π接头拉伸力学性能的试验和计算研究

采用试验和数值模拟的方法对整体化复合材料π接头在拉伸载荷作用下的力学特性进行研究。在Instron 8803电液伺服材料试验机上进行了π接头试验件的拉伸试验,记录试验过程中损伤产生及破坏过程,记录初始失效载荷和最终失效载荷。试验结果表明,填料是π接头破坏的关键部位,需要进行深入研究。提出了复合材料π接头力学性能数值模拟的基本假设和方法,基于通用有限元商用软件,建立π接头三维力学分析模型,获得π接头各部位应力分布情况;基于基本假设,对最大应力失效准则进行修正,并给出π接头各部位损伤载荷的预测值。计算预测π接头的初始损伤部位与试验吻合,初始失效载荷计算值与5个试件试验数据均值相比误差为0.53%,表明了数值分析方法的可行性。     

The Prediction of Fatigue Crack Initiation Life in Spot Welds

Abstract: In this paper, strain‐based fatigue life prediction method has been used to estimate the fatigue crack initiation life of spot‐welded joints of Mild Steel JSC270D and Ultra‐High Strength Steel JSC980Y. To do so, the joints were simulated using three‐dimensional finite‐element (FE) models, and then nonlinear FE analysis was performed to obtain the local stress and strain ranges and finally, the Morrow equation was applied to estimate the crack initiation lives. The results have been compared with those obtained from experimental crack growth morphology. In addition, the difference between fatigue limits for smooth specimens and spot‐welded joints for mentioned materials has been briefly discussed. It has been shown that mean stress values in the Ultra‐High Strength Steel can significantly decrease the fatigue limit of spot‐welded joint because even at very low load level the stresses exceed the yield point at the root of nugget of spot‐welded joint, while the amount of mean stress in the Mild Steel for the same load level is much less than that of Ultra‐High Strength Steel. The comparison between numerical results of fatigue crack initiation lives and experimental data provided good agreement between numerical predictions and crack growth morphology observations. The results also shows that in some cases, depending on the joint type, the life spent in the nucleation phase can be an important part of the final failure lifetime.     

Fatigue failure transition analysis in load‐carrying cruciform welded joints based on strain energy density approach

This paper details a study of the application of notch stress intensity theory to the fatigue failure mode analysis of the transition in load‐carrying cruciform welded joints. The weldment fatigue crack initiation point is difficult to predict precisely because it usually occurs in the vicinity of the weld toe or weld root. To investigate the relationship between fatigue failure location and the geometry of the weldments, we analysed the weld toe and root asymptotic notch stress fields were analysed using the notch stress intensity factors on the basis of the Williams' solution in Linear Elastic Fracture Mechanics (LEFM). Numerous configurations of cruciform joints of various plate thicknesses, transverse plate thickness, weld sizes and incomplete penetration size were used to investigate the location of the fatigue failure. The strain energy density (SED) surrounding the notch tip was introduced to unify the scalar quantity and preclude the inconsistency of the dimensionality of the notch stress intensity factors for various notch opening angles. The results of the investigation showed that the SED approach can be used to determine the transition zone for a variety of joint geometries. The validity of the SED criteria was verified by comparing the experimental results of this study with the complied results for load‐carrying cruciform welded joints reported in literature.     

三维编织复合材料弹性性能数值预测及细观应力分析

基于考虑纤维束面接触的细观结构模型, 引入周期性位移边界条件, 采用细观有限元方法建立了材料的弹性性能预报模型。模型数值结果与试件实测数据吻合较好, 证明了该模型的合理有效性。经详细分析单胞在典型工况载荷作用下的细观应力分布及变形, 表明模型体现了周期性相邻单胞表面力和位移的连续性, 能获得单胞更为合理的细观应力应变场。