拉伸速率对钢板胶接接头力学性能的影响

本文对两种钢板单搭胶接接头在不同的拉伸速率下(准静态、10m/s、20m/s)实验研究了不同拉伸速率对两种钢板接头力学性能的影响。结果表明钢板胶接接头在高速拉伸(10m/s、20m/s)时的强度相对于准静态(13mm/min)有明显提高,并且随着拉伸速率的增加而增大。这是由于在高速拉伸时接头及胶层高速形变,应变率大大增大,胶层粘性因素所产生的应力大大增加,使得接头强度提升。失效模式也随着发生改变,呈现出脆性断裂模式。被粘物材料性能的不同也会对接头强度产生影响,且这种影响随着拉伸速率的增加逐渐减小。     

硅烷处理对有机涂层／金属胶接接头力学性能的影响

研究了硅烷处理的胶接接头的力学性能,分析了硅烷处理对涂层/金属界面力学性能的影响.对碳钢表面进行硅烷处理,用环氧树脂胶黏剂粘接.对疲劳后的胶接接头施加静态载荷,通过分析硅烷处理胶接接头的应力-应变曲线及接头破坏形式,得出疲劳破坏与静载破坏的区别.结果表明:硅烷处理的胶接接头经一定周次疲劳后能提高接头的粘接强度,接头的破坏形式虽然为界面断裂但却为韧性断裂;接头静拉破坏形式为界面破坏和内聚破坏的混和破坏.     

刚度非平衡胶接接头的二维应力分析

建立一种通用的分析刚度非平衡胶接接头应力的二维弹性理论。该理论通过使用完整的几何方程和完整的本构方程,不但考虑被粘体的弯曲、拉伸、剪切效应和胶层的剪切和撕扯行为,而且严格满足包括接头端头处胶层剪应力为零的所有边界条件,适用于被粘体/胶层厚度和材料属性的任何组合。与二维线弹性有限元分析对比表明:该理论解有很好的精度。最后对刚度不平衡程度对胶层应力分布的影响进行参数研究。     

复合材料单搭接头的剪切强度对比实验研究

在常温和湿热高温的环境下,分别进行了三种不同的成碰工艺(RTM、引入缝纫的RTM和胶接)制备的单搭接头的剪切强度实验,研究了成型工艺对单搭接头的剪切强度的影响,并根据实验现象分析了单搭接头的剪切破坏机理.实验结果表明:引入缝纫的RTM成型试样的剪切强度性能最高,而胶接成型试样的剪切强度最低;环境温度对RTM和引入缝纫RTM成型试样的剪切强度影响不大,而对胶接成型试样的剪切强度有较大影响.     

封闭条件下胶接单搭接头固化过程的实验与数值模拟

汽车板胶粘件外部环境的封闭条件对胶接接头的固化情况影响很大。文中对封闭条件下单搭胶接接头的固化过程进行了实验研究,找出了钢板单搭胶接接头搭接区域温度以及胶粘剂固化度随固化时间的变化规律。为了预测封闭单搭接头固化过程中胶层的固化度变化规律,根据热传导以及固化动力学理论对其固化过程进行三维数值建模,利用实验对模型计算结果进行了验证,通过数值计算发现,固化过程开始时,接头升温速度较慢、且接头整体温度分布不均匀,搭接区域温度较低、两端温度较高,随着固化时间延长,接头升温速率加快,而接头总体温度分布越来越均匀。     

铺层方式对CFRP-铝合金单搭接胶接接头低速冲击损伤及剩余拉伸性能的影响

采用热压罐成型方法制备铺层方式为[+45/-45]_4s、[0/+45/-45/90]_2s和[0/90]_4s的碳纤维复合材料层合板,通过胶黏剂与铝合金板进行粘接获得异质材料单搭接胶接接头。利用落锤冲击试验机和万能电子试验机分别对三种接头进行低速冲击与冲击后静态拉伸测试,获得接头接触力-时间曲线和拉伸强度。通过CT扫描技术和数字图像相关(DIC)方法表征接头冲击损伤模式及表面应变演化过程,研究了铺层方式对接头抗冲击性能、冲击损伤模式以及剩余拉伸性能的影响。结果表明,复合材料铺层方式为[+45/-45]_4s时,接头在冲击载荷作用下具有较高的抗冲击性能,但胶层界面脱粘损伤较为严重。与胶层界面脱粘相比,接头剩余强度对层合板分层损伤更为敏感。相较于[+45/-45]_4s,[0/+45/-45/90]_2s和[0/90]_4s铺层方式接头的胶层界面脱粘范围与冲击后失效载荷退化程度较小,同时接头冲击后拉伸载荷主要集中于临近胶层的0°铺层且失效模式较为复杂...     

折曲长度对胶接接头应力分布影响的数值分析

运用有限元法研究了折曲长度对胶接接头应力分布的影响,结果表明,采用折曲的搭接方式能改善接头的应力分布,提高接头的承载能力;在一定范围内折曲长度增大,应力流线发生改变;接头应力分布越均匀;折曲长度取20mm时,接头界面以及胶层应力的分布较为理想.     

基于理论解的三种胶接接头简化有限元单元

建立了非对称胶接接头位移理论,它能严格满足包括胶层端头剪应力为零在内的所有边界条件。由于上被粘物、下被粘物具有不同材料和厚度,研究非对称胶接接头更具一般性。以位移理论解为基础,通过一组特定位移约束条件确立了被粘物纵向和横向位移函数,获得了非对称T形、L形和单搭接接头简化有限元单元的单元刚度矩阵。这些胶接接头简化单元能大幅降低整体有限元模型的自由度数量,避免以往胶层单元胶层厚度估计过大的不足,并考虑了被粘物间连续传力的特性,更适于大型有限元模型中对胶接接头的简化建模。精细有限元模型的数值验证表明,三种胶接接头简化有限元单元精度很好,使其应用到诸如汽车白车身、飞机等大型有限元模型中成为可能。     

嵌块长度对胶接接头应力分布影响的数值分析

利用弹塑性有限元方法研究了钢嵌块长度对单搭接接头应力分布的影响,结果表明,采用钢嵌块形成混合连接接头后,接头上的应力流线分布发生了变化,钢嵌块中存在的压缩轴向应力和负值剥离应力有利于提高接头的承载能力;嵌块长度的增加使胶层和被粘物中界面处的峰值应力显著增大,而嵌块中的应力变化不大,嵌块长度超过4mm后,胶层中的应力峰值急剧上升;在需用嵌块增强胶接接头时应注意采用适宜的嵌块长度.     

Z-pin增强树脂基复合材料单搭接头弯曲性能

为了研究Z-pin对单搭接头弯曲性能的影响,制备了不同参数Z-pin增强单搭接头试样,研究了Z-pin单搭接头在三点弯曲载荷下连接性能.结果表明:Z-pin(直径0.5mm)体积分数从0％～1.5％时,弯曲载荷随Z-pin体积分数的增加而增加,体积分数在1.5％～3.0％范围内时,试样的弯曲载荷随Z-pin体积分数的增加而下降,Z-pin体积分数为1.5％时达到最大值1303.2N;Z-pin直径为0.3～0.7mm时(体积分数1.5％),峰值载荷随着直径的增加而增加,0.7mm增强接头的弯曲载荷比0.3mm增强接头高出27.9％.Z-pin植入角度对单搭接头弯曲性能影响不大.另外,随着搭接长度的增加,单搭接头的弯曲性能提高.     

The effect of adherent thickness on fatigue life of adhesively bonded joints

The effect of adherent thickness on the fatigue performance, fatigue limit, and failure mode of adhesively bonded thin aluminum single lap joint (SLJ) was experimentally and numerically investigated. High‐cycle fatigue tests were performed, and fatigue life was estimated using various fatigue criteria and finite element modeling. Based on the experimental results, increase in adherent thickness leads to increase in fatigue limit. In addition, failure location changes from adhesive to adherent by increasing the adherent thickness. It seems that in adherent failure, selecting a sheet with higher fatigue strength is required to achieve higher fatigue life. Also, based on the analysis of different fatigue criteria, Smith‐Watson‐Topper criterion could predict the joint fatigue life more accurately by considering the mean stress effect and the plastic strain. Finally, as an important result, an unsymmetrical SLJ specimen was evaluated as an industrial case study, and the empirical estimated life was consistent with the experimental results.     

How defects in an adhesive layer influence the fatigue strength of bonded steel-sheet specimens

Fatigue specimens were manufactured with a number of artificial bond defects. The defects were different configurations of non-bonded areas within the nominally perfectly-bonded region. These defects included variants with a reduced degree of bond filling, bonds with a channel without adhesive, zig-zag-shaped bond edges, and finally bond areas with smooth corners. Fatigue testing was performed with the bond loaded in the peel mode. The stiffness was measured for the bonds and was found to vary significantly with defect type and size. The fatigue strength was also found to differ substantially for different bond defects. A finite element model combined with fracture mechanics was used to predict the stiffness drop during fatigue testing of the bonded specimens and to predict fatigue life. The effect of defects in the bond on the stiffness and life was predicted in a satisfactory way.     

胶粘剂在粘接接头内热分解动力学的计算

为了研究粘接接头内胶粘剂的耐热性能,采用X射线能谱分析确定了不同条件下粘接接头内胶粘剂的元素组成及其变化行为,利用X射线能谱计算了胶粘剂的热失重率,进而计算出聚酰亚胺薄膜粘接接头内胶粘剂的热分解动力学,并与空气环境下胶粘剂热分解活化能进行了比较.计算结果表明,粘接接头内胶粘剂的热分解速率低于空气环境下胶粘剂热分解速率,这种分析测试方法为原位表征粘接接头内胶粘剂耐热性能提供了一种新的分析方法.     

An innovative testing technique for assessing the VHCF response of adhesively bonded joints

In the last few years, the use of adhesive joints for structural applications has rapidly increased and adhesives are more often subject to fatigue loads during their in‐service life. In presence of a rapidly varying load, such as a high‐frequency vibration, adhesively bonded joints may undergo fatigue lives in the Very High Cycle Fatigue (VHCF) region that are significantly larger than those investigated in usual high‐cycle fatigue tests. The present paper proposes an innovative testing technique for performing accelerated fully reversed tension‐compression VHCF tests on adhesive butt‐joints. The procedure for the design of the adherends is described and then experimentally validated. Ultrasonic VHCF tests are finally carried out on a cyanoacrylate butt‐joint up to 10⁹ cycles: experimental results show that the proposed testing equipment permits an effective assessment of the VHCF response of the adhesive in a limited testing time.     

Fracture mechanics‐based progressive damage modelling of adhesively bonded fibre‐reinforced polymer joints

A quasi‐static progressive damage model for prediction of the fracture behaviour and strength of adhesively bonded fibre‐reinforced polymer joints is introduced in this paper. The model is based on the development of a mixed‐mode failure criterion as a function of a master R‐curve derived from the experimental results obtained from standard fracture mechanics joints. Consequently, the developed failure criterion is crack‐length and mode‐mixity dependent, and it takes into account the contribution of the fibre‐bridging effect. Energy release rate values for adhesively bonded double‐lap joints are obtained by using the virtual crack closure technique method in a finite element model, and the numerically obtained strain energy release rate is compared to the critical strain energy release rate given by the mixed‐mode failure criterion. The entire procedure is implemented in a numerical algorithm, which was successfully used for predicting the strength and R‐curve response of adhesively bonded double‐lap structural joints made of pultruded glass fibre‐reinforced polymers and epoxy adhesives.     

Crack path selection in adhesively bonded joints: the roles of external loads and speciment geometry

This paper investigates the roles of external loads and specimen geometry on crack path selection in adhesively bonded joints. First, the effect of mixed mode fracture on crack path selection is studied. Using epoxy as an adhesive and aluminum as the adherends, double cantilever beam (DCB) specimens with various T-stress levels are prepared and tested under mixed mode fracture loading. Post-failure analyses on the failure surfaces using X-ray photoelectron spectroscopy (XPS) suggest that the failure tends to be more interfacial as the mode II fracture component in the loading increases. This fracture mode dependence of the locus of failure demonstrates that the locus of failure is closely related to the direction of crack propagation in adhesive bonds. Through analyzing the crack trajectories in failed specimens, the effect of mixed mode fracture on the directional stability of cracks is also investigated. The results indicate that the direction of the crack propagation is mostly stabilized when more than 3% of mode II fracture component is present at the crack tip regardless of the T-stress levels in the specimens for the material system studied. Second, using a high-speed camera to monitor the fracture sequence in both quasi-static and low-speed impact tests, the effect of debond rate on the locus of failure and directional stability of cracks is investigated. Post-failure analyses including XPS, Auger electron spectroscopic depth profile, and scanning electron microscopy indicate that as the crack propagation rate increases, the failure tends to be more cohesive and the cracks tend to be directionally unstable. Last, as indicated by the finite element analyses results, the T-stresses, and therefore the directional stability of cracks in adhesive bonds, are closely related to the thickness of the adhesive layer and also the thickness of adherend. This specimen geometry dependence of crack path selection is studied analytically and is verified experimentally.     

Effect of manufacturing methods on the shear strength of composite single-lap bonded joints

The present paper experimentally addresses the effect of manufacturing methods on the strength of composite bonded joints. A total of 391 specimens, manufactured by four different fabrication methods, were tested. For each method, various overlap lengths, adherend thicknesses and lay-up patterns were examined. The failure strength was higher in thicker adherend joints and lower in specimens with larger overlap length. Results showed that the secondary bonded joints had higher strength than the co-bonded and adhesively cocured joints and yielded similar strength compared with the non-adhesive cocured case. Changes in the stacking sequence also affected the interlaminar stresses and failure loads.     

Effect of crack-growth mechanism on the prediction of fracture load of adhesive joints

This paper presents observations regarding the cracking behavior of tensile-loaded structural adhesive joints. Experiments showed that fracture occurred by the development and propagation of a damage zone, rather than a single, sharp crack, and that the presence of the adhesive spew fillet did not affect the fracture load of the adhesive joints studied. For joints bonded with the mineral-filled epoxy Cybond 4523GB (American Cyanamid), there was approximately 5 mm of subcritical crack propagation prior to final fracture. Fracture-load predictions based on the initial uncracked geometry made in previous papers were unaffected by this small change in geometry. For joints bonded with the rubber-toughened epoxy Permabond ESP 310, approximately 50 mm of subcritical crack propagation was observed. It was again found that predictions made in previous papers on the basis of the initial geometry gave a good estimate of the final fracture load even though this subcritical crack propagation significantly altered the geometry, and thus the applied energy release rates. The effect of shear deformations of the adherends was also investigated, and it was found that shear deformations could be neglected in engineering calculations for joints subject to remote tensile loading.     

高温老化对玄武岩纤维增强树脂复合材料-铝合金单搭接接头失效的影响

为了研究持续高温环境对车用新材料粘接结构力学性能的影响,加工了铝合金-铝合金（Al-Al）和玄武岩纤维增强树脂复合材料-铝合金（BFRP-Al）单搭接接头,在高温（80℃）环境下进行了0天（未老化）、5天、10天、15天的老化实验,并对胶粘剂和BFRP复合材料进行了DSC和FTIR测试,分析高温老化后胶粘剂、BFRP复合材料的玻璃化转变温度（T_g）和化学成分变化,通过准静态拉伸测试获得老化后接头的失效载荷,并对其失效模式进行分析。研究结果表明:高温环境下,胶粘剂会发生后固化及氧化反应,BFRP复合材料发生热分解及氧化反应;Al-Al接头的失效载荷随老化周期的增加而不断增大,老化前后的失效模式均为内聚失效,其性能变化主要由胶粘剂决定;BFRP-Al接头的失效载荷先增加后减小,不同老化周期的接头均发生内聚和撕裂的混合失效,其性能变化由胶粘剂和BFRP复合材料共同作用决定,且随着老化周期的增加,BFRP复合材料撕裂面积不断增大,BFRP-Al接头的失效模式越来越倾向于玄武岩纤维/树脂界面的破坏,BFRP复合材料老化对接头失效载荷的影响越来越显著。