有间隙胶接劈裂接头应力分布的数值模拟

建立了有间隙胶接劈裂接头的有限元模型，并运用弹塑性有限元法，研究了间隙位置和长度对劈裂接头胶层中部应力分布的影响。研究结果表明：合理的间隙不仅对劈裂接头的应力峰值和接头的承载能力无明显影响，而且有利于提高接头的胶接质量；间隙的中心位置对接头的应力峰值影响显著，而间隙长度对接头的应力峰值无明显影响；当接头末端无胶层时，因应力峰值显著增大，可能导致接头的名叉强度降低。     

搭接长度对胶接接头工作应力分布影响的数值分析

运用弹塑性有限元法对单搭接金属胶接接头承载后的应力分布特征进行分析，重点研究搭接长度对分别采用酚醛树脂和丙烯酸酯制备的接头应力分布和接头强度的影响。结果表明，胶粘剂的性能对应力分布有较大影响，酚醛树脂胶粘剂制备的接头中胶瘤承担了相当多的载荷，且随搭接长度的增加,von Mises等效应力峰值和剪切应力峰值均趋于向胶层内转移，胶层中各部位的应力亦均有下降；当采用丙烯酸酯胶制备的接头时，胶瘤承载作用并不明显，其应力峰值出现在胶层中被粘物拐角处。     

胶瘤入射角度对单搭胶接接头拉剪强度和应力分布的影响

通过试验研究了胶瘤入射角度对单搭胶接接头拉剪强度的影响,并建立了相应的有限元模型,分析了胶瘤入射角度对接头中剪切应力和剥离应力分布的影响。结果表明:当胶瘤入射角度为0°时,接头中剪切应力和剥离应力的峰值均很高;随着胶瘤入射角度从30°增加到90°,接头端部剪切应力和剥离应力的峰值先增大后减小;当胶瘤入射角度为30°时,剪切应力和剥离应力均相对较小,而接头的拉剪强度最大;有限元模拟结果与试验结果基本一致。     

胶层尺寸对铝锂合金单搭接胶接接头剪切强度的影响

通过试验研究了不同胶层尺寸对铝锂合金单搭接胶接接头剪切强度的影响,并建立了相应的有限元模型,详细分析胶层厚度和搭接长度对应力分布的影响。结果表明:胶接接头的剪切强度随胶层厚度的增加先升后降,合理的胶层厚度为0.2～0.6mm;胶接接头的剪切强度随搭接长度的增加呈非线性增加,合理的搭接长度为12～16mm;有限元模拟结果与试验结果基本一致。     

混元胶接单搭接头的应力与刚度分析

拉剪胶接接头的峰值应力常发生在搭接区端头,而中间区的应力非常小,为降低应力集中,提高接头强度和连接效率,系统研究胶层变刚度的混元胶接技术,将高弹性模量的脆性胶置于中间区,而低模量的韧性胶置于搭接区边缘.以胶接理论为基础,考虑被粘物剪切应变,建立单搭拉剪混元胶接接头的线弹性应力和刚度解析模型.理论模型中的正应力和剪应力与有限元模型吻合得较好,证实理论模型的正确性.有限元和解析解均表明,混元胶接接头在搭接区端头的峰值剪应力分别较单一刚性胶和柔性胶胶接时下降了52.1%和24.4%,参数研究中确定了影响混元胶接接头应力和刚度分布特征的关键耦合参数.     

轻质合金胶接接头强度的胶层厚度依赖性的实验研究

实验研究了胶层厚度对轻质铝合金单搭接头总体强度的影响规律,并探讨了接头总体强度-胶层厚度关系曲线变化趋势的相关影响因素,具体评估了胶黏剂韧性的影响。实验结果表明:当胶层厚度改变时,韧性胶黏剂对应胶接接头总体强度的变化程度,比脆性胶黏剂对应的情况要剧烈,当厚度处于较小范围的时候,这种现象表现得尤为明显。当胶层厚度大于临界厚度时,胶接接头的总体强度表现为胶黏剂的宏观剪切强度。实验结果与已有模型预测结果吻合较好。     

胶瘤弹性模量对铝单搭接接头应力分布的影响

利用弹塑性有限元法,研究四种不同弹性模量的胶粘剂 (丙烯酸酯胶、聚氨基甲酸乙酯胶、环氧树脂胶和酚醛树脂胶粘剂等) 形成的胶瘤对铝合金单搭接接头应力分布的影响.结果表明,当胶瘤采用不同于胶层的胶粘剂时,随着胶瘤弹性模量的减小,在胶层与胶瘤的连接处胶层中应力峰值显著提高,且均高于由单一胶所形成接头的应力峰值.对被粘物中紧邻界面层中的应力分布而言,峰值应力出现在胶瘤与胶层的连接处及靠近搭接区两端部处.随着胶瘤弹性模量的增加,靠近被粘物承载端的区域的应力越大,而自由端的应力越小,且靠近承载端的区域的应力峰值由胶瘤与胶层的连接处向承载端一侧转移,因而采用弹性模量低的胶粘剂形成胶瘤对接头的承载不利.     

胶厚对单搭粘接接头强度影响的试验与仿真研究

为研究不同胶层厚度对单搭粘接接头强度的影响,对胶层厚度为0.2 mm、0.7 mm、1.5 mm和2.5 mm的铝5052-铝5052(Al5052-Al5052)单搭粘接接头进行拉伸-剪切试验,对比不同胶厚对Al5052-Al5052单搭粘接接头强度的影响。仿真分析考虑材料非线性和几何非线性,模拟不同胶层厚度表面上的等效应力的分布情况,研究结果表明:胶层厚度影响粘接剂对Al5052-Al5052单搭粘接接头的粘接效果,胶层表面的von Mises应力随着胶层厚度的增加而增大,Al5052-Al5052单搭粘接接头的强度随着胶层厚度的增加而降低。     

基于DIC法的CFRP粘接参数及失效分析

对碳纤维-碳纤维以及碳纤维与异质材料的粘接搭接试样进行了单向拉伸试验,对搭接长度、粘接层厚度对接头强度的影响规律进行了详细的分析。采用数字图像相关方法(DIC法)对接头的面内应变和法向变形进行了监测,对搭接接头在拉伸过程的失效行为和失效顺序进行了系统地分析。结果表明,碳纤维粘接搭接接头的宏观失效存在碳纤维板纤维断裂、粘接层剪裂、撕裂、粘接界面破坏等多种破坏形式;碳纤维接头搭接长度12.5 mm-15 mm,粘接层厚度0.2 mm时接头刚度、强度较高;粘接层强度相对较弱时,碳纤维接头主要以粘接层剪裂为破坏形式,粘接层强度相对较强时,接头表层碳纤维撕裂引起界面剥离,界面剥离面积扩展,异侧界面剥离导致粘接层撕裂,引起接头失效。     

DP590钢/7075铝异种金属搅拌摩擦搭接焊界面组织与力学性能研究

对7075-T6铝合金和镀锌DP590钢板进行了搅拌摩擦搭接焊,并结合焊接过程中温度场、流场数值模拟结果,研究了金属间化合物(Intermetallic compound,IMC)厚度以及钩状结构对接头力学性能的影响规律。结果表明,IMC厚度较大时,IMC层在焊接残余应力作用下产生微裂纹,降低了接头冶金结合强度,当IMC厚度由0.8μm增大至4.3μm时,接头拉剪载荷降低17.8%。当钩状结构高度较大时,钩状结构上下两端宽度差较大,在拉剪载荷作用下钩状结构受力不均,薄弱部位易发生应力集中而断裂,降低了接头机械结合强度,接头性能随钩状结构高度的增大而下降。     

考虑弯曲效应的混元胶接单搭接头应力模型

混元胶接接头是利用多种不同剪切弹性模量的胶层来传递被粘物载荷的单搭接头。它兼具胶层连续性连接和降低端头应力集中等优点,因此能充分利用被粘物材料性能(如复合材料)以提高接头强度。以典型双元胶接接头为对象,考虑加载作用线偏心引起的弯曲效应和胶层剥离正应力,建立被粘物为各向同性的线弹性双元胶接接头应力解析模型。理论模型中的胶层切应力、剥离正应力和上被粘物纵向正应力与精细有限元模型吻合得较好,证实了理论模型的正确性。参数研究中确定了影响混元胶层应力分布的关键耦合参数。     

搭接长度对平纹机织复合材料胶接结构连接性能影响的多尺度分析

针对平纹机织复合材料层合板,首先基于均匀化方法确定细观模型的性能参数,其次采用Hashin准则分析细观模型损伤过程,最后引入连续损伤力学模型和内聚力模型建立层合板胶接结构宏观模型。研究结果表明,平纹机织复合材料层合板的数值曲线与试验结果吻合较好,验证多尺度模型的有效性;搭接长度在5~15 mm时,随着搭接长度的增大,单搭和双搭胶接结构的极限失效载荷逐渐增大,并趋于稳定,而搭接剪切强度逐渐减小;单搭和双搭胶接结构的失效形式随着搭接长度的增大逐渐由胶层剪切失效过渡到层间分层失效;相同搭接长度下,与单搭胶接结构相比,双搭结构的极限失效载荷较大。基于均匀化方法、Hashin失效准则、内聚力模型和连续损伤力学模型,提出一种平纹机织复合材料多尺度模型,对结构性能设计和使用寿命具有重要意义。     

Improving joint features and tensile shear properties of friction stir lap welded joint by an optimized bottom-half-threaded pin tool

To increase the lap shear failure load of friction stir lap welding (FSLW) joint, a tool with a bottom-half-threaded pin was designed in the present study. Using 7N01-T4 aluminum alloy as the research object, tools with the bottom-half-threaded pin and the traditional full-threaded pin were used to fabricate lap joints. Results showed that the thread end position on the pin greatly influenced the material flow behavior. The material concentrated zone using the bottom-half-threaded pin mainly located above the lap interface, which is beneficial to suppress the hook and cold lap. The lap shear failure load of the FSLW joint using the bottom-half-threaded pin was 17,644.7 N, which is equal to 122.8 % of the joint using the full-threaded pin.     

Creep simulation of adhesively bonded joints using modified generalized time hardening model

Creep behavior of double lap adhesively bonded joints was investigated using experimental tests and numerical analysis. Firstly, uniaxial creep tests were carried out to obtain the creep characteristics and constitutive parameters of the adhesive at different stress and temperature levels. Generalized time hardening model was used to predict the creep behavior of the adhesive. This model was modified to simulate the creep behavior at different stress and temperature levels. Secondly, the developed model was used to simulate the creep behavior of bonded joints using finite element based numerical analysis. Creep deformations of the joints were measured experimentally and good agreement was observed in comparison with the results obtained using numerical simulation. Afterward, stress redistribution due to the creep along the adhesively bonded joint was obtained numerically. It was observed that temperature level had a significant effect on the stress redistribution along the adhesive thickness.     

搭接长度对胶焊接头应力分布的影响

采用三维弹塑性有限元方法,对采用酚醛树脂和丙烯酸酯两种胶粘剂的胶焊单搭接头,研究了其搭接长度对接头中应力分布的影响,计算结果表明,酚醛树脂胶粘剂焊接头,搭接区边缘应力值高于焊点边缘应力值,丙烯酸酯胶粘剂的胸焊接头中,焊点边缘应力远高于搭接区边缘应力,搭接长度增大时,两种胶粘剂胶焊接头搭接区内,焊点边缘和搭接区边级处的峰应力值都减小,增中搭接长度可以提高胶焊接头的强度。     

The free vibration analysis and optimal design of an adhesively bonded functionally graded single lap joint

In this study, three-dimensional free vibration and stress analyses of an adhesively bonded functionally graded single lap joint were carried. The effects of the adhesive material properties, such as modulus of elasticity, Poisson's ratio and density were found to be negligible on the first ten natural frequencies and mode shapes of the adhesive joint. Both the finite element method and the back-propagation artificial neural network (ANN) method were used to investigate the effects of the geometrical parameters, such as overlap length, plate thickness and adhesive thickness; and the material composition variation through the plate thickness on the natural frequencies, mode shapes and modal strain energy of the adhesive joint. The suitable ANN models were trained successfully using a series of free vibration and stress analyses for various random geometrical parameters and compositional gradient exponents. The ANN models showed that the support length, the plate thickness and the compositional gradient exponent played important role on the natural frequencies, mode shapes and modal strain energies of the adhesive joint whereas the adhesive thickness had a minor effect. In addition, the optimal joint dimensions and compositional gradient exponent were determined using genetic algorithm and ANN models so that the maximum natural frequency and the minimum modal strain energy conditions are satisfied for each natural frequency of the adhesively bonded functionally graded single lap joint.