不同胶接参数对CFRP层合板单搭胶接结构强度的影响及优化设计

对于碳纤维增强基复合材料(Carbon fibre-reinforced polymer,CFRP)层合板单搭胶接结构的优化问题,首先利用连续损伤力学模型、三维Hashin准则和内聚力模型研究不同胶接参数对CFRP层压板单搭胶接结构力学性能的影响,其次采用拉丁超立方试验设计方法和响应面法构建了拉伸强度代理模型,最后基于遗传算法和代理模型进行联合优化.结果 表明,仿真与试验吻合较好,数值结果与试验结果的误差均低于10％,验证了有限元模型的精确性.随着搭接长度的增大,拉伸强度和层合板层间分层损伤程度逐渐增大,剪切强度和胶层自身剪切失效程度逐渐减小;胶接结构的力学性能及失效形式随着铺层方式的不同而改变.最佳铺层顺序、胶接长度、胶层厚度和搭接宽度分别为[03/903]2s、20 mm、0.0607 mm和10 mm.与常规单搭胶接结构相比,拉伸强度和剪切强度分别提高了25.92％和25.88％.采用遗传算法对CFRP层合板单搭胶接结构进行优化,对提高单搭接接头的力学性能具有重要意义.     

胶层缺陷对胶接-拉铆搭接剪切接头力学性能影响研究

近年来胶接-拉铆技术在载运工具和航空航天等领域得到了广泛应用,而大型结构连接部件的制备过程会不可避免地在胶层内部产生局部缺陷,进而影响接头服役性能。以胶接-拉铆单/双搭接接头为研究对象,通过在胶层区域设置不同形式的人工缺陷,模拟胶层制备过程中产生的胶层内部缺陷,研究其对胶铆接头搭接剪切力学性能的影响规律。以6061-T6铝合金为基底制备胶接-拉铆接头试件,考虑单、双搭接试件形式,胶层内部预先放置不同厚度、面积、形状、位置的聚四氟乙烯缺陷片,对固化后的接头进行准静态拉伸破坏试验,并采用宏观观测和扫描电镜分析胶层失效表面宏观和微观样貌,从而对胶层内部缺陷对其失效模式影响机理进行评价。试验结果表明,接头主要失效模式为内聚失效,胶层中缺陷的位置、面积、厚度会对接头失效载荷以及失效强度产生不同程度影响,而缺陷的形状对接头力学性能影响不大。无缺陷的双搭接试件胶层失效载荷是单搭接试件1.62倍,单搭接试件胶层失效强度是双搭接试件1.24倍。有圆形缺陷的双搭接试件失效载荷是单搭接试件2倍,而失效强度没有受较大影响。基于现有试验结果,可以为实际结构设计中含胶层缺陷胶铆复合接头失效强度提供有效评估方法。     

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。     

单搭接接头胶层间隙对强度和应力的影响

研究单搭接接头胶缝中预留间隙对接头拉剪强度和应力分布的影响。结果表明，随着间隙长度的增加，接头的承载能力趋于减小，但接头的实际剪切强度却持续上升；当间隙长度继续增加时，接头的实际强度趋于下降。研究中还发现间隙所处的位置对接头的抗剪强度有较大的影响，胶层端部预留间隙使接头的承载能力和实际强度均显著下降。有限元数值分析结果表明，间隙长度超过某特定值后胶层中的应力集中程度会急剧上升，间隙位于端部时胶层中的应力集中程度明显高于位于中部的场合。     

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。     

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.     

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。     

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。     

胶焊接头的三维弹塑性应力分析

采用三维弹塑性有限元方法,数值分析了胶焊搭接接头的应力分布,并与点焊接头、胶接接头的应力分布情况相比较。结果表明,胶焊接头搭接区中应力分布均匀,其焊点内部不存在点焊接头焊点中所具有的高应力,消除了点焊接头中焊点边缘处的应力集中。胶焊接头的应力分布特征与胶接接头十分相似。由应力分析预测的接头强度与已有的试验结果一致。     

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。     

Pre-stressed adhesive strap joints for thick composite sandwich structures

A simple but effective design to improve the strength of thick adhesive composite strap joints is validated with experiment and finite element method. The strap joint under investigation, with a particular application to naval ship structures, consists of two thick woven E-glass/vinyl ester laminates joined together with two steel doublers. Longitudinal tensile loads are applied to the joints, resulting in large concentrated shear and peel stresses near the free edges of bondlines. The new design intends to reduce the adhesive peel stress by application of through-the-thickness compressive pre-stress along the bondline and thus leads to an increase of joint strength. Experiment results show that all the joint failures are delamination of the top layer of the laminated adherends. The test further confirms that joint strength increases significantly by applying the transverse pre-stress. Finite element analysis reveals that the pre-stress can effectively reduce the magnitude even reverse the sign of the peel stress in the adhesive layer and the adherends. Recessing the adhesive leading edge could magnify the pre-stress effect and reduce the adhesive peel stress, but would increase the shear stress. For those composite joints with low transverse interlaminar strength and susceptible to delamination, this simple design/technique can considerably improve their joint strength.     

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.     

Friction stir weld-bonding defect inspection using phased array ultrasonic testing

Weight reduction is an important driver of the aerospace industry, which encourages the development of lightweight joining techniques to substitute rivet joints. Friction stir welding (FSW) is a solid-state process that enables the production of lighter joints with a small performance reduction compared to the base material properties. Increasing the FSW lap joint performance is an important concern. Friction stir weld bonding is a hybrid joining technology that combines FSW and adhesive bonding in order to increase the mechanical properties of FSW lap joints. FSW and hybrid lap joints were produced, using 2-mm-thick AA6082-T6 plates and a 0.2-mm-thick adhesive layer. Defect detection using the non-destructive test, phased array ultrasonic testing (PAUT), has been made. Microscopic observations were performed in order to validate the phased array ultrasonic testing results. Lap shear strength tests were carried out to quantify the joint’s quality. PAUT inspection successfully detected non-welded specimens but was not able to distinguish specimens with major hook defects from specimens correctly weld bonded with small hook defects.     

铜箔种类和厚度对钛/钢电阻点焊接头组织和性能的影响

以不同种类、不同厚度铜箔作为过渡层材料,对TC4钛合金和304不锈钢薄板进行电阻点焊,研究了铜箔种类和厚度对接头组织和性能的影响。结果表明:纯铜箔过渡层焊接接头的抗剪强度明显高于铜合金箔过渡层焊接接头的,且T4铜箔过渡层焊接接头的抗剪强度最高;随着T4铜箔厚度增大,接头反应区宽度减小,中间过渡区宽度增大,熔合区钛-铁金属间化合物减少,接头抗剪强度先增大后减小,在厚度为0.4 mm时达到最大。