胶瘤中嵌入金属块对单搭接接头强度的影响

研究了在胶瘤中嵌入三角形金属楔块对单搭接接头强度和应力分布的影响,结果表明,金属楔块能显著提高接头的强度。但随三角形锲块入射角度的增大,接头强度提高幅度逐渐降低。有限元数值分析的结果表明,三角形金属楔块使端部应力峰值和平均应力均大大降低,剥离应力降低明显。     

粘接接头的耐久性及破坏机理

一、前言与传统的连接方法相比,粘接具有很多明显的优点:可改善接头应力分布,提高抗疲劳性能;能粘接很薄的金属和其他材料,从而获得轻型结构;可粘接性质完全不同的材料,如金属与橡胶、塑料;可降低制造成本等.在实际应用中,妨碍粘接技术充分发挥作用的主要问题是粘接接头的耐久性及非破坏性测试未获得根本解决.本文目的在于讨论接头的耐久性,即环境对粘接接头强度     

陶瓷金属扩散焊接中金属过渡层的计算机优化选择

陶瓷/金属焊接接头中存在着分布复杂、数值较大的残余应力场,对接头强度产生有害的影响。本文利用热弹塑性有限元的计算方法,分析了陶瓷与金属扩散焊接中过渡层对接头残余应力的影响。着重分析和计算了过渡层材料的性能、厚度在降低接头残余应力中所起的作用。为扩散焊接陶瓷、金属及其它异种材料的连接选择中间过渡层材料提供了理论依据。     

含镶嵌块单搭接接头应力分布的数值分析

利用有限元方法研究了金属镶嵌对单搭接接头应力分布的影响。结果表明,采用镶嵌块组成混合连接接头,改变了接头的应力流线分布,镶嵌块承载,降低了搭接区中部胶层中的应力;同时使被粘物中部的应力增大,提高了接头搭接区中部的承载能力;在重要部件或承载较大等情况下使用胶接接头,建议采用金属镶嵌方式对接头增强,具有更强的承载能力和可靠性,有重要的实用价值。     

Al2O3/Ni–Ti/Kovar钎焊接头热循环试验

对采用活性钎焊的Al2O3/Ni-Ti/Kovar(可伐)接头进行了考察，实验结果显示，接头经热循环后强度异常增加. 对此结果从材料的热膨胀特性、焊料微观结构、循环温度等方面进行了详细分析. 结果表明，本实验条件下热循环能显著降低焊接残余应力，导致接头强度提高.     

达到使用寿命时粘接强度安全系数的计算法

1前言　在进行优化设计和临界设计时,要求能定量计算达到使用寿命时粘接强度安全率裕度.这是提高接头可靠性降低成本所必需的.目前,对于耐久性的评价,都是针对接头长期耐受单一环境或应力时进行的预测,而不能对复合环境因素、组合应力的长期作用下的耐久性准确评价.也未见粘接强度波动程度与接头强度劣化的关系.本文介绍粘接接头使用时间达到设计年限时,粘接强度安全率裕度的定量计算方法.     

胶粘剂特性和厚度对劈裂载荷作用下胶接接头应力分布的影响

运用三维弹塑性有限元法对劈裂栽荷作用下的胶接接头(即劈裂接头)承载后的应力分布特征进行了分析，重点研究了胶粘剂层厚度对劈裂接头应力分布的影响。结果表明，胶粘剂的性能对应力分布有较大影响，提高胶粘剂强度和减小胶层厚度，均导致胶层应力集中加剧，各向正应力峰值呈上升趋势，各向剪切应力则正好相反；并且劈裂接头中应力分布以三向主应力为主，剪切应力的存在亦不可忽略。故在不引起过大应力集中和较大胶层缺陷条件下采用高强度的胶粘荆和较厚胶层对提高劈裂接头强度有利，实验结果与有限元分析相吻合。     

微波助燃Ni-Al高温自蔓延连接CVD SiC

采用高放热反应且摩尔比为1∶1的镍-铝二元系作为焊料,利用微波引燃的方法使体系以内部加热的方式迅速升温到燃烧温度并发生自蔓延高温合成反应,最终实现化学气相沉积碳化硅陶瓷(CVD SiC)的连接,研究不同反应产物对连接强度的影响规律.研究表明:反应层平均厚度约300 μm,反应产物与碳化硅基体之间的界面结合良好,但接头内存在着大量气孔,致密度较低.母材与中间层产物的热错配应力问题使接头界面处存在大量微裂纹.由于自蔓延连接的复杂性与高度不平衡性使反应产物较难控制,接头断面的XRD结果表明不同接头中生成了不同相的镍-铝系金属间化合物以及氧化物,但均未检测到残余单质Ni或Al.氧化物的出现会极大影响接头的剪切强度,导致试样接头强度的数值偏差较大.     

PE80聚乙烯管道焊接接头的应力松弛模型验证及安全评价

采用实验方法研究聚乙烯（PE）管道焊接接头在机械载荷条件下的应力松弛行为,通过松弛试验得出用Prony级数表示的PE管道焊接接头的本构模型。结果表明,PE管道焊接接头的松弛曲线与PE管道木材的松弛曲线相似;结合有限元分析软件Abaqus,建立PE80焊接接头的裂纹缺陷模型,导入PE管道焊接接头与PE管道母材的Prony级数,对含裂纹缺陷PE管道的应力强度因子进行计算;借鉴GB/T 19624—2004金属管道的评定标准,给出适合PE材料的断裂判据,比较PE材料的临界应力强度因子（KIC）及计算得出的应力强度因子(KI)的大小,进而通过断裂判据对含缺陷PE管道进行安全评价。     

金属粘接设计与最新技术(1)——设计注意事项和事例

1、金属粘接接头的优缺点无论什么都一样,要获得好的结果,就必须要扬长避短. 金属粘接的优点如下: (1)可以将应力分散.由于粘接是面接触,可减少铆接和点焊时那种应力集中现象.因此在要求相同强度的情况下,用薄板粘接比铆接和点焊更为适用,还可减轻重量.     

An Experimental Technique on the Dynamic Strength of Adhesively Bonded Single Lap Joints

This paper reported an experimental technique on the shear strength of adhesively bonded single lap joints subjected to impact loads by means of a split Hopkinson tensile bar. The experiments were conducted at two velocities (V = 20 m/s, 7 m/s) and testing temperatures ranging from ?40°C to 80°C. The results indicated that the shear strength of the specimen decreased with the increase of temperature and increased with the increase of velocity. The strength degradation from room temperature to high temperature was more severe than that from low temperature to room temperature. The effects of the pins, thermal stress and peel stress were also examined and found to have limited effects on the determination of the shear strength of the joints. It was concluded that the shear strength of the adhesively bonded single lap joints under impact loads can be determined by this experimental technique.     

外加磁场对粘接接头剪切强度的影响

采用自制的装置研究了磁场对由环氧胶层连接的钢制单搭接接头剪切强度的影响，结果表明．在所采取的试验条件下．试样叠合后立即施加的磁场可显著影响接头的强度；垂直于胶层的磁场提高接头的剪切强度效果高于平行磁场，磁场处理的时间以4h左右为宜。     

预偏角对单搭接接头强度的影响

研究了在被粘物搭接区顸偏转角度对钢单搭接拉伸接头剪切强度的影响,并用弹性有限元法分析了预偏角变化时单搭接接头上胶层中的应力分布情况。数值分析的结果表明：当预偏角从0°增加到12°时,结构钢单搭接接头胶层中的所有应力峰值分量均显著下降。而在所采取实验条件下,接头的剪切强度最高值出现在预偏角为6°时。因而在进一步研究预偏角对单搭接接头承载能力的作用时,应将外载作用下接头的本征偏转情况考虑在内。     

Non-linear analysis and optimization of adhesively bonded single lap joints between fibre-reinforced plastics and metals

Non-linear finite element methods are applied in the analysis of single lap joints between fibre-reinforced plastics (FRP) and metals. The importance of allowing for both geometric and material non-linearities is shown. The optimization of single lap joints is done by modifying the geometry of the joint ends. Different shapes of adhesive fillet, reverse tapering of the adherend, rounded edges and denting are applied in order to increase the joint strength. The influence of the joint-end geometry is shown for different metal adherend/FRP adherend/adhesive combinations. The results of the numerical predictions suggest that with a careful joint-end design the strength of the joints can be increased by 90–150%.     

Experimental and Numerical Analysis of T-peel Joints for the Automotive Industry

The T-peel joint is commonly used in the automotive industry, especially in the panels of the load compartment in vans. In order to determine the effect of using a structural adhesive instead of spot-welding, a detailed series of tests and finite element analyses were conducted. The adhesive was a toughened epoxy and the adherend was mild steel used in the manufacture of the car bodyshell. Various parameters were investigated such as the bondline thickness and adherend radius. The spew fillet was maintained flush in all cases. Contrary to the case of lap joints, there are no stress concentrations around the fillet area and, therefore, it is possible to use the maximum uniaxial tensile stress as a failure criterion for these joints. The bending moment at failure was found to be constant across the different geometries modelled, and it was also similar to that found in lap shear joints in previous studies.     

The effect of orientations of metal macrofiber reinforcements on mechanical properties of adhesively bonded single lap joints

A method for improving the mechanical behavior of adhesive joints is embedding metal macrofibers to the adhesive layer. The effect of the orientation of metal macrofibers laid across the length and width of the joint (longitudinal and transversal directions) on the strength and elongation at failure of single lap joints (SLJs) was investigated experimentally by testing SLJs reinforced with metal macrofibers laid in different orientations. The experimental results indicated that increasing the number of metal macrofibers in the longitudinal direction improved the shear strength and elongation at failure of SLJs. However, the improvements were found to be dependent on the normalized horizontal distance between the metal macrofibers for which a proper value of 1 was determined. While embedding metal macrofibers in the transversal direction degraded the mechanical properties of SLJs. Finite element analyses were undertaken to investigate the effects of fibers orientation and horizontal distance on the adhesive peel and shear stress distributions. The results revealed that decreasing the horizontal distance between the metal macrofibers laid in the longitudinal direction decreased the adhesive shear stress values indicating improvement of the joint strength, while in SLJs reinforced with metal macrofibers laid in the transversal direction decreasing the fibers distance increased the adhesive peel stress values resulting in joint strength reduction.     

Comparison of fracture behavior between acrylic and epoxy adhesives

An experimental study was conducted on the strength of adhesively bonded steel joints, prepared epoxy and acrylic adhesives. At first, to obtain strength characteristics of these adhesives under uniform stress distributions in the adhesive layer, tensile tests for butt, scarf and torsional test for butt joints with thin-wall tube were conducted. Based on the above strength data, the fracture envelope in the normal stress-shear stress plane for the acrylic adhesive was compared with that for the epoxy adhesive. Furthermore, for the epoxy and acrylic adhesives, the effect of stress triaxiality parameter on the failure stress was also investigated. From those comparison, it was found that the effect of stress tri-axiality in the adhesive layer on the joint strength with the epoxy adhesive differed from that with the acrylic adhesive. Fracture toughness tests were then conducted under mode l loading using double cantilever beam (DCB) specimens with the epoxy and acrylic adhesives. The results of the fracture toughness tests revealed continuous crack propagation for the acrylic adhesive, whereas stick-slip type propagation for the epoxy one. Finally, lap shear tests were conducted using lap joints bonded by the epoxy and acrylic adhesives with several lap lengths. The results of the lap shear tests indicated that the shear strength with the epoxy adhesive rapidly decreases with increasing lap length, whereas the shear strength with the acrylic adhesive decreases gently with increasing the lap length.     

Analysis and design of adhesively bonded joints for fatigue and fracture loading: a fracture-mechanics approach

An experimental–computational fracture-mechanics approach for the analysis and design of structural adhesive joints under static loading is demonstrated by predicting the ultimate fracture load of cracked lap shear and single lap shear aluminum and steel joints bonded using a highly toughened epoxy adhesive. The predictions are then compared with measured values. The effects of spew fillet, adhesive thickness, and surface roughness on the quasi-static strength of the joints are also discussed. This fracture-mechanics approach is extended to characterize the fatigue threshold and crack growth behavior of a toughened epoxy adhesive system for design purposes. The effects of the mode ratio of loading, adhesive thickness, substrate modulus, spew fillet, and surface roughness on the fatigue threshold and crack growth rates are considered. A finite element model is developed to both explain the experimental results and to predict how a change in an adhesive system affects the fatigue performance of the bonded joint.