【作者】 朱定锋；

【导师】 游敏；

【作者基本信息】 三峡大学 ， 机械设计及理论， 2010， 硕士

【摘要】 本文采用有限元法,以单搭接接头及其搭接区为主要的研究对象,以优化接头应力分布、提高接头的强度为目标,对胶接接头的残余热应力分布、影响因素及调控措施进行研究,得出了如下主要结论:1)利用复合材料补片模型(Baker模型),得到胶接接头搭接区残余热应力的理论计算公式;建立残余热应力理论计算模型,推导出模型的残余热应力解析解公式。2)概述残余热应力研究所用有限元方法,建立胶接接头残余热应力分析有限元模型。利用ANSYS直接耦合方法,计算搭接区温度从胶粘剂常用固化温度80℃降低到20℃时搭接区的残余热应力分布,胶层中轴向残余热应力值为5.5Mpa,与理论计算值吻合。3)采用ANSYS概率设计PDS模块,采用蒙特卡罗抽样方法,确定影响胶接接头性能诸多因素中对残余热应力影响最显著因素:1)温度升降过程;2)温度差;3)胶粘剂弹性模量;4)异质被粘物;5)被粘物界面粗糙度。并将以上因素作为本文详细研究对象。4)研究升温、降温过程搭接区中的应力分布规律,结果表明:胶层应力升温过程为压缩应力,而降温过程为拉伸应力。在相同温度幅值的变化条件下,拉伸应力比压缩应力值大,胶接接头在降温过程产生的残余热应力对接头强度影响更大。5)研究不同温度差加载情况对搭接区中残余热应力的分布影响,结果表明:温度变化对胶接接头轴向残余热应力的分布影响大。温差越大,胶层和界面中的残余热应力越大。残余热应力与温度变化的比值,同有限元计算结果比较,得出跟实际情况更相符的理论计算公式。固在胶接接头制备和使用中,需采用合适的固化温度和使用温度,减小温度差值大小,能有效的控制残余热应力,提高接头的使用寿命。6)研究了胶粘剂弹性模量对胶接接头残余热应力的影响,结果表明:胶粘剂弹性模量对胶接接头残余热应力分布有显着的影响,随着弹性模量的增大,应力值增大。搭接区端部的各应力分量也随弹性模量的增大而增大,建议在温度变化较大的环境中使用胶接接头时,应当采用较低低弹性模量的胶粘剂,能有效的降低残余热应力。7)研究异质被粘物胶层以及界面的残余热应力分布情况,得出以下结论:上下被粘物采用相同材料时,胶层中的残余热应力大小主要取决于所选胶粘剂和被粘物的线膨胀系数差值。温度载荷下,异质被粘物接头中上下被粘物收缩量不一致,两被粘物通过胶层互相约束对方的变形,导致胶接接头中的残余热应力增大。8)改变界面幅值A和单峰间距S,分析被粘物的不同形貌对残余热应力分布的影响,得到以下结论:界面形貌对热应力分布的影响显著,正弦波形界面被粘物胶接接头中,形貌的凸起部分出现较大的应力峰值,对于系统来说是一个较为危险的区域。被粘物界面幅值A对残余热应力影响显著,影响胶接接头的填胶量,幅值越大,胶层越薄,导致温度载荷下的变形阻碍增大,接头中的残余热应力增大。比较幅值与单峰间距的影响,幅值较单峰间距对残余热应力影响更显著。借鉴热障涂层系统热应力研究方法,将凸起部分的尖点进行光滑处理,可以有效的改善接头中的残余热应力的分布,避免出现应力集中。9)研究了5种不同的胶接接头约束方式对残余热应力分布影响,得出以下结论:胶接接头在使用和制备固化时,不同的边界约束方式对接头中的残余热应力形成有很大的影响。约束方式的不同,会不同程度的阻碍接头温度载荷下的变形,导致在接头内产生残余应力。接头在温度变化过程中,对其约束的自由度越少,因温度变化产生的应力就能越有效的释放,在接头中的残余热应力就越小。10)胶接接头各层材料的热物性差异、材料性能的差异,在热循环过程中产生热应力,研究得到以下结论:胶层中的残余热应力随温度的循环变化而相应的变化,胶粘剂处于弹性变形阶段,其应力应变关系为εx =9 .91393 E -7 + 2.88542 E 9σx。11)研究了残余热应力与机械载荷作用下的工作应力叠加对胶接接头的应力分布影响,分析残余应力符号、方向及分布情况,判断其对接头强度产生的不同影响,结果显示:胶接接头在降温时所产生的残余拉应力,同接头承受拉伸外载时所产生的拉伸应力叠加,导致接头中的应力值增大,对接头承载能力有较大的影响。端部的应力集中峰值由不考虑热应力的7.48Mpa增大到考虑热应力的12.2Mpa,搭接区中部的轴向应力由0.2Mpa增大到5.5Mpa。更多还原

【Abstract】 The present study adopted the finite element method; the single-lap joint and its overlapping zone were the main research objects. The main purpose of the study is to find out ways to optimize the distribution of the joint stress and improve the joint strength. After investigating the residual thermal stress distribution, the main factors influencing the residual thermal stress and the adjustment measures were found, the main research results are as follows:1) The theoretical calculation formula of the thermal stress distribution in overlapping zone of the single lap joint was derived based on the metallic plate symmetrically repaired with composite patches (Baker model). Then the mathematical model for residual stress was established and the analytical solution formula was also derived based on this model.2) In this paper, the residual thermal stress finite element method was summarized and the finite element model of the residual thermal stress was also obtained. When the temperature dropping from the curing temperature (80℃) to the room temperature (20℃), the value of residual thermal stress distribution (axial stress) in the adhesive layer was 5.5Mpa with the direct-coupled method of ANSYS, it is coincide with the theoretical values (5.53 Mpa).3) Adopting the monte-carlo method of the probability design system (PDS), among the main factors influencing the joint properties, the most significant factors influencing the residual thermal stress were confirmed to be: 1) the process of temperature rising and falling; 2) the temperature difference; 3) the elastic modulus of the adhesive; 4) the dissimilar adherend and; 5) the interface roughness of adherend.4) The present study explored the effect of the temperature gradient on the residual thermal stress distribution in the overlapping zone by numerical simulation. The results showed that when the temperature rising, the residual thermal stress in the adhesive layer was a compressive stress, while the stress was a tensile stress when the temperature falls. The value of tensile stress was bigger than the compressive stress when the temperature changes within the same amplitude. The effect of the residual thermal stress on the strength of the adhesive bonded joints was evident, especially in the cooling process.5) The present research studied the effect of different levels of temperature difference on the residual thermal stress distribution in the overlapping zone. The results indicated that the changing of temperature exert an evident effect on the residual thermal stress. The greater the temperature difference is, the bigger the residual thermal stress will be. By comparing the ratio of the residual thermal stress and temperature difference with the result of FEM, the theoretical formula was obtained. In order to reduce the residual thermal stress to improve the joints, it is suggested by the present study that the suitable curing temperature and reduce temperature difference should be taken into consideration.6) This study also investigated the effect of the elastic modulus of adhesive on the residual thermal stress in the adhesive bonded joints. The results showed that the effect of the elastic modulus on the residual stress distribution was evident. When the elastic modulus of the adhesive was increased, the residual thermal stress in the middle of adhesive layer will also increase. At the free-end of overlapping zone, the stress will also increase. It is suggested that when using the adhesive bonded joints in the environment where the temperature change severely, the lower elastic modulus of adhesive should be used in order to reduce the residual thermal stress.7) In this paper, the heterogeneous adherend glue layer and the distribution of the interfacial residual thermal stress were investigated then the following conclusion was made: when the same materials were used in the upper and lower adherend, the value of the residual thermal stress was mainly decided by the linear expansion coefficient difference between the adhesive and adherend. At thermal loading conditions, the shrinkage of upper and lower adherents was inconsistency in the joints made of dissimilar adherend. The upper and lower adherend restricted the deformation of each other through the adhesive layer, resulting in the residual thermal stress increased in the adhesive bonded joints.8) Changing the interface amplitude (A) and single-peak spacing (S) of the adherend, then analyzing the different morphology of the adherend on the residual stress distribution, the results showed that the effect of interface morphology on the thermal stress distribution was evident. The protruding part of the sine wave-shaped interface adherend had a greater peak stress; it is a more dangerous area in the system. The amplitude (A) affected the filling glue between the adherend. The thick adhesive layer became thinner and thinner with the decreasing of the adherend interface amplitude A, which caused the increasing residual thermal stress. Comparing the effect of amplitude and the single-peak spacing on thermal residual stress, it can be known that the former exerts a greater influence on thermal residual stress than the latter. Referring to the thermal barrier coating system of the thermal stress method, smoothing the tip of the bulge point can effectively improve the joints in the distribution of residual thermal stress and avoid stress concentration.9) After examining the influence of the five different kinds of adhesive bonded jointss on the residual thermal stress distribution under different restriction conditions, the following conclusions can be drawn: When using, preparing and solidifying the adhesive bonded jointss, the effect on the residual thermal stress of the adhesive bonded jointss is tremendous under different boundary restriction conditions. When the boundary restriction condition is different, the distortion of the adhesive bonded jointss under thermal loading conditions will be influenced to some extent, accordingly the residual thermal stress will appear in the joints. During the process of the temperature changing, the degree of freedom is smaller, the more effectively the thermal stress caused by the temperature changing will release, the residual thermal stress in the joints will be smaller as well.10) The materials in different layers of the adhesive bonded jointss possess different thermal physical properties and different material properties; therefore the thermal stress is generated in the thermal cycling process. The following conclusion can be drawn based on this: the residual thermal stress in the glue layer will change with the temperature cycling; in the meantime the adhesives are in an elastic deformation stage. In this particular stage the strain relationship of the thermal stress can be expressed by the following formula:εx =9 .91393 E -7 + 2.88542 E 9σx.11) The paper also examined the influence of the residual thermal stress and the operation stress superposition on the stress distribution of the adhesive bonded jointss, analyzed the symbol, the direction and the distribution of the residual tress and then estimated their effects on the joint strength. The results indicate that the adhesive bonded joints will generate residual tensile stress when the temperature falls. This residual tensile stress will superpose with the tensile stress generated by the tensile load withstanding by the joint, which will enlarge the stress value of the joint, therefore it exert great influence on the bearing capacity of the joint. The peak stress concentration at the end part of the joint will increase from 7.48Mpa to 12.2Mpa. The axial stress in the middle part of the overlapping zone will also increase from 0.2Mpa to 5.5Mpa.更多还原