【作者】 严沾谋；

【导师】 游敏；

【作者基本信息】 三峡大学 ， 机械设计及理论， 2007， 硕士

【摘要】 运用弹塑性有限元法和试验,研究了间隙连接单搭接接头、间隙连接双搭接接头和间隙连接劈裂接头的应力分布,以及胶粘剂力学性能和被粘物外形对单搭接接头应力分布的影响。通过分析胶层和被粘物的应力分布以及胶层的应变,优化了接头的应力分布,提高了接头的强度,得出了如下主要结论:1)对于高弹性模量胶粘剂接头,间隙对单搭接接头的应力峰值无明显影响,在不降低接头名义强度的基础上极大地提高了接头的实际强度;而对于低弹性模量胶粘剂接头,间隙使得接头的应力峰值明显上升,显著地降低了接头的名义强度和实际强度。2)胶粘剂的弹性模量、泊松比、屈服强度和硬化模量对单搭接接头应力分布均有影响,但以弹性模量的影响最大。高弹性模量胶粘剂接头胶瘤的作用很大,而低弹性模量胶粘剂接头胶瘤的作用很小。胶瘤采用弹性模量和屈服强度很高的胶粘剂,可以提高单搭接接头的强度。采用有胶瘤的混合胶粘剂连接可以优化接头的应力分布,提高接头的强度。3)合理的间隙对双搭接接头胶层中部的应力峰值无明显影响,使得接头用胶量减少、重量减轻,在不损害接头的名义强度的同时极大地提高了接头的实际强度。间隙长度对接头的名义强度几乎无影响,却极大地提高了接头的实际强度。间隙接头的胶层被间隙分成了数段,胶层在固化过程中受到的约束比没有间隙的情况要小得多,因而内应力更小,对接头的强度有利。4)合理的间隙对劈裂接头的应力峰值无明显影响,不损害接头的名义强度。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。当接头末端不存在胶粘剂时,各应力峰值迅速增大,使得接头的名义强度显著降低。5)被粘物自由端的内倒角使得胶层中部应力峰值都得到了极大的降低,随着倒角高度的增大,拐角处的应力先减小后增大。随着倒角角度的减小,拐角处的应力先减小后增大,θ=30°左右时达到最小值。内倒角可以显著降低高弹性模量胶粘剂接头的应力峰值,并且各应力峰值由胶瘤向胶层转移,从而提高接头的强度;而对于低弹性模量胶粘剂接头,内倒角反而使接头的应力峰值升高,对接头非常有害。6)对于搭接区端部被粘物有外倒角的接头,随着胶粘剂弹性模量的降低,胶层中部的应力峰值随之降低。对于胶粘剂弹性模量高的接头,外倒角使得胶层中部的应力峰值得到了极大的下降;而对于胶粘剂弹性模量低的接头,外倒角对胶层中部的应力峰值影响较小。7)被粘物阶梯状外形使得胶层应力的峰值大幅度下降,应力由拐角处向搭接区中间转移,中部应力上升,阶梯长度对应力峰值影响很小。对于高弹性模量的胶粘剂接头,阶梯使得应力峰值显著降低;而低弹性模量接头,阶梯对各应力的峰值并无明显影响。8)被粘物凹槽使得胶层中部的应力峰值得到了显著降低。随着凹槽长度的增加,胶层中部的应力峰值先减小后增大。随着凹槽深度的增加,胶层中部的应力在拐角处的值逐渐减小,中间的应力值逐渐增加。在含凹槽的接头中,随着胶粘剂弹性模量的增加,胶层中部应力的峰值随之增大。对于低弹性模量的胶粘剂接头,凹槽对胶层中部应力的分布和峰值并无明显影响;而对于高弹性模量的胶粘剂接头,原来处于低应力状态的接头中间的应力明显上升,承担了更多的载荷,而拐角处的应力集中得到了明显的减缓,应力峰值显著降低。更多还原

【Abstract】 The elasto-plastic finite element method (FEM) and experiment were used to investigate the stress distribution of recessing bonded single lap joint, recessing bonded double lap joint and recessing bonded cleavage joint, and the influence of the mechanical properties of adhesive and the figuration of adherend on the stress distribution in adhesively bonded aluminium single lap joint. The stress distribution of joint was optimized and the strength was improved through the analysis of the stress and strain distribution of bondline and the stress distribution of adherend, and the following conclusions have been drawn:1) The influence of recess on the peak stress of joint bonded with high elastic modulus adhesive was not evident, improving the actual strength of joint largely basing on the nominal strength not being reduced evidently, but recess caused the peak stress of joint bonded with low elastic modulus adhesive to be raised evidently, reducing the nominal strength and actual strength of joint markedly.2) All of the elastic modulus, Poisson ratio, yield strength and hardening modulus of adhesive influenced the stress distribution of single lap joint, but the influence of elastic modulus was greatest. For the joint bonded with high elastic modulus adhesive, the function of adhesive fillets was very large, but the function of adhesive fillets was very small as that in the one bonded with low elastic modulus adhesive. If adhesive fillets were adopted adhesive with high elastic modulus and high yield strength, the strength of single lap joint could be improved. Bi-adhesive bonding with fillets could optimize the stress distribution of joint and improve the strength.3) The influence of reasonable recess on the peak stress of double lap joint in the mid-bondline was inconspicuous, reducing the quantity of used adhesive and lightening joint, meanwhile, increasing the nominal strength great and actual strength decreased little. The influence of recess length on the nominal strength could be negligible, but increased the actual strength great. Since the bondline of recessed bonding joint was divided into several segments, then the restriction of bondline in the course of curing was smaller than the state without recess, so the inner stress was lower and benefit for the strength of joint.4) The influence of reasonable recess on the peak stress of cleavage joint was negligible, and it was not harmful to the nominal strength. The influence of the location of recess center on the peak stress was evident, but the influence of recess length on the stress peak was negligible. Each peak stress increased rapidly when there was not adhesive at the end of joint, and the nominal strength reduced markedly.5) The inner chamfer in the unload ends of adherends reduced the peak stress in the mid-bondline enormously. As the chamfer height increasing or the chamfer angle decreasing, the stress in the corner decreased first and then increased again, and the stress reached minimum whenθ=30°. For the joint bonded with high elastic modulus adhesive, the inner chamfer reduced the peak stress remarkably and the peak stress transferred from fillets to the bondline, so that the strength increased. For the joint bonded with low elastic modulus adhesive, the inner chamfer increased the peak stress instead, so it was not benefit for the joint.6) The peak stress of mid-bondline reduced for the joint with outer chamfer when the elastic modulus of adhesive decreased. For the joint bonded with high elastic modulus adhesive, the outer chamfer reduced the peak stress remarkably, while the function of outer chamfer could be ignored for the joint bonded with low elastic modulus adhesive.7) The step figuration of adherend decreased the peak stress of mid-bondline markedly. The stress transferred from the corner to the middle of lap zone, and the stress of middle increased. The influence of the step length on the peak stress was little. The stress of joint bonded with high elastic modulus adhesive decreased markedly due to the existence of step, but the function of step could be ignored for joint bonded with low elastic modulus adhesive.8) The peak stress of mid-bondline decreased markedly when there were a couple of notches located in the out side of the adherend corresponding to the middle part of the lap zone. The peak stress decreased firstly and then increased again as the length of notch increased. For the stress around the corner decreased gradually as the depth of notch increased, and the stress of middle increased gradually. The peak stress of mid-bondline increased when the elastic modulus of adhesive increased. The influence of notch on the stress distribution and peak stress of mid-bondline with low elastic modulus adhesive could be negligible, but for the joint bonded with high elastic modulus adhesive, the stress in the middle of joint where there was low stress originally increased evidently, bearing more load, meanwhile, the stress concentration around the corner and the peak stress decreased markedly.更多还原