【作者】 邢保英；

【导师】 何晓聪；

【作者基本信息】 昆明理工大学 ， 机械设计及理论， 2014， 博士

【摘要】 目前,随着轻量化设计在汽车工业、航天工业等领域的发展,铝、镁合金,纤维增强塑性材料等轻质材料得到了广泛的应用。传统的连接方法已经很难实现这些轻质材料的连接。作为一种新型的连接方法-自冲铆连接技术,呈现出独特的优势。本文基于试验和有限元数值模拟分析方法,具体开展的工作大致分为如下几个方面：1.采用ANSYS/LS-DYNA软件分析铆接过程中基板的材料变形、流动情况及成形接头中的应力/应变分布,推测成形接头中危险部位将会出现在铆钉头与上板接触部位、铆钉管腿与下板接触部位。AA5052自冲铆接头的金相试验和硬度测量结果表明,塑性大变形部位的材料由等轴晶粒拉伸成为细长的纤维组织,晶粒结构尺寸被大幅度细化,产生了加工硬化效果。与母材硬度(72.3HV)相比,最大硬度提高了40.6%。2.学生氏t分布对静力学测试数据分析结果表明,0°接头的抗剪切强度最高,30°接头最低。随着预成型角的继续增加,强度增大。60°接头的位移变形和能量吸收最强。基板厚度和宽度增加,接头最大抗剪切强度提高40.1%和12.6%,变形位移提高11.7%和14.9%,能量吸收提高75.0%和11.7%。两颗铆钉接头(SDL和SDT)最大抗剪切强度提高88.2%和99.6%,变形位移提高39.0%和25.8%,能量吸收提高154.8%和115.6%。三颗铆钉接头(SMI和SMO)最大抗剪切强度提高175.2%和163.3%,变形位移降低17.6%和35.2%,能量吸收增加187.9%和130.4%。基板预成型角、厚度、宽度、铆钉数量及其分布结构对接头的宏观失效模式几乎没有影响,所以测试接头失效模式均为下板脱离铆钉和上板。失效断口分析表明,上板中断裂路径由中心向两侧扩展；下板中膨胀部位为失效的最初部位。上板变形特征对接头变形位移有直接影响。下板变形特征及其过程对接头变形位移和抗剪切强度有直接影响。3.自冲铆接头主要疲劳失效模式为下板断裂；断口表面存在黑色微动疲劳磨损产物。当疲劳载荷较大时,基板宽度、铆钉数量及其分布结构会使上板成为失效部位。基于变差系数法,选择二参数Wemull分布对疲劳寿命数据有效性进行分析。获得双对数坐标下疲劳数据的最小二乘拟合直线及其二参数幂函数方程,分别为NN=107.139F-4.799、NW=109.578F-7.158、NSDL=107572F-3.397、 NSDT=108.673F-5.112、NSMI=108.687F-4.531和NSMO=109.105F-5.005。基板宽度、铆钉数量及其分布结构对接头疲劳寿命和F-N曲线的斜率具有显著影响。随着铆钉数量的增加,其分布结构对F.N曲线斜率和疲劳强度的影响程度减弱。提出首要和次要承载顺序的存在,并发现疲劳断裂表面为首要承载顺序的所在位置。失效断口分析表明,上板断裂,疲劳裂纹萌生于铆钉头与上板接触部位；下板断裂,裂纹萌生于铆钉管腿与下板接触部位,损伤区域自铆钉管腿底部向上蔓延和扩张。铆钉表面黑色物质元素分析结果表明：Al元素含量最高,即其所在位置处发生了剧烈的微动磨损。因此减缓这些部位的摩擦作用,可提高接头疲劳寿命。4.粘接-压印复合和粘接-自冲铆复合接头中的承载部位分别为压印互锁和自冲铆互锁结构。学生氏t分布对静力学测试数据分析结果表明,与Y2纯铝(Y2)粘接接头相比,压印、自冲铆接头及它们与粘接的复合接头的抗剪切强度提高8.0%、231.9%、21.3%和246.2%,失效位移增加221.4%1271.4%、178.6%和978.6%,能量吸收增强300%、4186.4%、254.6%和3800%。与T型自冲铆接头相比,单搭剪切自冲铆接头抗剪切强度增加169.3%,变形位移和能量吸收降低188.2%和52.3%。与Y2压印和自冲铆接头相比,AA5052压印和自冲铆接头的抗剪切强度增加117.6%和70.2%,变形位移增加-25.2和9.5%,能量吸收增加45.5%和128.4%。更多还原

【Abstract】 As lightweight design is developing in manufacturing industries covering automobiles and aerospace components, lightweight materials such as aluminium alloy, magnesium alloy and fiber reinforced plastic material are increasingly being used. These lightweight materials are difficult or impossible to join by traditional joining methods. Self-piercing riveting (SPR) technology is a new joining method and has particular advantages. Based on experimental observations and Finite Element Analysis (FEA) of several types of joints, the research work was divided into several parts as follows:1. The deformation and fluxion state of substrate materials during the riveting process and the stress/strain distribution in shaped joints were analyzed using the ANSYS/LS-DYNA sofeware. Results showed that the interfaces between the rivet head and upper sheet and between the rivet shank and lower sheet were also the most vulnerable parts in shaped joints.Results of microscopic examination and hardness measure of SPR joints in AA5052showed that large plastic deformation of the joints resulted in the material structures of parts being stretched from the equiaxed grain into fibrous structures and also in significant thinning of the grain structure, which produced a work hardening effect. Compared with the hardness of parent metals (72.3HV), the hardness was improved by40.6%maximumly.2. The analysis results of static test data using the Student’s t distribution showed that the shear strength of joints with0°preformed angle was largest and the strength of joints with30°preformed angle was smallest. With the increase of preformed angles continuously, the strength was magnified. The failure displacement and energy absorption of joints with60°preformed angle were highest. With the increase of thickness and width of substrates, the strength of joints was improved by40.1%and12.6%respectively,11.7%and14.9%responding to failure displacement and75.0%and11.7%for energy absorption. The strength of joints with two-rivet (SDL and SDT) was improved by88.2%and99.6%respectively,39.0%and25.8%responding to failure displacement, and154.8%and115.6%for energy absorption. The strength of joints with three-rivet (SMI and SMO) was improved by175.2%and163.4%respectively,17.6%and35.2%responding to failure displacement and187.9%and130.4%for energy absorption.The preformed angle, thickness and width of substrates, the number of rivets and their distribution had little influence on the macro-scale failure mode of joints. In all test cases the interlock structure failed, with the lower sheet separating from the upper sheet and rivet. Analysis of failure surfaces showed that the fracture started at the centre of the joint and propagated outward to the two sides. The locations of the initial failures were the’swell’parts of the lower sheets. Deformation characteristic of the upper sheet influenced directly the deformation displacement of stressed joints. The deformation displacement and the strength of joints were influenced by the deformation characteristic and its failure process in the lower sheet.3. The fracture of the lower sheet was the main fatigue failure mode. Black oxide debris caused by fretting fatigue damage was found on the fracture surfaces. When a bigger fatigue load was applied, the failure mode could be influenced by the width of substrates, the number and distribution of rivets, which led to the uppere sheet fracture.Based on the method of coefficient of variation, the effectiveness of fatigue test data was analyzed assuming a two-parameter Weibull distribution. The least squares best fit lines of fatigue data and its two-parameter power function equations were obtained, corresponding to NN=107.139F-4.799,NW=109.578F-7.158,NSDL=107.572F-3.397,NSDT=10A8.673F-5.112, NSMI=108.687F-4.531and NSMO=109.105F-5.005.The fatigue life and the slope of the F-N curves were influenced significantly by the width of the substrates and the number and distribution of rivets. Increasing the number of rivets reduced the extent to which the slopes of F-N curves and fatigue strength were affected by the rivet distribution.The existence of primary and secondary load bearing sequences was proposed. The fatigue fracture surface was the location of the primary load bearing sequence. An analysis of fatigue surfaces showed that for the upper sheet fracture, the fatigue crack started at the contact interfaces between the rivet head and the upper sheet. For the lower sheet fracture, the fatigue crack started at the interface between the rivet shank and lower sheet. The fretting damage region spread from the bottom of the rivet shank toward the rivet head.Results of element analyses of black debris on the rivet surface showed that the element content of Al was highest. This indicated that the violent fretting damage happened at those locations. It can be inferred that reducing the friction at those locations can improve the fatigue life of joints.4. Load bearing part in adhesive bond-clinch hybrids and adhesive bond-SPR hybrids joints was the clinching and the SPR interlock structure respectively.The analysis results of static test data using the Student’s t distribution showed that compared with adhesive bonded joints in Y2, the strength of clinched, SPR and their adhesive bond hybrid joints was improved by8.0%,231.9%,21.3%and246.2%respectively,221.4%,1271.4%,178.6%and978.6%responding to failure displacement, and300%,4186.4%,254.6%and3800%for energy absorption. Compared with T-SPR joint, the strength, failure displacement and energy absorption of lap-shear SPR joints was enhanced by169.3%,-188.2% and-52.3%. Compared with clinched and SPR joints in Y2, the strength of clinched and SPR joints in AA5052was enlarged by117.6%and70.2%respectively,-25.2and9.5%responding to failure displacement, and45.5%and128.4%for energy absorption.更多还原