【作者】 李龙；

【导师】 胡平；

【作者基本信息】 吉林大学 ， 机械工程， 2011， 博士

【摘要】 车身结构粘接技术(Structural Adhesively bonded)作为一种新型的结构件连接技术,由于具有良好的异质材料连接性能,可以解决传统连接工艺中由于车身材料不断更新发展而带来的技术瓶颈问题,因此已被该领域工程师们所重视并逐步应用于现代汽车的生产制造中。同时粘接技术作为一种轻量化连接技术,也是未来汽车轻量化发展中的关键性技术之一,与传统点焊等连接方式相比,除了具有理想异质连接性能,同时还存在良好的密封性、抗疲劳性能等优势。因此,掌握粘接力学性能,完善典型粘接接头的强度预测方法及理论,不仅对该技术在车身连接结构设计及优化过程中的有效应用起到现实的指导作用,而且对国内汽车轻量化发展及自主研发能力的提高具有更深远的战略意义。在车身设计流程中,传统粘接技术一般应用于车身件的密封、减震和结构补强,而针对半承载件或承载件连接结构的粘接设计却应用较少,在国产自主研发的车型中,用于此目的的结构胶粘连接设计还未得到较为成功的尝试。随着更多的高强铝、镁合金板以及非金属材料在车身中的进一步应用,粘接工艺必然向结构连接方向发展,从而实现车身焊装线向“混合连装线”的逐渐演变。鉴于此,为了满足工程中的设计需求,亟待对车身典型粘接接头静强度力学性能进行研究,并提出有效的强度预测方法,为工程中的具体应用提供思路与设计手段。本文结合国家自然科学基金重点项目“高强钢板热成形关键力学问题研究”(编号:10932003)和国家高技术研究发展计划(863计划)“汽车概念车身数字化设计新方法与新技术”(编号:2209AA04Z101),基于试验与仿真相结合的方法,开展车身单搭接粘接接头的静强度力学性能的研究。目前,根据粘接自身的力学特性,车身中通常通过搭接结构拉伸载荷剪切受力的方式进行承载,从而可以表现出更为理想的粘接强度性能,并且单搭接形式在车身设计中易于实现,便于控制制造工艺与成本。但是该类型接头胶层应力分布复杂,同时粘接强度影响因素较多,相关的仿真与强度预测方法并不完善。针对上述问题,本文对粘接工艺进行了对比分析,建立了统一的粘接试件制作的试验流程;并对接头胶层应力的分布进行计算,基于应力准则对其强度进行预测;同时建立了胶层的梯形内聚力模型并对其单元进行数值实现;在此基础上通过拉丁正交超立方体试验方法,将试验与仿真相结合,对影响因素进行分析并建立强度预测模型;最后在两种温度场中考察粘接接头的力学特征,为不同温度载荷下的接头设计提供参考。具体开展以下几个方面的研究工作:1.粘接过程工艺参数研究及试验系统基于粘接机理,并结合试验对粘接工艺中的表面处理、涂胶粘合、固化等关键工艺参数进行了研究,对结构胶形成有效连接载体的物理过程进行了对比分析,从而确定了统一的粘接试验件制作流程,同时通过接头强度离散性分析,验证该工艺过程的可靠性。这些工作为后续研究提供了标准化的试验样件,为单搭接接头强度性能分析奠定了基础。另外,文中还通过拉伸载荷强度试验,对比几种典型接头的强度性能,提出车用粘接接头的基本设计准则,从而进一步明确研究对象。2.基于解析模型的接头胶层应力分析和失效载荷预测通过引入被粘体的弹性变形,建立了适用于异种材料粘接接头的应力解析模型;详细推导了考虑端部弯曲效应的一维梁理论模型,并通过对非平衡接头的端部载荷求解,扩展了后者对于非平衡接头的适用性;利用网格精细化的搭接接头平面有限元分析,对两种解析模型进行对比验证;同时基于应力准则,借助于解析模型对粘接试件进行强度预测,并讨论了此类模型对失效载荷预测的适用性。3.胶层内聚力单元在粘接仿真中的实现根据梯形内聚力本构关系,建立了Ⅰ+Ⅱ型混合裂纹模型;确立了初始失效及裂纹扩展的判断准则,并通过有限元理论对胶层平面内聚力单元和六面体内聚力单元进行数值实现;同时基于等效裂纹的概念,通过断裂力学试验法获得了胶层能量释放率;并对模型中的内聚参数进行了研究,最终成功实现了基于胶层内聚单元的单搭接接头有限元仿真。4.基于试验设计法的粘接影响因素分析及强度预测采用正交试验设计与拉丁正交超立方体试验设计法,分别对单搭接接头物理试验与计算机仿真试验进行了试验设计,同时在两者试验中考虑了较为全面的接头强度影响因素,并根据统计学的理论对其进行分析,最终建立了接头强度和各影响因素之间的映射模型,并结合试验数据对映射模型进行验证,这种基于试验设计法的强度预测理论可以给多因素分析提供较为理想的方法,也为深入考察强度影响因素之间的关系提供了帮助。5.温度载荷对粘接强度性能影响的试验研究分别针对恒定温度和循环温度两种温度场,对粘接接头进行静强度的研究;试验中考虑预置时间的变量,并考察这一参数对接头性能的影响;结合胶层在循环温度下的热应力效应,分析了接头强度下降的原因;结合第三章与第四章的内容,通过应力模型与内聚力单元的有限元仿真,对不同温度场中的接头强度预测进行了探讨。本文以试验为基础,结合应力解析模型与有限元仿真方法对粘接接头的应力形式、强度性能以及影响因素进行了系统的研究,研究结果对粘接技术在车用连接结构中的实现提供了有力的指导作用。更多还原

【Abstract】 Structural adhesively bonded is a new structural connection technology for automotive, which has higher flexibility to join different materials, allowing the choice of better material for each component of a structure. It can solve the problem that conventional joining methods faced resulting from the body material updating and its industrial applications. To benefit from this advantage this kind of jointing has been much accounted of and increasingly being used in the automotive industry. Moreover, adhesively jointing technology is one of the key techniques for lightweight of automobile, which also presenting better leaktightness and fatigue properties comparing other mechanically fastened joints, such as spot welding. Therefore, mastering the strength prediction theories and adhesives design methods, as well as mechanical property of adhesive layer has not only important practical significance to design and optimize bonded joints, but also far-reaching strategic significance to improve independent R & D capabilities for lightweight of automotive.In the development flow of automotive design, conventional adhesives are commonly used for sealing, damping and strengthening, while less used in structural jointing for bearing component or half-bearing component. Successful cases of adhesives design for this goal mentioned have not been achieved in vehicles of home products. Adhesives will be developed towards structural jointing as the high strength aluminium and magnesium alloy, even non-metal materials extensively being uesd in the manufacture of automotive, which converts the assembly line from welding to“mix-mode jointing”. In light of above mentioned situations, for satisfying the requirement of autobody engineering design, it necessary to carry on the research on static strength character of adhesive joints and to propose effective method of strength prediction to assess jointing design for practical application.This work is funded by“863”Project of China (No. 2009AA04Z101), the Key Project of the National Natural Science Foundation of China (No. 10932003), carries out researches on the static strength character of single lap adhesively joints based on expermential and simulation methods.At the present time, lap jointing is generally used under shear bearing with tension loading in the autobody structures, in respect that adhesive shear strength shows the outstanding performance for load bearing. And the single lap joints are easy to be realised in the design, as well as being satisfied manufacturing process and costing control. However the stress distribution of single lap joints is complex, factors having influence on joint strength is complicated, and simulation methods and design rules are still controversial issues. Depending on the situations mentioned above, a uniform adhesively expermental process flows is built basd on contrastive analysis. Secondly, the stress of adhesive layers is computed and prediction is carried on according to the stress criterion. The trapezoid cohesive mixed-model and adhesive element are built. And Latin Hypercube method is used to quantify the effect of the factors and to propose a predictive equation for joints strength based on experments and simulation. In the end, mechanical properties are respectively explored under two thermal fields which providing the effective guiding for adhesive design. The main contents are as follows:1. Adhesive bonded process and testing systemBase on the adhesive theory, the research of key process parameters of adhesive is carried on, such as surface treatment, adhesive painting and curing. The adhesive bonded process and testing system are built according to the experiment results of comparing the strength of joints under different cases, and the reliability of the process is proved at the same time. The research work mentioned above can supply a great help for high quality, normative and uniform SLJ, which is also the base of performance analysis for adhesively bonded. Strength tests under tension loading of typical joints have been conducted. From the tests, the basic criterion of adhesive design has been presented, which supplied the research object.2. Strength prediction and stress analysis for adhesive layer based on analytical modelA stress analytical model considering the elastic deformation of adhesions is created which can be used for adhesively joints with different materials. At the same time, the model based on beam theory is built which considering the bending effect. The end load of unbalanced joints is obtained which helps enlarging the scope of application of beam theory model. Verification of the two analytical models has been done using the FEM models with refinement mesh. And according to the models, strength prediction of SLJ was proceed under the criterion of stress, and the results can helps investigating their applicability in addition.3. Numerical realization of cohesive element of adhesive layer in FEM simulation A cohesive mixed-mode damage model is created; while the damage initiation criterion and failure criterion are established. Numerical realization of eight nodes brick and plane elements of adhesive layer are implemented based on finite element method. Adhesive toughness is gained by fracture mechanics test using the equivalent creak length. In addition, the cohesive parameters are studied. Finial, the FEM of adhesively joints is done successfully.4. Influencing factors analysis and strength prediction based on experimental designBased on orthogonal test and Latin hypercube method, physical and computer design of experiments are carrying out to evaluate the strength of adhesively bonded which considering many factors during the process. The regression model between strength of SLJ and influencing factors were established. This method of experimental design for predicting the strength with various parameters is an effective way which supplies the great help for studying the relation between strength and factors.5. Experimental research on strength of adhesively bonded under temperature fieldExperimental researches on strength of bonded were carried out under constant temperature fields and cycling temperature fields, during which the factor of storing time was considered. The reason for strength decreased was explored using the theory of thermal stress. Based on the above models and results, the effective methods for predicting strength under different temperature fields were investigated.The dissertation researched the stress distribution, strength performance and the influencing factors of adhesively joints based on physical tests, analytical model as well as FEM method. The research results have significant guidance meaning in the design of adhesively structure for automotive.更多还原