【作者】 张云青；

【导师】 董湘怀；

【作者基本信息】 上海交通大学 ， 材料加工工程， 2008， 博士

【摘要】 材料成形性能的研究,源于工业生产实践中的迫切需求,近年来受到日益广泛的关注。作为机制地毯一种较新的制造技术,汽车针刺地毯复合材料在其实际热成形过程中,经常出现拉破、起皱、定形不良等种种制品缺陷。面对当前针刺地毯实际生产中的这些问题,全球的各汽车地毯生产企业依然处于依靠经验、反复试错以获得解决方案的阶段。这导致了汽车针刺地毯新产品的开发周期延长,已有产品的质量波动。在我国,现有的汽车专用地毯生产能力满足不了当前国内迅速发展的汽车工业的需求,导致了汽车地毯每年都需要大量的进口。因此,本文在国家自然科学基金委的项目资助(项目编号:50305020)下,首次以汽车针刺地毯复合材料的热成形性能为中心,进行了比较系统和深入的研究。通过高温拉伸实验参数的确定以及多种实验设计方案的实施,本文积累了针刺地毯复合材料的基本力学性能数据。对三种汽车针刺地毯复合材料进行了不同传热条件下(恒温绝热和自然对流传热)的大量高温力学实验,总结了针刺地毯复合材料高温力学行为的共同特点;应用聚合物材料的粘弹性基本原理,分析了拥有典型结构的两类针刺地毯复合材料(1.针刺毯坯层涂覆背胶层的双层结构,2.针刺毯坯层涂覆聚丙烯(PP)热定形层再添加衬垫层的三层结构)在不同温度条件下的变形机理。基于复合材料宏观力学的观点,从不可逆热力学基本原理出发,本文推导出了针刺地毯复合材料非线性热力耦合粘弹性本构模型的框架。为了使提出的材料模型能够体现温度效应在不同传热方式下的差异性,按照不可逆热力学本构理论框架中关于温度的定义,描述了温度对针刺地毯复合材料力学行为的影响。针对汽车针刺地毯复合材料热成形时各个阶段不同的实际传热方式,本文将单面冷却传热模型和大空间自然对流大平板模型分别引入本构模型框架,并采用Laplace变换、Laplace逆变换的方法,得到了针刺地毯复合材料在三种换热条件(恒温绝热、自然对流传热和热传导)下粘弹本构关系的具体表达式。在这些不同传热条件下本构关系的具体表达中,模型参数只需通过基本力学实验和热学实验即可确定,使得建立的该材料模型便于工业应用。利用通用型非线性有限元分析软件ABAQUS/Explicit中的用户自定义材料模型接口VUMAT,编程实现了本文提出的材料模型。进行了两种针刺地毯复合材料在不同传热条件下单向拉伸变形和半球冲压变形过程的数值模拟,得到的数值结果同针刺地毯的实验数据基本吻合,验证了材料模型的有效性;选择ABAQUS材料库中自带的Marlow材料模型,完成了单向拉伸和半球冲压过程的对比数值运算,将两类材料模型的数值结果同实验结果进行对比,进一步证明了本文所提材料模型在热力耦合条件下的精确性。最后,依据针刺地毯复合材料高温拉伸时的特有变形特征,结合建立的材料模型,本文提出了评价针刺地毯材料热成形性能的三个指标。通过与相应实验结果的对比,各指标的有效性获得了验证。这些指标可以分别从极限强度、变形能力和温度敏感性的角度,对汽车针刺地毯复合材料的热成形性能进行评价,从而为汽车针刺地毯在实际生产时的材料选择、稳定工艺条件设置等方面提供参考。更多还原

【Abstract】 Studies of material formability, which comes from pressing demand of practical forming processes, have gained more attentions during the past years. As a relatively newly emerging manufacturing technology in modern carpet industry, automotive needlepunched carpet composites usually happen to be tearing, wrinkling and crushing during their practical thermoforming processes. By far the globe automotive carpet manufacturers have applied their engineers’experiences and trial and error method to solve these problems. This leads to postponement of new products and quality fluctuation of current products. In China, current production capability of automotive carpets has still remained far behind that of domestic automotives, which results in numerous automotive carpets import every year. So with the financial support of national science fund (project item: 50305020), we firstly focus on thermo formability of automotive needlepunched carpet composites, have a systemic and in-depth study.By parameters ascertainment of extensile experiment in high temperature and execution of many test schemes, basic mechanical data of automotive needlepunched carpet composites have been accumulated. With a large number of extensile experiments of automotive needlepunched carpets under different heat transferring conditions (isothermal condition, natural heat convection condition), the common mechanical characters of automotive needlepunched carpets in high temperature have been summarized. With the application of viscoelastic principle about polymer materials, the deformative mechanisms under different temperature conditions about two typical automotive needlepunched carpets (1. a needlepunched fabric layer plus a latex layer, 2. a needlepunched fabric layer, a polypropylene (PP) thermo figuration layer plus a mat layer. ), have been analyzed, respectively.With the viewpoint of composite macroscopic mechanics, a nonlinear viscoelastic constitutive framework, including temperature effect, for automotive needlepunched carpets has been proposed from thermodynamics of irreversible processes. In order to characterize the difference of temperature effect with different heat transferring conditions, the description on temperature effect in our model is based on the definition of temperature in thermodynamics of irreversible process.According to the specific heat transferring modes corresponding to the different thermoforming process stages in practice, a single side cooling model and a natural convection model of spaceless plate have been introduced our proposed model framework, respectively. Then with a method of Laplace transform and Laplace inverse transform, the specific expressions of viscoelastic constitutive equations for automotive needlepunched carpet composites for the three heat transferring cases (isothermal, heat convectional, and heat conductive), have been archived. Model parameters among these obtained constitutive equations can be characterized just by basic mechanical experiment and thermal test, which makes our proposed model convenient for industrial applications.Applying the user-defined subroutine interface VUMAT of general purposed nonlinear finite element analysis software ABAQUS/Explicit to code our proposed model for automotive needlepunched carpets, numerical simulations of uniaxial extensile deformation and stamping deformation with a hemisphere punch are implemented, respectively for the different heat transferring cases. Verification of our proposed model is proved by the comparison between the numerical results and the experimental data. To gain a relatively objective evaluation on the proposed model, the Marlow model, which is a built-in material model in ABAQUS, is selected to implement the similar numerical simulations for comparison. Comparisons between these numerical results and the actual experimental data have further proved verification and efficiency of our proposed model.Finally, depending on the deformation characteristic of automotive needlepunched carpets in high temperature, three formability indexes are proposed based on our built model. By comparisons with corresponding experimental data, these indexes verifications are proved. Each of them evaluates the thermo formability of automotive needlepunched carpets from different aspects, which are ultimate strength, deformation ability and temperature sensitivity, respectively. By the applications of them, helpful references to a steady and robust thermal forming operation for automotive needlepunched carpet composites in practice are able to be archived.更多还原