短纤维金属基复合材料与温度有关的宏细观力学行为数值研究

【作者】 姜云鹏；

【导师】 韩小平；

【作者基本信息】 西北工业大学 ， 一般力学与力学基础， 2003， 硕士

【摘要】 本论文首先较为详细地叙述了近10年来国内外在金属基复合材料(MMC)高温力学性能领域的研究状况，评述了已经取得的成果和需要解决的问题，对该领域未来的研究方向和需要开展的工作提出了自己的见解。 论文研究内容可分为五个方面： 第一部分：对金属基复合材料(MMC)双剪切试样进行有限元模拟并分析了在高温下的应力应变分布和影响因素。对试验中常用的几种剪切试样进行了综合评价，指出各自的优点和存在的缺陷，指出利用双剪切试样研究高温下的金属基复合材料复杂应力力学行为的可行性和优点。接着建立了有限元分析模型对双剪切试样中心区的应力应变分布进行计算分析，得到了其应力应变随时间的变化规律。通过五种代表性试样的分析，得出金属基复合材料双剪切试样的应力应变与纤维随机分布平面和加载方向夹角θ之间的相关性：随着角度θ的减小，蠕变应力分布越均匀；当角度θ=45°时，其稳态蠕变率γ最大。 第二部分：基于短纤维增强金属基复合材料(MMC)的单纤维三维模型(三相)，利用有限元分析方法对影响金属基复合材料的蠕变行为的因素进行了较为系统的分析。主要讨论了界面特性和纤维取向角对复合材料的蠕变性能的影响。研究发现，界面特性诸如厚度、模量和应力指数都对纤维最大轴应力和稳定蠕变率产生影响，同时不同的纤维取向也影响金属基复合材料蠕变时的应力分布和蠕变率。 第三部分：对金属基复合材料(MMC)的热机械循环进行了较为详细的计算分析。建立了金属基复合材料的单胞模型(3D)，对几种较为常见的循环载荷进行了有限元模拟。着重分析载荷类型对数次循环后纤维中残余轴应力和轴应变的影响以及循环过程中纤维中最大轴应力、轴应变的变化。最后指出，载荷类型明显影响着金属基复合材料的变形；对于外加载荷峰值相同的情况下，对称载荷比脉动载荷更早地达到残余应力、应变的稳定值；在循环过程中，对称载荷和脉动载荷对纤维最大正轴应力的变化影响截然相反。 第四部分：基于三相介质模型结合热传导理论建立可用于描述颗粒增强金属基复合材料热传导性能的理论模型，该模型充分考虑界面厚度、界面导热性能对宏观热传导行为的影响。该模型对导热率的预测结果较以往模型更接近于试验值，而且还可对界面性质的影响进行定量分析。由模型的分析结果得出，颗粒增强金属基复合材料的热传递系数随着颗粒直径的增大而增强。 第五部分：对单纤维断裂引起的多纤维体中的应力重新分布进行了初步定量研究，发现纤维间距会影响多纤维体中基体、纤维的应力应变；纤维排列形式也会在很大程度上影响多纤维体中纤维的载荷分配。最后利用Gurson模型对纤维断裂后裂纹的走势进行模拟，纤维间距也直接影响裂纹的延展方向。 作为附录，给出了由拉伸试样确定应力应变关系的一种方法。该方法有一定的广适性。更多还原

【Abstract】 At first, the thesis summarizes the studies on high temperature mechanic behavior of metal matrix composites in the recent 10 years world widely. Emphasis is placed on the accomplishments that have been achieved and questions that are needs to be solved from both theory and numerical simulation. Finally, some suggestions are put forward about the direction of this area in the future and the works to be carried out.The paper can be divided in five chapters:The first one: FEM (finite element method) is applied to study the stress and strain distribution of short fiber-reinforced MMC (metal matrix composites) DB(double shear specimens) at high temperature. The applicability of the DB to produce the multi-axial stress state is specially analyzed. The stress and strain distributions and the factors influencing the creep behavior of MMC have been obtained. In the first section, a comparison was carried on different kinds of multi-axial specimens used for isotropic materials. They cannot be used for the MMC, since MMC is anisotropic. A detail FEM model is developed for MMC DB. The distributions of stress and strain in the DB have been obtained, which show the DB can provide a relative uniform shear stress in the shear zone center. The influence of the orientation of the DB specimens on the fiber-existing plane on the behavior is depended on the orientations. When the angle- 9 between the applied shear stress direction and the fiber-existing plane is equal to 45?,the creep strain rate of DB specimens y is maximum. The homogeneous degree of stress distribution is improving with the angle 9 increasing.The second one: Based on the 3D unit cell model of short fiber enforced metal matrix composites, finite element method (FEM) is applied to analyze of the influence on the creep behavior. Special attention is put on the influence of the inter-phase properties and the direction of fiber axial direction to the loading direction. The study shows that the inter-phase properties suchas thickness, elastic and creep material properties have influence on the axial stress states andsteady creep rates of the composites. The loading direction relating to the fiber axial direction hasalso influences.The third one: the computation and analyses of thermal-mechanical cycle for MMC areconducted in this paper. At the first, the 3D unit cell model is founded. The simulation underseveral common cycle loading types are done. The emphasis is played on the residual axial stress,residual axial strain of fiber. A series of conclusions are arrived that the effect on axial stress, strainof fiber is different between symmetry and asymmetry.The fourth one: a new formula has been founded for predicting thermal conductivity rate. Bycomparison, it is more accurate to acquire thermal conductivity rate than methods usually adopted. The fifth one: the quantitative study is conducted on the stress redistribution in multi-fibersystem after single fiber fractured. Based on the detailed analysis, not only fiber space but alsofiber array in the matrix has an effect on the load redistribution among the surrounding fibers.Finally, the tendency of crack was modeled by adopting Gurson model after single fiber fractured;the fiber space can affect the extending of crack in the matrix directly.更多还原