基于构型力理论的相变及损伤耦合时损伤演化方向研究

The damage and its evolution are the main factors influencing the ductility of material. It was found from our latest research that it was affected tremendously by the phase transformation induced by the high stress near the damage defects. Thus, through controlling the characteristic of transformation (such as the mechanical stability of phase particles), the ductility of material could be enhanced. However, the internal mechanism of interaction between the transformation and damage is unclear till today, although a lot of research work invested. Coupling the problem of cracks, the disturb on the stress field from the transformation is rather complicated and only specific case can be solved. The internal mechanism have not obtained. .In this project, several types of damage, such as plastic deformation, defect and phase transformation induced by local high stress were considered. The evolution and propagation mode of these kinds of damage were investigated especially when all these damages occurred simultaneously in material. Because these different kinds of damage can be regarded as a process of energy dissipation, they can be incorporated into the framework of thermodynamics during analyzing. Therefore, in this study, based on the latest developmental configurational force theory, through using the second law of thermodynamics into the elastoplastic deformation and damage system, the multiple types damage and its evolution were analyzed. Especially, the influences on the material ductility of three kinds of damage were respectively investigated firstly. Further, the theory related to the characterization parameters, the internal control factors and evaluation mechanisms of mechanics were created. the criterion which control the damage evolution and its propagation mode is given.

损伤及其演化是影响材料韧性的主要因素。而应变诱发的相变对其影响较大。控制相变过程进而抑制损伤的演化是提高材料韧性的有效手段。然而，相变与损伤相互作用的内在机理，迄今尚不明晰。基于具体的应力场分析，难以揭示其影响的本质机理。本研究拟针对相变与损伤的耦合现象，基于热力学框架，运用最新发展的构型力理论，研究其耦合作用的内在力学机理。具体地，考虑材料的塑性变形和缺陷及其演化对材料韧性的影响趋势不同，将损伤区分为塑性变形型和以产生新表面为特征的缺陷型，同时也将相变看做一类损伤。导出对应不同损伤的守恒积分。探索表征真实损伤演化的构型力表征参数。引入热力学第二定律，推导表征损伤及其演化的构型力理论框架下的最小作用量原理。建立损伤发展方向及方式预测的构型力理论。通过这一研究，可拓展构型力理论至损伤与相变耦合的研究领域，预测材料损伤范围及发展方向，进而对相变增韧材料的设计及其损伤寿命预测提供有效的指导。

损伤及其演化是影响材料韧性的主要因素。而应变诱发的相变对其影响较大。控制相变过程进而抑制损伤的演化是提高材料韧性的有效手段。本研究针对相变与损伤的耦合现象，基于热力学框架，运用构型力理论，研究其耦合作用的内在力学机理。针对微裂纹形式的损伤，通过改变裂纹启裂角及路径，研究其对裂纹扩展过程中能量耗散的影响，以多晶材料为例，研究多晶硅中晶粒取向与裂纹路径和裂纹偏转的影响关系；考虑粘塑性材料及材料的率相关性，研究其对材料中裂纹扩展及断裂失效的影响规律；通过研究复合材料结构中结构变化对损伤演化的影响，进一步揭示相变与损伤耦合时结构的演化规律。.通过项目的研究，得到了以下重要结果：.1、基于构型力理论，利用M-积分表征了粘塑性材料本构的率相关性对材料中裂纹扩展及断裂失效的影响，构型力理论的M-积分可以作为表征粘塑性高温合金材料损伤特征的有效参数。.2、针对材料中弥散分布的相变夹杂非均质特征，考虑相变应变含体积膨胀应变和剪切应变两部分，研究了含相变夹杂材料中的断裂增韧和裂尖偏转问题。基于材料构型力理论，引入守恒Jk-积分表征含相变夹杂非均质材料中夹杂相变与裂纹之间的干涉作用，研究发现裂尖Jk-积分是比远场Jk-积分更有效的断裂控制参数。基于能量释放率公式，推导得到了判定裂纹扩展启裂偏转角的精确解表达式。.3、针对韧性材料中裂纹扩展的能量来源问题，通过实验定量地研究了韧性材料中弹性应变能与裂纹形成之间的关系。考虑到扩展裂纹面的不规则性及长度测量的不准确性，设计了两种实验方案。实验结果表明即使对于韧性材料，在裂纹启裂及扩展中，尽管伴随着较大的塑性变形，但其裂纹扩展长度（面积）总是与弹性应变能线性相关，不受塑性变形或塑性耗能的影响。因此材料中的弹性应变能变化能够成为描述韧性材料断裂乃至损伤的一个力学参数。.4、建立了损伤发展方向及方式预测的构型力理论。拓展构型力理论至损伤与相变耦合的研究领域，预测材料损伤范围及发展方向，进而对相变增韧材料的设计及其损伤寿命预测提供有效的指导。