含残余应力纳孔材料的宏细观弹-粘塑性力学行为研究

Nanoporous materials usually produce initial residual stresses (e.g. surface residual stress and inner gas pressure), which inevitably have effects on the mechanical behaviors of nanoporous materials. Subject to the working environments and loading conditions, the nanoporous material can exhibit elastoplastic and viscoplastic behaviors. The proposed project aims to develop a micromechanics model and a homogenization-based numerical approach, by taking the multiple residual stresses into account, to systematically investigate the influences of interface effects, inner gas pressures and void microstructures on the macro/micro elastoplastic and viscoplastic deformations of nanoporous materials. We will extend the classical second-order moment micromechanics model to incorporate multiple interface residual stresses and gas pressures, and investigate the overall elstoplastic properties of the materials. As for the viscoplastic deformation at high temperature, we will develop a micromechanics model to estimate the overall viscoplastic responses of the nanoporous material, where the interface effects, inner pressures, the evolution of porosity and the effect of temperature are fully taken into account. This establishment is built upon a unified homogenization scheme and a field-fluctuation method for the rate-dependent material. In addition, the homogenization-based numerical approach will be presented to compute the macro/micro elasto-viscoplastic properties. In order to test the applicability of the developed micromechanics model and numerical approach, we will conduct a series of representative experiments. The successful implementation of this project will provide an insight into the influence mechanism of multiple residual stresses and the void microstructure on the macro/micro elasto-viscoplastic properties, and lead to an extremely useful tool for the structural design and property assessment of nanoporous materials.

纳米多孔材料通常存在初始残余应力（界面残余应力、内压），其必然会对材料的力学行为产生影响。受制于工作环境和加载条件，纳孔材料会表现为弹塑性和粘塑性变形行为。本项目旨在发展含多相残余应力的细观力学模型和基于均匀化的数值方法，来研究界面效应、内压和孔洞微结构对纳孔材料宏细观弹塑性和粘塑性变形的影响。本项目拟将经典的二阶矩细观力学模型扩展到同时含多相界面残余应力和气体内压的情况，研究材料的宏观弹塑性性能。对高温下的粘塑性变形，充分考虑界面效应、内压和孔隙率演化，利用统一均匀化格式和率相关材料的场扰动方法，建立细观力学模型来预测宏观粘塑性响应。此外，发展基于均匀化的数值方法来计算纳孔材料的宏细观弹/粘塑性性能。最后，开展一系列典型的实验测试来验证理论和数值模型的有效性。本项目的实施有助于深刻理解多相残余应力和孔洞微结构对纳孔材料宏细观弹/粘塑性行为的影响机制，并对其结构设计和性能评价提供有力工具。

界面弹性及残余应力在纳孔材料力学性能研究中起着重要作用。本项目通过考虑界面效应及残余应力的影响，发展了一系列非线性细观力学理论模型和基于均匀化的有限元方法，并对纳孔材料的宏细观弹-粘塑性力学行为开展了系统研究。主要研究内容和结果如下：.1）针对含随机分布的椭球纳米孔的多孔材料，通过将椭球孔等效为横观各向同性夹杂，发展了预测该材料有效弹性性能的细观力学模型，基于二阶应力矩和场扰动方法建立了含椭球孔材料的弹塑性细观力学模型，分析了椭球孔界面弹性、孔洞形状及尺寸对材料弹塑性力学性能的影响。.2）针对含不同孔径球形孔的纳孔材料，建立了考虑界面残余应力的二阶矩弹塑性细观力学模型，研究了界面残余应力、孔径尺寸及尺寸差异性对材料宏观弹塑性力学行为的影响。.3）本项目基于无厚度界面模型与有厚度界面相模型的等效性，建立了含界面残余应力的界面相本构模型，通过编制UMAT子程序并将其嵌入到ABAQUS有限元软件中。利用开发的界面模型和均匀化方法，数值研究了纳孔铝的拉伸和压缩行为，并与理论结果进行了对比研究，证实了细观力学模型的准确性和可靠性。.4）构建了基于外点Eshelby张量的细观力学模型，研究了含椭球孔洞多孔材料在外载和流体内压作用下的局部弹性场问题。通过含内压和外载的核-壳结构经典基准解，证实了细观力学方法的准确性。.5）针对多孔/复合材料粘塑性力学行为，发展了考虑夹杂形变和旋转演化的细观力学模型，研究了含有限体分比椭球夹杂粘塑性力学变形行为，揭示了其运动演化机制。通过与基于均匀化的数值结果对比，验证了理论模型的准确性。在实验研究方面，对微纳米钛合金试样开展了应变率相关的动态压缩力学性能测试，得到不同温度、不同应变率条件下的压缩应力应变关系。.本项目研究成果对理解界面残余应力和孔洞微结构对纳孔材料弹-粘塑性力学行为的影响机制以及对该材料的结构设计和性能评价提供了理论依据和有益参考。