The damage and fracture behavior of in-situ TiB2 particle reinforced 2024-T4 aluminum matrix composites (TiB2/2024-T4) with particle volume fraction of 4.17％ were investigated experimentally by means of in situ tension and SEM observation.The test results show that the aluminum alloy matrix within the TiB2 particle segregation bands breaks earlier than that in the particle sparse region.Based on such phenomenon and with the same particle volume fraction as well as the randomly distributed particles,three 2D unit cell finite element models of different segregation band widths were established.Tensile load and periodic boundary conditions were imposed.The radial return algorithm in plane stress state was deduced and applied to the elastoplastic iteration procedure.The initiation and propagation of micro matrix cracks in TiB2 segregation bands were simulated with Rice-Tracey local failure criterion.The numerical results show that the matrix near the particle poles suffers serious damage.Particle segregation leads to rapid accumulation of matrix damage and soon grows into micro matrix cracks.The fracture strain decreases with the increase of particle segregation degree.In addition,the nonlinear part of the stress-strain curve of the TiB2/2024-T4 unit cell model is obviously lower than the real curve,indicating that besides the mechanism of load transfer strengthening,other indirect particle reinforcement mechanisms may also enhance the strength of the material to a certain extent.%利用SEM结合原位观测技术观察了颗粒体积分数为4.17％的原位自生TiB2颗粒增强2024-T4铝基复合材料(TiB2/2024-T4)的损伤断裂行为.试验结果表明,TiB2颗粒偏聚带中的铝合金基体比颗粒稀疏区域中的铝合金基体率先发生断裂.根据这一试验现象建立了三种含随机颗粒偏聚带的二维体胞有限元模型,并施加拉伸载荷和周期性边界条件,推导了平面应力状态下的径向返回算法,结合Rice-Tracey局部失效准则模拟了颗粒偏聚带中微裂纹的萌生及扩展过程.数值分析结果表明:就单个颗粒来说,颗粒两极附近基体损伤最严重.颗粒偏聚导致损伤在颗粒附近基体中迅速累积,并发展成为基体微裂纹,且随着颗粒偏聚程度加剧,材料断裂应变下降.另外,体胞模型应力-应变曲线的非线性部分低于实测曲线,说明除了本文模型反映的载荷传递强化机制外,还需要进一步考虑颗粒对基体的间接强化机制.
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