Wang Jiaqin, Tan Vincent B C
Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore.
Materials (Basel). 2022 Jul 14;15(14):4906. doi: 10.3390/ma15144906.
It is generally accepted that material inhomogeneity causes stress concentrations at the interface and thus reduces the overall strength of a composite. To overcome this reduction in strength, some groups experimented on coating the nanoinclusions with a layer of rubbery material, aiming for higher energy absorption. However, representative volume element (RVE) nanocomposite models, established with randomly distributed core-shell nanoparticles and single nanoparticle cells, show that the enhancement in strength observed in some experiments remains elusive computationally. By including a pre-existing crack in the matrix of the RVE, the stress concentration at the crack tip is reduced for cases where the nanoparticle and precrack are aligned away from the loading direction. This suggests that stress concentrations around inherent defects in materials can sometimes be reduced by adding nanoparticles to improve material strength. The effect is reversed if the crack and nanoparticle are aligned towards the loading direction. Parametric studies were also carried out in terms of the relative stiffness of the nanoparticle to the matrix and crack length. Validation tests were performed on 3D RVEs with an elliptical crack as the initial defect, and the results match with the 2D findings.
一般认为，材料的不均匀性会导致界面处的应力集中，从而降低复合材料的整体强度。为了克服强度的这种降低，一些研究小组尝试用一层橡胶材料包覆纳米夹杂物，以实现更高的能量吸收。然而，用随机分布的核壳纳米颗粒和单个纳米颗粒单元建立的代表性体积单元（RVE）纳米复合材料模型表明，一些实验中观察到的强度增强在计算上仍然难以捉摸。通过在RVE的基体中引入一个预先存在的裂纹，对于纳米颗粒和预裂纹与加载方向对齐的情况，裂纹尖端的应力集中会降低。这表明，通过添加纳米颗粒来提高材料强度，有时可以降低材料固有缺陷周围的应力集中。如果裂纹和纳米颗粒与加载方向对齐，效果则相反。还针对纳米颗粒与基体的相对刚度和裂纹长度进行了参数研究。对以椭圆形裂纹作为初始缺陷的三维RVE进行了验证测试，结果与二维研究结果相符。
