Harnessing impact-induced cracking via stiffness heterogeneity

Mechanical heterogeneity refers to the spatial inhomogeneity of the mechanical properties in materials, which is a common feature of composites consisting of multiple distinct phases. Generally, the effects of mechanical heterogeneity on the overall properties of the composites, such as stiffness and strength, are thought to follow the rule of mixture. Here, we investigate the cracking behavior of composite plates under impact and found that the rule of mixture may break down in describing the cracking resistance of composites with high stiffness heterogeneity. Our results show that the resistance of a composite plate, which consists of two phases of distinct stiffnesses, against dynamic cracking strongly depends on the hybridizing manner of the two phases. When the stiff phase is dispersed in the compliant matrix, the resulting composite plate exhibits superior cracking resistance compared to the monolithic plates made of either phase. In contrast, if the compliant phase is dispersed in the stiff matrix, the resulting composite plate displays reduced cracking resistance and thus higher absorption of the impact energy as compared to the monolithic controls. Our work provides an approach to harnessing the dynamic fracture by controlling the stiffness heterogeneity, which would be of great value to the design and fabrication of the protective armors and energy-absorbing shields.