SUMMARY

Material property heterogeneity is present ubiquitously in various natural and man-made materials, such as bones, sea shells, rocks, concrete, composites, and functionally graded materials. A fundamental understanding of the structure-property relationships in these material systems is crucial for the development of advanced materials with extreme properties. Well-developed homogenization schemes exist to establish such relationships in elasticity, electrostatics, magnetism, and other time- or history-independent material properties. Nevertheless, one’s understanding of the effective fracture properties of heterogeneous media is remarkably limited.
In this work, a combined experimental and modeling effort is made to examine and control fracture mechanisms in heterogeneous elastic solids. A two-phase laminated composite, which mimics the key microstructural features of many tough biological materials, is selected as a model material. Computationally, finite element analysis with cohesive zone modeling is used to model crack propagation and arrest in the laminated direction. The results indicate that the mismatch of elastic modulus is an important factor in determining the fracture behaviors of the heterogeneous model material. Significant enhancement in the material’s effective fracture toughness can be achieved with appropriate modulus mismatch. Systematic parametric studies are also performed to investigate the effects of various material and geometrical parameters. Concurrently, a novel additive manufacturing system is developed and used for fabricating test specimens with well-controlled structural and material properties. With optimized material and geometrical parameters, heterogeneous specimens are found to exhibit higher fracture toughness than their homogeneous counterparts, which is in good agreement with the computational predictions.