A study on the failure behavior of Al2O3-Ni micro-layered beams under three point bending

Ceramic-metal laminated composites consisting of alternating ceramic and metal micro-layers can create unique structural or composite properties superior to the material properties of individual constituent ceramics and metals. Those unique composite or structural properties cannot be adequately modeled by Linear Elastic Fracture Mechanics (LEFM) or Strength of Materials (SoM) since both models are limited to homogeneous materials. A recent composite fracture model with an approximate empirical solution is adopted in this study to determine both the structural or composite tensile strength and fracture toughness of micro-layered Al2O3-Ni laminar composites, which were prepared through gel-casting and hot-pressing. This simple empirical model considers the micro-cracking or damage zone in the highly stressed region, e.g. at notch tip, and the most prominent composite microstructure, i.e. the thickness C-ch of ductile Ni micro-layers. A linear relation between the maximum fracture loads P-max and the equivalent area A(e) was confirmed with the structural or composite tensile strength f(t) as the slope. The structural or composite fracture toughness KIC was then determined by f(t) and C-ch. This simple empirical model can also be used together with normal distribution so that both the mean and 95% reliability band can be predicted. The structural or composite properties determined by the simple composite fracture model were compared with rough approximations from LEFM and SoM (both should not be used for composites) so that readers can see the errors if those classic models suitable only to homogeneous materials are used.