Ductile phase toughening mechanisms in a TiAl-TiNb laminate composite

In this paper, toughening mechanisms in a laminate composite composed of alternating layers of brittle γ-TiAl and ductile TiNb reinforcements are studied. The TiNb phase comprising about 20% of the composite volume, contributed to toughening by both crack renucleation and bridging mechanisms, yielding a steep resistance curve and effective toughness more than ten times higher than the matrix value. In part, the extraordinary toughening is derived from large scale bridging effects, which occur when the size of the bridging zone s not small compared to the crack and specimen dimensions. Large scale bridging model predictions based on independent evaluations of the fundamental composite properties, including the reinforcement stress---displacement function, were in good agreement with the experimental observations. The authors demonstrate how the models can be used to optimize the composite properties for specific applications