Suppression of Fracture Failure of Structures by Composite Design Based on Fracture Mechanics

This paper discusses the use of fracture mechanics for the microstructure tailoring of a fiber reinforced Engineered Cementitious Composite (ECC) to achieve extreme tensile ductility at the composite scale. It demonstrates that fracture mechanics applied to control fracture phenomena at the micro and meso material scales can lead to suppression of fracture failure at the macro structural scale. Specifically, models of tunneling crack at the fiber/matrix interface and the steady state propagation of bridged flat matrix crack combine to provide insights on composite design. Interestingly, the micromechanics model indicates that low fiber/matrix interface fracture energy and low mortar matrix fracture energy are desirable for attaining high composite ductility. These concepts are verified by an expanding set of experimental data on structural elements tested to failure. The explicit suppression of commonly observed fracture mechanisms in reinforced concrete columns under reverse cyclic loading when the concrete is replaced by ECC is described.