The objective of the proposed research is to continue prior University of Washington studies on mixed-mode concrete fracture aspects of diagonal tension failure in reinforced concrete members. Specifically, the shear transfer mechanism, which is thought to resist stable crack growth, will be studied using crack-line wedge- loaded, double cantilever beam specimens with short starter cracks and various loading histories which are crack-length dependent. Moire interferometry will be used to measure simultaneously two orthogonal displacement fields from which the crack opening displacement and the slip of stably growing diagonal tension cracks will be determined. Moire data together with the loading data will be used interactively with a finite element code to deduce the crack closure and shear forces in the fracture process zone under mixed mode loading. Mixed mode stable crack growth criterion will be deduced from this hybrid experimental-numerical analysis. The results will be correlated with fractography and profilometer analyses of the fractured surfaces in order to assess the relative micromechanic contributions of the various constituents (hardened cement paste, coarse aggregate and fine aggregate, etc.) to mixed mode concrete fracture.
