Mixed‐Mode Fracture of Concrete Subjected to Impact Loading

Abstract

An analytical and experimental investigation of mode I (tensile) and mixed mode (combined tensile and shear) fracture of concrete subjected to impact loading was conducted. The rate of loading ranged from a slow strain rate of 10-6/s to an impact strain rate of 0.5/s. Mixed‐mode tests were conducted using beams with notches at different locations along the span of the beam. A new clip gage was developed to measure crack‐opening displacement at slow and impact rates of loading. A nonlinear fracture‐mechanics model was developed to predict the rate sensitivity of mode I and mixed‐mode fracture of concrete. This approach was based on the observation that the prepeak nonlinearity may be attributed to prepeak stable crack growth and that this prepeak crack growth decreased with an increase in the rate of loading. The mixed‐mode‐fracture‐mechanics study used finite element analysis with singular quarter‐point elements at the crack tip. Mixed‐mode experimental and analytical results indicate that impact loading could result in brittle diagonal tension‐shear failure of concrete structures as opposed to ductile flex‐ural failure at a slow rate of loading.