In the blast demolition of reinforced concrete structures, the effect of rebar must be considered. However, this effect has not been fully investigated. Therefore, in this study, the effect of partially dense regions on the propagation behavior of stress waves and crack initiation in reinforced concrete was investigated using a polymethyl methacrylate (PMMA) plate pierced with an aluminum bar. Two visualization techniques, namely the photoelasticity and digital image correlation (DIC) methods, were used to measure stress wave propagation and crack initiation. It was found that in a blast fracture, crack formation initiated near the rebar, even though its role is to increase structural strength. Furthermore, the stress wave visualization results obtained using the photoelasticity method and the strain propagation results obtained using the DIC method showed good agreement. This suggests that the DIC method can be used to visualize and quantitatively evaluate the propagation of stress waves in nontransparent materials, for which the photoelasticity method is not applicable.

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The present study explores the explosion risk of nitromethane in fluid hammer phenomena. Nitromethane flowed through the flowpath by the gas-pressurized feed method in this test. The tank pressure conditions are 0.4, 0.6, 0.8 and 0.95 MPaG. No explosion occurred in any case in the present study. The fluid hammer test of water is also conducted to compare with nitromethane. The experimental peak pressure is 5.15 MPaG, and the fluid hammer pressure rise is 4.59 MPaG in the tank pressure condition of 0.95 MPaG. The experimental pressure rise of nitromethane is close to the theoretical prediction given by the Joukowsky equation in the flow velocity condition of more than 3.0 m･s^-1 if the pressure propagation velocity is equal to the sonic speed. The peak pressure of the fluid hammer effect for water is the same with or higher than nitromethane. The other experimental fluid hammer test data indicates that nitromethane has similar fluid dynamic behaviors to water. Thus, the present investigation recommends using water for the fluid hammer test of the nitromethane feed system.

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