Strength evaluation method for brittle fracture at arbitrary strain rates

Fracture toughness is affected by strain rate. For most materials, fracture toughness under high strain rate such as impact loading is lower than static fracture toughness. Then it is necessary to develop the estimation method of fracture toughness at arbitrary strain rates. In this paper, we proposed the estimation method of fracture toughness at arbitrary strain rates on condition that static fracture toughness test results under some different test temperatures had been known. As a result of FE analyses, it turned out that strain rate-temperature parameter (R) keeps a certain constant value in fracture process zone at an arbitrary moment of loading process. Based on the investigation about this result, we postulated that fracture toughness is a function of R value in fracture process zone. Using this hypothesis, we developed the estimation method of fracture toughness under arbitrary strain rates. Moreover, we demonstrated the expansion technique of CTOD design curve in case of high strain rate. Then we found evidence of the validity of these approaches by evaluating brittle fracture accidents which occurred at Hanshin Great Earthquake.