Approximate Evaluation Method for Crack Growth Rates Under Repeated Large Plastic Deformation

Abstract

Abstract Many countries have suffered from large earthquakes in the past few decades. Extensive efforts are required to estimate the fracture behavior under cyclic plastic strains in steel components so as to prevent or minimize fatal accidents. Crack growth rates under cyclic loads have been generally analyzed by Paris’ law by using a linear elastic fracture mechanics concept, “ΔK”, stress intensity factor range. But, this approach cannot be valid in the domain of large plastic deformation. An alternative approach could be developed by substituting J-integral or crack tip opening displacement for stress intensity factor. However, this is yet not very easy to apply in real complicated structural components, as it takes much excessive computational time for the calculation of the governing fracture parameters. The present paper proposes an approximate method to evaluate crack growth rates under repeated large plastic deformation by using an easier formulation based on an approximate analysis of fracture parameters. Crack growth experiments have been conducted under cyclic axial plastic loadings in order to verify the validity of the proposed formula. Experimental results showed fairly good agreement to the proposed formula. Discussion is as well directed to the change in the feature of fracture surfaces during growth.