A Simple Method for Estimating the Effect of Loading Rate on Fracture Toughness

Abstract

Many fracture toughness tests under quasi-static condition suggest that fracture toughness is the function of yield stress at fracture initiation point. Since yield stress is the function of strain ratetemperature parameter (R) at arbitrary strain rate and temperature, we assumed that fracture toughness is the function of R value at fracture initiation point.In the previous paper, we reported that R value keeps some constant value in fracture process zone which is named Intensely Deformed Nonlinear Zone (IDNZ). (The following Rr, notes some constant R value in IDNZ.) Then we reported fracture toughness is the function of Rr, at fracture initiation. On the basis of this result, we enabled to estimate fracture toughness at arbitrary loading rate by fracture toughness test under quasi-static condition and thermal elastic-plastic FEM which is developed by us. But it is a lot of time and labor to estimate Rr value by using thermal elastic-plastic FEM.In this paper, the simple method to calculate strain rate and temperature rise due to plastic work on loading process is studied for the purpose of obtaining Rr value which is the function of strain rate and temperature in IDNZ. HRR singularity solution of stress and strain distribution in the vicinity of crack tip is adopted to calculate strain rate and temperature rise in this simple method.Then we investigate the validity of Rr value calculated by this simple method. As a result, we show the validity of this simple method to calculate Rr value.