Dynamic Fracture Initiation: A Comparison of Two Experimental Methods

Abstract

This paper presents a comparison of dynamic fracture initiation results obtained from two independent experimental methods: (1) the instrumented version of the precracked Charpy test and (2) a new dynamic fracture test developed at Brown University (BU). Dynamic fracture tests were conducted using both methods on 4340 steel at room temperature and on 1018 cold-rolled steel (CRS) at temperatures over the range −157 to 107°C. This range covered temperatures on the lower shelf, the transition regime, and the upper shelf of the transition temperature curve. Stress intensity rates of K̇I = 2.2 × 105 MN-m−3/2 /s and K̇I = 2.2 × 106 MN-m−3/2 /s were used in the instrumented precracked Charpy and BU tests, respectively. In the analysis of test results, both elastic (KIc ) and elastic-plastic (J-integral) fracture parameters were computed. Results of the two test methods were found to be generally in good agreement, except that some differences were observed between 1018 CRS test results on the upper shelf. Possible reasons for these differences are discussed.