Investigation of the notch depth effect on Charpy fracture energy and fracture surface features of API X65 steel

Abstract

ABSTRACT Different factors such as notch angle, notch depth, notch root radius, specimen size, hammer geometry and striker velocity affect the value of Charpy impact energy. The aim of present study is to measure the effect of notch depths (in the range from 1.25 to 3 mm) on fracture energy and fracture surface features of API X65 steel plates using Charpy impact tests. For this purpose, 24 specimens were made with 8 different notch depths (3 specimens per notch depth), which were tested to obtain the fracture energy. Furthermore, a computer simulation of the experiment was performed with a three-dimensional model based on Gurson's modified damage law via Abaqus software. The fracture surface morphology was observed using the SEM microscope to evaluate the fracture mechanisms. The experimental results revealed that the relationship between the fracture energy (E) and the notch depth (a) of the Charpy samples for the tested steel was E = 499.65e−0.3501a . Using this equation, the Charpy energy can be determined for this steel for any notch depth with an interpolation error of 3.31%. Fractographic observations indicated that various fracture mechanisms were observed by changing the notch depth, including brittle fracture with the river-like patterns, ductile-brittle fracture, ductile fracture, and fully brittle fracture.