Experimental and numerical study of mode-I and mixed-mode fracture of ductile U-notched functionally graded materials

Abstract

In the present study, ductile fracture of the U-notched samples made from bainitic Functionally Graded Steel (FGS) has been studied experimentally and numerically under the mode-I and mixed-mode conditions. The desired FGS plates were fabricated using the Electro Slag Remelting (ESR) technique. Then, the notched specimens were tested under the three-point bending condition. Effects of both the notch geometry and loading point position have also been investigated. A numerical scheme based on kinematic hardening constitutive model as well as Hollomon's equation has been utilized to define the material response including damage evolution. This numerical scheme is also able to predict the damage initiation point based on a method that uses both the stress triaxiality and equivalent stress values. Moreover, material properties of each point within the graded regions have been specified using the strain gradient plasticity theory, instability point concept and area under stress–strain curve. Comparing the experimental results with the numerical ones shows the capability of the numerical scheme. Also, the critical fracture loads of the notched samples made from FGS show the superiority of the present graded material over the homogeneous one.