Derivation of the Depth Dependent Mechanical Characteristics of Ion-Irradiated F82H Steels by Using a Finite Element Analysis

Abstract

Changes in mechanical material properties caused by neutron irradiation during the nuclear power plant operation are one of the key safety issues for the maintenance and long-term operation of nuclear power plants (NPPs). Ion-irradiation is widely used to simulate neutron irradiation condition in laboratory environment, such an irradiation effect on the material property is varied along the depth of a material subjected to ion irradiation. Since the ion irradiation induces a depth-dependent dose from the surface of a material. The load-depth (L-h) curve and nano-hardness measured from nanoindentation, which is used to obtain the material properties using small specimen, normal to the ion-irradiated surface is a result of complex average of varying mechanical property along the indentation depth. The present paper investigates a method to evaluate depth (or dose)-dependent mechanical properties by combining experiment and finite element (FE) analysis of nanoindentation. The method is applied to reduced activation ferritic-martensitic steel, F82H. The material was ion-irradiated using Fe3+ ions of 1.7 MeV accelerating voltage at 300°C. The applicability of reverse algorithm was reviewed, and separate FE analyses were performed to determine material parameters by using trial set of material parameters. The ion-damaged surface layer was divided into several layers in the FE modeling. The L-h curve using determined stress-strain curve by using trial set of material parameters was found to be better agreement than reverse algorithm with experimentally measured one by nanoindentation. The advantage and limitation of the method investigated in this study will be discussed in detail.