Simultaneous evaluation of residual stress and plastic deformation in ferromagnetic steel by using an integrated NDE method

To ensure the safety of nuclear power plants, the evaluation of material degradation due to mechanical micro-damages is of great importance. In previous researches, Non-destructive Evaluation (NDE) methods based on electromagnetic material properties such as the Magnetic Barkhausen Noise (MBN) method, the Magnetic Incremental Permeability (MIP) method and the Magnetic Flux Leakage (MFL) method were studied to evaluate the plastic deformation in ferromagnetic material such as the Reduced-activation Ferritic/Martensitic (RAFM) steel, which is a candidate fusion reactor material of special material property. However, the residual stress and plastic deformation are indivisible in most practical cases, which make the conventional NDE methods hard to be applied to a satisfactory precision. To develop a method for simultaneous evaluation of residual stress and plastic deformation in a structure of RAFM steel, a hybrid NDE method using the signals of MBN, MIP and MFL methods was proposed and experimentally validated in this paper. At first, an online integrated NDE system of these three magnetic NDE techniques was developed and was adopted to measure the NDE signals during loading process for RAFM steel test-pieces of different residual plastic strains. A strategy to get both the stress and strain information from groups of the measured NDE signals was then proposed and validated. It was demonstrated that the residual stress and plastic deformation can be properly evaluated based on some selected feature parameters of the measured magnetic NDE signals by using the proposed evaluation procedure based on the known NDE calibration information of the target material.