Enhancement of Nondestructive Evaluation Technique for Magnetic and Nonmagnetic Structural Components

磁性及び非磁性構造物における非破壊検査技術の向上

陳 振茂

not registered

本報告書はJNCにおいて行われた2年間のポストドクター研究の成果を取りまとめたものである。本研究は磁性及び非磁性の構造物を対象に電磁非破壊検査法の向上または新規開発を目指して、渦電流探傷法を用いた自然き裂の形状再構成及び損傷誘起磁化現象の解明と非破壊検査への応用に関する研究を実施した。渦電流検査法の向上には自然き裂の形状を再構成するアプローチを提案し、理想化したき裂モデルに対して再構成を行うことによってその有効性を実証した。自然磁化に関する研究では損傷誘起磁化と損傷の相関の解明及び弱磁性体のSUS304構造物の非破壊検査への適用妥当性を試験手法で評価した。また、測定した磁束漏洩信号から材料内部の磁化分布(損傷の状態と相関する)を再構成するために、最適化手法及びウェーブレットを用いた手法を提案し、実際に測定したデータの逆解析を行った。解析した結果はコロイド法によって計測した磁化に分布と定性的によく一致し、提案手法の有効性を確認した。

ln this report, research works performed in the Structura1 Safety Engineering Group of OEC/JNC are summarized as the final report of the doctoral fellowship. The main objective of this study is for the enhancement of the nondestructive evaluation techniques for structural components of both magnetic and nonmagnetic material. Studies in three topics have been carried out aiming at the quantitative evaluation of crack with the eddy current testing and the validation of a natural magnetic field based NDE method for detecting mechanical damages in a paramagnetic material. ln the first part of the study, an approach to the reconstruction of the natural crack was proposed and implemented with an idealized crack model for its validation. ln the second part, the correlation of the natural magnetization and the mechanical damages in the SUS304 stainless steel was investigated by using an experimental approach. ln part 3, an inverse method of the measured magnetic fields is proposed for the reconstruction of magnetic charges in the inspected material by using an optimization method and wavalet. As the first work, an approach to the reconstruction of an idealized natural crack of non-vanishing conductivity is proposed with use of signals of eddy current testing. Two numerical models are introduced at first for modeling the natural crack in order to represented it with a set of crack parameters. A method for the rapid prediction of the eddy current testing signals coming from these idealized cracks is given then by extending a knowledge based fast forward solver to the case of a non-vanishing conductivity. Based on this fast forward solver, the inverse algorithm of conjugate gradient method is updated to identify the crack parameters. Several examples are presented finally as a validation of the proposed strategy. The results show that both the two numerical models can give reasonable reconstruction results for signal of low noise. The model concerning the touch of ...