Life Prediction by Retardation Behavior of Fatigue Crack and its Nondestructive Evaluation

J. Ocean Eng. Technol. 1999;13(3):36-48.

Nam, Ki-Woo;Kim, Seon-Jin;

피로균열의 지연거동에 따른 수명예측 및 비파괴평가

남기우;김선진;

부경대학교 재료공학부;부경대학교 기계${cdot}$자동차공학부;

Keywords: Leak before Break, Fatigue, Crack Penetration Behavior, Retardation Behavior, Signal Characteristics, Acoustic Emission, Waveform

핵심용어: LBB, 파단전누설, 피로, 균열관통거동, 지연거동, 신호특성, 음향방출

Abstract

Fatigue life and crack retardation behavior after penetration were experimentally examined using surface pre-cracked specimens of aluminium alloy 5083. The Wheeler model retardation parameter was used successfully to predict crack growth behavior after penetration. By using a crack propagation rule, the change in crack shape after penetration can be evaluated quantitatively. Advanced, waveform-based acoustic emission (AE) techniques have been successfully used to evaluate signal characteristics obtained form fatigue crack propagation and penetratin behavior in 6061 aluminum plate with surface crack under fatigue stress. Surface defects in the structural members are apt to be origins of fatigue crack growth, which may cause serious failure of the whole structure. The nondestructive analysis on the crack growth and penetration from these defects may, therefore, be one of the most important subjects on the reliability of the leak before break (LBB) design. The goal of the present study is to determine if different sources of the AE could be identified by characteristics of the waveforms produced from the crack growth and penetration. AE signals detected in four stages were found to have different signal per stage. With analysis of waveform and power spectrum in 6061 aluminum alloys with a surface crack, it is found to be capabilities on real-time monitoring for the crack propagation and penetration behavior of various damages and defects in structural members.