A Study on Fatigue Crack Growth Retardation Phenomena of Al 7075--T6 Alloy under Multiple overload(I)

J. Ocean Eng. Technol. 1992;6(1):96-104.

다중 과하중에 의한 A1 7075-T6 합금의 피로균열 성장지연현상에 관한 연구

이택순,이유태

영남대학교 정밀기계공학과,영남대학교 정밀기계공학과

Keywords: Single Overload, Multiple Overload, Crack growth Retardation, Load Ratio, Overload Ratio, Overload Cycle Number, Overload Affected zone size

핵심용어: 단일과하중, 다중과하중, 구렬 성장지연 현상:하중화, 과하중화, 과하중 반복회수, 과하중 영향부, 균열 성장지연 사이클

Abstract

Aircraft structures and engineering structures are always subject to variable amplitude loads. Variable amplitude loads include some kind of loading history; for example, constant amplitude load, single peak overload and block overload etc. Crack growth under variable amplitude loading exhibits retardation effect. In this study, the 4 point bending fatigue test was performed by hydrolic servo fatigue testing machine on 7075-T6 Al-alloy. The retardation effect of overload ratio and numbers of overload cycle was quantitatively studied. 1) Change of retardation effect against increment of overload ratio is more evident when the multiple overload is applied than single overload is done. 2) The number of overload cycle is very important factor about the crack growth retardation effect when the overload ratio is more than 1.75; that is not when the overload ratio is less than 1.75. 3) Overload affected zone size increased gradually by increment of crack growth retardation effect. 4) Crack driving force is more greatly reduced when the crack tip branched off two direction than it sloped to one direction.