钉载孔挤压强化疲劳试验及断口分析

On Fatigue Testing and Fracture Analysis of Coldworked Fastener Holes under Pin and By-Pass Loadings

本文对在钉传和旁路载荷同时作用下,独立地对挤压孔的疲劳试验进行了研究。试验得到了挤压量与寿命的关系曲线,并且表明:挤压能大幅度提高钉孔构件的疲劳寿命。断口分析发现挤压孔的疲劳源并不发生在孔边,这一点为挤压孔疲劳裂纹形成寿命估算提供了有用的信息。通过对试验数据的分析,本文提出了对LY12CZ材料φ6孔的有利挤压范围。

Coldworked fastener holes have been employed in engineering practice toincrease fatigue life. The coldworking, referred to in this paper, consists ofpreexpanding the fastener holes radially with an oversize mandrel. Toor[1],Chompoux et al [2], and Mann et al [3] performed fatigue experiment on spe-cimens with coldworked holes, Petrak et al [4] and Cannon et al [5] perfor-med fatigue testing on real fasteners with coldworked holes. In all the abovetests only one kind of loading was used: either pin loading or by-pass loading.In this paper the authors present their experimental research in the more diffi-cult case of test specimens under simultaneous action of pin-loading and by-passloading. The authors believe their three contributions, of which the second is themain one, are as follows: (1) The curves relating fatigue lif e to amount of coldworking are obtai-ned experimentally. As exp cted, experiments confirm that coldworking can in-crease significantly the fatigue life of specimens, because the beneficial residualstresses due to coldworking can effectively counteract the stress concentrationcaused by the presence of holes. (2) Through fracture surface analysis, the authors discover that fatiguefailures, unlike that of holes without (?)ldworking, no longer occurs on the edgeof the hole. Such a discovery is useful infor nation for the theoretical analysisby the authors of the fatigue life of test specimen with coldworked holes. Sucha theoretical analysis is presented in Ref. [6]. (3) The authors give the beneficial range of coldworking for φ6mm hole ofLY12-CZ aluminum test specimen. It is common to use amount of interferenceto indicate the amount of coldworking required and the optimum range of in-terference in this case is 0.3-0.42mm.