An Experimental Study of the Interaction of Strain Fields between Coldworked Fastener Holes

摘要

This report describes the experimental study investigating the interaction of the residual surface strain fields caused by the coldworking of fastener holes in the near vicinity of one another. Testing was confined to 7075-T& aluminum alloy, 1/4 inch (6.4 mm) in thickness. Fastener holes were .261 inch (6.6 mm) in diameter and the center-to-center separation between adjacent fasteners was 1.75 and 2.0 diameters. Single-row in-line and double-row fastener patterns were the focus of this study. Consecutive and non-consecutive sequences of pattern coldwork were chosen to model possible field situations. Experimental results indicate a direct relation exists between the degree of interaction between strain fields and the center-to-center separation between adjacent fastener holes. As noted from the measurement of residual diametral expansions, unsymmetric hole edge motions result in unsymmetric strain distributions. Sleeve failure and the coldwork of adjacent fastener holes can lead to unwanted residual tensile strains at a hole edge boundary. (Author)