Threaded Fastener Locking With Safety Wire and Cotter Pins

Abstract

This paper presents test results and analyses of safety lock wire and cotter pins with castellated nuts used as locking features in threaded fasteners. These mechanical components are used to secure hardware in aerospace and other applications as well as to assess whether a fastener has been tampered with. Tests are performed on aerospace threaded fasteners. Locking moments up to safety lock wire and cotter pin failure are measured. Calculations of locking moment to failure are provided and compared to measured results. For fasteners with safety lock wire, the angle of turn with applied moment is measured and computed. For fasteners with cotter pins and castellated nuts, the angles of turn from clearances and applied moment are computed. Since both safety lock wire and cotter pin with castellated nut applications result in some angle of turn, analysis for loss of preload with angle of turn is developed. Calculations show modest loss in preload for typical angles of turn for long bolts, but a significant loss of preload is found for short bolts.