Failure mechanisms of mild steel bolts under different tensile loading rates

Abstract

Summary This paper examines the plastic deformation and failure behaviour of mild steel bolts subjected to tensile loads exerted at strain rates ranging from about 10 −5 to 10 2 s −1 . Three experimental techniques were used to generate different strain rates; these being tensile testing (for a strain rate of 2.5 × 10 −5 s −1 ), drop tower impact testing (~ 1–10 s −1 ), and underwater explosion shock testing (~ 10 2 s −1 ). Measurements of the tensile failure strengths of the shank and threads of the bolt revealed that the threads fail at loads which are significantly lower than the breaking strength of the shank. The threads were damaged under loading in a two-stage process: firstly their tips were sheared off, and then the remaining thread was severely plastically deformed. These findings are important considerations when determining the load-bearing capacity of bolted joints and structures under impact conditions.