FAILURE MECHANISMS OF MILD-STEEL BOLTS UNDER DIFFERENT TENSILE LOADING RATES

This paper examines the plastic deformation and failure behaviour of m ild steel bolts subjected to tensile loads exerted at strain rates ran ging from about 10(-5) to 10(2) s-1. Three experimental techniques wer e used to generate different strain rates; these being tensile testing (for a strain rate of 2.5 x 10(-5) s-1), drop tower impact testing (a pproximately 1-10 s-1), and underwater explosion shock testing (approx imately 10(2) s-1). Measurements of the tensile failure strengths of t he shank and threads of the bolt revealed that the threads fail at loa ds which are significantly lower than the breaking strength of the sha nk. The threads were damaged under loading in a two-stage process: fir stly their tips were sheared off, and then the remaining thread was se verely plastically deformed. These findings are important consideratio ns when determining the load-bearing capacity of bolted joints and str uctures under impact conditions.