Plasticity and ductile fracture of high-strength bolt materials under monotonic tension

Abstract

The plasticity and fracture properties of high-strength bolts are crucial to the mechanical behaviours of bolted connections subjected to extreme loadings. However, the material properties of high-strength bolts have not been comprehensively studied. This paper presents a collaborative experimental and numerical investigation to characterise the material plasticity and fracture properties of normal high-strength bolts (NBs) and weathering high-strength bolts (WBs) under monotonic tension. Eighteen cylindrical tensile coupons, cut from M20, M24 and M30 grade 10.9 NBs and WBs, are tested to capture the full-range engineering stress-strain relationships. The combined Swift-Voce weighting model is modified to describe and calibrate the material true stress-strain relationship of NBs and WBs. Then, a void-growth model (VGM) incorporated with the calibrated true stress-strain relationship is used to simulate the ductile fracture of tensile coupons. The calibration process collaborating experimental results and finite element (FE) simulations to obtain material parameters of high-strength bolts is demonstrated in detail. This collaborating method is further employed to simulate the plasticity and fracture properties of normal bolts with various grades under tension, as well as grade 10.9 high-strength bolts subjected to monotonic tension at elevated temperatures in literature. FE simulation results show a high accuracy with experimental results across all specimens, proving the rationality of the proposed method for material plasticity and fracture properties of high-strength bolts.