Effects of strain rate on tensile strength of steel specimens of HAZs with stress concentrations

Abstract

It is well known that the strain rate affects tensile behaviour; for example, it affects the tensile strength and fracture elongation of metals. When examining the tensile behaviour of steel, it is important to pay attention to the heat-affected zone (HAZ) as well as the base metal. The effects of the strain rate on the tensile strength were investigated by using specimens with stress concentrations; in particular, the tensile strength of SM400, SM490 and HT780 were obtained from HAZs by performing tensile tests at strain rates of 0.085%/s, 85%/s and 1000%/s. The HAZs were simulated by using a thermal/mechanical simulator. The main results are summarized as follows. (1) Regardless of the grade of steel, the tensile strength of specimens that underwent ductile fracture increase at high strain rates, whereas the tensile strength of specimens that underwent brittle fracture did not increase. (2) Regardless of the grade of steel and regardless of whether welding heat was supplied or not, the rate of increase in the tensile strength as a result of the high strain rate can be predicted from the tensile strength, which can be determined by static testing.

Keywords::

• heat-affected zone
• high strain rate
• tensile strength
• stress concentration
• synthetic HAS test

Acknowledgements

A part of this study was assisted by a subvention by a Grant-in-Aid for Scientific Research, Basic Research (C) (General) (Subject No.: 17560506) and by the Japan Iron and Steel Federation 2007 Students Research Scholarship Project; Engineering. We should also like to express our gratitude to Nakatsuji Yoshihiro of the technical staff of Osaka University for his assistance with tensile tests and Mr Horinouchi Tsutomu, also of the technical staff, for his assistance with simulated HAZ tests.

Notes

Presented at the Welded Structures Symposium, November 2009.

^1. Currently: Keihan Electric Railway Co. Ltd, Japan.