The influence of the dynamic loading rate on tensile failure properties of metallic materials

H Couque

doi:10.1051/epjconf/20122602012

Abstract

The influence of the dynamic loading rate on the tensile failure properties of a series of tungsten alloys and an austenitic stainless steel were investigated by evaluating the flexural strength with unnotched and notched Charpy specimens. These data were generated with a newly developed Hopkinson pressure bar technique. The technique consists in impacting with a striker, at velocities ranging from 25 to 160m/s, a round bar specimen placed against two incident Hopkinson pressure bars. Through the recording of the striker velocity before and after impact, failure energy is deduced. At impact velocities greater than 30m/s, the results reveal a surprising increase of the Charpy energy with the increase of the impact velocity for both types of metallic materials. The results have been interpreted through numerical simulations of the Charpy test, the dependence of the material flow stress with the strain rate, and observations of the failure mechanisms. It was found that at impact velocities greater than 30m/s, tangential strain rates exceed 3000s −1 at the failure initiation site of the Charpy specimen. These strain rates are within the strain rate regime where strengthening occurred due to the viscous behaviour of the dislocations. Data generated with moderate stress concentration using notched round bar Charpy specimens indicate that the strengthening occurring at high strain rates continues to pilot the tensile failure processes.

Highlights

Data on the influence of strain rate on the tensile strength of metallic materials generated with conventional tensile specimens are limited to strain rates of 2000 s−1 [1]
A newly Hopkinson pressure bar technique has been developed by the author to access these tensile properties through the analysis of flexural strength data generated at different loading rates involving a Charpy like specimen [2]
The results reveal a surprisingly increase of the Charpy energy with the increase of the impact velocity from 25 to 160 m/s

Summary

Introduction

Data on the influence of strain rate on the tensile strength of metallic materials generated with conventional tensile specimens are limited to strain rates of 2000 s−1 [1]. A newly Hopkinson pressure bar technique has been developed by the author to access these tensile properties through the analysis of flexural strength data generated at different loading rates involving a Charpy like specimen [2]. The present investigation reports on extended data generated with this technique for a series of tungsten alloys in the as-sintered and swaged conditions, along with a highly ductile austenitic stainless steel A304L. These metallic materials cover a large range in quasi-static yield stress from 500 to 1700 MPa and ductility from 6 to 50%, see Table 1.

Experimental procedure

Findings

Conclusions