Stress-Strain Curves of High Strength Steel Sheets at Strain Rates From 10-3 To 103/S Obtained With Various Types of Tensile Testing Machines

In order to evaluate the crashworthiness of impact energy absorbing parts for automobiles, it is very important to obtain accurate stress-strain (s-s) relationships for steel sheets under various strain rates. However, at high strain rates over 10/s, stress wave interference in the load cell obstructs precise measurement of the s-s relationship with conventional tensile testing equipment. Various new tensile testing machines have been developed to obtain accurate s-s relationships at high strain rates. Six of these machines (coaxial Split Hopkinson Pressure Bar method, Non-coaxial Split Hopkinson Pressure Bar method, One Bar method, Sensing Block Testing System, and two types using the Hydraulic Servo method) were used to obtain s-s relationships for high strength steel sheets. In this paper, the s-s relationships are compared and the characteristic of the curves was discussed. In the strain region over 5%, the same stress-strain relationships were obtained with all types of test equipment. However, in the small strain region below 5%, the relationship obtained at strain rates around 10³/s depended on the equipments. Moreover, validation of dynamic s-s curves in crashworthiness evaluation of auto body parts was confirmed.