This International Standard specifies methods for testing metallic sheet materials to determine the

stress-strain characteristics at high strain rates. This part of ISO 26203 covers the use of elastic-bar-type systems.

The strain-rate range between 10−3 to 103 s−1 is considered to be the most relevant to vehicle crash events based on experimental and numerical calculations such as the Finite Element Analysis (FEA) work for crashworthiness.

In order to evaluate the crashworthiness of a vehicle with accuracy, reliable stress-strain characterization of metallic materials at strain rates higher than 10−3 s−1 is essential.

This test method covers the strain-rate range above 102 s−1.

NOTE 1  At strain rates lower than 10−1 s−1, a quasi-static tesnile testing machine that is specified in ISO 7500-1 and ISO 6892-1 can be applied.

NOTE 2  This testing method may be applied to tensile test-piece geometries other than the flat test pieces considered here.

 

Principles

The stress-strain characteristics of metallic materials at high strain rates are evaluated.

At a strain rate higher than 10 s−1, the signal of the loading force is greatly perturbed by multiple passages of waves reflected within the load cell that is used in the quasi-static test. Thus, special techniques are required for force measurement. This may be accomplished in two opposite ways: 

⎯  one is to lengthen the force measurement device in the loading direction, in order to finish the

measurement before the elastic wave is reflected back from the other end (elastic-bar type systems);

⎯  another way is to shorten the force measurement device, thus reducing the time needed to attain dynamic equilibrium within the force measurement device and realizing its higher natural frequency (servo-hydraulic type systems).