Recently Developed Testing Techniques and Dynamic Tensile Properties of Steel Sheets for Automobiles

摘要

In order to analyze the dynamic behavior of parts of an automobile during a crash with sufficient accuracy, it is important to use a practical constitutive model that simulates the dynamic properties of the material of which the parts are composed. To establish the model, it is essential to study the dynamic properties of these materials over a wide strain-rate range and a wide strain range until the fracture. The recently developed tensile testing techniques based on the sensing block method enables to obtain the entire tensile stress-strain curves over a wide strain-rate range on the order of 10~(-3) ~ 10~3 s~(-1). The principle and features of the method were briefly summarized and numerical consideration for testing geometry ensuring the measuring accuracy of dynamic stress was conducted. The practical hydraulic testing system was built based on the developed technique. The entire tensile stress-strain curves of cold-rolled mild steel sheet (SPCE) and high strength steel sheets (SPFC440 and SPFC590) were obtained over a wide strain-rate range on the order of 10~(-3) ~ 10~3 s~(-1). It was found that the flow stress increases with the strain rate and that the values of the true fracture strength and the true fracture strain are substantially not affected by the strain rate over a wide range up to 10~3 s~(-1). The sensing block method can be applied for not only tensile testing of steel but also many kinds of dynamic testing. Examples of dynamic tensile test for plastic materials were also reported. By changing the capacity of a loading device and a sensing block, the method is useful for the component test as well as material test. Dynamic buckling test of an aluminum tube was conducted and the dynamic load was precisely measured.