Abstract
Keywords:
High speed tensile test, Dynamic material property, Intermediate strain rate, Load ringing phenomenon
Abstract
The crashworthiness for passenger safety becomes an essential factor in the design of vehicles. Material behavior in a high speed deformation is different from that of the static deformation due to the variation of the material strength. Dynamic material properties in the crash of vehicles become very important to assess the crashworthiness accurately. Since most members of vehicles such as a car and a train are composed of sheet materials, it is necessary to perform the research for material testing of sheet materials at the high strain rate which takes place in the crash of vehicles. In this paper, the material tensile testing procedure of sheet materials at the intermediate strain rate has been studied to obtain the dynamic material properties for the crash analysis since that method is not yet standardized in any material handbook. The high speed tensile testing machine of servo-hydraulic type used in the research has the maximum velocity of 7 m/sec and the maximum stroke of 300 mm. A special jig fixture was designed for a load cell to reduce the load-ringing phenomenon induced by unstable stress wave propagation at the high strain rate. The dimensions of specimens that can provide the reasonable results were determined by the finite element analysis. Tensile tests of sheet materials such as steel, aluminum alloy, magnesium and plastics were carried out at the intermediate strain rate to obtain stressstrain curves in terms of the stress and the strain rate.