Axial Crash Testing of Advanced High Strength Steel Tubes

Axial drop tower crash tests were carried out on a variety of 70-mm outer-diameter continuous-welded cylindrical steel tubes with several thicknesses (t). Ultimate tensile strength (UTS) ranged from less than 300 MPa for a fully stabilized steel to greater than 800 MPa for the advanced high strength steels (AHSS). In the tests, a 520-kg weight is dropped from a height of 3.3 meters to achieve impact velocities of 6.1 to 6.7 m/s (14 to 15 mph). Load and acceleration data are recorded as a function of time as the tube is crushed axially. The results show that, for a given impact condition, the peak and average crush loads of a steel tube is directly proportional to UTS × t², while axial crush distance is inversely proportional to UTS × t². As such, crash deformation can be reduced by substituting higher strength steels of the same thickness, or existing crash deformation can be maintained and weight reduction achieved by substituting higher strength steels with reduced thickness. Weld performance, collapse mode, and the implications toward automotive design are discussed.