Axial Crush of Strengthening Structural Members with Various Hat-Shaped Cross-Sections. 1st Report, Impact Test by a Drop Hammer.

Abstract

Impact and quasi-static tests for the axial compression of the strengthening automobile members with various types of hat-shaped cross-sections are carried out. Strengthening members play a role as an energy absorber in a car body at collision. A drop hammer type testing apparatus is used for the impact test, in which the impact velocity is set to be 10 in/s. The tested cross-sectional shapes are three types of rectangle whose height is 40, 30 or 20 mm with width of 40 mm, and a concave shape having many bent edge-corners. Test materials are a mild steel, SPCC, and 3 kinds of high tensile strength steel sheets, whose thickness is 1 mm. In the impact tests, progressive deformation patterns are recorded by a high-speed video camera. In both of the impact and quasi-static tests, an accordion type cyclic buckling mode is observed, in which the structure sufficiently absorbs the crush energy. Crush strength in the impact test is higher than that in the quasi-static test and it increases with decrease of the hat height. Increase of the number of bent edge-corners in the cross-section leads a higher crush strength. With respect to the rectangular cross-section, the crush strength is found to be roughly proportional to the material tensile strength (and its yield stress). The proportionality slope for the impact test is smaller than that for the quasi-static one.