In order to reduce high impact load occurring in axial collapse of a crush can, which is installed in the front part of car, the elastoplastic nonlinear behavior of short thin-walled frusta with square cross-section subjected to statically axial compression is studied by using finite element method. The square tubes 1.8mm in thickness, with upper cross-section of 85mm x 90mm and lower cross-section of 130mm x 135 mm, have different lengths ranging from 135mm to 225mm. A typical tensile stress-strain curve for aluminum is modeled as 2 straight-line hardening relationship.

The FEM code MSC.Marc is used to simulate the axial compression of thin-walled frusta of square cross-section. The load-displacement curves of frusta are obtained from the numerical analyses. It is found from the curves that in the axial collapse process of the frusta there are two peaks of the load, corresponding to the initial buckling and formation of the second wrinkle. Unlike the axial collapse of long tubes, however, the load due to the second wrinkle is higher in magnitude than the initial buckling load. The reason for high second peak load is that the frusta are too short to form the 2nd wrinkle.

The second peak load is very sensitive to the boundary condition on the lower end. Usually, high load occurs in a strong restraint.

Also, it is found the effects of holes in side plate of frusta on the second peak load are very complex. If the holes were located exactly right on the folding lobes, the second peak load could be reduced. The other methods to reduce the second peak load were also investigated. It seems that the most effective method for lowering load is shortening the wavelength of wrinkles.