Deformation analysis in impact testing of functionally graded foams by the image processing of high-speed camera recordings

We developed an image processing algorithm and applied it on high-speed camera recordings to characterize the deformation response of three-layered density-graded foam structures subjected to drop weight testing. Different densities (30, 40, 50 and 70 kg/m3) of weakly cross-linked polyethylene foam sheets were laminated together to achieve varying density distributions along the thickness, and the effect of layer order on the shock absorption capability was evaluated. Foam structures with a higher density top layer and a negative density gradient showed enhanced energy absorption in the initial stage of deformation, which resulted in lower maximum reaction forces. The positive effect of layer order modification was more dominant at higher impact energies. We provided a detailed explanation of the tendencies by investigating the differences in deformation propagation and the changes in the diameter of the deformation zone. The presented method can be utilized to design sports and packaging foam products.