The novel mechanical and recovery behaviors of 3D printed EVA under cyclic tensile loading

In this study for the first time, the cyclic mechanical properties and shape recovery behavior of 3D printed EVA were investigated. EVA with high elastic capability was successfully printed by direct material extrusion method and then a novel cyclic shape recovery test was conducted in which the tensile test was performed at three different strain levels (250, 500 and 1000%) in six cycles and after the end of each cycle by heating the samples, their recovery was measured. The results showed that in all strain levels and tensile cycles, the full recovery is observed, which is completed in two steps after unloading and after heating the sample. Upon exposure to hot water, the disruption of intermolecular forces facilitated the recovery of the material's original shape through increased molecular mobility and rearrangement of polymer chains. However, it was observed that with increasing strain levels (from 250% to 1000%), the recovery process became less effective, leading to a decline in mechanical properties. Also, by increasing the number of tensile cycles, the tensile stress value at the desired strain level and the rate of change decreases and after the second cycle, the cyclic behavior under tensile loading almost reaches a constant trend.