Mechanical Ageing Protocol Selection Affects Macroscopic Performance and Molecular Level Properties of Ethylene Vinyl Acetate (EVA) Running Shoe Midsole Foam

Existing attempts to evaluate footwear via cyclic compression fail to sufficiently represent biofidelic force-time curves or provide the underlying mechanism of EVA foam fatigue. A uniaxial biofidelic waveform was compared to a sine wave of the same frequency to examine differences in (1) net displacement, (2) absorbed energy, and (3) peak force from ASTM F1614. A non-destructive molecular-level technique (ATR-FTIR) recorded differences in hydroxyl, ester, and unsaturated moieties due to EVA degradation. It was concluded that (1) biofidelic waveforms may better simulate human running, (2) material degradation is discernible, and (3) inferences regarding polymeric degradation and macroscopic performance require further investigation.