A valid and efficient mechanical performance degradation assessment method for cushion member material EPDM based on H-1 DQ NMR inspection and static compression test

The aim of this study is to establish a valid and efficient inspection method for assessing macroscopic mechanical property degradation of ethylene-propylene-diene-monomer (EPDM) by examining crosslinked density variation of microstructure. Inspection methods of mechanical behavior and crosslinked density are based on static compression and H-1 double quantum nuclear magnetic resonance (H-1 DQ NMR), respectively. After introducing the hyperelastic constitutive model proposed by Yuhai Xiang and designing different conditions of heat-aging and fatigue load, the significant mechanical parameter variation is observed for the hyperelastic constitutive model. The significant impacted factors include heat-aging time and fatigue load except for heat-aging compression strain. The phenomenon is consistent with H-1 DQ NMR test results. We further analyze relationship between macro and micro properties of EPDM. After importing fitting assumption and limitation of H-1 DQ NMR data to control fitting error, the fractions of dangling and sol chains f and residual dipolar couplings constants D-res in H-1 DQ NMR parameters show moderate negative (R-2 = 0.6227) and high positive (R-2 = 0.7312) correlation with G(c) of constitutive model parameters, respectively. Thus the validity and precision of inspection method is proven to estimate behavior variation of EPDM and hopefully the method can be extended to analyze other rubber-like materials.