| In this research, Moiré interferometry techniques were developed for the study of strain distributions in low modulus elastomeric materials at temperatures where they exhibit significant visco-elastic behavior. Then the techniques were employed to study the strain distributions within and across the interfaces of multi-layer, polymer samples, which were fabricated as models for functionally modulus-graded materials, under three-point bending and compression loading.; The low modulus, thermoplastic elastomers used in this study were Tecoflex ® phase segregated thermoplastic poly (ether-urethanes). Attenuated total reflectance infrared spectrometry (ATR/IR), differential scanning calorimetry (DSC), thermal mechanical analysis (TMA), dynamical mechanical thermal analysis (DMTA) and tensile testing were used to characterize the morphology and viscoelastic mechanical properties. Among the three grades of Tecoflex used in this research, the EG60D had the highest hard microdomain content, and exhibited the properties associated with an interconnected hard microdomain morphology. The SG85A grade had the lowest hard microdomain content and exhibited properties characteristic of a discrete hard microdomain morphology. The degree of interconnected hard microdomain morphology in SG93A was between that of the EG60D and SG85A grades.; Sample preparation and grating replication steps for this Moiré interferometry study were devised that avoided the deformation of specimens and minimized the residual stresses in the sample.; In three-point bending analysis, the presented results clearly demonstrated that Moiré interferometry could be successfully applied in the field of low modulus elastomeric materials. The analysis of the Moiré patterns suggested that the soft elastomeric material under the contact point was subjected to a compressive strain, &egr;x, and pushed sideways. The analysis also showed that the maximum shear strain occurred where the deformation was constrained, which could possibly lead to a local fatigue failure in the sample.; In compression, of the three control samples (EG60D/EG60D/EG60D, SG93A/SG93A/SG93A, SG85A/SG85A/SG85A), EG60D exhibited the most time dependent deformation, and SG85A exhibited the least time dependent deformation, which was consistent with the TMA and DMTA analysis. For the two graded samples (EG60D/SG85A/EG60D, EG60D/SG93A/SG85A), loaded from the hard EG60D side, two types of interfaces, those formed from miscible and immiscible pairs, were observed. The analysis of the Moiré fringe patterns suggested the presence of a large normal strain, &egr;y, concentration at the polymer interfaces formed from immiscible pairs. This large normal strain was not observed at the interface formed from miscible pairs. These results suggested that in multi-layer materials, when polymer inter-diffusion occurs, the magnitude of the normal strain concentration at an interface will be significantly reduced regardless of the bulk material modulus difference between the layers. For the graded samples (SG85A/EG60D/SG85A, SG85A/SG93A/EG60D), loaded from the soft SG85A layer, most of the strain was concentrated in the SG85A layers and was not transferred significantly to the relatively hard, SG93A and EG60D layers. |
