Guidelines for performing storage modulus measurements using the TA Instruments DMA 2980 three-point bend mode II. Contact stresses and machine compliance

The effects of contact stresses and instrument compliance on the storage mo dulus, E', measurements for a rectangular sample with span-to-thickness rat io of about 17 is presented. Using finite element analysis, it has been fou nd that contact stress effects are negligible even when the applied force i s near the maximum limit. Machine compliance, however, appears to affect th e stiffness, and hence E' values, particularly at static loads less than 4 N. An analytical model describing machine compliance effects has been devel oped and can be used for correcting the stiffness measurements of the geome try studied. The model has been verified for three different rigid thermopl astics. (C) 2000 Elsevier Science Ltd. All rights reserved.