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 modulus, E′, measurements for a rectangular sample with span-to-thickness ratio of about 17 is presented. Using finite element analysis, it has been found that contact stress effects are negligible even when the applied force is near the maximum limit. Machine compliance, however, appears to affect the stiffness, and hence E′ values, particularly at static loads less than 4 N. An analytical model describing machine compliance effects has been developed and can be used for correcting the stiffness measurements of the geometry studied. The model has been verified for three different rigid thermoplastics.