Guidelines for performing storage modulus measurements using the TA Instruments DMA 2980 three-point bend mode I. Amplitude effects

An experimental study of the effects of oscillation amplitude on the elasti c storage modulus, EI, for a rigid thermoplastic measured using three point -bending is presented. The results are part of a wider investigation on the operating conditions needed to improve repeatability and reproducibility o f E' measurements for the recently commercialized TA Instruments 2980 Dynam ic Mechanical Analyzer. It has been found that sample alignment is required to achieve reliable E' values. Based on experiments performed on polycarbo nate at 1 Hz using a span-to-thickness ratio of 11, 17 and 33, respectively , the optimum amplitude for obtaining the lowest standard deviation under a mbient conditions is found to be about 100 mu m. It is also found that a sp an-to-thickness ratio of < 17 is very sensitive to: changes in amplitude. ( C) 1999 Elsevier Science Ltd. All rights reserved.