Effects of low temperature on the dynamic moduli of thick composite beams with absorbed moisture

The present investigation concentrates on the influence of low temperature and moisture on the dynamic moduli of thick S2-glass composite beams. By su pporting the beam sample in a free-free configuration, its natural frequenc ies were obtained through impact testing. Frequency dependence on the hydro thermal conditions was disclosed by testing the sample at different tempera tures and with different moisture contents. Based on the frequency measurem ents, a method was developed to predict the longitudinal Young's modulus an d the transverse shear modulus of the sample. The process involves iterativ e tuning of the moduli of a Timoshenko beam model via a stable characteriza tion scheme. Numerical sensitivity study shows that the moduli thus determi ned are insensitive to measurement errors rendering the method a possible s upplement for conventional static tests. Both frequencies and moduli of the beam sample were found to exhibit an increasing trend with reducing temper ature. Besides, freezing of the absorbed moisture enlarged the longitudinal Young's modulus of the material in a significant manner. (C) 2001 Elsevier Science Ltd. All rights reserved.