Prediction of internal stresses in a circular bilayered laminate glass-resin

A previous paper has shown how it is possible to determine the stress induced in a bilayered circular laminate glass‐resin under various conditions with a nondestructive method. In this paper a more precise mathematical analysis which allows prediction of the stress with time is given. In order to determine numerical values from the theoretical calculations, the relaxation function of the resin, g(t, T), and the shift factor, aT, of the time‐temperature superposition principle have to be known. The relaxation function measured with the experimental setup, under biaxial stress conditions appears to be identical with the one determined by another laboratory under uniaxial compression stress. A systematic exploration of the influence of the different parameters, g(t, T), aT and the thermal expansion coefficient, α(T), shows that the most difficult parameter to determine with sufficient precision is aT. Working under different cooling conditions the experimental results have been compared with the theoretical predictions. The agreement is generally good and even very good for the fast cooling cycle for the final stress if one takes into account the thermomechanical properties of the resin during and after its curing.