Applicability of empirical models for evaluation of stress ratio effect on the durability of fiber-reinforced creep rupture–susceptible composites
Fiber-reinforced polymer–matrix composites are known to exhibit loading rate- and time-dependent mechanical response. Their fatigue strength is determined by a complex interaction of damage processes governed by loading duration and cycle number. Apart from mechanistic approaches, a number of empirical models of various sophistication have been proposed to predict the durability of composites, differing in the amount of experimental data needed for their application. The accuracy of several such models is evaluated by comparing the prediction to the experimentally determined stress ratio effect on fatigue life of glass fiber-reinforced polyester–matrix composite. It is found that the accuracy of prediction generally improves with increasing the amount of test data needed for model calibration. However, the most accurate method of fatigue life estimation, among the selected ones, is by the modified Goodman diagram.
Effect of stress ratio on the fatigue of unidirectional glass fibre/epoxy composite laminae
Abstract Fatigue behaviour of unidirectional glass fibre/epoxy composite laminae under tension-tension and tension-compression loading is investigated. Stress/life experimental data were obtained for fibre orientation angles, θ, of 0, 19, 45, 71 and 90°. These tests were performed under stress ratios, R ( = σ min σ max ) , of 0.5, 0 and −1. A fatigue failure criterion is proposed based on the input strain energy. This criterion takes into account both the fibre orientation angle and the value of the stress ratio. A non-dimensional form of this criterion collapses all data points, obtained from different combinations of fibre orientation angles and stress ratios, onto a single curve.
The Multislope model : A new description for the fatigue strength of glass fibre reinforced plastic
A set of equations is proposed to describe the fatigue behaviour of E-glass laminates under loads with various means and amplitudes. The equations enable a simple method for life time predictions of laminate structures subjected to fatigue loads with continuously varying mean stress. The shape parameters describing the new model will be optimised by minimising the least square sum of the shortest distance. An extensive data set of measurements with constant amplitudes is used to demonstrate the accuracy of the model and clearly shows the fundamental difference in damage accumulation between a mean stress on tension and a mean stress on compression.