Fatigue crack propagation in unplasticized poly(vinyl chloride): 1. Effect of mean stress

The effect of mean stress on fatigue crack growth in an unplasticized poly(vinyl chloride) (uPVC) pipe material was investigated using single-edge-notched (SEN) specimens and the results analysed in terms of fracture mechanics. Three series of experiments were conducted. In the first the fatigue crack growth rates da dN were collected as a function of the applied stress intensity factor range ΔK(= K_max - K_min) by keeping the stress ratio R(= K_min K_max) constant. In the second series of experiments da dN were obtained as a function of ΔK when the mean stress intensity factor K_m was constant; and in the third series ΔK was maintained constant, da dN were obtained with increasing K_m. All experimental results were obtained and processed using computerized data acquisition systems. When the data were analysed in terms of the conventional log da dN versus log ΔK and log K_m plots the effects of R and K_m on fatigue crack growth rate were insignificant. However, there was a strong dependence of da dN on R when analysed in terms of Williams' line zone model for fatigue crack growth.