Temperature and loading frequency effects on fatigue crack growth in HDPE pipe material

High-density polyethylene (HDPE) pipes are being extensively used for gas, water, sewage, and waste water distribution systems. Laboratory tests appear to show that HDPE is more able to suppress rapid crack propagation, whilst remaining somehow resistant to slow crack growth failures observed in service. Procedures for estimating pipe life in service have been established by making use of the fatigue crack growth (FCG) results. These procedures are concerned mainly with room temperature applications with some safety factor to include the temperature effect. Use of HDPE pipes in water and gas distribution in the Gulf area has seen a net increase. This study addresses the combined effects of temperature and frequency on FCG properties of commercial HDPE pipe material. FCG accelerated tests were conducted on single-edge notch (SEN) specimens in the temperature range of-10 to 70°C at frequencies ranging from 0.1 to 50 Hz. The FCG tests are conducted at a stress amplitude level approximately 1/4 of room temperature yield stress and crack growth behavior was investigated using linear elastic fracture mechanics concepts. The stress intensity range ΔK, gave satisfactory correlation of crack growth rate (da/dN) at the temperatures of-10, 0, 23, and 40°C and at frequencies of 0.1, 1, and 50 Hz. The crack growth resistance was found to decrease with increase in test temperature and decrease with frequency. For 70°C no crack propagation was observed, the failure was observed to occur by collapse or generalized yielding. Fractographic analyses results are used to explain temperature and frequency effects on FCG. The effect of temperature on da/dN for HDPE material was investigated by considering the variation of mechanical properties with temperature. Master curves were developed by normalizing ΔK by yield stress.