Joerg Fischer, Patrick R. Bradler, Reinhold W. Lang, Gernot M. Wallner
Papers # 2016 Berlin
The present paper aims to study the crack growth resistance of a black-pigmented polypropylene pipe grade when exposed to elevated temperatures and various environmental media (air, deionized water, ionized water with a specific chloride content, and chlorinated water) under the simultaneous application of cyclic loads. At the temperature of 95 °C the fatigue crack growth rates are enhanced in air compared to the various liquid media. Moreover, the combination of the highest temperature with the environmental medium air represents the worst case in terms of fatigue crack growth resistance of PP, at least for slow crack growth rates.
To characterize the fatigue crack growth (FCG) behavior of a black-pigmented pipe grade polypropylene (PP) for solar-thermal applications under service near conditions, a method for superimposed mechanical-environmental loading of cracked round bar (CRB) specimens was implemented. Fatigue crack growth experiments were carried out at two different temperatures (95 °C and 80 °C) and in four environmental media (air, deionized water, ionized water with a specific chloride content, and chlorinated water). To perform the superimposed mechanical-environmental experiments, specific test devices and test arrangements for CRB specimens were implemented on an electro-dynamic test machine.
While the FCG resistance in general decreased with increasing temperature, a more complex dependence was found regarding the influence of the environmental media. At 95 °C, crack growth rates in air were found to be higher than in chlorinated water, at least in the slow crack growth rate regime. Conversely, at 80 °C and over the entire crack growth range investigated, crack growth rates in chlorinated water turned out to be higher than in air.