Fatigue crack growth analysis of polymonochlorotrifluoroethylene (CTFE)

Fatigue crack growth behavior of a polymonochlorotrifluoroethylene (CTFE) w as investigated. Tension-tension fatigue propagation tests on geometrically identical specimens were performed at different frequencies. Specimens wit h different notch to width ratios (a/w) were also tested. The applied stres s level in all tests was kept the same. The maximum stress was 16.0 MPa and the ratio of minimum stress to maximum stress was kept at 25%. Fatigue tes t data such as the number of loading cycles, the crack length, and the hyst eresis loops were recorded. The Modified Crack Layer (MCL) theory was emplo yed to analyze the FCP behavior of this CTFE material. Also the results wer e analyzed using the Paris equation for comparison. It has been found that the fatigue crack growth behavior of this material cannot be described by t he Paris power law due to the three distinct stages of the FCP kinetics. Th e MCL model was successfully used for extracting material parameters; gamma ', the specific energy of damage, and beta', the coefficient of energy diss ipation. The specific energy of damage for this CTFE was 855 kJ/m(3) and th e value of the coefficient of energy dissipation was 6.2 x 10(-6). It was f ound that the values of gamma' and beta' are independent of a/w and the fre quency (f), though the FCP kinetics and lifetime were dependent on a/w and f. The variation in gamma' and beta' when a/w changed from 0.04 to 0.1 were only +/-0.9% and +/-6.8%, respectively. For different frequencies (from 0. 5 Hz to 5 Hz), the variation of these two parameters were +/-0.6% and +/-1. 4%, respectively. In situ and post failure analysis of the fatigue fracture d samples revealed a clear damage zone adjacent to the main crack. The larg er the volume of the damage zone, the longer the fatigue lifetime. It was a lso found that a higher micro-crack density associated with a larger damage zone. A larger damage zone with higher micro-crack density consumes more e nergy and thus reduces the portion of energy required to fuel the main crac k growth.