Temperature effect on fatigue crack propagation in short-carbon-fiber reinforced PPS

The effect of test temperature on the fatigue crack propagation behavior was studied with center-notched specimens of PPS (polyphenylene sulfide) reinforced with 30 wt% short carbon fibers. Specimens were cut from injection-molded plates with 1 mm thickness at three angles of the loading axis relative to the molding flow direction, i.e. θ = 0° (MD), 45°, 90° (TD). Crack propagation tests were conducted under the stress ratio of 0.1 at four temperatures below and above the glass transition temperature Tg = 363 K：room temperature (RT = 298 K), 343 K, 373 K and 403 K. The macroscopic crack path was nearly perpendicular to the loading axis for MD and TD at all temperatures. The crack growth direction of 45° plates was inclined against the loading axis, and the inclined angle was decreased with increasing temperature. In the relation between the crack propagation rate, da/dN, and the stress intensity factor range, ΔK, da/dN was slowest for MD, and increased with increasing fiber angle at all temperatures. The crack propagation rate of each fiber angle was nearly the same at RT and 345K, and increased greatly at temperatures of 373 K and 403K above Tg. When da/dN was correlated to the J-integral range, ΔJ, the relations for different fiber angles came closer at each temperature, and also for each fiber angle the influence of test temperature on da/dN was decreased. The inelastic deformation of the matrix was mainly responsible for the acceleration of crack propagation seen in da/dN vs ΔK relation at high temperatures.