Influence of Loading Frequency on the Room‐Temperature Fatigue of a Carbon‐Fiber/SiC‐Matrix Composite

Abstract

The influence of cyclic loading frequency on the tensile fatigue life of a woven-carbon-fiber/SiC-matrix composite was examined at room temperature. Tension-tension fatigue experiments were conducted under load control, at sinusoidal frequencies of 1, 10, and 50 Hz. Using a stress ratio (um,,,/u,,,,) of 0.1, specimens were subjected to maximum fatigue stresses of 310 to 405 MPa. There were two key findings: (1) the fatigue life and extent of modulus decay were influenced by loading frequency and (2) the postfatigue monotonic tensile strength increased after fatigue loading. For loading frequencies of 1 and 10 Hz, the fatigue limit (defined at 1 X lo6 cycles) was approximately 335 MPa, which is over 80% of the initial monotonic strength of the composite; at 50 Hz, the fatigue limit was below 310 MPa. During 1-and 10-Hz fatigue at a maximum stress of 335 MPa, the modulus exhibited an initially rapid decrease, followed by a partial recovery; at 50 Hz, and the same stress limits, the modulus continually decayed. The residual strength of the composite increased by approximately 20% after 1 X lo6 fatigue cycles at 1 or 10 Hz under a peak stress of 335 MPa. The increase in strength is attributed in part to a decrease in the stress concentrations present near the crossover points of the 0" and 90" fiber bundles.

Multiscale Modeling of Advanced Materials for Damage Prediction and Structural Health Monitoring

“…The results from the simulation were plotted with the experimental results from Jacobsen and Brøndsted (2001), as seen in Figure 2.11. To determine if the as-produced mechanical state of the composite was accurately predicted, the initial tensile modulus was compared to experimental data from Jacobsen and Brøndsted (2001) and Shuler et al (1993). The initial tensile modulus is taken as the slope of the uniaxial tensile stress/strain curve before "yielding" or further damage occurs (i.e., first kink in the stress/strain response).…”

“…The initial tensile modulus obtained from the thermoelastic simulation was ~107.5 GPa. Experimental moduli of ~113.5 and ~100.0 GPa were obtained by Jacobsen and Brøndsted (2001) and Shuler et al (1993), respectively. A subsequent simulation was performed to determine the error that would result if the damage induced during the thermal cool-down of the plain weave CMC was ignored.…”

Effects of Temperature, Oxidation and Fiber Preforms on Fatigue Life of Carbon Fiber-Reinforced Ceramic-Matrix Composites

“…The monotonic tensile strength of 2D C/SiC composite is 420 MPa at room temperature, and the fatigue peak stresses are 0.80, 0.83, 0.86, 0.89, 0.91 and 0.96 tensile strength [16]; and the monotonic tensile strength of 2D C/SiC composite is 487 MPa at 550°C in air, and the fatigue peak stresses are 0.22, 0.36, 0.56 and 0.72 tensile strength [17].…”

Effect of laminate stacking sequence on the high frequency fatigue behavior of SCS-6 fiber-reinforced Si3N4 matrix composites

“…[7] The temperature associated with frictional sliding in CFCMCs has been documented in hotpressed Nicalon/CAS II composites and chemical vapor infiltrated C/SiC. [6,8] At a frequency of 85 Hz and R ratio ( min / max ) of 0.04 in C/SiC, a temperature rise of 50 K was observed.…”