Time-dependent failure in fiber-reinforced composites by fiber degradation
- Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Engineering Science and Mechanics
The failure of fiber-reinforced ceramic and metal matrix composites under a fixed load for extended times occurs because of strength degradation in the constituent fibers. Specifically, the ceramic fibers possess a Weibull strength distribution caused by crack-like flaws, which can grow according to a power-law growth mechanism. Failure of individual fibers causes interfacial slippage and stress redistribution to unfailed fibers, which in turn accelerates the degradation rate of the remaining fibers, and culminates in abrupt failure of the composite after sufficient damage has accumulated. This sequence of events is modeled both analytically and numerically within the Global Load Sharing (GLS) approximation previously utilized for quasi-static loading. Analytically, a general constitutive model for the relationship between the stress on the damaged fiber bundle, the strain in the unbroken fibers, and the extent of damage, is combined with a time-dependent damage evolution equation derived from the slow-crack-growth kinetics to yield an integral equation for the strain vs time at fixed applied load. A simple, accurate but approximate relationship between applied load, time to failure, fiber Weibull modulus, and slow crack growth exponent is presented. The numerical simulations of the same degradation process verify the general accuracy of the failure time obtained from the analytic results. The remaining tensile strength after some time at load but prior to failure is also studied, and the simulation results generally exhibited a more sudden-death failure than the analytical predictions. A specific application to the failure of a Nicalon fiber composite is presented.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE Assistant Secretary for Fossil Energy, Washington, DC (United States)
- OSTI ID:
- 474177
- Journal Information:
- Acta Materialia, Journal Name: Acta Materialia Journal Issue: 4 Vol. 45; ISSN 1359-6454; ISSN ACMAFD
- Country of Publication:
- United States
- Language:
- English
Similar Records
Damage-enhanced creep and creep rupture in fiber composites
Effect of loading rate on the monotonic tensile behavior of a continuous-fiber-reinforced glass-ceramic matrix composite