Probabilistic models of the stress-rupture of composite materials: summary. Final report, June 15, 1976-June 14, 1984
Time-dependent failure in the long term (stress- or creep-rupture) results from flaw growth in the fibers, and/or viscoelastic creep in the matrix. Progress has been made in modeling the failure process described. A matrix-impregnated bundle is viewed as a chain of short microbundles with localized load-sharing among fiber elements in a cross-section. The model for fiber failure has its roots in the thermal kinetics of molecular slippage and scission. Various localized load-sharing rules for fiber elements in a microbundle have been assumed. Early research focused on static small bundles. Subsequently, three powerful asymptotic methods were developed. Progress was made in modeling statistical failure in 3-D composites with fibers arranged in a hexagonal array, developing asymptotic analyses for the time-dependent problem where the load-sharing among fibers is elastic but the fiber strength decays stochastically in time and experimental verification of the model. Progress was also made in developing a powerful recursion analysis for k-failure in the time-dependent problem. In order to use the results in creep-rupture settings, we first modified the fiber model to allow for random initial fiber breaks and finite molecular length in our crystal model for fiber failure. A Markov analysis was developed for small bundles. Key limit theorems for k-failure were developed thus verifying the existence of the characteristic distribution for composite lifetime. Randomly spaced initial fiber breaks weaken the composite and increase its variability in lifetime. We also demonstrated how a Weibull shape parameter value of less than one can occur for fiber lifetime. Effect of gauge length on the strength distribution of filaments was examined, using Weibull statistics. Values for the shape parameter calculated at a fixed gauge length are lower than those obtained by a procedure based on varying the gauge length.
- Research Organization:
- Cornell Univ., Ithaca, NY (USA). Sibley School of Mechanical and Aerospace Engineering
- DOE Contract Number:
- AC02-76ER04027
- OSTI ID:
- 6755139
- Report Number(s):
- DOE/ER/04027-1; ON: DE84013477
- Resource Relation:
- Other Information: Portions are illegible in microfiche products
- Country of Publication:
- United States
- Language:
- English
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