| The strength and life behavior of a unidirectional graphite/epoxy laminate (AS3501-05) have been investigated experimentally in this thesis. Static strength tests, fatigue-life tests, proof-load tests, residual strength tests (tension and compression), and cumulative damage tests were conducted, each with a large number of specimens in order to make statistical conclusions. The test data were analyzed by means of the Weibull distribution with the maximum likelihood method for parameter estimation.; Results from these studies show that the proof-load procedure can be used to screen out weaker specimens and guarantee a minimum static strength; similarly, this procedure can also assure a minimum fatigue life. These results also verify the concept of equal rank between static strength and fatigue life. This latter concept is the basis for most existing fatigue degradation analyses that are statistical in nature.; The residual strength results show the effects of tensile fatigue on both the tensile residual strength and the compressive residual strength of the unidirectional composite. In general, tensile residual strength behaves in a manner of the so-called "sudden-death", while the compressive residual strength degrades continuously with increasing fatigue life.; Specimens subjected to more than one level of fatigue load (cumulative damage) were analyzed by the percent-life rule (Miner's rule) and the percent-failure rule. Differences between these two rules were discussed as they apply to the present test results. It was shown that the percent-failure rule prediction agrees well with the experimental results.; ; *All degree requirements completed in 1980, but degree will be granted in 1981. |
