Statistical Analysis of Strength and Life of Composite Materials.

Static strength and fatigue life of unidirectional graphite/epoxy composites are studied in terms of statistical models of fatigue degradation and residual strength. A two-segment Weibull distribution for fatigue life, and a cumulative damage rule for fatigue are introduced. Experimental tests performed support the assumption that a specimen's rank in strength is equal to its rank in fatigue life. Fatigue weakens the matrix, and thus degrades the residual compression strength, and not the residual tension strength in early life. In some cases, residual tension strength initially increases. Proof tests can guarantee a minimum strength, and to a lesser extent, a minimum fatigue life. (Author)