DETERMINATION OF FIBER STRENGTH DISTRIBUTIONS FROM BUNDLE TESTS USINGOPTICAL LUMINESCENCE SPECTROSCOPY

The tensile strength distribution of fibres is a key constitutive prop erty of fibre reinforced composites and is often described using Weibu ll statistics. However, the standard experimental methods used for obt aining the Weibull parameters are tedious and prone to error. In this paper, Weibull parameters of polycrystalline alpha-Al2O3 fibres (Nexte l 610) are determined from piezospectroscopic measurements using photo stimulated Cr3+ luminescence (fluorescence) during fibre bundle tests. The fibre bundle stress, the stress on the surviving fibres and the s urvival probability can all be obtained by deconvolution of the lumine scence spectra. Furthermore, a qualitative method is developed to asse ss whether the fibres in a bundle are aligned by monitoring the broade ning of luminescence linewidth as a function of the applied load. The tensile strength distributions of Nextel 610 fibres are evaluated in t he as-received condition and following heat treatments at 1000, 1200 a nd 1300 degrees C in air. The strength of fibres extracted from an Al- 0.8% Mg alloy matrix composite are also characterized. The results sho w a significant strength degradation after heat treatment above 1000 d egrees C with a broadening of the fibre strength distribution. The tes t of the extracted fibres also indicates no degradation in fibre stren gth during processing of a metal matrix composite (MMC) at 780 degrees C.