INTERNAL-STRESSES IN PLANAR RANDOM FIBER ALUMINUM COMPOSITES .2. TENSILE TESTS AND CYCLIC BAUSCHINGER EXPERIMENTS AT ROOM-TEMPERATURE AND 77 K

Internal stresses in planar random alumina fibre reinforced aluminium with a range of fibre volume fractions have been studied theoretically and in tensile tests and cyclic Bauschinger experiments at room tempe rature and 77 K. The Eshelby S tensor for a planar random array of fib res is calculated, which allows the mean field model to be used to pre dict the internal stresses. The conventional Orowan-Wilson method of a nalysing cyclic Bauschinger experiments is modified, enabling the plas tically and thermally induced matrix mean stresses to be separated. Th is analysis is applied to experimental results and the plastic mean st ress and the initial magnitude of the thermal mean stress in the matri x are measured. The results for the thermal matrix mean stress are com pared with measurements from monotonic flow curves and generally good agreement is observed. The measured thermal matrix mean stress in thes e composites is approximately independent of fibre volume fraction.