1989 Volume 38 Issue 427 Pages 391-397
Since there is a considerable degree of thermal expansion mismatch between fiber and matrix in a γ-Al2O3/Al composite, this system inevitably is in a residual thermal stress state after cooling down from its fabrication or annealing temperature. In this study a programmable automated system of X-ray stress analysis with a para-focusing Ω-diffractometer was developed and applied to in-situ measurements of the matrix thermal stress during the thermal cycling process of the composites. The results obtained are as follows:
(1) X-ray diffraction technique is found to be an effective method for determining thermally induced stresses in the Al matrix of this composite system.
(2) On cooling the composite from the annealing temperature of 600K to room temperature (RT) the Al matrix showed a tensile residual stress of 30Mpa. Thereafter, on cooling the composite to liquid nitrogen temperature and heating back to RT a compressive residual stress of -27Mpa was observed in the matrix. On the subsequent reheating process from RT to 530K the matrix plastically deformed in compression.
(3) When the composite underwent a change in temperature, the Al matrix deformed in such a way as to modify thermal expansion mismatch between fiber and matrix. In the case of reheating process after cooling the composite from 530K to RT, the Al matrix showed a remarkable Bauschinger effect.
(4) During the repeated thermal cycling between RT and 530K, the Al matrix plastically deformed and a steady state of the thermal stress-temperature hysteresis loop was observed after only one cycle.
