The strength and toughness of whisker- and fiber-reinforced composites are controlled to a large extent by the nature of the bonding between the fibers/whiskers and the matrix. An important problem in the development of metal matrix and ceramic-ceramic matrix composites is the simultaneous measurement of whisker and matrix residual stress. In certain systems, chemical bonding should be nonexistent and frictional forces at the interfaces provide the necessary link between the fiber and the matrix. In metal matrix composites, stresses in the fibers can lead to thermal-cyclic fatigue damage. Strain measurements have been acquired nondestructively for alumina/silicon carbide and titanium/silicon carbide composites by means of neutron diffraction techniques at the Argonne National Laboratory Intense Pulsed Neutron Source. Analysis of the experimental results shows that the in situ measurement of stress in the laboratory by neutron diffraction techniques is practical. The accumulated strain data could be used to calculate residual stresses in the fibers and the matrix (including stresses at the interface) simultaneously, or to determine stresses resulting from external loading.

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