Mechanical behaviour of fiber-reinforced ceramic matrix composites

A detailed investigation of the matrix crack distribution and frictional heating phenomena in fiber-reinforced ceramic composites was undertaken. The distribution of matrix cracks in a uniaxial ceramic composite was examined to determine how the matrix strength distribution influences the distribution in matrix cracks.;The analysis shows that matrix strength statistics have a significant effect on the distribution of matrix cracks in a uniaxial composite loaded in tension and that a large variance is to be expected in the crack spacing distribution even when the matrix strength is relatively homogeneous. In the limiting case of a completely homogeneous material, the crack spacing distribution tends to an inverse square distribution between l;Frictional heating in a unidirectionally fiber-reinforced ceramic composite is strongly dependent upon loading frequency and mean crack spacing. A mechanism of internal heating which involves the frictional slip of fibers within debonded slip-zones was proposed. Internal heating begins at a peak fatigue stress which was approximately 50% below the monotonic proportional limit strength of the composite. For a constant loading frequency and matrix crack spacing, the maximum temperature rise exhibits an approximately linear dependence on stress range or strain range. The dynamic interfacial shear stress remained approximately constant for cyclic loading frequencies from 5 to 25 Hz. During long duration cyclic loading at a frequency of 25 Hz and peak stress of 180 MPa, the dynamic interfacial showed an initially rapid decrease, followed by a partial recovery.;A potential advantage of the frictional heating technique for determining interfacial shear stress is that an average value of frictional shear stress is obtained, rather than a value based upon discrete measurements made on individual fiber/matrix interfaces. The technique can also be readily extended to allow determining the temperature dependence of interfacial shear stress. (Abstract shortened with permission of author.)...