A novel mechanism for debonding at a weak interphase in an all-oxide composite is introduced. This methodology involves the use of alumina platelets that have a diameter of 10-15 or 5-10 mum and a thickness of 1 mum, The platelets induce constrained sintering of the ceramic powder, which results in permanent porosity. For room-temperature properties, only minor additions (0-3 vol%) of matrix powder yield sufficiently weak debonding interphases, The platelets lie in random, three-dimensional orientations and provide a debonding mechanism that is independent of temperature, in chemically compatible matrixes. Laminated composites with two types of matrixes-mullite and alumina-have been fabricated with modified fibrous monoliths of alumina in a triple-layer "core/interphase/matrix" arrangement. In the laminated systems, the intimate mixing of strong versus tough microstructures has been tailored by alternating various matrix:interphase thickness ratios. Preliminary load-displacement curves clearly demonstrate characteristics of "graceful failure" and notable improvements in the work of fracture. Scanning electron microscopic observation of the crack paths confirms the viability of platelets for producing permanently porous, debondable interphases at elevated temperatures in air.