A design and processing approach to fabricate ceramic laminates with high mechanical reliability, i.e., high failure resistance, limited strength scatter, and increased damage tolerance is presented in this paper. Different ceramic layers are stacked together to develop a specific residual stress profile after sintering. By changing the composition of the laminae and the composite architecture it is possible to produce a material with predefined failure stress which can be evaluated from the fracture toughness curve correlated to the residual stresses. In addition, by tailoring the fracture toughness curve, surface defects can be forced to grow in a stable way before reaching the critical condition, thus obtaining a unique-value strength ceramic material. Laminates composed of alumina/mullite composite layers are designed and created in this work by the implementation of the proposed approach. The material obtained shows a ''constant'' strength of 456 MPa (standard deviation o7%) even when large surface damage is produced by Vickers indentation.

ABSTRACT:The toughening enhancement of Polyamide 6 blended with different types of functionalized elastomers was studied. Morphological analysis by scanning electron microscopy (SEM) were performed on undeformed samples in order to determine particle-size distribution. Yet more SEM examination of the damage zone ahead of notch tip in uniaxial tensile test provided insight into the failure mechanisms. The best impact strength was achieved with the PA6/EPDM-g-MA (terpolymer ethylene-propylene-diene monomer grafted with Maleic Anhydride) blend, unlike ULDPE-g-MA (ultra-low-density polyethylene grafted with maleic anhydride), which possesses the poorest toughening efficiency even though opposite results would be expected from particle-size evaluation. The higher cavitation resistance of EPDM compared to UL-DPE observed during low strain rate tensile test plays a crucial role in understanding the best performances of its blends.

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