Crack Deflection in Ceramic Laminates Using Porous Interlayers

Mechanical properties and mechanical behaviour of SiC dense-porous laminates

“…Though these ligaments of matter are made of the same material as the dense layers, and might be expected to have the same fracture energy, theoretical analyses show that if the tip of a growing crack comes sufficiently close to a microcrack 11 or a pore, 12 the stress intensity factor at the tip of the crack is increased and then, the apparent fracture energy of the ligament is reduced. This reduction varies with the relative density, and for a cubic array of spherical pores, Blanks et al 7 derived a minimum level of porosity equal to 37% to ensure crack deflection, in good agreement with their experimental results for silicon carbide. Assuming that the fracture energy of the dense ligament is related to that of the porous layer, G P , by the relation:…”

“…The data were fitted by a (1 − P) m form, since Blanks et al 7 have obtained for SiC a good description of Young's modulus with E P = E 0 (1 − P) 2 . Such an equation was also established by Wagh et al 19 for a model derived from an previous analytical one developed by Wong et al 20 in efforts to explain charge and mass transport through the random pore structure of rocks.…”

“…The aim of the work presented in this paper was to determine the porosity dependence of the mechanical properties of a SiC material densified by liquid phase sintering on a wide range of porosity, and to compare the mechanical behaviour of dense-porous laminates to that obtained by Blanks et al 7 for silicon carbide densified by solid state sintering.…”

Effective fracture toughness in Al2O3–Al2O3/ZrO2 laminates

“…1,2 Laminates can improve mechanical performance since surface compression introduces a closure stress that protects against flaws. Two strategies of laminate design have been previously presented: first, laminates with a weak interface that deflects cracks, thus preventing catastrophic failure 3,4 and second, laminates with strong interfaces. Since strong interfaces will transmit residual stresses during cooling from sintering temperature, one can benefit of a phase transformation 4 or a thermal mismatch 5 to induce compressive stresses at the surface.…”

Edge cracking due to a compressive residual stress in ceramic laminates

“…This can be achieved by using weak interfaces including layers of pyrocarbon, for instance [2][3][4]. Another approach consists in adding thin interphases of a porous ceramic between the dense layers [5][6][7]. More recently, the idea was to create strong compressive residual stresses in some intermediate layers in order to trap the growing cracks in the compressive layers [8][9][10][11].…”