R. Lakshminarayanan et al., TOUGHENING OF LAYERED CERAMIC COMPOSITES WITH RESIDUAL SURFACE COMPRESSION, Journal of the American Ceramic Society, 79(1), 1996, pp. 79-87
Effects of macroscopic residual stresses on fracture toughness of mult
ilayered ceramic laminates mere studied analytically and experimentall
y, Stress intensities for edge cracks in three-layer, single-edge-notc
h-bend (SENB) specimens with stepwise varying residual stresses in the
absence of the crack and superimposed bending were calculated as a fu
nction of the crack length by the method of weight function. The selec
ted weight function and the method of calculation were validated by ca
lculating stress intensities for edge cracks in SENB specimens without
the residual stresses and obtaining agreement with the stress-intensi
ty equation recommended in ASTM Standard E-399. The stress-intensity c
alculations for the three-layer laminates with the macroscopic residua
l stresses mere used to define an apparent fracture toughness, The the
oretical predictions of the apparent fracture toughness were verified
by experiments on three-layer SENB specimens of polycrystalline alumin
a with 15 vol% of unstabilized zirconia dispersed in the outer layers
and 15 vol% of fully stabilized zirconia dispersed in the inner layer,
A residual compression of similar to 400 MPa developed in the outer l
ayers by the constrained transformation of the unstabilized zirconia f
rom the tetragonal to the monoclinic phase enhanced the apparent fract
ure toughness to values of 30 MPa . m(1/2) in a system where the intri
nsic fracture toughness was only 5 to 7 MPa . m(1/2).