An indentation fracture mechanics analysis is developed to characterise the toughening effects of a compressive surface layer in brittle materials. The analysis is used to describe the enhanced toughness of cordierite glass-ceramic laminate composites, in which thermal-expansion mismatch effects induced uniform stress in the exterior layers of the symmetric exterior:interior: exterior structures. Interpretation of indentation crack length viewed as experiencing discrete regions of decreasing stabilisation on propagation from small cracks & complete containment within the compressive layer to large cracks & partial extension into the compensating tensile interior. The observations are described using a stress-intensity factor for circular cracks in linear stress fields that includes different base/surface values for extended cracks.
