Alumina agglomerate effects on toughness-curve behavior of alumina-mullitecomposites

Toughness-curve (T-curve) behavior of composites of spherical, polgcrystall ine, coarse-grained, alumina agglomerates dispersed throughout a constant-t oughness, fine-grained, 50-50 vol% alumina-mullite matrix has been evaluate d as a function of agglomerate content for the range 15 to 45 vol%. T-curve behavior was evaluated using the indentation-strength method, Increasing a lumina agglomerate content resulted in a progressive increase of large inde ntation load strengths with negligible change of plateau strength levels at small indentation loads, This behavior is consistent with underlying T-cur ves that rise to greater values and are shifted toward longer crack lengths with increasing agglomerate content, suggesting that both bridge spacing a nd bridge potency increase with increasing agglomerate content over the ran ge tested. The proposed relationships between bridge spacing and agglomerat e content, and bridge potency and agglomerate content, are rationalized in terms of residual stress considerations. The indentation-strength data also demonstrated that the composite containing the greatest alumina agglomerat e content, 45 vol%, exhibited the greatest flaw tolerance.