Abstract
Taking account of a combined singular stress state near a crack tip, we present a new hypothesis for determining fracture toughness criterion of rock-like materials under mixed mode I and mode II loading. The combined stress hypothesis gives a reasonable KIIc/KIc which is in good agreement with published data on rock-like materials. Finally, the mixed mode fracture criterion derived by the hypothesis is tested by the measurement of KI and KII of flyash cement paste using the cracked disk specimens. The results are presented to confirm the use of this hypothesis for the problem of mixed mode fracture toughness including negative KIc.
