Abstract: Brittle thin plate with a straight-through crack under biaxial and uniaxial tension in-plane was investigated by thermomechanical method. The
critical stress intensity factor under those two loading modes was measured with disk-shaped specimens of glass and ceramics. The results show that the
crack resistance of brittle materials increases with increasing stress parallel to the crack plane. The effects of biaxial stress reveal that the conventional
criterion with the stress intensity factor is imperfect for biaxial stress issues. It is demonstrated that the crack opening and growth is governed by
the strain at the crack tip.

Key words: brittle materials, biaxial stress, stress intensity factor, thermomechanical method