Evaluation of biaxial bending strength in damaged soda-lime glass

In applications of brittle materials such as soda-lime glass and ceramics, they are usually subjected to a multi-axial stress state. Brittle materials with cracks or damage caused by foreign impacts are apt to fracture abruptly from cracks because of their low fracture toughness. Depending upon the crack pattern developed, the strength using a multi-axial stress state might be different from the one using a uniaxial stress. As a result, when a small size crack was introduced by Vicker's indentation, the residual strength using a biaxial stress state obtained by the ball-on-ring test was greater than that using a uniaxial stress by the 4-point bending test. In the case of the specimens cracked by a spherical impact, there was overall decrease in the bending strength with increasing an impact velocity.