A glass sample with length L and square cross-section, h b, mounted onto a wall at its top edge. The sample contains an inner (or internal) through-thickness crack at the center, as depicted in the figure below. A constant load P = 20 kN is applied uniformly across the bottom facet. Determine the critical crack length for which brittle fracture occurs, and determine whether the brittle fracture occurs. 2 70 ; 0.5 S J E GPa m L h b = 1 m 160 mm 100 mm