On crack branching angles in glasses and ceramics

Cracks branch when they run unstably at high velocities and there is sufficient energy to create new fracture surfaces. Observations of crack branching angles are useful in component fractographic analysis since they can be used to estimate the stress state in a part when it breaks. Uniaxial loading causes branch angles of 30-45 degrees, although scatter can be large. Biaxial tensile loading causes larger branching angles. The first quantitative trend of crack branching angle with stress state was shown by Frank Preston in a brief paper in 1935. Over the decades many researchers have obtained smaller branching angles than those shown by Preston. A review of the literature and some new data in this work show that Preston's 1935 trend must be corrected. A new version is presented.