Wallner lines revisited

Wallner lines, named after the scientist who explained them, constitute a unique "postmortem" tool for evaluating crack velocity in brittle materials. These lines are delicate tracks observed on fractured surfaces of brittle materials induced by the interaction of the crack front and transverse acoustic waves generated either naturally by discontinuities such as reflections at sample edges or artificially by a transducer. Here we offer a simple accurate method to analyze Wallner lines. This method is based on first principles and yields in addition to crack velocity, also the velocity in which the information about crack initiation moved up to the Wallner line origin. In addition it brings forth the points of origin of the fracture and the Wallner line.