Low velocity surface fracture patterns and energies in poly(methyl methacrylate)

Steady‐state fracture techniques were used to investigate the surface fracture patterns and surface fracture energies of poly(methyl methacrylate) at low velocities (10 cm/sec to 10 −5 cm/sec). Several anomalies were discovered: (1) Small surface cracks, running parallel to the crack front, which were initiated by imperfections; (2) a “zero velocity” transition from the normal surface fracture patterns to a “laminar” pattern; and (3) a subsequent transition from the laminar pattern to a “turbulent” pattern. The velocities at which these anomalous fracture patterns occurred were of the order of 10 −4 to 10 −6 cm/sec. The corresponding surface fracture energies were as low as 10 5 erg/cm 2 .