Time–temperature dependent brittle fracture of viscoelastic solids

The Griffith formulation is used to study fracture behavior of poly(methyl methacrylate) (PMMA) as a function of strain rate and temperature over the range 4.4 × 10 −5 ≤ ε ≤ 4.4 × 10 −2 in./in./sec and 25°C ≤ T ≤ T g , T g being the glass transition temperature. It is found that the transition from brittle to ductile failure occurs abruptly at a temperature T f which is dependent on strain rate and is approximately the same as the glass transition temperature of the material. The Griffith brittle fracture criterion is found to apply below T f for all strain rates. The brittle fracture behavior is shown to obey the time–temperature equivalence principle in the same way as the material's other viscoelastic properties, having the same shift function.