Fracture Stress & Strain

When a sample is tested to fracture it may fail either by Brittle Fracture or by Ductile Fracture.

In brittle fracture no plastic deformation occurs before a crack propagates through the sample causing it to fail. The stress level at which this occurs is the "fracture stress" and the strain at this stress level is the fracture strain. Since failure occurs in the elastic response region, the fracture stress and strain are related by Hooke's Law: s_F = Ee_F

In ductile fracture, considerable plastic deformation before the material fractures. The fracture stress and strain correspond to that point on the plastic deformation curve at which rapid crack propagation takes place and the material separates into two parts.