Brittle materials have , such that the material has a maximum fracture strain of 0.05. Fracture strain is the strain at which a material ultimately fails or breaks.
Instead of in the ductile case, we use and , which are the ultimate tensile and compressive strengths.
Applicable failure theories to determine fracture criteria:
- Maximum Normal Stress Theory
- Generally not used
- Only works well in first and third quadrant
- Issues when applying to second and fourth
- Modified Mohr Theory
- Works well overall
- Does best job in fourth quadrant, particularly when compared to MNS
- Brittle Coulomb-Mohr Theory
- More conservative
