The intention of a single point fracture toughness test is to measure a material's tolerance to the presence of a flaw in terms of a single parameter such as KIc, critical J or critical CTOD (see FAQ: What is a fracture toughness test?). Unlike tearing resistance fracture mechanics tests, which measure the material's toughness as a function of crack extension (see FAQ: What is a tearing resistance curve?), single-point fracture mechanics tests are generally only interested in measuring one value of fracture toughness, for example at the initiation of brittle crack extension, or at the maximum load plateau.
Examples of single-point measurements of fracture are:
- KIc, the plane strain fracture toughness, a measure of the resistance of a material to crack extension when the crack tip stress state is predominantly plane strain.
- δc or Jc, the critical values of CTOD and J associated with brittle extension of a crack, under conditions where minimal ductile crack extension occurs ( Δa<0.2mm)
- δu or Ju, the critical values of CTOD and J associated with brittle extension of a crack, under conditions where ductile crack extension ( Δa ≥0.2mm) precedes brittle extension.
- δm or Jm, the values of CTOD and J at the first attainment of a maximum load plateau
- J0.2BL/ δ0.2BL, the values of J or CTOD corresponding to attainment of 0.2mm of stable ductile tearing, often used as a single-point measurement of toughness for ductile materials (see FAQ: What is a tearing resistance curve?)