ASTM E2899-24e1

Note 1:Constraint-based framework. In the context of this test method, constraint is used as a descriptor of the three-dimensional stress and strain fields in the near vicinity of the crack tip, where material contractions due to the Poisson effect may be suppressed and therefore produce an elevated, tensile stress state (3, 4). (See further discussions in Terminology and Significance and Use.) When a parameter describing this stress state, or constraint, is used with the standard measure of crack-tip stress amplitude (K or J), the resulting two-parameter characterization broadens the ability of fracture mechanics to accurately predict the response of a crack under a wider range of loading. The two-parameter methodology produces a more complete description of the crack-tip conditions at the initiation of crack extension. The effects of constraint on measured fracture toughness are material dependent and are governed by the effects of the crack-tip stress-strain state on the micromechanical failure processes specific to the material. Surface crack tests conducted with this test method can help to quantify the material sensitivity to constraint effects and to establish the degree to which the material toughness correlates with a constraint-based fracture characterization.

Note 2:TASC. The use of TASC relieves the user of the burden of performing unique elastic-plastic finite element analyses for each test performed in the elastic-plastic regime. For the purposes of this standard, TASC calculations are equivalent to finite element analysis results. Users of TASC should follow the methodologies in Annex A6 for establishing analysis material property inputs. Documentation on the development, verification and validation of TASC is provided in references (5, 6, 7, 8).