Quantifying T-stress controlled constraint by the master curve transition temperature T-0

Specimen size, crack depth and loading conditions may effect the materials fracture toughness. In order to safeguard against these geometry effects, f racture toughness testing standards prescribe the use of highly constrained deep cracked bend specimens having a sufficient size to guarantee conserva tive fracture toughness values. One of the more advanced testing standards, for brittle fracture, is the master curve standard ASTM E1921-97, which is based on technology developed at VTT Manufacturing Technology. When applie d to a structure with low constraint geometry, the standard fracture toughn ess estimates may lead to strongly over-conservative estimate of structural performance. In some cases. this may lead to unnecessary repairs or even t o an early "retirement" of the structure. In the case of brittle fracture, essentially three different methods to quantify constraint have been propos ed, J small scale yielding correction, Q-parameter and the T-stress. Here, a relation between the T-stress and the master curve transition temperature T-0, is experimentally developed and verified. As a result, a new engineer ing tool to assess low constraint geometries with respect to brittle fractu re has been obtained. (C) 2001 Elsevier Science Ltd. All rights reserved.