Fracture mechanics tests with specimens under low constraint conditions - Standardisation work by ASTM and ISO

Fracture mechanics test standards usually require a state of plane strain in the specimen, thus generating lower bound material properties, which in many applications lead to very conservative structural assessments. This applies in particular to lightweight structures, which are characterised by thin walls and hence plane stress conditions. Based on work by NASA Langley and GKSS Geesthacht, ASTM and ISO have initiated standardisation work to cover this area. It is proposed to determine the crack tip opening angle (CTOA) or the R-curve in the terms of delta(5) = f(Deltaa) on thin-walled C(T) and M(T) specimens. The various experimental techniques are presented.