EFFECTS OF THE STATE OF STRESS ON THE TENSILE AND CREEP-PROPERTIES OFGAMMA-TIAL

Tensile stress-strain tests at 20, 450 and 750 degrees C and creep exp eriments at 750 degrees C have been performed on plain and circumferen tially notched bars of the candidate gas turbine blade material gamma- titanium aluminide (gamma-TiAl). Two notch shapes were examined to pro duce different stress states in the notch root region. In all cases no tch strengthening was observed. Finite element calculations have also been carried out to determine the stress distributions developed in th e notched bars during the tensile and creep tests. The tensile propert ies were represented by a Ramberg-Osgood relation with a range of stra in-hardening exponents, m, and the creep behaviour by a Norton-type cr eep law with different stress indices, n. It has been found that a ske letal point exists in the notch cross-section where the stress state i s independent of the values chosen for m and n. It is shown that the e xperimental results can be explained in terms of the state of stress d eveloped at the skeletal point of each notch shape.