THE STANDARD RIDGED UNIAXIAL TESTPIECE - COMPUTED ACCURACY OF CREEP STRAIN

The creep rupture behaviour and the accuracy of the measured strains for the uniaxial tensile testpiece with extensomenter ridges have been studied by use of the Continuum Damage Mechanics (CDM)-based creep finite element solver, DAMAGE XX. Multi-axial creep constitutive equations with multi-damage state variables were used in the computer modelling process. The procedure models the development of failed regions of the testpiece due to the stress concentration in the transition regions from the parallel portion to the extensometer ridges. The accuracy of the creep strain measurement for the testpiece was investigated with the variation of time, gauge length, and stress levels. The computer modelling results show that although the error of the creep strain measurement is a fuction of time, it is dependent upon the stress sensitivity of the material law. For power-law material the maximum error is invariant of the normalized stress, but dependent upon the value of n; and for the sinh-based material law the maximum error is dependent upon the magnitude of the applied stress.