3.1.2 Determination and Calibration of the Model Parameters
The cyclic constitutive parameters identification used in the UVP model are conducted on the cyclic plasticity test data from the high temperature uniaxial LCF tests on SSFS specimen at 600 °C for FV5661. The UVP model adopted in this work employs 8 parameters in total. The determination of the material parameters follows a step-by-step procedure, with elastic parameter determined initially and followed by the remaining isotropic hardening and kinematic hardening parameters. The parameter d in Eq. (8) can be evaluated through the slope in the regression of the plot, whilec is determined from the difference in maximum stresses between the first and the saturated cycle using the SSFS experimental LCF data at 600 °C, as illustrated in Fig.4a. The SSFS experimental LCF data at 600 °C from the tensile part of the initial cycle and the corresponding regression fitting curves are provided in Fig.4b, illustrating the derivations of kinematic hardening parameters, an and bn in Eq. (7.1). More detailed information about the total procedures of how to obtain the initial guess of the UVP parameters can be found in the author’s previous work1-3,49. These initial parameters are then regarded as the starting points to obtain the optimized parameters using a first order non-linear least square minimization1,3, where the minimum in the difference between the numerical and the experimental results is sought using two objective functions, i.e., i) experimental hysteresis loop of every cycle, and ii) experimental cyclic softening curve. The total set of the optimized UVP parameters for the FV566 at 600 °C is given in Table 1.