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.