MPC Project Omega model

The MPC Project Omega creep model is described in the standard “API 579-1/ASME FFS-1 2007 Fitness-For-Service” chapters 10.3.5.3 a F.7.1.1.

The creep strain rate is defined in (10.1) as $\dot\varepsilon_c = \dot\varepsilon_{c0}\exp(\Omega_m\varepsilon_c),$ where $\dot\varepsilon_{c0}$ is the creep strain rate in the beginning of the time interval, $\Omega_m$ is the multiaxial damage parameter, and $\varepsilon_c$ is the accumulated creep strain. The values of $\dot\varepsilon_{c0}$ and $\Omega_m$ are determined accoring to the section F.7.1.1 of the standard.

Input quantities

The MPC Project Omega model is activated by the parameter $\mathtt{KCRP}=5$ in the file name.iP. All materials used must be assigned to the elements using the file name.DAT. The material parameter files have the following structure:

* * Comments * AKONSTANTY

$A_0$

$A_1$

$A_2$

$A_3$

$A_4$ BKONSTANTY

$B_0$

$B_1$

$B_2$

$B_3$

$B_4$ BETA_OMEGA

$\beta_\Omega$ ALFA_OMEGA

$\alpha_\Omega$ SR_DELTA

$\Delta_\Omega^\text{sr}$ CD_DELTA

$\Delta_\Omega^\text{cd}$

The number of initial comment lines is unlimited.
There must be an empty line before each block.
The blocks AKONSTANTY, BKONSTANTY, BETA_OMEGA, ALFA_OMEGA, SR_DELTA a CD_DELTA contain all 14 parameters of the model.

Model parameters
$A_0$ to $A_5$	material constants defined in table F.30 of the standard
$B_0$ to $B_5$	material constants defined in table F.30 of the standard
$\beta_\Omega$	the parameter of the MPC project
$\beta_\Omega$	$=0.33$	(constant)
$\Delta_\Omega^\text{cd}$	the correction parameter for creep toughness
	$=-0.3$	ductile material
	$=+0.3$	brittle material
$\alpha_\Omega$	the parameter of the MPC project
	$=3.0$	a sphere or spherical bottom of a pressure vessel with an internal overpressure
	$=2.0$	a cylinder or cone with an internal overpressure
	$=1.0$	other shapes and loadings
$\Delta_\Omega^\text{sr}$	the corection parameter for creep properties dispersion
	$=-0.5$	lower bound
	$=+0.5$	upper bound

Example

There is only one matterial used in the creep problem.

name.iP

; KREST NLC NCYC KMOD KCRP KLARG KCNT
IP  1    11   1    0    5    0     0  3*0  11*2
RP 10*0 0 1 100 1000 10000 30000 80000 120000 160000 200000 250000
EN
EN

name.DAT

number 1
mpcpo.dat

mpcpo.dat

************************************************************************
*                                                                      *
*     API 579-1                                                        *
*                                                                      *
*     parameters   description                                         *
*                                                                      *
*     A(0) - A(4)  model constants from the table F.30                 *
*     B(0) - B(4)  model constants from the table F.30                 *
*     BETA_OMEGA   parameter (always 0.33)                             *
*     ALFA_OMEGA   parameter of the MPC project                        *
*                     3.0 sphere or spher. bottom w/ int. overpressure *
*                     2.0 cylinder or cone w/ internal overpressure    *
*                     1.0 other                                        *
*     SR_DELTA     correction par. for the creep properties dispersion *
*     CD_DELTA     correction parameter for the creep toughness        *
*                                                                      *
************************************************************************

AKONSTANTY
-16.3
38060.0
-9165.0
1200.0
-600.0

BKONSTANTY
-1.0
3060.0
135.0
-760.0
247.0

BETA_OMEGA
0.33

ALFA_OMEGA
1.00

SR_DELTA
-0.5

CD_DELTA
-0.3