Norton law creep model

You can use either Eq. C 0 is calculated in the SI units, so you need to apply conversion factors. In the Material dialog box, select Include Creep Effect to activate the creep calculation for the selected material model. Creep calculations are considered only for nonlinear studies. Creep effect is not available for the linear elastic orthotropic and viscoelastic material models. Use the form below to send your comments and suggestions about this topic directly to our documentation team.

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All rights reserved. Creep Model Creep is a time dependent strain produced under a state of constant stress. Parent topic Material Models. Elasticity Models. Plasticity Models. Hyperelasticity Models. Viscoelastic Model. Nitinol Material Model. To extend these laws to multiaxial creep behavior, the following assumptions are made: The uniaxial creep law remains valid if the uniaxial creep strain and the uniaxial stress are replaced by their effective values. Material is isotropic The creep strains are incompressible.

From the reference creep data below, you calculate the creep constants for the equation of creep state. These data refer to Stainless Steel - Grade Solver Settings for Creep Calculations In the Material dialog box, select Include Creep Effect to activate the creep calculation for the selected material model.

Creep calculations are supported only for nonlinear studies with solid mesh. Creep effects are not supported for shells or beams. Creep consideration is not available for the linear elastic orthotropic and viscoelastic material models. When you consider creep effects in a nonlinear study, select option Automatic autostepping to improve chances of convergence Nonlinear study dialog box.

If the solver exceeds the maximum equilibrium iterations required to reach convergence, the solution terminates, and the solver issues appropriate error messages with corrective actions. For Solver , select Automatic Solver Selection. Enter End time in seconds Nonlinear study dialog box.

Thank you for your comments. The creep strain rate is calculated by solving the rate equation. The trace of the creep strain rate tensor, the volumetric creep strain rate , equals the user input. Volumetric creep is not generally used to model creep in metals, but it is commonly used to model creep in soils or other geological materials.

Here, n D is a deviatoric tensor coaxial to the stress tensor. The deviatoric tensor n D is defined as. Deviatoric creep is very popular to model creep in metals and alloys. The effective creep strain and the effective creep strain rate are available in the variables solid. The creep strain tensor is calculated by time-integration the user defined symmetric creep strain rate tensor. It is defined by. Norton creep is a deviatoric temperature-dependent creep model, with a creep rate equation written as.

See also the description of the Norton material model in the Solid Mechanics interface documentation. A common model for modeling primary and secondary creep together is the so-called Norton-Bailey or Bailey-Norton model. Here, the creep strain is proportional to a power of time and to a power of the equivalent stress. Differentiating with respect to time will give the rate form. Norton-Bailey creep is a deviatoric temperature-dependent creep model, furbished with either a time-hardening or a strain-hardening primary creep model.

The strain-hardening variant of this creep law is implemented as. The time and frequency shifts in Equation and Equation serve two purposes:. They can be used to initialize a study where some hardening has already taken place. This singularity is weak in the sense that the time integral is well defined, but it will cause problems for the numerical solution. You can then add a small shift to overcome this problem.

See also the description of the Norton-Bailey material model in the Solid Mechanics interface documentation. At very high stress levels, the creep rate is proportional to the exponential of the equivalent stress. Garofalo showed Ref. Garofalo creep is also a deviatoric creep model with a creep rate proportional to the hyperbolic sine function. See also the description of the Garofalo hyperbolic sine material model in the Solid Mechanics interface documentation.

At low stress levels and high temperatures, Nabarro and Herring Ref. See also the description of the Nabarro-Herring material model in the Solid Mechanics interface documentation. Coble creep Ref. Coble creep is more sensitive to grain diameter than Nabarro-Herring creep.

See also the description of the Coble material model in the physics interface documentation. Generally, the stress exponent n takes values between 3 and 5.

A general relation between creep rate and several material parameters is the Mukherjee-Bird-Dorn equation Ref. See also the description of the Weertman material model in the Solid Mechanics interface documentation. Especially, in the hot section of turbines of commercial and military plants this can be a crucial factor for the design process and optimize costs. Creep can be divided in three different stages: primary creep, secondary creep and tertiary creep:.

It occurs after a certain amount of time and slows down constantly. It lasts for the first hour after applying the load, and is essential in calculating the relaxation over time. The strain rate is now constant over a long period of time. The strain rate in the tertiary creep stage is growing rapidly until failure. This happens in a short period of time and is not of great interest.

Therefore, only primary and secondary creep are modeled on the SimScale platform. Two fundamental creep law types defined as creep strain rate equations are available in SimScale:. The creep stress index depends on the temperature and the stress level and can be determined with help of an Ashby deformation mechanism map.

On basis of these basic laws, four different creep formulations are currently available on the platform:. In this formulation, the creep strain rate only depends on the stresses. In this formulation, the creep strain rate depends on the stresses and the creep strains.

The choice of the formulation to be used varies from problem to problem and depends on the data of the temperature and stress field of the problem.

Creep behavior can be applied to Linear Elastic and Elasto-Plastic material models. To define the model, follow the steps given below:. Supported analysis types.

A creep material behavior can only be defined for the following analysis types: Nonlinear static analysis Dynamic analysis Nonlinear thermomechanical analysis.