11-12-2012, 04:51 PM
Creep Material Curve Fitting
Creep Material.doc (Size: 126.5 KB / Downloads: 44)
ANSYS provides thirteen creep models, along with the tools to generate and fit derived coefficients to your experimental data. Interactive (GUI) or command line (batch) input is available. You input your experimental data, choose a model from one of the supplied creep models, and then perform a regression analysis. You then graphically view the curve-fitting result, and compare it for fit with your experimental data. If the curve is acceptable, you write the fitted coefficients to the database as ANSYS nonlinear data table commands (ANSYS TB command format) for the subsequent finite element analyses.
Prepare Experimental Data
You need to provide accurate experimental test data in order to achieve valid curve-fitting results. For creep analyses, you use either the creep strain value or creep strain rate, derived as a function of time, temperature, stress, and/or creep strain. The type of data you need to provide will depend on the creep model you choose. The experimental data is named "creep" to distinguish it from other types of data, such as uniaxial, tension, biaxial, etc. The creep data must be a plain text file that contains the headers and the test data in table form, delimited by a space or a comma.
Input the Data into ANSYS
The experimental data must be read into ANSYS from a plain text file. You prepare this file according to the previous section, including both header information and formatted test data. The header portion is required for creep analyses. Each file is viewed as a data set in ANSYS, and can be a complete set of experimental test data or a part of a series of files of experimental test data. You can include several data sets, such as tests performed at different stress levels and/or temperatures, when you perform creep curve fitting. There are two ways to input the experimental data.
Select a Material Model Option
The 13 models available for creep curve fitting are defined in Table 10.6: Creep Models and Abbreviations. Pick the one that best satisfies your requirements, and use the creep model abbreviation from the table in subsequent fitting operations. You'll find it helpful to view the formula before you solve. It will help you determine the initial coefficients you might use and also help you determine the format of your experimental data. Also see Table 10.6: Creep Models and Abbreviations to determine a starting point for the initial creep model coefficients.