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In general, the regularization is more difficult if the smallest interval defined by the user is small compared to the range of the independent variable. If more than 200 intervals are required to obtain an acceptable regularized curve, the analysis stops during the data checking with an error message. Example of user data that are difficult to regularize.Ībaqus/Explicit attempts to use enough intervals such that the maximum error between the regularized data and the user-defined data is less than 3% however, you can change this error tolerance.
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Figure 3 shows a case in which the user has defined data that are not regular.įigure 4. To illustrate the implications of using regularized material data, consider the following two cases. It is important to understand the differences that might exist between the regularized material curves used in the analysis and the curves that you specified. These regularized material curves are the material data used during the analysis. For each material point calculation, the state of the material must be determined by interpolation, and, for efficiency, Abaqus/Explicit fits the user-defined curves with curves composed of equally spaced points. Material data can be functions of temperature, external fields, and internal state variables, such as plastic strain. When performing an analysis, Abaqus/Explicit may not use the material data exactly as defined by the user for efficiency, all material data that are defined in tabular form are automatically regularized. While there are few differences between the nominal and true values at small strains, there are very significant differences at larger strain values therefore, it is extremely important to provide the proper stress-strain data to Abaqus if the strains in the simulation will be large. The plastic strain is obtained by subtracting the elastic strain, defined as the value of true stress divided by the Young's modulus, from the value of total strain (see Figure 1). You must decompose these total strain values into the elastic and plastic strain components. Instead, they will probably be the total strains in the material. The strains provided in material test data used to define the plastic behavior are not likely to be the plastic strains in the material. The first piece of data given defines the initial yield stress of the material and, therefore, should have a plastic strain value of zero. The plastic data define the true yield stress of the material as a function of true plastic strain. Any number of points can be used to approximate the actual material behavior therefore, it is possible to use a very close approximation of the actual material behavior.
ENGINEERING STRESS VS TRUE STRESS VS ULTIMATE STRESS SERIES
Abaqus approximates the smooth stress-strain behavior of the material with a series of straight lines joining the given data points. The classical metal plasticity model in Abaqus defines the post-yield behavior for most metals. These relationships are valid only prior to necking.