Users manual > Database > Deformed materials

Two types of deformed materials are available in the database: Homogeneous and Mixture. The default material type is Homogeneous, in which case the material properties are conventionally described as a single phase. This material type is used for most calculations of metal forming processes.

If material type Mixture is selected, it is possible to specify the properties of the different phases of the material, while also specifying the conditions type of phase transformations. This material type is commonly used in the simulation of heat treatment processes.

Constant value

In this case, the flow stress is assumed to be constant over the entire volume of the workpiece.

Tabular function

The flow stress is specified point by point and can depend on temperature, accumulated strain and strain rate.

	Information
In QForm UK only logarithmic (true) strains are used.

	Information
When specifying tabular values and graphing, only plastic deformation is used.

The number of arguments on which the function will depend can be varied by checking the boxes in the window Select parameters:


The function depends on one parameter		Selecting the required parameters		The function depends on three parameters

Up to three parameters can be selected. Thus, the table can be two-dimensional: of two columns (if the function depends on one parameter), of several columns (if the function depends on two parameters) or three-dimensional (if the function depends on three parameters). The order in which these parameters are presented also matters. The first parameter corresponds to row headings, the second parameter corresponds to column headings, and the third parameter corresponds to tab headings under the table. The parameter sequence can be switched. To do this, you need to click on the drop-down list and select a different parameter.

	Information
If the parameter sequence is switched, the table will be rearranged according to the specified sequence. In this case, the table will contain the same values as before the rearrangment.

2 lines Plastic strain

3 columns Strain-rate

4 tabs Temperature

3 lines Strain-rate

4 columns Temperature

2 tabs Plastic strain

Data preparation is possible in third-party programs. Import and export table options are provided for this purpose.

Load data from file - import table function from file with extension *.csv, *.xlsx, *.xls.

Export to file - export table function to a file with extension *.csv, *.xlsx, *.xls.

	Information
To avoid errors when preparing data for import, it is recommended to first use the command Export to fileto create a template for the imported file..

In case the function depends on one or two parameters, the imported file must contain only one tab (sheet). For a single parameter dependency, the left column should contain the values of the argument, the right column should contain the corresponding values of the function. For dependence on two parameters, the first row starting from the second column must contain the values of one argument, the left column starting from the second row must contain the values of another argument. In this case, the value of the function is specified in the cell at the intersection of rows and columns.

In case the function depends on three parameters, the imported file must contain several tabs (sheets). The number of sheets should correspond to the desired number of values of the third argument. The data is specified similarly to the two parameter dependency case, except that each tab specifies the parameter value to be assigned to the third argument in the upper left corner.

	Important
When importing, the data will be set according to the specified parameter sequence. When exporting, the data has the same structure as the database table.

	Important
Imported files with extension .xlsx or .xls must not contain empty tabs (sheets). If you try to import files with tabs (sheets) that do not contain data, an error will occur.



Export to *.xlsx		Export to *.xlsx with a different sequence of parameters

Interaction with files *.csv is similar to Interaction with *.xlsx and *.xls files. The key difference when working with *.csv-files is that such files cannot contain tabs (sheets). Instead of tabs, individual *.csv files act as tabs.

In case the function depends on one or two parameters, the export will create 1 file with *.csv extension. Importing from *.csv will require selecting 1 file.

In the case the function depends on three parameters, when exporting to the *.csv extension, the number of files will correspond to the number of tabs. When importing from *.csv it is required to select the number of files corresponding to the desired number of values of the third argument:


Structure of one of the imported *.csv files		Selecting imported files		Result of importing several *.csv files

If the flow stress curves are specified point by point as a tabular function, the intermediate flow stress values and values outside the area of definition are calculated as follows:

oBelow the minimum set value of the temperature Tmin and above the maximum set value of the temperature Tmax there is no extrapolation, the last known value is taken. A linear interpolation is performed between the set temperature values in the system :

oBelow the minimum and above the maximum set values of the plastic strain there is no extrapolation. A linear interpolation is performed between the set values in the system :

oBelow the minimum set value of the strain-rate there is no extrapolation. Above the maximum set value of the strain-rate linear extrapolation in logarithmic coordinates parallel to the line approximating all values is performed. A linear interpolation is performed between the set values in the system :

	Important
The dependence of flow stress on strain rate is the only tabulated function for which extrapolation of function values is performed when the values exceed the limits of specified values. Extrapolation is only performed beyond the maximum value

Subroutine

In this case, the flow stress is given by a function described in a special subroutine in the language LUA

Formula

The flow stress is given by one of the formulas provided in the program.

It is necessary to select one of the proposed formulas (A), set parameter values (B) and specify constraints (C).


The formulaic method of assignment		Formula selection

Below the specified minimum value and above the specified maximum value, the flow stress is not calculated according to the formula (the last known value is taken), except for the maximum value of the flow stress dependence on the strain rate.

	Important
The dependence of flow stress on strain rate is the only formulaic dependence for which extrapolation of function values is performed when exiting the boundaries of values specified in columns Min and Max.

Below the minimum set value of the strain rate there is no extrapolation. The maximum value of the strain rate is irrelevant, parameter is used only for setting the display of the function graph.

The following formulas are provided in the program:

a)Abbreviated version of the Hensel-Spittel formula

, where:

– flow stress (MPa);

– temperature (0C);

– plastic strain;

– strain rate (1/s);

– empirical coefficients.

This model describes the dependence of flow stress on temperature, strain, and strain rate. Compared to the full Hensel-Spittel model, worse describes the flow stress in large limits of strain rate. Also does not account for dynamic recrystallization.

Information

Sources used:
1) Hensel A., Spittel T.. Kraft- und Arbeitsbedarf bildsamer Formgebungsverfahren // VEB Deutscher Verlag für Grundstoffindustrie. - Leipzig, 1978. - 280 p.

2) Spittel M., Spittel T. Hensel-Spittel Model for Flow Stress Calculation // Metal Forming Data / Ed. by T. Altan. - Berlin: Springer, 2009. - P. 1-42.

b)Full version of the Hensel-Spittel formula

, where:

– flow stress (MPa);

– temperature (0C);

– plastic strain;

– strain rate (1/s);

– empirical coefficients.

This model describes the dependence of flow stress on temperature, strain, and strain rate. Describes well the nonlinear nature of the change. Applicable over a wide range of temperature and strain rate. It also describes complex thermomechanical effects (dynamic recrystallization, etc.) well

Information

Sources used:
1) Hensel A., Spittel T.. Kraft- und Arbeitsbedarf bildsamer Formgebungsverfahren // VEB Deutscher Verlag für Grundstoffindustrie. - Leipzig, 1978. - 280 p.

2) Spittel M., Spittel T. Hensel-Spittel Model for Flow Stress Calculation // Metal Forming Data / Ed. by T. Altan. - Berlin: Springer, 2009. - P. 1-42.

c)The Zener-Hollomon formula

, where:

– flow stress (MPa);

– empirical coefficient related to the stress sensitivity of the material;

– inverse hyperbolic sinus;

– material-dependent coefficient;

– strain rate (1/s);

– hot deformation activation energy (J/mole);

– universal gas constant (J/(mole*K));

– absolute temperature (0K);

– coefficient characterising the sensitivity of stress to strain rate.

This model describes the dependence of flow stress on temperature and strain rate. Includes a Zener-Hollomon parameter equal to

Information

Sources used:
1) Zener C., Hollomon J.H.. Effect of Strain Rate Upon Plastic Flow of Steel // Journal of Applied Physics. - 1944. - Vol. 15, no. 1. - P. 22-32.

2) Sellars C.M., Tegart W.J.McG. On the Mechanism of Hot Deformation // Acta Metallurgica. - 1966. - Vol. 14, no. 9. - P. 1136-1138.

d)The Johnson-Cook formula

, where:

– flow stress (MPa);

– yield stress of material at zero strain (MPa);

– hardening coefficient (MPa);

– true (logarithmic) plastic deformation;

- hardening factor;

– strain rate sensitivity coefficient;

– strain rate (1/s);

– reference strain rate (1/s);

– current material temperature (0C);

– room (initial) temperature (0C);

– material melting temperature (0C);

– thermal unstrengthening index.

This model describes the dependence of flow stress on temperature, strain and strain rate. In doing so, the model explicitly separates these three factors. Performs well over a wide range of strain rates and temperatures.

	Information
Sources used: 1) Johnson G. R., Cook W. H. A constitutive model and data for metals subjected to large strains, high strain rates and high temperatures // Proceedings of the 7th International Symposium on Ballistics. - The Hague, 1983. - P. 541-547.

e)The Ghosh/Hockett-Sherby formula.

, where:

– flow stress (MPa);

– Share of contribution of the model Hockett-Sherby;

– hardening coefficient (MPa);

– initial strain;

– plastic strain;

– hardening index;

– initial stress (MPa);

– the ultimate stress to which the stress tends as the strain increases;

– saturation rate parameter;

– yield stress (MPa);

– empirical coefficient.

This combined model (Ghosh model + Hockett-Sherby model) describes the flow stress dependence on strain. It is flexible, because it describes cases with fast initial hardening (in case the Ghosh model dominates ()) and with subsequent asymptotic approximation to the limit value (in case the Hockett-Sherby model dominates ()). However, this formula does not take into account the effect of temperature and strain rate.

	Information
Sources used: 1) Hockett, J. E., & Sherby, O. D. (1975). "Large strain deformation of polycrystalline metals at low homologous temperatures". Journal of the Mechanics and Physics of Solids, 23(2), 87-98.

A formulaic approximation of the experimental data is available in the case of the full Hensel-Spittel formula.

To do this, you need to import a file with extension *.csv, *.xlsx or *.xls. To import data you need to click on Import from experimental data and select the desired file.

Importing experimental data

If you import a file with extension *.xlsx, *.xls, the order of the columns must correspond to the order of the parameters in the constraint setting window and after them there must be one more column with the values of flow stress at the corresponding parameters.

If a file with extension *.csv is imported, the values should be written in a similar order:

Order of parameters in the constraint setting window

A) plastic strain

B) strain rate

C) temperature

Order of columns with values, in case the file has extension *.xlsx, *.xls

A) plastic strain

B) strain rate

C) temperature

D) flow stress

Order of values, in case the file has *.csv extension

A) plastic strain

B) strain rate

C) temperature

D) flow stress

After importing the data, approximation will take place automatically and the calculated coefficients will appear in the corresponding windows. In the same way, there will be windows displaying the average and maximum deviations from the experimental values. The Find best solution and Update buttons will appear to the right of the calculated coefficients.

By default, the approximation will involve those coefficients that will result in the smallest deviation from the experimental data. That means that not all coefficients can be activated automatically.

Results of automatic approximation

As you can see from the example, the coefficients m7 and m8were not calculated (equal to zero). This allowed for the least amount of deviation.

You can activate all coefficients if needed, and after clicking Update the coefficients will be recalculated.

Results of approximation with all coefficients

In this example, the inclusion of all coefficients worsened the approximation result.

Also, if you click on Find the best solution, all coefficients will be activated automatically and recalculated.

Thus, with this tool, you can create your own material with properties based on experiments.

These parameters are mandatory for the calculation of the thermal problem in the workpiece.

There are several control methods for specifying density, specific heat, and thermal conductivity:

•Constant value;

•Table function.

Density, specific heat and thermal conductivity are specified by points and may depend on temperature.

These parameters are mandatory for the simulation considering elastic-plastic deformations.

There are several ways to specify Poisson's ratio and temperature expansion coefficient:

•Constant value;

•Table function.

There are several ways to specify Young module:

•Constant value;

•Table function;

•Formula.

Young module and Poisson's ratio may depend on temperature and accumulated deformation. Linear temperature expansion coefficient can only depend on temperature.

When specifying the coefficient of thermal expansion in the form of a tabular function, there are two options for specifying this coefficient: instantaneous (differential) and average (engineering).

The average (engineering) coefficient of thermal linear expansion is calculated with reference room temperature 200C as the tangent of the angle in the graph below:

This type of coefficient of thermal linear expansion is specified for different ranges of temperature variation, but all of these ranges take into account the reference temperature 200C(20 - 1000C; 20 - 2000C; 20 - 3000C; 20 - 4000C; etc.).

Instantaneous (differential) coefficient - This is the coefficient of thermal expansion at any point in time. Thus, this is the tangent of the angle of the tangent to the function dL/L from temperature:

This type of coefficient of linear thermal expansion is specified for differentiated ranges of temperature changes (for example, 20 - 30 0 C; 30 - 40 0 C; 40 - 50 0 C; 50 - 60 0 C, etc.). The smaller the range, the more accurate the calculation of linear thermal expansion.

As can be seen from the graph above, the instantaneous coefficient of linear expansion can also be negative.

Activation of this parameter allows you to specify a model for the evolution of the material microstructure.

Activation of this parameter allows the proposed plasticity resource exhaustion models to be applied to the calculation of the standard subroutine of the same name.

Activating this parameter allows you to specify a material model for simulation of diffusion saturation processes.

The model contains the following nested parameters Diffusing element, Diffusion coefficient and Activity coefficient and is selected using the drop-down list. There are several ways to set the Diffusion coefficient and Activity coefficient:

•Constant value;

•Table function;

•Formula.

Activating this parameter allows you to specify the material model for the simulation of induction heating.

The model contains the following parameters Specific electric resistance and Relative magnetic permeabilityand is selected using the drop-down list. There are several control methods for specifying Specific electrical resistance and Relative magnetic permeability:

•Constant value;

•Table function.

Material models in the QForm UK database can be exported and imported into text file with extension *.qdat. To do this, select the desired material and click the appropriate button on the database toolbar.

Export (A) and import (B) of material model

When exporting a material model from QForm UK database into a text file with the extension *.qdat.

Fragment of saved text file *.qdat with exported data

It is possible to import a deformed materials model created in the software JMatPro (http://www.sentesoftware.co.uk/). To do this, the material model calculated in the JMatPro® program should be exported to a text file with *.qdat extension

Export material model from JMatPro® program

	Information
If you select one of the proposed standards, only those material models will be displayed for which the database has an analogue for this standard.

File name:		AISI/SAE:		BS \| DIN \| GOST \| GB \| JIS