 # How to Use APDL Command TBdata、TBpt、TBtemp — The difference You Must Know

As an essential step in simulation, material definition is crucial. ANSYS APDL offers numerous commands to define materials. This article provides a complete guide to help you understand the methods used for defining materials in ANSYS.

In general, material definitions are divided into two major categories: linear and nonlinear. Both linear and nonlinear material definitions are related to temperature points. Every temperature point corresponds to a material. You may wonder why temperature is not defined when defining materials. It’s because the backend system defaults to a temperature of 0 degrees Celsius.

Therefore, when defining materials in ANSYS, you only need to understand three elements: temperature, linear and nonlinear.

1. Linear material definition

The commands used for material definition are MP, MPTEMP, and MPDATA.

Here’s the rule to remember: when the material properties are independent of temperature, you only need the MP command for linear material definition. However, when material properties are related to temperature, you need the Mptemp and Mpdata commands for linear material definition.

Mptemp defines the temperature points of the material, while MPdata inputs the values of material properties corresponding to each temperature point. Both commands have a parameter, Sloc, which determines the starting position of data points. Since these two commands define a maximum of six points at a time, you must start another command line if you have more than six temperature points.

For example, let’s say a material’s elastic modulus is related to temperature:

! Define seven temperature points
/prep7
Mptemp,1,20,30,40,50
Mptemp,5,60,70,80
!Sloc=5, starting from the fifth point
! Values of material 1’s elastic modulus at seven temperature points
Mpdata,ex,1,1,1e3,2.2e3,5.5e3,6.2e3
Mpdata,ex,1,5,1e4,5.5e4,9.8e4
! Values of material 1’s Poisson’s ratio at seven temperature points
Mpdata,prxy,1,1,0.2,0.23,0.26,0.27
Mpdata,prxy,1,5,0.31,0.35,0.45
! Values of material 2’s density at seven temperature points
Mpdata,dens,2,1,2100,2300,2500,2600
Mpdata,dens,2,5,2300,4200,5200
! Draw the curve of material 1’s elastic modulus with temperature
Mpplot,ex,1
! Draw the curve of material 2’s density with temperature
Mpplot,dens,2  As seen above, MPdata and MP commands are the same, except for the added SLoc parameter for tabular data.

1. Nonlinear material definition

When defining the linear portion of a material using the MP or MPdata command, only the linear part of the material is defined. However, if you want to define the elastic-plastic portion of the material, you need to use a combination of TBdata, TBtemp, and TBpt commands.

To define the nonlinear portion of a material, follow these steps:

Step 1: Define the linear portion of the material, such as the first point tangent modulus of the constitutive curve, Poisson’s ratio, and density using the MP or MPdata command.

Step 2: Declare the type of nonlinearity used for the material using the TB command, such as Miso, Mkin, or Biso.

Step 3: Define the specific constitutive curve stress-strain or material parameter values using the TBdata and TBpt commands.

There are many types of TB commands that can be defined, such as MKIN, MISO, and BISO. Each type requires different parameter types to be entered. You can view Help for a detailed explanation of the input parameters for each type.

If the material is temperature-dependent, you must first use the TBtemp command to define the temperature point. It’s worth noting that after defining the temperature point using the Tbtemp command, the subsequent command should immediately follow with the TBpt or TBdata command to define the specific constitutive curve or material parameter at that temperature point.

TBdata has many uses, and its name is easy to understand. It stands for “table+data”. When using TBdata, you define the specific table type and the data type that needs to be filled. Then, Tbdata fills in the specific data content according to the type defined in TB. In general, TBdata has a much wider range of use than TBpt.

TBpt is generally used specifically for defining material constitutive curves, that is, inputting stress-strain points. Generally, each TBpt command only inputs two parameters per line, that is, stress-strain values are inputted at the same time. Therefore, there may be multiple TBpt commands when defining the constitutive curve.

For example:

! define concrete failure criterion

TB,concr,1

! Input parameters C1-C8 of the concrete failure criterion

Tbdata,1,0.5,0.95,2.1,-1

Tbdata,5,0,0,0,0

Since parameters C5-C8 are 0, the above command is equivalent to the following:

TB,concr,1

Tbdata,,0.5,0.95,2.1,-1

Note that the TBdata command also has an Sloc parameter, which specifies the starting point of the table data. If not specified, it defaults to 1. You may mistakenly assume that it is the material number, which often leads to errors in defining materials. Example 1: Defining an ideal elastic-plastic material model that varies with temperature

!define the linear part of the material:
Mptemp,1,20,100,500,1000
Mpdata,ex,10,1,3.09e11,2.05e11,1.33e11,0.85e11
!Declare the material as Bkin, with a material number of 10 and four temperature points:
Tb,bkin,10,4
!Input the material data for each temperature point
!For the first temperature point
Tbtemp,20,1
Tbdata,1,345e6,3.09e10
!For the second temperature point
Tbtemp,100,2
Tbdata,1,275e6,2.05e10
!For the third temperature point
TBtemp,500,3Tbdata,1,200e6,1.33e10
!For the fourth temperature point
Tbtemp,1000,4
Tbdata,1,120e6,0.85e10

! Lastly, we’ll plot the data using the command Tbplot.
Tbplot Example 2: Defining a MISO material model’s constitutive curve:

First, we’ll define some material properties:

fck=26.8
Mp,ex,100,fck*0.19/0.0002
Mp,prxy,100,0.2
Mp,dens,100,2600e-12

Then, we’ll declare the material as MISO elastic-plastic:

TB,PLAS,,,MISO

Next, we’ll input the material data for each strain point:

tbpt,,0.0002,fck0.19
tbpt,,0.0004,fck0.36
tbpt,,0.0006,fck0.51
tbpt,,0.0008,fck0.64
tbpt,,0.001,fck0.75
tbpt,,0.0012,fck0.84
tbpt,,0.0014,fck0.91
tbpt,,0.0016,fck0.96
tbpt,,0.0018,fck*0.99
tbpt,,0.002,fck
tbpt,,0.0033,fck

In summary, while TBdata, TBpt, and TBtemp all deal with material data, they each have a distinct purpose. TBdata is used to input material data for a specific temperature point, TBpt is used to input material data for a specific strain point, and TBtemp is used to set the current temperature point. By mastering the use of these commands, you can more effectively model complex material behaviors in your simulations.

Good Luck!   