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The ABAQUS FAQ


5. ABAQUS - Materials

Q5.1 : How do I find what material properties are needed for a particular analysis ?

Read the relevant section in Chapter 6 : Analysis Procedures (User's manual Vol. I). This gives an overview about the analysis and has more information about the material properties.
Read also the following sections in Chapter 17 : Materials Introduction of the ABAQUS User's manual.
Section 17.1.3 lists the material model combination tables. Several models are available to define the mechanical behaviour (elastic, plastic).
Some material options require the presence of other material options. Some exclude the use of the other material options. For example *DEFORMATION PLASTICITY completely defines the material's mechanical behaviour and should not be used with *ELASTIC.
Once you have all the relevant keywords to define the material properties consult the keyword Manual for each of the keywords. This will explain what data is required for each of the keyword.

Q5.2 : What material properties need to be specified in a thermal-electrical analysis ?

Referring to Section 17.1.3 of the ABAQUS User's manual you will require the heat transfer properties as well as the electrical properties. These are listed below :
This forms the complete set of properties. If Piezoelectric elements are not used then *PIEZOELECTRIC and *DIELECTRIC properties will not be required.
If only the steady state heat transfer response is of interest then *SPECIFIC HEAT properties are not required. Similarly if there are no phase changes involved then *LATENT HEAT is not required.
*JOULE HEAT FRACTION is used to specify the fraction of electrical energy that will be released as heat.
Example problem 5.2.1 - thermal-electrical modelling of an automotive fuse illustrates the thermal-electrical analysis.
ABAQUS allows for redundant material properties to be specified. It will simply ignore the material properties not required for the current analysis.
Typical example of material properties :
*MATERIAL, NAME=ZINC
*CONDUCTIVITY
 0.1121,  20.0
 0.1103, 100.0
*ELECTRICAL CONDUCTIVITY
 16.75E3,  20.0
 12.92E3, 100.0
*JOULE HEAT FRACTION
  1.0
*DENSITY
  7.14E-6
*SPECIFIC HEAT
  389.0


Q5.3 : What material properties need to be specified in an analysis using temperature- displacement elements ?

Referring to Section 17.1.3 of the ABAQUS User's manual you will require the heat transfer properties as well as the mechanical properties. These are listed below :

Q5.4 : What material properties need to be specified in an analysis using piezoelectric elements?

Referring to Section 9.1.3 of the ABAQUS User's manual you will require the electrical properties. These are listed below :

Q5.5 : What material properties need to be specified in modeling concrete with reinforcements?

Use the concrete model available with rebar to model the reinforcements.
Section 1.1.5 of the ABAQUS Example's manual gives an example of the collapse analysis of a concrete slab subjected to a central point load.
The data file for that example is collapse example.
The complete set of ABAQUS input files can be obtained by using the following command :
   abaqus fetch j=collapseconcslab*
*CONCRETE
  3000., 0.      abs. value of compressive stress, abs. value of plastic strain.
  5500., 0.0015                "                              "

*FAILURE RATIOS
  1.16, 0.0836

This is used to define the shape of the failure surface (see section 11.5.1 of the ABAQUS USER's manual Vol. II).
The first parameter is the ratio of the ultimate biaxial compression stress, to the uniaxial compressive stress. Default is 1.16.
The second parameter is the absolute value of the ratio of uniaxial tensile stress at failure to the uniaxial compressive stress at failure. Default is 0.09.

Tension Stiffening

*TENSION STIFFENING  
  1., 0.
  0., 2.E-3

First parameter is the fraction of remaining stress to stress at cracking. The second parameter is the absolute value of the direct strain minus the direct strain at cracking.
This defines the retained tensile stress normal to the crack as a function of the deformation in the direction of the normal to the crack.

Shear Retention

*SHEAR RETENTION
Not used for this example.

Reinforcement modelling


*REBAR is used to model the reinforcement.
*REBAR,ELEMENT=SHELL,MATERIAL=SLABMT,GEOMETRY=ISOPARAMETRIC,NAME=YY
SLAB, 0.014875, 1., -0.435, 4
*REBAR,ELEMENT=SHELL,MATERIAL=SLABMT,GEOMETRY=ISOPARAMETRIC,NAME=XX
SLAB, 0.014875, 1., -0.435, 1

Here SLAB is the element name or name of the element set that contains these rebars. The geometry is ISOPARAMETRIC. Other choice is SKEW. ELEMENT can be BEAM, SHELL, AXISHELL or CONTINUUM type. The following are the other parameters specified :

Alternate Method o modelling REBAR Reinforcements

Alternatively REBAR can be modelled as follows :
*NODE 
....
....
**-------------------END NODES FOR REBAR BEAM ELEMENTS
     501,         0.0,        0.15,       -0.02
     541,         1.5,        0.15,       -0.02
     601,         0.0,        0.15,       -0.07
     641,         1.5,        0.15,       -0.07 
     701,         0.0,        0.60,       -0.02
     741,         1.5,        0.60,       -0.02
     801,         0.0,        0.60,       -0.07
     841,         1.5,        0.60,       -0.07 
....
....
**---------------------GENERATE INTERMEDIATE NODES
*NGEN, NSET=BAR10TF
 701, 741, 2
*NGEN, NSET=BAR10TB
 801, 841, 2
...
...
**--------------------GENERATE THE BEAM ELEMENTS
*ELEMENT, TYPE=B31
701, 701, 703
801, 801, 803
*ELGEN, ELSET=BAR10TF
701, 20, 2, 1, 1, 1, 1
*ELGEN, ELSET=BAR10TB
801, 20, 2, 1, 1, 1, 1
...
...
**---------------------DEFINE THE MATERIAL PROPERTIES
*MATERIAL, NAME=BAR8
**
**  8 mm dia bar
**
*ELASTIC, TYPE=ISO
197.E6, 0.3
*PLASTIC
 354.E3, 0.
 364.E3, 0.0018
**
**---------------------DEFINE THE SECTION PROPERTIES
...
...
*BEAM SECTION, SECTION=CIRC, MATERIAL=BAR10, ELSET=BAR10TF
  0.005
*BEAM SECTION, SECTION=CIRC, MATERIAL=BAR10, ELSET=BAR10TB
  0.005
...
**--------------------DEFINE AN ELEMENT SET WHICH CONTAINS
**--------------------THE ELEMENTS THROUGH WHICH THE REBAR
**--------------------ELEMENTS PASSES.
....
*ELSET, ELSET=TOP, GENERATE
 5, 80, 5
**
**--------------------
*EMBEDDED ELEMENT,HOST ELSET=TOP
BAR10TF,BAR10TB
**


Q5.6 : What material properties need to be specified in using the deformation plasticity model ?

See section 11.2.11 of the users' manual (Vol. II). See also section 23.4.7 of the users' manual (Vol. III), keyword section.


For example :
*DEFORMATION PLASTICITY
  1.E3,  0.3,  2.,  3,  0.396

Here the data line contains the Young's modulus, Poissons ratio, Yield stress, Exponent, Yield offset respectively. If it is necessary to define the dependence of these parameters on temperature then the 6th parameter will be the temperature. Then repeat the dataline for different temperatures as required.

Q5.7 : What are the appropriate units for analysis using Critical State Models - Modified Cam Clay? (27 April 2012)

L -  metres
Stress - kPa
Density - KN/m^3
Unit weight of water - Kg/m^3
Using Pascals for stress resulted in convergence problems.
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Last updated: 27 April 2012