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16.1.2 Sequentially coupled thermal-stress analysis

Products: Abaqus/Standard Abaqus/CAE

References

Defining an analysis, Section 6.1.2

Heat transfer analysis procedures: overview, Section 6.5.1

Predefined fields for sequential coupling, Section 16.1.1

Creating and modifying output requests, Section 14.4.5 of the Abaqus/CAE User's Manual

Defining a temperature field, Section 16.11.9 of the Abaqus/CAE User's Manual

Overview

A sequentially coupled heat transfer analysis:

is used when the stress/deformation field in a structure depends on the temperature field in that

structure, but the temperature field can be found without knowledge of the stress/deformation

response; and

is usually performed by first conducting an uncoupled heat transfer analysis and then a

stress/deformation analysis.

A thermal-stress analysis in which the temperature field does not depend on the stress field is a common

example of a sequential multiphysics workflow and is one case of the more general workflow described inPredefined fields for sequential coupling, Section 16.1.1. In such thermal-stress analyses, temperature is

calculated in an uncoupled heat transfer analysis (Uncoupled heat transfer analysis, Section 6.5.2) or in a

coupled thermal-electrical analysis (Coupled thermal-electrical analysis, Section 6.7.3).

Saving the nodal temperatures

Nodal temperatures are stored as a function of time in the heat transfer results (. f i l ) file or output

database (. odb) file by requesting output variable NT as nodal output to the results or output database file.

See Node output in Output to the data and results files, Section 4.1.2, and Node output in Output to

the output database, Section 4.1.3.

Transferring the heat transfer results to the stress analysis

The temperatures are read into the stress analysis as a predefined field; the temperature varies with position

and is usually time dependent. It is predefined because it is not changed by the stress analysis solution.

Such predefined fields are always read into Abaqus/Standard at the nodes. They are then interpolated to the

calculation points within elements as needed (see Interpolating data between meshes in Predefined

fields, Section 33.6.1). The temperature interpolation in the stress elements is usually approximate and one

order lower than the displacement interpolation to obtain a compatible variation of thermal and mechanical

strain. Any number of predefined fields can be read in, and material properties can be defined to depend on

them.

For more information, see Transferring temperatures as temperature fields in Predefined fields for

sequential coupling, Section 16.1.1.

.2 Sequentially coupled thermal-stress analysis http://400d-97732:2080/v6.12/books/usb/pt04ch16s01at38.html

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Initial conditions

Appropriate initial conditions for the thermal and stress analysis problems are described in the heat transfer

and stress analysis sectionsfor example, see Heat transfer analysis procedures: overview, Section 6.5.1;

Coupled thermal-electrical analysis, Section 6.7.3; Static stress analysis procedures: overview, Section

6.2.1; and Dynamic analysis procedures: overview, Section 6.3.1. See also Initial conditions in

Abaqus/Standard and Abaqus/Explicit, Section 33.2.1.

Boundary conditions

Appropriate boundary conditions for the thermal and stress analysis problems are described in the heat

transfer and stress analysis sectionsfor example, see Heat transfer analysis procedures: overview,

Section 6.5.1; Coupled thermal-electrical analysis, Section 6.7.3; Static stress analysis procedures:

overview, Section 6.2.1; and Dynamic analysis procedures: overview, Section 6.3.1. See also Boundary

conditions in Abaqus/Standard and Abaqus/Explicit, Section 33.3.1.

Loads

Appropriate loading for the thermal and stress analysis problems is described in the heat transfer and stressanalysis sectionsfor example, see Heat transfer analysis procedures: overview, Section 6.5.1; Coupled

thermal-electrical analysis, Section 6.7.3; Static stress analysis procedures: overview, Section 6.2.1; and

Dynamic analysis procedures: overview, Section 6.3.1. See also Applying loads: overview, Section

33.4.1.

Predefined fields

In addition to the temperatures read in from the heat transfer analysis, user-defined field variables can be

specified; these values only affect field-variable-dependent material properties, if any. See Predefined

fields, Section 33.6.1.

Material options

The materials in the thermal analysis must have thermal properties such as conductivity defined (see

Thermal properties: overview, Section 26.2.1). Any mechanical properties such as elasticity will be

ignored in the thermal analysis, but they must be defined for the stress analysis procedure. See Part V,

Materials, for details on the material models available in Abaqus/Standard.

Thermal strain will arise in the stress analysis if thermal expansion (Thermal expansion, Section 26.1.2)

is included in the material property definition.

Elements

Any of the heat transfer elements in Abaqus/Standard can be used in the thermal analysis. In the stress

analysis the corresponding continuum or structural elements must be chosen. For example, if heat transfer

shell element type DS4 is defined by nodes 100, 101, 102, and 103 in the heat transfer analysis, three-

dimensional shell element type S4R or S4R5 must be defined by these nodes in the stress analysis

procedure. For continuum elements heat transfer results from a mesh using first-order elements can be

transferred to a stress analysis with a mesh using second-order elements (see Using second-order stress

elements with first-order heat transfer elements (the midside node capability) in Predefined fields,

Section 33.6.1).

Output

The nodal temperatures must be written to the heat transfer analysis results or output database file by

requesting the output variable NT (see Output to the data and results files, Section 4.1.2). These


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temperatures will be read into the stress analysis procedure.

Appropriate output variables are described in the heat transfer and stress analysis sections. All of the output

variables are outlined in Abaqus/Standard output variable identifiers, Section 4.2.1.

Input file template

A typical sequentially coupled thermal-stress analysis consists of two Abaqus/Standard runs: a heat transfer

analysis and a subsequent stress analysis.

The following template shows the input for the heat transfer analysis heat . i np:

*HEADI NG*ELEMENT, TYPE=DC2D4

(Choose the heat transfer element type)

*STEP*HEAT TRANSFER

Apply thermal loads and boundary conditions

** Wr i t e al l nodal t emper at ur es t o t he resul t s or** out put dat abase f i l e, heat . f i l / heat . odb*NODE FI LE, NSET=NALL NT*OUTPUT, FI ELD*NODE OUTPUT, NSET=NALL NT

*END STEP

The following template shows the input for the subsequent static structural analysis:

*HEADI NG*ELEMENT, TYPE=CPE4R

(Choose the continuum element type compatible with the heat transfer element type used)

*STEP*STATI C

Apply structural loads and boundary conditions

*TEMPERATURE, FI LE=heat

Read in all nodal temperatures from the results or output database file, heat . f i l / heat . odb*END STEP


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Abaqus Analysis User's Manual (6