Civil Engineering Reference
In-Depth Information
5.6.2.4 Fully Coupled Thermal-Stress Analysis
A fully coupled thermal-stress analysis is performed when the mechanical
and thermal solutions affect each other strongly and, therefore, must be
obtained simultaneously. The analysis requires the existence of elements
with both temperature and displacement degrees of freedom in the model
and can be used to analyze time-dependent material response. The analysis
cannot include cavity radiation effects but may include average-temperature
radiation conditions and takes into account temperature dependence of
material properties only for the properties that are assigned to elements with
temperature degrees of freedom. In ABAQUS (Standard), a fully coupled
thermal-stress analysis neglects inertia effects and can be transient or steady
state. On the other hand, in ABAQUS (Explicit), a fully coupled thermal-
stress analysis includes inertia effects and models transient thermal response.
Fully coupled thermal-stress analysis is needed when the stress analysis is
dependent on the temperature distribution and the temperature distribution
depends on the stress solution. In ABAQUS (Standard), the temperatures are
integrated using a backward-difference scheme, and the nonlinear coupled
system is solved using Newton's method. ABAQUS (Standard) offers an
exact as well as an approximate implementation of Newton's method for
fully coupled temperature-displacement analysis.
A steady-state coupled temperature-displacement analysis can be per-
formed in ABAQUS (Standard). In steady-state cases, modelers should
assign an arbitrary “time” scale to the step. This time scale is convenient
for changing loads and boundary conditions through the step and for obtain-
ing solutions to highly nonlinear (but steady-state) cases; however, for the
latter purpose, transient analysis often provides a natural way of coping with
the nonlinearity. Alternatively, modelers can perform a transient coupled
temperature-displacement analysis. By default, the initial temperature of
all nodes is zero. Modelers can specify nonzero initial temperatures. Bound-
ary conditions can be used to prescribe both temperatures (degree of free-
dom 11) and displacements/rotations (degrees of freedom 1-6) at nodes in
fully coupled thermal-stress analysis. Shell elements in ABAQUS (Standard)
have additional temperature degrees of freedom 12, 13, etc., through the
thickness. Boundary conditions applied during a dynamic coupled
temperature-displacement response step should use appropriate amplitude
references. If boundary conditions are specified for the step without ampli-
tude references, they are applied instantaneously at the beginning of the step.
Thermal loads that can be prescribed in a fully coupled thermal-stress
analysis comprise concentrated heat fluxes, body fluxes, and distributed
Search WWH ::
Custom Search