Temperature history is available after a linear transient heat transfer analysis. One step transient thermal stress analysis is used to apply this temperature history (at multiple time steps) to a structural analysis. Linear transient Heat Transfer Analysis is run first, and the entire temperature history is now available for subsequent static analysis. The static analysis can be a linear or nonlinear subcase. For a linear OSTTS solution, after the transient heat transfer run, multiple linear static subcases are internally spawned (equal to the number of temperature loads from transient heat transfer) and the stress state is calculated for each “time-step” based on the applied temperature loads. For a nonlinear OSTTS run, multiple nonlinear static subcases are internally spawned (with CNTNLSUB). Therefore, the nonlinear state of each internally spawned subcase is applied as the initial state of the next subcase (in addition to temperature loads from transient heat transfer).

Linear and nonlinear OSTTS runs provide displacement and stress history for the duration of transient heat transfer.

Input cards for one step transient thermal stress analysis

A linear transient heat transfer subcase and a static subcase should be defined to perform a one-step transient thermal stress analysis. TEMPERATURE case control entries with the HTIME keyword can be used in the static subcase to select specific or all time steps to perform the stress analysis. Below is a sample input deck:

SUBCASE 100

TITLE = Transient thermal subcase

ANALYSIS = HEAT

THERMAL(sort1, punch)=ALL

FLUX=ALL

TSTEP = 100

IC = 20

DLOAD = 200

$

SUBCASE 200

TITLE = One step transient thermal stress subcase

SPC = 1

TEMP(LOAD,HTIME=ALL) = 100

DISPLACEMENT=ALL

STRESS=ALL

Temperature history and peak stress history from OSTTS are shown in Figure 1. The peak temperature is 43.27 degrees Celsius at 145 seconds, while the stress peak is 42.35 Mpa at 165 seconds. Note that the peak stress is not required to occur at the same time as the peak temperature or at the initial or final time step. This illustrates that OSTTS is useful in capturing the stress peak over the duration of the transient analysis.

Figure 1: Temperature history and peak stress of one step transient thermal stress analysis

Note