Time Step for Temperature-dependent Material — Lesson 9

When solving structural analyses with the temperature-dependent coefficient of thermal expansion, how small of a time step do I need to ensure accuracy?

In purely structural analyses, deformation is the degree of freedom (DOF), so materials that are dependent on strain (or deformation) trigger a nonlinear solution. The temperature-dependent coefficient of thermal expansion (CTE) or temperature-dependent elastic modulus do not cause a nonlinear structural solution, as temperature is a known input. (Note that while CTE may be a nonlinear function of temperature, for example, it is still considered a linear material insofar as structural analyses are concerned, as CTE is not a function of deformation or of strain.) These materials are also not path dependent, so the time step size will not affect solution accuracy.

If temperature-dependent plasticity or creep is present, the accuracy will be dictated by the time step size because these materials are path dependent, whether or not they are temperature dependent.

In a heat transfer analysis, temperature-dependent materials will always trigger a nonlinear solution because temperature is the DOF in thermal analyses. Therefore, any materials dependent upon temperature will require Newton-Raphson method in heat transfer analyses.