Temperature-dependent material properties are evaluated at each integration point. Elements for which this applies include SHELL181, PLANE182, PLANE183 , SOLID185, SOLID186 , SOLID187, SOLID272, SOLID273, SOLID285, SOLSH190, BEAM188, BEAM189, SHELL208, SHELL209, REINF264, SHELL281, PIPE288, PIPE289, and ELBOW290.
The LINK180 element uses a closed form solution (without integration points) and has its material properties evaluated at the average temperature of the element.
Other cases:
For the structural elements PLANE13 and SOLID65, the nonlinear material properties (TB commands) are evaluated at the integration points, but the linear material properties (MP commands) are evaluated at the average element temperature.
Numerically integrated structural elements PLANE25, SHELL61, and PLANE83 have their linear material properties evaluated at the average element temperature.
Non-structural elements have their material properties evaluated only at the average element temperature, except for the specific heat (Cp) which is evaluated at each integration point.
Whether shape functions are used or not, materials are evaluated at the temperature given, i.e. no account is made of the temperature offset (TOFFST command).
For a stress analysis, the temperatures used are based directly on the input. As temperature is the unknown in a heat transfer analysis, the material property evaluation cannot be handled in the same direct manner. For the first iteration of a heat transfer analysis, the material properties are evaluated at the uniform temperature (input on the BFUNIF command). The properties of the second iteration are based on the temperatures of the first iteration. The properties of the third iteration are based on the temperatures of the second iteration, etc.
See Temperature-Dependent Coefficient of Thermal Expansion for a special discussion about the coefficient of thermal expansion.