At room temperature, an unloaded fiber-filled composite structure already has non-zero self-equilibrating stresses at the constituent level. This is caused by the initial cooling of the structure from its elevated cure temperature to room temperature. At the constituent level (fiber/matrix), the thermal residual stresses are caused in part by differences in the thermal expansion characteristics of the fiber and matrix materials and the anisotropic nature of the structure due to the spatially varying fiber orientations.
Advanced Material Exchange can account for these constituent-level thermal residual stresses that exist prior to any externally applied mechanical or thermal loads. In this case, the thermal residual stresses contribute to the total stress state of the composite material and thus influence the mechanical load level at which the material fails.
To include the effects of thermal residual stresses in the structural analysis, you must create a HIN file with the following keyword:
*CURE STRESS
The HIN file (.hin) is an auxiliary text file that can be used for special analysis features such as modeling thermal residual stresses. The HIN file must have the exact same name as the input file (.inp) and structural interface file (.sif) with a .hin extension. Place the HIN file in the same directory as the input and structural interface files before you run the analysis.
The modeling of thermal residual stresses and warpage is very sensitive to element selection and mesh density. Whenever possible, use higher-order elements (i.e. C3D10M) and avoid using 4-noded tetrahedral structural elements. If you plan to simulate residual stresses frequently, it is recommended that you perform a sensitivity test on the mesh density and element type and correlate the results to experimental data.