# Orthotropic Strain Values in Thermomechanical Analysis

Hello,
I’m new to thermomechanical analysis and I’m curious about obtaining orthotropic strain values through thermomechanical simulations. Could someone please provide guidance on the constraints required for conducting a thermomechanical analysis to derive strain values?.

Thanks,
Bhavita

If you don’t have a specific problem in mind then start with a simple cube (can consist of a single hex element) and play with different BCs. The typical setup for such single element tests is that 3 faces orthogonal to each other have normal displacements fixed.

I have been trying some examples such as the following links- CalculiX/test/thermomech.inp at master · Dhondtguido/CalculiX · GitHub
I want to adapt the thermomechanical simulation solve procedure and model it for the 3d printing process. If there are any cases or examples for such it would be greatly helpful.

With 3D printing, do you mean fused deposition modelling (“FDM”)?

In that case you’re dealing with a stream of liquid material that cools and solidifies. CalculiX is not set up to deal with phase transitions.

You could model the geometry of the individual layers as “flattened cilinders” and analyze that as in this example from Prof. Kraska.
BTW, those examples are an excellent learning materials for CalculiX! Highly recommended.

The problem with analyzing such materials is to decide which stress levels will lead to failure. It is well-known that e.g. the adhesion strength of 3D printed layers can vary significantly depending process parameters like the use and temperatures of a heated bead or build volume, local cooling et cetera.

If you search this forum, there are quite a few threads related to AM process simulations. Usually done with *MODEL CHANGE but also discussing other aspects. There’s even this document: https://www.researchgate.net/publication/319617932_Simulation_of_additive_manufacturing_using_Calculix_Procedure_to_calculate_the_temperature_distribution_during_additive_manufacturing

and the previous one from the same author, covering welding simulations.

To be honest, thermal expansion is of least concern in those analyses. Figuring out how to properly simulate the material addition, moving heat flux and other crucial aspects of the AM processes is much worse.

Abaqus has very comprehensive examples in this field but recreating them in CalculiX would be really time-consuming and difficult. Starting from simple cubes is always a good idea.

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