## Structural Mechanics Tutorials: Adding Initial Strain and Thermal Stress

##### Andrew Griesmer April 4, 2013

Back in January, I presented a video tutorial introducing the Structural Mechanics Module here on the blog. The video described the steps necessary to perform a static linear analysis on a bracket geometry. Now, to help you better understand the extra functionalities that exist within COMSOL Multiphysics and the Structural Mechanics Module, we are also creating additional tutorial videos of this bracket. The first two “mini-tutorials” to accompany the static linear analysis video focus on adding initial strain and thermal stress, and you can watch them here.

### Including Initial Strain in a Structural Mechanics Model

In real-life situations the conditions are rarely perfect and certain measures need to be taken to account for varying circumstances. One of these unforeseen circumstances is a strain in the geometry, before an outside force is applied. For this example, an initial strain is added, simulating a reduction in pin length from 216 mm to 215 mm. The resulting von Mises stresses are calculated, and the initial strain in the x-direction can be seen.

### Modeling Thermal Expansion in a Structural Mechanics Model

Heat transfer is another circumstance that can affect a structural model. That is why the Structural Mechanics Module includes a *Thermal Stress* interface to model structural interactions resulting from heat transfer. The interface contains all the options that exist in the *Solid Mechanics* and *Heat Transfer* interfaces. In this video, the bracket arm holes are heated to 100 degrees Celsius, as if it was holding a structure at this temperature, and the resulting structural deformations are calculated and shown.

### Structural Mechanics Tutorial Video Series

With both of these examples, the boundary load from the original static linear analysis is disregarded for simplicity. However, these two tutorials are paired together because they are not replacement models to the static linear analysis, but they can be *added* to the static linear analysis. You can start with a static linear analysis and then add either initial strain or thermal stress, or you could add both. We gave you the means, now it’s up to you to put all the pieces together.

Here’s a sneak peek at upcoming mini-tutorial videos in this series:

- Adding a Rigid Connector
- Adding Spring Conditions
- Modeling with the Shell Physics Interface
- Transient Analysis
- Eigenfrequency Analysis
- Prestressed Eigenfrequency Analysis
- Frequency Response Analysis
- Prestressed Frequency Response Analysis
- A Geometric Non-linear Problem: Linear Buckling Modeling
- Material Non-linearity: Elasto-plastic Material
- Modeling Contact Problems

We will continue to create structural mechanics videos over the next few weeks, but in the meantime you can find the complete model documentation for all of the analyses at www.comsol.com/bracket.

## Comments

KAI RENNovember 16, 2017 1:49 amDear Griesmer,

I have a question about transferring strain fields between two different mph files. Is there a method to transfer strain field in different mph files (when thermal strain, plastic strain are involved), so the later mph file can utilize the result of the former mph file as initial value?

As there exists “initial strain and stress” tag, I wonder how to add initial plastic strain and thermal strain to let comsol distinguish constitution of different strains.

Many thanks,

Kai