Stresses and Strains in a Wrench

You are viewing the documentation for an older COMSOL version. The latest version is available here.

PDF

Stresses and Strains in a Wrench

This tutorial demonstrates how to set up a simple static structural analysis. The analysis is exemplified on a combination wrench during the application of torque on a bolt.

Despite its simplicity, and the fact that very few engineers would run a structural analysis before trying to turn a bolt, the example provides an excellent overview of structural analysis in COMSOL Multiphysics.

Model Definition

The model geometry is shown below.

The bolt’s fixed constraint is at the cross section shown below. A load is applied at the box end of the combination wrench.

Here, assume that there is perfect contact between the wrench and the bolt. A possible extension is to apply a contact condition between the wrench and the bolt where the friction and the contact pressure determines the position of the contact surface.

COMSOL_Multiphysics/Structural_Mechanics/wrench

Modeling Instructions

From the menu, choose .

In the window, click

.

1

In the window, click

.

2

In the tree, select .

3

4

5

In the tree, select .

6

Import 1 (imp1)

1

In the toolbar, click

.

2

In the window for , locate the section.

3

4

Browse to the model’s Application Libraries folder and double-click the file wrench.mphbin.

5

.

6

button in the toolbar.

1

In the toolbar, click

to open the window.

2

Go to the window.

3

In the tree, select .

4

Click in the window toolbar.

5

In the toolbar, click

to close the window.

Global Definitions

1

In the window, under click .

2

In the window for , locate the section.

3

In the table, enter the following settings:


Name	Expression	Value	Description
F	150[N]	150 N	Applied force

Solid Mechanics (solid)

Fixed Constraint 1

1

In the window, under right-click and choose .

2

button in the toolbar.

3

Select Boundary 35 only.

Boundary Load 1

1

In the toolbar, click

and choose .

2

Select Boundary 111 only.

3

In the window for , locate the section.

4

From the list, choose .

5

Specify the Ftot vector as


0	x
0	y
-F	z

The minus sign means that the force is applied downward.

Use finer mesh because the geometry contains small edges and faces.

1

In the window, under click .

2

In the window for , locate the section.

3

From the list, choose .

4

.

If your computer has more than 4 GB of RAM, you can skip the following four instructions and continue directly to compute the solution. Otherwise, follow these steps to use an iterative solver:

Solution 1 (sol1)

1

In the toolbar, click

.

2

In the window, expand the node.

3

In the window, expand the node.

4

Right-click and choose .

Iterative solvers require less memory but can be less robust than direct solvers.

Compute the solution

In the toolbar, click

.

The default plot group shows the von Mises stress in a plot with the displacement visualized using a subnode. Change to a more suitable unit as follows.

1

In the window, expand the node, then click .

2

In the window for , locate the section.

3

From the list, choose .

4

In the toolbar, click

.

5

button in the toolbar.

First Principal Strain

1

In the window, right-click and choose .

2

In the window for , type First Principal Strain in the text field.

1

In the window, expand the node, then click .

2

In the window for , click in the upper-right corner of the section. From the menu, choose .

3

In the toolbar, click

.

Notice that the maximum principal strain is lower than 2%, a result that satisfies the small strain assumption.