Stress Analysis Contacts
Caulk Gun Animation
View animated component displacements from the caulk gun simulation.
In this Skill Builder, explore how to use contacts to simulate interactions between assembly components in Inventor 2010 Stress Analysis.
Expected completion time: 45 minutes
Use with: Inventor Simulation 2010 or Inventor Professional 2010
We recommend that you familiarize yourself with the Stress Analysis environment by performing the FEA tutorials.
In the structural analysis of an assembly involving multiple parts, you create contacts to define the relationship between the parts. Contacts transfer load between parts while preventing parts from penetrating each other. Contacts can simulate interaction between bodies that separate or come into contact during loading. Without contacts, parts do not interact with each other in the simulation.
There are several different contact types you can use to simulate the physical behavior of an assembly. This skill builder presents an assembly modeled with many of the types of contact available in Inventor 2010 Stress Analysis. The contacts have already been created, either automatically or manually, in the model.
Open the Assembly
A model of a caulk gun illustrates different contact types and how to use them in a static, structural analysis.
- Download caulk_gun.zip and extract all files.
- In Inventor, navigate to Caulk Gun.ipj and make it your active project.
- Open Caulk Gun.iam.
How a Caulk Gun Works
We considered the following mechanics of the caulk gun when creating the simulation.
- User holds the handle  and pulls back on the trigger .
- The pin end of the trigger  pushes the actuator  forward.
- The actuator tightly engages the plunger  and pushes it forward.
- The plunger head  pushes the caulk tube bottom.
- The tube is held in place by a ring  at the end of the caulk gun.
The caulk gun is an assembly which consists of several parts, some of which can move. Several operational scenarios can exist for the caulk gun, but we chose to simulate the assembly in a static equilibrium state.
This simulation investigates when the trigger is pulled and the pushing force on the bottom of the caulk tube is about to overcome the internal tube resistance. At this instant, just before caulk exits the tube, the assembly is in static equilibrium.
To enter the Stress Analysis environment:
- On the ribbon, click the Environments tab.
- On the Environments tab, Begin panel, click Stress Analysis. Stress Analysis commands populate the ribbon.
Expand Caulk Gun.iam in the Stress Analysis browser. Note that we exclude the following components from the simulation:
- Caulk Tube 
- Actuator Spring  (not modeled, but simulated with Spring contact)
- Lock Spring 
- Lock 
Inventor Stress Analysis provides the following Contact types:
- Sliding / No Separation
- Separation / No Sliding
- Shrink Fit / Sliding
- Shrink Fit / No Sliding
In the Stress Analysis browser, expand the Contacts node to view the contact types currently in use for the caulk gun simulation. As you create or edit contacts, they are added under existing contact type nodes or to newly created nodes.
In the browser, right-click a contact and select Edit Contact. The Edit Automatic Contact or Edit Manual Contact dialog box displays and shows the available contact types:
The following sections detail each type of contact used in the analysis of the caulk gun assembly.
The Bonded contact simulates rigid bonding of faces to each other. Typical Bonded contacts include weld or glue joints between two parts.
In the model, the Front Frame-Main Frame and the Front Frame-Handle interfaces are weld joints, as shown in the following image. You use Bonded contacts to simulate these joints in the simulation.
The Separation contact allows separation between parts but prohibits part penetration.
In the model, the pin end of the trigger contacts the actuator. When you pull the trigger, the pin end of the trigger pushes the actuator forward. When the trigger is released, the pin end and the actuator can separate. Since the pin end cannot penetrate the actuator and separation can occur between the parts, the contact relationship is simulated with the Separation contact.
Sliding/No Separation Contact
The Sliding/No Separation contact allows relative sliding between contact faces, but prohibits separation.
Sliding/No Separation can occur between planar faces like the Trigger-Handle interface.
It can also occur between circular faces such as the Pin-Handle and Pin-Trigger interfaces.
Separation/No Sliding Contact
The Separation/No Sliding contact allows contact faces to separate, but prohibits relative sliding when they touch.
For the Actuator-Plunger interface, the Separation/No Sliding contact is appropriate. When the trigger is pulled, the actuator is pushed forward. This results in separation between the top surface of the plunger and the actuator. At the same time, engagement occurs between the bottom surface of the plunger and the actuator. It is reasonable to assume that the engagement/separation occurs without slippage between the actuator and plunger.
In the following image, note that the surfaces of the plunger and actuator are split into multiple faces. In this manner, the contact surfaces are more explicitly defined.
Shrink Fit/No Sliding Contact
The Shrink Fit/No Sliding contact simulates conditions like Separation/No Sliding with the parts in an initial state of interference.
The model has a ring that tightly fits the front frame and prevents the caulk tube from exiting the caulk gun when the plunger moves forward. The front face of the ring registers against the front frame without penetration. Therefore, this interface is simulated with the Separation contact.
The outer diameter of the ring has an interference fit with the front frame. The ring is press fit into the frame so that it remains in position without a caulk tube in place. This press fit allows the operator to push the ring out easily and replace it with a different size, as appropriate. The outer diameter of the ring and the front frame can separate without sliding. Since they are initially in a state of interference, the Shrink Fit/No Sliding contact is appropriate.
The Spring contact simulates conditions of a spring between two faces.
In the model, the actuator spring is simulated using a Spring contact. The use of the Spring contact eliminates complexities associated with modeling the physical spring part.
Loads and Constraints
With the contacts defined, let’s proceed further with the model analysis.
To use the caulk gun, you hold the handle and pull the trigger. From the static analysis point of view, the components are under force and deform before the plunger head moves the bottom of the tube. We can reasonably assume that the components deform relative to the main frame. As such, we can apply a:
- Fixed constraint on the main frame edge 
- Force on the handle 
- Force on the trigger 
- Force on the plunger head 
- Force on the ring 
The tube is held in place by the front frame, ring, and plunger head. When the force from plunger head is large enough, the bottom of the tube moves further into the tube and pushes caulk out of the nozzle. For the static analysis, we simulate the instant at which the force on the tube bottom is in equilibrium with the tube resistance. At this point, just prior to the tube bottom moving, we examine the stress and deformation of the whole structure and components.
- On the Stress Analysis tab, Solve panel, click Simulate.
- On the Simulate dialog box, click Run to begin the simulation.
The Simulate dialog box remains open, displaying the progress bar, until the computation is complete.
When the simulation finishes, a deformation plot of the model is shown in the graphics window. The Von Mises Stress results are also displayed using the default color bar settings. On the Display panel, click Show Max Value to view the maximum stress and its location.
The maximum Von Mises Stress of approximately 278 MPa occurs on the Pin. To view the location of maximum stress, turn off the visibility of all parts except the Pin.
As this stress is greater than the Pin material (steel) yield strength of 207 MPa, the analysis indicates the Pin will yield. To meet strength criteria, you modify the design or change the Pin material.
To investigate design workflows further using Inventor Stress Analysis, refer to other Help documents and tutorials included with Inventor. You can also find additional Skill Builders online.
In this Skill Builder, the model is intended to illustrate the contact types and their application. Some contact areas such as the Plunger-Actuator interface are very small. Take care when providing spring stiffness and force values as the displacement and stress results are sensitive to parameter values. Also note that some parts may have areas of large deformation, which are better suited to a non-linear analysis.