One of the many misunderstood elements of correctly setting up a SOLIDWORKS Motion Simulation study is the definition of solid body contacts. We see and experience contact conditions every day and don’t give them a second thought. When it comes to translating that wealth of experience into a computer model, many SOLIDWORKS Motion users initially get it wrong. Hopefully these next few paragraphs will demystify SOLIDWORKS Motion contacts.
The first scenario is quite simple and even new SOLIDWORKS Motion users get this one correct. When inserting a 3D Contact into the study, only two bodies are selected. Take a look at the screen capture of the SOLIDWORKS Motion Contacts Property Manager. In this scenario, the first selection effectively becomes ‘Set 1’ and the second selection becomes ‘Set 2’. To SOLIDWORKS Motion, the ‘Material 1’ definition applies to the first body while the ‘Material 2’ definition applies to the second body. Since only one contact between the two selected bodies can occur, this is a simple element to set up. In the picture the wheel (first selection) assumes the properties of dry rubber while the ground (second selection) is analyzed as dry steel.
The second scenario is slightly more complex. Here there are more than two unique assembly components selected for the 3D Contact. When the body selection includes more than two selections, there is an assumed potential contact between each selected component. As far as SOLIDWORKS Motion is concerned, whether or not they could come into contact with one another is irrelevant. In the picture I selected the four wheels followed by the ground. Each wheel is mated to the axle of the vehicle with a hinge mate. It is not possible that any of the four tires will ever come into contact with one another using this mate scheme. SOLIDWORKS Motion, however, indicates that ten possible contact conditions could occur. The material definitions for both Set 1 and 2, though different, would not be correctly applied to the tires or ground. Fortunately there is a way to correctly set up this 3D contact.
The correct SOLIDWORKS Motion setup for a 3D Contact between multiple components is to select the option ‘Use contact groups’. By utilizing this option, all four of the tires can be selected as ‘Group 1 Components’ while the ground will be the only selection for ‘Group 2 Components’. Notice that SOLIDWORKS Motion correctly reports that there are four contact pairs with this 3D contact definition. Using the contact groups option there are no contacts calculated between the bodies in each group. The only contacts that are calculated are between the body selections for each contact set. Also, the ‘Material 1’ and ‘Material 2’ definition will be correctly assigned.
The next time you are setting up a SOLIDWORKS Motion study, you will have confidence that the 3D contacts definition is correct. Now go make your products better with SOLIDWORKS Simulation!