Contact mechanics is the analysis of stresses and strains arising in interacting parts. When two parts come in contact, equal and opposite forces due to the contact are generated on the opposing surfaces. These forces can be split into components in the normal and tangential directions. The normal component arises due to the non-penetration condition, and the tangential component arises from friction between the surfaces.
To model contact, OnScale Solve uses different algorithms depending on the situation. For bonded contact, a multi-point constraint method is used that exactly constrains one surface to another. For contact where separation is allowed, Solve uses the penalty method, where the contact is treated similar to a stiff spring between points on the interacting surfaces. The spring applies a restoring force that resists the penetration. This is a stable method that accurately represents contact in complex interactions. While this method doesn’t enforce an exactly zero penetration, the stiffness is chosen large enough to reduce the final penetration to very close to zero.
Contact can be enabled in Static simulations in OnScale Solve. Solve automatically solves the nonlinear simulation and provides the final static solution.
OnScale Solve users can either manually assign contact between parts or faces or use the automated contact detection tool known as General Contact.
After uploading the CAD model, users are prompted to select the initial contact type between parts. Two options are available: Bonded and Unbonded.
- Bonded Initial Contact will create a continuous mesh throughout the geometry and coincident faces will be joined together. No slip, separation, or penetration will be allowed. This option is recommended if the geometry has several coincident surfaces that should be represented as bonded. However, if the bonded surfaces have high curvature, the mesher may not be able to create a continuous mesh at the interface. In this case, it is better to select ‘Unbonded’ and create individual surface pair bonds as described below. If `Bonded` Initial Contact is chosen, individual surface pairs can also be unbonded using Individual Contact Interactions.
This Initial Contact setting can also be changed by going to the Toolbar,Select Physics > Global Settings > Select Unbonded > Click Done.
- Unbonded Initial Contact causes parts to be meshed separately with discontinuous interfaces between them. Surfaces that are initially coincident should be specified as unbonded if it is intended that they will separate or slide relative to each other during the simulation. It’s recommended to select this option and enable General Contact if the simulation requires separating contact between initially coincident surfaces. Exceptions to this setting can be made by creating Individual Contact Interactions with Bonded settings.
This Initial Contact setting can be changed anytime by going to the Toolbar, Select Physics > Global Settings> Select Bonded> Click Done.
To enable General Contact. Go to the Toolbar, Select Physics > Global Settings > Turn on General Contact > Click Done.
Enabling the General Contact option will:
- automatically detect the interaction between different surfaces during the simulation,
- automatically assign contact settings such as contact stiffness based on the material properties and the mesh,
- automatically enforce no penetration between all interacting surfaces
Individual Contact Interactions
Contact interaction between any set of surfaces can be also set up manually. To do so, go to the Toolbar, select Modeler, choose the Interaction icon , select the type and sides of the contact. Each side of the contact interaction needs to be defined by specifying the surfaces on Side A (Guide side) and Side B (Follower side).