In this course, we discussed the different methods of connecting parts together for predicting accurate results of stress analysis. Let’s summarize the key points from each lesson.
Connecting Parts of an Assembly Together:
- It is important to connect different parts of an assembly to capture their correct behavior with respect to each other.
- The two common methods for connecting parts are shared topology and contacts.
- Shared topology is a functionality available within Ansys SpaceClaim that helps to connect parts by sharing mesh nodes at the common interfaces.
- Contacts is a functionality available within Ansys Mechanical that helps to connect parts with the help of contact region without sharing the mesh nodes.
- It is recommended to use shared topology for connecting parts if they are mostly “bonded” or “welded” with each other.
- It is recommended to use contacts for connecting parts if one of them is not of interest but is present to provide appropriate load path. This type of connection provides flexibility of meshing parts not of interest with coarser mesh without significantly increasing the mesh count of the model.
- If the connecting parts are expected to separate or slide with respect to each other, contact should be used for connecting such parts.
Understanding Basics of Contact:
- There are different types of contact and contact formulations available in Ansys Mechanical for connecting parts.
- By default, contact is detected based on the proximity and orientation of the faces.
- Although the Auto Contact Detection feature is more efficient in creating contacts automatically, such contacts should be checked to ensure that the connections are valid and identify any contact that are created in unintended areas.
- The Contact tool can be used for initial contact solution and postprocessing contact results.
- A force reaction probe can be scoped to the contact region for calculating the force reaction in a contact region.
Checking Initial Contact Conditions Prior to Solving:
- Improperly defined initial contacts can result in rigid body motions.
- Improper initial contact setup can lead to a singular matrix that cannot be solved in a static analysis.
- Since initial contact information is dependent on mesh, altering the mesh to capture important features of the geometry can also alter the initial contact information.
- It is important to have a good understanding of the initial contact for building a correct loading path and help prevent rigid body motion.
- There are several ways to avoid rigid body motion for contacts like revising the geometry, or numerically treating the contacts using various interface treatment options.
Utilizing Remote Points Properly:
- Remote points can be utilized to simplify the kinematics of certain portions of the geometry.
- Remote points have six degrees of freedom – three translations and three rotations.
- Remote points can have deformable or rigid behavior. Rigid behavior is generally used when the entity whose kinematics are being approximated by the remote point are very stiff compared to the part of interest. Deformable behavior is used when the entity being represented by the remote point has much less stiffness when compared to the modeled geometry.
- The region of two remote boundary conditions should not overlap, or that could over-constrain the problem. Instead, it is better to promote the remote point and reuse it in multiple remote boundary conditions.
- Care should be taken while using remote boundary conditions. It is a good practice to visually confirm the location of the remote point where the load is being applied.
Creating Kinematic Constraints Between Parts:
- Kinematic behavior between parts can be captured using simplified connections like springs, beam connections, and joints without modeling the detailed interaction via contact elements.
- Spring connections represent parts whose stiffness predominately acts along the length, such as helical springs.
- The beam connections are often used to represent fasteners or other parts with axial and bending stiffness. Pretension loads can also be applied to a beam connection.
- The joint connections are used to define kinematic constraints between parts, and there are a variety of joint types for different purposes.
- Unlike Contact which provides a comprehensive simulation without any simplification or limitations on the degrees of freedom, these connections need significantly less computing effort than Contact but simplify the representation of the connection.