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In FEA, accurately defining the interaction between components is essential for realistic simulations. Contact properties are one of the aspects of how objects interact under loading; contact formulation (e.g., penalty method, augmented Lagrange, direct constraint) and solver parameters also significantly influence the results
Contact properties are one of the aspects of how objects interact under loading; contact formulation (e.g., penalty method, augmented Lagrange, direct constraint) and solver parameters also significantly influence the results
Among these, two primary interaction types are contact and glued connections. Understanding their differences is crucial where engineers need to know the behavior of objects interacting together with contact.
This article explores the fundamental characteristics of contact and glued connections, their applications, and key considerations for selecting the appropriate method in FEA simulations.
For more on this topic, see Contact conditions in FEA.
What Are Contact vs. Glued Connections in FEA?
In FEA, how two components are connected can significantly affect the accuracy and stability of your simulation. This is where the concept of connections—also known as contact definitions—comes into play. Broadly speaking, these fall into two main categories: contact connections vs. glued connections involving linear and non-linear behavior. Each behaves differently and is suited for specific types of engineering problems.
Linear vs. Nonlinear Contact
In linear contact:
- Material behavior is assumed to be linear elastic.
- The stiffness matrix is not updated during the solution (i.e., no geometric or material nonlinearity).
- It is suitable for stiff materials like steel or aluminum under small deformations, where the structure doesn’t yield, buckle, or change significantly in geometry.
A classic example is a steel punch pressing against a rigid surface. If stresses stay below the yield point, the behavior remains nearly linear, and linear contact can be a reasonable simplification. This can drastically reduce computation time and avoid convergence issues in FEA software.
Nonlinear contact is necessary when:
- Large deformations occur,
- Materials yield or exhibit plasticity,
- Contact conditions change drastically during the simulation (e.g., surfaces separating or engaging).
Contact Connections
Contact connections simulate physical interfaces where surfaces may come into and out of contact during loading. They can capture a range of real-world interface phenomena, including:
- Sliding (tangential movement),
- Separation (surfaces pulling apart),
- Frictional effects (resistance to sliding),
FEA solvers support various contact formulations to accommodate engineering requirements:
- Frictionless contact allows sliding without resistance.
- Frictional contact accounts for resistance due to friction.
- No-separation contact allows sliding but prevents the surfaces from pulling apart.
See how friction and load transfer work in joint design and analysis.
These interaction types are essential in mechanical systems where relative motion, load transfer through contact, or potential detachment may occur, such as in bearings, gears, bolted joints, and press-fit components.
Glued Connections
Glued connections (often called bonded contact) assume the connected surfaces are permanently fixed—no separation, no sliding, no relative motion. From a mathematical point of view, these are simpler than contact interactions because they don’t require detection or enforcement of contact conditions at each load step.
Glued interactions are ideal when simulating:
- Welded joints
- Adhesively bonded components
- Monolithic parts meshed with different element regions
- Tied or bonded contact prevents separation and sliding, keeping the surfaces effectively tied together.
Glue-type springs in FEA simulate adhesive joints by representing the bond as springs with defined stiffness, allowing some elastic flexibility and limited relative movement between parts. This models the behavior of glued interfaces more realistically than fully rigid bonds.
Glued connections can be used when you do not have any sliding and you do not expect any separation, for example where you have only compression force which is ‘closing’ the contact.
Weld connections represent permanent, rigid joints where parts are fused together, preventing any relative motion or separation. In FEA, welds are typically modeled as glued (bonded) contacts, making the connected components behave as a single solid piece.
For implementation tips, see modeling welded joints in FEA.
They simplify modeling and analysis, reduce solution time, and are stable even in complex models. However, using glued interactions inappropriately—such as in a bolted assembly where parts should move—can result in non-physical behavior and misleading stress results.
Also, in mechanical assemblies, all contacts between components can occur through various types of interactions, including surface-to-surface, surface-to-edge, edge-to-edge, and vertex-to-surface contacts, as illustrated in the figure below.
(source)
Key Differences Between Contact and Glued Connections
| Feature | Contact Connections | Glued Connections |
| Separation | Can separate under force | No separation allowed |
| Sliding | Allows relative motion | No relative motion |
| Stress Transfer | Dependent on contact area | Full load transfer |
| Computational Cost | Higher | Lower |
| Application | Bolted joints, friction interfaces | Welds, bonded materials |
Implementing Contact Properties in FEA Software
Structural design and analysis software, such as SDC Verifier, provides robust tools for setting up and managing contact properties in FEA models.
In SDC Verifier, contacts can be applied either directly to the geometry or within the finite element model, providing flexibility in how interactions between components are defined and simulated. Setting up contact conditions involves managing three key entities: Contact Properties, Contact Regions, and Connectors.
Contact Properties define the behavior of the contact interface and are created via Model > Contacts > Contact Properties > Add. Within the contact properties, users specify the type of interaction, which can be either Contact (Regular) or Glued. Regular contact allows for sliding, separation, and frictional behavior, while glued contact assumes a permanent bond without relative motion.
Key parameters for contact properties include:
- Friction coefficient: Defines static friction for contact pairs; uniform friction values are recommended for consistency.
- Search distances: Minimum and maximum search distances govern how the solver detects potential contacts, with negative values enabling modeling of interference fits where surfaces overlap.
- Iteration controls: Maximum force and status iterations, alongside convergence tolerances, regulate the numerical solution’s accuracy and stability.
- Initial penetration handling: Options to handle gaps or penetrations at the start of analysis, influencing how the model simulates press-fit or perfect initial contact conditions.
These features are useful in press-fit and interference modeling using SDC Verifier’s automation.
- Shell offset and z-offset: Control whether shell thickness and element offsets are included in contact calculations.
For glued connections, additional parameters govern the glue formulation, which can be:
- Spring-type glue, modeling adhesive bonds via spring connectors allowing limited elastic flexibility.
- Weld-type glue, representing rigid, weld-like joints with no relative motion.
Penalty factors determine the stiffness of contact or glue elements, with automatic scaling options available to improve convergence.
Contact Regions define the physical segments where contact or glued interactions occur. These regions can be assigned to deformable or rigid bodies and are created by selecting entities such as elements, nodes, surfaces, or curves (Model > Contacts > Contact Regions > Add). The regions control which surfaces or edges are involved in the interaction and support options for offset adjustments and output definitions.
Learn more about defining contact regions in SDC Verifier.
In case of surfaces, it is important to choose correct surface side which may be in contact.
Finally, Connectors establish the link between source and target contact regions using defined contact properties (Model > Contacts > Connectors > Add). This step enables the solver to apply the specified contact or glued conditions between the designated surfaces or bodies.
When to Use Contact vs. Glued Connections
Use Contact Connections When:
- Simulating bolted, riveted, or press-fitted joints.
- Modeling interactions where parts may detach or slide.
- Contact models stress discontinuities.
- Evaluating frictional effects between components.
- Investigating wear and fatigue behavior in moving parts.
Use Glued Connections When:
- Modeling welded, adhesive-bonded, or composite joints.
- Simulating rigid or semi-rigid connections.
- Glued connections assume stress continuity.
- Reducing computational effort in large models.
- Ensuring full load transfer between components.
Also, mesh quality plays a critical role in contact behavior and solver performance.
Conclusion
Selecting the appropriate connection type is essential for obtaining accurate and efficient structural analysis results. Contact connections are best for modeling interfaces with potential separation or sliding, while glued connections are ideal for rigid bonding. Engineers should consider the mechanical behavior, computational cost, and practical application when choosing between these methods in finite element simulations.
