• Bonded—There is no separation or sliding allowed between references that are in contact. Bonded contacts have zero degrees of freedom between interfacing components and can be considered as glued together. Bonded components do not separate from each other during a simulation study. This type of contact allows for a linear solution since the contact length or area does not change during the application of the load.

• No Separation—Similar to bonded contacts, separation of the references in contact is not allowed during a simulation study. However small amounts of frictionless sliding can occur along references in contact.

• Free—The connected components or surfaces may move freely relative to each other. The components may separate from each other or even interpenetrate each other. The applied forces do not transfer between the connected components or surfaces.

• Frictionless—This setting models standard unilateral contact; that is, normal pressure equals zero if separation occurs. Thus gaps can form in the model between bodies depending on the loading. This is a nonlinear case, because the area of contact may change as the load is applied. This option assumes a zero coefficient of friction allowing free sliding. The model should be well constrained when using this contact setting.

• Frictional—In this setting, the two contacting geometries can carry shear stresses up to a certain magnitude across their interface before they start sliding relative to each other. The model defines an equivalent shear stress at which sliding on the geometry begins as a fraction of the contact pressure. Once the shear stress is exceeded, the two geometries will slide relative to each other. The coefficient of friction can be any non-negative value.

• Rough—This setting models perfectly rough frictional contact where there is no sliding between edges or surfaces. By default, no automatic closing of gaps is performed. This case corresponds to an infinite coefficient of friction between the contacting bodies.

• Coefficient of friction—The coefficient of friction is a dimensionless number that is defined as the ratio between frictional force and normal force for two regions in contact. The value can be any non-negative number that is greater than zero and less than infinity.

• Formulation—This option allow you to specify which algorithm the software uses for a particular contact pair computation. The following types of formulation are provided:

◦ Program controlled—This is the default and recommended formulation.

◦ Augmented Lagrange—Also a penalty-based method. Compared to the Pure penalty method, this method usually leads to better conditioning and is less sensitive to the magnitude of the contact stiffness coefficient. However, in some analyses, the Augmented Lagrange method may require additional iterations, especially if the deformed mesh becomes too distorted

◦ Pure penalty—Basic contact formulation based on Penalty method.

◦ Multi-point constraint—Available for Bonded and for No Separation contact behavior types. Multi-point constraint equations are created internally to tie the bodies together. This can be helpful if truly linear contact is desired or to handle the nonzero mode issue for free vibration that can occur if a penalty function is used. Note that contact based results (such as pressure) will be zero.

◦ Normal Lagrange—Enforces zero penetration when contact is closed, making use of a Lagrange multiplier on the normal direction and a penalty method in the tangential direction. Normal stiffness is not applicable for this setting. Normal Lagrange adds contact traction to the model as additional degrees of freedom and requires additional iterations to stabilize contact conditions. It often increases the computational cost compared to the Augmented Lagrange setting.

• Contact Detection—Selecting the contact detection method enables you to choose the location of contact detection used in the analysis in order to obtain a good convergence. Select one of the following contact detection methods:

◦ Program Controlled—This is the default and recommended mechanism for detecting contacts.

◦ Contact detection radius—Enables contact within the region defined by the specified radius value. This is similar to the Tolerance setting. The default value for the detection radius is 1.0.

◦ Detection radius factor—Multiplies the automatically calculated contact detection radius by a fixed value that you specify in the Value box.

• Modeling Gaps and Overlaps—For the nonlinear contact types—frictional, frictionless, and rough you can also model gaps, and more accurately model the area in contact. You can specify the following additional options:

◦ Adjust gap/overlap—Select one of the following methods of modeling gaps or overlapping geometry:

▪ Program controlled—This is the default mechanism where the software determines the method to be used to handle gaps and overlapping geometry.

▪ Fix unintentional gaps/overlap—Closes unintentional gaps and ignores interference between surfaces in contact to simulate a stress-free state.

▪ Define offset value—Specifies a value by which to move the surfaces in contact. The value must be a real number. A positive value means that a contact surface is moved towards the target surface in order to close a gap. A negative value means that the contact surface is moved away from the target surface to resolve an overlap. In both cases stresses due to offset movement are simulated in related components.

◦ Stiffness factor—Normal stiffness factor. Multiplies the auto-calculated stiffness factor by the constant value specified here. Available for the nonlinear contact types—frictional, frictionless, and rough.