Contacts and Constraints

While we introduce new functionalities in Abaqus 2019 in contacts and constraints like we have done for other functionalities in similar blogs, I would retrospect into 2018 and clarify an important point: what’s the difference between FD and FP (hot fix). Believe it or not, they are not the same and the table below clarifies it for 2018 release.

Now let’s look at enhancements

• One of the biggest enhancement in contact is that 2D and axisymmetric models are now supported in general contact for explicit. This general contact capability was already available in standard. This has been done on many customer requests in the past. Please note that 3DX platform does not support 2D axisymmetric models yet.

• Another major enhancement is that analytical rigid surfaces are now supported in general contact for standard. This capability was already available in explicit general contact. Most common benefit of analytical rigid surface is precise geometrical data of simple surfaces.

• Threaded interface approximation has undergone correction to include effects of right handed or left handed threads. This is an enhancement to existing capability in *clearance, bolt keyword entry. The image below shows the effect of thread direction on contact normal.

Further enhancements have been made to differentiate between one way and two-way threads. A two-way thread can resist both tension as well as compression unlike one way thread.

• Another major enhancement is the introduction of general contact in pure heat transfer as well as coupled thermal-electrical step. Moreover, general contacts defined in any one of these steps can be carried forward and used in subsequent steps such as general static.
• New Output Variable: CEDGEACTIVE: Dynamic feature edge criteria. It is now possible to visualize active feature edges at any stage of the simulation. This can be of great use in explicit analysis for applications such as air bag deployment.

CSLIPEQ: Relative equivalent tangential slip while in contact. It was present in explicit but now has been introduced in standard as well.

CSLIP_PL: Introduced to quantify plastic slip when shear stress exceeds critical frictional stress.

CICPS: Integral of contact pressure over the surface. It is different from CFN because normal direction is not considered.

Perhaps key differentiator is the situation below in which CFN output is zero due to symmetry but CICPS has a finite value.

• Moment correction due to shell offset: When shell offset is defined, nodes shift from shell midplane and so does any forces acting on shell edge thereby creating a false moment about the midplane. This affect has been corrected by introducing a counter moment at the nodal force location so that effective location of edge force is at the shell midplane.

• Deprecate old contact controls: Changes in certain contact controls by user will now result in fatal error by default. These controls are approach, automatic tolerances, Lagrange Multiplier etc. It has been observed that changes in such controls often results in performance degradation. In earlier releases only warning messages were issued that users have tendency to ignore. The default settings can be changed by the user.

• Initial contact stress: The initial contact stress is now equal to stress of underlying elements instead of being zero. This now obviates the use of penetrations and sliding to generate contact stresses. The feature can be of much use in geotechnical applications.

• FRIC_COEF enhancement: This subroutine has been enhanced to pass user defined, solution dependent state variables. Now coefficient of friction can be defined as a function of user defined state variable. GETVRC utility routine can be accessed from within FRIC_COEF to access various state variables to define friction coefficient.