I kindly ask for assistance regarding contact in 2-dimensional simulations.
I am running two-dimensional simulations in ABAQUS 6.13-1 Explicit.
Three axially aligned cylinders, all composed of elements CAX4R (the
outer cylinders) and CAX4RT (the central cylinder), have contact at
their flat interfaces from the very beginning and are compressed along
their common axis by pulse loading. The outer cylinders remain elastic,
the central one is elastic-plastic. It is a simulation for a Split
Hopkinson Pressure Bar in the compression mode.
The surfaces are element-based. Contact for both interfaces is defined
by contact pairs, mechanical constraint=penalty.
The sta-file reports:
***WARNING: Some elements underlying deformable surface
ASSEMBLY_SPECIMENFRONT are referenced by a *CONTACT PAIR option. In
addition These elements have material properties that allow the elements
to fail. For elements that can fail, contact should be defined using the
*CONTACT option. A element set named "WarnElemFailElemInContact"
containing these elements is created to help the user locate the elements.
for both interface pairs.
Result: the simulated transmitted wave (proportional to the stress in
the specimen in the SHPB test) is poor.
I also experimented with node-based surfaces and mixed defintions
(element-based and node-based) and kinematic mechanical constraint, but
to no avail.
See manual, chapter "36.5.1 Defining contact pairs in Abaqus/Explicit":
"Element-based surfaces should not be used in contact pairs if the
underlying elements may fail (see “Dynamic failure models,” Section
23.2.8, for more information). Use general contact (“Defining general
contact interactions in Abaqus/Explicit,” Section 36.4.1) or node-based
surfaces (“Node-based surface definition,” Section 2.3.3) in such cases."
I am completely lost here. The manual states:
User's Guide chapter 36.4.1 Defining general contact interactions in
Abaqus/Explicit: "Abaqus/Explicit provides two algorithms for modeling
contact and interaction problems: the general contact algorithm and the
contact pair algorithm. The general contact algorithm in Abaqus/Explicit
... can be used only with three-dimensional surfaces"
and 'contact pair' produces the above warning. How can this inherent
contradiction be solved ?
Is there a more appropriate method to define contact in two-dimensional
simulations in Abaqus/Explicit ?
Also in chapter "36.5.1 Defining contact pairs in Abaqus/Explicit": "The
surface normals of a surface must point toward the other surface that it
may contact except when the surface is double-sided, as discussed below."
How can I define a surface normal ? To the best of my knowledge, the
element faces are firmly identified in the section on "Node ordering and
face numbering on elements" for the elements in the model.
My three-dimensional simulations achieve a perfect match to theory.
Thank you for sharing your kind expertise
This is not really a solution to the conundrum, but may still help: In such situations, I always revert to a 3D simulation with one element in the z-direction and appropriately defined boundary conditions in that direction. This the allows to use generalized contact and works well for models with failure (I used it for machining simulations).
In reply to this post by Abaqus Users mailing list
Try to switch to Abaqus/Standard and define general contact there. General contact is not available in Abaqus/Explicit for 2-D and axisymmetric elements. Another option would be to take the equivalent 3D model where general contact can be defined in Abaqus/Explicit.
a "Split Hopkinson Pressure Bar" is a testing machine for dynamic tests. Thus, I am obliged to use Abaqus/Explicit. As stated in my original posting, my "three-dimensional simulations achieve a perfect match to theory."
I got a hint stating that Simulia had discontinued the contact modeling in 2d. Can that be true ? The problem is so fundamental, it is hard to believe.
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