When performing contact-based nonlinear analysis using ANSYS, contact regions and target regions are typically defined to implement contact analysis. Through contact definition, it is ensured that the two bodies will not penetrate each other during subsequent analysis.
According to the relative behavior between the two bodies, ANSYS currently defines five contact types:
Bonded Contact: The contact surfaces are bonded together, no separation, no sliding.
No Separation Contact: Allows frictionless sliding, but no separation.
Frictionless Contact: Allows separation and sliding with no resistance (friction coefficient = 0).
Rough Contact: Allows separation, but sliding is not permitted.
Frictional Contact: Allows separation and sliding with friction. Users can define the friction coefficient.
Among the above five types, frictional contact can be considered the most realistic representation of actual object contact, while bonded contact is the easiest type to simulate and calculate. This leads to bonded contact being overused in certain situations, resulting in seemingly correct but actually incorrect simulation conclusions.
To illustrate the impact of contact type on simulation results, Shuige will use a simple case study below. The case details are as follows:
1. Rectangular plate with a hole in the middle
2. A pin inserted into the hole with some clearance
3. Small displacement applied at one end of the plate
4. The pin end is fixed
The simulation objective is to evaluate the stress intensity of the plate behind the pin, ensuring it remains below 100 MPa.
The model schematic is shown below:
Calculations are performed using bonded contact and frictional contact respectively. The results are as follows:
1. Results Using Bonded Contact
When defining bonded contact, the hole surface and pin surface have no sliding or separation. The stress on the plate behind the pin is mostly below 100 MPa, as shown in the stress intensity contour plot below.
But is this really the case? Shuige believes that using bonded contact underestimates the horizontal shear force, so let’s try switching to frictional contact.
2. Results Using Frictional Contact
With a friction coefficient of 0.2, considering frictional contact, the hole surface and pin surface will produce mutual sliding. The stress intensity contour plot is shown below:
From the contour plot, it can be seen that the stress on the plate behind the pin is significantly higher than in the bonded contact case. The pin and plate show extrusion and separation, reflecting the real situation. Shuige believes the horizontal shear force can be accurately estimated at this point.
Conclusions
From the calculation results of the two different contact types above:
1. Different contact types can result in vastly different results, especially in very sensitive ranges involving limit regions.
2. Finite element software simulation results are only a response to the current model input. Having calculation results does not mean the simulation is error-free.
3. Building finite element models is very important. This includes boundary conditions, load application, connection methods, etc. A reasonable finite element model is the prerequisite for ensuring reliable simulation results!
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