OS-E: 0135 Contacts and Pretensioning of Bolts

Nonlinear Static analysis involving contacts and pretensed bolts is demonstrated.

Figure 1. FE Model, Along with the Load Application from all Three Subcases


Model Files

Before you begin, copy the file(s) used in this example to your working directory.

Model Description

The model mimics a typical bolt pretension scenario in powertrain applications which could be followed by duty cycle loads.

The operational loading involves three steps (or subcases). In the first subcase, a pretensioning force of 5.0E+3 N is applied on both bolts that are connected to the flange. In the second subcase, a force of 1081.66 N (600 N in X, 900 N in Z) is applied on the dependent node of the RBE3 distributing the load to the ring attached to the flanges. In the third subcase, a force of 8652.3 N (5850 N in X, -6375 N in Z) is applied on the dependent node of the other RBE3.
Case 1
Nonlinear Static Analysis
Bolt pretension
Case 2
Nonlinear Static Analysis
Bearing (LOAD) as continuation load after (CNTNLSUB) pretension (STATSUB(PRETENS))
Case 3
Nonlinear Static Analysis
Bearing (LOAD) as continuation load after (CNTNLSUB) pretension (STATSUB(PRETENS))
FE Model
Bolts and Ring
CHEXA
Flange
CTETRA

Subcase 2 and 3 are both continued from the pretension subcase using the CNTNLSUB card.

The non-linearity in this model is introduced by the contact definitions between the various components.
Contact Type 1
Friction Contact
Static Friction Coefficient = 0.3
Components Involved
Top and Bottom: Top and Bolt
Contact Type 2
PCONT Contact
Static Friction Coefficient = 0.3
Clearance = -0.15
Components Involved
Top and Ring: Bottom and Ring
Contact Type 3
FREEZE Contact
Components Involved
Bottom and Bolt
The linear material properties for MAT1 are:
Steel for Bolts
Values
Young’s Modulus
2.08E5 MPa
Poisson's Ratio
0.3
Density
7.8E-9 ton/mm3
Aluminum for Flanges
Values
Young’s Modulus
7.4E4 MPa
Poisson's Ratio
0.33
Density
2.6E-9 ton/mm3
Bronze for Ring
Values
Young’s Modulus
1.22E5 MPa
Poisson's Ratio
0.35
Density
8.8E-9 ton/mm3

Results

The displacement results for bolts in Subcase 1 are presented in Figure 2. Bolt total forces in different subcases can be extracted from .pret file. In Figure 2, observe the displacement result snapshots from all three subcases.

The displacement contours of Subcase 2 and 3 varies according to force applied (magnitude and direction) in both the subcases.
Figure 2. Displacement Results from all Three Subcases (N2S and S2S)


This is a nonlinear static analysis involving various contacts, and output requests for Contact Results can be requested by activating the CONTF card. In Figure 3, observe the Contact-force results.
Figure 3. Contact Force Results from all Three Subcases (S2S)


The second run of this model was done with all Node to Surface (N2S) contacts. You can change the DISCRET field of all CONTACT entries with N2S and rerun the model to generate the N2S model results. An N2S discretization generally leads to quicker convergence and you can read the .out file of both the runs for finding out the time taken to run the simulation. In this case, the S2S run was 1.6x slower than the N2S run on the same machine. However, S2S contact discretization provides more accurate results in most cases.

In Figure 4, observe the Contact-force results snapshot from all the 3 subcases from the N2S run.
Figure 4. Contact Force Results from all Three Subcases (N2S)