De Herrera

8/12/2019 De Herrera

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2002 ABAQUS Users Conference 1

Analysis of a Rubber Oil Pan Gasket RTV Pad UsingABAQUS Explicit

Milton A. DeHerrera, Ph.D

Computational Mechanics Group*

Freudenberg-NOK General Partnership

50 Ammon Drive

Manchester, NH 03103

USA

*Current affiliation: Edwards Lifesciences LLC

One Edwards Way

Irvine, CA 92614

Abstract: Automotive Powertrain sealing components like gaskets are required to maintain sufficient contact pressure to prevent leakage of fluids to the engine exterior and to keeptensile strains small enough to avoid gasket failure. An existing Oil Pan gasket RTV paddesign was analyzed to numerically confirm observed failures that resulted in gasketdisintegration and oil leakage. Because of the relatively complex 3D T-Joint geometryand subsequent size of the FEA model, ABAQUS/Explicit was used to analyze the model.The results of the analysis, together with observations from engine tear-downs, are

presented in this paper.

1. Introduction

In a previous paper [DeHerrera, Heim, 2000] we presented the rationale behind using ABAQUS/Explicit tosolve difficult sealing problems involving confined elastomers. Space limitations and the introductory

nature of that paper prevented us from discussing the most useful application of ABAQUS/Explicit in ourbusiness: The 3D analysis of Powertrain sealing components.


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2 2002 ABAQUS Users Conference

As stated in [DeHerrera, Heim, 2000], the principal objectives of sealing components in Powertrainapplications are to (1) prevent the escape of oil and other fluids to the exterior of the engine, (2) maintaininternal pressure during operating conditions, (3) provide sufficient resistance to the engine environment sothat failure does not occur within a specified amount of time and/or mileage and (4) meet all of the aboveconditions at a reasonable cost. Contact pressure distribution is the most important parameter in designingsealing components, closely followed by the maximum tensile strain.

1.1 Phenomenological Strain Energy Model

Because of previous FEA work with similar components, we have used the two-term Mooney-Rivlinphenomenological strain energy law to describe the strain energy for both elastomers used in this study:

U = C 10 (I1 - 3) + C 01 (I2 - 3) + (1/D 1)(Jel

- 1)2

(See Abaqus Theory Manual for more details).

Most of the elastomers we currently use at Freudenberg-NOK have D 1 values in the order of 0.01 (MPa)-1

.

There are occasions when other users wish to know the value of the Poisson ratio in order to gage hownear the material lies to the incompressible limit of = . From the formula relating the initial bulkmodulus K 0 and initial shear modulus 0 to the Poisson ratio :

= (3K 0 - 2 )/(3K 0 + 0 )

and the relationship between K 0 , 0 and the Mooney-Rivlin parameters C 10 and C 01 :

0 = 2(C 10 + C 01 )

and

K 0 = 2/D 1

Then the Poisson ratio can be written as:

= (3 - 2 D 1 [C 10 + C 01 ])/(3 + D 1 [C 10 + C 01 ])

The D 1 value for both elastomers used in this study is 0.497. While this value is close to theincompressible limit, it is sufficiently far from 0.5 to allow the use of ABAQUS/Explicit.

2. Problem Statement

The goals of this analysis were threefold: (1) To evaluate the design of a competitors single-beaded carrieroil pan gasket RTV pad that was being used in a current production engine, (2) to see if the FEA wouldprovide supporting evidence for observed leaking at the gasket RTV pad and (3) to compare the resultsobtained (for the same geometry) between the C3D4 and C3D10M tetrahedral elements.

The gasket RTV pad was modeled using both C3D4 and C3D10M elements, and the front cover gasketprotrusion was modeled with C3D6s.


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The Mooney-Rivlin constants for the HNBR material used to model the Oil Pan gasket RTV pad are:

C10 = 0.35 MPa

C01 = 0.06 MPa

D1 = 0.014 (MPa)-1

And for the 60 durometer material used to model the protrusion they are

C10 = 0.42 MPa

C01 = 0.08 MPa

D1 = 0.011 (MPa) 1

The gasket RTV pad was compressed to the height of the metal carrier, or 2.54mm. The pad wascompressed by two rigid surfaces (representing the girdle and front cover setup of the engine) into a

supporting rigid surface representing the pan rail. The front cover gasket protrusion was modeled as arubber block that extends 1.0 mm past the surface of the front cover. A vertical step of 0.35mm was alsoincluded in the model. The front cover block with the protrusion was shifted 0.35mm away from the pad.Figures 1 and 2 represent the 3D models used for each analysis. Figure 3 illustrates the deformableelements that represent the T-Joint being analyzed.

2.1 ABAQUS Explicit Model Setup and Run

The gasket geometry was initially generated from a partially defeatured Unigraphics version 16 productionCAD model. The model was imported into MSC/PATRAN where its mesh and that of the adjacent rigidbodies was generated and exported.

There were two deformable bodies in this model: The gasket RTV pad was modeled with 41,484C3D4/C3D10M tetrahedral elements with 25,474 and 60,990 nodes respectively, and the Front Cover

gasket protrusion by 492 C3D6 wedge elements with 385 nodes. There were a total of 7 contact pairs, outof which two involved deformable-to-deformable contact and the rest deformable-to-rigid contact. Theproblem was initially run under ABAQUS Explicit version 5.8-18 and subsequently rerun with ABAQUSExplicit version 6.2-1. We shall only discuss the results from version 6.2-1.

Both problems were run on an HP J5600 2-CPU computer. The C3D4 problem ran in 4 hours and 59minutes of wall clock time, and the C3D10M problem ran in 25 hours and 40 minutes of wall clock time.

3. Results

Figures 4-9 show results for field quantities such as maximum true tensile strain and contact pressure forboth the C3D4 and C3D10M runs. We have used the mass-scaling feature of ABAQUS Explicit to run theproblem quasi-statically and in much less time than would be required for an unscaled problem. Figures10, 11 show a plot of the internal, kinetic and artificial energies for the C3D4 and C3D10M models,respectively. A cursory inspection of these figures shows that the problems indeed ran in a quasi-staticfashion.


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Figures 12-13 show scanned pictures from an actual warranty return. These pictures show the deformedgasket RTV pad and can be used to correlate FEA predictions of pad deformations to an actual deformedpad. It can be seen that the deformed shape predicted from the C3D10M run is quite similar to that of thegasket from a warranty return. The most important observation is that the FEA predicts a troublesome lowcontact pressure region on the RTV pad that seems to confirm the leaking of oil that had been noticed inthis particular engine.

4. Conclusions

ABAQUS Explicit can be used to analyze complex 3D elastomeric problems, preferably with the use ofhigher order tetrahedral elements. Whereas contact pressure distribution is not greatly affected by thechoice of C3D4 versus C3D10M, that does not seem to be the case for other field quantities.

5. Acknowledgements

I wish to thank Ms. Katie Olsen for providing the gasket pictures from the warranty return and othertechnical assistance.

6. References

1. DeHerrera, M. A, and D.R. Heim Using ABAQUS Explicit to Model Behavior of ElastomericSealing Components, Proceedings of the ABAQUS Users Conference at Newport, RI, May-June2000.

2. Abaqus Theory Manual, version 6.2, Hibbitt, Karlsson & Sorensen, Inc., 2001.


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Figure 1. Isometric view of FEA model (Girdle not shown)

Figure 2. Side view of FEA model.


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Figure 3. Undeformed model of RTV Pad/Front Cover gasket protrusion T-Joint


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Figure 4. Deformed shape of gasket RTV pad modeled with C3D4 elements after a 2.23mmcompression to a 2.54mm carrier height

Figure 5. Deformed shape of gasket RTV pad modeled with C3D10M elements after a2.23mm compression to a 2.54mm carrier height


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Figure 6. Maximum tensile true strain (mm/mm) in gasket RTV pad modeled with C3D4elements after a 2.23mm compression to a 2.54mm carrier height

Figure 7. Maximum tensile true strain (mm/mm) in gasket RTV pad modeled with C3D10Melements after a 2.23mm compression to a 2.54mm carrier height


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Figure 8. Maximum contact pressure distribution in gasket RTV pad modeled with C3D4elements after a 2.33mm compression to a 2.54mm carrier height

Figure 9. Maximum contact pressure distribution in gasket RTV pad modeled withC3D10M elements after a 2.33mm compression to a 2.54mm carrier height


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Figure 10. Energy curves for gasket RTV pad modeled with C3D4 elements after a 2.33mmcompression to a 2.54mm carrier height

Figure 11. Maximum contact pressure distribution in gasket RTV pad modeled withC3D10M elements after a 2.33mm compression to a 2.54mm carrier height


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Figure 12. Gasket RTV pad taken from a warranty return

Figure 13. Gasket RTV pad taken from a warranty return

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De Herrera