Example63 O-Ring with Initial Strain

General

  • The contact analysis is performed on a model which has an initial strain as the body attribute.

  • As the material of O-ring is rubber, it is treated as hyperelastic material.

  • The deformation, the strain energy distribution and the nodal contact force are solved.

  • Unless specified in the list below, the default conditions will be applied.

  • See [Analysis of Hyperelastic Materials] for more details.

Analysis Space

Item

Setting

Analysis Space

Axisymmetric

Model Unit

mm

Analysis Condition

To use hyperelastic material, select [Large displacement] in [Large deformation]

[Large strain] is also necessary to select as the strain is expected to become large.

Item

Setting

Solver

Stress analysis [Galileo]

Analysis Type

Static analysis

Large Deformation

Select both “Large displacement” and Large strain”

Model

A ring-shaped material (outer), a disc with groove on its circumference (inner),

and an O-ring (ring) constitute an axisymmetric model.

 

The ring-shaped material (outer) is enlarged in a radial direction than the actual dimensions so as not to interfere with the O-ring (ring).

In order to match the inner diameter of the ring-shaped material (outer) and the outer diameter of the disc (inner) in the end,

the anisotropic initial strain, where only components 1 and 2 shrink, is set to the ring-shaped material (outer).

 

For the boundary condition, the fixed displacement in Z direction is set to the bottoms of the ring-shaped material and the disc.

The contact face (contactor) is set to the O-ring. The contactee face (target) is set to the inner area of the ring-shaped material and

the surface of the disc groove, both of which are expected to contact with the O-ring.

 

Body Attributes and Materials

The anisotropic axial strain is set as the body attribute [outer]. As the ring-shaped material (outer) is larger than the actual dimensions by (1+sr),

the initial strain of -sr/(1+sr) is set so as to bring it back to the actual dimensions. sr is a variable. It is set to 0.1.

Body Number/Type

Body Attribute Name

Initial Strain

Material Name

Body2/Sheet

inner

 

007_ABS_resin (shock-resistant)*

Body3/Sheet

ring

 

EPDM_rubber (hardness: 65Hs)

Body4/Sheet

outer

 

Specified by: Axial strain

 

Anisotropy: Anisotropic

 

Initial Strain Vector:

 

1 -sr/(1+sr)
2 -sr/(1+sr)
3 0

sr is a variable. It is set to 0.1.

 

007_ABS_resin (shock-resistant)*

* Available from the material DB

Boundary Condition

Displacement and contacting face are set as follows.

Boundary Condition Name/Topology

Tab

Boundary Condition Type

Setting

Fix_z/Edge

Mechanical

Displacement

Select the Z Component.
UZ=0

Contactor/Edge

Mechanical

Contact surface

Contactor face

Target/Edge

Mechanical

Contact surface

Contactee face

 

The following contact pairs are set in “Boundary Pair” dialog.

Boundary Pair

Coefficient of friction:

Contactor-Target

0.5

Results

The number of substeps is set to 20 in the nonlinear analysis. The initial strain is reflected step by step from 0.05 up to 1.

20 results are output in total.

 

The pressure on the contacting faces and strain energy density in steps 0.5, 0.75, and 1 are shown as below.

 

 

 

The initial strain is reflected on the ring-shaped material in steps, and the contact of the O-ring and the resin materials progresses.

Eventually, the O-ring is largely compressed, and the contact face pressure and the strain energy are generated.

 

 

In the actual assembly process, two resin materials are slid in the vertical direction to achieve the sealing state by O-Ring.

If the contact state between the O-ring and the surrounding materials is complex, the contact analysis may not be stable.

 

In that case, using the initial strain is effective to stably analyze the final state.