Comparison between Bolt and Virtual Spring Bolt

The purpose of this test is to compare a bolt tightening connection property and a virtual bolt tightening connection property. You will use 3D models.

Reference:

Comparison of the two models.

Specifications

Geometry Specifications

Bolt tightening connection property

Virtual bolt tightening connection property

  • Screw:

    R1 = 35 mm
    R2 = 20 mm
    L1 = 15 mm
    L2 = 120 mm

  • Hood:

    R1 = 600 mm
    R2 = 500 mm
    R3 = 200 mm
    L1 = 200 mm
    L2 = 80 mm
    r = 50 mm
    d1 = 60 mm
    e = 50 mm

  • Base:

    R1 = 400 mm
    R2 = 500 mm
    R3 = 600 mm
    L1 = 70 mm
    L2 = 140 mm
    d1 = 40 mm

  • Assembly:

    For the bolt connection property model, the hood, the base and six screws are assembled. For the virtual bolt connection property, only the hood and the base are assembled.

    Bolt tightening connection property

    Virtual bolt tightening connection property

Analysis Specifications

Young Modulus (material):

  • Screw: E = 70 GPa

  • Hood and base: E = 200 GPa

Poisson's Ratio (material):

  • Screw: ν = 0.25

  • Hood and base: ν = 0.266

Mesh Specifications:

  • Linear tetrahedron elements (TE4)

  • Mesh sizes:
    • Screw: 8.45 mm
    • Hood and base: 120.02 mm

Contact Connections:

  • Bolt

    • Plane/plane contact: upper surface of the base with lower surface of the hood

    • Six plane/plane contacts: lower surface of the screws with upper surface of the hood

    • Six cylinder/cylinder contacts: screw cylinders with hood cylinders

  • Virtual bolt

    • Plane/plane contact: upper surface of the base with lower surface of the hood
Restraints:
The base is clamped on surface A

Loads:
Surface force density on hood's inner surface F = 150000 N/m2

The stiffness of the virtual bolt's spring depends on the length of the spring element, not on the length of the bolt used in the bolt tightening connection property.

Stiffness is given by the formula:

So for each component:

  • Translation stiffness 1: 9.91 x 107 N/m
  • Translation stiffness 2: 9.91 x 107 N/m
  • Translation stiffness 3: 1.3 x 109 N/m
  • Rotation stiffness 1: 295566 N.m/rad
  • Rotation stiffness 2: 295566 N.m/rad
  • Rotation stiffness 3: 113636 N.m/rad
 

Results

The general shape is the same for the two models:

Values of maximum displacement are:

Bolt tightening connection

Virtual bolt tightening connection

Relative error
υ1 - υ2 / υ1

-0.613 %

Maximum displacement υ1 = 0.00816 mm

Maximum displacement υ2 = 0.00811 mm

You can also use parabolic tetrahedron elements (TE10). The difference is then -4.545 %

To Perform the Test:

The bolt_with_screw.CATAnalysis document presents a complete analysis of this case.

The bolt_without_screw.CATAnalysis document presents a complete analysis of this case.

To compute the case, proceed as follow:

  1. Open the CATAnalysis document.

  2. Compute the case in the Generative Structural Analysis workbench.