# 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.