Modeling Bolted Structures with ADINA

Bolted structures show complex mechanical behavior. Modeling such structures presents many challenges: meshing these complex structures with bolts, sequential load applications with proper pre-stressing, contact conditions between bolted parts and also between parts and bolts, to name a few. These typical requirements are easily handled using the ADINA System, which provides very efficient and practical bolt analysis capabilities supported by robust meshing algorithms.

The following analysis options are available in the ADINA program for bolted structures:

• Static analysis: bolts can be pre-stressed (or loosened) at any time during the solution process

• Implicit dynamic analysis using the Bathe composite or Newmark method: bolts can be pre-stressed at the beginning of the solution process and the pre-stressing can be changed at any time during the solution process

• Explicit dynamics in a restart run: the bolts need to be pre-stressed in a static solution and then, using the restart option, explicit time integration can be used

• Frequency and modal analyses: the bolts (with contact conditions) can be pre-stressed in a static run and then the restart option can be used to calculate frequencies and mode shapes, or bolt pre-stressing and frequency/modal analysis can be requested in the same run

• Thermo-mechanical coupling (TMC)

• Fluid-structure interaction (FSI) with or without thermal coupling

In this News, we show the application of ADINA in an analysis involving the standard industrial practice of sequential bolt tightening. The bolted structure shown in Figure 1 is modeled. The above animation shows the calculated stresses in the bolts as they are loaded. The animation also demonstrates how 3-D solid bolts are modeled in ADINA: for each bolt, a bolt pre-stressing is included in a single bolt element constrained between two bolt-cutting surfaces. This allows contact conditions between all connected parts to be included.

Figure 1  Bolted structure modeled, courtesy of Volvo Penta

Figure 2 shows the finite element mesh of the entire bolted model generated using ADINA. There are 23 bodies in the model, each of which is meshed with ADINA's free-form brick mesher. This meshing process comprises 3 main steps:

1. quadrangulation of all body's faces,

2. tetrahedronization of the body and

3. brick (hexahedron) creation from the boundary inwards.

Figure 2 Mesh of the bolted structure

The resulting mesh is a combination of mostly bricks and some pyramids and tetrahedra. Clearly, for such a complex model, the mesh quality is remarkable.

The bolt analysis options in ADINA, together with the advanced meshing capabilities, allow engineering analysts to model bolted structures easily and confidently.

Keywords:
Bolted assemblies, bolt element, contact, friction, sequential, tightening, pre-stress