The 3Dbolt in ADINA
In the constructions of many structures, bolts are used to hold structural parts together, and there can be many bolts in a model of a structure. It is important to be able to model the bolts and their interactions with the parts of the structure effectively.
Some difficulties in modeling bolts are that each bolt has to carry a prescribed tension or shortening after its application, and the tightening of bolts is to be carried out in a given sequence in order to ensure an overall acceptable structural behavior.
Since there can be many bolts in the structure, the modeling needs to be effective.
In this News we briefly highlight the 3Dbolt option in ADINA. As shown in Figure 1, the program also offers the beambolt option but the accuracy of modeling a bolt is clearly higher when using the 3Dbolt feature.
Figure 1 Different bolt modeling techniques: (a) bolt modeled with beambolt elements, (b) beambolt elements used for bolt shank and (c) bolt modeled with 3D bolt element group
The supported bolttype loadings are:
 bolt tensioning, i.e., the axial force in the bolt is specified
 bolt shrinkage, i.e., the bolt shortening (reduction in bolt length) is specified
In both of these cases, the deformations of the rest of the structure are considered — meaning that after a bolt loading has been applied, the axial force in the bolt, or the reduction in length, has the given value and acts upon the rest of the structure, causing structural deformations.
Using ADINA, of course, any number of bolts can be included in the model. The bolts can all be loaded simultaneously, or the bolts can be loaded sequentially.
To introduce a 3Dbolt in the model, a 3D element group is designated as a 3Dbolt. The direction of the bolt is defined by a cutting plane, and then the geometry of the 3Dbolt is arbitrary. The bolt can be governed by small or large displacements, small or large strains, the sides and faces of the elements representing the bolt can be straight or curved, and any material model, any number of nodes per element, and contact conditions can be used. The mixed u/p formulation and the incompatible modes formulation can be employed.
Also —

The bolt loading can change from bolt tensioning to bolt shrinkage at different
stages of the analysis.

The bolts can be tightened/shrunk in a static analysis or an implicit dynamic analysis.

An explicit dynamic analysis can be performed after a restart from a bolt loading in
an implicit solution.

A frequency analysis can be performed with the bolts in place, including the contact conditions.

Bolts can be modeled with the heat flow options, for coupled TMC solutions, with the fluidstructure interaction options, for FSI solutions, and with the electromagneticstructural interaction options to model Maxwell stress effects.
Figures 2 and 3 below are given to define a simple problem in which the 3Dbolt ADINA analysis feature is used.
The two parts of the bracket are bolted together. After the parts are bolted together, the
tension in the bolt is to be 2000 N and thereafter a pressure load is applied.
Figure 2 Bolted assemblage considered
Figure 3 Assembly sequence: (a) parts bolted and pretension applied and (b) pressure load applied
In this model, the bolt and nut combination is modeled using a 3Dbolt element group, see Figure 4. The bolt element group and bracket element groups are allowed to come into contact. Some results of the analysis are given in Figures 5 and 6.






Figure 4 3Dbolt element group defined in the model 

Figure 5 Results: effect of bolt pretension and applied pressure 
Figure 6 Results: (a) stresses in the 3Dbolt element group and (b) contact gap
The movie at the top shows the stress vectors in the bolt and nut.
This capability of modeling bolts is a very powerful ADINA feature for structural analysis
and is quite easy to use for the various analysis options mentioned above — including general nonlinear analyses and multiphysics simulations.
Keywords:
Bolt, 3D modeling, nonlinear, large displacements, large strains, contact, static, dynamic, multiphysics
