About Virtual Bolts

A bolt passes through a hole in each component and consists of a bolt head, a nut, and a shank, all of which are coaxial with the bolt hole. The bolt head is attached to one component, and the nut is attached to the other component. The bolt tension acts along the axis of the bolt hole between the bolt head and the nut and keeps the two components attached. A bolt can translate or rotate along with the two components; however, the bolt head, nut, and shank remain coaxial and their relative position remains fixed. Alternatively, the bolt tension can keep two coaxial regions of the same component attached.

A virtual bolt is an abstract representation of a real bolt. It does not model the bolt head and the nut explicitly, and you cannot apply a side load or a remote torque to the bolt.

To create a standard bolt, you must select the edge of a circular hole as the support for the bolt head. To create a countersunk bolt, you must select a conical face as the support for the bolt head. In both cases, you must select the edge of a concentric circular hole or a cylindrical face (the threads of the bolt) as the support for the nut to define a through hole. The app determines the diameter of the bolt head and the nut and the nominal diameter of the bolt based on the dimensions of the supports you selected. The nominal bolt diameter is also used to calculate rotational stiffness.

Standard and countersunk bolts in through holes are shown in the following figure:

Alternatively, you can select a concentric cylindrical face (the threads of the bolt) as the support for the nut and create a blind threaded hole. Standard and countersunk bolts in blind threaded holes are shown in the following figure:

To create a tight fitting bolt, you must select a cylindrical face. Tight fitting bolts exhibit shear force along the selected cylindrical faces rather than surface pressure from contact of the bolt head and nut. A tight fit bolt with head combines the attributes of tight fit and standard bolts, requiring only a circular edge selection to define both the bolt shaft and the head. An additional circular edge is required to define the support for a nut if one is used.

With grounded bolts, the bolt position is fixed, but motion is possible along the bolt axis. Add a bolt restraint to prevent motion along the axis.

The following coupling types are available:

• No connection: The intermediate layers are not coupled to the bolt.
• Standard: Extends the coupling region beyond the edge of the hole according to a washer diameter you define.
• Tight fit: Couples the nodes on the edge of the hole.

Intermediate layers cannot be used with a bolt to ground.

Once you create a template file, you can load the parameters back into the editor when you create other bolts. After you have loaded parameters into your bolt definition, you can edit any of the parameters for that bolt as required. If you edit a template after bolts have been created using the template, the bolt definitions are not updated automatically. To apply the changes, you need to reload the template file into the bolt definitions.

You can save the following parameters to a template file:

• Bolt head type
• Nut type
• Mechanical behavior
• Axial, shear, torsional, and bending stiffness
• Material and radius (for beam mechanical behavior)
• Intermediate layers connection type
• Whether or not to allow preloading
• Coupling type

After you have created a bolt, you can use the Bolt Replication tool . The bolt replicas must connect the same two parts and pass through holes with the same dimensions as the original.

Free Placement Method

With the Free placement method, the bolt detection tool searches the selected supports for bolt locations based on the criteria that you specify. You can restrict the bolt creation to holes of a particular size, and you can control which parts the bolt connects.

You can restrict the search to look for circular holes only, or you can have it look for all holes. For noncircular holes, you can specify both height and width of matching holes.

Points Placement Method

With the points placement method, you select points to determine bolt locations. For some points there might be more than one possible combination of layers that the bolt can connect. You can limit the possibilities by specifying minimum and maximum bolt lengths.

Automatic bolt detection with the points placement method does the following:

1. Looks for the bolt hole that is closest to the placement point.
2. Searches other layers for holes aligned with the first.
   • If the distance to another hole is within the specified minimum and maximum lengths that you specify, it forms a bolt between the holes.
   • If more than one other bolt hole is within that length range, it uses the hole that creates the longest bolt length.
   Note: If you define the bolt properties to include connections to intermediate layers, the hole closest to the placement point might be either a bolt head or an intermediate layer. This hole can be an intermediate layer if the specified length range is large enough to include layers on both sides of the placement point.

Lines Placement Method

With the lines placement method, you select lines to determine bolt locations. There might be more than one possible combinations of layers that the bolt can connect. You can limit the possibilities by specifying minimum and maximum bolt lengths, or you can use the line length itself to determine which layers the bolt connects.

Bolt detection with the lines placement method does the following:

1. Searches for the bolt hole that is closest to the start point of the selected placement lines.
2. Searches other layers for holes along the line direction.
   • If a hole is within the specified minimum and maximum lengths, it forms a bolt between them.
   • If more than one other bolt hole is within that range, it uses the hole that creates the longest bolt length.

The bolt load is specified in terms of the axial force that is applied along the cylindrical axis of the bolt. This force is a tension that pulls the bolt head and nut together.

You can apply the bolt tension load directly, or the simulation can calculate the tension from the bolt diameter and a specified torque and torque coefficient. The torque coefficient, K, is a constant value used internally to convert the torque load to an axial load using the following formula:

where

P = resulting axial force (tension) on the bolt,

T = torque value,

K = torque coefficient (this value has a default of 0.2 or can be found in a standard reference manual; it is a function of the bolt geometry, the materials being assembled, and the joint lubrication), and

D = nominal diameter of the bolt.

When you apply virtual bolts to solid bodies that are idealized as a shell mesh on the midsurface of the original solid, be aware of the geometry sets used for the virtual bolts.

Midsurface models often include other idealizations, such as trimmed, extended, or split features used to simplify the solid and create a shell representation at the midsurface.

If you create virtual bolts on an idealization feature, they are usually transferred to the midsurface geometry set. This is intended to preserve model intent in the event of a change to the idealized features. However, it could result in an error if the virtual bolt requires information from the idealization feature.