Mechanical APDL Basic Analysis Guide - Ansys

Chapter 2: Loading
Main Menu> Solution> Define Loads> Settings> Replace vs Add> Reset Factors
2.8. Defining Pretension in a Joint Fastener
Preloads in bolts and other structural components often have significant effect on deflections and stresses.
Two ANSYS features, the PRETS179 pretension element and the PSMESH pretension meshing command,
can be used for this type of analysis. If the fastener has been meshed in two separate pieces, the pretension
elements can be inserted between the pieces using the EINTF command.
The pretension load is used to model a pre-assembly load in a joint fastener. The fastener can be made up
of any 2-D or 3-D structural, low- or high-order solid, beam, shell, pipe, or link elements. When using the
PSMESH command, the pretension section, across which the pretension load is applied, must be defined
inside the fastener (shown in Figure 2.20 (p. 64) for a bolted joint).
2.8.1. Applying Pretension to a Fastener Meshed as a Single Piece
The easiest way to apply pretension elements to a fastener is via the PSMESH command. You can use the
command only if the fastener is not meshed in separate pieces. The command defines the pretension section
and generates the pretension elements. It automatically cuts the meshed fastener into two parts and inserts
the pretension elements. If you decide that you want to remove the pretension elements, they can do so
automatically by deleting the pretension section (Main Menu> Preprocessor> Sections> Delete Section).
This feature also allows you to “undo” the cutting operation by merging nodes.
Figure 2.20 Pretension Definition
The normal direction is specified via the PSMESH command and is part of the section data. This is in contrast
to the previous method (the PTSMESH command), which used real constants to specify the normal direction.
The meshed pretension section does not need to be flat. The elements underlying the pretension section
can have almost any shape: line, triangle, quadrilateral, tetrahedron, wedge, or hexahedron. However, there
must be coincident nodes on the two sides (A and B) of the pretension section. Sides A and B on the pretension
section are connected by one or more pretension elements, one for each coincident node pair.
A pretension node (K) is used to control and monitor the total tension loads. The pretension load direction
of the pretension section can be specified relative to side A when the section is created by the PSMESH
command. All pretension elements on a specific pretension section must use the same section, and must
have the same pretension node K. Node K is the third position for the pretension element definition.
2.8.2. Applying Pretension to a Fastener Meshed as Two Pieces
If the fastener has been meshed in two separate pieces (such as in an existing, legacy model), the pretension
elements (PRETS179) can be inserted between the pieces using EINTF,TOLER,K (Main Menu> Preprocessor>
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