ABAQUS Analysis User's Manual  


23.3.1 Tube-to-tube contact elements

Product: ABAQUS/Standard  

References

Overview

Tube-to-tube elements:

  • model the finite-sliding interaction between two pipelines or tubes where one tube lies inside the other or between two tubes or rods that lie next to each other;

  • are slide line contact elements, in the sense that they assume that the relative motion of the two tubes or pipes is predominantly along the line defined by the axis of one of the tubes (the relative rotations of the tube or pipe axis are assumed to be small);

  • can be used with pipe, beam, or truss elements; and

  • do not consider deformations of the tube or pipe cross-section.

Chapter 21, “Defining Contact Interactions,” contains a general discussion of contact modeling.

Typical applications

The tube-to-tube contact elements can be used to model two specific classes of tube-to-tube contact problems: internal (tube within a tube) contact and external contact, where the two tubes are roughly parallel and contact each other along their outer surfaces. It is not possible to use the surface-based contact approach for problems where two three-dimensional tubes contact each other.

Choosing an appropriate element

Use ITT21 elements with two-dimensional beam, pipe, or truss elements. Use ITT31 elements with three-dimensional beam, pipe, or truss elements. Each of these elements is defined by a single node.

Associating the tube-to-tube contact elements with a slide line

You must indicate which set of tube-to-tube contact elements will interact with a particular slide line. Details on defining slide lines are discussed below.

Input File Usage:           
*SLIDE LINE, ELSET=element_set_name

Defining the element's section properties

You must associate the geometric section properties with a set of tube-to-tube contact elements.

Input File Usage:           
*INTERFACE, ELSET=element_set_name

Defining the radial clearance when modeling contact between a pipe within another pipe

You define the radial clearance between the pipes. Give a positive value to model contact between two pipes when one pipe (the one with the tube-to-tube contact elements) lies inside of the other pipe. The value given is the difference between the inner radius of the outer pipe and the outer radius of the inner pipe.

Input File Usage:           
*INTERFACE
radial clearance

Defining the radial clearance when modeling contact between the outer surfaces of two pipes

You can model external tube-to-tube contact by specifying a negative value for the radial clearance. The magnitude of the value must be the sum of the outer radii of the two pipes or rods.

Local basis for contact output variables

The element output variables for ITT elements are given in a local basis system associated with the slide line. The first tangent vector, , is defined by the sequence of the nodes forming the slide line. The direction of contact, , is the normal to the slide line that points toward the nodes of the ITT elements. For ITT31 elements ABAQUS/Standard forms a second tangent vector, , that is orthogonal to both and . As the elements move, the local basis system will rotate with the axis of the slide line.

Choosing which pipe (beam or truss) will have the slide line

In the case of internal tube-to-tube contact, the slide line can be placed on the inner tube or the outer tube. Generally the slide line should be associated with the outer tube (see Figure 23.3.1–1); however, if the inner tube is stiffer than the outer tube, the slide line should be attached to the inner tube.

Figure 23.3.1–1 Internal tube-to-tube contact example.

If contact occurs between the exterior surface of the tubes, the slide line should be associated with the stiffer tube if the materials or tube radii are different or with the tube with the coarser mesh if they are the same.

Defining the slide line

You can specify the nodes that make up the slide line, or they can be generated as described below. If you choose to specify the nodes directly, you must specify them in a sequence that defines a continuous slide line. The nodal sequence defines a tangent vector for the slide line. The slide line must be made up of linear segments.

Input File Usage:           
*SLIDE LINE, ELSET=element_set_name, TYPE=LINEAR
first node number, second node number, etc.

Generating the slide line nodes

Alternatively, you can indicate that the slide line nodes should be generated and specify only a first node number, a last node number, and an increment between node numbers.

Input File Usage:           
*SLIDE LINE, GENERATE
first node number, last node number, increment between node numbers

Smoothing the slide line

Convergence is often improved by smoothing the discontinuities in surface tangents between slide line segments, thereby providing a smoothly varying tangent along the slide line. For details about smoothing slide lines, see “Contact formulation for ABAQUS/Standard contact pairs,” Section 21.2.2.

Defining nondefault mechanical surface interactions with tube-to-tube contact elements

By default, ABAQUS/Standard uses “hard,” frictionless contact with tube-to-tube contact elements. You can assign optional mechanical surface interaction models. The following mechanical surface interaction models are available: