Oasys LS-DYNA Environment 8.1 VOLUME 3 ... - Oasys Software

Oasys LS-DYNA Environment: User Guide (Version 8.1)
The Belytschko-Schwer beam is explicitly formulated and generates a moment which varies
linearly along the length of the beam. The elements have the "correct" elastic stiffnesses and
detect yielding at their ends. For example, a cantilever loaded statically at its tip can be
represented accurately in both elastic and plastic regimes using a single element. If Material type
29 is used, the following non-linear behaviour is catered for:
a) Axial crushing, where the crush force-strain relationship is supplied by the user.
b) Rotation at plastic hinges, where the moment-rotation relationship is supplied by the user.
The hinges can form at either end of each element.
As with the Hughes-Liu beam, the mass is lumped onto the nodes, so finer meshes may be
required for dynamic problems where a correct mass distribution is important.
The Truss element is similar to the Belytschko-Schwer beam but carries axial loads only.
The Discrete Beam is similar to a spring element, in that relationships between force and
deformation are input directly by the user.
RIGID BODIES
All element classes can be declared as rigid bodies. Rigid bodies are covered in detail in Section
8.
DISCRETE ELEMENTS
Discrete mass, spring and damper elements are also available.
Spring elements generate a force which depends on displacement (i.e. change of length of the
element; length is defined as the dot product of the line from node 1 to node 2 with the element
axis direction. Usually this means the change of absolute length between the nodes of the
element irrespective of any rotation of the element.). The force is applied along the element axis.
For example, a positive force (tension) acts along the positive axis direction on node 1 and along
the negative axis direction on node 2.
By default, the element axis lies along the line from node 1 to node 2. When the element rotates,
the line of action of the force also rotates. Alternatively, the user may select a fixed axis or a
fixed plane onto which the element will be projected to obtain the axis. A further option is to
define a moving axis defined by any two nodes. These options are selected using Orientation
Vectors. It should be noted that the sign of the displacement depends on the direction of the axis;
if the dot product of the selected axis and the line from node 1 to node 2 is negative, elongation
of the spring will result in compressive displacements. That is, the definition of tension and
compression will become reversed. This does not matter if the force-displacement relationship
is the same in tension and compression.
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