Question

Briefly answer

1). In an FE simulation with Abaqus, if the unit for the length is μm and the unit for the force is Netwon, what is the correct unit for the elastic modulus? Why?

8). List two approaches to define rigid bodies in an FE model with Abaqus.

9). Explain the meaning of the following two lines in an Abaqus input file:

*Boundary 3, 1, 3,

10). Explain the meaning of the following two lines in an Abaqus input file:

*ELEMENT, TYPE=CPE4 100, 101, 3, 4, 501

Answer 1

8) Rigid Bodies

In ABAQUS a rigid body may be a collection of nodes and elements whose motion is governed by the motion of one node, referred to as the rigid body reference node, as shown in Figure. Shape may be as analytical surface obtained by revolving or extruding a 2-d geometric profile or as a discrete rigid body obtained by meshing the body with nodes and elements. the form of the rigid body doesn't change during a simulation but can undergo large rigid body motions. The mass and inertia of a discrete rigid body are often calculated supported the contributions from its elements, or they will be assigned specifically.

Rigid body slave nodes Rigid body reference node

Figure - Elements forming a rigid body.

The motion of a rigid body are often prescribed by applying boundary conditions at the rigid body reference node. Loads on a rigid body are generated from concentrated loads applied to nodes and distributed loads applied to elements that are a part of the rigid body or from loads applied to the rigid body reference node. Rigid bodies interact with the remainder of the model through nodal connections to deformable elements and thru contact with deformable elements.

Determining when to use a rigid body

Rigid bodies are often wont to model very stiff components that are either fixed or undergoing large rigid body motions. they will even be wont to model constraints between deformable components, and that they provide a convenient method of specifying certain contact interactions. After that ABAQUS is then applied for quasi-static forming analyses, rigid bodies are ideally fitted to modeling tooling (such as punch, die, drawbead, blank holder, roller, etc.) and should even be effective as a way of constraint.

It may be useful to form parts of a model rigid for verification purposes. for instance , in complex models where all potential contact conditions can't be anticipated, elements distant from the contact region might be included as a part of a rigid body, leading to faster run times while developing a model. When the user is satisfied with the model and get in touch with pair definitions, rigid body definitions are often removed and an accurate deformable finite element representation are often incorporated throughout.

The principal advantage to representing portions of a model with rigid bodies instead of deformable finite elements is computational efficiency. Element-level calculations aren't performed for elements that are a part of a rigid body. Therefore some computational effort is required to update the motion by the nodes of the rigid body and to assemble concentrated and distributed loads, the motion of the rigid body is decided completely by a maximum of six degrees of freedom at the rigid body reference node.

Components of a rigid body

To create a discrete rigid body, use the *RIGID BODY option because the property reference for the weather forming the rigid body. REF NODE use for parameter to assign a rigid body reference node to the rigid body. A rigid body reference node has both translational and rotational degrees of freedom and must be defined for each rigid body. The place of the rigid body reference node isn't important unless rotations are applied to the body or reaction moments a few certain axis through the body are desired. In either of those situations the node should be placed such it lies on the specified axis through the body.

*RIGID BODY, REF NODE=<node>, ELSET=<element set name>,
PIN NSET=<node set name>, TIE NSET=<node set name>

In addition to the rigid body reference node, discrete rigid bodies contains a set of nodes that are generated by assigning elements and nodes to the rigid body. These nodes, referred to as the rigid body slave nodes (see Figure 3–7), provide a connection to other elements. Nodes that are a part of a rigid body are one among two types:

Pin nodes, having only translational degrees of freedom.

Tie nodes, having both translational and rotational degrees of freedom.

The rigid body node type is decided by the sort of elements on the rigid body to which the node is attached. The node type can also be specified or modified when assigning nodes on to a rigid body. For pin nodes only the translational degrees of freedom are a part of the rigid body, and therefore the motion of those degrees of freedom is constrained by the motion of the rigid body reference node. In tie nodes both degrees the translational and rotational degrees of freedom are a part of the rigid body and are constrained by the motion of the rigid body reference node.

The nodes describing the rigid body cannot have any boundary conditions, multi-point constraints, or constraint equations applied to them. Boundary conditions, multi-point constraints, constraint equations, and loads are often applied, however, to the rigid body reference node.

9) Boundary 3,1,3 means

Node or node set, first degree of freedom, last degree of freedom

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