NX NastranGlossary

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TAUCS Version 2.0, November 29, 2001. Copyright (c) 2001, 2002, 2003 by Sivan Toledo,Tel-Aviv University, stoledo@tau.ac.il. All Rights Reserved.

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2 Glossary

Chapter

1 Glossary

Anisotropic Material

A material that has a different property in each direction at any givenlocation in the structure. There is no material plane of symmetryassociated with an anisotropic material. This material can bedescribed by 21 independent elastic constants in the stress-strainrelationship. See Homogeneous Material, Isotropic Material, andorthotropic material.

Axisymmetric

A type of finite element (or problem) in which the elements crosssection is symmetric about an axis of rotation. Used to modelstructures, such as shafts and rotationally-symmetric pressurevessels (which can be geometrically represented as surfaces or solidsof revolution).

Basic CoordinateSystem

NX Nastrans default, built-in rectangular coordinate system. Alluser-defined (local) coordinate systems ultimately must be able tobe transformed back into the basic coordinate system. The basiccoordinate system is often called the global coordinate system in manyfinite element programs and textbooks. The global coordinate systemhas a special meaning in NX Nastran. See also Global CoordinateSystem and Local Coordinate System.

Beam OrientationVector

A user-defined vector that is used to orient cross-sectionalproperties of CBAR and CBEAM elements with respect to the modelsgeometry. This information defines a unique beam orientationrelative to the model geometry.

Bulk Data SectionThe section of the NX Nastran input (.dat) file containing modelgeometry, element connections and properties, loads, constraints, andmaterial properties. This section follows the Case Control Section.

Case Control Section

The section of the NX Nastran input (.DAT) file containing commandsthat select the type of analysis output required (displacements, forces,stresses, etc.). Case Control also manages sets of Bulk Data input(e.g., loads and constraints) to be used in analysis subcases. The CaseControl Section follows the Executive Control Section and precedesthe Bulk Data Section.

Comment Entry

An entry used to insert user-specified comments anywhere in theinput (.dat) file. The first character is a dollar sign ($) in column 1,followed by any character. When echoed, only the first 80 characterswill be printed in your .f06 file.

Glossary 1-1

Chapter 1 Glossary

Composite Material

When two or more materials are combined together on a macroscopicscale. Generally each of these materials by itself may not provide thedesired material properties for your design. However, by combiningthese materials into a composite material, the desired materialproperties may be obtained. When speaking of composites, mostpeople think of fibrous composites (e.g., kevlar, graphite, etc.).There are many other types of composite that are encounteredevery day, such as plywood and steel reinforced concrete. Also seeGlossaryAnisotropic Material and Orthotropic Material.

Computational Zero See Machine Zero.

Consistent Load

The equivalent loads at the grid points computed from the appliedloads on elements. The same shape function that is used in derivingthe element stiffness and mass matrices is used for the derivation ofthe load-hence the name consistent load.

Constraint

The enforcement of a particular displacement (translation and/orrotation) on a grid point or points. The boundary conditions of a staticstructure typically require a zero displacement constraint on variousdegrees of freedom in the model. Constraints may also be defined interms of displacement with respect to other degrees of freedom inthe model or in terms of an enforced nonzero value of displacement.Also see MPC and SPC.

ContinuationAn extension of an entry when the entry requires more than one lineof input data. Continuations may or may not be required, dependingon the particular Bulk Data entry and its options.

Coordinate SystemSee the specific type (Basic Coordinate System, DisplacementCoordinate System, Global Coordinate System, Local CoordinateSystem, Material Coordinate System, and Output File).

CPU TimeStands for central processing unit time. The CPU time is a measureof the computational speed of your computer. Also see Elapsed Time,I/O Time, and Turnaround Time.

Data Block

Basic units used by NX Nastran to store your data. The data blockcan be a matrix or table. As an example, the g-set stiffness matrixis stored as the kgg data block; thel-set stiffness matrix is stored asthe kll data block.

.dat File

Also called the input file, the .dat file contains the complete NXNastran finite element model. The input file is submitted to NXNastran which then executes the analysis. The input file containsthe following principal sections:

NASTRAN statement OptionalFile Management Section (FMS) OptionalExecutive Control Section RequiredCEND Required DelimiterCase Control Section RequiredBegin Bulk Required DelimiterBulk Data Section RequiredENDDATA Required Delimiter

1-2 Glossary

Glossary

.DBALL File

A file created by running NX Nastran that contains the permanentdatabase. By default, the extension .DBALL is appended to thefilename. This database file is needed if you want to perform a restart.See also .MASTER File. By default, all information pertaining to yourmodel and solution is stored in this file.

Decomposition

The first step in solving a system of linear equations, decompositionbreaks the stiffness matrix [K] into lower and upper triangular factors.This process is one of the most computationally time-consuming stepsin linear static analysis.

Degrees of Freedom(DOFs)

The motion of each grid point can be described by three orthogonaltranslational and three orthogonal rotational components ofdisplacement. Each component is called a degree of freedom andadds one unknown to the system of simultaneous linear equationsrepresenting the structure. Unlike a grid point, a scalar point hasonly one (non-dimensional) degree of freedom associated with it.

DelimiterAn entry in the NX Nastran input (.DAT) file that indicates thebeginning or end of a section. CEND, BEGIN BULK, and ENDDATAare required delimiters in all input files.

Differential Stiffness

The stiffness term resulting from the inclusion of the higher-orderterms of the strain-displacement relationships. The differentialstiffness softens the linear stiffness matrix in the case of acompressive axial load and stiffens the linear stiffness matrix in thecase of a tensile axial load. The differential stiffness is often calledthe geometric stiffness.

Discretization

The basic process of finite element modeling wherein a continuousstructure is broken up-discretized-into an assembly of individualelements. The goal is to choose types and quantities of elements suchthat the mathematical behavior of the model faithfully represents thebehavior of the structure. Properly discretizing the structure requiresboth knowledge of the structure and engineering judgement.

DisplacementCoordinate System

Each grid point may have a unique displacement coordinate system,as selected in field 7 (the CD field) of the GRID Bulk Data entry.Displacements, constraints, and other grid point-based quantities arecalculated and printed based on this coordinate system. The basiccoordinate system is NX Nastrans default displacement coordinatesystem.

DisplacementMethod

A method of structural analysis used by NX Nastran in whichdisplacements are the unknown quantities to be determined.

DMAP

Acronym for Direct Matrix Abstraction Program. DMAP is NXNastrans high-level programming language. DMAP allows advancedusers to access NX Nastrans internal modules to modify existingsolution sequences or to create customized solution methods. See theNX Nastran DMAP Programmers Guide for further details.

Glossary 1-3

Chapter 1 Glossary

DMAP Alters

A convenient method of providing you with a new analysis capability,increased efficiency, alternate solution methods, additional printouts,and/or otherwise unavailable user conveniences. A library of usefulalters is delivered with your delivery media (see the NX NastranUsers Guide and the NX Nastran DMAP Programmers Guide forfurther details). You can also create your own DMAP Alters to suityour need.

DOF(s) See Degrees of Freedom (DOFs).

Echo

A listing of the input file (.dat) written into the .f06 results file. Theinput file can be unsorted (it appears exactly like the .dat listing),sorted (it is alphabetized and comment entries removed), or both, asspecified by the ECHO Case Control Command. This command canalso be used to create a sorted copy of the whole Bulk Data file.

Elapsed Time

Also known as the wallclock time. The elapsed time is the time fromthe start of your jobs execution to the end of the job. This timeincludes the effect of your computer speed (CPU), the amount ofmemory available on your machine, the I/O speed, and the swappingof multiple jobs on your machine. See CPU Time, I/O Time, andTurnaround Time.

Element CoordinateSystem

Each element has an element coordinate system based on theelements particular geometry and grid point ordering sequence. Formany elements, quantities, such as element force and stress, areoutput in the element coordinate system.

Elemental StiffnessMatrix

The stiffness matrix of an individual finite element, which isoften denoted as [k]. The stiffness matrix describes the elementsdisplacement response for a given load. See also Global StiffnessMatrix.

Epsilon

A measure of numerical accuracy and roundoff error provided inthe .f06 results file of linear static analysis runs. A small value ofepsilon, approximately less than |10-9|, indicating a numericallystable problem. A large value of epsilon is evidence of numericalill-conditioning. An acceptable value may also be machine dependent.See also Ill-conditioning.

Executive ControlSection

A required section of the input file that appears before the CaseControl Section. This section contains requests for the solutionsequence type (the SOL statement), the CPU time limits (the TIMEstatement), and an optional identification entry (the ID statement).User-provided DMAP Alters are also inserted in this section.

.f04 File

A file created by running NX Nastran that contains databaseinformation and the module execution summary. By default, theextension .f04 is appended to the filename. The .F04 file is a valuabletool for debugging and evaluating the performance of your run.

.f06 FileA file created by running NX Nastran that contains the results ofyour analysis (e.g., stresses, forces, displacements, etc.). By default,the extension .f06 is appended to the filename.

Fatal Error See User Fatal Message.

1-4 Glossary

Glossary

Fiber Direction

A term used when describing composite materials. The fiber directionis commonly referred to as the longitudinal direction or 1-direction.This is the direction that possesses the highest strength for the fibercomposite material. See Composite Material and Matrix Direction.

File ManagementSection (FMS)

An optional input file section used primarily to attach or initialize NXNastran databases and FORTRAN files. The FMS section, if used,precedes the Executive Control Section. This section is mostly used inconjunction with large problems.

Finite Element

The basic building block of the finite element method. Finiteelements are the regularly, or nearly regularly, shaped mathematicalidealizations of simple structures (e.g., beams, plates, solids) withknown mathematical solutions. When individual elements arecombined to represent a complex irregular structure, the resultingmathematical model approximates the behavior of the real structure.

Free Field Format Input data format in which data fields are separated by commas orblanks.

Geometric Stiffness See Differential Stiffness.

Global CoordinateSystem

The union of all the coordinate systems defined on all the CD fields onall the GRID entries. The global coordinate system in NX Nastran is,therefore, not a single unique system. Note that the basic coordinatesystem may also, but not necessarily, be a part of the global coordinatesystem. Many commercial finite element programs and textbooksuse the term global coordinate system to describe the coordinatesystem that NX Nastran calls its basic (default) coordinate system.See also Basic Coordinate System, Displacement Coordinate System,and Local Coordinate System.

Global StiffnessMatrix

The stiffness matrix of the entire structure. The global stiffnessmatrix is an assembly of the elemental stiffness matrices of individualelements in terms of the global coordinate system. See also ElementalStiffness Matrix.

Grid Point

A geometric point that defines model geometry and provides a pointto which finite elements are connected. Grid points are located inspace with respect to a particular coordinate system and are displacedwith the loaded structure. Analysis results, such as displacementsand reaction forces, are reported at grid points. The basic equations offinite element analysis are written in terms of grid point displacement.

Grid Point Stress A rational scheme to interpolate and/or extrapolate known elementand vertex stresses over a surface or volume.

Hencky-von MisesStress See von Mises stress.

HomogeneousMaterial

A material that has the same property in all directions at all locationsin the structure. See Anisotropic Material, Isotropic Material, andOrthotropic Material.

Glossary 1-5

Chapter 1 Glossary

Ill-conditioning

A system of linear equations is said to be ill-conditioned if smallperturbations in the system lead to large changes in the solution.NX Nastran checks for evidence of ill-conditioning in the system ofequations representing the structural model. A high value of epsilonindicates a potential ill-conditioning problem. Ill-conditioning doesnot necessarily result in a fatal error but can result in inaccurateanswers. Possible causes of ill-conditioning include a high differencein stiffness between adjacent elements in the model, unconnecteddegrees of freedom, rigid body motion, or the presence of mechanisms.See also Epsilon.

InformationMessage See User Information Message (UIM).

Input File See .dat File.

I/O Time

Stands for input/output time. I/O time is the time it takes yourcomputer to transfer data between different locations in yourcomputer during runtime (e.g., from memory to scratch disk). SeeCPU Time, Elapsed Time, and Turnaround Time.

Isoparametric A modern type of finite element formulation which offers highaccuracy with good efficiency (i.e., relatively low computational cost).

Isotropic Material

A material that has the same material property in all directionsat a given location in a structure. This material can be defined bytwo independent elastic constants in the stress-strain relationship.See Anisotropic Material, Homogeneous Material, and OrthotropicMaterial.

Lamina

A term used to describe composites. A lamina is a single layerconsisting of a group of unidirectional fibers (or sometimes wovenfibers) arranged to form a flat plate or curved shell. A lamina makesup the basic building block of a two-dimensional composite element.

Laminae More than a single lamina.

LaminateA stack of laminae bonded together. The principal direction of eachlamina may be oriented in a different direction to obtain the desiredstrength and stiffness properties.

Large Field FormatInput format for Bulk Data entries in which the data fields are 16columns wide, allowing numerical data to have a greater numberof significant digits.

Line Element

Elements, such as bars, rods, and beams. A line element is typicallyconnected by two grid points and is also known as a one-dimensional(1-D) element. One-dimensional elements do not imply that theelements can only be used for a 1-D structure; rather, it can be usedfor a 1-D, 2-D, or 3-D structure. An example of an application of 1-Delements in a 3-D structure is the use of CBARs/CRODs for framesand stringers of aircraft structures.

Linear StructureA structure whose displacements are linearly proportional to theapplied load. Once the load is removed, the structure returns to itsoriginal undeformed configuration.

1-6 Glossary

Glossary

Load

A general term referring to forces, moments, pressure loads, thermalloads, electromagnetic loads, etc. In NX Nastran analysis, loadsare known quantities that are applied to the structural model. NXNastran then solves for the unknown displacements of the structure.

Local CoordinateSystem

A user-specified coordinate system that accommodates the input ofgeometry data or the reporting of analysis results. Local coordinatesystems can be rectangular, cylindrical, or spherical, and are definedwith respect to the basic (default) coordinate system or another localcoordinate system. The only rule in NX Nastran is that the localcoordinate system ultimately must be able to be transformed backinto the basic coordinate system. See also Basic Coordinate System,Displacement Coordinate System, and Global Coordinate System.

.log File

A file created by running NX Nastran that contains systeminformation and system error messages. By default, the extension.LOG is appended to the filename. You should always check this fileif your job appears to fail for no apparent reason. This failure canresult from such problems as insufficient disk space or that the jobwas cancelled by the operator. In many cases, the .LOG file providesyou with a clue to the cause of the problem.

Machine Zero

A value of zero with a small amount of computer roundoff error added.In a typical structural model, a number such as 1.2345E-12 may beconsidered a machine zero. This term is also known as computationalor numeric zero.

.MASTER File

A directory file created by running NX Nastran containing a list ofall of the database sets used in your run, an index pointing to allthe data blocks created and where they are stored, and the NDDL.By default, the extension .MASTER is appended to the filename.This file is needed if you want to perform restarts. See also NDDLand .DBALL File.

Material CoordinateSystem

An optional coordinate system used to orient orthotropic or anisotropicmaterial properties. For isotropic materials, a material coordinatesystem is not needed.

Matrix Direction

A term used to describe composite materials. Matrix direction iscommonly known as the transverse direction or 2-direction. Thematrix material by itself has very low strength; however, it holds thefibers together to form a structure that produces a high strength toweight ratio (see Composite Material and Fiber Direction).

MechanismA mechanism occurs when part of a structure is capable of rigidbody (strain-free) motion. In linear static analysis, the presence of amechanism produces a singularity failure in the solution.

Mesh

The pattern formed by a collection of finite elements. Relatively fewelements result in a coarse mesh. Adding more elements produces afiner mesh, which can more closely represent an irregularly shapedstructure. In general, a finer mesh is more accurate, but it is alsomore computationally expensive.

ModuleA set of NX Nastran program subroutines designed to perform aparticular mathematical or data-related task. Users have directaccess to NX Nastrans modules via DMAP. See also DMAP.

Glossary 1-7

Chapter 1 Glossary

MPC See Multipoint Constraint.

MultipointConstraint

A convenient way to impose a linear relationship between two or moredegrees of freedom. Common applications of the multipoint constraintinclude: defining the relative motion between two grid points as adegree of freedom or defining the average of the motions of severalgrid points as a degree of freedom.

NASTRANStatement

An optional statement that, if used, appears at the beginning ofthe NX Nastran input file. The NASTRAN statement is used tooverride the default values for certain operational parameters of theprogram. See nastran Command and NASTRAN Statement in theNX Nastran Quick Reference Guide for further information.

NDDL

Stands for NX Nastran Data Definition Language and is the internalNX Nastran language that descibes the database. The NDDLdescribes the content of the data blocks, checks whether data blocksand parameters are permanently stored, and sets up dependencychecks for efficient restarts. Knowledge of the NDDL is not requiredto use NX Nastran efficiently.

Nonlinear(Geometric)

Structural displacements that are larger than those allowed by smalldisplacement-based theory are said to be geometrically nonlinear.Large displacements require the use of special nonlinear solutionsequences in NX Nastran (e.g., Solution 106).

Nonlinear (Material)

A material in which stress is not linearly proportional to strain, suchas rubber. When the load is removed, your structure may not returnto its original undeformed state. Nonlinear materials require the useof special nonlinear solution sequences in NX Nastran (e.g., Solutions601 and 106).

Normal ModesAnalysis

An analysis used to determine the natural frequencies and modeshapes of a structure.

Numeric Zero See Machine Zero.

One-Dimensional(1-D) Element See Line Element.

OrthotropicMaterial

This is a special anisotropic material that can be used for plateand shell elements. It contains three orthogonal planes of materialsymmetry at a given location in the structure. This material can bedefined by nine independent elastic constants in the stress-strainrelationships. See Anisotropic Material, Homogeneous Material, andIsotropic Material.

Output File See the .f04 File, .f06 File, and .log File.

PARAM,AUTOSPC

A parameter that controls the detection and constraint of obvioussingularities in the model. PARAM,AUTOSPC is in operationby default in all solution sequences except for Solution 24.PARAM,AUTOSPC produces a grid point singularity table in the .f06output file; this table lists the singularities that were detected andconstrained. You should always check this singularity table to makesure that it is your intention for these DOFs to be constrained.

1-8 Glossary

Glossary

Parameter

Parameters are used to request special program features and to inputdata relating to these features. Parameters are specified on PARAMBulk Data entries and PARAM Case Control commands. A completelisting of parameter functions is included in Parameters in the NXNastran Quick Reference Guide.

.pch

A file created by running NX Nastran with the ECHO=PUNCH CaseControl command. By default, the extension .pch is appended to thefilename. The punched file is an ASCII file that can be used as part ofa future input file.

.plt A file created by running NX Nastran that contains the NASTRANplotter file. By default, the extension .plt is appended to the filename.

Postprocessor

A graphics package that is designed to help you interpret and displayyour finite element results. Common postprocessing operationsinclude x-y plots of numerical data, deformed shape plots of modelgeometry, and color stress contour plots.

PreprocessorA graphics package designed to help to create the finite elementmodel. Typical preprocessors create geometry, create mesh elements,apply loads and constraints, and perform certain types of error checks.

Restart A procedure that allows you to systematically continue from aprevious analysis without re-doing your problem from the beginning.

Results File See the .f06 File.

Rigid Body Motion

Rigid body motion occurs when the structural model is free todisplace in one or more directions (displacement without strain).A simple example of rigid body motion occurs when you move apencil from one location on your desk to another. No strain occursin the pencil-only translation and rotation as a rigid body. In staticanalysis, the possibility of rigid body motion due to an insufficientlyconstrained structure results in a singularity in the stiffness matrix.Consequently, the solution of the problem fails during decompositionof the stiffness matrix.

Rigid Element

Also known as an R-type element. The name rigid element issomewhat misleading since it includes both rigid and interpolationelements. Rigid elements consist of RBAR, RBE1, RBE2, RROD,and RTRPLT; these elements create a rigid connection between theconnected degrees of freedom. Interpolation elements include theRBE3 and RSPLINE. The RBE3 is often used to distribute loads andmass. The RSPLINE is often used to model mesh transition.

RotationDisplacement about a coordinate axis. A grid point has threerotational degrees of freedom, one about each axis. See also Degreesof Freedom (DOFs) and Translation.

Scalar PointA scalar point is defined by the SPOINT entry. It is associated withonly one degree of freedom and has no geometric location associatedwith it.

Set A collection or grouping of selective items in the NX Nastran model.It is primarily used for limiting the amount of output data.

Glossary 1-9

Chapter 1 Glossary

Single-PointConstraint (SPC)

The constraint of one or more degrees of freedom at a grid point,thereby enforcing displacement (often zero displacement) of thegrid point in the affected component directions. For example, thegrid point at the fixed end of a cantilever beam is constrained (i.e.,SPCd) in all six DOFs. Reaction forces, called forces of single-pointconstraint (SPCF), may be recovered at these grid points.

Singularity

Amathematical condition prohibiting matrix inversion. Consequently,the system of equations representing the structure cannot be solved.Common sources of singularities in linear static analysis include thepresence of unconnected or very weakly connected degrees of freedomor an inadequate prescription of constraints on the model resulting inrigid body motion.

Slowly AppliedLoads

A basic assumption of static analysis: loads must be slowly appliedso that no significant dynamic effects are caused.

Small Displacements

A requirement of linear structural analysis. Displacements mustbe sufficiently small enough so that they do not violate certainmathematical assumptions inherent in the design of the finiteelements used. Large displacements require nonlinear solutionmethods.

Small-Field Format Input format for Bulk Data entries in which the data fields are eightcolumns wide.

Solid Element

Elements resembling bricks (eight corners), wedges (six corners),or pyramids (four corners). Also called three-dimensional elements.Popular NX Nastran solid elements include the CHEXA, CTETRA,and CPENTA.

Solution Sequence

A prepackaged set of DMAP instructions designed to solve a particulartype of engineering problem. The SOL command in the ExecutiveControl Section is used to inform NX Nastran which solution sequenceto use; for example, SOL 101 is used to specify linear static analysis.See also DMAP.

SPC See Single-Point Constraint (SPC).

Spring Element

An element representing a simple, single degree of freedomextensional or rotational spring. Also called a zero-dimensionalelement or scalar element. The CELASi family of elements are springelements.

Static

In the finite element sense, static means that the structural model isconstrained to prevent rigid body motion (static equilibrium exists)and that loads are assumed to be slowly applied, thereby inducingno dynamic effects.

Stiffness Matrix See Global Stiffness Matrix and Global Stiffness Matrix.

Subcase

Subcases allow multiple individual load cases and/or multipleboundary conditions to be analyzed in the same NX Nastran run,thereby achieving greater computational efficiency than with separateruns.

SuperelementAnalysis

A very efficient method used by NX Nastran to perform sub-structureanalysis.

1-10 Glossary

Glossary

Surface Element

Elements, such as thin plates (which are flat) or shells (which arecurved). Also called two-dimensional (2-D) elements. Popular NXNastran surface elements include the CQUAD4 (quadrilateral) andCTRIA3 (triangular) elements. Two-dimensional elements do notimply that the elements can only be used for a 2-D structure; rather,it can be used for a 1-D, 2-D, or 3-D structure. An example of theuse of 2-D elements in a 3-D structure is the use of CQUAD4s formodeling the panels of an automobile.

Symmetry

A geometric property in which a structure has one or more planes ofsymmetry. Structural symmetry can be exploited to produce a smallermodel (appropriate constraints are used to model the boundaryconditions on the axis or axes of symmetry). NX Nastran contains aset of solutions sequences called cyclic symmetric solution sequencesthat perform this task automatically.

System Message System Messages refer to diagnostics associated with program orsystem errors. Analogous to User Messages.

TranslationDirect, linear displacement along a coordinate axis. A grid point hasthree translation degrees of freedom, one along each axis. See alsoDegrees of Freedom (DOFs) and Rotation.

Turnaround Time

The time from when you submit your job to when you obtain results.Turnaround time includes the effect of queuing at your computer site;therefore, it may be longer than the elapsed time. See CPU Time,Elapsed Time, and I/O Time.

Two-Dimensional(2-D) Element See Surface Element.

User Fatal Message(UFM)

An NX Nastran message describing an error severe enough to causethe program to terminate.

User InformationMessage (UIM)

An NX Nastran message that provides general information. Theissuance of an UIM is not necessarily indicative of a problem. NXNastran does not terminate due to an UIM.

User WarningMessage (UWM)

An NX Nastran message warning of an atypical situation; the usermust determine whether or not a problem exists. In general, NXNastran does not terminate due to an UWM.

.usrobj File

A file created by running NX Nastran that contains the object fileof the user-written DMAPs. By default, the extension .USROBJ isappended to the filename. This file can be deleted, and is deleted bydefault, if you are not creating your own DMAP.

.usrsou File

A file created by running NX Nastran that contains the source fileof the user-written DMAPs. By default, the extension .USRSOU isappended to the filename. This file can be deleted, and is deleted bydefault, if you are not creating your own DMAP.

von Mises Stress

This is a failure criteria commonly used for ductile materials. Thisstress value is an invariant quantity that is independent of theelement coordinate system used; it is always a positive number. Fora general stress state (nonprincipal axes), von Mises stress is givenby the following equation:

Glossary 1-11

Chapter 1 Glossary

.xdbAn optional file created by running NX Nastran that contains thegraphical database used by certain graphic packages. By default, theextension .xdb is appended to the filename.

1-12 Glossary

ContentsProprietary & Restricted Rights Notice1. Glossary