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Entire Model verse Individual Components or Groups“Pregrouping” should not pose an inconvenience for investing a single component in an assembly, given that is always good modeling practice to create separate groups for each component in assembly modeling.

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Types of Output Data

I. DisplacementsIn addition to the display of displacement magnitudes, you will generally be allowed to request the display of components with respect to either the global coordinate system or a user-defined coordinate system.

RotationsYou should be able to request the display of rotation results for nonsolid elements only. When torsional rigidity is important, such as in vehicle frame structures, these are useful quantities.

Velocities and Accelerations

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II. Strain Quantities

Max, Mid, Min Principal Strain

The max principal strain is the most positive of these, the min principal is the least positive, and the mid principal has a numerical value between the former two.

Normal and Shear Strain

These quantities will generally be displayed relative to global coordinate system directions, although you may be given the option to select a user-defined coordinate system instead.

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Shell Membrane and Transverse Shear Strain

Shell membrane strains refer to a biaxial strain state along the mid-plane of the shell element. This definition utilizes the local coordinate system of each element, where the Z axis is normal to the shell. Shell transverse shear strains occur along the mathematical thickness of the shell element, reported with respect to the elemental X and Y directions.

Strain Energy

This quantity is useful for predicting high stress areas in ductile materials, and is the basis for the derivation of the von Mises stress. For all elements, a total strain energy may be reported .

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For shell elements, a membrane value per unit area due to the stretching of such elements’ mid-planes may be displayed. Shell and line elements may report both bending and shear strain energies per unit length. Tensile and torsion strain energies per unit length may also be available for line elements only.

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III. Stress Quantities

Max, Mid, Min Principal Stress

Normal and Shear Stresses

Von Mises Stress

The von Mises stress is defined by the distortion energy theory as a combination of all principal stress, which are themselves a combination of all normal and shear stresses.

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IV. Reaction and Resultant Forces and Moments

Analysis goals will often include determining the reaction forces and moments occurring at each model constraint. These reactions may then be used as input loads to separate models of the supporting attachments that your constraints have attempted to simulate. On other occasions you will be more interested in resultant forces that occur internally in the model. These in turn can be used to evaluate the strength of internal structural joints in assembly modeling, or as load parameters in a simplified model of a section of the original.

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Line Element Results1. Strain and stress

Line element strain and stress results are usually divided into axial, bending, torsional, and total by the postprocessor for display purposes.

2. Resultant Force and Moments

Resultant forces can be displayed in either axial or shear components. Resultant moments may also be separated into bending and torsional.

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Shell Element ResultsFor a given strain or stress state, the postprocessor must be directed as to the location along the thickness of the shell for which to report the results. The choices generally available are top, bottom, maximum, and minimum.

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I. Types of Results Displays

II. Animation

III. FringeIn reality, strain, stress, and resultant force values are continuous through the material of the structure. By comparison, due to the discretization inherent in the technology, these FEA calculated quantities are virtually never continuous across two elements. However, because these quantities should be continuous, most codes allow for averaging in fringe plots. You should nonetheless always look first at inaveraged results so that errors in the mesh are not hidden by the display.

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Appearing below are a few important notes on averaging.

• Never average between elements of different type

• Never average between elements of different material property

• Never average between shell of different thickness

• Never average between line elements of different cross sections

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III. Isolines and Isosurfaces

Whereas fringe plots will color fill the areas between the limiting boundary values of each range, a contour plots will color outline the boundaries themselves.

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IV. Query

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V. Vector Plots

Quantities that may be displayed with vectors include displacement, velocity , and acceleration magnitudes and their rotational equivalents, and max and min principal stresses. The most useful vector plot is arguably that of max and min principal stresses, which displays the directions of both principal quantities. This is extremely helpful in determining strain gauge placement and orientation when conducting correlation testing.

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VI. Graphs

Graphs are very useful in determining the continuity of results, and therefore, results quantity. As your solution reaches better convergence, these graphs should become smoother.

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Results Interpretation: Quality Inspection and Verification TechniquesI. Convergence Issues

The first thing you must determine in FEA results interpretation is whether the solution to the analysis has converged. The quality of your results is an indication of , and depends on, this convergence criterion.

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II. Correlation to Expectations (Common Sense)

Consult with your peers. Take a closer look at your boundary conditions, element properties, and all other assumptions. You should never continue past this point until you are convinced that what you are seeing on the screen is real. The farther you progress in FEA, the more projects you take to completion, the better tuned your common sense or engineering judgment will become.

III. Qualification and Review of Assumptions

Each one of your loads, constraints, properties, and modeling and solution choices carried an assumption. You should always keep a record of assumptions as you progress through the setup process.

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IV. Correlation to Closed Form Equations

V. Use of Test Models

If you are attempting to use a new modeling technique, evaluating it in a small and simple test model is much more efficient than in a full, and probably complex and resource intensive, analysis. A good rule of thumb to use with test models is “one question, one answer.” develop test models to isolate the technique or quantity of interest.

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VI. Correlation to Testing

A guideline for correlation with FEA is that you always analyze what you test, and test what you analyze. The boundary conditions of a test fixture will often be different from those of the actual application, and this difference must be accounted for in your model. VII.Relation to Problem Goals