Margin of safety calculations

A calculation is a set of the following items that the software uses to calculate a margin of safety:

• The method that forms the basis for the margin of safety calculation.

• The load case set from which to extract results for the calculation.When the software performs the margin of safety calculation, it repeats the margin of safety calculation for each load case in the load case set. That is, the software does not superpose the results from each load case in a load case set into a single result. Rather, it evaluates the margin of safety for each load case separately.For more information on load case sets, see Load case sets (margin of safety).

• The parameters such as material properties and physical dimensions that are required for the calculation.

• The results to use in the calculation. The results can be obtained in the following ways:From the analysis results.From values that you manually enter. For information, see Manual load extraction.From nodal force report results. For information, see Nodal force report extraction.When you obtain the results from the analysis results, you must do the following:Specify the result type and, if applicable, the component of the result type to use in the calculation.Select the nodes or elements for which to retrieve the results.You can select the nodes or elements directly or indirectly from groups or parent/child relationships.For more information on parent/child relationships, see Parent/child behavior in margin of safety calculations.Specify the options to extract a single value from the set of results for each load case in the load case set.For more information on these options, see Extracting a single value from the set of results (margin of safety).

The software allows you to create multiple margin of safety calculations. You can create them individually, or for calculations where the only difference is the nodes or elements from which the software obtains the results for the calculation, you can create them all at once.

Calculations appear in the Simulation Navigator under the Calculations node.

Method selection

The software has an extensive variety of built-in methods that allow you to evaluate yielding of ductile materials, buckling of columns, plates, and shells, and fastener-related failures.

When you select most built-in methods, in the Calculation - Method Selection dialog box, a diagram appears that contains the physical dimensions, constraints, and loads that are used in the method. You can also open a window that contains detailed technical information on the built-in method that you can refer to when defining the parameters for the method.

In addition to the built-in methods, you can also create your own methods. Such methods are referred to as custom methods.

For more information on custom methods, see Custom methods.

Parameters for methods

The parameters for a method can include material properties and physical dimensions, among others.

For example, when you select the Tresca plane stress method, the allowable shear strength of the material is the only parameter. When you select the Euler column buckling method, the cross section area, length, second-moment of the area, and end fixity coefficient of the column, and the elastic modulus of the column material are the parameters. When you select a composite plate buckling method, in addition to physical dimensions, laminate information and edge support conditions are parameters.

When you define parameters for methods, you can typically type numerical values directly into the entry box, or you can click in the entry box to define the parameters with:

• Measurements in the graphics window.

• Lengths and thicknesses associated with FE and geometric entities in the model.For more information, see Property extraction.

• Material properties for materials in the library of materials or custom materials that you define

• Expressions and functions

• Fields

• Beam cross section propertiesFor more information on how to define parameters with beam cross section properties, see Beam cross section property extraction.

• Laminate propertiesFor more information on how to define parameters and conversion factors with laminate properties, see Laminate property extraction.

For example, you can use fields and expressions to account for functional relationships in parameters such as temperature-dependent material properties.

Laminate selection

Some built-in and custom methods may require you to select a laminate as an input of the method. To do so, you can use laminate extraction.

For more information, see Laminate extraction.

Result selection

You can select any result type that is available in the post-processor. The result types that are available in the post-processor depend on the output requests in the SOL 101 linear static or SOL 144 static aeroelastic response solution.

For information on how to edit output requests, see SOL 101 setup for margin of safety.

For each load that is required to perform the margin of safety calculation, the software retrieves a single result value for each node or element that you select. Because element-nodal results have multiple result values at a node, when you select an element-nodal result type, you must specify how the software obtains a single result value from the multiple result values at a node.

For example, you can have the software average all of the values into a single value, or you can have the software use the algebraic maximum or minimum value, and so on.

Node and element selection

You have a number of options for selecting the nodes or elements for which the software retrieves the results to use in the margin of safety calculation for each load case in the selected load case set. You can:

• Select nodes or elements directly from the graphics window.

• Use a selection box to select nodes or elements directly from the graphics window.

• Select nodes or elements directly by their identification number.

• Select nodes or elements indirectly by selecting parent polygon geometry in the graphics window.

• Select nodes or elements indirectly by selecting groups that include nodes, elements, and parent geometry.

Individual calculations

You use the Create Calculation command to create a calculation. The loads that are used in the calculation are extracted from the set of results created from the results for all the nodes or elements that you select for the calculation. You can select the nodes or elements directly or indirectly through parent/child relationships. For information on indirect selection through parent/child relationships or groups, see Parent/child behavior in margin of safety calculations.

The result type that you select determines whether the software uses results from nodes or elements. If in the Load Extraction dialog box, in the Result group, you set Result Type to a nodal or element-nodal result, the software uses results for nodes. If you set Result Type to an elemental result, the software uses results for elements.

For example, suppose that in the Load Extraction dialog box you set Result Type to an elemental result type. If you set Entities Type to Elements, and select elements directly from the graphics window, the software creates the results set for the calculation from the elemental results for the elements that you select.

If you set Entities Type to Edges, and select polygon edges directly from the graphics window, the software creates the results set for the calculation from the elemental results for the elements that have an element edge that lies on the polygon edges that you select.

Where do I find it?

Application	Pre/Post
Prerequisite	An active margin of safety solution
Simulation Navigator	Right-click Calculations→Create Calculation

How do I

Create a margin of safety calculation

Import values from a spreadsheet

Extract the area from a beam cross section

Extract a projected length

Create a margin of safety calculation using an allowable method

Bolt shear method example

Column Euler method example

Nodal force report extraction example

Learn more

Parent/child behavior in margin of safety calculations

Extracting a single value from the set of results (margin of safety)

Manual load extraction

Nodal force report extraction

Extracting shell element plane stress components relative to a common CSYS

Property extraction

Beam cross section property extraction

Laminate extraction

Laminate property extraction

Sources manager (margin of safety)

Displaying result sources for margin of safety calculations

Look up more details

Methods for buckling of orthotropic laminates

Quick links

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Margin of Safety methods documentation

Margin of safety calculations, Simcenter 3D 2021.1 Series

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