Introduction

The Model Input, or simply Input, dialog provides access to the various Input classes, including Geometry, Mesh, Section Properties, Thickness, Material, Load, Constraint, and Solution ID (Figure 1). The Input dialog provides a tab for each available input class. These tabs are ordered in a way consistent with a typical model creation sequence: create/modify geometry, attach a mesh, assign attributes, apply loads and constraints, etc.

At the top of the Input dialog are the C/A/O/M combo-boxes for selecting the desired combination of Class (e.g. Geometry), Action (e.g. Create), Object (e.g. Box), and Method (e.g. Locate). In the center of the Input dialog are the input fields and combo-boxes which relate to the specific class of Input chosen with the tab. At the bottom of the dialog is a set of buttons which are used to invoke a command (e.g. Accept, Delete). Some dialogs contain a summary of the data records corresponding to a particular class of Input. This listbox gives the user access to data previously entered so that it may be altered and replaced. For Geometry and Mesh Input classes, A/O/M-specific object lists, with useful filters & sorting options, can be viewed by selecting the “Index” subtab.

The Input dialog can be displayed on the screen by selecting “Input” from the Main Menu “Edit” pulldown menu, or by selecting an Input class such as Geometry, Mesh, Thickness, etc., from the Main Menu “Class” pulldown menu. Alternatively, the Input dialog may be activated by selecting the “Create Model” icon in the Main Toolbar.

Model Reference

By default, the three-dimensional (3D) model reference is assumed. However, the model reference may be modified before, and in some cases after, the model inputs are provided (Figure 2). The following rules govern how models may be constructed within a selected reference:

• Planar: models must be constructed in the Global XY-plane in order to be analyzed in the Planar reference.
  • When defining material properties, the user may specify whether the analysis is to be Plane Stress or Plane Strain.
• 3D: there is no limitation on model orientation/plane of analysis when models are constructed in the 3D reference.
  • Models which are valid in the Planar reference may be converted to thin solid (StressCheck shell) element representations by changing the reference from Planar to 3D.
  • Thin solid elements must be slope-continuous, and all six (6) rigid body modes in three-dimensions must be properly constrained, before executing a 3D analysis. By default, thin solid elements have thru-thickness discretization set to p=1.
• Extrude: models which are valid in the Planar reference may be converted to a fully 3D solid representation by changing the reference from Planar to Extrude.
  • The Planar mesh is extruded +/- t(x,y) in the Global Z-axis, where t(x,y) is the thickness at each location in the Planar mesh.
  • The resulting mesh will be pentahedra (if triangles in Planar) and hexahedra (if quadrilaterials in Planar).
  • Once a model has been extruded, it is possible to add to or modify existing load and constraint records before executing the analysis.
  • Note that when going from Planar to Extrude all six (6) rigid body modes in three-dimensions must be properly constrained before executing an Extrude analysis.
• Axisymmetric (Axisym.): models must be constructed in the Global RZ-plane in order to be solved in the Axisym. reference.
  • Additionally, the domain should be defined in such a way that all nodes and elements of the mesh should be located at R≥0.
• Plate: models must be constructed in the Global XY-plane and loaded normal to that plane (in the Global Z-axis) in order to be solved in the Plate reference.

Note: when a Global plane (XY or RZ) is required for model construction, it is automatically set when selecting the model reference.

Model Length Units

With the adoption of Parasolid as the geometric modeling kernel, it is necessary to consider the choice of units of measurement before creating or importing any geometry in StressCheck (Figure 3).

Standard Units

Length units are now chosen as part of a standard system of units. The choices are Other, in/lbf/sec/F, and mm/N/sec/C. The “Other” option indicates that the units are unknown. In all cases, it is the user’s responsibility to insure that units are given consistently throughout the program. When StressCheck starts up, the default units are “in/lbf/sec/F”. The default units may be chosen as part of the preference settings (File > Options).

When loading in an existing StressCheck model file, the units will be assumed to be “Other” unless the StressCheck .sci, .scw or .scp file contains a specific record assigning specific units. To manually select your system of units, use the Edit > Units menu option or use the Unit selector from the Reference/Theory/Units toolbar. Note: you may change the system of units only if no geometry has yet been defined.

Upper Units Threshold

To allow the correct handling of precision within Parasolid, all parts of a body must be contained within a box whose size is 1000 x 1000 x 1000 units, and centered at the origin. In Parasolid the default unit is one meter, therefore 500 meters is the maximum distance in any one direction that can be modeled. Hence, it is necessary to introduce a system of units so that the objects represented in Parasolid will be properly scaled to fit within this cube.

Lower Units Threshold

Parasolid recommends that the size of any geometry object or feature be greater than ~1e-4 meters (0.1 mm, 3.94e-3 in).

Model Inputs

Below are the model inputs supported in StressCheck, and accessible via the Input dialog tabs.

Geometry

To access the Geometry input, from the Class menu select Geometry or the Geometry tab in the Input dialog (Figure 4). The options under Geometry provide for the definition of the solution domain using points, lines, circles, ellipses, rectangles, etc. StressCheck lets you separate the definition of boundaries from the definition of the finite element mesh. Separation of geometric objects from mesh objects provides for a great deal of flexibility in modeling. Geometric objects may be defined parametrically so that the domain may be easily changed by adjusting individual design variables. Since boundary conditions may be attached to geometric boundaries, the finite element mesh may be easily changed without affecting boundary condition definitions.

To learn more about the geometry inputs, visit the following articles:

• Geometry Overview
• 2D Primitive Geometry Objects
• 3D Primitive Geometry Objects
• Sheet Body Operations
• 3D Solid Body Operations

Mesh

To access the Mesh input, from the Class menu select Mesh or the Mesh tab in the Input dialog (Figure 5). The options under Mesh provide for the specification of the solution domain using nodes, elements, fasteners, etc. Meshes may be generated manually (i.e. hand-meshed) or automatically via the MeshSim automesher.

To learn more about the mesh inputs, visit the following articles:

• Meshing Overview
• Manual Mesh Generation
• Node Creation Methods
• MeshSim Automesh Generators
• MeshSim Automesh Generation Methods

Section Properties

The Section Properties input class is used for assigning cross sectional properties to beam elements. To access the Section Properties input, select the corresponding tab in the Input dialog (Figure 6). The section property interface under the Planar Elasticity reference contains three subtabs: User, Library and Database.

To learn more about the section property inputs, visit the Section Properties Overview.

Thickness

The Thickness input class is used to assign thicknesses to 2D elements in the Planar reference or to extruded elements in the Extrude reference. To access the Thickness input, from the Input dialog select the Thickness tab (Figure 7). The thickness for an element, a group (set) of elements or all elements can be given as a constant, parameter, or formula. Note: thicknesses may be piecewise, constant, or parametric. Switching to the Extrude reference will extrude the Planar mesh in the global Z-axis to +/- 1/2 of its thickness.

To learn more about the thickness inputs, visit the Thickness Overview.

Material

To access the Material input, from the Input dialog select the Material tab. The Material input handled in two parts: One is the definition of the material properties and the other is the assignment of material properties to the elements. The Define tab (Figure 8a) is used for defining the material properties (e.g. elastic modulus and Poisson’s ratio for linear elastic materials) while the Assign tab (Figure 8b) is used for assigning the defined properties to the elements in the mesh.

To learn more about the material inputs, visit the Materials Overview.

Load

To access the Load input, in the Input dialog select the Load tab (Figure 9, depending on the Theory selector, this tab will read Load for Elasticity, or Flux for Heat Transfer). You may specify a unique name which identifies the load case you are about to enter (load ID). A load ID may contain any number of load records/assignments. In engineering practice often multiple load cases must be investigated. Each load case must be given a unique name in the ID field. Load methods such as Traction (applied stress), Force/Moment, Spring Displacement, Bearing (cosine traction distribution), Body Force and Point Loads are available in StressCheck. Note also that the content of the Load tab depends on the selected reference (Planar, 3D, Axisymmetric, Plate or Extrude).

To learn more about the load inputs, visit the Loads Overview.

Constraint

To access the Constraint input, in the Input dialog select the Constraint tab (Figure 10, depending on the Theory selector, this tab will read Constraint for Elasticity, or Temperature for Heat Transfer). You may specify a unique name which identifies the constraint case you are about to enter (constraint ID). A constraint ID may contain any number of constraint records/assignments. In engineering practice often multiple constraint cases must be investigated. Each constraint case must be given a unique name in the ID field. Constraint methods such as General, Spring Coefficient, Symmetry, Built-In and Rigid Body are available in StressCheck. Note also that the content of the Constraint tab depends on the selected reference (Planar, 3D, Axisymmetric, Plate or Extrude).

To learn more about the constraint inputs, visit the Constraints Overview.

Solution ID

To access the Solution ID input, in the Input dialog select the Solution ID tab. Because StressCheck allows more than one load case and constraint case to be defined, it is necessary to associate a unique solution name (ID) with each desired constraint and load name pair. In the Solutions subtab (Figure 11a), enter a solution name in the solution ID field and select a constraint ID and load ID from the existing records. Click on the Accept button and the solution, constraint, and load names will appear in the scrolling list area at the top of the dialog box. For advanced control of solution ID’s, the Configurations subtab (Figure 11b) may be explored.

To learn more about the solution ID inputs, visit the Solution ID Overview.

p-Discretization

To access the p-Discretization input, in the Input dialog select the p-Discretization tab (Figure 12). The use of p-Discretization enables the user to select any group of elements and limit or fix the polynomial degree (i.e. p-level) for those elements. When a solution is initiated, the initial and final p-levels given in the StressCheck Solver input are assigned to ALL elements as a default setting. Explicit p-Discretization settings may be assigned to individual elements that will override the default settings. Individual elements may be assigned p-Discretization attributes that are Variable, Bounded, or Fixed.

To learn more about the p-Discretization inputs, visit the P-Discretization Overview.

h-Discretization

To access the h-Discretization input, in the Input dialog select the h-Discretization tab (Figure 13). The use of h-Discretization enables the user to select manually meshed elements, faces, edges or nodes for further mesh refinement by subdivision. Note: refinement of automeshed elements is performed in the Mesh tab of the Input dialogue, under Create > Mesh. An h-Discretization assignment record can be added that describes the reference objects, method, and refinement attributes for each h-Discretization operation (there may be more than one h-Discretization necessary). Each h-Discretization assignment record must be given a unique name, a layer attribute, and some additional attributes that depend on the object and method of discretization (Uniform, Simple Graded or Boundary Layer).

To learn more about the h-Discretization inputs, visit the H-Discretization Overview.

Sets

To access the Sets input, in the Input dialog select the Sets tab (Figure 14). Sets are a convenient way of grouping objects together in user-defined collections for visualization, assignment of attributes, extractions, etc. Sets may be defined through manual selection of objects from the Model View, by selection of a bounded group of surfaces (i.e. geometric shell) or by using a box location/pick tolerance approach. Set names with the prefix “SET” are automatically generated by StressCheck during assignments of materials, loads, boundary conditions, and p- or h-Discretizations using the objects selected from the Model View.

To learn more about the sets inputs, visit the Sets Overview.

Parts

To access the Parts input, in the Input dialog select the Parts tab (Figure 15). StressCheck provides a facility for organizing the components of a particular model into user-defined Parts. Parts are just a generalization of the more familiar set definition in StressCheck, and are useful for applications such as Multi-Body Contact and Solution Configurations.

To learn more about the parts inputs, visit the Parts Overview.