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Overview

Quickfem models consist of points, lines and polygons.  The polygons are called "features" and can have different thicknesses, materials, constraints, loads and colours.  Quickfem automatically meshes the features during editing to the element size of the model.  The model element size can be changed to refine the model.  During meshing, features with coincident element edges are connected, the nodes are equivalenced.  Model default thickness, materials and loads are applied to speed up model creation.

Geometry Menus

Points, Lines and Features each have contextual menus.  To raise these menus, selecting on the geometry entity to highlight and then tap again; or double tap for speed.  The selection order is Points then Lines then Features, if you have trouble selecting Lines or Feature pinch to zoom and try again.

Feature Creation

To create a feature press "+Feature".   Tap to create points, tap back onto the first point to close the polygon and finish the feature.  All Features will modelled as coincident notes, effectively joined, if one or more elements share edges.  A thin feature boundary line indicates a join.

Geometry Menus

Points, Lines and Features each have contextual menus.  To raise these menus, selecting on the geometry entity to highlight and then tap again; or double tap for speed.  The selection order is Points then Lines then Features, if you have trouble selecting Lines or Feature pinch to zoom and try again.

Model Types

The model types available in Quickfem are

• 2D Plane Stress
• 2D Plane Strain
• 2D Axisymmetric

Any model can be converted between these types at any time via the Model/Model Type menu item.

2D Plane Stress Models

Features have individual, user defined thicknesses.  Both point loads and line loads are applied as total loads, not running loads.  The Line menu will display both running loads and total loads; only total loads can be entered.

2D Plane Strain Models

Features have a unit thickness, which is dependent upon which unit for length is default for the particular model  ie. if length units are "mm" and load units are "N" then all feature thicknesses = 1mm and loads are all in "N/mm".  Both line loads and point loads are then displayed as total load per unit thickness.

2D Axisymmetric Models

All features are axisymmetric and don't really have a thickness.  The axis system is RZ, ie. R is horizontal and Z is vertical.   Point loads are applied as total loads applied to 2.pi.R of length.  Line loads are applied as pressures and applied over the entire swept area the line creates about the vertical axisymmetric axis.

Editing Features

Move a feature

• Long press in centre of the feature then drag

Insert a Point

• Highlight a line, then long press to insert a point

Delete a Point

•  Double tap a point to invoke the point menu, select delete point

Delete a Feature

• Double tap the centre of the feature and select "Delete Feature"

Duplicate a Feature: Via the feature menu

• Double tap the centre of the feature and select "Duplicate Feature"

Arcs, Fillets, Holes

To create an arc, double tap on a line and enter an arc angle between +180 and -180.   A positive angle will produce a bulge, a negative angle makes a cut-out.  Make a hole in a panel by creating two halves with cut-outs and then join together.  To remove an arc, set the Arc angle back to zero, or delete surrounding feature points.

Meshing

Meshing is automatic and happens in real time during feature creation and editing.  The features are meshed to the model element size which is defined under the "Model" menu bar.  The default element size (for new models) can be altered via the Model/Element Size menu option.

Mesh smoothing can be turned off via Model/Mesh Smoothing.  This will increase meshing speed if this is desired.

Constraints

To add or alter constraints, press the menu bar button "Constrain" repeatedly to apply different constraints to a highlighted point or line.   The cycled values are:

Point

• Fixed
• Simply supported
• Free

Lines

• Fixed
• Roller (only implemented for vertical or horizontal lines)
• Free

Thermal Loads

Under the Model menu, add a temperature via "Thermal Loads".  The resulting strains are the mechanical strains due to thermal loads.

Fasteners

To add a fastener, double tap a feature to and select "Add Fastener".  The fastener will be added to the feature at the location of the double tap.

A "Fastener" in Quickfem is either a grounded node or a coincident node between overlapping features.  Two or more features can be connected this way.

Note that fasteners are effectively singularities when modelled this way hence using a very fine mesh will produce unrealistically high stresses.

Materials

Multiple materials can be defined and stored within the model files, the *.QFM file.  A set of default materials are added to each new model.  These can be updated via the Model/Add Standard Model menu item.  This will overwrite ALL of the default materials with the materials in the currently loaded model.

Currently, only isotropic materials are available

Units and Precision

Are stored with the model file, default units and precision are attributed to new models

Results

Several different result types are available and these are dependent upon the type of model.

Displacements

The "+" and "-" buttons scale the displacements, the size of scale is listed in the message box.  Fringe options are dx, dy and dtot (dx^2 + dy^2)^0.5.   For Axisymmetric models, dx = dr and dy  = dz.

Strain

Quickfem calculates shear strains as Engineering Shear Strain, gxy is engineering strain

• gxy = dv/dx + du/dy

Stress

Principle Stress

• s1 = (sx + sy)/2 + (((sx - sy)/2)^2 + sxy^2))^0.5
• s2 = (sx + sy)/2 - (((sx - sy)/2)^2 + sxy^2))^0.5

Principle Stress for Axisymmetric models

• s1 = (sr + sz)/2 + (((sr - sz)/2)^2 + srz^2))^0.5
• s2 = (sr + sz)/2 - (((sr - sz)/2)^2 + srz^2))^0.5

Equivalent Stress, Von Mises Stress

• seq = (((s1 - s2)^2 + s1^2 + s2^2)/2)^0.5

Reaction Loads

Can be displayed as vectors or as x, y components