Overview
Quickfem is a 2D finite element analysis tool designed for quick model creation.
Video Help
If you prefer to learn via video rather than text, a set of tutorial videos is provided below. Please note that the latest major release V4 (Dec-2024) of Quickem has many visual differences and improvements compared to previous versions.
Part 1 Basic Creation
Part 2 3D Views, Model Types, Results, Units
Conventions
Quickfem has several conventions which are helpful to understand up front.
Models are made with shapes called “Features”
Each model consists of one or more shapes called features.
Each feature has control points, thickness, a defined material, constraints, loads and colours.
Auto Meshing
Quickfem meshes automatically, after exiting from Create or Edit modes.
Snap to Grid
Geometry points (feature points) always snap to a grid – this makes it easy to create shapes using touch.
Tap to Select
Tap on the model to select, tap twice for menus.
Long Press to Drag
To drag geometry, features, loads, constrains and axis, simply long press.
Two meshing types, Grid and Delaunay
With the release of v4.62 on iOS and v62 on Android, a new meshing algorithm is introduced Delaunay mesher. The Delaunay meshes can handle holes and more complex geometry. It also doesn’t require the element size to be equal to the grid size.
Element Size = Grid Size (except for Delaunay Mesher)
The element size is equal to the grid size when using the “Grid Mesher”
Changing the element size will change the grid size. All feature control points will “snap” to the new grid size – this can sometimes lead to unintended consequences, especially during coarsening operations as the geometry snaps into the new positions.
Alternatively, switching to the meshing type “Delaunay Mesher” decouples grid size from element size. See the video snippet below for a demonstration of this.
Use Undo if things go wrong
If/when things go wrong you can always hit Undo. If in Edit mode, tap outside the features to get into View mode, the Undo is now available.
Refining the Mesh is FAST
Quickfem meshes fast, really fast.
You should not be afraid to refine and coarsen the mesh at will.
- a course mesh helps with editing geometry
- a fine mesh increases accuracy of model results
Refining the Mesh is EASY
The Refine or Coarsen commands halve or double the element size, however, this also affects the geometry points.
- Halving element size won’t change feature point locations
- Doubling element size may change feature point locations depending on whether the grid size is a divisor of the feature location
For finer control, you can manually set the size via an entry field
Feature Boundaries
Features with coincident element boundary edges are assumed to be connected, hence, these nodes are equivalenced and the meshes effectively are joined.
Thin boundary lines indicate where features are connected.
The “Grid Mesher” has a more generic connected boundary finding method than the Delaunay mesher.
To ensure that feature boundaries match when using Delaunay, ensure that any matching feature edges have coincident feature control points. This is because the Delaunay Mesher seeds each line of a feature with the element length size whereas the original Grid Mesher seeds each line with grid intersection points.
This snippet from the Help video explains this best.
Set your Environment
Moving beyond first steps, you will want to setup your Quickfem environment for the type of models you are looking to create.
- Set units types
- Set decimal places
- Set default loads and thickness
- Choose colour theme
Operation Modes
Quickfem has 4 modes of operation, View, Create, Edit and Solved.
View Mode
View mode is the default mode. From here selecting “Create” will switch to Create mode (see below) where new feature shapes can be made. To edit the model geometry, simply tap on a feature.
Create Mode
Create mode is where new features can be made. Tap anywhere to start, close the polygon to finish the shape.
Lines can be converted to arcs and fillets once the feature is first created.
Edit Mode
Tap on any feature to get into Edit mode, tap outside the features to go back into View mode.
Touchable points are highlighted with circles and can be tapped for menus or long pressed to drag.
To select a different feature, just tap it. Features can be dragged with long press also.
Solved Mode
To solve a model, hit Solve, to go back to View mode, hit Clear.
Deformation scale, result types, free body loads, fringe display options can all be set here.
Panning
Simply drag a fingertip anywhere in the model to pan
Zoom and Fit
Use the pinch gesture anywhere to zoom in and out.
Double tap anywhere in clear space, that is not on an feature, to fit the model to the screen.
3D Viewing and Rotation
Quickfem has a 3d setting that is useful for seeing feature thicknesses and Axisymmetric arrangements.
To rotate the model, long press in a space where there is no feature, and then drag. Zooming in and out using pinch gestures can help here also.
Contextual Menus
Geometry Menus
Tapping twice on any point, line or feature will display menus.
In selection, Points have priority then Lines then Features.
If you have trouble selecting Lines or Features, simply pinch to zoom and try selecting again.
Editing Tips
How to Insert a Point
To insert a point into a feature boundary, first select the line then long press. A new point should appear.
How to Delete a Point
Double tap on a point to invoke the point menu. Then select “Delete Point”
Delete a Feature
Double tap the centre of the feature and select “Delete Feature”
Duplicate a Feature
Double tap the centre of the feature and select “Duplicate Feature”
Holes (Method 1)
There are 2 ways to create holes, the simplest way is to double tap on the interior area of feature to bring up the Feature menu – then select Add Hole.
The first time a hole is added to a feature, two things happen
- a hole is created with a default diameter = two times the element size
- the mesher type changes to the new advanced Delaunay mesher
The hole diameter can be adjusted by double tapping the hole object to launch the hole menu.
Holes can be dragged into different positions, but always snap to the grid.
Holes can be deleted.
Arcs, Fillets, Holes (Method 2)
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.
Arcs can also be used to make a hole 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.
Scaling the Model
The entire model can be scaled by a factor by selecting Model / Scale the model and entering a scale factor.
Technical
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 menu Model then Model Type.
When solving the model, the model type will appear under the fringe scale.
2D Plane Stress Models
2D plane stress models require features to have thickness. Thickness is set via the feature context menu (double tap a feature). Switching to 3D view helps to check thicknesses visually.
2D Plane Strain Models
2D plane strain models have infinite thickness. Switching to 3D view shows a zero thickness dimension.
Point loads are applied per unit of thickness. For example, if you are using Newtons and millimeters then point loads are all in “N/mm”.
Line loads can only be applied as pressures – this simplifies whole head scratching scenario of trying to apply running loads to an infinite thickness model!
2D Axisymmetric Models
2D axisymmetric models don’t have thickness. The axis system used is RZ, where 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 that the line creates about the vertical axisymmetric axis.
Meshing Smoothing
Mesh smoothing can be turned off via Model/Mesh Smoothing. This will increase meshing speed if this is needed.
Constraints
To add, remove or alter constraints, select a point or a line and then press the “Constrain” repeatedly to cycle through different constraint options.
Point Constraints
Points can be in 4 different constraint states, that are then applied to the node of the element that is attached.
- Free
- Simply supported in “x”
- Simple supported in “y”
- Free
Point constraint symbols have handles that can be used to rotate the symbol. For fixed constraints, the orientation of the symbol has no effect as the attached element. For simply supported constraints, the handle will “snap” into either x or y orientation.
Line Constraints
Lines can have 3 different constraint states that are then applied to all nodes attached to that line.
- Free
- Roller*
- Fixed
*Note that roller constraints can currently only be applied to perfectly vertical or horizontal lines.
Loads
To add or remove loads, select a point or a line and then press the “Load” to cycle through on/off scenarios. Loads can also be applied or deleted via the point and line context menus.
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, first select a feature then tap again in the feature. The feature menu should appear, select “Add Fastener”. The fastener will be added to the feature at the location of the single or 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 (.QFM). 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
As of Dec-2024, units and precision are now a user setting and are not stored with the model file. Hence all models read in will display in the current user preferred units and precision. The values themselves are not affected, these are (and were) always stored in SI units in the model file anyway.
Results
Several different result types are available and these are dependent upon the type of model.
Displacements
The “Deform More” and “Deform Less” buttons scale the visualized displacements. The current size of the displacement scaling is listed under the fringe scale legend.
Displacements can also be presented as a fringe, the fringe options are dx, dy and dtot = (dx^2 + dy^2)^0.5.
For Axisymmetric models, dx = dr and dy = dz.
Strain
Quickfem calculates for Plane Stress and Plane Strain models the following values for strain
- ex
- ey
- gxy = dv/dx + du/dy. (engineering strain)
For Axisymmetric the following strain values are calculated
- er
- ez
- etheta
- grz
Stress
Quickfem calculates for Plane Stress and Plane Strain models the following values for stress
- sx
- sy
- sxy
- s1 = (sx + sy)/2 + (((sx – sy)/2)^2 + sxy^2))^0.5
- s2 = (sx + sy)/2 – (((sx – sy)/2)^2 + sxy^2))^0.5
For Axisymmetric the following stress values are calculated
- sr
- sz
- s1 = (sr + sz)/2 + (((sr – sz)/2)^2 + srz^2))^0.5
- s2 = (sr + sz)/2 – (((sr – sz)/2)^2 + srz^2))^0.5
For all model types equivalent stress (Von Mises stress) is calculated using
- seq = (((s1 – s2)^2 + s1^2 + s2^2)/2)^0.5
Reaction Loads
Reaction loads, also known as Grid Point Forces (GPFs) can be presented for constraint locations on the model.
These forces can be displayed as vector resultants, hence one arrow, or as x, y components, hence two arrows.
Reaction forces can also be presented between features. To do this, select on Results/Single feature fringe and then Solve the model. Selecting on a feature will switch which feature shows the reaction forces.
Fringe Presentation Types
Fringe plots can be presented in slightly different ways using the Result/Averaging Type options. There are three options
- None
- All
- Feature Only
Selecting “None” means that there is no averaging across elements, hence each element has one color, the value calculated at the center of the element. The colour plots will appear more jagged, however, this is a more accurate presentation of the model results.
Selecting “All” means that the fringe values are calculated at each node, by averaging the values from all the connected elements. The plots will appear smooth as the colors are interpolated linearly between each of the nodes.
Selecting “Feature Only” is the same as “All” except that averaging is only done using elements within the feature. This is important for plots where materials or thicknesses are different between features.