Tagged: AIM tutotrial, discoveryaim, structures


September 26, 2022 at 10:00 amWatch & LearnParticipant
This example is taken fromÂ Cornell Universityâ€™s ANSYS AIM Learning Modules
Learning Goals
In this tutorial, you will learn to:
 Determine the displacements and stresses in a bike crank using 3D FEA capabilities in Discovery AIM
 Verify the finiteelement results from Discovery AIM by refining the mesh and also comparing with hand calculations
Problem Specification
Consider the following bike crank model.
To orient ourselves, the following figure shows the location of a similar bike crank mounted on a bicycle.
Material properties: The bicycle crankâ€™s material is Aluminum 6061t6. The Youngâ€™s modulus is 10,000 ksi, and the Poissonâ€™s Ratio is .33.
Boundary conditions: Apply a load of 100 lbf in the ydirection on the right hole surface and fix the 3 left hole surfaces as shown below. Note that this is an approximation of the actual loads and constraints on the bike crank.
Using Discovery AIM, determine the following:
 Deformed shape and displacement field
 Stress distribution
PreAnalysis
In the preanalysis step, we review the:
 Mathematical model
 Numerical solution strategy
 Hand calculations of expected results
Geometry
The geometry has been created in SolidWorks and saved as a Parasolid file.Â Â Download the Parasolid file.
The following video shows you how to navigate Discovery AIM and import the Parasolid file.
Mesh
The video below demonstrates the steps to mesh the geometry using Hexahedral elements which look like boxes. Hexahedral (or hex) elements yield higher accuracy compared with the default tetrahedral (or tet) elements for the same number of nodes.
Physics Setup
We need to create a new material and assign it to the model as shown in the following video. Otherwise, ANSYS will use the Youngâ€™s modulus and Poissonâ€™s ratio for structural steel which is the default. This step is easy to overlook. Â Next, we apply the boundary conditions i.e. displacement constraints at the 3 left holes and traction on part of the right hole. Boundary surfaces where we neither apply a displacement constraint nor traction are assumed by ANSYS to be free surfaces with zero traction.
Summary of steps in above video:
 Change the material from default to a newly created material
 Change the properties of the new material to those of AL 6061T6 in the problem description
 Create a fixed support at the three holes
 Create a force acting on the inside facing circular hole
 Specify the ycomponent to be 100lbf
 Solve the physics
Numerical Results
The following video shows how to plot the deformed shape and use it to check if the displacement constraints have been applied correctly. Â We next take a look at variation in stress in XdirÂ in the model.Â We interrogateÂ variation in stress in XdirÂ in the interior of the model using a plane.
Summary of steps in above video:
 Evaluate the 2 predefined results â€“Â equivalent stress and displacement magnitude
 View deformation of the crank
 Create a new contour to view normal stress in X direction
 Create a new plane along crosssection of crank and create a new contour to view the stress variation along cross section
 Create a force reaction result to check force balance
Verification and Validation
 Check that the solution agrees with the mathematical model
 Are the boundary conditions on displacement and traction satisfied?
 Is equilibrium satisfied?
 Do the reaction forces balance the applied load?
 Check that the numerical error is acceptable
 Are the ANSYS results reasonably independent of the mesh?
 We can refine the mesh by reducing the Size Controls and updating the solution. Â We can then compare the results to the original mesh.
 Are the ANSYS results reasonably independent of the mesh?
 Compare with hand calculations for the bending stress and maximum displacement

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