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You can either create the geometry directly in MSC Apex Generative Design or import already existing files. You can import for example .xb, .xt, .step, and .sldprt files into the program.
Import/create the Design Space including the Non-Design Spaces in MSC Apex Generative Design as one solid. For this Hook the already prepared Design Space was imported.
Open the Optimization Tools to select the imported Geometry as the Design Space
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Material Assignment
Create the material in the Materials editor and assign it to the Design Space
Assuming the part should be printed with a Manufacturing Method like FFF, a Transversely Isotropic material is applied. The z-axis of the PCS is always the build direction ( * ) and differs from the two in-plane directions y and x. The values for the materials have to be entered accordingly. For the input the main axis (1-2-3) are used which are equal to (z-y-x).
The specific values needed are the Young's Modulus in build direction (E1) (1700 MPa) and in in-plane direction (E2) (1900 MPa), the Shear Modulus (G12) (730 MPa) and the Poisson ratio (0.3) for xy (NU23) and (0.39) for yz (NU12). The density is set to 0.9e-6 kg/mm3.
As the last input the material limits should be entered. Which of these are required depends on the optimisation intention and the chosen Failure Criterion. In this case we want to take advantage of the directional dependent material limits as well as different limits for tension and compression (directional dependent Tsai-Wu).
These values are optional, if a different Failure Criterion is selected, less material input is required
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Go to the Loads & Boundary Condition Tool to enter the loads and fixations. Displacements, Forces, Moments, Gravity and Pressure Loads can be applied using different selection options.
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Name | Direction |
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Constraint 1 | x, y, z (=0) |
Therefore, the Loads & Boundary Condition Tool is needed.
Under Displacement Constraints a “clamped” constraint can be chosen, which locks translations in all three directions. On the left side of the Tool the relevant geometry choice can be selected. In this case the inner surface of the hole is selected to attach the constraint.
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Step 4: Interface Creation
Interfaces have to be created for every functional surface - so every surface where a boundary condition is applied to. With this Tool an offset to the inside with the input “Non-Design Space Thickness” and an offset to the outside with the input “Machining Allowance” is created. The Offset Distance is expanding the Interface to the set value to create material on front faces.
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The next steps are defined in the Studies area.
All boundary conditions must be assigned to the specific load cases, which are defined as Events. The number of Eventscan be changed by adding/deleting Eventsto the GD Scenario. The assignment of the boundary conditions to the Eventscan be made in the Loads & Constrains Window. The already created loads and constraints that concern the Design Space are listed in this window and can be activated for each Eventindividually.
Event1: Force-Moment 1, Constraint 1
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The optimisation parameters are selected in the Studies Area as well.
Now the Build Direction will be adjusted. Therefore the Build Direction Tool can be activated with the coordinate system symbol and any surface can be selected. To rotate the Build Direction either the visualized coordinate system can directly be manipulated to align the Build Direction with the x-Axis of the model or the Euler Angles can be entered directly (90,00 °; 90,00 °; 270,00 °).
For each scenario the Build Direction can be easily changed, then the Build Direction for the Design Rules as well the material properties are rotated accordingly. This way multiple Build Directions can be checked in one project. Afterwards the optimisation results can be compared in the Post Processing and the best build orientation can be picked
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Select the Manufacturing Method: FFF
Selected the Failure Criterion: Directional Dependency (Tsai Hill)
Enter the Safety Factor: 4
Select the Strut Density: Medium
Select the Shape Quality: Balanced
Set the Complexity Setting: 10
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Tip: Take a look at the Safety Factor calculation:
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The material limits are scaled with the Safety Factor! The values in brackets are the goal of the optimisation.
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You can check the status of the optimisation in the GD Status and get more information on Warning and Error messages. This can be done directly in the Post-Processing as well as in the Studies tab for an optimisation that has already been executed.
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If all data is correct, the optimisation can be started and tracked in the Post Processing. The Analysis Readiness function checks if all information is provided and the optimisation can start.
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Step 8: Visualization of Failure Criteria, Displacements etc.
Inside the Post Processing the Failure Criteria, the displacements, the optimisation achievement index and the volume/mass are visible for all iterations
The Scale can be influenced individually
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Influence of Material Properties & Failure Criteria
The chosen material properties and Failure Criteria influence the resulting design. The Failure Criterion with the chosen material limits for all directions uniformly (von Mises), directional dependent (FFF-Thumb Rule or Tsai-Hill) or taking into account different tension and compression strength besides directional dependency (Tsai-Wu) has the biggest impact on the Design.
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The stiffness of the material is in all directions uniformly. As the Failure Criterion the FFF Thumb Rule is calculated. With the FFF Thumb Rule the maximum allowable Stress (Stress Goal) in build direction can be scaled. This is especially useful for a Manufacturing Method like FFF. The result is shown in the following picture with the same optimisation set up except the material properties and Failure Criterion.
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The stiffness of the material is in all directions uniformly. As the Failure Criterion the von Mises Stress is calculated. The result is shown in the following picture with the same optimisation set up except the material properties and Failure Criterion.
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Mass: 53.7 g – This is a weight increase of 21 % compared with the transversely isotropic material by taking advantage of higher allowable stresses for the in-plane directions and compression (Directional dependent Tsai-Wu Failure Criterion)!
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The whole MSC Apex Generative Design projects with all results for the different anisotropic behaviour settings can be downloaded here:
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File Name | Material Stiffness | Failure Criterion |
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Hook_2022-4_Iso_vM.7z | Isotropic | von Mises |
Hook_2022-4_Iso_TR.7z | Isotropic | FFF Thumb Rule |
Hook_2022-4_TransIso_TH.7z | Transversely Isotopic | Directional Dependency (Tsai-Hill) |
Hook_2022-4_TranIso_TW.7z | Transversely Isotopic | Directional Dependency (Tsai-Wu) |
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In case of anisotropic material stiffness and the directional dependent Tsai-Wu transversely isotropic Failure Criterion with huge material property differences for the in-plane directions and the build direction, as well for the maximum allowable tensile and compression strength, the optimisation may not give stable results. How to handle this here. |
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