The application of CT Scanning is becoming more commonplace for the inspection of engineering parts for geometric (tolerance, warping, wall thickness, etc.) and material (void, defect, microstructure) analysis. Industrial CT Scanning is also playing an important role in increasing the adoption of Additive Manufacturing by acquiring the “as-manufactured” geometry of the printed part to detect any shape change due to warping as well as material defects due to unmelted metal powder or keyhole cavities.

Figure: (left) CT Scanning capturing Material Defects [1]. (middle) Material Microstructure [2]. (right) Warping and other shape deviations [3].

Currently, to analyze the performance impact of geometry and material deviation when compared to the original CAD design, the standard practice is to create a 3D surface model from the CT Scan data so that it can be imported back into CAD-CAE systems. It has two bottlenecks

❌ Conversion of CT Data to a CAD representation (Brep or polygonal surface)

❌ Meshing the CAD representation to get a volume mesh for CAE

✅ CAE Directly from CT Scan Data

Intact’s Immersed Methods of Moments technology allows FEA directly on the CT Data without any conversion or preprocessing steps, therefore removing the above bottlenecks. In addition, the simulation workflow can be fully automated and directly integrated into CT Scan Software.

Figure: (left) Simulation on CT model using Immersed Method of Moments. (right) Results of stress analysis on CT scans of some sample parts (right) [4]

⚙️ CT Scan Simulation Workflow

Simulation workflow for a CT Scan of Femur with Titanium screws (STL)

  1. The first step is to extract the pixels that represent the femur after thresholding the pixel density. The filtered pixels essentially are a voxel model of the femur
  2. Then the screws are placed in the femur
  3. Boundary Conditions are applied on faces (surface mesh) in approximately the area that will experience load and restraints. If the CAD model is available, these faces can be directly be extracted from the CAD model after registering with the CT scan.
  4. Specify the material and run the simulation. No surface extraction and meshing!

Figure: (left) Voxel model from the CT Scan of a femur with titanium screws (STL) later embedded. (middle) Load is applied on the red surface and green surface is fixed. (right) stress results in the femur after simulation.

Demo video

🗂️ Case Studies

1. Warped Print from Additive

This case study demonstrates the simulation of a thermally warped bracket made from additive manufacturing. The bracket [5] experienced thermal warping on the base (left side) as well as overhang issues stemming from support structure issues (right). The left plate was restrained in all directions and a 100 N load in the positive x-direction was applied to the right plate. The ensuing difference in results between the designed model and the warped printed part demonstrates the value of analysis on manufactured parts. The warped part experienced a 13% decrease in maximum displacement and a 30% increase in maximum Von Mises stress relative to the designed model.

2. Bone Implant

Here, a fully fractured tibia of a 5’6”, 140 lb female was repaired using an intramedullary rod [6]. The knee area of the bone was restrained, and a 3,238 N compressive load was applied to the ankle area to simulate the load experienced in the stance phase of gait [7]. Both the healthy tibia bone and the fractured bone with implant were analyzed using voxels. Relative to the healthy bone, total displacement in the implant increased by 12%, and maximum stress increased by three times. The stress in the healthy bone was spread over the middle of the bone, while the stress in the surgically repaired bone was predictably concentrated on the area of the implant that bridges the bone fracture. The maximum stress observed in the implant is about 26% of titanium’s yield strength of 880 MPa [8], meaning that the patient can immediately begin walking with confidence in the structural integrity of their implant.

Sources

[1] https://en.wikipedia.org/wiki/Industrial_computed_tomography#cite_note-11

[2] https://doi.org/10.1002/adem.201600725

[3] https://www.aerospacemanufacturinganddesign.com/article/x-ray-computed-tomography-verifies-3d-metal-printing/

[4] https://grabcad.com/library/optimized-handle-stem-1

[5] https://grabcad.com/library/step-bracket-1

[6] https://grabcad.com/library/tibial-intramedullary-nail-1

[7] Bouguecha, A, et.al(2011). Numerical simulation of strain-adaptive bone remodeling in the ankle joint. Biomedical Engineering Online, Vol. 10, 58-71

[8] http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=mtp641