Porosity for Synthetic Graphite

Overview

In this project, Simpleware software was used to convert CT data into finite element models suitable for simulating the effect of porosity on the elastic properties of synthetic graphite in COMSOL Multiphysics®. Porosity is formed in synthetic graphite during processing, and can have a significant effect upon its industrial performance. X-ray tomography was used to obtain a stack of images of synthetic graphite that could be processed and meshed as 3D computational models in Simpleware. The study’s successful use of FEM to help characterise synthetic graphite provides insight into how Simpleware software can contribute to a straightforward workflow for analysing composite material performance in COMSOL and other solvers.

Characteristics:

  • 3D FE models from X-ray CT images
  • Segmentation of solid and porous regions
  • Generation of an analysis ready volume mesh
  • Simulation of stress-strain responses for porous samples in COMSOL Multiphysics®
  • Development of a workflow for future modelling

Thanks to

GrafTech International Holdings Inc., Parma, Ohio, USA:
G. Sowa • R. Paul • R.E Smith

Image Processing

A stack of X-ray computed tomography images were imported into ScanIP. 2D slices were immediately rendered in 3D after import, and rapidly segmented using automated thresholding tools into solid and porous regions. Segmentation was carried out based on greyscale scan values. Colour mapping was also used to better visualise porous and solid regions.

Mesh Generation

Simpleware +FE was then used to convert the solid part of the segmented image data into a robust, analysis-ready mesh. Experiments were conducted with FE Grid and FE Free options to obtain an optimum mesh quality with sufficient elements for a high resolution model. Efforts were also made to maintain a reasonable computing time when meshing. The final volume mesh was directly imported into COMSOL Multiphysics® for simulation.

Simulation

Tensile stress-strain responses were simulated in COMSOL Multiphysics® for a range of synthetic graphite samples of varying porosity. Pore-free solid properties were calculated to simulate experimentally measured properties, and a successful workflow was developed for future modelling. Simulations found that the presence of pores reduced the solid modulus by 18% to 62% and the solid Poisson’s ratio by 1% to 8%. The development of a robust finite element model in Simpleware software consequently enabled researchers to easily set up a method for studying the different properties of synthetic graphite without physical testing.