EDEM Simulation

Simulating complex cohesive materials in EDEM

By Carles Bosch Padros on 12 Oct 2017

Bulk materials are complex in nature and simulating their flow can be challenging. Choosing the right contact model in your simulation is critical to capture realistic behavior.

Here I would like to introduce a contact model that has been developed by EDEM academic users at the University of Edinburgh to simulate complex cohesive materials such as fine dry powders, organic materials, soil and ore fines.

Such materials exhibit a behavior which can be characterized by elasto-plastic deformation under loading and accompanied by an increase in cohesion. The complexity of these materials means they are beyond the scope of standard contact models.


THE EDINBURGH ELASTO-PLASTIC ADHESION (EEPA) MODEL

The Edinburgh Elasto-Plastic Adhesion (EEPA) model has been developed by a team of researchers of the University of Edinburgh including Dr. J. P. Morrissey, Dr. S. Thakur, Prof. J.Y. Ooi, Dr. J.Sun and Prof J-F. Chen. This model was initially developed using EDEM’s Application Programming Interface (API) and as part of EDEM 2018 it is now built-in and available to use as a standard contact model in EDEM. The EEPA offers a solution for cohesive granular solids whose behavior changes depending on the stresses experienced by the material beforehand. In other words, this contact model accounts for the stress history of the granular material, which helps defining its cohesive behavior.

In a real situation, we would have a bulk material or powder being compressed together. During this procedure, some of the deformations would be elastic and some others plastic. Once the compression has stopped and the material has finished the unloading (force=0), an overlap will remain. The EEPA contact model is non-linear and able to capture both the elasto-plastic deformation and the contact-area dependent cohesion.

I will not go into details about the model itself here but full documentation is available to our customers in the EDEM Documentation. Instead let me show you a couple of simulation examples to illustrate the applications of this model.


APPLICATION EXAMPLE #1: DUMP TRUCK UNLOADING MATERIAL


Dump trucks have to be as efficient as possible in order to reduce the time and travels needed for transportation. Using the elasto-plastic contact model in EDEM in this case would give us insight into:

  • Regions where the material is likely to stick
  • Quantity of material that will stick
  • The effect of geometry on material adhesion

The difference in the amount of material stuck in the dump after the unloading is due to its initial filling level. The initial compression of the material affects the level of cohesion showed by it. In this case, the truck on the left was filled with a heavier load than the right truck, which compressed the material more and, hence, offered a higher level of stickiness, as seen at the end of the video.


APPLICATION EXAMPLE #2: SOIL-TYRE INTERACTION: TRACTOR


When looking at machine-material interaction EDEM can provide insights into:

  • Regions where the material is likely to stick
  • More realistic traction forces
  • More realistic pressure distribution


APPLICATION EXAMPLE #3: PHARMACEUTICAL TABLETTING


In this example EDEM gives insights into:

  • Initial bulk density and porosity in the mould
  • Change of volume and bulk density during compaction
  • Forces during compaction
  • Tablet stability after compaction


APPLICATION EXAMPLE #4: STORAGE AND DISCHARGE: SILOS




Using the EEPA model in EDEM provides information on:

  • Cohesive flow discharge
  • Arching phenomenon in silos
  • Material state during storage (Bulk Density, Porosity etc.)
  • Silo wall pressure distribution during storage and discharge

These are just some examples of applications of the Edinburgh Elasto-Plastic Adhesion model. This versatile model can represent complex cohesive materials and phenomena such as fine agglomeration, attrition and flow.

If you want to find out more about this model or want to chat about other advanced applications, get in touch!

Source: EDEM Simulation Blog