# Particle Shear Modulus – It Can Save You Time

**Altair Employee**

I posted a blog "EDEM Simulation Run Time" outlining how this is one of the key considerations when planning any simulation.

**Particle Shear Modulus** is one of the key parameters we can use to influence the time taken to run a simulation. Reducing the Shear Modulus to allow for larger time-step sizes and faster simulations is a commonly used practice when running DEM Simulations. Used with caution and material calibration this method is very effective in allowing practical run times to be achieved.

Within EDEM we use the Shear Modulus and material Poisson’s ratio to calculate the Young’s Modulus, reducing the Shear Modulus/Young’s Modulus reduces the contact stiffness of the particles.

I’ve run the same bucket simulation below with Shear Modulus values of 1e5 Pa to 1e10 Pa and you can see from the results that bulk material behavior only changes significantly if you go too low.

*Comparing bulk material behavior with different Particle shear modulus values*

Although the bulk behavior doesn’t change significantly above 1e6 Pa for this case, the run times do change. All simulations were run at 20% Raleigh Time-Step and the run times were:

*Run time variations*

As you can see you get a **10x speed up** for every reduction in Shear Modulus by a factor of 100.

The Shear Modulus value should be set before the calibration step, so any material calibration takes the change in Shear Modulus into account.

The analysis above focuses around the material bulk behavior. If the result of the final simulation after calibration is an investigation and analysis of the material flow properties, then calibration of the material bulk properties with a reduced Shear Modulus is an effective way to reduce the simulation time required, so long as this reduction is within reasonable limits.

If *force* rather than material flow properties is the required analysis then this method can also be used, but does require additional consideration. The force impacted on a piece of equipment by a pile of material at a set repose angle is consistent regardless of material stiffness. The images below show the force on the bucket at 1e6 Pa Shear Modulus (65.7 kN) and 1e9 Pa Shear Modulus (65.2 kN), the force in this case is within any expected variation for the instantaneous analysis shown.

*Comparing forces acting on bucket with Shear modulus of 1e6 Pa Shear Modulus and 1e9 Pa*

If; however, a different type of simulation analysis is required, for example force analysis of high velocity impacts, then this method would require some further investigation.

For more details on Shear Modulus and its influence you can also review the EDEM technical papers for example a good reference is:

Lommen, S., Schott, D. and Lodewijks, G. (2014). DEM speedup: Stiffness effects on behavior of bulk material. *Particuology*, 12, pp.107-112.

Related :

- EDEM Benchmarks
- EDEM Simulation Run Time
- EDEM Particle Simulation: CUDA GPU and Precision Modes
- How to select a GPU (Graphics Processing Unit) for EDEM
- 10 Common Questions about EDEM GPU Answered
- Estimating EDEM simulation run time

To get started with EDEM: