Micromechanism Investigation of Geomaterials using Particle Manifold Method (PMM)

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1 NUMERICS in GEOTECHNICS and STRUCTURES 2012, 27 years ZSOIL.PC Micromechanism Investigation of Geomaterials using Particle Manifold Method (PMM) by Liang SUN Laboratory of Rock Mechanics(LMR), EPFL August 31, 2012, ELP 120, EPFL

2 Introduction Contents Particle Manifold Method (PMM) Investigation on Dynamic Strength using Dynamic Brazilian Test Conclusions NMM - Theoretical Basis Particle Representation Failure Description Multiscale 2 Liang SUN

3 Introduction Background: Rock Mechanics, Geomechanics Method: Numerical Modelling Problems: Micro Mechanism, Fracturing, Dynamic Effects, etc. We do: Develop a new integrated numerical tool Significance: Provide mobility/possibility for new ideas or theories 3 Liang SUN

4 Introduction Features of PMM: Continuous-discontinuous Multiscale Micro mechanism (failure and contact) High performance computation (HPC) - GPU 4 Liang SUN

5 NMM What? DDA, an implicit DEM for rock mechanics Developed by Shi (1991), combine FEM and DDA Continuous-discontinuous method Polygon / polyhedron Large deformation and movement Cross the river: 5 Liang SUN

6 NMM How? Similar concept with some XFEMs or meshfree methods (T. Belytschko et al., 1996) 6 Liang SUN

7 PMM Particle model: some regulations Replace the physical domain in NMM Physical parameters: no calibration Size: <= a continuous REV Distribution: uniform and random Linked or contacted Virtual and Realistic 7 Liang SUN

8 Failure Description Brazilian Test (maximum tensile strength) 8 Liang SUN

9 Uniaxial test (Mohr-Coulomb) Failure Description 9 Liang SUN

10 Fracture propagation Failure Description 10 Liang SUN

11 Multiscale PMM NMM & PMM Macro zone & Micro zone Polygon integration & particle integration Polygon contact & particle contact Non failure & particle failure Coarse mesh & fine mesh 11 Liang SUN

12 GPU Parallelization GPU parallelization SIMD (Single Instruction Multiple Data) CPU vs. GPU Logic-intensive vs. Data-intensive Merits: high performance, low cost Drawbacks: not easy to do (NVIDIA, 2009) 12 Liang SUN

13 Dynamic Strength Split-Hopkinson Pressure Bar System (SHPB) 13 Liang SUN

14 Dynamic Strength Dynamic Brazilian Disc Test Experiments & Numerical model Multiscale PMM 14 Liang SUN

15 Experiment: Dynamic Strength Not clear, too fast, equipment is slow 15 Liang SUN

16 Loading rates Dynamic Strength 16 Liang SUN

17 Low loading rate Dynamic Strength 17 Liang SUN

18 Dynamic Strength Mediate and high loading rates 18 Liang SUN

19 What we get? Dynamic Strength Stress in the sample is not balanced. Loading still increases after the sample begin to fail until complete failure. For small sample, failure is very fast, too difficult to observe in experiments. The dynamic strength is the observed strength when or after the complete failure. 19 Liang SUN

20 Dynamic Strength Stress is not balanced: a proof Aluminum foam (S.L. Xu, 2012) 20 Liang SUN

21 Dynamic Strength Strength is really rate-dependent? How to explain the spalling test? Rate-dependency is different for different samples (failure patterns) Bar spalling is a 1-D problem, instant failure! 21 Liang SUN

22 Dynamic Strength Material deformation needs time! Air: Sound Barrier (compress fast, physical properties change) Solid: limited deformation (fracturing) velocity (Google image, 2012) 22 Liang SUN

23 Effect of loading rate Illustration Dynamic Strength (Viktor N Nikolaevskij, 1990) 23 Liang SUN

24 Conclusions Dynamic strength: ideas Critical strength exist Does not change with external conditions Loading rate effect: phenomenon, not essential Dynamic strength: assumptions Failure initializes in a limited area Fracture propagation needs time Speed of fracture propagation is limited 24 Liang SUN

25 Conclusions References: L. Sun (2012). Particle manifold method (PMM) for multiscale continuousdiscontinuous analysis. PhD thesis, EPFL, Switzerland. L. Sun, G. F. Zhao, and J. Zhao (2012). Particle Manifold Method (PMM): A New Continuum-Discontinuum Numerical Model for Geomechanics. International Journal for Numerical and Analytical Methods in Geomechanics, DOI: /nag J. Zhao, L. Sun, J. B. Zhu (2012). Modelling P-wave Transmission across Rock Fractures by Particle Manifold Method (PMM). Geomechanics and Geoengineering, DOI: / L. Sun, G. F. Zhao, and J. Zhao (2011). Contact description in numerical simulation for rock mechanics. Proceedings of 12th Congress of the International Society for Rock Mechanics, Beijing. p L. Sun, G. F. Zhao, and J. Zhao (2011). An Introduction of Particle Manifold Method (PMM). Proceedings of 10th International Conference on Discontinuous Deformation Analysis, CRC Press/Balkema: Honolulu. p Experiment data and photos provided by Qianbing Zhang, EPFL-LMR 25 Liang SUN

26 The End Thanks for your attentions! 26 Liang SUN

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