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1 Siegen 2012, October 1th-2th
Modeling of contact interactions of micrometer-
sized particles under compression
Hamburg University of Technology
Institute of Solids Process Engineering and Particle
Technology
S. Kozhar, S. Antonyuk, S. Heinrich
2 Siegen 2012, October 1th-2th
Introduction Research objectives
Birkenfeld
Setting up the measurement
system
Measurements of particle-particle
and particle-wall contact
interactions
Capturing of the 3D shape
of particles
Hamburg
Determination of materials
parameters from experiments
Selection and calibration of
appropriate contact models for each
material
DEM/FEM-simulations of single
particle and bulk material
PiKo B4 project
The aim of the project is to describe the mechanical interactions of finely
dispersed particles with diameter of 20…100 µm by using experimentally
calibrated contact models
3 Siegen 2012, October 1th-2th
Piezo drive Particle
Experimental part Experimental set-up
Current set-up
allows to carry out tests of
particles at compressive
and tensile loading with
adjustable relative humidity
and temperature in climate
box
Device Minimum
value
Maximum
value
Resolution
Piezo drive 0 µm 250 µm 0.2 nm
Laser vibrometer -∞ ∞ 0.2 nm
Force sensor - 200 mN + 200 mN 40 µN
Box (Temperature) 15 °C 35 °C 1 °C
Box (Relative humidity) 10 % 90 % 2 %
20 mm
Microscope Force sensor
4 Siegen 2012, October 1th-2th
Experimental part Tested materials
Maltodextrin particles elastic-(visco)plastic
2 µm
Hollow glass particle pure elastic
Titan dioxide particles elastic-plastic
5 Siegen 2012, October 1th-2th
Parameter Unit Value
Diameter [µm] 39.1 ± 9.5
Displacement
at breakage [µm] 6.7 ± 3.7
Breakage force [mN] 98 ± 53
Breakage strain [%] 18.3 ± 12.3
Compressive strength [MPa] 92.6 ± 67.8
E-Modulus [GPa] 3.3 ± 1.7
Mean values of mechanical characteristics of titan dioxide
under compression
Experimental part Titan dioxide
6 Siegen 2012, October 1th-2th
Experimental part Titan dioxide
Cyclic compression test of titan dioxide
particle with constant maximum force
7 Siegen 2012, October 1th-2th
Experimental part Titan dioxide
Cyclic compression test of titan dioxide
particle with increasing maximum force
8 Siegen 2012, October 1th-2th
Modulus of elasticity of titan dioxide particles
determined from cyclic compression tests
Experimental part Titan dioxide
E-Modulus [GPa]
Loading part of cycle 18.2 ± 6.9
Unloading part of cycle 37.8 ± 19.2
Titan dioxide particles:
have irregular shapes
behave elastic-plastically
demonstrate cyclic hardening behavior
9 Siegen 2012, October 1th-2th
Experimental part Maltodextrin
25°C 28% r.h.
Cyclic compression test of maltodextrin
particle with constant maximum force
10 Siegen 2012, October 1th-2th
Experimental part Maltodextrin
Cyclic compression test of maltodextrin
particle with increasing maximum force
25°C 31% r.h.
11 Siegen 2012, October 1th-2th
Experimental part Maltodextrin
Loading type E-Modulus
[GPa]
Loading Increasing of maximum force in cycle
at 115 mN/s
5,4 ± 2.9
Unloading 6.8 ± 4.9
Loading Increasing of maximum force in cycle
at 460 mN/s
4.6 ± 2.9
Unloading 7.9 ± 3.9
Loading Constant maximum force at higher
loading rate
2.2 ± 0.2
Unloading 4.4 ± 0.6
Modulus of elasticity of maltodextrin particles
determined from cyclic compression tests
Maltodextrin particles:
have irregular shapes
behave elastic-viscoplastically
demonstrate cyclic hardening behavior
12 Siegen 2012, October 1th-2th
Experimental part Hollow glass particles
Cyclic compression tests of hollow
glass particles
Glass particles:
have spherical shapes
behave elastically
Stiffness
[N/mm]
Loading 1.47 ± 0.16
Unloading 1.35 ± 0.14
13 Siegen 2012, October 1th-2th
Modeling Contact models
Contact models for normal load
Linear and nonlinear
(visco)elastic models
Elastic-plastic models
with hysteresis
Hertz
Sadd
Schäffer
Tsuji
Kuwabara & Kono
…
Walton & Braun
Thornton & Ning
Tomas
Vu-Quoc & Zhang
Mangwandi
…
Tomas, J. Mechanics of Particle Adhesion. Manuscript, Magdeburg (2008)
Kruggel-Emden,H, et al. Review and extension of normal force models for
Discrete Element Method. Powder Technology. 171, 157-173 (2006)
14 Siegen 2012, October 1th-2th
Aims of modeling by contact models
Modeling Contact models
Contact models must
be simple in order to be implemented into DEM code
good reproduce the real particle behavior at mechanical
contacts
Two proposed ways to represent cyclic behavior of tested
particles
use of the averaged loading-unloading curve for fitting by
contact models with following conditions
𝑠0 =1
𝑁 𝑠0,𝑗 =
𝑁
𝑗=1
s0,ave
use the saturation function to reproduce the decrease of
residual displacement in loading cycle
𝑠𝑚𝑎𝑥 =1
𝑁 𝑠𝑚𝑎𝑥,𝑗
𝑁
𝑗=1
= 𝑠𝑚𝑎𝑥,𝑎𝑣𝑒 𝑒𝑒𝑞 =1
𝑁 𝑒𝑒𝑞,𝑗
𝑁
𝑗=1
15 Siegen 2012, October 1th-2th
Fo
rce
Displacement
Equivalent restitution coefficient
Modeling Contact models
WL – total energy during loading
WUN – energy released at unloading
Wdiss– dissipated energy 𝑒𝑒𝑞 =
𝑊𝑈𝑁𝑊𝐿=
= 1 −𝑊𝑑𝑖𝑠𝑠𝑊𝐿
smax s0
Fmax
16 Siegen 2012, October 1th-2th
Modeling Fitting of average loading-unloading curve
Model of Walton & Braun
𝑾𝒅𝒊𝒔𝒔,𝑚𝑾𝒅𝒊𝒔𝒔,𝑎𝑣𝑒
= 1.21
𝑒𝑒𝑞,𝑚𝑒𝑒𝑞,𝑎𝑣𝑒
= 1.16
𝑠0,𝑚𝑠0,𝑎𝑣𝑒= 1.0
Titan dioxide
17 Siegen 2012, October 1th-2th
Modeling Fitting of average loading-unloading curve
Model of Tomas
𝑾𝒅𝒊𝒔𝒔,𝑚𝑾𝒅𝒊𝒔𝒔,𝑎𝑣𝑒
= 1.25
𝑒𝑒𝑞,𝑚𝑒𝑒𝑞,𝑎𝑣𝑒
= 1.11
𝑠0,𝑚𝑠0,𝑎𝑣𝑒= 0.89
Titan dioxide
18 Siegen 2012, October 1th-2th
Modeling Fitting of average loading-unloading curve
Model of Thornton & Ning
𝑾𝒅𝒊𝒔𝒔,𝑚𝑾𝒅𝒊𝒔𝒔,𝑎𝑣𝑒
= 1.50
𝑒𝑒𝑞,𝑚𝑒𝑒𝑞,𝑎𝑣𝑒
= 1.10
𝑠0,𝑚𝑠0,𝑎𝑣𝑒= 0.91
Titan dioxide
19 Siegen 2012, October 1th-2th
Aims of modeling by contact models
Modeling Contact models
Contact models must
be simple in order to be implemented into DEM code
good reproduce the real particle behavior at mechanical
contacts
Two proposed ways to represent cyclic behavior of tested
of particles
use of the averaged loading-unloading curve for fitting by
contact models with following conditions
𝑠0 =1
𝑁 𝑠0,𝑗 =
𝑁
𝑗=1
s0,ave
use the saturation function to reproduce the decrease of
residual displacement in loading cycle
𝑠𝑚𝑎𝑥 =1
𝑁 𝑠𝑚𝑎𝑥,𝑗
𝑁
𝑗=1
= 𝑠𝑚𝑎𝑥,𝑎𝑣𝑒 𝑒𝑒𝑞 =1
𝑁 𝑒𝑒𝑞,𝑗
𝑁
𝑗=1
20 Siegen 2012, October 1th-2th
Modeling Modeling by using the saturation function
Equivalent restitution coefficient as
function of number of cycles Walton & Braun model
𝐹𝑛 = 𝑘𝐿𝑠, 𝑠 ∈ [0; 𝑠max]
𝑘𝑈𝑁 𝑠 − 𝑠0 , 𝑠 ∈ [𝑠0; 𝑠max]
Residual displacement
𝑠𝑜 = 𝑠𝑚𝑎𝑥 1 −𝑘𝐿𝑘𝑈𝑁
Proposed saturation function
𝑘𝑈𝑁 = 𝑐𝑜𝑛𝑠𝑡
𝑁 - number of cycles
𝐴, 𝑏 - parameters
𝑒𝑒𝑞 = 𝑓(𝑘𝐿) = 𝐴(1 − 𝑒−𝑏∙𝑁)
Titan dioxide
21 Siegen 2012, October 1th-2th
Modeling Modeling by using the saturation function
𝐹𝑛 = 𝑘𝐿𝑠, 𝑠 ∈ [0; 𝑠max]
𝑘𝑈𝑁 𝑠 − 𝑠0 , 𝑠 ∈ [𝑠0; 𝑠max]
Walton & Braun model
Residual displacement
𝑠𝑜 = 𝑠𝑚𝑎𝑥 1 −𝑘𝐿𝑘𝑈𝑁
Proposed saturation function
𝑒𝑒𝑞 = 𝑓(𝑘𝐿) = 𝐴(1 − 𝑒−𝑏∙𝑁)
𝑘𝑈𝑁 = 𝑐𝑜𝑛𝑠𝑡
𝑁 - number of cycles
𝐴, 𝑏 - parameters
Residual displacement as function of
number of cycles
Titan dioxide
22 Siegen 2012, October 1th-2th
Modeling Modeling by using the saturation function
Comparison
𝑠0,𝑒𝑥𝑝 = 2.28 µ𝑚
𝑠0,𝑚𝑜𝑑𝑒𝑙 = 2.09 µ𝑚
Titan dioxide
23 Siegen 2012, October 1th-2th
Modeling Test with increasing maximum force in cycle
Walton & Braun model for cyclic
compression with increasing force
𝑒𝑛 =𝑘𝐿𝑘𝑈𝑁 ,
𝑘𝑈𝑁 = 𝑐𝑜𝑛𝑠𝑡
𝑘𝐿 = 𝑐𝑜𝑛𝑠𝑡,
𝑠0,𝑒𝑥𝑝 = 0.87 µ𝑚
𝑠0,𝑒𝑥𝑝 = 0.85 µ𝑚
𝑒𝑒𝑥𝑝 = 𝑒𝑚 =0.76
Titan dioxide
Fo
rce
[m
N]
Fo
rce
[m
N]
24 Siegen 2012, October 1th-2th
Elastic properties of spherical maltodextrin particles
Modeling Spherical maltodextrin
0
1000
2000
3000
4000
5000
6000
20% r.h. 30% r.h. 40% r.h. 60% r.h. 70% r.h.
Mo
du
lus
of
ela
sti
cit
y [M
Pa]
25 Siegen 2012, October 1th-2th
FEM simulation of contact FEM as additional tool
3D particle shape from CLSM FEM meshing
Import into FEM software FEM calculus
IA-MESH
ANSYS
ABAQUS
26 Siegen 2012, October 1th-2th
Preliminary FEM simulation Hollow glass particle under compression
891 elements of CAX4R type
Particle elastic properties (fused silica)
E = 73 GPa ν = 0.17
Determination of wall thickness
with the help of FEM model
Wall: rigid body
27 Siegen 2012, October 1th-2th
Preliminary FEM simulation Hollow glass particle under compression
Wall thickness [µm]
measured values 0.6…0.8
determined by FEM 0.81
10 µm
Outer diameter [µm]
mean value 83.5 ± 3.1
value of FEM model 82
Loading stiffness [N/mm]
mean value 1.41 ± 0.15
FEM-model 1.41
28 Siegen 2012, October 1th-2th
Preliminary FEM simulation Spherical particle under compression
Simulation of compression test – 2D case
Wall: rigid body Particle elastic properties
E = 70 GPa ν = 0.17
ANSYS ABAQUS
Hertz
Contact force [N] 0.274 0.294 0.275
Maximum contact
pressure [MPa] 6891 7188 7624
Determination of normal contact parameters
at interference of s = 1,38 µm
29 Siegen 2012, October 1th-2th
Simulation of compression test – 3D case
Wall: rigid body Particle elastic properties
E = 70 GPa ν = 0.17
ANSYS ABAQUS
Hertz
Contact force [N] 0.268 0.293 0.275
Maximum contact
pressure [MPa] 7141 7512 7624
Determination of normal contact parameters
at interference of s = 1,38 µm
Preliminary FEM simulation Spherical particle under compression
30 Siegen 2012, October 1th-2th
Simulation of compression test - 2D case
Preliminary FEM simulation Spherical particle under compression
Wall: rigid body Particle elastic properties
E = 70 GPa ν = 0.17
Frictionless contact
of „nodes to surface“ type
31 Siegen 2012, October 1th-2th
Simulation of compression test - 2D case
strain hardening
Preliminary FEM simulation Spherical particle under compression
Wall: rigid body Particle elastic properties
E = 70 GPa ν = 0.17
Particle plastic properties
sy = 500 MPa
𝑠𝑌 = 0,028 µm
𝑃𝑌 = 0,02 mN
𝑝𝐹 = 733 MPa
𝐸𝑇/𝐸 = 0; 0,23; 0,33; 0,5
Frictionless contact of
„node-to-surface“ type
s/𝑠𝐹 = 13,5 s/𝑠𝐹 = 1,2 s/𝑠𝐹 = 108,1
32 Siegen 2012, October 1th-2th
Simulation of compression test - 2D case
strain hardening
Preliminary FEM simulation Spherical particle under compression
Wall: rigid body Particle elastic properties
E = 70 GPa ν = 0.17
Particle plastic properties
sy = 500 MPa
𝑠𝑌 = 0,028 µm
𝑃𝑌 = 0,02 mN
𝑝𝑌 = 733 MPa
33 Siegen 2012, October 1th-2th
Future work
Planned Measurements
Adhesion of particle-particle and particle-wall systems
Tests under shear loading and torsional loading
Influence of climatic condition on material response
Modeling
Allowance for adhesion forces
Choice of theoretical contact model for each
material and loading type
Further determination of material parameters
Simulations
Implementation of contact models into simulation
software
Reproducing of irregular particle shapes in
simulation
DEM simulation of powder behavior
34 Siegen 2012, October 1th-2th