RE: [LS-DYNA] Impact simulations and Johnson Cook model
James M. Kennedy
Dear Venkatesh,
Jiang, F., and Vecchio, K.S., “Hopkinson Bar Loaded Fracture Experimental Technique: a Critical Review of Dynamic Fracture Tests”, Applied Mechanics Reviews, 060802-2, Vol. 62, November, 2009.
Sincerely,
James M. Kennedy
KBS2 Inc.
January 24, 2021
From: James M. Kennedy [mailto:j...@kbs2.com]
Sent: Wednesday, February 19, 2020 10:03 AM
To: 'LS-...@yahoogroups.com' <LS-...@yahoogroups.com>
Cc: 'ls-pr...@googlegroups.com' <ls-pr...@googlegroups.com>
Subject: RE: [LS-DYNA] Impact simulations and Johnson Cook model
Dear Venkatesh,
The *MAT_002 material model (data included) was employed to represent the S2-glass/
vinyl ester composite material:
Hossain, M.K., "Dynamic Simulation of Split Hopkinson Pressure Bar (SHPB) for
Composite Materials Using LS-DYNA", Senior Project, Department of Mechanical
Engineering, University of Nevada Las Vegas, Las Vegas, Nevada, December, 2003.
http://www.egr.unlv.edu/~bj/MEG_795_E_Methods/PDF_Files/Kamal%20SHPB.pdf
This thesis aimed to compare the high-pressure, quasi-static compaction behaviour of
sandy soils, and to investigate how this behaviour was affected by changes in strain
rate and moisture content. LS-DYNA soil material models *MAT_005. *MAT_016,
*MAT_025, *MAT_079, and *MAT_173 (data included) were validated using SHPB
experiments and evaluated for sandy soils. None were found to be fully acceptable for
this study:
Barr, A., "Strain-Rate Effects in Quartz Sand", Ph.D. Thesis, Department of Civil and
Structural Engineering, University of Sheffield, Sheffield, England, United Kingdom,
August, 2016.
Barr, A.D., Clarke, S.D., Petkovski, M., and Rigby, S.E., "Modelling Split-Hopkinson
Pressure Bar Tests on Quartz Sand", The Annual Postgraduate Research Student
Conference - 2015, pp. 38-42, University of Sheffield, Sheffield, United Kingdom,
April, 2015.
http://www.gruppofrattura.it/ocs/index.php/gigf/aprsc2015/paper/viewFile/12157/11545
Gupta, S.K., and Moulick, S.K., "Study the Effect of Different SHPB Test Parameters
Using Numerical Simulation Technique", International Journal of Modern Engineering
Research, Vol. 4, Issue 1, pp. 48-54, January, 2014.
http://www.ijmer.com/papers/Vol4_Issue1/AG414854.pdf
Sincerely,
James M. Kennedy
KBS2 Inc.
February 19, 2020
p.s. I recommend the use of *CONTACT_AUTOMATIC_SURFACE_TO_SURFACE_ID instead of
*CONTACT_SURFACE_TO_SURFACE_ID.
------------------------------------------------
Contact overview
Automatic vs. Non-automatic:
Automatic contacts are recommended for most explicit simulations. Non-automatic
contacts (in which contact orientation is important) are sometimes used for metal
forming simulations where the geometries are very straightforward and contact surface
orientation can be reliably established before the simulation is conducted. Non-automatic
contacts are generally recommended for "implicit" simulations.
I recommend that you use the newer "automatic" option. Please consider the placement
of your shell mid-surface when using this newer contact.
Automatic contact types in LS-DYNA are identifiable by the occurrence of the word
AUTOMATIC in the *CONTACT command. The contact search algorithms employed
by automatic contacts make them better-suited than older contact types to handling
disjoint meshes. In the case of shell elements, automatic contact types determine the
contact surfaces by projecting normally from the shell mid-plane a distance equal to
one-half the 'contact thickness'. Further, at the exterior edge of a shell surface, the
contact surface wraps around the shell edge with a radius equal to one-half the contact
thickness thus forming a continuous contact surface. We sometimes refer to this off-
setting of the contact surfaces from shell mid-planes as considering shell thickness offsets.
------------------------------------------------
From: LS-...@yahoogroups.com [mailto:LS-...@yahoogroups.com]
Sent: Sunday, February 16, 2020 6:58 AM
To: LS-...@yahoogroups.com
Cc: ls-pr...@googlegroups.com
Subject: Re: [LS-DYNA] Impact simulations and Johnson Cook model
Dear Dr. Kennedy,
Thank you for the resources you have sent me for reading. I have read many resources already like Salahi et al. (2016), Gupta's thesis, Optional strain rate formulations, Varmintal database. I am going through the rest of the papers. So far I have not used damage parameters of Johnson Cook model for any simulations. Can I request you to go through my LS-DYNA model? There might be something other than material modelling which I am not able to catch. Briefly, I am explaining my thought process to modelling and simulations. May be even without seeing my .k file, you can tell me something.
Before making my own model, I did 2 validation studies to check if my incident stress-time curve matches with that given in the literature. I got a good match (one comparision is shown in Figure 1 of attached pdf). Incident stress-time history is calculated from the centre element on the bar located behind the pulse shaper (that's incident bar). To see what happens in the pulse shaper, I plotted stress vs time (Fig 2) and effective plastic strain vs time (Fig 3) for a center element in the pulse shaper from LS-DYNA. Thus, from these two plots, I understood that within a short time (here around 80 us), the plastic strain reaches its maximum value and then remains constant.
This part I have not been able to achieve in my own experimental simulations. My bars are 76 mm dia, rest of the details are given in the model attached. As you can see in Fig 4, the development of stress in the incident bar (Legend Numerical4) is very slow, it is getting loaded very slowly but unloading is happening fast. I deleted the first 400 us time history and plotted the rest (Legend Numerical1). So something is wrong with the way pulse shaper is getting loaded. The corresponding stress vs time (Fig. 5) and effective strain vs time for pulse shaper are shown in Fig 5 and 6 respectively. Clearly, the stress in pulse shaper is not constant at an early stage and starts dropping only after 500 us and same holds for effective plastic strain. Note that diameters of the bar and the pulse shaper in the validation study and my own study are different and hence loading durations will also be different. So please do not compare the two results.
I have been careful in evaluating my quasi static data parameters (A, B and n) at epsilon_0= 9.524 times 10^-4 i.e very close to 0.001. This same value of epsilon_0 is used in MAT_015
Quasi static true stress vs true plastic strain plot is shown in Fig 7. I have not been able to do high strain rate testing for copper. I dont have SHPB facility for that. Hence I dont have my own stress vs strain data for different strain rates. My current facility can test brittle materials like rock and concrete. Thats the end goal I am moving to. Hence I am relying on to literature data for copper to input strain rate dependent parameters.
So I need help in where I am not doing it right: a. Is it mesh density, boundary conditions, etc? b. Is it material modelling parameter?
Contains a LS DYNA .k file and pdf.
Pardon me if I have explained too much. I would really appreciate any help in this matter. Thanks.
Regards,
Venkatesh M Deshpande
PhD scholar
Indian Institute of Technology, Delhi
Official email id: cez1...@iitd.ac.in
On Sat, 15 Feb 2020 at 22:56, 'James M. Kennedy' j...@kbs2.com [LS-DYNA] <LS-...@yahoogroups.com> wrote:
Dear Venkatesh,
Several Johnson-Cook presentations involving copper under high strain rates
which may be of interest:
Gupta, S., "The Constitutive Behavior of Copper at High Strain Rate as
Determined by the Free Expansion Ring Test".
https://etd.ohiolink.edu/!etd.send_file?accession=osu1366200117&disposition=
inline
M Burley, JE Campbell, J Dean, TW Clyne , "Johnson-Cook Parameter Evaluation
from Ballistic Impact Data via Iterative FEM Modelling".
https://www.sciencedirect.com/science/article/pii/S0734743X17307820
Al Salahi, A.A., and Othman, R., "Constitutive Equations of Yield Stress
Sensitivity to Strain Rate of Metals: A Comparative Study".
https://www.hindawi.com/journals/je/2016/3279047/
Sincerely,
James M. Kennedy
KBS2 Inc.
February 15, 2020
-----Original Message-----
From: James M. Kennedy [mailto:j...@kbs2.com]
Sent: Saturday, February 15, 2020 11:06 AM
To: 'LS-...@yahoogroups.com' <LS-...@yahoogroups.com>;
'ls-pr...@googlegroups.com' <ls-pr...@googlegroups.com>
Subject: RE: [LS-DYNA] Impact simulations and Johnson Cook model
Dear Venkatesh,
See if this might be of some help:
The FAA has sponsored research for developing computational models for
simulating fan blade-off containment and engine-related impact events. Truly
predictive models that can accurately replicate the transition from petaling
to plugging failure modes of metals without tuning the model to match
specific tests is essential for acceptable certification analysis. These
efforts have results in the implementation of new tab- ulated Johnson-Cook
plasticity models *MAT_224, *MAT_224_GYS, and *MAT_264 in LS-DYNA:
Cordasco, D., Emmerling, W., and Du Bois, P., "A Status Review of Failure
Simulation at the Federal Aviation Administration", 11th European LS-DYNA
Users Conference, Salzburg, Austria, May, 2017.
http://www.dynalook.com/11th-european-ls-dyna-conference/crash-metal-failure
/a-status-review-of-failure-simulation-at-the-federal-aviation-administratio
n
--------------------------------
The Johnson-Cook model is probably the most widely used constitutive law for
rate- dependent plasticity, and also accounts for thermal and stress-state
effects. The flow stress is defined as a product decomposition of the
effects of equivalent plastic strain, plastic strain rate, and temperature
on work hardening,
Might I also suggest reading some of the Johnson-Cook papers for details.
Johnson, G.R. and Cook, W.H., "A Constitutive Model and Data for Metals
Subjected to Large Strains, High Strain Rates, and High Temperatures," 7th
International Sympos- ium on Ballistics, pp. 541-547, The Hague,
Netherlands, April, 1983.
Johnson, G. R., and Cook, W. H., "Fracture Characteristics of Three Metals
Subjected to Various Strains, Strain Rates, Temperatures and Pressures",
Engineering Fracture Mechanics, Vol. 21, Issue 1, pp. 31-48, 1985.
Jutras, M., "Improvement of the Characterisation Method of the Johnson-Cook
Model", Master's Thesis, Faculte des Sciences et de Genie, Universite Laval,
Quebec, Canada, 2008.
http://www.theses.ulaval.ca/2008/25087/25087.pdf
https://corpus.ulaval.ca/jspui/browse?type=author&order=ASC&rpp=20&authority
=8624a488-7058-4415-901d-39d797be6ad4
Schwer, L., "Optional Strain-Rate Forms for the Johnson Cook Constitutive
Model and the Role of the Parameter Epsilon_0", 6th European LS-DYNA User's
Conference, Gothenburg, Sweden, May, 2007.
http://www.dynalook.com/documents/6th_European_ls-dyna/2.2.3.pdf
--------------------------------
Parameter notes -
D1 alone defines the plastic strain at failure without considering all
potential effects of pressure, strain rate, temperature, etc., which can be
addressed in the damage function.
D1, D2, and D3 together provide the pressure-stress effect, D4 the
strain-rate effect, and D5 the temperature effect.
The following basis paper should provide some additional help in the
under-standing of these damage parameters:
Johnson, G. R., and Cook, W. H., "Fracture Characteristics of Three Metals
Subjected to Various Strains, Strain Rates, Temperatures and Pressures,"
Engineering Fracture Mechanics, Vol. 21, Issue 1, pp. 31-48, 1985.
http://isn-csm.mit.edu/literature/1985-efm-johnson.pdf
Lesuer, D.R., "Experimental Investigations of Material Models for Ti-6Al-4V
Titanium and
2024-T3 Aluminum," DOT/FAA/AR-00/25, September, 2000.
http://aar400.tc.faa.gov/aar-430/reports/00-25.pdf
Kay, G., "Failure Modeling of Titanium 6Al-4V and Aluminum 2024-T3 with the
Johnson- Cook Material Model," DOT/FAA/AR-03/57, September 2003.
http://www.tc.faa.gov/its/worldpac/techrpt/ar03-57.pdf
Jutras, M., "Improvement of the Characterisation Method of the Johnson-Cook
Model", Master's Thesis, Faculte des Sciences et de Genie, Universite Laval,
Quebec, Canada, 2008.
http://www.theses.ulaval.ca/2008/25087/25087.pdf
--------------------------------
Perhaps this data (including effective plastic failure strain) might be of
some help.
If you have a need for mat_018 (mat_power_law_plasticity), mat_015
(mat_johnson_cook),
mat_098 (mat_simplified_johnson_cook) and mat_024
(mat_piecewise_linear_plasticity) material behavior data, you might look at
Varmint Al's Engineering Page. He indicates that he has (text files in
LS-DYNA format) the necessary property coefficients for 1044 materials.
http://www.varmintal.com/aengr.htm#Mats-for-LS-DYNA
http://varmintal.com/material.txt
An earlier note on Al's work:
http://www.feapublications.com/news_2008/FEA_News_Sept_2008.pdf
An addition to mat_098 and mat_018 which now includes Effective Plastic
Failure Strain for the 1044 materials in the database.
------------------------------------------------
The Johnson-Cook strain and temperature sensitive plasticity is sometimes
used for problems where the strain rates vary over a large range and
adiabatic temperature increases due to plastic heating cause material
softening.
Murugesan, M., M., and Jung, D.W., "Johnson Cook Material and Failure Model
Parameters Estimation of AISI=1045 Medium Carbon Steel for Metal Forming
Applications", Materials, Vol 12, pp. 609, 2019.
https://webcache.googleusercontent.com/search?q=cache:ytorN_S5MUYJ:https://w
ww.mdpi.com/1996-1944/12/4/609/pdf+&cd=11&hl=en&ct=clnk&gl=us
Burley, M., Campbell, J.E., Dean, J., and Clyne, T.W., "Johnson-Cook
Parameter Evaluation from Ballistic Impact vis Iterative FEM Modelling",
International Journal of Impact Engineering, Vol. 112, pp. 180-192,
February, 2018.
https://www.sciencedirect.com/science/article/pii/S0734743X17307820
Sobolev, A.V., and Radchenko, M.V., "Use of Johnson-Cook Plasticity Model
for Numerical Simulations of the SNF Shipping Cask Drop Tests", Nuclear
Energy and Technology, Vol. 2, Issue 4, pp. 272-276, December, 2016.
https://www.sciencedirect.com/science/article/pii/S2452303816301194
Zhang, Y., Outerio, J.C., and Mabrouki, T., "On the Selection of
Johnson-Cook Constitutive Model Parameters for Ti-6Al-4V Using Three Types
of Numerical Models of Orthogonal Cutting", Procedia CIRP, Vol. 31, pp..
112-117, 2015.
http://ac.els-cdn.com/S2212827115002504/1-s2.0-S2212827115002504-main.pdf?_t
id=dff541b0-9997-11e7-8e36-00000aab0f01&acdnat=1505426503_6aa940c7827c762e73
51f520c510bae9
--------------------------------------
*MAT_224 is a recently developed material model for LS-DYNA. This material
model, known as the tabulated Johnson-Cook model, is more versatile than the
analytical Johnson-Cook and other plasticity models because it uses
tabulated stress strain curves at various strain rates and temperatures.
Stress state dependence was incorporated by tabulating a fracture locus, or
equi- valent plastic strain versus one or more stress state variables. The
ongoing goal of this project was to acquire and report data from a
comprehensive test series in order for the team to gener- ate the best
possible material model
*MAT_224 or *MAT_TABULATED_JOHNSON_COOK
This is Material Type 224. An elasto-viscoplastic material with arbitrary
stress versus strain
curve(s) and arbitrary strain rate dependency can be defined. Plastic
heating causes adiabatic temperature increase and material softening.
Optional plastic failure strain can be defined as a function of triaxiality,
strain rate, temperature and/or element size. This material model resembles
the original Johnson-Cook material (see *MAT_015) but with the possibility
of general tabulated input parameters.
An equation of state (*EOS) is optional for solid elements, tshell
formulations 3 and 5, and 2D continuum elements, and is invoked by setting
EOSID to a nonzero value in *PART. If an equation of state is used, only the
deviatoric stresses are calculated by the material model and the pressure is
calculated by the equation of state.
*MAT_224_GYS or *MAT_TABULATED_JOHNSON_COOK_GYS
This is Material Type 224_GYS. This is an isotropic elastic plastic material
law with J3 depend- ent yield surface. This material considers
tensile/compressive asymmetry in the material response, which is important
for HCP metals like Titanium. The model is available for solid elements.
--------------------------------------
Sincerely,
James M. Kennedy
KBS2 Inc.
February 15, 2020
-----Original Message-----
From: LS-...@yahoogroups.com [mailto:LS-...@yahoogroups.com]
Sent: Saturday, February 15, 2020 10:30 AM
To: ls-pr...@googlegroups.com; LS-...@yahoogroups.com
Subject: [LS-DYNA] Impact simulations and Johnson Cook model
Dear Sir/Madam,
Greetings!
I am doing impact simulations in LS DYNA of split Hopkinson Pressure Bar
(SHPB). A striker bar impacts incident bar. In between a copper coin
typically known as pulse shaper is attached on the incident bar face. The
copper filters out high frequency oscillations of the pulse generated due to
the impact. My questions are related to modelling of the copper material in
LS DYNA. My questions are:
1. Copper is being subjected to very high strain rate above 1000/s. At such
strain rates, Johnson-Cook (JC) model is not accurate enough to model the
plastic deformation of metals. Can you suggest a suitable model integrated
in LS DYNA which can do this? I chose different values of C parameter in JC
model and ran more than 200 simulations but it is not successful.
2. The other option I have been thinking is to edit the user subroutine
material code for Johnson-Cook (JC) model (MAT_015) available in LS-DYNA.
Briefly, I have explained the original and modified JC formulations in the
attached figure. This has to be done to improve accuracy of the model at
high strain rates beyond 1000/s. As you can see in the attachment, in
addition to log-linear strain rate dependency, a power law dependency has
been added. Do you have the user material code for MAT_015? Since I have to
add 2 more terms in the way flow stress is calculated, it would be easy to
edit an already existing code rather than making a new one from the scratch..
So far I have not been successful to obtain the code from LS DYNA technical
support team.
Regards,
Venkatesh M Deshpande
PhD scholar
Indian Institute of Technology, Delhi
Official email id: cez1...@iitd.ac.in
[Non-text portions of this message have been removed]
------------------------------------
Posted by: Venkatesh M Deshpande <venkatesh...@gmail.com>
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