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# high strain rate modelling in abaqus

Mon, 2013-06-17 06:01 - aeroy6244

how to do modelling in abaqus for high strain rate. i am beginner. please help me regarding this. i have theoretical idea about johnson cook model.

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## Comments

## regarding johnson and cook model

i want to know that for one material why johnson and cook model constants vary.

## Re: why johnson and cook model constants vary for one material

I don't understand what you mean by your question. Could you explain in more detail?

More generally, what you think of as "one material" may not actually be one material in the sense that the chemistry may vary, the crystal structure may vary, processing history may vary etc. The best one can expect in nonlinear materials is a range of behavior that is within reasonably tight bounds.

For a general discussion of the topic see http://www.tam.northwestern.edu/tb/computability_w_figs.pdf ( Belytschko, T., and K. Mish. "Computability in non‐linear solid mechanics."

International Journal for Numerical Methods in Engineering52.1‐2 (2001): 3-21.)-- Biswajit

## regarding johnson and cook model

thank you sir for your reply. can you tell me how to implement johnson cook model in abaqus. i have got the constants for johnson cook model fro particular material through literature review. please tell me the procedure. i tried but failed.

## Johnson-Cook in abaqus

Johnson-Cook plasticity is already implemented in Abaqus.

If you need help you will have to be more explicit about what you're trying to do. I cannot read your mind.

-- Biswajit

## regarding johnson and cook model

thak you for your reply sir.

actually i have material constants for jc model. i want to generate stress strain curve for given material constants of jc model. at first i want to do this. kindly tell me procedure step by step.

## Re: Johnson and Cook plasticity

First, are you interested in temperature-dependence? If you are, things get a bit complicated and you have have to solve a ODE.

If you are not, then assume a constant strain rate, start with zero strain and increment strain in small steps, find the yield stress, and then plot the yield stress versus strain.

-- Biswajit

## regarding johnson and cook model

thank you sir for your reply. but i want to get stress strain curve in abaqus using johnson cook model. i saw jc model in plasticity module of abaqus but i am not getting how to do modelling in abaqus. what i want to do is to make geometry give material constants of jc model which is inbuilt in abaqus and get stress strain curve.if it is not possible then any alternative way to do modelling for high strain rate test. i am following cylinder impact test as my experiment. is thee any way to model that experiment in any software. kindly please tell me the procedure.

thank you

waiting for your reply sir

## Verifying the Johnson-Cook model in Abaqus

I'm still not sure I understand you correctly. There areat least two possible interpretations of your question:

1) You want to verify the J-C implementation in Abaqus.

2) You want to validate Abaqus simulations against your experimental data.

Let me assume that you want to verify the J-C model in Abaqus. That means you want to check that, given a set of parameters, Abaqus will generate the same results as a simple algebraic evaluation of the model.

To do that, one way of proceeding is as follows:

a) Create a single cubic element.

b) Assign the element a set of properties corresponding to the J-C model.

c) Load the element at a fixed rate by applying a constant velocity along one side and keeping the opposite side fixed. You have to be careful about whether you want to apply uniaxial strain or uniaxial stress.

d) Extract the stresses and strains at the Gauss points (or at the nodes if available). Make sure that the deformation is homogeneous (or close to homogeneous).

e) Plot stress vs. strain for each node/Gauss point and compare with the algebraic curve.

On the other hand, if you are trying to validate the Abaqus model against split-Hokpinson pressure bar data, Taylor impact test data, flyer plate data etc., you will need to model the experiment and compare experimental outputs with simulation outputs. Stress-strain curves can be generated only for pressure-bar data because the deformation is approximately homogeneous (and uniaxial strain). You can't generate uniaxial stress-strain curves from simulations that involve complex three-dimensional stress states.

-- Biswajit

## regarding taylor cylinder impact test

hello sir,

thank you for your reply. i want to perform cylinder impact test. how to decide rigid target support dimensions. kindly please help me regarding this.

## More on Taylor impact tests

Manish,

Your other question was:

"there is a formula for calculating stress in taylor cylinder impact

test. but that formula only depends on final length of cylinder. once

cylinder hits the rigid target cylinder will have elastic and plastic

deformation. we can extract plastic deformation data through experiment.

my question is is can we apply that formula for every plastic

deformation reading rather than just applying that for final cylinder

length. formula is given here. here l is initial height. L1 is aftet

imapact total final length, H is height of cylinder it means after

impact cylinder shape is preserved for some portion so H is dat height.

after impact cylinder takes mushrom shape and after mushroom shape the

cylindrical shape starts. rho is material density and v is impact

velocity.

formula is sigma= rho*v^2*(l-H)/(2*(l-L1)*ln(l/H)"

The first step is to determine how this equation was derived. In general, such equations cannot be used for intermediate steps in the deformation of a cylinder.

The Taylor cylinder does not have a unqiue homogeneous stress. However, several simplifying assumptions can be made to come up with some sort of effective response that may or may not have any connection with reality.

For a recent review see: http://rspa.royalsocietypublishing.org/content/465/2103/769.full.pdf+html

-- Biswajit

## regarding taylor cylinder impact test

sir i want to simulate cylinder impact test in ansys workbench. is it correct to simulate cylinder impact test in ansys workbench. or suggest me soem other software to simulate cylinder impact test. what i want to plot is stress versus strain curve for particular strain rate and temperature.

## Taylor impact simulations

You can take a look at what I've done in the past (at http://arxiv.org/abs/1201.2476 ) on Taylor impact simulations to get n idea of what is involved.

From your questions I gather that you are running into one or all of the following :

1) You want to determine anvil dimensions. Answer: As large as you need it to be. Typically 2.5-3 times the diameter of the impacting material. My paper above will help you get an estimate for your material. You can do without anvil dimensions if you are impacting against a rigid wall.

2) You want to use Ansys Workbench. Answer: Sorry, haven't used that.

3) Other FE software: Answer: Abaqus/Explicit, LS-Dyna etc.

4) How to plot stress-strain curve: Answer: Don't use a Taylor impact test. It's extremely difficult, if not impossible, to generate such a curve because of the complex stress-strain states in a severely deformed cylinder. Each point along the length of the cylinder will have a different strain rate and temperature as the deformation progresses (even if the deformation is perfectly symmetrical about the axis of symmetry).

From your questions it appears that you are a graduate/undergraduate student/fresh researcher. If that is the case, the first person you should pose your questions to is the one who has assigned you this next to impossible task.

-- Biswajit

## regarding taylor cylinder impact test

thank you for your reply sir. but i have only cylinder impcat test set up to perform high strain rate experiments. otherwise i can not perform any other experiments. that is why i am focusing much cylinder impact test. any other suggestion for performing high strain rate experiments. SHPB test is not possible beacuse of non availability of set up. kindly suggest me some other experiments which can be set up easily to perform high strain rate experiments. yes i am masters student(m.tech.) just started involving to work for my thesis work. as far as guide is concerned, you can understand why i am using imechanica. if he were helping me why i would come on imechanica.