# MAT LAW

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I am doing tensile test of an HDPE Plastic material. I have only few material properties such as Young's modulus, Density, tensile strength etc. Which material law can be used in this case?

I go through tutorial but I dont have the properties which are used in that tutorial.

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Hi,

With these inputs you can try modelling with material law 2.

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Hello,

I think Mat Law 2 require Hardening parameter (b) and plastic hardening exponent (n)...

How to calculate them?

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Hi,

I'm attaching an excel sheet for /MAT/LAW2.

Enter Ultimate Stress, Yield Stress and percentage elongation of the material so that it will calculate and will provide the b and n values. a is the yield stress value.

b&n_Law2.xlsx

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Hello George ,

Thank you very much.

Just one query.... Value use in formula....205000.... Is it a Young's modulus?

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Hi,

I don't think its Young's Modulus.

Please  check open web resources on hardening parameters.

In the latest HyperWorks version (From 14 onwards) we can input the yield and UTS directly and the solver will directly calculate these parameters.

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Hello George,

Thank you..

I will try for it

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On 2017/12/29 at 7:53 PM, George P Johnson said:

Hi,

I'm attaching an excel sheet for /MAT/LAW2.

Enter Ultimate Stress, Yield Stress and percentage elongation of the material so that it will calculate and will provide the b and n values. a is the yield stress value.

Hi George,

Could you explain the background theory of this Excel sheet for /Mat/law2?

From this excel, n=0.45*elongation，b=(Ultimate-yield)/(n-(Ultimate/205000))^n      How this formula come from?   And what's the scope of the formula?

Roy

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Hi Roy,

From this they have developed that excel sheet with the formula. I recommend you to go through the open web resources on Johnson-Cook material parameters.

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Hi George,

I'm sorry for the late reply.

I know the formula of Johnson-Cook model you showed. I just cannot understand the expressions in the Excel.

So how to understand this formula?

From this excel, n=0.45*elongation，b=(Ultimate-yield)/(n-(Ultimate/205000))^n

Roy

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Hi Roy,

This excel sheet was using long back , now we don't recommend this.

From RADIOSS version 14, you can directly input the tested values (Yield stress, UTS and strain at UTS), by switching on the I_flag to 1 and so this seems to be obsolete.

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