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RADIOSS Johnson cook material

Altair Forum User

Hi sir,

I have a doubt regarding Johnson cook material that

1.if we take Iflag=0, can we take b(defined as hardening parameter) as the ultimate tensile strength of the material.

2. Or if I flag=1, Can I take n(hardening exponent) value as % elongation of the material.

Note: For my material stress-strain curve is not available.

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Radioss

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Altair Forum User

Hi,

For /MAT/LAW2 if Iflag=1, b parameter is the ultimate tensile stress (UTS) whereas if Iflag=0, b is the plastic hardening parameter.

When Iflag=1, n is the engineering strain at UTS.

Altair Forum User

Hi sir,

My doubt exactly is whether we can take if we Iflag=0, b(defined as hardening parameter) as the ultimate tensile strength of the material & if I flag=1, can I take n(hardening exponent) value as % elongation of the material asI don't have hardening parameter data for my material and second case I dont have hardening exponent respectively.

Altair Forum User

Hi,

No, it's not possible. If you putting Iflag=0 the inputs should be accordingly.

I'm sharing an excel sheet with you where the user will be providing the yield, ultimate and % elongation values and it will provide the b and n values. You can try this.

Unable to find an attachment - read this blog

omerfkale

Hi,

No, it's not possible. If you putting Iflag=0 the inputs should be accordingly.

I'm sharing an excel sheet with you where the user will be providing the yield, ultimate and % elongation values and it will provide the b and n values. You can try this.

Dear George,

I have a question reagarding to iflag2 parameter in Law2 material.

As you know most of material parameter can be found as in image below.

Can i use 'elongation at break' as Engineering Strain at UTS or should i do some extra calculations?

image.png.41b48bc064adda57e22d0a93bc3e1619.png

Unable to find an attachment - read this blog

Altair Forum User

Hi,

I think you can use this value directly.

omerfkale

Hi,

I think you can use this value directly.

Thanks George.

Altair Forum User

Hi sir,

My doubt exactly is whether we can take if we Iflag=0, b(defined as hardening parameter) as the ultimate tensile strength of the material & if I flag=1, can I take n(hardening exponent) value as % elongation of the material asI don't have hardening parameter data for my material and second case I dont have hardening exponent respectively.

Hi,

As I observed in some example of steel with Iflag=0, the parameter b is seems to be the ultimate strength. Is it the ultimate strength or some other value. And as per your excel attached @George P Johnson 'n' value seems to be very high

attaching file below.

aa.JPG.799f8a2effcee980d45592643b102c1a.JPG

Altair Forum User

Hi,

This issue with the example values is already known and we will be correcting it soon in the example file.

But, thank you notifying the issues as we can improve our documentation much better.

omerfkale

Hi,

No, it's not possible. If you putting Iflag=0 the inputs should be accordingly.

I'm sharing an excel sheet with you where the user will be providing the yield, ultimate and % elongation values and it will provide the b and n values. You can try this.

Hi George,

I setup a basic tensile model to understand calculations for iflag parameters.

I've created a model with iflag=1 and iflag=0 compared them. As i understand when we choose iflag=1, solver first computes true-stress and strain, then computes a,b,n parameters using them.

I've attached excel file that i use to calculate this parameters and starter outs of both analysis. Can you please check calculations?

image.png.87565b53e63e0d00774dd04ca24113f2.png

Unable to find an attachment - read this blog

Altair Forum User

Hi @omerfkale

WIth Iflag 1 one has to provide Stress/strain at UTS which are used to calculate Johnson cook parameters.

If Iflag is zero one has to directly provide the a,b,n coefficient values.