Strain rate units for Mat Law 36 PLAS_TAB

Hello All,

Greetings!!

I am using mm, kg, ms units system in HyperCrash and using Mat Law 36 or PLAS_TAB for different parts.

Therefore I have taken strain rate unit as 1/ms.

But general standard unit for the strain rate is 1/sec. Therefore I ran simulation with units as 1/sec as well.

Results: Simulation results of Strain rate with 1/sec units are closer to experimental results as compare to 1/ms simulation results.

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Above screen shot is from Radioss_10.0_Reference_Guide2.

Please guide me what unit (1/sec or 1/ms) to use for accurate material modelling in Radioss.

Thanks and Regards

Nitin Jain

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Pranav Hari

Hi Nitin Jain

Hypermesh/Hypercrash in non-dimensional. It is up to the user to use consistent units and convert values accordingly at each instance. There is no default unit system for Hypercrash.. If you have given values in seconds for your model, then it will display results for the same unit(s) and vice versa.

Check this forum post too.

https://community.altair.com/community?id=community_question&sys_id=59a60c7a1b2bd0908017dc61ec4bcb09

Thanks

Altair Forum User

Hi Pranav Hari,

I believe that is not the case with Hypercrash. When you start HyperCrash, you have an option to select Units system. Please find following screen shot for more details:

image.png.9146c8977d84e1e6a18dc21f65e052d0.png

Regards

Nitin Jain

Pranav Hari

Hi Nitin Jain

Yes. if you have selected the unit system, then you can give values accordingly to that unit system.

Thanks

Altair Forum User

Hi Pranav Hari,

Here my problem lies. If I select ''ms'' as strain rate unit, then the difference between simulation results and physical testing results is very high.

On the other hand, if I take ''sec'' as strain rate unit, then the difference is acceptable.

My concern is Altair has missed to assign unit system to Strain rate and by default it took values only in ''sec''.

Please share your opinion.

Regards

Nitin Jain

Simon Križnik

Hi @Nitin Jain

there is no specific unit system for RADIOSS solver: the user has to maintain the consistency in the inputs provided.

Hypercrash is a preprocessor to create Radioss solver decks. The unit system selection on HC startup is equivalent to the Header Card (Analysis>Control cards> header card) in Hypermesh preprocessor, where you define scale factors and input/output units.

image.png.54a68c4e8a9a3ff69cca78d61e7ef21f.png

The utility of selecting unit system in HC is when you import solver decks with different unit system, HC can detect the inconsistency and resolve the conflict (provided the solver decks being imported have unit type defined in Header card).

Using the set of consistent units the strain rate units will be the same as time units.

image.jpeg.550a69cd5540d866830db2c3d4699195.jpeg

Altair Forum User

Hi @Ivan

Thank you for your reply. It has answered my query.

Regards

Nitin Jain