Is it possible to have time-dependent material properties?

[Anonymous]

Hi, I am new in autodesk but have run a few examples from the tutorial and would like to understand the limitation of the Simulation 2012. In transient thermal analysis, is there a way to modify (or create) a material that have time-dependent properties? I know temperature-dependent thermal properties seems available but can one assign mateial properties depending on other variables? I am also interested in stress analysis and have materials poperties (mechanicall and thermal) that can change over time. Is there an option to creat user-defined element or user-defined material input? Any reply will be appreciated.

[S.LI]

I'm assuming "rate-dependent" material is what you are talking about.

For material properties, we are not talking "time" directly.

Usually, the most important thing is the relation between stress and deformation, deformation rate or even stress rate, instead of time directly.

Of course, you can see "rate" is the entry of time.

"rate-dependent" material models are complicated in both theory and simulation. There are some in 2012, such as creep, some visco-elastic models etc.

2012 doesn't support user-defined element/material/load directly, but it does allow users to input their material properties for some material models. For examples, you can input stress-strain curve for elasto-plastic material model according to your experiments. In hyper-elastic models, curve-fitting feature is provide to estimate material properties from users' data. For some thermal elastic material models, users are allowed to input material properties varying with temperatures.

Just share some of my thoughts, not sure if it's helpful.

[Anonymous]

Thank you for your reply.  I am intereted in material properties that are changing over time or maybe I should say "age"-dependent.  Is it an option for any of the Algor model or multiphysics simulation?  Thanks.

[Joey.X]

It is reasonable to ask for time dependent material property in transient thermal analysis; it may help modeling dynamic processes such chemical reactions driving process, with ignoring the complicated chemical reaction process, but knowing the material property changes with the time, the whole domain could be simulated in transient thermal analysis. Unfortunately, Autodesk simulation MP V2012 does not support this feature in transient thermal analysis.

[xli]

Off the top of my head, no, we do not have a material directly dependent on time. Only temperature distribution for thermal loading can be time dependent (step by step) and then some material properties is temperature-dependent. Another thing is kind of time dependent... is PD in MES which is activated or deactiviated by its active-range which gives death&birth times for the PD.

As an idea, it may assign a load curve to a "time dependent - material property", providing a multiplier to the value in updating matrix etc. It sounds feasible not that complicated. So this gives some thoughts for possible new features... thanks.

-xli

[S.LI]

One workaround is "restart from another analysis".

The material properties could be changed when switching to another ds.

[Anonymous]

Thanks for your replies.  

Hi, xli and S.Li, Could you explain a little bit more about how to do 'matrix updating' or 'restart' to update material properties?   Can these be executed automatically at different tme steps during transient analysis? Appreciated.

[S.LI]

Autodesk simulation provides a feature called "restart from another analysis" for MES analysis type.

By this feature, you can simulate a model, e.g. in DS1, then continue it in DS2. At this time, you are allowed to use different material properties in DS2. And you can continue DS2 with DS3, ... ...

This is not automatic so far, and you have to do "stop", "restart", "setting model" manually.

[Anonymous]

'As an idea, it may assign a load curve to a "time dependent - material property", providing a multiplier to the value in updating matrix etc.'

Hi xli, could you explain your procedures? can this matrix updating be done automatically at different time steps? Thanks.

[xli]

Hi, I am sorry for possible misunderstanding here. I was thinking an idea for developer to implement this "time-dependent" material feature, not a workaround.

S.Li's suggested workaround is the one I can think for now. But you have to do a sequency of analysis to get there, a little bit not convinent.

-xli 

[Anonymous]

Do you have any plan to include this feature (time-dependent material properties) in the transient thermal analysis (or other autodesk/Algor simulation) in the near future?

[John_Holtz]

Hi HL,

Unfortunately, we cannot discuss when any particular feature may be implemented. I believe this restriction is imposed by the US Government so that companies do not get revenue on a product that "might have a new feature within X time frame". And even from a business perspective, there is some risk in telling a customer or prospect that function Y will be released on this date, and then finding that it needs to be removed from the release due to quality issues or some other reason.

• Out of curiosity, what is the application where the material properties are changing with time? Are you adding mass to the system and want to change the mass density versus time?
• What properties are changing over time?
• Is there some way to use the changing temperature to change the material properties?

The answers to those questions may influence when such a feature gets implemented. (Also, I would need to understand the use and workflow so that I can design it 😉

Otherwise, it seems that the "restart" analysis is the current option. Actually, I think you do not want to do the restart but to run a new analysis with the different material properties, starting with the last temperatures from the previous analysis. These models could be created ahead of time in different design scenarios and analyzed together by scheduling the analyses.

See "Help > Autodesk Simulation > Setting Up and Performing the Analysis > Setting Up Part 2 > Thermal Analyses > Analyses Parameters > Transient Heat Transfer" and "Help > Autodesk Simulation > Setting Up and Performing the Analysis > Set Up Analyses Part 3 > Perform Analyses - Run Simulation > Schedule Analyses".

[S.LI]

Do you have any reference on this kind of materials, such as paper, book, professor, or even formulations?

With these details, we can understand more.

Basically, I don't think material properties should connect with time directly. To associate with some other physical quantities will make more sense, such as life cycles in Fatigue analysis.