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DanStro
2011-01-17, 14:38
I know that g_i and k_i need to be between 0 and 1 but does this requirement also apply to tau_i?

The help manual doesn't say that it is a ratio so I have been assuming that it doesn't need to be between 0 and 1 but when I look in some journal articles they all have the values for tau<1, usually much less than 1. I currently am working with a model that was created by someone else that has values ranging from around 5 to 1000 and for reasons I cannot get into I am unable to ask the creator of the model.

In case it matters I am modeling glass at around its transformation temperature (but not melted).

Any help is appreciated.

Dan

manfred
2011-01-24, 06:55
. . . well relaxation time constants tau_i can have values being very small as well as being very big! Depends on the problem considered as well as on the scale (units) used (seconds, ours, months, years, etc)!

I know that g_i and k_i need to be between 0 and 1 but does this requirement also apply to tau_i?

The help manual doesn't say that it is a ratio so I have been assuming that it doesn't need to be between 0 and 1 but when I look in some journal articles they all have the values for tau<1, usually much less than 1. I currently am working with a model that was created by someone else that has values ranging from around 5 to 1000 and for reasons I cannot get into I am unable to ask the creator of the model.

In case it matters I am modeling glass at around its transformation temperature (but not melted).

Any help is appreciated.

Dan

DanStro
2011-01-24, 07:47
Thanks manfred.

That's what I thought but I wanted to make sure. All of the journal articles that I've seen dealing with this type of simulation have tau_i's < 1 while mine is >>1.

Dan

biofriend
2011-01-25, 09:10
Hi Dan,

It can be any value. But beforehand one needs to make sure if the tau_i which you gonna use as input is from relaxation or is from the creep point of view. They can differ very much and the correct one needs to be used. may be these tau_i in the model you are refering to is from the other experiment than those reported in those papres.

DanStro
2011-01-25, 13:24
Thanks biofriend,

Since I've only been working with creep test data I didn't really think about the differences between the two test types.

Dan

biofriend
2011-01-25, 14:54
I am not sure but I think Abaqus may use relaxation characteristic time in prony series - I dont know about experimental test data- hence if you have the creep data you may need to convert it. This may be the difference in the scale of the times that are reported in different literature.