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Roy Duan

How to understand the visco-elastic property of material LAW70

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Hi all,

From the Reference Guide of /MAT/LAW70, it says this material model is a visco-elastic foam material. However, I cannot find the right parameter which time dependent. So how to understand the visco property of this material model?

 

Roy

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Hi Roy,

A viscoelastic material will return to its original shape after any deforming force has been removed even though it will take time to do so. We create this behavior in the material model using the stress strain curve, ie loading and unloading curves.

4.PNG

 

Viscoelastic materials respond differently depending on how fast they are stretched, and that is related to strain. So the strain rate defines how fast the material is stretched. Based on this strain rate we can make the material more viscous in nature. In general, high strain rates cause more elastic responses whereas lower strain rates cause more viscous behavior.

 

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Hi George,

Loading and Unloading curves (two different curves) show a hysteresis effect of this material. However, I don't think this gives the Visco property. 

From Wikipedia, it shows follows. In /mat/law70, which parameter gives the viscosity of the material? If the strain rate effect is not considered, that is to say only two curves are defined for loading and unloading, is there any visco property in this model? 

2018-01-13_142001.png.fafebf83061f05b207e7582121a2bde0.png2018-01-13_142303.png.cce8e39f62f9b0fd5dd28985b2d7ef2a.png

 

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Hi George,

How does the material consider the viscous effect if strain rates are included? Which parameter or equation shows the viscous effect?

 

In LS-DYNA, it includes decay constant parameter in the input of *mat_low_density_foam, please see the attach file.

 

Roy

MAT_LOW_DENSITY_FOAM (MAT_057).pdf

Edited by Roy Duan

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Hi Roy,

In the above attached dyna material model they are using Prony series. If you are looking for a similar material law you can check /MAT/LAW42 for RADIOSS, which defines a hyperelastic, viscous, and incompressible material specified using the material models.

For /MAT/LAW70. the viscosity of the material solely depends on the stress-strain curve definition for different strain rate. 

 

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