Measurement of Dominant Deformation Modes - Constitutive Models
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/
PolymerFEM.com Discussion Boarden-USMon, 24 Jun 2024 17:50:50 +0000wpForo60
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/paged/2/#post-11037
Mon, 19 Aug 2013 05:03:20 +0000I am really unsure that would work. The equation you point at is not objective, i.e. frame independent. One could look at a state of shear, rotate the axis a bit and recover a state of uniaxial tension!]]>Constitutive Modelsbw_compositehttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/paged/2/#post-11037
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11029
Fri, 02 Aug 2013 06:07:09 +0000After the simulation you can use the equation to determine the strain mode of the elements.In Abaqus for example, you can use the create field output tool to calculate m for all elements.Then you will see which strain modes the rubber part has, and you can determine which tests you need calibrate a suitable hyperelastic material model.]]>Constitutive Modelsunrahulhttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11029
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11027
Thu, 01 Aug 2013 12:38:25 +0000that is an interesting paper, but how do you put it at use? The deformation measure they introduced is local!]]>Constitutive Modelsbw_compositehttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11027
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11025
Wed, 31 Jul 2013 11:43:26 +0000Constitutive Modelsunrahulhttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11025
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11022
Fri, 26 Jul 2013 04:49:27 +0000Back to your problem, I am not so sure I understand your plan. If you compare principal stretches you are automatically comparing quantities defined in different coordinate systems. I mean, however complex the deformation, the computation of principal stretches implies locally rotating the coordinate system to an orientation such that the strain tensor is diagonal. The key aspect in uniaxial deformation is that such rotation is nihil everywhere, i.e. if you select your global orientation as the one for which the strain tensor of an arbitrary point is diagonal, then the strain tensor is diagonal in this system for all material points.Let me clarify with an example. Imagine a bar of material undergoing uniaxial strain, apart from a small region undergoing localized shear (shear band, for example). Then you can choose the shear strain in such a way the principal strain is in magnitude constant! which if I understood you correctly, would invalidate your approach (your metric would suggest the deformation being uniaxial)That us why i proposed to quantify the rotation needed to bring the strain tensor in an arbitrary point in the diagonal form. If your manager prefers colour plots, you can still: 1) choose a region of the product where the strain field in mainly uniaxial2) Compute the principal strain orientation and consider this your reference orientation3) For all other integration points, you compute the prinical stretches: the difference between their orientation and the orientation chosen at step 2) is then a scalar field you can use to obtain a colour plot.As a variation of the procedure, you can also assign different weights to different material points, based on the principal stretch magnitude: in this way your metric will assign more importance to areas characterized by high strains.Hope this is of some help, let us know how it goes!PS: On second thought, why not try something simpler for our manager? Show him a plot (after performing a good selection of the global reference system, i.e. aligned as much as possible with the prevailing uniaxial strain field)) of the diagonal terms in the strain tensor (linked to normal strains), and the off-diagonal terms (linked to shear). In an uniaxial deformation the second plot should be zero everywhere!]]>Constitutive Modelsbw_compositehttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11022
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11021
Thu, 25 Jul 2013 09:18:52 +0000As to the topic...One idea I have is to use the principal streches of hte mateiral point compared to what the principle stretches should be for Uniaxial Tension, Biaxial Tension, and Planar Tension. I can calcualte a series of ratios if I assume that the max principla strecth to be the main strethc. The closer these coefficents are to 1.0 the more likely the mode of deformation falls into the category. Below are the ratios I came up with:s1, s2, s3 = (max, mid, min) principal stretchesUniaxial TensionUT_N = s2 * sqrt(s1)UT_M = s3 * sqrt(s1)Biaxial TensionEB_N = s1*s2EB_M = s1^2 * s3Planar TensionPT_N = s2PT_M = s1 * s3]]>Constitutive ModelslolefeanceVekhttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11021
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11020
Thu, 25 Jul 2013 08:42:20 +0000forgive the unnecessary sarcasm, but if you and your colleagues can not find an agreement on such a matter, based on your common sense, I doubt any metric will do the trick!Anyhow, I would start with showing them a plot of the orientation of the first principal strain. If the loading were uniaxial the plot would be trivial.The next level might be (thinking maybe out loud) to choose arbitrarily a reference direction, and then plot for each integration point (or a selection thereof), the distance of the strain tensor from the closest diagonal tensor. This provides a measure of how far each point is from the uniaxial deformation in the direction selected arbitrarily at the beginning of the procedure.Are you dealing with an compressible elastomer? In this case the volumetric strain tensor might be a good indicator, as uniaxial tension is volume-preserving.Hope I was of some help...]]>Constitutive Modelsbw_compositehttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-11020Measurement of Dominant Deformation Modes
https://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-28820
Wed, 24 Jul 2013 12:42:34 +0000Thank You]]>Constitutive ModelslolefeanceVekhttps://polymerfem.com/community/constitutive-models/measurement-of-dominant-deformation-modes/#post-28820