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Natural frequency of mems structure from material with residual stress

Posted 30.12.2011, 15:00 GMT-5 Materials, Modeling Tools & Definitions, Parameters, Variables, & Functions, Structural Mechanics Version 3.5a 5 Replies

Sungwan Cho
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Hello,

I'm trying to see the resonant mode and resonant frequency of doubly-clamped beam resonator.

We make our devices with pre-stressed(residual tensile stress) silicon nitride, I tried to introduce

stress along the x and y axis(on the plane)

As it is doubly clamped structure, I fixed both ends and by using solid mechanics and linear elastic

material model.

Although I could see the resonant frequency and mode with silicon nitride without stress(as shown in attached
file), its frequency is much different from that of our device with silicon nitride with residual tensile stress.

I tried to find the way to introduce tensile stress to material, but I couldn't.

What should I do to introduce stress to the material?

Attachments:

5 Replies Last Post 23.05.2012, 16:07 GMT-4
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 31.12.2011, 02:12 GMT-5
Hi

Have you checked the model of a film with prestress from the model library. It is difficlt to define a stress (all tensors elements) correctly, I always load the model from a temperature dependence or a preload, then use that stationary solution as the linearisation point for my eigenfrequency analysis (the latter is a linear analysis by "design"

--
Good luck
Ivar
Hi Have you checked the model of a film with prestress from the model library. It is difficlt to define a stress (all tensors elements) correctly, I always load the model from a temperature dependence or a preload, then use that stationary solution as the linearisation point for my eigenfrequency analysis (the latter is a linear analysis by "design" -- Good luck Ivar
TSL
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Posted: 1 decade ago 23.05.2012, 14:53 GMT-4
Hi Ivar,

I am using 3.5a here. Would you please let me know how to load a static analysis result into a eigenfrequency analysis?

I think I need to use MATLAB script to do that in 3.5a but can't find good example in tutorial and COMSOL user guide.

I would like to use a 2D contact model to find the stress due to contact (This has been done). And then I would like to import the stress into eigenfrequency analysis into to find the frequency of 1st mode at different stress levels.

TSL
Hi Ivar, I am using 3.5a here. Would you please let me know how to load a static analysis result into a eigenfrequency analysis? I think I need to use MATLAB script to do that in 3.5a but can't find good example in tutorial and COMSOL user guide. I would like to use a 2D contact model to find the stress due to contact (This has been done). And then I would like to import the stress into eigenfrequency analysis into to find the frequency of 1st mode at different stress levels. TSL
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 23.05.2012, 15:03 GMT-4
Hi

indeed I seem to remember that you needed to use matlab in 3.5a.
But I do believe there were a few threads with some examples.
Try a search, it could be that it was Remi who left some scripts a few years ago concerning this

--
Good luck
Ivar
Hi indeed I seem to remember that you needed to use matlab in 3.5a. But I do believe there were a few threads with some examples. Try a search, it could be that it was Remi who left some scripts a few years ago concerning this -- Good luck Ivar
TSL
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Posted: 1 decade ago 23.05.2012, 15:20 GMT-4
Hi Ivar,

Would you please suggest the keywords for search?

I tried to search "Remi Magnard" and found one post regarding the state space export. However, I don't quite understand how this relates to my model.

Thanks for your time and suggestion.

TSL
Hi Ivar, Would you please suggest the keywords for search? I tried to search "Remi Magnard" and found one post regarding the state space export. However, I don't quite understand how this relates to my model. Thanks for your time and suggestion. TSL
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 23.05.2012, 16:07 GMT-4
Hi

indeed I'm not sure what is going on, I cannot even search the Forum, I get no hits, perhaps they are reindexing it, strange

--
Good luck
Ivar
Hi indeed I'm not sure what is going on, I cannot even search the Forum, I get no hits, perhaps they are reindexing it, strange -- Good luck Ivar

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