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Cantilever beam fracture

Posted Jul 31, 2012, 5:38 p.m. EDT Low-Frequency Electromagnetics, MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Geometry, Modeling Tools & Definitions, Parameters, Variables, & Functions, Results & Visualization, Studies & Solvers Version 4.2, Version 4.2a, Version 4.3 3 Replies

Bahar
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Hi Everybody

I have a question regarding analysis of deflection of the cantilever beam.
As it is clear, If I apply a small force on tip of the cantilever it will deflect. However in simulation I don't know how I can evaluate if the deflection (or applied force) is small enough to avoid fracture (breaking) of the beam. [beam dimensions are as follow: Length 500 to 100 um , width 30 to 50 um, thickness 0.7 um] and the force is in range of 100 pN
Can anybody give me some idea?


-I went through some mechanical books and they said the maximum stress that a material can tolerate before fracture is equal to yield stress (or fracture strength), but i don't know in my simulation I should compare which parameter with yield stress.
3 Replies Last Post Aug 20, 2015, 6:34 a.m. EDT
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago Aug 2, 2012, 2:15 p.m. EDT
Hi

here too there are seldom a clear unique answer, yield stress levels are very shape dependent, as you easily get stress concetration around sharp edges or small holes, or defects in the material.

I often use the calculated von Mises stress, but then i use a security factor of 2-3, or more, even twice this if its my first simulation and I do not have any measurements or tests to validate my models.

You are there talking about MEMS devices, here the surface roughness can play you important games, easily a factor 10 in maximum stress levels, and you have often differences in maximum compression strength and traction strength

The best is to compare your model to some simple tests, but be sure you have measured the shapes correctly, and the surface roughness, particularly in he high stress regions

--
Good luck
Ivar
Hi here too there are seldom a clear unique answer, yield stress levels are very shape dependent, as you easily get stress concetration around sharp edges or small holes, or defects in the material. I often use the calculated von Mises stress, but then i use a security factor of 2-3, or more, even twice this if its my first simulation and I do not have any measurements or tests to validate my models. You are there talking about MEMS devices, here the surface roughness can play you important games, easily a factor 10 in maximum stress levels, and you have often differences in maximum compression strength and traction strength The best is to compare your model to some simple tests, but be sure you have measured the shapes correctly, and the surface roughness, particularly in he high stress regions -- Good luck Ivar
Anirudha Devadkar
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Posted: 1 decade ago Mar 10, 2014, 3:17 a.m. EDT
what type physics should i choose to get deflection by applying compression and tensional forces on cantilever surfaces of pizeoresistve materials .
what type physics should i choose to get deflection by applying compression and tensional forces on cantilever surfaces of pizeoresistve materials .
Srikanth Hannabeprakash
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Posted: 9 years ago Aug 20, 2015, 6:34 a.m. EDT
@Ivar Kjelberg
sir, I am interested to model a force based piezoelectric cantilever. I dont know any tutorial or reference where a force is used to obtain the von mises stress curves. Plz tell me from what type of study you had taken and how to put forces on the tip of the cantilever
@Ivar Kjelberg sir, I am interested to model a force based piezoelectric cantilever. I dont know any tutorial or reference where a force is used to obtain the von mises stress curves. Plz tell me from what type of study you had taken and how to put forces on the tip of the cantilever

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