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4 points bending experiment
Posted 14 feb 2014, 05:40 GMT-5 MEMS & Nanotechnology, MEMS & Piezoelectric Devices, Results & Visualization, Structural Mechanics 1 Reply
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Hello,
I am doing a 4 points bending experiment, where I measure the maximum Principal Stress and Strain for an applied force of 5N at the outer load points.
Theoretically these forces may induce a constant bending moment on the test sample and therefore an homogeneous stress and stress distribution between the inner two points. The maximum value of strain and strain may be also between the inner two points, because the center of the sample has the maximum deformation.
I calculated analytically the maximum stress and strain for a silicon cantilever of 25mm*381µm with an elastic modulus of 130GPa, and a Poisson coefficient of 0.28. The maximum value of principal stress is 340Mpa and maximum principal strain is 2.6e-3.
When I run my COMSOL simulation, I don't get maximum First principal stress and strain value between the inner two points and I know the stress distribution its not in good agreement with theory. I also get very low values: 80MPa for stress and 4e-4 for strain.
Why is the COMSOL simulation result so different from the analytic calculus/real experiment?
Can anybody help me please?
Best regards,
Juliana
I am doing a 4 points bending experiment, where I measure the maximum Principal Stress and Strain for an applied force of 5N at the outer load points.
Theoretically these forces may induce a constant bending moment on the test sample and therefore an homogeneous stress and stress distribution between the inner two points. The maximum value of strain and strain may be also between the inner two points, because the center of the sample has the maximum deformation.
I calculated analytically the maximum stress and strain for a silicon cantilever of 25mm*381µm with an elastic modulus of 130GPa, and a Poisson coefficient of 0.28. The maximum value of principal stress is 340Mpa and maximum principal strain is 2.6e-3.
When I run my COMSOL simulation, I don't get maximum First principal stress and strain value between the inner two points and I know the stress distribution its not in good agreement with theory. I also get very low values: 80MPa for stress and 4e-4 for strain.
Why is the COMSOL simulation result so different from the analytic calculus/real experiment?
Can anybody help me please?
Best regards,
Juliana
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1 Reply Last Post 15 feb 2014, 17:52 GMT-5
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Posted:
1 decade ago
Hi,
I am not a structural engineer.
I see that you have fixed constraints on two edges, can you keep one as it is and put a roller condition for the other?
Suresh
I am not a structural engineer.
I see that you have fixed constraints on two edges, can you keep one as it is and put a roller condition for the other?
Suresh