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Stress intensity factor- Fracture mechanics

Posted 14 mar 2018, 18:24 GMT-4 Structural & Acoustics, General Version 5.2a 3 Replies

Cristina Aguanell Garrido
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Hi everyone,

I’m working in fracture mechanics, trying to find out how to calculate the stress intensity factor in mode I. I saw the example of Single Crack, and I didn’t end up understanding why the prescribed displacement is made. I think that it is to block the body movement in some point or to avoid the growth the crack.

Apart from that I would like to know if I can simulate a 3 point bending test using a similar methodology (the example one), because I was trying to do it, but I didn’t arrive to a good result comparing with real experiments.

Thanks a lot for any reply,

Best regards, Cristina

3 Replies Last Post 15 mar 2018, 10:35 GMT-4
Etienne
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Posted: 7 years ago 15 mar 2018, 08:53 GMT-4

Could you please provide the model, or the link to the Single Crack example ?

Could you please provide the model, or the link to the Single Crack example ?
Cristina Aguanell Garrido
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Posted: 7 years ago 15 mar 2018, 09:01 GMT-4

Yes of course.

https://www.comsol.com/model/single-edge-crack-988

And thank you for your reply

Yes of course. https://www.comsol.com/model/single-edge-crack-988 And thank you for your reply
Etienne
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Posted: 7 years ago 15 mar 2018, 10:35 GMT-4

I think the prescribed displacement on the x axis, at the crack tip point, is to prevent the rigid body movement along the X-axis. I expect that the result will be the same if this constraint is applied to any other point of the geometry. Maybe, this point is chosen to have zero displacement at the crack tip, which is easier for the post-processing. It is not to block the propagation of the crack, because it is a quasi-static computation. The propagation of the crack is determined afterward by energy consideration (Griffith's criterion). It is not this simple to model the actual crack propagation with a finite propogation velocity for instance.

I do not see any difference for a 3-points bending case... except that an initial crack length as to be specified relative to the thickness of the beam, and that the beam thickness as to be small relative to its length...

best regards,

I think the prescribed displacement on the x axis, at the crack tip point, is to prevent the rigid body movement along the X-axis. I expect that the result will be the same if this constraint is applied to any other point of the geometry. Maybe, this point is chosen to have zero displacement at the crack tip, which is easier for the post-processing. It is not to block the propagation of the crack, because it is a quasi-static computation. The propagation of the crack is determined afterward by energy consideration (Griffith's criterion). It is not this simple to model the actual crack propagation with a finite propogation velocity for instance. I do not see any difference for a 3-points bending case... except that an initial crack length as to be specified relative to the thickness of the beam, and that the beam thickness as to be small relative to its length... best regards,

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