more stressed points [sdc]

[reye]

good morning to all, in the attached file there is an open section stressed to bending, cutting and torque moment. In the case of torsion, the most stressed points are not all those to the contours, given the butterfly trend? and, considering also cutting, how do I establish that points 3 and 4 are more stressed? and also, in paragraphs 1 should not be considered the torsion itself? Thank you.

 

[Fulvio Romano]

you have to calculate the three stresses and then sum them with the overlap of effects, exploiting von mises. attention to the directions of stress! the cutting and twisting tau, in some areas are added, in others they are subtracted.

 

[reye]

in point 3 is the tau not negative?

 

[reye]

is there no twist in points 1? does not my prof consider it because?

 

[tortellino]

He does not consider it because he is one who understands us.

 

[reye]

excellent answer, perhaps formulated without considering that he who asked the question (me himself) had to deal with exercises carried out discordant in which, in the same section and in the same points, sometimes it is considered the tau da torsione, sometimes not

 

[Fulvio Romano]

the fact of "not considering" a stress means that this is negligible. If you do not understand why, the suggestion is not to neglect it at all. calculations and numbers will see if it is negligible.

the suggestion referred to in post #2 remains valid. calculated all the stresses.

bending: I think it's pretty simple, you'll find a butterfly pattern with zero sigma on the neutral axis and gradually increasing.

cut: apply jourawsky formulas. you will have a maximum stress on the neutral and zero axis at the end. convert to equivalent sigma with von mises and remember that these sigma have a opposite trend to those of the bending, so be careful when you look at them. you can't sum the maximum of one with the maximum of the other because they are in different points of the section

torsion: apply formulas for open thin sections. Remember that the tau rotor is constant. see in which points the tau is maximum, and converts into equivalent sigma of von mises. you don't think you're adding cut tau with twisters, which are orthogonal between them. the sum must be made following the criterion of von mises

now, sum everything, point by point, and see what and where it is maximum and minimum.

final question. Why von mises? Why not use tresca, rankine, grashof or anything?

because von mises is a multidirectional energy criterion. . I hope you don't want to solve the problem of cauchy in manina or with mohr corollars when you have a ready formula, do you? By the way, the formula. Do you know what it means or apply it right because it's written on the book?

attention to science examination. every single comma happens on the book, otherwise a trivial domandina at the exam can bring down all the certainties.