verification

[<n<]

Good morning to all,
I find myself having to check the section of a tree in which are mounted tabs type a. for reasons of couple and encumbrance I had to put 3: in order to satisfy the condition of 'collasso' with pamm, as well as taoamm. the doubt is: for fatigue testing, the coefficient k of concentration of the efforts how should I consider it? multiplied by 3?

the reference k table is this:https://i.imgur.com/xjg7qf3.png (Laughter but I don't understand how to add images in the new editor)

 

[meccanicamg]

the fatigue effect has a somewhat peculiar behavior. first you are working on a net section that is not that of the smooth tree but it is to subtract the volume of three tabs. literature does not treat the behavior described by you but only the tree with a tab or the channeled tree.
the shadow effect is often to be considered. This phenomenon is nothing more than you have repeated geometries but efforts see the first obstacle as a concentration and continues as such (see trees with n series of quarries for o-ring....it is enough one and the others are in shadow, as if they did not exist).
Therefore tell you that the cut coefficient is 3 times the single cut coefficient is not true.
what you can do is create a fem model and determine the carving coefficient in a simulated way to really understand the behavior of that application.
Alternatively, you can look at the coefficient of concentration of the grooved efforts.

 

[<n<]

Thank you for the exhaustive answer! fem simulations for the moment I can't do it either for lack of tools or time (especially :frown: ).
I went from kt 4 to kt 5 and therefore I still have a great margin on the safety coefficient.
This chart is for the twist, for when it concerns the bending I find no trace anywhere unfortunately.. probably does not change anything since the sigmaz stress lines are perpendicular and the 3 tabs are spread to 120°, so to understand also the concentrations are displaced and do not interact with each other (they do not sum up at least). Could it be a bit like the shadow effect you mentioned?

 

[meccanicamg]

for bending you should consider the single tab.the behaviour should be symmetrical with n tabs, provided the bending lax is always perpendicular to the tab section.

 

[<n<]

therefore with the lowest curve in the image I had put.. should be the same. Thank you very much for the clarity!