I am in the process of designing a system with a spline transmission (rotating shaft) and to size these splines it is necessary to have the permissible pressure of the material.
I searched on the internet but I can't find anything very coherent. Do you know how to find this value?
From what I understand, it depends on:
-the compressive strength of the material (approximately the tensile strength, so Re)
- the quality of the machining of the shaft and hub (play or preloading)
- type of effort (intensity and regularity)
Is this good and if so, how can this permissible pressure be precisely determined?
I searched in my library and I find lots of formulas but few references on the characteristics of the materials.
There is only in the guide to calculus in mechanics by Spenlé and Gourhant that there is a table (taken up in the Wikipedia article on matting by the way).
Moreover, in they take an "extreme" theory because at first they consider that the whole couple passes on one tooth, then in a second time they consider that 40% of the teeth transmit the effort (it already seems more realistic to me). At the end of the day, I think that the biggest problem in defining the permissible pressure is to know what percentage of the teeth will actually transmit the torque. As for the "type of effort" as I called it in my question, I think there must be coefficients.
I also came across this board and for the moment it is the one I used as a reference to make my calculations but I couldn 't find it anywhere else so I had a doubt about its reliability. According to the annotation of the author of this Wiki, these values come from the Spenlé and Gourhant guide of 2003 (noted "SG2003" page 141) so you confirm the Wiki sources , that's already a good point.
I also found these articles:
http://help.autodesk.com/view/INVLT/2016/FRA/?guid=GUID-8AAB0A6A-8372-4023-A667-B0DBBAE8B1A5 (but it doesn't seem reliable to me)
https://moodle.insa-toulouse.fr/file.php/52/Polycopie_internet10_v1.pdf (page 176) and there they consider that 50% of the teeth transmit the effort.
So whatever the documents, they all say that the permissible pressure depends in part on the machining quality of the splines without giving the tolerances for which the percentage of "working" teeth is given.
After that, we still have to find the supposed coefficient in relation to the type of effort.
All this seems to me very complicated, or pifometric.
Well, I thought that there were more precise values than those given on the Spenlé and Gourhant guide. When automotive subcontractors make "x" million gimbals on which they try to save every gram of material and every second of machining, or when a manufacturer of multi-ton gearboxes like the one I put in PJ design their products, they have to size the splines more precisely than that.
So I'll leave the question open if one day someone has more precise values.
In the meantime thank you for your help gt22 and stefbeno.