Stb Axle Design

[djw2k3]

Basically I have a fixed shaft (no rotation) through two blocks spaced about 100mm apart with the the shaft effectively cantilevered out 100mm from one face of the blocks (total shaft length ~200mm). The load is applied in one direction on this cantilevered section. If I do the calcs on bearing stress in the block (nearest the load)the stress is okay. Wanting to be thorough I modelled it using FEA, the latter approach showed that the stress is significantly greater where the shaft intersects the block - which stands to reason as it is really a concentrated load here.

Basically I am after an analytical estimation for this stress which gives a more accurate answer than just using a bearing stress calc. Or is it just a matter of adding an appropriate stress concentration factor??

thanks

Dave

 

[sancat]

One way to reduce the stress concentration would be to use a Very Large radius on both ends of your support blocks. Due to the load you are applying the shaft flexes, thus, it would need a slightly bigger diameter, and a bending radius to accomodate this effect. I dont know the diameter of your shaft, and the width of the blocks, but, a radius that starts about a third of the width of the block, and has a value of perhaps 100mm could work. On the other hand, it will increase the effective deflection
sancat

 

[dooron]

I think a paper by:
Melcon and Hoblit "development in the analysis of lugs and pins" Product Engineering June 1953 may give you insite into the loads on the pin at the two extremes of lug.

 

[atlarson]

How much clearance is there between the holes and the shaft? If there is very little, and the blocks are reletivley stiff, then the block furthest from the load may be seeing very little load. If this is the case you can assume that opposite (but unequal) bearing forces are acting over 10 to 20 percent of the hole's projected surface area at both ends of the closest block. This will give a much closer approximation of the bearing stress.

Andy

 

[djw2k3]

Thanks all,

atlarson, you are correct in assuming that the blocks are relatively stiff and clearance is just enough to get the shaft into the blocks ;-) then weld/machine etc. I ended up over sizing the block (faticgue concerns etc). The 10-20% theory works pretty well.

Dave