John Carmack wrote: JC> The axles are 1/2" 316 stainless, which should be fine for the couple JC> hundred pounds of static force they should see. Vibration may be an issue, JC> we will have to see...
The yield strength of 316 is only about 250 MPa. If the downward force on the vane had for example a lever of .05 m with respect to the bearing then a force of roughly 1 kN (225 lbf) would produce a bending stress of 250 MPa in the axle at the plane of the first bearing. The fatigue strength of 316 especially at elevated temperature will be considerably less than the yield strength. I do not know the real forces on your jet vanes but on a gut level I would recommend to make the axles not thinner than 3/4". The bending and torsional strength of an axle goes up with the third power of the diameter. There is no law that forbids the use of a hollow axle and it is not said, that the axle has to be made the same section throughout it`s length. JC> The bearings are high temperature graphalloy in cast iron housings. Graphalloy bearings are a good choice for high temperature applications. The bearings close to the actuators could eventually be normal self adjusting ball bearings as the stainless steel you use for the axle has rel. low thermal conductibility. JC> I thought cast iron was especially good for dampening vibrations, which is JC> why it is common in bearing mounts. On a 1600 pound vehicle, I don't sweat JC> five pounds of bearings at all, but I would be interested in hearing about JC> brittle breaking issues with cast iron mounts. I give you every guaranty that in your definitive vehicle you will sweat every pound to get the performance needed. Cast iron is basically used in most machine tool, where the beter damping (compared to steel)is appreciated and the fact that it can be easily machined to high precision. But weight to strength is rather poor and in the case of heavy impact loads it will break with virtually no plastic deformation. For that reason gray cast iron is not used in suspension parts of road vehicles. There are cast iron nuances that have more ductility the so called spherulitic graphite iron. Compared to stainless or mild steel still much less ductile. Hans Ulrich Ammann mailto:[EMAIL PROTECTED] http://www.spl.ch _______________________________________________ ERPS-list mailing list [EMAIL PROTECTED] http://lists.erps.org/mailman/listinfo/erps-list
