Max Interference for Press-Fit Bushing
Max Interference for Press-Fit Bushing
(OP)
What is the detrimental effect of increasing the interference between a metallic part's hole and a steel press fit bushing? For argument sake let's say this is a cheap, small lug and that it is fracture critical.
If the part doesn't break nor deform significantly upon the bushing installation is it "good". I can't seem to find any example of premature failure due to extreme hoop stresses.
If the part doesn't break nor deform significantly upon the bushing installation is it "good". I can't seem to find any example of premature failure due to extreme hoop stresses.
RE: Max Interference for Press-Fit Bushing
Most engineers I've met use the 50% SCC threshold, that is any sustained tensile stress must not exceed 50% of the SCC threshold. I'm not so sure about why that number (50%) is so magical, some say it's to acount for additional, non-sustained stresses, others simply because it's always worked in the past.
It's easy to break that 50% rule with high interferences in aluminum and magnesium parts, especially in the ST direction. I do know of one such failure where the housing hole was in a magnesium part.
RE: Max Interference for Press-Fit Bushing
RE: Max Interference for Press-Fit Bushing
Also, and probably more importantly, there is often some bending stress due to stiffness variation in the external element; this is usually true in a lug, where bending stress occurs as wall thickness changes.
In addition to SCC concerns, added interference stresses may hasten fatigue failure.
Unless the added stress can be shown to improve the design, as in the case of helpful residual compression, for example, it is usually best practice to minimize the stress.
Hope this helps.