Originally Posted By: Tegger
Boot failure has nothing to do with any of those things.
You know how a paper clip will break if you bend it back-and-forth a few times? That's the same mechanism by which CV boots break. This phenomenon is exacerbated by COLD (not heat!) and driveshaft angles. But this mechanism can be defeated (or at least made to work at a disadvantage) with proper boot-design.
Many newer-design, much-longer-lasting boots are made of different materials than the ones made 20-years-ago. Plus they often have a radius in the bottom of each pleat. This radius is a variant of the sort you would use to eliminate the stress-riser at the end of a cut into a given material. You can tell this kind because they actually form a kind of pit at the bottom of the pleat. Plus this type of boot has many more pleats than the old-style.
Beg to differ though: we are talking non-metallic polymer that is created for just that task (of bending in extreme angle, repeatedly over a very long period of time, exposure to hydrocarbon based lubricants, hold up to extreme heat and cold, etc.).
Similar to piece of rubber band: these polymers will break down due to the aforementioned conditions (heat, chemical attacks, UV, ozones, etc.).
Your comparison with a paper clip (metal, not polymer-plastic) is not what I would expect in this case for metal will exhibit fatique if you bend it repeatedly.
Q.