What are the units of mechanical wear?
What are the units of mechanical wear?
(OP)
I need to calculate the mechanical wear of a machine. I have the velocity and applied force (load), and have been told to approximate Wear as ([Cubic mean load]^3)*Velocity*[Duration of wear], which would give units of (Newtons^3)*meters. Are these the right units for wear? Can these units be rearranged into a more familiar combination? What other physical quantities have units of N^3*m? If you can suggest a basic textbook or reference, that would be helpful.





RE: What are the units of mechanical wear?
It states that the volume of removed material per unit time is proportional to the power dissipated by friction:
d = k * f * p * w
d = thickness of material removed per unit time
k = coefficient
f = friction coefficient
p = pressure exchanged by the surfaces in contact
w = relative velocity between the surfaces
I don't know the origin of your formula, however I would say that you should obtain something like an energy (N*m) or a volume (m^3).
Maybe the cubic mean load must have the exponent 1/3.
Hope it helps.
Stefano
RE: What are the units of mechanical wear?
w has dimensions m/sec
p has dimensions N/m2
f has no dimensions
k has dimensions m2/N ?
i notice that d is defined as volume removed/sec, and figure you've divided both sides by A area of contact (since p would act over A to give you a normal force, to multiply by f to give you the friction force ...)
RE: What are the units of mechanical wear?
RE: What are the units of mechanical wear?
Yes, the area is eliminated since it is found on both sides of the equation. Obviously the coefficient k must take into account the difference in measuring units between d and fpw.
RE: What are the units of mechanical wear?
Regards,
Cockroach
RE: What are the units of mechanical wear?
Probably meant
M^3/NM
where
N^3 is the volume removed
and
NM is the friction energy that causes the removal
RE: What are the units of mechanical wear?
RE: What are the units of mechanical wear?
RE: What are the units of mechanical wear?
If the lube viscosity is high enough for the rpm and bearing geometry, Elastohydrodynamic (EHD) lubrication and full surface separation is achieved, and there is no wear of the ball and races.
If the equivalent load is low enough, ( FAG says CO/8, SKF publishes fatigue load limits) and lubrication conditions are good then the bearing life can be "infinite".
If your ball and roller bearings are actually wearing, there is likely something wrong with the lubricant or its cleanliness.
Surface distress from wear, or just non EHD conditions can induce surface fatigue at otherwise modest bearing loads, and cause failures when the life >could< be "infinite."
There are some who don't buy the infinite life theory,
https://www.stle.org/assets/document/tlt_July_cove...
but I don't think many deny that at lower loads and with good lube the l10 life calculations are an order of magnitude or more too conservative
RE: What are the units of mechanical wear?
http://www.google.com/url?sa=t&rct=j&q=&am...
RE: What are the units of mechanical wear?
Regards,
Cockroach