Help please!

I know it's a bit off topic but I need help right now and you guys are
so knowlegeble!

I have an urgent query about static friction for a design I'm working
on this morning. I know that the friction force is the sum of the
normal force x the friction coefficient. Is the area of the brake pad
really irrelevant?

By way of example, would the braking force of a pad 10mm x 10mm under
force of say 100N be the same as a pad 20mm x 20 mm with the same 100N
force?

Is the area of the friction pad simply related to wear rate?

Thanks in advance.

 

Is the area of the friction pad simply related to wear rate?

I don't claim to know anything about it, but would guess heat dissipation
and wear would be factors that drive Area.

I've never heard or read of it being a factor in developed braking force
calcs. If it is in practice its probably small and outside predictability
with stiffness of pad supports being more significant?

I think I'd go on about it like I knew what I was doing, but a web search
for the terms

"pad area" brake | braking force

will turn up a lot of information and disinformation for you to sort thru.
8~)

 

I'm no expert on brakes themselves, but I've dealt with friction and wear a
fair amount in other contexts. It depends upon the accuracy with which you
are working. The friction coefficient in most cases is dependent on the area
and the normal force. As examples, think about how hard a rug is to slide
across the floor when it is laid out flat compared to when it is rolled up,
or why higher performance cars have wider or taller tires with bigger
contact patches. If you're trying to calculate your braking force very
accurately, you would probably need to account for that variation and the
area of the brake pad would be relevant. If you're doing a more basic
analysis, you can probably ignore it. In that case, the area of the brake
pad would be irrelevant.

Wear is even trickier than friction. At the simplest level, the volume of
wear material is assumed to be proportional to the normal force times the
distance traveled. In that case, the area of the pad would be inversely
related to the thickness of the wear layer lost on the brake pad itself.
When you start to dig into it farther, the product of the pressure
(inversely proportional to your area) and the velocity is often very
important in determining the rate of wear. It all depends on the materials
you're using.

Jerry Steiger
Tripod Data Systems
"take the garbage out, dear"

 

As a general rule of thumb yes.

The assumption is that the force is distributed more or less evenly and
that there are no regenerative effects as there would be in a band
brake or drum brake.

 

YES, YES and YES!!!!

It does not matter what the area is!!!!!!!!!!!!!!!!!!!
It is only effected by a normal force and friction coefficient

EXAMPLE:
if you have two boxes on the table, one is very small and another is very
large, both weigh 20 lb
Which one is easier to push?

Answer: the SAME (it would require the same force to push it)



Mike

 

A good explanation to rationalize this is such. Picture the two surfaces
that are contacting each other, as in the box bottom and the table. On some
scale level, you will see that the surfaces are actually a whole bunch of
peaks & valleys. The greater the load, the more those peaks smash just a
bit to force themselves down into the valleys. If you increase the surface
area, you don't embed as deeply, but you have more peaks resisting the
motion. Therefore, coefficient of friction is unitless, and more
specifically, independent of surface area..

WT

 

Interesting thought - have to ponder that one.

WT

 

Why don't they make tires out of Aluminum?

 

However, it is also true that in general sliding friction is less than
static friction. Usually by a factor of 2.