[MUSIC]

Hi and welcome back.

In today's module, we're going to continue covering

the factor of safety in Unit Two, Static Failure.

So the learning outcome today, again is to calculate the factor of safety.

Hopefully, you guys have gone through worksheet two and

completed it to the best of your ability.

And then today, we're going to go through the solution.

So again, Factor of Safety is the loss-of-function strength divided

by your allowable stress and here's the problem that we had.

So, we saw this aluminum rod had a certain radius and

there was a range of load that could be applied to it.

It was a static load.

It said that, any deformation could cause

complete loss of component functionality.

And it gave us an ultimate strength and a yield strength and

a program mandated factor of safety that the design needs to hit, which was n=3.

So, what we start out knowing is that our factor of

safety is equal to strength divided by stress.

Now in this case, it says that any plastic deformation

results in a loss of component functionality.

So, our loss-of-function strength is going to be our yield strength.

And most of the time in this class, you'll be looking at yield strength.

So, the next thing we need to figure out is our stress.

So, we know our yield strength.

Our yield strength is equal to 500 megapascals

that was given down here in the problem and

we know that since this is a tensile axial load,

that our stress is equal to force divided by area.

So now, we need to think about which force do we use and which area do we use?

Let's start with area.

First off, it's a rod.

So, it's going to look something like this and

the load applied is going to look something like that.

So, our cross-sectional area is going to be pi r squared.

So the problem is we've been given a radius of 2 millimeters plus or

minus 0.2 millimeters and here's the trick in design,

you always want to start with your worst case scenario.

You can possibly back out of that worst case scenario if you need to, but

you want to start at worst case and worst case scenario is your highest stress.

Your highest stress is going to give you your lowest factor of safety.

So, we need to calculate what would be the highest stress and

our highest stress will be caused by the lowest cross-sectional areas.

So we're going to assume that since it's acceptable to have a rod that could

be 2 minus 0.22 millimeters that, that's what's happening.