And so the first thing we need to do is utilize this chart to calculate Kt

which is the stress concentration factor

before we adjust based off of the notch sensitivity of this particular steel.

And in this case, for Kt, we have a shaft again,

with two different diameters located or loaded in bending and

you can see that we're going to need to calculate the r/d ratio and the D/d ratio.

So, if we go ahead and start to do that, what we see is r/d is the fillet radius

at the point of interest, right here, divided by the smaller diameter,

right here, which is 0.1 and D/d is the large diameter divided by

the small diameter which is 1.5 divided by one, which is 1.5.

And so if we go ahead and look at this chart,

we can see at 0.1 and we hit this 1.5 line right here,

and that correlates to a Kt of about 1.7.

So now that we have our Kt value, we can go ahead and

calculate our Kf value, which is the fatigue stress concentration

factor that we'll multiply our fully reversed stress by.

So to do that, we're going to start with this Kf = 1 + q(Kt - 1) and

then, we're going to have to go ahead and calculate Q.

And so Q is going to be equal to 1 / 1 +

the square root of a divided by the square root of r.

So we already know r equals 0.1 and what we need is to calculate a.

And a is going to be, the equation for

the square root of a for a steel right,

because we have a steel in bending is 0.246-

3.08 x 10 to the -3 times the ultimate

strength which here was given to us as 240 ksi.

So, 240 ksi, this equation is in ksi,

so you can just leave the stresses

exactly in ksi plus 1.5 + 10 to

the negative fifth (240 ksi) and

then -2.67 x 10 to the -8 (240 ksi).

And this ultimate strength is cubed and this one I forgot to put in is squared.

So if we go ahead and we solve this equation,

we end up with the square root of a = 0.0075.

And that gives us a q factor of 1 /

1 + 0.0075 /square root of 0.1,

which is a q factor of 0.97.

And that indicates that this material is very sensitive to notches, right?

We're right almost at q equals 1.

So, what we can go ahead at this point is calculate our Kf,

which is our fatigue stress concentration factor and

that's 1 + 0.97 (1.7- 1), and we get our Kf is 1.68.

So it's just slightly lower than our Kt.

And so then, when we knew the fully reversible stress at point A,

we could go ahead and calculate the maximum stress that's happening here.

So our sigma max reversible at point A will end

up being Kf times our sigma nom reversible.

Okay, so that's it for today's module.

Next time we'll look how to add all of these steps together and

solve the entire problem.

I'll see you next module.

[MUSIC]