00:01
I've drawn an image here of the bar of the rectangular cross section made of steel.
00:05
It's assumed to be elastoplastic with a sigma delta of 270 megapascals subjected to a couple m parallel to the z axis.
00:25
And for a, we're asked to determine the moment m of the couple for which yield first occurs.
00:34
Okay, before the yield first occurs, the cross section is still under elastic deformations.
00:39
So, and solving for m, this will equal the moment of inertia cross section will be i will be b d cubed 12.
01:00
This will equal 12 times 15 cubed divided by 12.
01:07
And this will be 3375 cubic millimeters.
01:22
And let's see when the yield first come, the yield first occurs at the edge of the cross section.
01:37
That's where this is going to first occurred.
01:42
Ok, so by putting all these values into one into this equation, what we'll end up with is m equals 270 times 3375 divided by 7 .5.
02:11
Let's see what we get here.
02:20
Let's see, 270 times 3375 divided by 7 .5.
02:26
And that's going to be equal to 121 .500.
02:31
That'll be newton millimeters.
02:38
And, okay, newton millimeters.
02:43
And that will be, i think i'm asked if we get this in newton meters.
02:54
So let's go to the next page here.
03:00
M will be equal to 121 .5.
03:13
Oops, that was wrong.
03:18
121 .500.
03:25
There we go.
03:25
So my m will be 121 .5 newton meters.
03:44
There's my answer for a.
03:48
B, something just fell off me.
03:55
I've been outside working.
03:56
For b, we are asked to determine the moment m of the couple when for which the plastic zones at the top and bottom are 5 millimeters.
04:40
Okay, let's see.
04:45
So let's see here.
04:48
So what we're doing here, if this is 15 and this is 12, then this is 7 .5.
05:33
This is 7 .5.
05:37
Okay, so let's try this.
05:41
Let's use m equals, then we'll have b c squared times 1 minus 1 third over.
06:05
Okay, so we're told with 5 millimeters here, that means that our sketch, i'm going to go to the next page and do another sketch.
06:20
So i'm going to have my 15 centimeters and my 12 centimeters or millimeters.
06:39
My bad.
06:41
Okay, so this is the middle.
06:43
So this is 7 .5.
06:48
This is 7 .5...