Fatigue Testing

0:00okay we're at our first fatigue testing

0:03machine and let's talk about safety

0:05first of all we have some guards so you

0:07can't reach in to the area here

0:09and the other thing we have is a plug

0:12where we can plug and unplug this

0:14machine when we're loading the sample

0:16into the machine I want this to be

0:18unplugged okay that way if somebody

0:20comes up here and hit start the machine

0:22doesn't take off with you on there so

0:24unplug this when we're loading the

0:26sample

0:27so we have our safety guards on the

0:29machine and what we're going to be

0:31working on is the front side of the

0:32machine we're going to take the guards

0:34off and we're going to work from this

0:35side mounting our sample into the

0:37machine

0:38okay we just tighten these up and I have

0:40the sample to the left side of the

0:42aluminum block there so at this point we

0:44just tighten this up I'm going to slide

0:45this into this housing all the way to

0:47the back and then I'm going to come in

0:49here

0:50and turn in these screws back here in

0:52the back

0:53I'm going to get it where it's snug and

0:55then I'm going to take my wrench and put

0:57underneath there and make sure that we

0:59tighten those up

1:00so that we're securely holding this in

1:02the fixture

1:03okay we just finished mounting our

1:05sample and now what we're going to

1:07measure is the amount of displacement

1:09that we go up and down as this rotates

1:13okay so we don't want to do this too

1:15many times but you notice it's going to

1:16find that spot where it's level right

1:19here so we're going to have our digital

1:20calipers here and one of the nice

1:23feature we have on this is if we were to

1:25move it down here we can hit zero

1:27and it was Zero off there and then if we

1:29change something we can measure that

1:31displacement that's going to help you

1:32out with math errors on this so what I'm

1:34going to do is come in here and I'm

1:36going to measure the very back corner

1:39right here okay on the sample I'm going

1:42to measure that from the table then I'm

1:45going to cycle this where this comes up

1:48to its maximum value

1:50I'm going to measure that same Dimension

1:51so I'm going to come in here

1:55and probably put my tool this way where

1:58it's down on the bottom of the table and

1:59then pull up and I'm going to measure

2:01off to the end of that so this is going

2:02to require your teammates to help you

2:04out and right there I can zero that out

2:06okay so I've zeroed that out and then

2:09I'm going to come up here and with that

2:11on there

2:12I can measure the top of that stroke

2:14right there and I've got my value now

2:17while we're talking about this I can

2:19change how much I change that stroke of

2:22going up and down but right here and so

2:24we have it set at one so hopefully we

2:25should be getting the same values if we

2:27change it it will do a percentage

2:29difference on either side so we can

2:31actually change the amount of fatigue we

2:33have in this machine

2:35before going up and down and that's

2:37going to change our fracture line that's

2:39going to develop in that broken sample

2:41we anticipate that we're going to have a

2:42line dead center when it breaks and

2:44we've talked about that in the lecture

2:45the next thing to do is come in and

2:48reattach the guard so that we don't get

2:51into the machine there now at this point

2:53we're ready to plug the machine in and

2:55so I'm going to come in and go ahead and

2:56plug it in and the power is going to

2:58come on and we have a series of controls

3:01here the first thing we have is a

3:03counter and if you hold this counter it

3:05will Zero out so we want to zero the

3:07counter out that's going to track how

3:09many times this thing goes around for

3:11one cycle if you notice we also have a

3:14little reflector tape on the top that's

3:16going to allow us to come in and measure

3:19the speed of the spindle using this tool

3:21right here and so we can come in here

3:23and push that and it would tell us the

3:25RPM of the spindle as it turns so we're

3:28going to need to record that RPM once we

3:31turn it on now let's talk about how we

3:32turn this on the first thing is we have

3:34a speed knob leave it at zero come in

3:37here and hit start nothing's turning and

3:39anytime you can hit stop and it will

3:41stop if it doesn't unplug it right there

3:43you've got access to unplugging it if

3:45something happens so I'm on start

3:48and what I'm going to do is come in here

3:49and slowly turn this on to about and you

3:53can hear it clicks on there there's a

3:55secondary click I'm going to turn this

3:57on until I can get to about 500 RPM and

4:00again I'm going to come in here and be

4:02testing and aim this at that and right

4:04now I'm doing 170 something so you and

4:07your teammates can sit there make sure

4:08you stay out of the machine there and

4:10I'm going to go up to about

4:12400 RPM

4:19okay so I'm close to 400 RPM and I'm

4:22letting my test run it's counting how

4:24many cycles and I'm just going to let it

4:26run and we'll see how many hours of use

4:29we get out of this

4:39once the sample breaks you just need to

4:41reach up here and hit stop Don't Unplug

4:44the machine yet because you need to read

4:46the value of how many cycles it took to

4:48break that sample once you record that

4:50you can unplug the machine and then

4:52unmount your samples and then go look at

4:54the microscope at the fractured surface

4:56okay we're at The Rotary bending fatigue

5:00tester let's talk about some of the

5:01components we have we have an emergency

5:02stop up here we have a guard that goes

5:05over the part and there's going to be a

5:07sensor down here that this guard has to

5:08be in place for this experiment to run

5:11kind of keep our hands out of that area

5:13as it's running anything happens just

5:15reach up here and press the e-stop and

5:17everything will stop so to uncycle that

5:19just unturn twist it and it'll pop back

5:21up

5:22other things that we have on here this

5:24is a motor controller that's going to

5:25run the spindle we're going to be

5:27running about 5000 RPM in this

5:29experiment this is a beam loading system

5:32right here that's going to allow us to

5:33pull on the samples at these two points

5:36and so we're going to be setting weights

5:37on this to set the weight value on the

5:41unit

5:42so let's go over and start talking a

5:44little about how to load our sample into

5:45this now before we do that we need to

5:47make sure we have the weights off of

5:49this arm we can lift this up and there's

5:51a little lever right here that we can

5:52pull out and that's going to keep this

5:54arm from going down so we want to have

5:56that off so we're not putting any

5:58tension on this system pulling on the

6:00samples and it's going to let us load

6:01the samples in okay at this point we're

6:03ready to remove the cover and I've got

6:05this off right here it slides off and

6:08I'm going to set it back over here out

6:09of the way

6:11and this is where we're going to load

6:12our sample now these are basically ER

6:14collets that we see very commonly used

6:17in Machining and this has this nice

6:19little wrench that's going to fit on

6:21these hexes and it's going to slide down

6:23inside the machine right here so we can

6:26slide the sample into the spindle here

6:28now what I recommend doing is sliding it

6:31far enough back that you can bring this

6:32one in to play

6:34and then slide these up where you're

6:37pretty centrally loaded here now the

6:39next thing we've got is a series of

6:40scales on this side and you're going to

6:42need to come in here and set this

6:45portion at seven and a half inches and

6:47this one at seven and a half inches so I

6:50now have these both set at seven and a

6:51half inches

6:53and I've got my sample centralized here

6:55so what I'm going to do next is come in

6:57here and tighten up these collets

7:00and I need them fairly tight because

7:01this thing is going to have a lot of

7:02force on it I've got that tight still at

7:05seven and a half and seven and a half

7:07I'm going to move over here to the other

7:09side

7:10and support that and again I need to

7:13tighten this one down and so both of

7:15these are tight I'm in the center

7:16everything is centrally loaded I'm at

7:18seven and a half and seven and a half

7:19inches now this system can move around

7:23if I pull this out it can move okay so

7:26you want to make sure that you're at

7:28seven and a half inches

7:29on both sides and that basically these

7:33are running parallel these two surfaces

7:35this could be kicked over at an angle so

7:37make sure that you're parallel at seven

7:40and a half parallel at seven and a half

7:41we're tight I would say this sample is

7:44loaded and ready to go now let's talk

7:46about your Statics here your

7:47calculations you're gonna have to have

7:48first thing you're going to need to do

7:50is come in here and you're going to need

7:52to measure from here to here these are

7:55your pivot Points so these are like your

7:57support loads these are basically like

7:59arrows pushing this direction okay so

8:01it's like pushing that direction right

8:04there

8:05because we're pushing this direction via

8:07these two cables so we're going to need

8:09to take some more measurements you're

8:10going to take the measurement from here

8:12to here

8:13then you're going to take the

8:14measurement from here to where it's

8:15pulling right here so I know that

8:17distance likewise I want to know how far

8:19it is from here so I want to know those

8:21four measurements the overall

8:22measurement here the measurement here

8:24and the measurement here and then you

8:25can even double check it here and cross

8:27check your math now we can go do our

8:30Statics and figure out what kind of

8:32bending moment we're putting on this

8:34sample now we're bending this sample so

8:37if I had this ruler up here for example

8:38I'm bending that sample okay

8:42and we're bending it the highest stress

8:44is going to be at the thinnest section

8:46which is right here so you're going to

8:47need to measure that diameter of that

8:50sample before we break it so measure

8:52that record that diameter calculate your

8:54moment of inertia your I value and we're

8:56going to be able to do our Statics and

8:57calculate what kind of stress we're

8:59putting on there

9:01now once we have all this mounted up

9:03we're ready to come in and put our guard

9:05back on

9:07and I'm going to set this on here

9:09and set it up and check over here and it

9:12looks like the safety switch is going to

9:13be lined up and this is properly mounted

9:15again stay out of this area don't remove

9:17it while the machine is on so at this

9:19point we need to clear out some of the

9:21previous data and to do that we're going

9:23to go to zero right here read the menus

9:25don't just start pushing buttons the

9:27only thing we want to zero out is going

9:29to be the revolutions which is number

9:33four right here so zero out number four

9:36and now we're at zero revolutions do not

9:38zero out the load we already have that

9:41zeroed out and as we put load on it it's

9:43going to come up we actually have some

9:44load on it right now and as you see we

9:46can go basically to zero when we take

9:47the loads off so don't come in and zero

9:51out the load Force just the revolutions

9:53now what we're gonna have to do is put

9:55our load onto the structure and you have

9:57a weight over here you're gonna have to

10:00figure out where to put that and you

10:01have a wrench that you can adjust and

10:03move these two weights and you have to

10:05come in there and get your weights set

10:07up such that I can come up here to 65

10:12pounds okay now you're going to probably

10:13get within a half a pound or so and

10:16that's going to be pretty good what I'm

10:18going to do is I'll do my final

10:19adjustment here I am going to have to

10:21put the safety strap on that weight so

10:24it doesn't vibrate and pull off so what

10:26you're going to need is go around the

10:27Yoke of the weight right here

10:30and this beam right here and make sure

10:33they're held tight so it doesn't slide

10:34off so at this point we have our weight

10:36to 65 pounds and we're ready to start

10:38this and all we have to do is come up

10:40here and hit the start button and it's

10:41going to start capturing our revolutions

10:43the other thing is capture the time that

10:45you started and record the time to

10:48failure

10:50once it stops and breaks if it doesn't

10:52stop hit stop and it will stop the motor

10:55and then we can remove the guard and

10:57remove the sample and again we're going

10:58to be able to record the revolutions

11:00that it broke out we're at the zoom

11:03microscope and normally we take images

11:04on this of our fractured surfaces some

11:06of these are so irregular in height and

11:09valleys that the focus doesn't maintain

11:10on this so what you may want to do is

11:12Mount the samples in the fixture that we

11:14normally use and then get your phone and

11:17come in here and zoom in and take a nice

11:21picture and focus of that failure and

11:25again I've got both specimens that we've

11:26broke I've got them illuminated where I

11:29can see them real well and focused and

11:31then take a picture and that way you can

11:34kind of look at the fractured surfaces

11:35there