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<?xml version="1.0"?>

<!DOCTYPE TEI.2 SYSTEM "base.dtd">





<publicationStmt><distributor>BASE and Oxford Text Archive</distributor>


<availability><p>The British Academic Spoken English (BASE) corpus was developed at the

Universities of Warwick and Reading, under the directorship of Hilary Nesi

(Centre for English Language Teacher Education, Warwick) and Paul Thompson

(Department of Applied Linguistics, Reading), with funding from BALEAP,

EURALEX, the British Academy and the Arts and Humanities Research Board. The

original recordings are held at the Universities of Warwick and Reading, and

at the Oxford Text Archive and may be consulted by bona fide researchers

upon written application to any of the holding bodies.

The BASE corpus is freely available to researchers who agree to the

following conditions:</p>

<p>1. The recordings and transcriptions should not be modified in any


<p>2. The recordings and transcriptions should be used for research purposes

only; they should not be reproduced in teaching materials</p>

<p>3. The recordings and transcriptions should not be reproduced in full for

a wider audience/readership, although researchers are free to quote short

passages of text (up to 200 running words from any given speech event)</p>

<p>4. The corpus developers should be informed of all presentations or

publications arising from analysis of the corpus</p><p>

Researchers should acknowledge their use of the corpus using the following

form of words:

The recordings and transcriptions used in this study come from the British

Academic Spoken English (BASE) corpus, which was developed at the

Universities of Warwick and Reading under the directorship of Hilary Nesi

(Warwick) and Paul Thompson (Reading). Corpus development was assisted by

funding from the Universities of Warwick and Reading, BALEAP, EURALEX, the

British Academy and the Arts and Humanities Research Board. </p></availability>




<recording dur="00:32:44" n="4584">


<respStmt><name>BASE team</name>



<langUsage><language id="en">English</language>



<person id="nm0827" role="main speaker" n="n" sex="m"><p>nm0827, main speaker, non-student, male</p></person>

<person id="sm0828" role="participant" n="s" sex="m"><p>sm0828, participant, student, male</p></person>

<person id="sm0829" role="participant" n="s" sex="m"><p>sm0829, participant, student, male</p></person>

<person id="sm0830" role="participant" n="s" sex="m"><p>sm0830, participant, student, male</p></person>

<personGrp id="ss" role="audience" size="m"><p>ss, audience, medium group </p></personGrp>

<personGrp id="sl" role="all" size="m"><p>sl, all, medium group</p></personGrp>

<personGrp role="speakers" size="6"><p>number of speakers: 6</p></personGrp>





<item n="speechevent">Lecture</item>

<item n="acaddept">Engineering</item>

<item n="acaddiv">ps</item>

<item n="partlevel">UG2</item>

<item n="module">Metallurgy</item>




<u who="nm0827"> now today we're going to talk about <pause dur="0.2"/> fatigue <pause dur="1.1"/> and that doesn't mean that i'm going to <pause dur="0.3"/> pack the lecture in half way through because i'm worn out <pause dur="0.9"/> although with you lot <pause dur="1.0"/> the ability to feel knackered after a lecture is very easy <pause dur="0.2"/> i will say that <pause dur="1.0"/> # <pause dur="0.6"/> you've all got i hope this piece of <pause dur="0.3"/> paper these notes come on <pause dur="1.2"/> which i've given out <pause dur="0.2"/> take this please <pause dur="2.8"/> we're not going to get on to this yet <pause dur="0.2"/> but we will in a moment <pause dur="0.9"/> now <pause dur="0.4"/> fatigue <pause dur="0.4"/> is a strange <pause dur="0.6"/> phenomenon <pause dur="0.8"/> and it's <pause dur="0.2"/> to do <pause dur="0.2"/> with <pause dur="1.1"/><kinesic desc="writes on board" iterated="y" dur="7"/> loading <pause dur="1.8"/> which varies <pause dur="6.8"/><kinesic desc="writes on board" iterated="y" dur="11"/> it varies <pause dur="1.8"/> so in other words it's oscillating <pause dur="0.4"/> well here's some good words <pause dur="0.3"/> oscillating <pause dur="0.3"/> or fluctuating <pause dur="3.8"/> loads <pause dur="1.2"/> so a classic example of this would be a car going over a bumpy road what's <pause dur="0.2"/> # <pause dur="0.2"/> does the # <pause dur="0.2"/> suspension experience <pause dur="0.6"/> what about an out of balance piece of machinery <pause dur="0.5"/> some pieces of machinery of course are deliberately out of balance <pause dur="0.6"/> # <pause dur="0.3"/> if you want to crush things you very often will have an out of balance thing to give a

sort of hammer effect <pause dur="0.8"/> and <pause dur="0.4"/> things like jackhammers that you use for <pause dur="0.5"/> # making holes in the road <pause dur="0.5"/> these also <pause dur="0.3"/> are <pause dur="0.8"/> # <pause dur="0.3"/> they're not out of balance but they're <trunc>c</trunc> <pause dur="0.2"/> controlled by air <pause dur="0.5"/> yep <pause dur="3.1"/> we're on air so be on your best behaviour <pause dur="2.2"/> so <pause dur="0.5"/><vocal desc="sigh" iterated="n"/><pause dur="0.6"/> rotating machinery <pause dur="1.1"/><kinesic desc="writes on board" iterated="y" dur="3"/> is <pause dur="2.0"/> a very important example of this and we'll come on to an example of that at the end <pause dur="0.3"/> as a sort of case study which is what you've got your <pause dur="0.5"/> # notes on <pause dur="1.3"/> now <pause dur="0.9"/> the <pause dur="0.5"/> simplest way <pause dur="0.2"/> to understand fatigue and indeed to understand the history <pause dur="0.5"/> how how it came to be <pause dur="0.5"/> a <pause dur="0.2"/> topic <pause dur="0.7"/> is to consider <kinesic desc="writes on board" iterated="y" dur="7"/> what happens in a spoked <pause dur="0.2"/> wheel <pause dur="1.9"/> so you have <pause dur="0.2"/> some sort of wheel it could be a horse and cart wheel it could be a bicycle wheel it could be a <pause dur="0.8"/> gun wheel i don't know anything you <trunc>wa</trunc> <pause dur="0.2"/> name it <pause dur="0.3"/> think of what it <pause dur="0.5"/> looks like <pause dur="0.4"/> now <pause dur="0.7"/> obviously <pause dur="0.3"/> if you have a wheel <pause dur="0.8"/> # <pause dur="0.4"/> let's say <pause dur="0.2"/> # <pause dur="2.9"/> right you'll get shot <pause dur="2.6"/> let's say that's the front wheel of your bike or something or other <pause dur="0.4"/> your weight on the frame <pause dur="0.4"/> pushes down <pause dur="0.9"/> on there <pause dur="0.3"/> so

there is a vertical loading or a # <pause dur="0.3"/> an inclined loading <pause dur="0.5"/> on <pause dur="0.3"/> the axle <pause dur="0.2"/> which is here <pause dur="1.0"/> okay <pause dur="0.2"/> so you've got that <pause dur="1.0"/> now <pause dur="0.7"/> the question then is what prevents the fork of the bike going into the ground <pause dur="0.3"/> well obviously because the wheel is pushing back on the end of the fork <pause dur="0.4"/> so that if we take that spoke as an example <pause dur="0.4"/> this spoke is pushing back <pause dur="1.5"/><kinesic desc="writes on board" iterated="y" dur="9"/> but because the hub if you like does come down a bit because you've got a tyre it's squidgy <pause dur="0.4"/> the <pause dur="0.3"/> spoke above <pause dur="0.2"/> is coming down <pause dur="0.6"/> so if you think about it the upper spoke is in tension <pause dur="0.4"/> and the lower <pause dur="0.2"/> spoke <pause dur="0.3"/> is in <pause dur="0.2"/> compression <pause dur="0.9"/> at that <trunc>p</trunc> particular instant <pause dur="0.5"/> and so if the vehicle is stationary <pause dur="0.5"/> that is a stress pattern <pause dur="0.3"/> which will be there <pause dur="0.5"/> # as long as you leave it in that condition <pause dur="1.3"/> if you consider other spokes at angles well they have <pause dur="0.3"/> some load in them <pause dur="0.4"/> # <trunc>w</trunc> i'm not going to bother <pause dur="0.3"/> to work out <pause dur="0.6"/> how you <pause dur="0.4"/> # <pause dur="0.3"/> calculate what <pause dur="0.5"/> <trunc>f</trunc> force is in the spokes <pause dur="0.4"/> but the general idea is that below <pause dur="0.5"/> the middle <pause dur="0.5"/> there is compression and above <pause dur="0.5"/> the <pause dur="0.2"/> middle <pause dur="0.2"/> there is tension <pause dur="1.7"/> now the

next question is what happens when this thing starts to move <pause dur="1.1"/> so that <pause dur="0.2"/> this now goes forward <pause dur="0.2"/> so that that point there <pause dur="1.0"/><kinesic desc="indicates point on board" iterated="n"/> # if we move the wheel <pause dur="0.2"/> along we rotate it through <pause dur="0.4"/> # a hundred-and-<pause dur="0.2"/>eighty degrees <pause dur="0.6"/><kinesic desc="writes on board" iterated="y" dur="12"/> what happens <pause dur="1.8"/> well what we find of course is that that <pause dur="0.2"/> blobbed point there <pause dur="0.8"/> is now down here <pause dur="0.7"/> and so here are the spokes <pause dur="0.2"/> et cetera et cetera <pause dur="1.1"/> and so what it means is that that spoke <pause dur="0.2"/> which was above the axis <pause dur="0.2"/> is now below <pause dur="0.9"/> and what was below <pause dur="0.2"/> a hundred-and-eighty degrees later is now above <pause dur="1.2"/> but the stress state <pause dur="0.4"/> what the wheel has to do to hold the thing up <pause dur="0.3"/> is exactly the same as before <pause dur="0.6"/> so this bottom thing is in compression <pause dur="0.4"/> and <pause dur="0.2"/> the top one <pause dur="0.2"/> is in <pause dur="0.3"/> tension still <pause dur="1.2"/> but this one <pause dur="0.3"/> was up there <pause dur="1.2"/> so what was in tension <pause dur="0.5"/> is now in compression <pause dur="0.7"/> and if you roll it another a hundred-and-eighty degrees it goes back to where it was <pause dur="0.6"/> and <pause dur="0.3"/> so <pause dur="0.3"/> the tension has become compression <pause dur="0.2"/> has become tension has become <trunc>pompre</trunc> # progression <pause dur="0.3"/><vocal desc="whistle" iterated="n"/> <pause dur="0.6"/> tension <pause dur="0.2"/> has become compression <pause dur="0.3"/> has become tension <pause dur="1.2"/> so if you were

to plot this out <pause dur="0.5"/><kinesic desc="writes on board" iterated="y" dur="45"/> as <pause dur="0.7"/> the force <pause dur="0.6"/> experienced <pause dur="0.4"/> by the spoke force in spoke <pause dur="0.6"/> against <pause dur="0.2"/> # <pause dur="0.4"/> rotation <pause dur="1.9"/> revolutions whatever you want to call it <pause dur="1.0"/> of the wheel <pause dur="2.2"/> what you'd have <pause dur="0.2"/> is <pause dur="0.7"/> a <pause dur="0.4"/> load up there <pause dur="0.2"/> if we consider one spoke <pause dur="0.3"/> tension <pause dur="0.7"/> it drops down to nothing when it's half way <pause dur="0.8"/> because the horizontal spokes don't have anything in them <pause dur="0.3"/> because they're not resisting any <pause dur="0.3"/> horizontal <pause dur="0.3"/> motion <pause dur="0.2"/> if <pause dur="0.3"/> the <pause dur="0.8"/> force is <pause dur="0.4"/> truly vertical <pause dur="0.7"/> and then <pause dur="0.3"/> going on a bit more <pause dur="0.4"/> it goes below <pause dur="0.5"/> and goes to an equal value <pause dur="0.4"/> but in <pause dur="0.5"/> compression and then it does this and so on and so forth <pause dur="2.3"/> and <pause dur="0.5"/> this <pause dur="0.5"/> you can show with a bit of trigonometry i'm not going to do it today <pause dur="0.2"/> but in fact it's a sine curve <pause dur="3.4"/> so the process of rolling or rotating a wheel or an axle or <pause dur="0.7"/> anything like that <pause dur="0.6"/> produces <pause dur="0.2"/> alternating <pause dur="0.2"/> tension and compression <pause dur="1.6"/> so that the <pause dur="0.4"/> spoke of the wheel <pause dur="0.3"/> is experiencing <pause dur="0.2"/> this <pause dur="0.3"/> phenomenon of <pause dur="0.5"/> a varying <pause dur="0.3"/> tension compression <pause dur="0.2"/> alternating <pause dur="0.3"/> fluctuating <pause dur="0.4"/> oscillating whatever the those words you wish to use <pause dur="1.3"/> and the question <pause dur="0.2"/> is

well so what <pause dur="1.6"/> why should we be worried <pause dur="0.8"/> well we have to be worried <pause dur="0.2"/> because it turns out <pause dur="0.5"/> that this oscillating loading <pause dur="0.2"/> can <pause dur="0.2"/> break things <pause dur="0.2"/> can fail things <pause dur="0.5"/> at much <pause dur="0.3"/> lower <pause dur="0.2"/> stresses <pause dur="0.6"/> than you would <pause dur="0.6"/> work out <pause dur="0.2"/> on the basis of a simple <pause dur="0.3"/> single <pause dur="0.3"/> monotonic <pause dur="0.3"/> pull <pause dur="0.3"/> or push <pause dur="1.9"/> that's why it's important <pause dur="2.9"/> who first thought about this <pause dur="0.8"/> well you might think that people with <pause dur="0.2"/> horses and carts go up to the Museum of English Rural Life up the top of campus <pause dur="0.4"/> have a look in there you might have thought that farmers might have been interested in this <pause dur="0.7"/> and perhaps they were <pause dur="0.3"/> but if you think of the state of roads before eighteen-thirty forty or fifty or whatever <pause dur="0.5"/> they were sort of rutted tracks <pause dur="0.2"/> even the so-called turnpikes <pause dur="0.4"/> and therefore if anything broke it was probably because <pause dur="0.2"/> there was a big pothole in the road <pause dur="0.4"/> in the way that we all <pause dur="0.5"/> have problems with cars and bikes if we <pause dur="0.5"/> go over a <pause dur="0.6"/> what appears to be a puddle but in fact it's a <pause dur="0.5"/> like a <pause dur="0.2"/> bucket-shaped hole full of water and you damage your front

suspension and so on <pause dur="1.0"/> so <pause dur="0.9"/> and what you've got <pause dur="0.4"/> is the problem <pause dur="0.2"/> of <pause dur="0.9"/> # <pause dur="0.6"/> rotating <pause dur="0.2"/> machinery <pause dur="0.9"/> rotating wheels <pause dur="0.7"/> in the old days there were fractures but they never thought about it <pause dur="0.7"/> what <pause dur="0.2"/> made this an important subject <pause dur="0.2"/> was the growth of railways <pause dur="2.5"/><kinesic desc="writes on board" iterated="y" dur="3"/> because for the first time you had a smooth <pause dur="0.2"/> track <pause dur="0.9"/><kinesic desc="writes on board" iterated="y" dur="5"/> and you had <pause dur="0.3"/> wheels <pause dur="0.3"/> going along that smooth track <pause dur="1.7"/> and of course <pause dur="0.2"/> the engineers of the day <pause dur="0.4"/> although <pause dur="0.7"/> they were <pause dur="0.4"/> not <pause dur="0.6"/> # given all the materials that we have today we've done a bit of that a bit of the history wrought iron <pause dur="0.5"/> malleable iron <pause dur="0.2"/> et cetera et cetera Bessemer steel <pause dur="0.4"/> not coming along until the eighteen-fifties this in fact held up <pause dur="0.2"/> the <pause dur="0.5"/> growth of railways because all of the manual methods of making <pause dur="0.4"/> ductile <pause dur="0.4"/> # steel before that <trunc>han</trunc> before that time <pause dur="0.7"/> # <pause dur="0.3"/> nevertheless you had a reasonably smooth <pause dur="0.5"/> thing <pause dur="0.6"/> system with a reasonably smooth wheels and all the rest of it <pause dur="0.5"/> and what they discovered was that these axles were breaking the axles were breaking not so much the wheels <pause dur="0.5"/> they might have had spokes but

they might have been solid wooden blocked wheels it doesn't matter <pause dur="0.9"/> why were the axles breaking <pause dur="0.4"/> well <pause dur="0.3"/> let's look <pause dur="0.2"/> at <pause dur="0.2"/> this picture <pause dur="0.7"/><kinesic desc="indicates point on board" iterated="n"/> but looking at it from the <pause dur="0.3"/> end this way <pause dur="0.3"/> and let it not be a bicycle wheel any more <pause dur="0.3"/> let it be <pause dur="0.4"/> # <pause dur="0.2"/> two wheels on an axle <pause dur="0.2"/> like a railway <pause dur="0.5"/> axle so this <pause dur="0.3"/><kinesic desc="writes on board" iterated="y" dur="20"/> look at it sideways <pause dur="0.5"/> and you've got this <pause dur="0.3"/> sort of <pause dur="0.6"/> device <pause dur="0.8"/> and there <pause dur="0.4"/> is the <pause dur="0.6"/> axle <pause dur="2.2"/> and here is the wheel <pause dur="0.5"/> # <pause dur="0.6"/> and there is the <pause dur="0.8"/> the rail <pause dur="2.0"/> do you know <pause dur="0.4"/> by the way some clever <pause dur="0.9"/> character <pause dur="0.2"/> said there was a method of preventing <pause dur="0.4"/> trains coming off <pause dur="0.6"/> rails <pause dur="1.3"/> and what he said was <pause dur="0.5"/><kinesic desc="writes on board" iterated="y" dur="16"/> that when you look end on like this what you actually need <pause dur="0.6"/> is a <pause dur="0.3"/> wheel <pause dur="1.1"/> which looks like this <pause dur="2.0"/> and the <pause dur="0.3"/> you know the rail is in there <pause dur="1.6"/> and so <pause dur="0.2"/> you know <pause dur="0.2"/> the wheel wouldn't come off <pause dur="2.8"/> that a good idea <pause dur="2.8"/> well it isn't a good idea <pause dur="0.4"/> but you know the original explanation for why it wasn't a good idea <pause dur="1.0"/> because they said that's no good <pause dur="0.3"/> you'd have to go to the end of the track to get the vehicles on <pause dur="3.4"/><vocal desc="laughter" n="ss" iterated="y" dur="1"/> think of it <pause dur="1.3"/> right <pause dur="0.6"/> now <pause dur="0.4"/> if you have <kinesic desc="indicates point on board" iterated="n"/> this system <pause dur="0.6"/> and if you have outside

bearings <pause dur="0.3"/> so it's like a goods wagon with <pause dur="0.2"/> springs and so on <pause dur="0.8"/><kinesic desc="writes on board" iterated="y" dur="5"/> there's the <pause dur="0.3"/> axle box <pause dur="0.3"/> there here's the spring the force is pushing down there <pause dur="1.5"/> so <pause dur="0.4"/> what does that do <pause dur="0.3"/> well obviously if you think about it <pause dur="0.3"/><kinesic desc="writes on board" iterated="y" dur="6"/> it must bend the axle <pause dur="0.4"/> i'm exaggerating it but that's what <pause dur="0.3"/> happens the axle gets <pause dur="0.2"/> bent <pause dur="2.7"/> what happens when you bend a beam <pause dur="0.3"/> you've had <gap reason="name" extent="2 words"/>'s lectures last year <pause dur="0.5"/> when you bend a beam that bit goes into tension <pause dur="0.6"/> the <pause dur="0.2"/> underneath goes into compression <pause dur="1.4"/> that is a hogging beam remember the word hogging from <pause dur="0.6"/> pigs <pause dur="0.8"/> sagging and hogging that's hogging <pause dur="0.7"/> tension <pause dur="0.8"/> compression <pause dur="1.9"/> what happens <pause dur="0.2"/> a hundred-and-eighty degrees later <pause dur="0.3"/> well this bottom bit has gone on the top the top's gone on the bottom <pause dur="0.2"/> it's exactly the same as this it's the top and bottom of the axle now <pause dur="0.4"/> not the <pause dur="0.6"/> upper and lower spokes <pause dur="0.4"/> and so <pause dur="0.4"/> the <pause dur="0.3"/> stress state in that <pause dur="0.5"/> axle is exactly the same <pause dur="0.9"/> as <pause dur="0.3"/> the stress state in the spoke <pause dur="0.6"/> and in fact in those wheels if they were spoked wheels <pause dur="0.2"/> the spokes were being fatigued <pause dur="0.3"/> and the axles were also <pause dur="0.3"/>

being <pause dur="0.3"/> fatigued <pause dur="1.4"/> anyway <pause dur="0.2"/> these <pause dur="0.3"/> axles <pause dur="0.2"/> began to break <pause dur="0.4"/> for no apparent reason <pause dur="0.8"/> and <pause dur="0.6"/> so <pause dur="0.6"/> the <pause dur="0.4"/> people in charge of the railways <pause dur="0.5"/> <trunc>s</trunc> thought well <pause dur="0.4"/> either we're not making the wheels very <pause dur="0.2"/> well <pause dur="0.2"/> or <pause dur="0.9"/> there is a problem <pause dur="0.3"/> that we don't understand <pause dur="0.7"/> and it was a problem that they didn't understand and the problem was this thing called fatigue <pause dur="0.9"/> and the man who <pause dur="0.5"/> started all this work off <pause dur="0.5"/> was an Austrian <pause dur="0.3"/><kinesic desc="writes on board" iterated="y" dur="4"/> whose name was Wöhler <pause dur="0.7"/> that name keeps coming up <pause dur="1.1"/> W-O-umlaut-H-L-E-R Wöhler <pause dur="0.9"/> who was <pause dur="0.7"/> not sure what he was might be some sort of chief engineer of the Austrian railways one of the Austrian railway companies <pause dur="0.5"/> anyway he <pause dur="1.8"/> started to investigate this <pause dur="0.4"/> business <pause dur="1.0"/> and <pause dur="0.2"/> he very cleverly <pause dur="0.4"/> came up <pause dur="0.2"/> with a sort of test <pause dur="0.6"/> which <pause dur="0.2"/> in many ways is still used as a fatigue test even <pause dur="0.3"/> today <pause dur="0.8"/> and the

best way for you to think about it is to think of going downstairs into the workshop <pause dur="0.7"/> and going to one of <gap reason="name" extent="1 word"/> <pause dur="0.3"/> <gap reason="name" extent="1 word"/>'s lathes <pause dur="0.5"/> and saying okay here <pause dur="0.4"/><kinesic desc="writes on board" iterated="y" dur="4"/> is a chuck <pause dur="0.2"/> on the lathe <pause dur="1.1"/> can't spell <pause dur="0.2"/> chuck <pause dur="0.9"/> and what you do <pause dur="0.2"/> you have a <pause dur="0.2"/> normal round <pause dur="0.4"/> tensile <pause dur="0.3"/> test piece <pause dur="0.7"/> which you <pause dur="0.4"/><kinesic desc="writes on board" iterated="y" dur="4"/> are used to <pause dur="0.2"/> so <pause dur="0.2"/> here is this round <pause dur="0.4"/> tensile test piece <pause dur="0.3"/> but instead of putting it in one of <gap reason="name" extent="2 words"/>'s machines and pulling it until it breaks or whatever you're doing <pause dur="0.6"/> what you do is you stuff one end into the chuck <pause dur="1.1"/> so you lock it in the chuck <pause dur="0.4"/> and if you <pause dur="0.3"/> turned the lathe on <pause dur="0.2"/> the thing would <pause dur="0.2"/> rotate <pause dur="2.1"/> but what Wöhler then did was to say right <pause dur="0.3"/> at this end <pause dur="0.2"/><kinesic desc="writes on board" iterated="y" dur="3"/> i'm going to put some sort of collar <pause dur="0.5"/> with <pause dur="0.5"/> roller bearings or ball bearings it doesn't matter <pause dur="0.6"/> so here's looking <pause dur="0.2"/> from the end elevation <pause dur="0.8"/><kinesic desc="writes on board" iterated="y" dur="7"/> there <pause dur="0.4"/> is the specimen <pause dur="0.4"/> here is a sort of collar <pause dur="0.2"/> going round it with <pause dur="0.9"/> ball bearings and things like that <pause dur="0.4"/> and from that <pause dur="0.2"/> you hang a weight you put a mass on it <pause dur="1.4"/> and so <pause dur="0.2"/>

obviously <pause dur="0.6"/> the weight <pause dur="0.2"/> on the end of this thing <pause dur="0.5"/> what is it <pause dur="0.2"/> it's a cantilever <pause dur="0.4"/> and it's like the things that you solved in part one <pause dur="1.0"/> so you can work out the deflection you can work out the bending stress and you can do everything else <pause dur="3.7"/> and what happens well <pause dur="0.5"/> the cantilever the top is tension the bottom's compression <pause dur="1.1"/> hundred-and-eighty degrees later <pause dur="1.3"/><kinesic desc="writes on board" iterated="y" dur="4"/> the <pause dur="0.4"/> compression has become tension and the tension has become <trunc>p</trunc> <pause dur="0.2"/> compression et cetera et cetera <pause dur="1.4"/> and old Wöhler <pause dur="0.5"/> very clever <pause dur="0.6"/> he started to do <pause dur="0.3"/> tests <pause dur="2.1"/> what sort of tests did he do <pause dur="1.7"/> he put different weights <pause dur="0.4"/> on <pause dur="1.3"/> these <pause dur="0.2"/> test pieces <pause dur="0.8"/><kinesic desc="writes on board" iterated="y" dur="9"/> so he changed <pause dur="0.2"/> this <pause dur="1.2"/> W <pause dur="0.5"/> weight <pause dur="1.6"/> and he rotated the lathe <pause dur="1.3"/> and he found out <pause dur="0.3"/> how many rotations it took <pause dur="0.4"/> before <pause dur="0.4"/> the specimen broke <pause dur="2.3"/> all right <pause dur="2.0"/> and <pause dur="0.5"/> he then <pause dur="0.6"/> plotted <pause dur="1.4"/><kinesic desc="writes on board" iterated="y" dur="12"/> the load <pause dur="1.5"/> against the number of cycles N <pause dur="0.2"/> cycles <pause dur="0.6"/> to failure <pause dur="0.8"/> and failure here is breakage <pause dur="3.3"/> i say it's breakage because of course <pause dur="0.6"/> you could define failure <pause dur="0.3"/> and <pause dur="0.5"/> in <pause dur="0.4"/> part three i'll teach you plasticity and failure of course could be <pause dur="0.3"/> permanently being bent <pause dur="1.1"/> obviously if

an axle <pause dur="0.5"/> permanently gets bent it's not much good as an axle <pause dur="1.1"/> # so you always design within the elastic stress range we've already been through this in this course <pause dur="1.1"/> so he's got load <kinesic desc="indicates point on board" iterated="n"/> he's got number of cycles to failure <pause dur="0.4"/> now <pause dur="0.5"/> if you have <pause dur="0.5"/> no cycles <pause dur="0.8"/> it's really just bending bending bending bending bending until it breaks <pause dur="0.9"/> and that's like a static quasi-static test <pause dur="0.5"/> and you'd have a a value there <pause dur="0.5"/><kinesic desc="writes on board" iterated="y" dur="2"/> say <pause dur="3.1"/> if you then <pause dur="0.3"/> increase <pause dur="0.3"/> the weight <pause dur="1.1"/> and <pause dur="0.6"/> start the machine up <pause dur="0.8"/> and <pause dur="0.6"/> wait for something to happen <pause dur="0.5"/> you'll find <pause dur="0.5"/> that <pause dur="0.7"/> the <pause dur="0.7"/> lifetime or the number of cycles to failure <pause dur="1.0"/><kinesic desc="writes on board" iterated="y" dur="12"/> is <pause dur="0.8"/> lower <pause dur="2.1"/> in other words <pause dur="0.8"/> if you want the thing to last <pause dur="1.4"/> a hundred cycles a thousand cycles <pause dur="1.4"/> it will only take a certain load <pause dur="0.4"/> and then it'll break <pause dur="1.5"/> he puts <pause dur="1.2"/><kinesic desc="writes on board" iterated="y" dur="1"/> more weights on <pause dur="0.4"/> and he finds that he <pause dur="0.9"/><kinesic desc="writes on board" iterated="y" dur="9"/> can <pause dur="0.6"/> go out <pause dur="0.3"/> there <pause dur="1.5"/> more cycles lower <pause dur="0.2"/> loads <pause dur="0.4"/> so these loads are dropping <pause dur="0.6"/> all the time <pause dur="0.9"/> and he finds <pause dur="0.2"/> that sort of behaviour <pause dur="2.1"/> and that is a <pause dur="0.2"/> classic <pause dur="0.2"/> sort <pause dur="0.2"/> of so-called fatigue curve <pause dur="1.7"/> and in the literature <pause dur="0.3"/> you'll find these things called <pause dur="0.2"/> <kinesic desc="writes on board" iterated="y" dur="5"/>

S-<pause dur="1.3"/>N <pause dur="0.4"/> curves <pause dur="1.3"/> now <pause dur="0.4"/> we these days use sigma <pause dur="0.2"/> for stress <pause dur="1.1"/> # <pause dur="0.2"/> and <trunc>h</trunc> originally of course he used load <pause dur="0.2"/> but you can convert it to stress <sic corr="very">verily</sic> easy <pause dur="0.2"/> easily using bending theory <pause dur="1.6"/> so <pause dur="0.4"/> in the books you'll find that <pause dur="0.2"/> called very often an S-N curve <pause dur="0.4"/> and it means a fatigue curve <pause dur="6.0"/> now <pause dur="0.9"/> because <pause dur="0.4"/> these numbers of cycles in fact are very high they go into the millions <pause dur="0.9"/> you don't normally <pause dur="0.2"/> plot it on Cartesian coordinates <pause dur="1.0"/> you can have load or stress <pause dur="0.2"/><kinesic desc="writes on board" iterated="y" dur="9"/> here <pause dur="0.4"/> in <pause dur="0.3"/> Cartesian coordinates <pause dur="0.4"/> but here <pause dur="0.2"/> you have the log <pause dur="0.4"/> you do it on a semi-log plot <pause dur="0.4"/> of log <pause dur="0.2"/> numbers of cycles <pause dur="1.3"/> and what you find <pause dur="0.6"/> more or less <kinesic desc="writes on board" iterated="y" dur="6"/> is that the data follow <pause dur="0.5"/> some sort of falling line like that <pause dur="1.0"/> and maybe <pause dur="0.3"/> that's <pause dur="0.2"/> ten-to-the-six so that's a million cycles <pause dur="0.5"/> ten-five ten-four ten-three thousand cycles <pause dur="0.5"/> hundred cycles <pause dur="0.3"/> ten and <pause dur="1.0"/> et cetera one remember there's <trunc>no</trunc> not a zero <pause dur="0.2"/> on a log scale <pause dur="0.2"/> what's the log of zero <pause dur="2.0"/> come on what <pause dur="2.2"/> what is it </u><u who="sm0828" trans="overlap"> <gap reason="inaudible" extent="1 word"/> </u><pause dur="0.4"/> <u who="nm0827" trans="pause"> log of zero <pause dur="0.5"/> no the log of one is zero what's the log of zero </u><u who="sm0829" trans="overlap"> <gap reason="inaudible" extent="1 sec"/></u><pause dur="2.8"/> <u who="nm0827" trans="pause"> it may be in Dublin dear boy

but it's minus-infinity in the rest of the world <pause dur="1.2"/><vocal desc="laugh" iterated="n"/><vocal desc="laughter" n="ss" iterated="y" dur="1"/> the log of zero is <pause dur="0.4"/> bloody big it's minus-infinity <pause dur="0.3"/> so the zero on a scale is <pause dur="0.5"/> over <pause dur="0.3"/> there somewhere <pause dur="0.4"/> so never put a zero on a log scale <pause dur="0.8"/> now <pause dur="0.9"/> old Wöhler <trunc>f</trunc> was playing around with steel <pause dur="0.6"/> and he discovered <pause dur="0.9"/> that <pause dur="0.9"/> after about <pause dur="1.5"/> ten-to-the-six after about a million cycles <pause dur="0.5"/> the thing levelled out <pause dur="2.4"/> that was pretty interesting really <pause dur="0.8"/> and so that was called <pause dur="0.3"/> an endurance <pause dur="1.0"/><kinesic desc="writes on board" iterated="y" dur="3"/> limit <pause dur="5.1"/> and remember <pause dur="0.7"/> he <pause dur="0.2"/> was dealing with <pause dur="0.2"/> steels <pause dur="0.2"/> or <pause dur="0.6"/> wrought irons or <pause dur="0.6"/> some ferrous <pause dur="0.9"/> object <pause dur="0.3"/> anyway <pause dur="2.9"/> and that was for simple <pause dur="0.2"/> so-called <pause dur="0.2"/> reversed bending <pause dur="0.7"/> and reversed bending is like Wöhler and his cantilever <pause dur="0.5"/> where <pause dur="0.2"/> you have that so it goes from <kinesic desc="writes on board" iterated="y" dur="6"/> plus-<pause dur="0.7"/>T <pause dur="0.5"/> to minus-C those are equal magnitudes <pause dur="0.3"/> and you go through <pause dur="0.2"/> zero in the middle <pause dur="3.0"/> now <pause dur="1.5"/> if you have an endurance limit <pause dur="0.8"/> that's <pause dur="0.4"/> great <pause dur="1.1"/> if you think about it <pause dur="0.9"/> because what it means is <pause dur="0.5"/> according to this diagram <pause dur="0.9"/> that if you have that <kinesic desc="indicates point on board" iterated="n"/> sort of loading system <pause dur="0.6"/> providing you keep

your stresses below this endurance limit <pause dur="0.8"/> then you have an <pause dur="0.3"/> infinite <pause dur="0.2"/> life <pause dur="3.3"/> so you can have <pause dur="0.3"/> a life forever <pause dur="0.8"/> providing <pause dur="0.4"/> you <pause dur="0.8"/> recognize that there is an endurance limit <pause dur="0.5"/> or what is sometimes called a fatigue <pause dur="0.2"/><kinesic desc="writes on board" iterated="y" dur="6"/> limit <pause dur="2.2"/> i'll explain there is a difference and i'll explain that in a minute <pause dur="0.8"/> but fatigue limit or endurance limit <pause dur="0.5"/> and that happens for steels <pause dur="7.3"/> now <pause dur="3.7"/> if you <pause dur="3.6"/> don't <pause dur="0.6"/> test it just in bending which is what we've <pause dur="0.2"/> been doing here <pause dur="0.7"/> you might for example <pause dur="0.4"/> want to test something in axial fatigue so you would have your specimen in the usual way <pause dur="0.6"/> but you would <pause dur="0.2"/> oscillate it <pause dur="0.2"/> in the axial direction <pause dur="0.2"/> this would be like trying to <pause dur="0.4"/> estimate what's going on with the spokes <pause dur="1.2"/> 'cause they're going <pause dur="0.5"/> tension compression tension <trunc>compre</trunc> <pause dur="0.3"/> but in <pause dur="0.6"/> unidirectional loading not in bending <pause dur="0.5"/> is there a difference <pause dur="0.9"/> can you make a machine <pause dur="0.3"/> which <pause dur="0.2"/> does this well of course you can do it on the types of testing machines down in <gap reason="name" extent="2 words"/>'s lab <pause dur="0.6"/> these are screw-driven machines <pause dur="0.4"/> and if you think about it you just drive

the screw one way drive the screw the other way and you can do <pause dur="0.2"/> this <pause dur="1.8"/> you might be saying to yourself well <pause dur="0.5"/> # <pause dur="0.5"/> it's all very well <pause dur="0.2"/> talking about rotation <pause dur="0.4"/> speed <pause dur="0.2"/> of oscillation frequency of oscillation <pause dur="0.3"/> but does <pause dur="0.3"/> how fast you do it matter <pause dur="0.6"/> is there a difference between sort of oscillating very slowly <pause dur="0.5"/> and <pause dur="0.3"/> oscillating <pause dur="0.3"/> you know like a <pause dur="0.9"/> i don't know <pause dur="1.0"/> a # <pause dur="0.2"/> bird flaps its wings or something else something very very fast <pause dur="0.4"/> and the answer is yes there is <pause dur="0.9"/> and it's particularly important in things like plastics <pause dur="0.6"/> where because you are <pause dur="0.3"/> oscillating the load you're obviously doing work <pause dur="0.5"/> force point of application <pause dur="0.6"/> that work <pause dur="0.3"/> becomes heat <pause dur="0.6"/> in a metal <pause dur="0.2"/> the heat tends to be dissipated but in plastics it tends to be localized where the thing is happening <pause dur="0.7"/> that then alters as we saw the other week <pause dur="0.3"/> the properties <pause dur="1.0"/> the strength varies with the temperature and the speed at which you're doing it and so on <pause dur="0.4"/> so the speed does matter <pause dur="0.8"/> but <pause dur="1.2"/> whilst in the lab with the <gap reason="name" extent="2 words"/> type machine <pause dur="0.2"/><kinesic desc="indicates point on board" iterated="n"/> the oscillation rate is <pause dur="0.6"/> pretty

limited <pause dur="0.3"/> pretty limited <pause dur="0.6"/> you can have very <pause dur="0.2"/> fast <pause dur="0.2"/> <trunc>v</trunc> <pause dur="0.7"/> axial oscillations <pause dur="0.5"/> and the firm that <pause dur="0.2"/> invented the <pause dur="1.0"/><kinesic desc="writes on board" iterated="y" dur="2"/> method of doing this is a firm called Amsler <pause dur="0.4"/> who are in Switzerland <pause dur="0.6"/> and what they did was really very clever <pause dur="0.7"/> because <pause dur="0.3"/> they <pause dur="0.2"/> attached what amounts to a whacking great big <pause dur="0.2"/> tuning fork <pause dur="0.2"/> to the bottom of the specimen <pause dur="0.8"/> i mean a big one <pause dur="0.5"/> really big <pause dur="1.1"/> the biggest Amsler machines the tuning fork would be <pause dur="0.3"/> about <pause dur="0.3"/> the size of <pause dur="0.3"/> where i am here <pause dur="1.2"/> and you can get that resonating <pause dur="0.6"/> and of course it puts the <pause dur="0.6"/> # <pause dur="0.2"/> device into <pause dur="0.3"/> oscillation <pause dur="0.9"/> and you <pause dur="0.5"/> by altering the amplitude of the tuning fork <pause dur="0.2"/> you <pause dur="0.2"/> alter the load you can set this on the machine <pause dur="0.8"/> and <pause dur="0.2"/> then you can generate <pause dur="0.4"/> # these same sort of data <pause dur="0.9"/> well what do you get <pause dur="0.4"/> what do you get what do you get well <pause dur="0.9"/> it's like this <pause dur="0.5"/> but <pause dur="0.6"/> this plot if i say this is bending pure bending <pause dur="1.0"/><kinesic desc="writes on board" iterated="y" dur="1"/> if you have the <pause dur="0.3"/> axial thing <pause dur="0.5"/> this <pause dur="0.7"/> says the same sort of thing <pause dur="0.3"/> but <pause dur="0.4"/> goes to a lower <pause dur="0.2"/> value <pause dur="0.4"/> before it <pause dur="0.2"/> levels out <pause dur="1.4"/> so this would be axial <pause dur="1.0"/><kinesic desc="writes on board" iterated="y" dur="1"/> fatigue <pause dur="2.7"/> and you might also say <pause dur="0.5"/> # <pause dur="0.2"/> well what about other methods of

loading <pause dur="0.6"/> what about if we <pause dur="0.2"/> twist things you've heard of torsional suspensions on motor cars <pause dur="0.5"/> what happens if you think of having <pause dur="0.2"/> a tube or a rod <pause dur="0.3"/> which itself is <pause dur="0.4"/> not <pause dur="0.2"/> being twisted monotonically but is fluctuating in the twist what happens there <pause dur="0.7"/> well <pause dur="0.4"/> # the same sort of thing <pause dur="0.3"/> but this time <pause dur="0.2"/><kinesic desc="writes on board" iterated="y" dur="4"/> it goes down <pause dur="0.3"/> <trunc>h</trunc> even lower <pause dur="1.8"/> down to there <pause dur="0.3"/> not drawn that very well <pause dur="2.1"/> so that this endurance limit <pause dur="0.4"/><kinesic desc="writes on board" iterated="y" dur="6"/> although <pause dur="0.4"/> it's very good <pause dur="2.7"/> the values that you have depend on the mode <pause dur="0.5"/> of <pause dur="0.9"/> deformation so bending to axial <pause dur="0.5"/> # to torsion to twist <pause dur="6.6"/><kinesic desc="writes on board" iterated="y" dur="5"/> now <pause dur="1.0"/> # before the days of what's called fracture mechanics which is the subject i shall teach you next term <pause dur="0.6"/> where we are talking about the progression of cracks <pause dur="0.5"/> through bodies <pause dur="0.2"/> before that time <pause dur="0.9"/> people <pause dur="1.1"/> were <pause dur="1.8"/> limited in a sense as to what they could use for data <pause dur="0.4"/> and they tended rightly or wrongly <pause dur="0.5"/> to reference everything to the simple tension test <pause dur="0.8"/> so in the simple tension test which you know about <pause dur="0.5"/><kinesic desc="writes on board" iterated="y" dur="10"/> load against extension or stress against strain <pause dur="0.5"/> # engineering stress and

strain <pause dur="1.0"/> there is your yield <pause dur="0.9"/> there is the <pause dur="0.2"/> ultimate tensile strength we discussed this in the corresponding lectures in part one <pause dur="0.6"/> so what these <pause dur="1.1"/> chaps <pause dur="0.2"/> did from about eighteen-fifty up until well up until the second war and even now in fact <pause dur="0.5"/> for a for an empirical sort of <trunc>corre</trunc> correlation <pause dur="0.3"/> they said <pause dur="0.3"/> what's that value bend or axial or torsion <pause dur="0.3"/> as a proportion of something that i can easily measure <pause dur="0.5"/> and the thing that they could easily measure was the ultimate tensile strength <pause dur="0.2"/>

maximum load over the starting area <pause dur="1.6"/> all right <pause dur="1.0"/> so <pause dur="1.0"/> when you look at these types of diagrams <pause dur="0.4"/> you will find labelled on to the diagrams <pause dur="0.4"/> what these levels are <pause dur="1.0"/> so <pause dur="0.3"/> if i <pause dur="1.3"/> just rub that out <pause dur="0.4"/> put them in again <pause dur="2.3"/><kinesic desc="writes on board" iterated="y" dur="8"/> you'll find that the <pause dur="0.2"/> bending-only one <pause dur="0.4"/> is about <pause dur="0.2"/> and it's very rough <pause dur="0.3"/> about point-five of the U-T-S <pause dur="0.7"/> so in other words if you had a piece of steel with a U-T-S of about three-hundred megapascals <pause dur="0.4"/> # that value for pure bending <pause dur="0.4"/> pure reverse bending Wöhler bending would be about <pause dur="0.4"/> # three-hundred-over-two <pause dur="0.2"/> which is a hundred-and-fifty <pause dur="1.8"/> if you have the <pause dur="0.3"/> axial fatigue <pause dur="0.5"/> that value is about <pause dur="0.2"/> point-four-three of U-T-S <pause dur="0.7"/><kinesic desc="writes on board" iterated="y" dur="2"/> i don't know that i believe the point-three <pause dur="0.6"/> i suppose i believe the point-four <pause dur="0.2"/> but it's that sort of thing <pause dur="1.2"/> and if you go down to torsion <pause dur="0.6"/><kinesic desc="writes on board" iterated="y" dur="2"/> the <pause dur="0.8"/> lowest one there <pause dur="0.3"/> it's about point-three of the U-T-S <pause dur="0.7"/> so again a three-hundred megapascal very weak <pause dur="0.3"/> low carbon steel in torsion <pause dur="0.5"/> would not <pause dur="0.2"/> take <pause dur="0.7"/> more <pause dur="0.3"/> than <pause dur="0.4"/> three-hundred-over-three <pause dur="1.0"/> # <pause dur="0.2"/> about <pause dur="0.2"/> a hundred <trunc>megapa</trunc> pascals <pause dur="0.3"/> reversed <pause dur="0.2"/> twist <pause dur="0.5"/> so you need to

think about that if you're designing a torsional suspension for a motor car <pause dur="2.4"/> now then <pause dur="2.4"/> this is all very well <pause dur="1.6"/> but <pause dur="1.7"/> is it true for all materials <pause dur="0.5"/> and unfortunately the answer it is not true <pause dur="0.4"/> for all materials <pause dur="1.7"/> what i've drawn there <pause dur="0.2"/> with these endurance limits <pause dur="0.5"/> are true <pause dur="0.6"/> only <pause dur="0.3"/> of <pause dur="0.2"/> irons and steels <pause dur="0.3"/> <unclear>as</unclear> <pause dur="0.2"/> for practical purposes <pause dur="0.7"/> titanium and one or two other funny things perhaps <pause dur="0.5"/> # <pause dur="0.3"/> # <pause dur="0.4"/> have these sort of features <pause dur="0.6"/> but <pause dur="0.5"/> the important thing <pause dur="0.3"/> is and in particularly in terms of normal engineering <pause dur="0.4"/><kinesic desc="writes on board" iterated="y" dur="13"/> is that aluminium alloys <pause dur="4.0"/> do not have <pause dur="0.9"/> there's no fatigue limit <pause dur="3.2"/> so if you were to plot these types of things for aluminium alloys <pause dur="0.5"/> you would have this just going down and down and down and down and down <pause dur="2.5"/> and <pause dur="1.2"/> so <pause dur="0.3"/> if <pause dur="0.2"/> ten-to-the-six a million cycles <pause dur="0.5"/> is the endurance limit for <pause dur="0.5"/> # steels <pause dur="0.6"/> then <pause dur="0.7"/> it doesn't level out <pause dur="0.14"/> for <pause dur="0.2"/> most <pause dur="0.3"/> aluminium <pause dur="0.2"/> alloys <pause dur="2.5"/> you check <pause dur="0.2"/> in the books <pause dur="0.6"/> which particular metals obey <pause dur="0.5"/> the endurance limit idea <pause dur="0.3"/> and which don't <pause dur="1.2"/> the <pause dur="0.5"/> important ones <pause dur="0.4"/>

as i say are the ferrous <pause dur="0.2"/> and <pause dur="0.4"/> aluminium <pause dur="0.2"/> alloys <pause dur="1.2"/> but what does that mean <pause dur="1.0"/> what does that mean if you want to design an aeroplane <pause dur="0.6"/> which is made <pause dur="0.2"/> mostly <pause dur="0.2"/> out <pause dur="0.2"/> of <pause dur="0.6"/> aluminium <pause dur="0.4"/> alloys </u><pause dur="2.7"/> <u who="sm0830" trans="pause"> has to be scrapped after ten years <gap reason="inaudible" extent="2 secs"/> </u><u who="nm0827" trans="overlap"> <vocal desc="laughter" iterated="y" dur="1"/> <pause dur="0.5"/> ten years <pause dur="0.5"/> no well good idea <pause dur="0.5"/> well <pause dur="0.2"/> the implication of this is that of course you cannot design for infinite life <pause dur="0.5"/> that is very true <pause dur="1.3"/> and what it does say is that you have to be very very careful about inspections <pause dur="1.1"/> you have to look for cracks it's cracks that we're dealing round to and i'll be showing you some pictures of fatigues in a minute <pause dur="0.9"/> you have to look <pause dur="0.2"/> for <pause dur="0.5"/> # cracks <pause dur="0.6"/> now <pause dur="1.0"/> of course <pause dur="0.2"/> if you have <pause dur="0.4"/> a piece of steel <pause dur="0.6"/> and you <pause dur="1.1"/> are <pause dur="0.2"/> in an application where <pause dur="0.7"/> you don't want it to last <pause dur="0.3"/> more than a million cycles <pause dur="0.8"/> then you don't have to limit yourself to working below here you can work up here <pause dur="1.3"/> and a typical example of that would be a gun barrel <pause dur="0.5"/> think of the old naval guns <pause dur="0.2"/> you know twelve inch shells whatever <pause dur="0.7"/> i'm reading a book at the moment by Edmund Blunden called Undertones of War

about all the ghastly things in the trenches in the First World War and he goes on about these <pause dur="0.4"/> whizz-bangs that go over <pause dur="0.5"/> and <pause dur="0.3"/> you know these are <pause dur="0.2"/> ten inch shells which just plop in the mud <pause dur="0.2"/> and they're duds they don't go off <pause dur="1.3"/> if they do go off <pause dur="0.3"/> he wouldn't have been around to <pause dur="0.6"/> write the book <pause dur="0.8"/> anyway these big gun barrels you're not going to fire that barrel <pause dur="0.3"/> a million times <pause dur="0.2"/> naval guns <pause dur="0.4"/> if you read Jane's Ships and things like that naval guns <pause dur="1.0"/> those big guns were not even after things like Jutland were not fired that many times <pause dur="0.6"/> so you might argue <pause dur="0.4"/> that you could be in a thousand cycles <pause dur="0.2"/> and so you could design <pause dur="0.4"/> at the higher stress level <pause dur="1.2"/> if you design at the higher stress level of course you want less material <pause dur="0.8"/> so it's this weight <pause dur="0.2"/> business that comes into this <pause dur="1.4"/> and this is important in relation to aluminium because of you know <pause dur="0.4"/> space vehicles aerospace <pause dur="0.5"/> light<pause dur="0.3"/>weight <pause dur="0.5"/> materials <pause dur="0.3"/> very high specific strengths toughnesses and so on and so forth <pause dur="0.5"/> so <pause dur="0.9"/> you don't have to go

below there but if you want the thing to last for a long time and you don't want your customers coming back and saying oi i you know bought something from you and it's broken <pause dur="0.5"/> you don't want to have the reputation of being the Arthur Daley of # engineering design or whatever it is <pause dur="0.5"/> then you have to <pause dur="0.2"/> think about these things and of course there are standards which say <pause dur="0.4"/> you <pause dur="0.2"/> must <pause dur="0.2"/> design below these stresses if it satisfies this particular standard <pause dur="0.7"/> but you don't have to and in some circumstances you needn't <pause dur="0.6"/> but the problem is <pause dur="0.4"/> that <pause dur="0.3"/> although this part of the diagram is called the <pause dur="0.3"/><kinesic desc="writes on board" iterated="y" dur="3"/> finite <pause dur="0.3"/> life <pause dur="1.2"/> region and of course this is the infinite <pause dur="0.2"/> life <pause dur="0.5"/> region <pause dur="0.9"/> you have a problem with the

aluminium alloys 'cause you don't know where you are <pause dur="0.7"/> because it's all <pause dur="0.3"/> finite <pause dur="0.2"/> life <pause dur="5.3"/><kinesic desc="writes on board" iterated="y" dur="5"/> there is not an infinite life with those things <pause dur="1.8"/> you've still got a design <pause dur="0.2"/> you still have to tell people how good or how bad <pause dur="0.3"/> aluminium alloys are <pause dur="0.5"/> so what happens is you still quote <pause dur="0.3"/> this value here <pause dur="0.6"/> in the same way that you quote this value here <pause dur="0.3"/> even though it <pause dur="0.2"/> doesn't <pause dur="0.2"/> plateau <pause dur="0.2"/> out <pause dur="1.8"/> and you don't call it the endurance limit <pause dur="0.6"/> you call it the fatigue limit which was the other word you see <pause dur="1.7"/><kinesic desc="writes on board" iterated="y" dur="2"/> # those of us like me who tend to be a bit sloppy we use the things <trunc>in</trunc> <pause dur="0.2"/> interchangeably <pause dur="0.8"/> but strictly endurance limit is the ferrous thing and fatigue limit is a chosen value <pause dur="0.7"/> at a given number of cycles