专业英语资料1.docx

专业英语资料1.docx

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专业英语资料1

Chapter1

BasicConceptsinMechanic

1.Force

Insimpleterms,aforceisapushorapull.Forcemaybecausedbyelectromagnetism,gravity,oracombinationofphysicalmeans.

2.Netforce

Netforceisthevectorsumofallforcesthatactonanobject,includingfrictionandgravity.Whenforcesareappliedinthesamedirectiontheyareadded.Forexample,iftwo10Nforceswereappliedinthesamedirectionthenetforcewouldbe20N.

If10Nofforcewereappliedinonedirectionand20Nofforceappliedintheoppositedirection,thenetforcewouldbe10Nandobjectwouldmoveinthedirectionofthegreaterforce.If10Nofforcewereappliedequallyinbothdirections,thenetforcewouldbezeroandtheobjectwouldnotmove.

3.Torque

Torqueisatwistingorturningforcethatcausesanobjecttorotate.Forexample,aforceappliedtotheendofalevercausesaturningeffectortorqueatthepivotpoint.Torque（M）istheproductofforceandradius（leverdistance）.

M=Force×Radius

IntheEnglishsystemtorqueismeasuredinpound-feet（1b-ft）orpound-inches（N-in）.If10Nofforcewereappliedtoalever1ftlong,forexample,therewouldbe10N-ftoftorque.

Anincreaseinforceorradiuswouldresultinacorrespondingincreaseintorque.Increasingtheradiustotwoft,forexample,resultin201b-fttorque.

4.Speed

Anobjectinmotiontravelsadistanceinagiventime.Speedistheratioofthedistancetraveledandthetimeittakestotravelthedistance.

Speed=Distance/Time

5.LinearSpeed

ThelinearspeedofanobjectisameasureofhowlongittakestheobjecttogetfrompointAtopointB.linearspeedisusuallygiveninaformsuchasmeterspersecond（m/s）.Forexample,ifthedistancebetweenpointAandpointBwere10meters,andittook2secondtotravelthedistance,thespeedwouldbe5m/s.

6.Angular（Rotational）Speed

Theangularspeedofarotatingobjectisameasurementofhowlongittakesagivenpointontheobjecttomakeonecompleterevolutionfromitsstartingpoint.Angularspeedisgenerallygiveninrevolutionsperminute（rad/min）.Anobjectthatmakestencompleterevolutionsinoneminute,forexample,hasaspeedof62.8rad/min.

7.Acceleration

Anobjectcanchangespeed.Anincreaseinspeediscalledacceleration.Accelerationoccursonlywhenthereisachangeintheforceactingupontheobject.Anobjectcanalsochangefromahighertoalowerspeed.Thisisknownasdeceleration（negativeacceleration）.

Arotatingobject,forexample,canacceleratefrom62.8rad/minto12.56rad/min,ordeceleratefrom125.6rad/minto62.8rad/min.

8.Inertia

Mechanicalsystemsaresubjecttothelawofinertia.Thelawofinertiastatesthatanobjectwilltendtoremaininitscurrentstatesofrestormotionunlessacteduponbyanexternalforce.Thispropertyofresistancetoacceleration/decelerationisreferredtoasthemomentofinertia.TheEnglishsystemofmeasurementispound-feetsquared（1b-ft2）.

Ifwelookatacontinuousrollofpaper,forexample,weknowthatwhentherollisstoppeditwouldtakeacertainamountofforcetoovercometheinertiaoftherolltogetitrolling.Theforcerequiredtoovercomethisinertiacancomeformasourceofenergysuchasamotor.Oncerolling,thepaperwillcontinueunwindinguntilanotherforceactsonittobringittoastop.

9.Friction

Alargeamountofforceisappliedtoovercometheinertiaofthesystematresttostartitmoving.Becausefrictionremovesenergyfromamechanicalsystem,acontinualforcemustbeappliedtokeepanobjectinmotion.Thelawofinertiaisstillvalid,however,sincetheforceappliedisneededonlytocompensatefortheenergylost.

Chapter2

KindsofSteels

Therearetwogeneralkindsofsteels:

carbonsteelandalloysteel.Carbonsteelcontainsonlyironandcarbon,whilealloysteelcontainssomeother“alloyingelements”suchasnickel（镍）,chromium（铬）,manganese（锰）,molybdenum（钼）,tungsten（钨）,vanadium（钒）,etc.

1.Carbonsteels

1）Lowcarbonsteelcontainingfrom0.05to0.15percentcarbon,whichisalsoknownasmachinesteel;

2）Mediumcarbonsteelcontainingfrom0.15to0.06percentcarbon;

3）Highcarbonsteelcontainingfrom0.06to1.50percentcarbon,whichissometimescalled“toolsteel”.

2.Alloysteels

1）Specialalloysteel,suchasnickelsteel,chromiumsteel;

2）High-speedsteelalsoknownasself-hardeningsteel.

Carbonsteelsarethemostcommonsteelsusedinindustry.Thepropertiesofthesesteelsdependonlyonthepercentageofcarbontheycontain.Lowcarbonsteelsareverysoftandcanbeusedforboltsandformachinepartsthathavenostrengthrequirements.Mediumcarbonsteelisabettergradeandstrongerthanlowcarbonsteel.Highcarbonsteeliscanbehardenedbyheatingittoacertaintemperatureandthenquicklycoolingitinwater.Themorecarbonthesteelc