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7.7Thepre-ModernPeriod; Coulomb andNavier 149

7.7 Thepre-ModernPeriod; Coulomb andNavier

75 Coulomb (1736-1806)was a French militaryengineer,Fig.7.16, as was the rstto publish

Figure7.16:Coulomb

thecorrectanalysisof the ber stressesin
exedbeamwithrectangularcrosssection(Sur

uneApplicationdesRegles demaximiset minimisa quelquesproblemesdestatiquerelatifs

a l'architecturein 1773). HeusedHooke'slaw,placedtheneutralaxisin itsexactposition,

developed theequilibriumof forcesonthecrosssectionwithexternalforces,andthencorrecly

determinedthestresses.Healsoworked on friction(\Coulomb friction")andon earthpressure.

76 Coulomb didalso research on magnetism,friction, andelectricity. In 1777 he invented

thetorsionbalanceformeasuringtheforceof magneticandelectricalattraction. Withthis

invention,Coulomb was ableto formulatetheprinciple,now knownas Coulomb'slaw, governing

theinteractionbetweenelectriccharges. In 1779Coulomb publishedthetreatiseTheoriedes

machinessimples(Theoryof SimpleMachines),ananalysisof frictionin machinery. Afterthe

war Coulomb cameoutof retirement andassistedthenewgovernment in devisinga metric

systemof weights andmeasures. Theunitof quantity usedto measureelectricalcharges,the

coulomb, was namedforhim.

77 Navier(1785-1836)Navierwas educatedat theEcolePolytechniqueandbecamea professor

therein 1831. Whereasthefamousmemoirof Coulomb (1773)containedthecorrectsolution

to numerousimportant problemsin mechanicsof materials,it tookengineersmorethanforty

yearsto understandthemcorrectlyandto usethemin practicalapplication

78 In 1826hepublishedhisLecons(lecturenotes)which is consideredthe rstgreattextbook

in mechanicsforengineering.In it he developed the rstgeneraltheoryof elasticsolidsas well

as the rstsystematictreatment of thetheoryof structures.

79 It shouldbe notedthatnocleardivisionexistedbetweenthetheoryof elasticity andthe

theoryof structuresuntilaboutthemiddleof thenineteenthcentury(Coulomb andNavier

wouldtoday be consideredprofessionalstructuralengineers).

80 Threeotherstructuralengineerswhopioneeredthedevelopment of thetheoryof elasticity

fromthatpoint onwereLame, Clapeyron anddeSaint-Venant. Lam'epublished the rst

book onelasticity in 1852,andcreditedClapeyronforthetheoremof equality betweenexternal

andinternalwork. deSaint-Venant wasperhaps thegreatestelasticianswhoaccording to

Southwell...combinedwithhighmathematicalability anessentiallypracticaloutlookwhich

gave directionto allhiswork". In 1855-6hepublishedhisclassicalworkontorsion,
exure,