AAE 454 Session 13 - AAE 454 Spring 2013 AAE 454 Lesson 13...

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AAE 454 - Spring 2013©2013 A. F. Grandt, Jr.1AAE 454: Design of Aerospace Structures (Spring 2013)A F Grandt Jr1A. F. Grandt, Jr.Room 3235 Armstrong Hallemail: [email protected]telephone: 49-45141Last Time3-d principal stressesHydrostatic stressTodayAAE 454 – Lesson 13AAE History tidbitsStart buckling2Aeronautical Engineering (1920’s)1921--1st aeronautical engineering classes taught by ME– Prof G. A. Young--head– 25 staff, 603 ugrads, 16 grads• 1921-1941--Aero option in ME1921-1941--Aero option in MEAeronautics lab developed in Heavilon Hall• Faculty– Martin L. Thornburg (1921-24)– Elbert F. Burton & Alan C. Staley (1924)– Major William A. Bevan (1926-29)Captain George W. Haskins(1929-37)3Professor (Captain) George W. Haskins (1929-37)Born 11 March 1892 1916: BSME Purdue1917-1922 U.S. Air Service • 1919: First alum to land1919: First alum to land aircraft on Purdue campus1929-37: Headed Purdue Aeronautics Division as ME professorLeft Purdue 30 June 1937 returned to Air Corpslater Civil Aeronautics BoardJanuary 1930 photographCurtiss Robin Aircraft Loan(January 1930)Professor George W. Haskins (left) and Richard Arnett with cabin plane loaned by the Curtiss Services Corp. for class work (-200F)Purdue Wind Tunnel (November 1931)Professors George W. Haskins (left) and Hollister (right) examine wind tunnel
AAE 454 - Spring 2013©2013 A. F. Grandt, Jr.2Amelia Earhart and Professor George W. Haskins -1936Amelia Earhart and Professor George W. Haskins - 1936Session 13AssignmentHW # 4 due Friday, 8 FebruaryRead (blackboard)9AFG Review of Preliminary Concepts –Section 2.6 Failure ModesBuckling Notes 1Buckling Notes 2Yield Criteria for Ductile Metals(AFG Section 2.6.2)Maximum shear stress (Tresca) yield criterion– Yields when τmaxat point ≥ σys/2– where τmax = ⏐σ1σ3/210– Here σ1, σ3= principal stressesVon Mises yield criterion (also known as octahedral shear stress) - Eq. 2.34– Yields when()()()()YS2yz2xz2xy2zx2zy2yx621στττσσσσσσ+++++Yield Criteria for Brittle Metals(AFG Section 2.6.2)Maximum Normal stress (Eq. 2.35) yield criterion– Yields when σ1at point ≥ σys(or σult)– Whereσ1= max principal stresses11Maximum Normal Strain yield criterion (also known as St. Venant) - Eq. 2.36– Yields when()tconstanmaterialEE3211+=σσνσε()ult321whenFailsσσσνσ+3-d States of Stress12
AAE 454 - Spring 2013©2013 A. F. Grandt, Jr.33-d Principal Stresses13(See Sun Eq. 2.3.4)3-d Mohr’s Circleτmax= [σ1σ3]/214τ1= [σ2 σ3 ]/2max1 3 τ3= [σ1 σ2 ]/23-d Stress Example(thin-walled pressure vessel)15Example – Danger of Hydrostatic StressThe state of hydrostatic stress σHcan Uniaxial stress yields in shear –ductile behavior

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