LECTURE+1+COE-3001-A

During loading linear variable differential

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Unformatted text preview: l, i.e., produces conInuous recording of Δl(t) ✏yy (t) = 1/7/13 l(t) (engineering strain determined from extensometer) l0 M. Mello/Georgia Tech Aerospace 12 l TENSILE TEST 1/7/13 COMPRESSION TEST M. Mello/Georgia Tech Aerospace 13 ENGINEERING STRESS AND STRAIN F First recall engineering stress and strain definiIons: F A0 ✏yy = l yy l0 = y y0 t x A0 w z Engineering stress- strain curve 1/7/13 M. Mello/Georgia Tech Aerospace 14 l 0 = y0 engineering stress: engineering strain: = y EXPERIMENTAL STRESS- STRAIN CURVES Fig.1 Stress–strain curve showing typical yield behavior for nonferrous alloys. Stress (σ) is shown as a funcIon of strain (ε) 1: elasIc region 2: ProporIonality limit 3: ElasIc limit 4: Offset yield strength 1/7/13 Fig 2. A stress–strain curve typical of structural steel 1. UlImate Strength 2. Yield Strength 3. Rupture 4. Strain hardening region 5. Necking region. A: Apparent stress (F/A0) B: Actual stress (F/A) M. Mello/Georgia Tech Aerospace 15 P STRESS- STRAIN DIAGRAMS TRUE STRESS- STRAIN CURVE NOTE hrp://www.youtube.com/watch?v=K28WiL21Sgs&feature=related (ADMET ASTM E8 Metal Tensile Test ) M. Mello/Georgia Tech Aerospace 1/7/13 hrp://www.youtube.com/watch?v=5QaqwmZ7Sic advance to 2:12 aluminum necking in center of specimen (forward to t= 2 minutes) 16 STRESS- STRAIN SIGNATURES OF VARIOUS MATERIALS BRITTLE FAILURE 1/7/13 M. Mello/Georgia Tech Aerospace 17 Stress- strain curves for 3 steel alloys strain hardening (flow strength rises) Stress Units: MPa = 106 Pa GPa = 109 Pa kPSI = 103 psi •  U.Y.P = upper yield point (U.Y.P is rate sensiIve, increased strain rate leads to increased U.Y.P) •  L.Y.P = lower yield point •  Y.S. = yield strength (0.2% offset) 0.2% offset Yield strength Metal Rolling operaIon 1/7/13 M. Mello/Georgia Tech Aerospace Reference: Crandall, Dahl, Lardner, IntroducIon to the Mechanics of Solids, McGraw- Hill, 2nd ediIon with SI units, 1978 18 Stress- strain curves for 3 Aluminum alloys Units: MPa = 106 Pa GPa = 109 Pa kPSI = 103 psi Solest polycrystalline Aluminum Note: y- axis limit (σmax=2000 MPa) intenIonally kept same as previous σ-ε plots for steel alloys for sake of comparison 1/7/13 M. Mello/Georgia Tech Aerospace Reference: Crandall, Dahl, Lardner, IntroducIon to the Mechanics of Solids, McGraw- Hill, 2nd ediIon wi...
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