This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: 1 Mechanical Properties of Metals and Alloys: DeFnitions and Units • Stress $ = F/A, MPa = 10 6 N/m 2 • Strain % = & L/L o (engineering strain) • Elastic Modulus or Young’s Modulus E = $ / % when % << 1 • Poisson Ratio ’ =  % L / % A ! L ! A 2 Mechanical Properties of Metals and Alloys: DeFnitions and Units • Shear Stress ! = F/A, MPa = 10 6 N/m 2 • Shear Strain " = tan # • Shear Modulus G = ! / " when " << 1 G = E 2(1 + " ) for linear elastic materials A F F F F ! 3 Young’s Modulus • Measure of resistance against elastic deformation • Directiondependent – For iron, average E = 205 GPa; – E(111) = 280 GPa; E(100) = 125 GPa 4 Yield Strength • Measure of the stress level at which permanent or plastic deformation begins • 0.2% offset yield strength de¡ned for metallic systems Material Yield Strength (MPa) Annealed 1100 Al alloys 35 Annealed 304 SS 200 Aged 7075 Al alloys 500 Ti6Al4V 800 177PH SS 1200 5 A “Typical” StressStrain Curve 0.2% strain Stress $ y $ u Strain Ultimate tensile strength Yield strength True stress/strain Eng. stress/strain 6 Plastic Strain " tot = " el + " pl = # E + " pl total strain Stress Strain elastic strain plastic strain 1 2 3 7 Hardness • Rockwell • Vickers • Knoop • ….. 8 Vickers Hardness • (4face) Pyramidal diamond indentor • Indent at load force F • Measured area A total = A proj / cos 68 o • H V = F / A total Indentor ( # = 136 o ) Projected indented area 9 Plastic Deformation • When stressed beyond elastic limit, metals often develop slip bands • Slip band due to sliding of crystallographic planes 10 Slip Bands Side view Top view 200 μ 11 Critical Shear Stress • Expect shear stress to initiate permanent or plastic deformation to be about 1/4 G • More precise analysis gives about 1/10 G • Experiment: 1/100 to 1/1000 G ~0.5 R 2R 12 Critical Shear Stress Why is the actual shear strength so much smaller?...
View
Full
Document
 Spring '10
 MatSci

Click to edit the document details