(Mechanical Properties)

Μέγεθος: px

Εμφάνιση ξεκινά από τη σελίδα:

Download "(Mechanical Properties)"

Δάφνη Κανακάρης-Ρούφος
5 χρόνια πριν
Προβολές:

1 Engineering Materials (Mechanical Properties-I) 1 (Mechanical Properties) Sheet Metal Drawing / (- Deformation) () 3 Force -Elastic deformation -Plastic deformation -Fracture Fracture 4

Mode of Deformations + Material Characteristic (1)

Fracture F n A F n = Normal force = (Tensile Stress)

force stress cross sectional area Stress stress ( )

force cross sectional area cm x cm =0.0004m 4cm x 4cm =0.

2 Mode of Deformations + Material Characteristic (1) Stress () Elastic deformation Plastic deformation Fracture F n A F n = Normal force = (Tensile Stress) (Compressive Stress) 5 6 Stress:! force stress cross sectional area Stress stress ( ) force cross sectional area shear stress( ) shearing force cross sectional area cm x cm =0.0004m 4cm x 4cm =0.0016m 400N N/m = Pa stress stress stress N m 0.5MPa stress N m 0.5MPa 7 8

() Strain () L - L e L0 L0 L 0 =1, L=1.01 1.01-1 e 1 m 0.01 m?

Initial. Small load 3. Unload Linear 11 Elastic means reversible!

3 () Strain () L - L e L0 L0 L 0 =1, L= e 1 m 0.01 m? %Strain strain x 100% 1% 0 L Tensile test Stress 9 Strain Initial. Small load 3. Unload Linear 11 Elastic means reversible! F F bonds stretch return to initial Linear-elastic Non-Linear-elastic 1

4 1. Initial. Small load 3. Unload bonds stretch & planes shear p lanes still sheared (Proportional Limit), (Elastic Modulus, Young s Modulus) elastic + plastic F plastic *** (Elastic Limit) F Plastic means permanent! linear elastic plastic linear elastic 13 (Proof Stress or Yield Stress) 14 () stress-strain diagram Lower Yield Point Yield Strength (b) (Yield point phenomena)

$35) e L % El f L L 0 100% 0 where L f = gauge length at fracture, L o$

5 (Ductility) 1) (% Reduction Area) % RA A A 0 A 0 f 100% 17 A f = () A o = 18 ) (% elongation) Gauge Length = L 0, v (Poisson s ratio) (Lateral Strain) el v 0.33 ( ) e L % El f L L 0 100% 0 where L f = gauge length at fracture, L o = original gauge length 19 Tensile () + () 0

Resilience : Modulus of Resilience = - U r 1 y y 1 y y y E E Toughness () : - 1 (Hardness test) (Plastic deformation) Indentation ------->Metallurgist Wearing ------->Lubrication Engineer Scratching

6 Resilience : Modulus of Resilience = - U r 1 y y 1 y y y E E Toughness () : - 1 (Hardness test) (Plastic deformation) Indentation >Metallurgist Wearing >Lubrication Engineer Scratching >Mineralogist Cutting >Machinist Flow stress >Design Engineer Static indentation test (Reproducible, Accurate) Rockwell (ASTM E18), Brinell (ASTM E10), Knoop (ASTM E384), Vickers (ASTM E9) Dynamic hardness test Scleroscope (ASTM Practice E 448 standard) Scratch test Mohs, file hardness test 3 4

67) 10-30 sec microscope Load 500, 1000, 1500, 000, 500, 3000 kgf 500 kgf: soft metal Cu, Al alloys 3000 kgf:

7 Brinell, Vicker, Knoops Hardness Number = Rockwell Hardness Number = 130 or 100 m test Brinell Vickers Knoop Rockwell 5 6 Brinell Hardness Testing 5-10 mm Harden steel ball (up to 444 HB) Tungsten carbide ball (444 to 67) sec microscope Load 500, 1000, 1500, 000, 500, 3000 kgf 500 kgf: soft metal Cu, Al alloys 3000 kgf: steel, hard metal (Brinell Principle) HB d HB d HB sec D=10 mm, F=3000 kgf,.0 mm ----> HB = ASTM E10 8

8 9 Vickers/Knoop Microhardness Testing Load < 1000 gf mm < 19 (foil, wire) microscope Vickers microhardness 10 kgf ( Rockwell C) 30 ASTM E384 HK P( kgf ) A( mm ) 14.9P L vickers 1:7 1:1 HV P( kgf ) P A( mm ) d knoop 31 3

Rockwell hardness testing Soft metal to very hard steel 5 10

Standard Test Method for Rockwell Hardness 34 and Rockwell

pp116-19 (Rockwell Principle) *** () 10 Spheroconical

1/8, 1/4, 1/, (in diameter) For soft material 35 Diamond

10kgf Major load = 60, 100, 150 kgf Minor load = 3kgf Major

9 Rockwell hardness testing Soft metal to very hard steel 5 10 (manual, auto) Sensitive to specimen support anvil 33 Standard Test Method for Rockwell Hardness 34 and Rockwell Superficial Hardness of Metallic Materials", ASTM E18-97a, pp (Rockwell Principle) *** () 10 Spheroconical diamond indenter Hard steel, carbide Harden steel ball 1/16, 1/8, 1/4, 1/, (in diameter) For soft material 35 Diamond Steel Ball Rockwell Superficial Rockwell () Minor load = 10kgf Major load = 60, 100, 150 kgf Minor load = 3kgf Major load = 15, 30, 45 kgf + minor load + major load > Rockwell Scale (~30) 36

11 Hardness:Strength Hardness( HB) C y surface treatment! 41 4 Hardness:Strength UTS( MPa) 3.45( HB) () surface treatment! 43 File test 44

Σχετικά έγγραφα

MECHANICAL PROPERTIES OF MATERIALS

MECHANICAL PROPERTIES OF MATERIALS! Simple Tension Test! The Stress-Strain Diagram! Stress-Strain Behavior of Ductile and Brittle Materials! Hooke s Law! Strain Energy! Poisson s Ratio! The Shear Stress-Strain