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Karakterisasi Material (S2) ENMT802007 SIFAT MEKANIK (REVIEW) (Mechanical Properties)

Prof. Dr. Ir. Anne Zulfia, M.Sc.

Departemen Metalurgi & Material Fakultas Teknik Universitas Indonesia

Mechanical Properties of Engineering Materials Strength Tension, compression, shear, and Flexure Static, impact, and endurance Stiffness Elasticity/Plasticity Ductility/Brittleness Hardness & Wear resistance Creep & Fatigue

Plastic (Permanent) Deformation (at lower temperatures, i.e. T < Tmelt/3)

• Simple tension test: Elastic+Plastic at larger stress

engineering stress, s

Elastic initially permanent (plastic) after load is removed

ep

engineering strain, e plastic strain

When force becomes larger, atoms become sliding past each other. It is called slip.

Yield Strength, sy • Stress at which noticeable plastic deformation has occurred. when e = 0.002 tensile stress, s

sy

p

sy = yield strength Note: for 2 inch sample e = 0.002 = z/z  z = 0.004 in

engineering strain, e

ep = 0.002

Adapted from Fig. 6.10 (a), Callister 7e.

See figure 6.10 and page 144 for more definitions!

Yield Strength: Comparison Metals/ Alloys

Graphite/ Ceramics/ Semicond

Polymers

Composites/ fibers

2000

200

Al (6061) ag Steel (1020) hr Ti (pure) a Ta (pure) Cu (71500) hr

100 70 60 50 40

Al (6061) a

30 20

10

Tin (pure)

¨

dry

PC Nylon 6,6 PET PVC humid PP HDPE

LDPE

Hard to measure,

300

in ceramic matrix and epoxy matrix composites, since in tension, fracture usually occurs before yield.

700 600 500 400

Ti (5Al-2.5Sn) a W (pure) Cu (71500) cw Mo (pure) Steel (4140) a Steel (1020) cd

since in tension, fracture usually occurs before yield.

1000

Hard to measure ,

Yield strength, sy (MPa)

Steel (4140) qt

Room T values Based on data in Table B4, Callister 7e. a = annealed hr = hot rolled ag = aged cd = cold drawn cw = cold worked qt = quenched & tempered

Tensile Strength, TS • Maximum stress on engineering stress-strain curve. Adapted from Fig. 6.11, Callister 7e.

TS

F = fracture or ultimate strength

engineering stress

sy

Typical response of a metal

Neck – acts as stress concentrator

strain engineering strain • Metals: occurs when noticeable necking starts. • Polymers: occurs when polymer backbone chains are aligned and about to break.

Tensile Strength: Comparison Metals/ Alloys

Tensile strength, TS (MPa)

5000 3000 2000 1000

300 200 100 40 30

Graphite/ Ceramics/ Semicond

Polymers

C fibers Aramid fib E-glass fib

Steel (4140) qt AFRE(|| fiber) GFRE(|| fiber) CFRE(|| fiber)

Diamond W (pure) Ti (5Al-2.5Sn)aa Steel (4140)cw Si nitride Cu (71500) Cu (71500) hr Al oxide Steel (1020) ag Al (6061) a Ti (pure) Ta (pure) Al (6061) a Si crystal <100>

Glass-soda Concrete

Room Temp. values Nylon 6,6 PC PET PVC PP HDPE

20

Composites/ fibers

Graphite

wood(|| fiber) GFRE( fiber) CFRE( fiber) AFRE( fiber)

LDPE

10

wood (

1

fiber)

Based on data in Table B4, Callister 7e. a = annealed hr = hot rolled ag = aged cd = cold drawn cw = cold worked qt = quenched & tempered AFRE, GFRE, & CFRE = aramid, glass, & carbon fiber-reinforced epoxy composites, with 60 vol% fibers.

Ductility • Plastic tensile strain at failure:

Lf - Lo x 100 %EL = Lo

smaller %EL

Engineering tensile stress, s

larger %EL

Lo

Ao

Af

Adapted from Fig. 6.13, Callister 7e.

Engineering tensile strain, e

• Another ductility measure:

Ao - Af %RA = x 100 Ao

Engineer needs to know ductility to prepare for maximum amount of deformation and prevent from sudden failure.

Lf

Selective Mechanical Properties of Metals

These properties are sensitive to any prior deformation, the presence of impurities, and heat treatment. Only modulus of elasticity is intrinsic characteristic.

Temperature Effect of Ductility High temperature promotes atomic movements. Material softens and becomes ductile. Low temperature freezes atoms in their own positions and material becomes brittle.

Resilience, Ur • Ability of a material to store energy – Energy stored best in elastic region

Ur = 

ey

0

sde

If we assume a linear stress-strain curve this simplifies to

1 Ur @ sy e y 2

nt/m2 • m/m = nt • m /m3 = J/m3

Toughness • Energy to break a unit volume of material • Approximate by the area under the stress-strain curve. Engineering tensile stress, s

small toughness (ceramics) large toughness (metals) very small toughness (unreinforced polymers)

Adapted from Fig. 6.13, Callister 7e.

Engineering tensile strain, Brittle fracture: elastic energy Ductile fracture: elastic + plastic energy

e

nt/m2 • m/m = nt • m /m3 = J/m3

True Stress and Strain It seems to suggest that the sample is weakening after M but in reality necking takes place after M and the effective cross section area is reduced significantly. So taking this into account, the stress level continues rising up till fracture.

TS F = fracture or ultimate strength

engineering stress

sy

Typical response of a metal

strain engineering strain

Neck – acts as stress concentrator

True Stress & Strain Note: S.A. changes when sample stretched

• True stress • True Strain

sT = F Ai

eT = ln i  o 

sT = s1  e  eT = ln1  e 

Adapted from Fig. 6.16, Callister 7e.

Elastic Strain Recovery

Adapted from Fig. 6.17, Callister 7e.

Indentation Hardness Testing of Metals • Brinell Hardness Test (ASTM E 10) Commonly used. • Rockwell Hardness Test (ASTM E 18) Commonly used. Indentor and loads are smaller than with the Brinell test. • Vickers Hardness Test (ASTM E 92) Similar to Rockwell. Uses a squarebased diamond pyramid for the indentor. • Knoop (Tukon) Hardness Test - used for very thin and/or very small specimens.

Hardness • Resistance to permanently indenting the surface. • Large hardness means: --resistance to plastic deformation or cracking in compression. --better wear properties. apply known force

measure size of indent after removing load

e.g., 10 mm sphere

D most plastics

brasses Al alloys

Smaller indents mean larger hardness.

d easy to machine steels file hard

cutting tools

increasing hardness

nitrided steels

diamond

Hardness Test Method and Their Formula

Hardness: Measurement • Rockwell – No major sample damage – Each scale runs to 130 but only useful in range 20-100. – Minor load 10 kg – Major load 60 (A), 100 (B) & 150 (C) kg • A = diamond, B = 1/16 in. ball, C = diamond

• HB = Brinell Hardness – TS (psia) = 500 x HB – TS (MPa) = 3.45 x HB

Brinell Hardness • A Load applied to a 10mm diameter ball. • Measure diameter of the indentation to the nearest 0.02 mm under a microscope. • Compute the Brinell Hardness Number (Bhn)

– D = diameter of ball (mm) D = 10mm – d = diameter of indentation (mm) – P = applied load (units = kg) Load mass P Bhn = = indented area D D - D - d 2 2

2



Indentation of Brinell

Material

Brinell Hardness

Pure Aluminum

15

Pure Copper

35

Mild Steel

120

304 Stainless Steel

250

Hardened Tool Steel

650/700

Hard Chromium Plate

1000

Chromium Carbide

1200

Tungsten Carbide

1400

Titanium Carbide

2400

Diamond

8000

Sand

1000

Vickers Hardness Test • In general, vickers method is similar to Brinell method, but their difference is the type of indenter. • Indenter : Pyramid diamond - 136o • The Indented shape : cubic, measured by optical microscope

-d= - d

d1 + d2 2 = 0,375 D

Vickers Hardness Vickers Indenter

vickers hardness Equipment

Indented Shape (see by optical microscope)

Vickers Hardness (ASTM E 92) The formula :

VHN =

1,8544 P d2

P = Load (kg) 1-120 kg d = Length of diagonal (mm)

Rockwell Hardness (ASTM E 18)  Invented by S.P Rockwell in 1922  Indenter :

 Rockwell C using a Diamond - 120o  Rockwell B using a Hardened Steel Ball

 It is easy to perform and the hardness number is obtained directly from the testing machine.  The test consists of applying a minor load of 10 kg to seat the indenter and then applying a major load (typically 100 kg) to create a permanent depression beyond that caused by the minor load.  The hardness number, which is read directly from a dial or digital scale on the testing machine, is inversely related to the additional penetration caused by application of the major load

Aplication for several Materials Scale Symbol

Indenter

Major Load, kgf

Dial Figure

Typical Applications

A

Diamond

60

Black

Cemented carbides, thin steel, and shallow case-hardened steel

B

1/16" ball

100

Red

Copper alloys, soft steels, aluminum alloys, malleable iron

C

Diamond

150

Black

Steel, hard cast irons, pearlitic malleable iron, titanium, deep case-hardened steel, and other materials harder than HRB 100

D

Diamond

100

Black

Thin steel and medium case-hardened steel and pearlitic malleable iron

E

1/8" ball

100

Red

Cast iron, aluminum and magnesium alloys, bearing metals

F

1/16" ball

60

Red

Annealed copper alloys, thin soft sheet metals

G

1/16" ball

150

Red

Phosphor bronze, beryllium copper, malleable irons. Upper limit is HRG 92, to avoid possible flattening of ball.

H

1/8" ball

60

Red

Aluminum, zinc, lead

K

1/8" ball

150

Red

L

1/4" ball

60

Red

M

1/4" ball

100

Red

P

1/4" ball

150

Red

R

1/2" ball

60

Red

S

1/2" ball

100

Red

Bearing metals and other very soft or thin materials. Use smallest ball and heaviest load that do not give anvil effect.

Setting for Rod Specimen

Kekerasan Knoop  One of MCRO HARDNESS method for small and thin materials  The hardness value provides by pressing a diamond into the material to be tested under an applied force.  The results of Indentation is between 0.01mm 0.1mm  The load applied to te material surface is 5 gr to 5 Kg.  The surface must be prepared to be metallographic samples.

Knoop Indentation

Relationship of Hardness to Tensile Strength of Materials UTS = 500 BHN (pound/in2) UTS = 500 BHN (MPa) UTS = Ultimate tensile Stress HB = Hardness of Brinell

Hardness is proportional to the tensile strength – but note that the proportionality constant is different for different materials.

ASTM STANDARD

Document Number

Document Title

E10

Standard Test Method for Brinell Hardness of Metallic Materials

E18

Standard Test Methods for Rockwell Hardness of Metallic Materials

D785

Standard Test Method for Rockwell Hardness of Plastics

BRINELL TEST for WELDED MATERIALS Testing Machine

Specimen

Design or Safety Factors • Design uncertainties mean we do not push the limit. • Factor of safety, N Often N is

sworking =

sy

between 1.2 and 4

N

• Example: Calculate a diameter, d, to ensure that yield does not occur in the 1045 carbon steel rod below. Use a factor of safety of 5.

sworking = 220,000N  d2 / 4





5

sy N

1045 plain carbon steel: sy = 310 MPa TS = 565 MPa

d = 0.067 m = 6.7 cm

F = 220,000N

d Lo

Perlakuan Panas Untuk Industri Komponen Otomotif, 7 - 12 Mei 2007

44

46

Summary • Stress and strain: These are size-independent measures of load and displacement, respectively. • Elastic behavior: This reversible behavior often shows a linear relation between stress and strain. To minimize deformation, select a material with a large elastic modulus (E or G). • Plastic behavior: This permanent deformation behavior occurs when the tensile (or compressive) uniaxial stress reaches sy. • Toughness: The energy needed to break a unit volume of material. • Ductility: The plastic strain at failure.