ENGINEERING MATERIALS AND TEIR PROPERTIES

DISUSUN OLEH:FITRI HANDAYANI (0804102010003)ANDRIANSYAH (0804102010025)

JURUSAN TEKNIK MESINFAKULTAS TEKNIK

UNIVERSITAS SYIAH KUALA2010

INTRODUCTIONa) Material boleh dikatakan sebagai makanan dari

design.b) Suksesnya produk dilihat dari: tampilan yang baik yaitu memiliki nilai uang dan

memberikan kepuasan kepada si pengguna menggunakan material terbaik untuk pekerjaan

tersebut dengan memanfaatkan sepenuhnya potensi dan karakterstik yang ada.

a) Material yang kita cari adalah material yang ciri dan sifat tertentu.

b) Material yang bagus adalah material yang telah kita ketahui moduli, strength , damping capacities, konduktivitas listrik dan thermal.

The Families of Engineering Material

composites, sandwichses

Hybridssegmented structures,

lattices weaves

Steels, Cast Irons, Al-

alloysMetals

Cu-alloys, Zn-alloys, Ti-

alloysPP, PE, PC,

PS, PA, PMMK

PlasticsPhenolics, Expoxies

Isoprene, Neoprene,

Butyl rubberElastomersNatural rubberSilicons EVA

Soda glass, borosillicate

glass.Glasses

Silica glasses,Glass-

ceramics

Aluminas,Silicon

CeramiccarbidasZirconia

The Material Properties General properties : 1) Densitas 2) Harga Mechanical properties : 1) ultimate strength2) Compressive strength2) Failure strength3) Hardness 4) Fatique endurance limit5) Thoughness6) Damping capacity

Stre

ss

σ =

F/A

o

M eta ls

σ u

σy Ao F

L

Slope E = σ /ε

0.2% offset

Strain ε = δ L /L

Stre

ss σ

= F

/Ao

X Brittle: T << Tg

Polymers

Limited plasticity: T = 0.8 Tg

Ao F

σy Cold drawing: T = TgLViscous flow: T >> Tg

1% strainStrai ε = δL/L

Polymers

Thermal properties:1) melting point2) Glass temperatur3) Maximum service4) Minimum service5) Specific heat6) Thermal conduktivity7) Thermal expansion coefficient8) Thermal shock resistance Electrical properties:1) Electrical resistivity2) Diaelectric constant3) Breakdownpotential4) Power factor Optical properties: optical,

transfarent, translucent, opaque, Referactive index.

E-co properties: energy/kg to extract material, CO2 /kg to extract material.

Environmental resistance properties: Corrotion rates, Oxidation rates, wear rate constant.

Mechanical Properties

Ao F  

Tension Strain ε = δL/L

σf (compression) Ceramics

Stre

ss σ

= F

/Ao

Compression

Slope E = σ/ε Lσt (tension)

Kekuatan pada keramik dan glass bergantung dengan kekuatan pada bentuk pembebanan. Intension, ‘‘strength’’ berarti kekuatan sebelum patah, tIn compression itu maksudnya the crushing strength c, yang memiliki daerah yang lebih luas dengan tipe tersendiri.

Stre

ss a

mpl

itude

∆σ

Endurance limit

σ u

Ao ∆F

L

Endurance limit

∆ σ e

107 cycles

The endurance limit, e, is the cyclic stress that causes failure in Nf ¼ 107 cycles. 

Hardness is measured as the load P divided by the projected area of contact, A, when a diamond-shaped indenter is forced into the surface.

Stre

ss σ

= F

/Ao

Fracture toughness

σ c

2c

K1C = σ c(π a ) 1/2

The fracture toughness, KIC, measures the resistance to the propagation of a crack.The failure strength of a brittle solid containing a crack of length 2c is KIC ¼ Y ð ,where Y is a constant near unity.

=

F/A

o

Loss coefficient Area

∆U A ∆F

Area U The loss-coefficient, (a

dimensionless quantity), measures the degree to which a material dissipates vibrational energy (Figure 3.9). If a material is loaded elastically to a stress, max, it stores an elastic energy per unit volume. If it is loaded and then unloaded, it dissipates an energy

I U ¼ d"

 

Hea

t fl

ux

q

Thermal conductivity T T2

X

Heat input q W/m2

Heat sink

q W/m2

nsulation Sample Slope λ

q = − λ ∆T ∆X

Thermal PropertiesTwo temperatures, the melting temperature, Tm, and the glass temperature, Tg (units for both: K or C) are fundamental because they relate directly to the strength of the bonds in the solid. Crystalline solids have a sharp melting point, Tm. Non-crystalline solids do not; the temperature Tg characterizes the transition from true solid to very viscous liquid. It is helpful, in engineering  design, to define two further temperatures: the maximum and minimum service temperatures Tmax and Tmin (both: K or C). Temperature gradient (T1 T2)/X

The

rmal st

rain

ε =

δL/

L

Thermal expansion

Slope α α =

1 ∆L L ∆T

L

∆L α

Insulation Heater Sample

Thermal ExpansionThe thermal strain per degree of temperature change is measured by the linear thermal- expansion coefficient, (units: K 1 or, more conveniently, as ‘‘microstrain/C’’ or 10 6 C 1). If the material is thermally isotropic, the volume expansion, per degree, is 3 . If it is anisotropic, two or more coefficients are required, and the volume expansion becomes the sum of the principal thermal strains.The thermal shock resistance Ts (units: K or C) is the maximum tem- perature difference through which a material can be quenched suddenly without damage. It, and the creep resistance, are important in high- temperature design.

Temperature change ∆T

Electrical Properties

The electrical conductivity is simply the reciprocal of the resisitivity. When an insulator is placed in an electric field, it becomes polarized and charges appear on its surfaces that tend to screen the interior from the electric field. The tendency to polarize is measured by the dielectric constant, Ed (a dimensionless quantity). Its value for free space and, for practical purposes, for most gasses, is 1. Most insulators have values between 2 and 30, though low-density foams approach the value 1 because they are largely air.

Pot

entia

l dif

fere

nce

∆V

Electrical resistivity

∆V

ι ι

Resistance

X

Resistivity

Area A

R = ∆V/ι ∆V A ρe =

X ι Current ι

Optical PropertiesAll materials allow some passage of

light, although for metals it is exceed- ingly small. The speed of light when in the material, v, is always less than that in vacuum, c. A consequence is that a beam of light striking the surface of such a material at an angle , the angle of incidence, enters the material at an angle , the angle of refraction.

Eco - PropertiesThe contained or production energy (units

MJ/kg) is the energy required to extract 1 kg of a material from its ores and feedstocks. The associated CO2 production (units: kg/kg) is the mass of carbon dioxide released into the atmosphere during the production of 1 kg of material.

Environmental Properties3.4 Summary and conclusions 43

Wea

r vo

lum

e V

Wear rate

P3 P2 P1

Load P

W = V/S Sliding velocity v

Environmental resistance is conventionally characterized on a discrete5-point scale: very good, good, average, poor, very poor. ‘‘Very good’’ meansthat the material is highly resistant to the environment, ‘‘very poor’’ that it is completely non-resistant or unstable. The categorization is designed to help with initial screening; supporting information should always be sought if environmental attack is a concern. Ways of doing this are described later.

Summary There are six important families of materials for

mechanical design: metals, ceramics, glasses, polymers, elastomers, and hybrids that combine the properties of two or more of the others.

Within a family there is certain common ground: ceramics as a family are hard, brittle, and corrosion resistant; metals are ductile, tough, and good thermal and electrical conductors; polymers are light, easily shaped, and electrical insulators, and so on — that is what makes the classification useful.

In design we wish to escape from the constraints of family, and think, instead, of the material name as an identifier for a certain property-profile

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