Physics Study ProgramFaculty of Mathematics and Natural SciencesInstitut Teknologi Bandung

FI-1101Fisika Dasar IA

Kuliah 18

ELASTISITAS

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PHYSI S

Materi Hari Ini

Tegangan (stress) Regangan (strain) Modulus Elastisitas

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ElastisitasAdalah cabang dari Fisika yang menjelaskan tentang bagaimana suatu benda berubah bentuk ketika diberikan suatu gaya

Real rigid bodies are elastic we can slightly change their dimensions by pulling, pushing, twisting or compressing them.

Stress: Deforming force per unit areaStrain: Unit deformation

Tensile stress: associated with stretching

Shearing stress Hydraulic stress

Stress = Elasticity Modulus x Strain

Elastic modulus: describes the elastic behavior (deformations) of objects

as they respond to forces that act on them

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(1) Stress = cte x Strain Recovers original dimensions when stress removed.

(2) Stress > yield strength Sy specimen becomes permanently deformed.

(3) Stress > ultimate strength Su specimen breaks.

Tension and compression:

A

FStress

L

LStrain

( F= force applied perpendicular to the area A of the object)

( fractional change in length of the specimen)

Stress = (Young’s modulus) x StrainL

LE

A

F

Shearing:

A

FStress ( F= force in the plane of the area A)

L

xStrain

( fractional change in length of the specimen)

Units of Young modulus: F/m2

L

xG

A

F

Stress = (Shear modulus) x Strain

Hydraulic stress:

A

FppressureFluidStress

V

VStrain

Hydraulic Stress = (Bulk modulus) x Hydraulic compression

V

VBp

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Young’s Modulus Everything is a

spring…

LF Y A

L

…until it breaks!

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Shear Modulus0

XF S A

L

Shear moduli and Young moduli are comparable in magnitude for most materials

(Liquids have zero shear modulus)

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Pressure and Bulk Modulus Pressure is defined as force per

unit area Unit of pressure is N/m2 = Pascal (Pa) Atmospheric pressure ~ 105 Pa=

15psi 1 psi = 1 pound per square inch Bulk modulus B relates

fractional volume change to pressure change

0

VP B

V

FP

A

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Stress, Strain and Hooke’s law

F/A or pressure are known as “stress”

Fractional changes in length or volume are known as “strain”

Above relations between stress and strain account for “elastic” behavior and Hooke’s law

0

VP B

V

0

/X

F A SL

/

LF A Y

L

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PHYSI S

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