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SME 4133 Failure of Engineering Components and Structures MODULE 3 ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 1 MODULE 3 ASPECTS OF MATERIALS FAILURE

Transcript of MODULE 3 - Universiti Teknologi Malaysiataminmn/pdf-files/SME4133_Module_3_Aspects_… · SME 4133...

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SME 4133 Failure of Engineering Components and Structures

MODULE 3

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM1

MODULE 3

ASPECTS OF MATERIALS FAILURE

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SME 4133 Failure of Engineering Components and Structures

FAILURE OF MATERIALS

Modes of failureMechanical properties and behaviorFailure (yield) theoriesFactor of safety

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM2

Factor of safetyOverview of fracture mechanics

Stress states at crack tipStress intensity factorFracture toughnessDuctile-to-brittle transition behavior

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SME 4133 Failure of Engineering Components and Structures

Failure Versus FractureFailureInability of a component to perform according to its intended function.

FractureSeparation of a component into two or more parts.

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM3

Separation of a component into two or more parts.

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SME 4133 Failure of Engineering Components and Structures

Modes of Failure

• Gross Yielding

• Fatigue Fracture

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM4

• Fatigue Fracture

• Creep Rupture

• Buckling

• Static Delayed Fracture

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SME 4133 Failure of Engineering Components and Structures

Fracture of a Specimen in a Tension Test

Load cell

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM5

Specimen

Load cell

Specimen grips

Crosshead

Data acquisition system

Extensometer

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SME 4133 Failure of Engineering Components and Structures

Teg

asan

( M

Pa)

600

Properties Values

σy0.2% (MPa) 429

σu (MPa) 604

Mechanical Properties and Behavior

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM6

Terikan

0.0 0.1 0.2 0.3 0.4 0.5

Teg

asan

( M

Pa)

0

200

400

Ujikaji AUjikaji B

Stress-strain curves for Type 316 SS

σu (MPa) 604

E (GPa ) 208

n 0.0935

K ( MPa ) 682.65

r2 0.9857

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SME 4133 Failure of Engineering Components and Structures

Mechanical Properties of Some Materials

MATERIALS E GPa (106psi)

So

MPa(ksi)SU

MPa(ksi)

AISI 1040steel

207(30)

413(60)

620(90)

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM7

steel (30) (60) (90)

Stainless Steel 314

193(28)

205(30)

515(75)

7075Al alloy

72(10.5)

105(15)

230(33)

Gray cast iron - - 152(22)

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SME 4133 Failure of Engineering Components and Structures

Yield Criterion

The material of a component subjected to complex loading will start yielding when the (parametric stress) reaches the (characteristic stress)in an identical material during a tensile test.

Theory of Failure

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM8

in an identical material during a tensile test.

f(σ) =κ

Other parameters:

Strain

Energy

Specific stress component (shear stress, maximum principal stress)

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SME 4133 Failure of Engineering Components and Structures

Theory of Failure Maximum-distortion-energy theory

22221

21 Yσσσσσ =+−

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM9

( ) ( ) ( ) 2213

232

221 2 Yσσσσσσσ =−+−+−

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SME 4133 Failure of Engineering Components and Structures

Theory of Failure

Maximum-normal-stress theory

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM10

ult

ult

σσ

σσ

=

=

2

1

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SME 4133 Failure of Engineering Components and Structures

Factor of Safety

allow

fail

F

FSF =..

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM11

Ffail is determined from experimental testing of the material

Fallow is the allowable or working load

F.S. ≥ 1.0 to avoid failure

allowF

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SME 4133 Failure of Engineering Components and Structures

Fracture Mechanics - Overview

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM12

WWII Liberty Ships

Photo by Neil Boenzi, The New York Times.

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SME 4133 Failure of Engineering Components and Structures

A branch of mechanics that studies the relationships between external loads applied to a deformable body and the intensity of internal forces acting within the body.

Mechanics of Materials

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM13

within the body.

The mechanics that describes the response of materials to loading in the presence of crack or crack-like defects.

Fracture Mechanics

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SME 4133 Failure of Engineering Components and Structures

Scope of Fracture Mechanics

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM14

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SME 4133 Failure of Engineering Components and Structures

Linear Elastic Fracture Mechanics (LEFM)

q Fracture mechanics within the confines of the theory of linear elasticity.

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM15

q Analytical procedure that relates the stress magnitude and distribution in the neighborhood of a crack to:§ the nominal applied stress§ crack geometry (size, shape) and orientation§ material properties

q An underlying principle is that unstable fracture occurs when the stress-intensity factor at the crack tip reaches a critical value.

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SME 4133 Failure of Engineering Components and Structures

Basic Loading of Cracked Bodies

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM16

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SME 4133 Failure of Engineering Components and Structures

Stress Field Ahead of Crack Tip

Complex state of stress exists in the vicinity of a crack tip

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM17

( )θπ

σ yyI

yy fr

k

2=

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SME 4133 Failure of Engineering Components and Structures

Crack-tip Stress

Stress magnitude at the crack tip approaches

( )θπ

σ yyI

yy fr

k

2=

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM18

crack tip approaches (mathematically) an infinite value

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SME 4133 Failure of Engineering Components and Structures

Crack-tip Plasticity

There is always a plastic zone at the crack tip

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM19

2

2

2

2*

22 yield

a

yield

Ip

kr

σ

σ

πσ==

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SME 4133 Failure of Engineering Components and Structures

The stress intensity factor, KI describes the crack tip stresses.σyy

σ

Stress Intensity Factor

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM20

2a

Crack

τxy

σxy

θr

σ

β (or Y) – geometry factor

aK I βσ=

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SME 4133 Failure of Engineering Components and Structures

SIF – Finite Width Correction

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM21

For 2a<<W,

aK I πσ=

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SME 4133 Failure of Engineering Components and Structures

Values of KI for different loading conditions and geometries

σ σ

units of K :

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM22

2a2a aa

K = σ πa K = 1.1σ πa

units of K :

MPa m

or ksi in

Adapted from Fig. 8.8, Callister 6e.

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SME 4133 Failure of Engineering Components and Structures

Stress Intensity Factor

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM23

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SME 4133 Failure of Engineering Components and Structures

Stress Intensity Factor

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM24

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SME 4133 Failure of Engineering Components and Structures

Graphite/ Ceramics/ Semicond

Metals/ Alloys

Composites/ fibersPolymers

Mg alloysAl alloys

Ti alloys

Steels

30

C-C(|| fibers)1

40506070

100

Fracture toughness represents the resistance of materials to resist cracking.

Fracture Toughness of Some Materials

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM25

5

KIc(M

Pa ·

m0.5)

1

Mg alloys

Si crystalGlass-soda

Concrete

Si carbide

PC

Glass6

0.5

0.7

2

4

3

10

20

30

<100>

<111>

Diamond

PVC

PP

Polyester

PS

PET

0.6

67

Al oxideSi nitride

C/C( fibers)1

Al/Al oxide(sf)2

Al oxid/SiC(w)3

Al oxid/ZrO2(p)4Si nitr/SiC(w)5

Glass/SiC(w)6

Y2O3/ZrO2(p)4

Based on data in Table B5,Callister 6e.

materials to resist cracking.

Fracture toughness values are determined from fracture toughness tests.

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SME 4133 Failure of Engineering Components and Structures

Fracture Toughness of Some Materials

MATERIALS KIC

MPa√m

Aluminum2024 26

SY

(MPa)

455

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM26

202470757178

262435

SteelBS 816M40BS816 M40BS 535 A99

996014

TitaniumIMI 318IMI 318

11555

455495490

86015152070

9101035

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SME 4133 Failure of Engineering Components and Structures

Condition for Fracture

σ

Fracture occurs when the applied stress intensity factor, KI reaches the value of the fracture toughness, KIC of the material

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM27

σ

aa

K = 1.1σ πa

IC

ICI

KπaYσ

KK

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SME 4133 Failure of Engineering Components and Structures

Impact Test

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM28

(Charpy)

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SME 4133 Failure of Engineering Components and Structures

Impact Energies of Some Materials

MATERIALS Impact energyJ (ft-lb)

AISI 1040 48.8

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM29

AISI 1040steel

48.8(36)

Gray cast iron (class 20)

20(15)

Ti-6Al-4V 22(16)

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SME 4133 Failure of Engineering Components and Structures

Fracture Surfaces of Impact Test Specimens

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM30

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SME 4133 Failure of Engineering Components and Structures

Ductile-to-Brittle Tansition (DBT) Temperature, TDBT

Ene

rgy

abso

rbed

BCC

FCC

ductile Transition Temperature (ASTM specification)

The temperature at which

ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM31

TDBT

Ene

rgy

abso

rbed

Temperature

FCC

Brittle

specimens show a fracture of 50 pct. shear and 50 pct. cleavage.

Nil-ductility temperature (NDT)

The ref. point in the transition range giving the limiting condition of temperature-stress combination under which catastrophic fracture can occur.