MODULE 3 - Universiti Teknologi taminmn/pdf-files/SME4133_Module_3_Aspects_آ  SME 4133 Failure of...

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Transcript of MODULE 3 - Universiti Teknologi taminmn/pdf-files/SME4133_Module_3_Aspects_آ  SME 4133 Failure of...

  • 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

  • SME 4133 Failure of Engineering Components and Structures

    FAILURE OF MATERIALS

    Modes of failure Mechanical properties and behavior Failure (yield) theories Factor of safety

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 2

    Factor of safety Overview of fracture mechanics

    Stress states at crack tip Stress intensity factor Fracture toughness Ductile-to-brittle transition behavior

  • SME 4133 Failure of Engineering Components and Structures

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

    Fracture Separation of a component into two or more parts.

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 3

    Separation of a component into two or more parts.

  • SME 4133 Failure of Engineering Components and Structures

    Modes of Failure

    • Gross Yielding

    • Fatigue Fracture

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 4

    • Fatigue Fracture

    • Creep Rupture

    • Buckling

    • Static Delayed Fracture

  • 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, UTM 5

    Specimen

    Load cell

    Specimen grips

    Crosshead

    Data acquisition system

    Extensometer

  • SME 4133 Failure of Engineering Components and Structures

    T eg

    as an

    ( M

    P a)

    600

    Properties Values

    σy0.2% (MPa) 429

    σu (MPa) 604

    Mechanical Properties and Behavior

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 6

    Terikan

    0.0 0.1 0.2 0.3 0.4 0.5

    T eg

    as an

    ( M

    P a)

    0

    200

    400

    Ujikaji A Ujikaji B

    Stress-strain curves for Type 316 SS

    σu (MPa) 604

    E (GPa ) 208

    n 0.0935

    K ( MPa ) 682.65

    r2 0.9857

  • SME 4133 Failure of Engineering Components and Structures

    Mechanical Properties of Some Materials

    MATERIALS E GPa (106psi)

    So MPa(ksi)

    SU MPa(ksi)

    AISI 1040 steel

    207 (30)

    413 (60)

    620 (90)

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 7

    steel (30) (60) (90)

    Stainless Steel 314

    193 (28)

    205 (30)

    515 (75)

    7075 Al alloy

    72 (10.5)

    105 (15)

    230 (33)

    Gray cast iron - - 152 (22)

  • 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, UTM 8

    in an identical material during a tensile test.

    f(σ) =κ

    Other parameters:

    Strain

    Energy

    Specific stress component (shear stress, maximum principal stress)

  • SME 4133 Failure of Engineering Components and Structures

    Theory of Failure Maximum-distortion-energy theory

    22 221

    2 1 Yσσσσσ =+−

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 9

    ( ) ( ) ( ) 2213232221 2 Yσσσσσσσ =−+−+−

  • SME 4133 Failure of Engineering Components and Structures

    Theory of Failure

    Maximum-normal-stress theory

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 10

    ult

    ult

    σσ

    σσ

    =

    =

    2

    1

  • SME 4133 Failure of Engineering Components and Structures

    Factor of Safety

    allow

    fail

    F

    F SF =..

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 11

    Ffail is determined from experimental testing of the material

    Fallow is the allowable or working load

    F.S. ≥ 1.0 to avoid failure

    allowF

  • SME 4133 Failure of Engineering Components and Structures

    Fracture Mechanics - Overview

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 12

    WWII Liberty Ships

    Photo by Neil Boenzi, The New York Times.

  • 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, UTM 13

    within the body.

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

    Fracture Mechanics

  • SME 4133 Failure of Engineering Components and Structures

    Scope of Fracture Mechanics

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 14

  • 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, UTM 15

    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.

  • SME 4133 Failure of Engineering Components and Structures

    Basic Loading of Cracked Bodies

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 16

  • 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, UTM 17

    ( )θ π

    σ yy I

    yy f r

    k

    2 =

  • SME 4133 Failure of Engineering Components and Structures

    Crack-tip Stress

    Stress magnitude at the crack tip approaches

    ( )θ π

    σ yy I

    yy f r

    k

    2 =

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 18

    crack tip approaches (mathematically) an infinite value

  • 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, UTM 19

    2

    2

    2

    2 *

    22 yield

    a

    yield

    I p

    k r

    σ

    σ

    πσ ==

  • 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, UTM 20

    2a

    Crack

    τxy

    σxy

    θr

    σ

    β (or Y) – geometry factor

    aK I βσ=

  • SME 4133 Failure of Engineering Components and Structures

    SIF – Finite Width Correction

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 21

    For 2a

  • 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, UTM 22

    2a2a aa

    K = σ πa K = 1.1σ πa

    units of K :

    MPa m

    or ksi in

    Adapted from Fig. 8.8, Callister 6e.

  • SME 4133 Failure of Engineering Components and Structures

    Stress Intensity Factor

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 23

  • SME 4133 Failure of Engineering Components and Structures

    Stress Intensity Factor

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 24

  • SME 4133 Failure of Engineering Components and Structures

    Graphite/ Ceramics/ Semicond

    Metals/ Alloys

    Composites/ fibersPolymers

    Mg alloys Al alloys

    Ti alloys

    Steels

    30

    C-C(|| fibers)1

    40 50 60 70

    100

    Fracture toughness represents the resistance of materials to resist cracking.

    Fracture Toughness of Some Materials

    ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM 25

    5

    K Ic (M

    P a ·

    m 0 .5 )

    1

    Mg alloys

    Si crystal Glass-soda

    Concrete

    Si carbide

    PC

    Glass6

    0.5

    0.7

    2

    4

    3

    10

    20

    30

    Diamond

    PVC

    PP

    Polyester

    PS

    PET

    0.6

    6 7

    Al oxide Si nitride

    C/C( fibers)1

    Al/Al oxide(sf)2

    Al oxid/SiC(w)3

    Al oxid/ZrO2(p)4 Si 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.

  • SME 4133 Failure of Engineering Components and Structures

    Fracture Toughness of Some Materials

    MATERIALS KIC MPa√m

    Alu