module 3 - universiti teknologi malaysiataminmn/pdf-files/sme4133_module_3_aspects_… · sme 4133...
TRANSCRIPT
SME 4133 Failure of Engineering Components and Structures
MODULE 3
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM1
MODULE 3
ASPECTS OF MATERIALS FAILURE
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
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.
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
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
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
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)
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)
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 =−+−+−
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
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
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.
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
SME 4133 Failure of Engineering Components and Structures
Scope of Fracture Mechanics
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM14
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.
SME 4133 Failure of Engineering Components and Structures
Basic Loading of Cracked Bodies
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM16
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=
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
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==
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=
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=
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.
SME 4133 Failure of Engineering Components and Structures
Stress Intensity Factor
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM23
SME 4133 Failure of Engineering Components and Structures
Stress Intensity Factor
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM24
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.
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
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
≥
≥
SME 4133 Failure of Engineering Components and Structures
Impact Test
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM28
(Charpy)
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)
SME 4133 Failure of Engineering Components and Structures
Fracture Surfaces of Impact Test Specimens
ASPECTS OF MATERIALS FAILURE M.N. Tamin, UTM30
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.