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TRANSCRIPT
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Fractography
George F. Vander Voort, Consultant
Principal Engineer
P.O. Box 10
Wadsworth, IL 60083-0010
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Fracture Modes
Transgranular: Cracking across grains
without preference for grain boundaries
Intergranular: Cracking between grains, the
crack propagates in the grain boundaries
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Fracture Mechanisms
Ductile
Brittle
Fatigue
Torsion
Stress Corrosion Cracking
Liquid Metal Embrittlement
Hydrogen Embrittlement and HIC
Creep
Wear
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Ductile Fracture in Tension
Top View Side View
Large shear lips, substantial necking down
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Ductile FractureCharpy V Notch Specimen
2% Nital Etch
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Ductile Fracture
Microvoid Coalescence
SEM SEIPH 13-8Mo Stainless Steel Tensile Fracture
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Ductile Fracture: X-750 Rising Load Test
Bright field (left) and dark field (right) light microscope images of a
ductile fracture in an X-750 Ni-base superalloy rising load test fracture.
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Ductile Fracture Popsac Vessel
70 F, Burst at 8500 psi
-50 F, Burst at 9000 psi
7.375 inch diameter, 0.125 inch thick 1030
carbon steel vessel, design strength 4475 psi
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Tensile Fractures Begin Internally
Partially Broken Tensile Specimen
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Brittle Fracture
Brittle fractures suggest that the
design, manufacture or materialsquality were improper for the safe use
of the part.
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Brittle Fracture in Tension
Top View Side View
Small shear lips, no visible necking down
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Brittle FractureCharpy V Notch Specimen
2% Nital
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Brittle FractureCharpy V Notch Specimen
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Cleavage Fracture in Carbon Steel
100 m50 m
Fracture profile of brittle fracture of a carbon steel specimen (nickel
plated, 2% nital etch).
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Cleavage Cracks in Carbon Steel
Cleavage cracks in a carbon steel (nital). Cracks off of the main fracture.
20 m 20 m
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Cleavage Cracks in a Low-Carbon Steel
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Cleavage Cracks in a Low-Carbon Steel
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Direct and Indirect Views of a Brittle Fracture
LOM - Profile LOM - Fracture SEM - Fracture
LOM - Replica SEM - Replica TEM - Replica
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Charpy V-
Notch Series to
Evaluate the
Ductile-to-
BrittleTransition
Temperature
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T il d CVN C f
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Tensile and CVN Curves for
NiCrMoV Forging Grade
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Brittle Fracture of Fe2.2% Si Slab
Brittle fracture of a silicon electrical steel slab during mill handling. The
slab measured 8.5-inch thick x 41-inch wide (21.6-cm x 104-cm).
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Brittle Fracture of Fe2.2% Si Slab
Coarse columnar grain structure of the Fe2.2% Si electrical steel slab,
etched with nital. The rolling direction is vertical.
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CVN Curves for RMS Titanic Plate Steel
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Brittle Fracture of Fe-Al-Cr Ingot
Note that the ingots grain structure can be clearly seen in the fracture pattern.
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Large Brittle Fracture of Steel Part
Fracture was initiated at the stress concentrator (arrow)
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Boyds Model for Chevron Cracks
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Boyds Model for Chevron Crack Growth
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Brittle Fracture of a Railroad Rail
The apex of the chevrons point back to the origin of the fracture
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Ship Steel Drop-Weight Test Fractures
Note transition from ductile to chevron to flat cleavage fracture with
decreasing temperature. Chevrons are most pronounced at50 F (-45 C).
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Cleavage in Fe2.5% Si
Bright field (left) and dark field (right) views by light microscopy of a
brittle cleavage fracture in Fe2.5% Si broken at173 C.
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Cleavage Fracture of Fe-2.5% Si
SEM SEI, 14 mm WD SEM BSEI, 14 mm WD
Same area viewed with the Everhard-Thornley detector;
the backscattered image is easier to interpret
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X-60 Line Pipe Tested 8 F Above DWTT
Full scale line pipe test, loaded to 40% of the yield strength, tested at 56 F, 8
F above the 50% shear area drop-weight tear test transition temperature
(+48 F). A 30-grain charge was detonated beneath an 18-inch notch cut in
the pipe. The crack speed was 279 fps. The crack propagated 33-inch in full
shear and then 18-inch in tearing shear before stopping.
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X-60 Line Pipe Tested 2 F Below DWTT
After a small amount of brittle fracture, the crack became ductile and stopped;
average crack speed was 566 fps.
X 60 Li Pi T t d 10 F B l DWTT
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X-60 Line Pipe Tested 10 F Below DWTT
Fracture was brittle, ending in ductile shear; average crack speed was 1550 fps.
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X-60 Line Pipe Tested 40 F Below DWTT
This line pipe fractured in a wave pattern for a full wave-length by cleavage
with
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SEM 1000x
SEM 1000x
SEM 5000x
SEM 5000x
TEM Replica 5000x
TEM Replica 5000x
Brittle (Top) and Ductile (Bottom) Fractures
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Unusual Intergranular Fracture in Fe-Cr-Al Alloy
LOMBright Field LOMDark Field
SEM SEI
i C
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Unusual Intergranular Fracture in Fe-Cr-Al Alloy
Dark Field LOM SEM SE Image
Two additional views of the unusual stepped intergranular fracture in the
Fe-Cr-Al alloy.
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Intergranular Cracking in Ni-Base Alloy
Bright field (left) and dark field (right) light microscopy images of an
intergranular fracture in a Ni-base superalloy.
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Intergranular Fracture in Ni-Base Alloy
Secondary electron (left) and backscattered electron (E-T) SEM images of the
intergranular fracture in a Ni-base superalloy.
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Fatigue Fractures
Fatigue fractures occur due to repeated
cyclic loading below the static yieldstrength. It is important to determine if
fatigue was high-cycle or low-cycle, as the
remedies for each are different.
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U idi ti l B di F ti i B lt
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Unidirectional Bending Fatigue in Bolt
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Reversed Bending Fatigue
Railroad Coupling Pins
Rotating Torsional Fatig e of 4320 Shaft
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Rotating Torsional Fatigue of 4320 Shaft
Failure started at keyway (B) and ended at Csmall size of final rupture
zone indicates a relatively low load
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Torsional Fatigue Fracture in 51B60
Railroad Spring
1.625 inch diameter spring (arrow points to the origin)
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Fatigue Cracks in Al
Broken specimen, Kellers reagent
Non-broken specimen, Kellers reagent
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Fatigue in Carbon Steel
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Fatigue Crack in Carbon Steel
2% Nital
Fatig e in Carbon Steel
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Fatigue in Carbon Steel
Fatigue crack grown from a notch in a
carbon steel (above and above right, 2%
nital).
F ti C k i C b St l
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Fatigue Crack in Carbon Steel
Ni Plating
2% Nital
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Fatigue Fracture of Carbon Steel
Fatigue fracture in a carbon steel fracture covered with electroless nickel
(nital). Crack moving left to right.
100 m 50 m
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Fatigue Crack in 304 Stainless Steel
Glyceregia, Bright Field
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Fatigue Crack in 304 Stainless Steel
15 HCl10 Acetic10 HNO3; Nomarski DIC
50 m
Fatigue Crack in 304 Stainless Steel
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Fatigue Crack in 304 Stainless Steel
Glyceregia, Bright Field
Fatigue in 316 SS
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100 m
20 m
20 m
Fatigue in 316 SS
Fatigue crack grown from a notch
(above and above right) and the carck
path through the microstructure
(glyceregia).
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Fatigue Crack in 304 Stainless Steel
15 mL HCl10 mL Acetic10 mL HNO3, DIC
Fatigue Crack in 304 Stainless Steel
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Fatigue Crack in 304 Stainless Steel
Left: Glyceregia, Bright Field; Right: 15 mL HCl10 mL Acetic
10 mL HNO3, DIC
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Examples of Striation Patterns
F t f P lit St i ti
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Fracture of Pearlite vs Striations
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Fatigue Fracture: X-750 Rising Load Test
Bright field (left) and dark field (right) light microscopy images of an X-750
Ni-base superalloy fatigue fracture.
F ti F t X 750 Ri i L d T t
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Fatigue Fracture: X-750 Rising Load Test
Secondary electron SEM image of a fatigue pre-cracked surface in an X-750
Ni-base superalloy specimen.
Fatigue Striations in Rising Load Test
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Fatigue Striations in Rising Load Test
Specimen of Ni-Base Superalloy
Fatigue Failure of Rail at FAST
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Fatigue Failure of Rail at FAST
Top View
Side View
Fracture made
in lab to reveal
extent offatigue crack
propagation
Circular Spall in Hardened Steel Roll
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Circular Spall in Hardened Steel Roll
A large inclusion was found at the origin (arrow)
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Line Spall in
Hardened SteelRoll
Section Cut From Failed HSR
Re-Austentized Regions at Spalls
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Re Austentized Regions at Spalls
Frictional heat from fatigue crack growth can re-austenitize regions
(arrow) producing as-quenched martensite upon cooling (3% nital)
Spalled Section of Hardened Steel Roll
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Area A, 5x
Spalled Section of Hardened Steel Roll
Spalled Hardened Steel Roll
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Area B, 10x Area C, 10x
Spalled Hardened Steel Roll
Close-up views of fatigue propagation marks at initiation
site areas B and C on the roll fracture.
Spalled Hardened Steel Roll
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Spalled Hardened Steel Roll
Fatigue propagation marks at initiation site D.
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Examples of Fatigue Pre-Cracked
Charpy V-Notch Specimens ofDifferent Materials Broken at 0 F
Fatigue Pre-Crack and Ductile
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Fracture of Al CVN Specimen
TEM Replica 10,000x SEM 10,000x
Images of the fatigue pre-cracked part of the Charpy
V-notch impact specimen
Fatigue Pre-Crack and Ductile Fracture of
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g
Al CVN Specimen
TEM Replica, 5000xSEM SE Image, 2000x
Views of the ductile rupture portion of the fatigue pre-
cracked Charpy V-notch specimen
Fatigue Pre-Crack and Ductile Fracture of
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Fatigue Pre Crack and Ductile Fracture of
304 Austenitic Stainless Steel CVN Specimen
TEM Replica, 5000x LOM Image, 500x SEM SE Image, 5000x
Views of the fatigue pre-cracked portion of a 304 austenitic stainless steel
Charpy V-notch specimen
Fatigue Pre-Crack and Ductile Fracture of
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Fatigue Pre Crack and Ductile Fracture of
304 Austenitic Stainless Steel CVN Specimen
SEM SE Image, 2000xTEM Replica, 5000x
Views of the ductile overload fracture of the fatigue
pre-cracked Charpy V-notch specimen
Fatigue Pre-Crack and Ductile Fracture of a
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g
Carbon Steel CVN Specimen
TEM Replica, 5000x
Views of the fatigue pre-cracked portion of the carbon
steel Charpy V-notch specimen
SEM SE Image, 5000x
Fatigue Pre Crack and Ductile Fracture of a
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Fatigue Pre-Crack and Ductile Fracture of a
Carbon Steel CVN Specimen
TEM Replica, 5000x LOM Image, 500x SEM SE Image, 5000x
Views of the brittle fracture portion of the fatigue pre-cracked carbon steel
Charpy V-notch specimen broken at 0 F
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Corrosion and Embrittlement
Failures
SCC of 4340 in Salt Water
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SCC of 4340 in Salt Water
Two regions along SCC secondary cracks in a 4340 fastener used on an oil rig
raiser in salt water. The fracture face was badly corroded, destroying the fine
details, but appeared to be intergranular. It was too hard at 38 HRC for this
application. Etched with saturated picric acid + 0.5% HCl and a wetting agent at
80C (500x).
20 m
SCC in 4340 in Salt Water
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Secondary cracks in 4340 fasteners that failed by SCC in sea water; etched with
saturated picric acid + 0.5% HCl + wetting agent at 80C to show the PGBs.
500x
Intergranular SCC in 304 Stainless
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g
Mixed AcidsSEM SEI of Fracture
304 stainless steel wire tested in boiling MgCl2
I t l Ri i L d F t
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Intergranular Rising Load Fracture
SEM SEI, 15 mm WD, 15Tilt SEM ET-BSEI, 15 mm WD, 15Tilt
Fatigue-Intergranular Interface in an X-
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Fatigue Intergranular Interface in an X
750 Rising-Load Test Specimen
Bright field (left) and dark field (right) light microscopy views of the interface
between the fatigue-pre-crack zone (left side) and the intergranular test fracture
(right side) in an X-750 Ni-base rising load test specimen.
Fatigue-Intergranular Interface in an X-
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g g
750 Rising-Load Test Specimen
SEM SEI, 13 mm WD, 4Tilt SEM ET-BSEI, 13 mm WD, 4Tilt
SEM views of the interface between the fatigue pre-crack zone (left side of
fracture) and the intergranular test fracture (right side) in an X-750 rising load
test specimen.
Unusual Intergranular Fracture
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Unusual Intergranular Fracture
LOM - DF SEM SE Image