K3 Types Fracture
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Transcript of K3 Types Fracture
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JENIS-JENIS KERUSAKAN
DEPARTEMEN METALURGI & MATERIALS
FAKULTAS TEKNIK UNIVERSITAS INDONESIA
Dr. Ir. Winarto, M.Sc.
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INTRODUKSI
Logam dapat patah dalam berbagai cara dan untuk penyebabyang berbeda-beda. Sumber informasi yang paling penting
yang kaitannya dengan penyebab perpatahan adalah
permukaan patahan itu sendiri.
Permukaan Patahan merupakan rekaman detail dari rangkaiansejarah komponen yang patah karena berisi :
- data sejarah pembebanan
- data pengaruh lingkungan
- data kualitas bahan/material
Teknik untuk menganalisa bukti (evidence) adalah SEM
FRACTOGRAPHY tujuannya : mengerti bagaimana
komponen tsb patah & bagaimana lingkungan mempengaruhinya.
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CONTOH TAHAPAN - FA
http://www.tms.org/Students/Winners/Davidson/figure-p1.gif -
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Micro Structure Observation
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Surface Observation
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Optical Microscope
Ferrite 90X Austenite 325X Pearlite Cementite 1000X
Macro-fractography
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4 Jenis Perpatahan
Berdasarkan Jejak Perpatahannya (fracture path), maka
perpatahan dibagi menjadi 4 bagian :
1. Perpatahan Ulet (dimple rupture)
2. Perpatahan Getas (cleavage rupture)
3. Perpatahan Fatik (fatigue rupture)
4. Perpatahan dekohesif (decohesive rupture)
Tiap jenis perpatahan memiliki penampakan permukaan dan
mekanisme penjalaran retak.
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Trans-crystalline Fracture
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Inter-crystalline Fracture
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Jejak Perpatahan
Intercrystalline failures Transcrystalline failures
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Perpatahan Ulet & Getas
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Example of Micro-void
Coalescence or Dimple Fracture
High Carbon Steel
ts = 74,000 psi
Specimen broke in tension
AISI 10B21 Steel
ts = 218,000 psi
Specimen broken in tension
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Example of Micro-void
Coalescence or Dimple Fracture
Aluminum 2024 Alloy
ts = 66,000 psi
Specimen broken in tension
Titanium Alloy
ts =153,000 psi
Specimen broken in
high cycle fatigue
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Perpatahan Getas
Faktor-faktor utama :
Stress konsentrasi
Tegangan tarik
Temperatur relatif rendah
Ciri-cirinya :
1. Tidak Ada deformasi plastis
2. Permukaan terang dan kristalin
3. Permukaan patahan utama4. Adachevron marksatauhearingbonemarks
Apek struktur-mikro :
1. Butir kasar
susunan facet pada permukaan belah atau
pola sungai (r iver patern)
2. Kadang-kadang antara ciri-ciri cleavageada dimple
3. Pada Polifase (perlite + Fe3C) terdapat garisdan
dimple.
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Chevron marks
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Patah Getas (TEM)
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Example of Transgranular Cleavage
Nickel-Base Alloy
ts = 141,000 psi
Specimen broke under
low cycle fatigue
Silicon Carbide (SiC)
flexural = 105,850 psi
Specimen broke in tension
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Perpatahan Fatik
Tahapan perpatahan :
1. Inisiasi
2. Perambatan
3. Patahan akhir
Ciri-cirinya :
1. Deformasi plastis sedikit sekali atau hampir tidak ada2. Perpatahannya progresif, berawal dari retak halus yang
merambat akibat beban ber-fluktuatif
3. Adabeach marksataurachet marks
beach marksvsrachet marks :
1. Beach marks
deformasi plastis di ujung retakan
2. Rachet marks permukaan patahan fatik dan
merangkai beberapa awal (initial) fatik yang berdekatan.
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Striation
Low Carbon Steel (SEM 2000X) Al-alloy (SEM 4900X)
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Perpatahan Fatik
Striation :
1. Karakteristik utama fatik pada tahap 2 retak
merambat dan meninggalkan tonjolan (ri dge, striation)
pada permukaan
2. Aspek ukuran: kecil, hanya tampak dengan SEM/TEM3. Aspek penyebab: kemajuan rambatan retak akibat
sekali pembebanan.
Beach marksvsstriation
Beach marks:1. Merupakan deformasi plastis di ujung retakan
2. Aspek ukuran: cukup besar & dapat diamati dengan
kasat mata
3. Aspek penyebab: lokasi posisi front retak setelah
terhenti.
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Striation vs Beach Marks
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Example of Fatigue Fracture
Nickel Based Alloy
ts = 141,000 psi
Specimen broke under
low cycle fatigue
Notice the white lines followed
by dark bands. Individually they are
called fatigue striations
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Example of Fatigue Fracture
Fracture of Nickel Based Alloy
and striations are more jagged
than the examples before
Titanium Alloy
ts = 153,000 psi
Specimen broke under
high cycle fatigue
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Permukan patah akibat fatigue bending
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This high tensile steel bolt failed under low stress high cycle
conditions with a fatigue crack running from 9 o'clock as shownby the beach marks. The SEM image of the fatigued surface(shown left) is found to have no striations due to the high yield
strength and high cycle conditions.
Permukan patah akibat low stress high cycle
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Torsion Fatigue
Reversed torsional fatigue failure of splined shaft from a
differential drive gear
Torsion & Bending Fatigue
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Springs suffer a combination of bending and torsion and fatigue
cracks propagate at right angles to the principal stresses. Hence
the fracture surface is complex even at higher magnification. Thesurface morphology is also influenced by any texture in the
drawn wire used in manufacture.
Torsion & Bending Fatigue
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Pencegahan Fatigue Failure
The most effective method of improving fatigueperformance is improvements in design:
Eliminate or reduce stress raisers by streamlining thepart
Avoid sharp surface tears resulting from punching,stamping, shearing, or other processes
Prevent the development of surface discontinuitiesduring processing.
Reduce or eliminate tensile residual stresses caused bymanufacturing.
Improve the details of fabrication and fasteningprocedures
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Jenis Perapuhan (embrittlement)
By temperature factors (intergranular mechanism):1. Strain Age Embrittlement
aging
2. Quench Age Embrittlement carbide precipitated
3. Blue Brittleness precipitation hardening (, , Impact);230 - 370C
4. Tempered Embrittlement
impurities (Sb, Sn, As), T: 370 - 575
C.
5. Sigma-phase Embrittlement Stainless Steel T sevice 560 - 980 C.
6. HAZ Graphitization
Carbon Steel welds at T 425
C ; waktu lama.7. Inter-metallic Compound Embrittlement Galvanized Steel at T
420C ; waktu lama Fe-Zn intermetalic compound
By environmental factors (intergranular mechanism) :
1. Neutron Embrittlement
neutron radiation at nuclear reactor2. Hydrogen Embrittlement pickling, electroplating, welding, H2S
exposure
3. Stress Corrosion Embrittlement Corrosive environment
4. Liquid Metal Embrittlement salt-bath process(glass making process)
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Li id M t l E b ittl t
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Liquid Metal Embrittlement
The liquid metal can not only reduce the ductil i ty but
signi f icantly reduce tensile strength. L iquid metal embrittlement is an insidious type of failureas it can occur at loads below yield stress. Thus,catastrophic failure can occur without signif icant
deformation or obvious deter ioration of the component. I ntergranular or transgranular cleavage fracture arethe common fracture modes associated with l iquid metalembr ittlement. However reduction in mechanical
properties due to decohesion can occur . This results in a ductile fracture mode occurr ing atreduced tensi le strength. An appropr iate analysis candetermine the effect of l iquid metal embrittlement on
failure.
H d E b ittl t
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Hydrogen Embrittlement
When tensile stresses are applied to a hydrogen embrittled
component it may fail prematurely. Hydrogen embrittlement failures are frequently
unexpected and sometimes catastrophic.
The threshold stresses to cause cracking are commonlybelow the yield stress of the material.
High strength steel, such as quenched and tempered steelsor precipitation hardened steels are particularly susceptibleto hydrogen embrittlement.
Hydrogen can be introduced into the material in service orduring materials processing.
H d E b ittl t
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Hydrogen Embrittlement
Tensile stresses, susceptible material, and the presence of hydrogenare necessary to cause hydrogen embrittlement.
Residual stresses or externally applied loads resulting in stressessignificantly below yield stresses can cause cracking. Thus,catastrophic failure can occur without significant deformation orobvious deterioration of the component.
Very small amounts of hydrogen can cause hydrogen embrittlementin high strength steels.
Common causes of hydrogen embrittlement are pickling,electroplating and welding, however hydrogen embrittlement is notlimited to these processes.
Hydrogen embrittlement is an insidious type of failure as it canoccur without an externally applied load or at loads significantlybelow yield stress.
While high strength steels are the most common case of hydrogenembrittlement all materials are susceptible
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Perapuhan
I t t li C d E b ittl t
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Intermetalic Compound Embrittlement
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Example of Decohesive Rupture
Stainless Steel
ts =195,000 psi
fractograph show
hydrogen embrittlement
C-Mn Steel
ts = 76,000 psi
Specimen failed due to
stress corrosion cracking
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Example of Decohesive Rupture
Low Carbon Steel
ts = 43,000 psi.
Fractograph show
a thin layer of oxide
on the above specimen
Gray Cast Iron (ASTM 247)
ts = 33,000 psi
The white "fuzz"
are sulfate deposits
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Home Work1. Jelaskan jenis perpatahan.
2. Jelaskan perbedaan klasifikasi inter & trans-crystalline.
3. Jelaskan perbedaan ciri-ciri patah ulet dan patah getas
4. Jelaskan perbedaan dari striasi dan beach marks
5. Jelaskan mekanisme tahapan perpatahan akibat fatik berikutgambar.
6. Jelaskan beberapa pencegahan agar terhindar dari patah fatik
7. Jelaskan mekanisme patahan akibat perapuhan
(embrittleness) & beri beberapa contoh yang saudara ketahui8. Apakah setiap jenis perpatahan material disebabkan oleh
hanya satu jenis perpatahan. Jelaskan menurut saudara
dengan memberikan contoh.