k3 types fracture

8/10/2019 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


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


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.

k3 types fracture

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