Teknologi Bahan_2 Analisis Kegagalan Material_Herman(1)

7/26/2019 Teknologi Bahan_2 Analisis Kegagalan Material_Herman(1)

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by: Herman Saputroby: Herman Saputroby: Herman Saputroby: Herman Saputro

Selendang Ayu suffered a catastrophic fracture in number 4 hold in December 2004.

The 1980s and 1990s were a very unsafe time for bulk carriers. Many bulkerssank during this time, 99 were lost between 1990 and 1997. The latest case isSelendang Ayu in Desember 2004.

KASUSKASUSKASUSKASUS KASUS KEGAGALANKASUS KEGAGALANKASUS KEGAGALANKASUS KEGAGALAN

The leading causes:

1. Stability problems2. Structural problems


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On March 27th, 1980, the semi-submersible platform Alexander Kielland suddenlycapsized during a storm in the North Sea, because one of its five vertical columnssupporting the platform was broken off. 123 workers among the 212 people on

board were killed in the accident.

The investigation showed that a fatigue crack had propagated

from the double fillet weld.


http://www.weldreality.com/navy%20weld%20problems.htm

An oil tanker that fractured in a brittle manner by crack propagation

around its girth. (Photography by Neal Boenzi. Reprinted with permissionfrom The New York Times.)

Each year from 1995 to 2001, an average ofEach year from 1995 to 2001, an average ofEach year from 1995 to 2001, an average ofEach year from 1995 to 2001, an average of 408 tankers break apart at sea408 tankers break apart at sea408 tankers break apart at sea408 tankers break apart at sea or barelyor barelyor barelyor barelyescaped that fate, according to the International Association of Independent Tankerescaped that fate, according to the International Association of Independent Tankerescaped that fate, according to the International Association of Independent Tankerescaped that fate, according to the International Association of Independent TankerOwners, known asOwners, known asOwners, known asOwners, known as IntertankoIntertankoIntertankoIntertanko. The leading cause was collision, but nearly as many. The leading cause was collision, but nearly as many. The leading cause was collision, but nearly as many. The leading cause was collision, but nearly as manysuffered suffered suffered suffered unknown structural failuresunknown structural failuresunknown structural failuresunknown structural failures or technical problems. or technical problems. or technical problems. or technical problems.



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Aloha Airlines On April 28, 1988, a Boeing 737-200 (line number 152)

The investigation determined that the failure mechanism was a result of multiple sitefatigue cracking of the skin adjacent to rivet holes along the lap joint upper rivet row and tearstrap disbond which negated the fail-safe characteristics of the fuselage. Finally, the fatiguecracking initiated from the knife edge associated with the countersunk lap joint rivet holes;the knife edge concentrated stresses that were transferred through the rivets because of lapjoint disbanding.

http://lessonslearned.faa.gov/ll_main.cfm?TabID=4&LLID=20&LLTypeID=2



Southwest Airlines planeSouthwest Airlines planeSouthwest Airlines planeSouthwest Airlines plane

The plane's nose gear collapsed as theaircraft landed on Runway 4


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ANALISISANALISISANALISISANALISIS KEGAGALANKEGAGALANKEGAGALANKEGAGALAN

The cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the following

categories:categories:categories:categories:1. Negligence during design, construction or operation of the structure.2. Application of a new design or material, which produces an unexpected (and

undesirable) result.

Why structure fail ???Why structure fail ???Why structure fail ???Why structure fail ???

FailureFailureFailureFailure in structures leads to lostlostlostlost of propertiesof propertiesof propertiesof properties and sometimes lost ofhuman lives.

Failure analysisFailure analysis is an engineering approach to determining how and why equipment or acomponent has failed.

The goal of a failure analysis is to understand the root cause of thefailure so as to prevent similar failures in the future.

ANALISISANALISISANALISISANALISIS KEGAGALANKEGAGALANKEGAGALANKEGAGALAN

The cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the followingThe cause of most structural failures generally falls into one of the followingcategories:categories:categories:categories:1. Negligence during design, construction or operation of the structure.

2. Application of a new design or material, which produces an unexpected (andundesirable) result.

Why structure fail ???Why structure fail ???Why structure fail ???Why structure fail ???

FailureFailureFailureFailure in structures leads to lostlostlostlost of propertiesof propertiesof propertiesof properties and sometimes lost ofhuman lives.

Failure analysis

Failure analysis is an engineering approach to determining how and why equipment or a

component has failed.

The goal of a failure analysis is to understand the root cause of thefailure so as to prevent similar failures in the future.


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Failure TheoriesFailure TheoriesFailure TheoriesFailure Theories

Failure under load can occur due to excessive elastic deflections or due toexcessive stresses.

Failure prediction theories due to excessive stresses fall into two classes:

1. Failure when the loading is static or the number of load cycles is one orquite small, and

2. Failure due to cyclic loading when the number of cycles is large often inthousands of cycles.

FailureFailureFailureFailure underunderunderunder staticstaticstaticstatic loadloadloadloadParts under static loading may fail due to:a)a)a)a) DuctileDuctileDuctileDuctile behaviorbehaviorbehaviorbehavior:::: Failure is due to bulk yielding causing permanent

deformations that are objectionable. These failures may cause noise, lossof accuracy, excessive vibrations, and eventual fracture. In machinery,

bulk yielding is the criteria for failure. Tiny areas of yielding are OK inductile behavior in static loading.

b)b)b)b) BrittleBrittleBrittleBrittle behaviorbehaviorbehaviorbehavior:::: Failure is due to fracture. This occurs when thematerials (or conditions) do not allow much yielding such as ceramics,grey cast iron, or heavily cold-worked parts

Ductile vs. Brittle FailureDuctile vs. Brittle FailureDuctile vs. Brittle FailureDuctile vs. Brittle Failure

Adapted from Fig. 8.3, Callister 7e.

ductile fracture in aluminum

brittle fracture in a mild steel

Ductile materials - extensive plastic deformation and energy absorption (toughness)

before fracture

Brittle materials - little plastic deformation and low energy absorption before fracture


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Ductile fractureDuctile fractureDuctile fractureDuctile fracture

Cup-and-cone fracture inaluminum.

Final shearfracture.

Initial necking.

Small cavity

formationCoalescence ofcavities to form acrack

Crackpropagation

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Microvoid Formation, Growth And Coalescence

MicrovoidsMicrovoidsMicrovoidsMicrovoids are easily formed at inclusions,intermetallic or second-phase particles and

grain boundaries.GrowthGrowthGrowthGrowth andandandand coalescencecoalescencecoalescencecoalescence of microvoids progress

as the local applied load increases.

Random planar arrayof particles acting asvoid initiators

Growth of voidsto joineach other asthe appliedstress increases.

Linkage orcoalescenceof these voids toform free fracturesurface.




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Ductile Fracture of Alloys

If materials is stretched, itfirstly deforms uniformly.

Inclusions stress concentrators



1)1)1)1) DecohesionDecohesionDecohesionDecohesion at particle -matrix interface.2) Fracture of brittle particle

3) Decohesion of an interface associatedwith shear deformation or grainboundary sliding.

Decohesion of carbide particlesfrom Ti matrix.

Fractured carbides aidingmicrovoid formation.

Microvoids are from by:




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Brittle FractureBrittle FractureBrittle FractureBrittle Fracture


Fractografic Studies


Transgranular fracture: Crackspass through grains. Fracturesurface: faceted texturebecause of different orientationof cleavage planes in grains.

Intergranular fracture: Crack propagation is along grainboundaries (grain boundaries areweakened/ embrittled byimpurity segregation etc.)



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Intergranular Fracture

Intergranular failureIntergranular failureIntergranular failureIntergranular failure isa moderate to low energybrittle fracture mode resultingfrom grain boundaryseparation or segregation ofembrittling particles orprecipitates.

Embrittling grainboundary particles are

weakly bonded with thematrix, high free energyand unstable, which leads topreferential crackpropagation path. Intergranular fracture with and without

microvoid coalescence



Characteristic for ceramics and glassesCharacteristic for ceramics and glassesCharacteristic for ceramics and glassesCharacteristic for ceramics and glasses

Distinct characteristics of brittle fracturesurfaces:

1) The absence of gross plastic deformation.2) Grainy or Faceted texture.3) River marking or stress lines.

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Strength and Toughness

Strength

Resistance of a materialto plastic flow

ToughnessResistance of a material

to the propagationof a crack

How concerned should you be if you read in thepaper that cracks have been detected in thepressure vessel of the nuclear reactor of thepower station a few miles away?


TESTING FOR TOUGHNESS

This type of test provides a comparison of the toughness ofmaterials

however, it does not provide a way to express toughness asa material property (no true material property that isindependent on size and shape of the test sample)

Tear test Impact testMeasuringthe energy


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INTRODUCTION TOINTRODUCTION TOINTRODUCTION TOINTRODUCTION TOFRACTURE MECHANICSFRACTURE MECHANICSFRACTURE MECHANICSFRACTURE MECHANICS

The fracture strength of a solid material is a function of thecohesive forcescohesive forcescohesive forcescohesive forces that exist between atoms.

On this basis, the theoretical cohesive strength of a brittle elastic solid

has been estimated to be approximately E/10, where E is the modulusof elasticity.

The experimental fracture strengths of most engineering materialsnormally lie between 10 and 1000 times below this theoretical value.

Why?

surface energy

unstrained interatomic spacing

STRESS CONCENTRATIONSTRESS CONCENTRATIONSTRESS CONCENTRATIONSTRESS CONCENTRATION

Crack reduces the cross section =>increase in stress

What will happenwith tough material?

Cracks concentrate stress

Flaws are detriment to the fracture strength because an appliedstress may be amplified or concentrated at the tip, the magnitude ofthis amplification depends on crack orientation and geometry.


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What Force Is Required To Break The Samples?

THEORIES OF BRITTLE FRACTURETHEORIES OF BRITTLE FRACTURETHEORIES OF BRITTLE FRACTURETHEORIES OF BRITTLE FRACTURE


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STRESS CONCENTRATORS

Schematic stress profile along the lineXX

the magnitude of this localized stressdiminishes with distance away from the crack tip

The maximum stressat the crack tip

stress

concentration

factor

A measure of the degree to

which an external stress is

amplified at the tip of a crack

PROBLEMPROBLEMPROBLEMPROBLEM

1. Consider a circular hole in a plate loaded in tension. When will material nearthe hole yield?

2. A plate with a rectangular section 500 mm by 15mm carries a tensile load of 50kN. It is made of a

ductile metal with a yield strength of 50 MPa. Theplate contains an elliptical hole of length 100 mmand a minimum radius of 1 mm, oriented as shownin the diagram.

What is

(a) the nominal stress(b) The maximum stress in the plate?(c) Will the plate start to yield?

(d) Will it collapse completely?


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THEORETICAL STRESSCONCENTRATION FACTOR

CURVES

GRIFFITH THEORY OF BRITTLEGRIFFITH THEORY OF BRITTLEGRIFFITH THEORY OF BRITTLEGRIFFITH THEORY OF BRITTLEFRACTUREFRACTUREFRACTUREFRACTURE

Inherent defects in brittlematerials lead to stress

concentration.

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If stress exceeds thecohesive strength ofbonds, crackextension is possible.

Thermodynamic criterion:There are two energies to be taken into

account when a crack propagates:(1) New surfaces should be created and

a certain amount of energy must beprovided to create them;

(2) Elastic strain energy stored in thestressed material is released during

crack propagation.


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THEORY OF BRITTLE FRACTURETHEORY OF BRITTLE FRACTURETHEORY OF BRITTLE FRACTURETHEORY OF BRITTLE FRACTURE

The stress required to

create the new crack

surface

Critical stress for crack propagation

G 2G 2G 2G 2

PROBLEMPROBLEMPROBLEMPROBLEM

A relatively large plate of a glass is subjected to a tensile stress of 40 MPa. Ifthe specific surface energy and modulus of elasticity for this glass are 0.3J/m2 and 69 GPa, respectively, determine the maximum length of a surface flaw that is possible withoutfracture.


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PROBLEM: PROPERTIES OF SIALON CERAMICS

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Assume that an advanced ceramic, SiAlON (silicon aluminum oxynitride),has a tensile strength of 414 MPa.

Let us assume that this value is for a flaw-free ceramic. (In practice, it isalmost impossible to produce flaw-free ceramics.)A crack 0.025 cm deep is observed before a SiAlON part is tested.The part unexpectedly fails at a stress of 3.5 MPa by propagation of the crack. Estimate the radius of the crack tip.

BASIC MODES OF CRACK TIP DEFORMATION

KIC the critical stress intensity inmode I fracture (plain strain)

critical stress forcrack propagation

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K = (EG) 1/2


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FRACTURE TOUGHNESS

FT is a material propertymaterial propertymaterial propertymaterial property;Value is independent of the way it is measured;Can be used for designCan be used for designCan be used for designCan be used for design

Fracture toughness of a material is obtained by determiningthe ability of a material to withstand the load in the presence

of a sharp crack before failure.

Y is a dimensionless parameter or function

that depends on both crack and specimen

sizes and geometries, as well as the manner

of load application33

Crack propagates when the stressintensity factor exceeds a critical value.

ENERGY RELEASE RATE

Irwin later modified the Griffith theory by replacing the

term 2 with the potential strain energy release rate G

When a samples fractures, a new surface is created =>

necessary conditions for fracture sufficient energy

release

G 2The critical condition to which the crackpropagates to cause global failure is when this

G value exceeds the critical value

Irwin showed that G is measurable and can

be related to the stress intensity factor, K

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Y VALUES OF VARIOUS CRACK GEOMETRIESY VALUES OF VARIOUS CRACK GEOMETRIESY VALUES OF VARIOUS CRACK GEOMETRIESY VALUES OF VARIOUS CRACK GEOMETRIES

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PROCESS ZONE

A plastic zone forms at thecrack tip where the stress

would otherwise exceedthe yield strength

Size of process zone:

36


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BRITTLE CLEAVAGE FRACTURE

Materials of high yield strength

Near tip stress are very high =>tear the atomic bonds apart =>increase in the crack length results in increase in K,causing crack to accelerate

FRACTURE TOUGHNESS AND DESIGNFRACTURE TOUGHNESS AND DESIGNFRACTURE TOUGHNESS AND DESIGNFRACTURE TOUGHNESS AND DESIGN

If the KIC value of material is known and the presence of a crack isallowed, we can then monitor the crack propagation during service priorto failure =>How long we can use the component before it fails.

Brittle materials, for which appreciableplastic deformation is not possible in front ofan advancing crack, have low KIc values and

are vulnerable to catastrophic failure.

Crack length necessaryfor fracture at a materials

yield strength


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Tough metals are able to containlarge cracks but still yield in apredictable, ductile, manner

Critical crack lengths are a measure of thedamage tolerance of a material

DAMAGE TOLERANCE

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FRACTURE RESISTANCE

The ability of a material to resist the growth of a crackdepends on a large number of factors:

Larger flaws reduce the permitted stress. The ability of a material to deform is critical.

Increasing the raterateraterate of application of the load, such asthat encountered in an impact test, typically reducesthe fracture toughness of the material.

Increasing the temperature normally increases thefracture toughness.


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VARIABLES AFFECTINGVARIABLES AFFECTINGVARIABLES AFFECTINGVARIABLES AFFECTINGFRACTURE TOUGHNESSFRACTURE TOUGHNESSFRACTURE TOUGHNESSFRACTURE TOUGHNESS

Metallurgical factorsMetallurgical factorsMetallurgical factorsMetallurgical factors

Microstructure, inclusions,impurities Composition Heat treatment Thermo-mechanical processing

FRACTURE TOUGHNESS MODULUS CHART

Values range from 0.01 100 MPam


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Transition crack length plotted on chart values can range from near-atomic dimensions for ceramics to almost a meter for ductile metals

FAIL-SAFE DESIGN

Yield-before-break

Requires that the crack will

not propagate even if thestress causes the part to yield

Leak-before-break

Requires that a crackjust large enough to

penetrate both the innerand outer surface of the

vessel is still stable

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DESIGN USING FRACTURE MECHANICSDESIGN USING FRACTURE MECHANICSDESIGN USING FRACTURE MECHANICSDESIGN USING FRACTURE MECHANICS

Consider the thin-walled spherical tankof radius r and thickness tthat may beused as a pressure vessel.

One design of such a tank calls for yielding of the wall material prioryielding of the wall material prioryielding of the wall material prioryielding of the wall material priorto failureto failureto failureto failure as a result of the formation of a crack of critical size and itssubsequent rapid propagation.Thus, plastic distortion of the wall may be observed and the pressure

within the tank released before the occurrence of catastrophic failure.Consequently, materials having large critical crack lengths aredesired.

On the basis of this criterion, rank the metal alloys listedin Table, as to critical crack size, from longest to shortest.

wall stress

DESIGN PROCESSDESIGN PROCESSDESIGN PROCESSDESIGN PROCESS YIELDYIELDYIELDYIELD----BEFOREBEFOREBEFOREBEFORE----FRACTUREFRACTUREFRACTUREFRACTURE

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Requirement:The stresses are everywhere lessthat required to make a crack ofcritical length to propagate.BUT!!! It is not safe

Requirement:Crack should not propagateeven if the stress is sufficient tocause general yield for then thevessel will deform stably in a waythat can be detected.

Tolerable crack size


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DESIGN PROBLEM - LEAK-BEFORE-BREAK

An alternative design that is also often utilized with pressure vessels is termed leak-

before-break. Using principles of fracture mechanics, allowance is made for the growth

of a crack through the thickness of the vessel wall prior to the occurrence of rapid crack

propagation. Thus, the crack will completely penetrate the wall without catastrophic

failure, allowing for its detection by the leaking of pressurized fluid.

With this criterion the critical crack lengthac (i.e., one-half of the total internal crack

length) is taken to be equal to the pressure vessel thicknesst.

Using this criterion, rank

the metal alloys in Table as

to the maximum allowable

pressure.47

2a = t

FORENSIC FRACTURE CASE

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K1c

of the tank material measured to be

45 MPam

10 mm crack found in longitudinal weld

Stress based on

maximum design

pressure

Stress at which a plate with the given K1cwill fail with a 10 mm crack


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DUCTILE-TO-BRITTLE TRANSITION

At low temperatures some metals and all polymers become

brittle

As temperatures decrease, yield strengths of most materials

increase leading to a reduction in the plastic zone size

Only metals with an FCC structure remain ductile at the lowest

temperatures

The ductile to brittle transition temperature is the temperature atwhich the failure mode of a material changes from ductile to brittle

fracture.

DUCTILE TO BRITTLE TRANSITIONBEHAVIOUR

Some metals and polymers experience ductile-to-brittle transition behaviour

when subjected to decreasing temperature, resulting from a strong yield stress

dependence on temperature.

Metals possess limitedslip systems available at low

temperature, minimising the

plastic deformation during the

fracture process.

Increasing temperature

allows more slip systems to

operate, yielding general

plastic deformation to occur

prior to failure.


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WHEN DUCTILE TURN TO BRITTLE

The criterion for a material to change its fracture behaviour from ductile

to brittle mode is when the yield stress at the observed temperature is larger

than the stress necessary for the growth of the micro-crack indicated in the

Griffith theory

The criterion for ductile to brittle

transition is when the term on the

left hand side is greater than the right

hand side.

is the lattice resistance to dislocation

movement

k is a parameter related to the release of

dislocation into a pile-up

D is the grain diameter (associated with slip

length).

G is the shear modulus

is a constant depending on the stress system

WHY DONT SOME MATERIALSUNDERGO TRANSITION?

Unlike steel, aluminium does not undergo a ductile-brittle transition. The reason can

be explained in terms of their crystal structure.

The yield stress of steel is temperature sensitive because of its BCC structure. At low

temperatures it is more difficult for the dislocations to move (they require a degree of

diffusion to move due to the non-close packed nature of the slip planes) and thereforeplastic deformation becomes more difficult. The effect of this is to increase the yield

stress at low temperatures.

Aluminium has a FCC structure, this means

that it has lots of easily operated close-

packed slip systems operating at low

temperatures. As a result its yield strength is

not temperature sensitive and aluminium

remains ductile to low temperatures.


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BAD LUCK OF TITANIC

The sinking of the Titanic was caused primarily by the brittleness of thesteel used to construct the hull of the ship.

In the icy water of the Atlantic, the steel was below the ductile to brittle

transition temperature.

FACTORS AFFECTING MODES OFFRACTURE

The yield stress of steel is temperature

sensitive. The fracture stress remains relatively

constant with temperature.

At room temperature steel is a ductile material, this

means that it will undergo plastic deformation before

fracture i.e. the yield strength of the material is less

than the fracture stress.

At low temperatures the yield stress of steel

increases, when the yield stress increases above

the fracture stress the material will undergo a

ductile-to-brittle transition.


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THE STRENGTH-TOUGHNESS TRADE-OFF

Increasing the yieldstrength of a metal

decreasing the size

of the plastic zone

surrounding a crack

this leads to decreased

toughness

INSPECTIONS

1. Visual2. Liquid Penetrant

3. Magnetic

4. Ultrasonic5. Eddy Current

6. X-ray


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Most basic and common

inspection method.

Tools include fiberscopes,

borescopes, magnifying

glasses and mirrors.

Robotic crawlers permit

observation in hazardous or tight

areas, such as air ducts, reactors,

pipelines.

Portable video inspection unit

with zoom allows inspection

of large tanks and vessels,

railroad tank cars, sewer lines.

1. VISUAL INSPECTION

INSPECTIONS

A liquid with high surface wetting characteristics is applied to

the surface of the part and allowed time to seep into surface

breaking defects.

The excess liquid is removed from the surface of the

part.

A developer (powder) is applied to pull the trapped

penetrant out the defect and spread it on the surface where it

can be seen.

Visual inspection is the final step in the process. The

penetrant used is often loaded with a fluorescent dye and the

inspection is done under UV light to increase test sensitivity.

2. LIQUID PENETRANT INSPECTION

INSPECTIONS


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3. MAGNETIC PARTICLE INSPECTION

The part is magnetized. Finely milled iron particles coated with a dye pigment

are then applied to the specimen. These particles are attracted to magnetic fluxleakage fields and will cluster to form an indication directly over thediscontinuity. This indication can be visually detected under proper lightingconditions.

INSPECTIONS

Magnetic Particle Crack Indications

INSPECTIONS


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4. RADIOGRAPHY

The radiation used in radiography testing is ahigher energy (shorter wavelength) version of

the electromagnetic waves that wesee as visible light. The radiation can comefrom an X-ray generator or a radioactivesource.

High Electrical Potential

Electrons-+

X-rayGenerator orRadioactive

Source CreatesRadiation

Exposure Recording Device

Radiation

Penetratethe Sample

INSPECTIONS

5. EDDY CURRENT TESTING

Eddy current testing is particularly well suited for detecting surface cracks but can also be

used to make electrical conductivity and coating thickness measurements. Here a small

surface probe is scanned over the part surface in an attempt to detect a crack

INSPECTIONS


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High frequency sound waves are introduced into a material and they are reflected backfrom surfaces or flaws.

Reflected sound energy is displayed versus time, and inspector can visualize a crosssection of the specimen showing the depth of features that reflect sound. f

plate

crack

0 2 4 6 8 10

initialpulse

crackecho

back surfaceecho

Oscilloscope, or

flaw detector screen

6. ULTRASONIC INSPECTION (PULSE-ECHO)

INSPECTIONS

ULTRASONIC IMAGING

Gray scale image produced using the

sound reflected from the front surface

of the coin

Gray scale image produced using the

sound reflected from the back surface of

the coin (inspected from heads side)

High resolution images can be produced by plotting signal

strength or time-of-flight using a computer-controlled scanning

system.


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COMMON APPLICATION OF NDT

Inspection of Raw Products

Inspection Following Secondary Processing

In-Services Damage Inspection

INSPECTION OF RAW PRODUCTS

Forgings, Castings,

Extrusions, etc.


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Machining

Welding Grinding Heat treating Plating etc.

INSPECTION FOLLOWINGSECONDARY PROCESSING

Cracking

Corrosion

Erosion/Wear

Heat Damage

etc.

INSPECTION FORIN-SERVICE DAMAGE


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POWER PLANT INSPECTION

Probe

Signals produced by

various amounts of

corrosion thinning.

Periodically, power plants are

shutdown for inspection.

Inspectors feed eddy current probes

into heat exchanger tubes to checkfor corrosion damage.

Pipe with damage

WIRE ROPE INSPECTION

Electromagnetic devices andvisual inspections are used to findbroken wires and other damage tothe wire rope that is used inchairlifts, cranes and other lifting

devices.


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STORAGE TANK INSPECTION

Robotic crawlers useultrasound to inspect thewalls of large above

ground tanks for signsof thinning due tocorrosion.

Cameras on longarticulating armsare used to inspectunderground

storage tanks fordamage.

AIRCRAFT INSPECTION Nondestructive testing is used

extensively during the manufacturingof aircraft.

NDT is also used to find cracks andcorrosion damage during operation

of the aircraft. A fatigue crack that started at the site

of a lightning strike is shown below.


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JET ENGINE INSPECTION

Aircraft engines are overhauled afterbeing in service for a period of time.

They are completely disassembled,cleaned, inspected and then reassembled.

Fluorescent penetrant inspection is usedto check many of the parts for cracking.

Sioux City, Iowa, July 19, 1989

A defect that went

undetected in an engine

disk was responsible for the

crash of United Flight 232.

CRASH OF UNITED FLIGHT 232


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PRESSURE VESSEL INSPECTION

The failure of a pressure vessel can

result in the rapid release of a large

amount of energy. To protect against

this dangerous event, the tanks areinspected using radiography and

ultrasonic testing.

RAILINSPECTION

Special cars are used to inspectthousands of miles of rail tofind cracks that could lead to aderailment.


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BRIDGE INSPECTION

The US has 578,000 highwaybridges.

Corrosion, cracking and otherdamage can all affect a bridgesperformance.

The collapse of the SilverBridge in 1967 resulted in lossof 47 lives.

Bridges get a visual inspectionabout every 2 years.

Some bridges are fitted with

acoustic emission sensors thatlisten for sounds of cracksgrowing.

NDT is used to inspect pipelines toprevent leaks that could damage theenvironment. Visual inspection,radiography and electromagnetic testingare some of the NDT methods used.

Remote visual inspection using arobotic crawler.

Radiography of weld joints.

Magnetic flux leakage inspection. This

device, known as a pig, is placed in thepipeline and collects data on thecondition of the pipe as it is pushedalong by whatever is being transported.

PIPELINE INSPECTION


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SPECIAL MEASUREMENTS

Boeing employees in Philadelphia were given the privilege of evaluatingthe Liberty Bell for damage using NDT techniques. Eddy current methodswere used to measure the electrical conductivity of the Bell's bronzecasing at various points to evaluate its uniformity.

REFERENCES

1. Dieter, G.E., Mechanical metallurgy, 1988, SI metric edition,McGraw-Hill, ISBN 0-07-100406-8.

2. Sanford, R.J., Principles of fracture mechanics, 2003, Prentice Hall,New Jersey, ISBN 0-13-092992-1.

3. Callister WD, Material Science anda Engineering an Introduction,six edition, 2003, John Wiley & Sons, Singapure.

Teknologi Bahan_2 Analisis Kegagalan Material_Herman(1)

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