Monday, September 22, 2014 3:56 PM

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Types of Failure

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Characteristics of Brittle failures

Characteristics of Ductile failures

Fracture occurs along specific crystal direction (forming cleavage)•There is zero (or very little) plastic deformation•It is transgranular (within crystal)•Sometimes it is intergranular (along GB)•Fracture surface is perpendicular to the force.•

It involves plastic deformation

NeckingStages are:

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Crack Length, a

Necking○

Formation of microvoids○

Formation of elliptical cracks○

Crack grows perpendicular to the force○

Failure happens in shear mode, 45 degrees cut (cup and cone)○

Surface has dimples○

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Formula

Cracks are more effective inside than on the surfaceCracks are more effective for brittle samples than ductile.

Example:

Inside crack outside crack

3 modes:

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A flaw detection system can measure cracks more than a=3 mm long. For a sample with KIC=85 Mpa(m)-0.5 , what is the critical size of the crack (inside and outside) which can be detected by this system? Can this method be used to detect a crack if sample is loaded less than its yield strength of 1700 Mpa?

Example: An airplane part made from Aluminum (KIC =25000PSI(in)0.5, failed during a test flight. Examination of the fracture surface revealed a crack 0.1mm long on the surface. What is the Max stress experienced by the part?

Example: A steel sample has an internal crack 1.2 mm long subjected to a stress level 10% higher than it's yield strength of 60KSI. Would the sample survive the load? E=30Mpa,. Tensile strength = 210KSI

so a crack of 1.4 mm (inside) or 0.7 mm (on the surface ) can be detected

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How to increase Fracture Toughness:

Reduce flaw size.1-Increase Ductility2-Increase working Temp.3-Choose sample with smaller Grain dia.4-

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http://www.youtube.com/watch?v=tpGhqQvftAo

Link to video:

Charpy and Izod test

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https://www.youtube.com/watch?v=24KWN6nH1fI

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TYPES OF LOADING

Examples:

Examples:

Sun-Dial bridge in

FROM: http://www.twi-global.com/technical-knowledge/published-papers/review-

of-fatigue-assessment-procedures-for-welded-aluminium-structures-december-2003/

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Formula:

Sun-Dial bridge in Redding

Examples:

mean stress

stress amplitude.

stress Ratio

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Link for airplane fatigue test

http://www.youtube.com/watch?v=

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3-

Effect of CWCW2>CW1

Effect of temperatureT2>T1

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(cold flow)

Surface finish

S2 is smootherthan S1

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Effect of T

Stages of creep:

3 stages of creep (from : http://en.wikipedia.org/wiki/Creep_%28deformation%29 )

1st stage : In the initial stage, or primary creep, the strain rate is relatively high, but slows with increasing time. This is due to work hardening.

2nd stage: The strain rate eventually reaches a minimum and becomes near constant. This is due to the balance between work hardening and annealing(thermal softening).

3rd stage: the strain rate exponentially increases with stress because of neckingphenomena.

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Video: creep test of lead: https://www.youtube.com/watch?v=gJnuBfcpZGU

Example: A sample 200 m long, is made from S-590 is exposed to 300 Mpa stress at 650 C. Find its elongation after 1 month.

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NDE and NDT: See https://www.nde-ed.org/GeneralResources/MethodSummary/MethodSummary.htm

Also from : http://en.wikipedia.org/wiki/Nondestructive_testing

Acoustic emission testing (AE or AT)•Blue Etch Anodize (BEA)•Dye penetrant inspection Liquid penetrant testing (PT or LPI)•

Alternating current field measurement (ACFM)

Electromagnetic testing (ET) •

Liquid Penetrant test: https://www.youtube.com/watch?v=bHTRmTQDZzg

Magnetic Particle inspection: https://www.youtube.com/watch?v=qpgcD5k1494

Ultrasonic inspection: https://www.youtube.com/watch?v=UM6XKvXWVFA

Eddy current inspection: https://www.youtube.com/watch?v=T0DMHIbaPnc

X-ray testing

From This to this!

Visual Inspection

OTHERS…..

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Alternating current field measurement (ACFM)○

Alternating current potential drop measurement (ACPD)○

Barkhausen testing○

Direct current potential drop measurement (DCPD)○

Eddy-current testing (ECT)○

Magnetic flux leakage testing (MFL) for pipelines, tank floors, and wire rope○

Magnetic-particle inspection (MT or MPI)○

Magnetovision○

Remote field testing (RFT)○

Ellipsometry•Endoscope inspection•Guided wave testing (GWT)•Hardness testing•Impulse excitation technique (IET)•

Thermographic inspection○

Infrared thermal microscopy○

Infrared and thermal testing (IR) •

Electronic speckle pattern interferometry○

Holographic interferometry○

Low coherence interferometry○

Profilometry○

Shearography○

Laser testing •

Absolute pressure leak testing (pressure change)○

Bubble testing○

Halogen diode leak testing○

Hydrogen leak testing○

Mass spectrometer leak testing○

Tracer-gas leak testing method Helium, Hydrogen and refrigerant gases○

Leak testing (LT) or Leak detection•

Magnetic resonance imaging (MRI) and NMR spectroscopy•Metallographic replicas [10][11]•Near-infrared spectroscopy (NIRS)•Optical microscopy•Positive Material Identification (PMI)•

Computed radiography○

Digital radiography (real-time)○

Neutron Imaging○

SCAR (Small Controlled Area Radiography)○

X-ray computed tomography (CT)○

Radiographic testing (RT) (see also Industrial radiography and Radiography) •

Resonant Acoustic Method (RAM) [12]○

Resonant Inspection •

Scanning electron microscopy•Surface Temper Etch (Nital Etch)•

ART (Acoustic Resonance Technology)○

Electro Magnetic Acoustic Transducer (EMAT) (non-contact)○

Laser ultrasonics (LUT)○

Internal rotary inspection system (IRIS) ultrasonics for tubes○

Phased array ultrasonics○

Time of flight diffraction ultrasonics (TOFD)○

Time of Flight Ultrasonic Determination of 3D Elastic Constants (TOF)○

Ultrasonic testing (UT) •

Vibration Analysis•

Pipeline video inspection○

Visual inspection (VT) •

Weight and load testing of structures•Corroscan/C-scan•

Industrial CT Scanning○

3D Computed Tomography •

Heat Exchanger Life Assessment System•RTJ Flange Special Ultrasonic Testing•

From <http://en.wikipedia.org/wiki/Nondestructive_testing >

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