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Mechanical Testing

Mechanical Testing of welded joints may be carried out fo the Following reasons• Welding Procedure approval• Welder Approval• Production Quality Approval

Welding consumables manufacturers will carry out all weld metal tests for each consumable type

Parent Material is normally subjected to extensive testing prier toIts acceptance

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In mechanical Testing representative test samples produced under similar conditions to the in service components are normally used and comparison is made

The main purpose of mechanical Testing is to asses the properties of welded Joints

The most frequently used mechanical tests areTensileBendNick BreakFracture ImpactHardnessMacroscopic / MicroscopicCTOD

Mechanical Testing

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Tensile Test

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Tensile Test

In tensile test stress is applied in opposite direction to pull the two ends apart

Tensile test is used to asses the following• Yield point of the specimen• The ultimate tensile strength• Ductility of the specimen, expressed as % elongation

The different types of tensile test are• Transverse tensile test• All weld tensile test• Cruciform Test

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The reduction in the cross sectional area indicates the ductile fracture

Steel specimen which do not exhibit any necking usually rejected

U.T.S = Maximum Load Applied / least cross sectional area

% elongation( strain ) = Increase of gauge length x 100 / original length

Tensile Test

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Bend Test

The bend test is carried out to determine the soundness of the weld zone

The commonly applied bend test is the transverse bend testThere are three ways to perform this type of bend test• The root bend test• Face bend test• Side bend test

The specimen width of bend test is usually at least 1.5 times the thickness and the weld reinforcement is usually dressed flushedOn both sides

The specimen are usually bent through 90o,120o , 135o and , 180o 90o,

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Bend Test

The diameter of the Firmer is typically four times the specimen thickness

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Impact Test

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Impact Test

Impact test is performed to Asses notch toughness by measuring the energy absorbedDuring the impact

Two main impact tests are• Charpy v-notch • Izod Test

• Both tests use a swinging Pendulum• The pendulum hits the notched Specimen positioned in the Machine• The specimen immediately fractures in the notch• More energy is absorbed by tougher specimen during the fracture

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Hardness Test

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Harness Test

This test is used to know the hardness gradient across the weld zone and parent material for comparison purpose

Hardness of the weld and HAZ will give an indication of the Weldability of the material

Hardness also gives the idea about the correct selection of welding Parameters

Two common hardness tests are• Vickers Pyramid Hardness Test• Brinnell Hardness Test

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Hardness Test

Vickers Hardness Test:

The test uses small pyramid shaped diamond indenter with an angle of 136o

A force is applied to press the indenter into the surface for 10-15 seconds

The force applied is variable from 1-120 kg

The diamond indenter leaves a pin tip sized square indentation on the surface

The size of this indentation is the indication of hardness of the specimen

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Hardness Test

Brinell Hardness Test

The test is carried out by forcing the hardened 10 mm dia steel ball into the surface of the specimen

The force used is 500,1500,or 3000 kg for 15 seconds

An in built microscope with a calibrated lens is used to Measure the width of indentation.

The size of this indentation is the indication of hardness of the specimen

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Nick Break Test

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Nick break test

Nick break test is used to evaluate the presence of weld defects across the fractured surface

Two nicks are cut each on either side of the of the weld

The test specimen are broken by bending or striking with hammer

This causes the weld to fracture along the weakest setion

The fractured faces are then examined visualy

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Fillet Weld Fracture Test

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Fillet Weld Fracture Test

• To evaluate the presence of weld defects across the fractured surface• A saw cut is made along the center line of the weld face on a fillet weld• The specimen is broken by hammer strikes•

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CTOD

• This test is to determine metals resistance to initiate the crack from any notch• A notch is cut in the specimen, The specimen is subjected to high speed cyclic load to induce a crack at the root of the notch• Then study three point bending force is applied to open this crack• A clip gauge is fixed to the mouth of the notch to accurately measure the rate of crack opening • A load sensing device shows the load applied for this crack opening