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MEASUREMENT OF
RESIDUAL STESS IN
WELDMENTS

N PRAKASAN
ME METALLURGY
1
Measurement of Residual Stress in weldments
INTRODUCTION
Residual

Stress

 Residual

stress refers to the stress that ...
Measurement of Residual Stresses in weldments
INTRODUCTION
Residual

Stress

 Tensile

stress : Weld metal and adjacent...
Measurement of Residual Stresses in weldments
INTRODUCTION
 Residual

Stress distribution in the weldment

4
Measurement of Residual Stresses in weldments
Classification

of Techniques
Measurement of Residual Stress:
Stress relax...
Measurement of Residual Stresses in weldments
MEASUREMENT

BY STRESS RELAXATION
The
residual stress is determined by
mea...
Measurement by stress relaxation
Sectioning

using electric-resistance strain

gauges:




Electric-resistance strain g...
Measurement by stress relaxation
Sectioning

using electric-resistance strain

gauges:


The Residual stresses can be de...
Measurement by stress relaxation
Mathar-Soete drilling technique:








When a small circular hole is drilled
in a ...
Measurement by stress relaxation

 Gunnert








drilling technique:

This technique involves, the drilling
of four...
Measurement by stress relaxation
Rosenthal-Norton sectioning technique:







This technique is used for determining...
Measurement of Residual Stresses in weldments
MEASUREMENT

BY DIFFRACTION :
Elastic strains in metals can be determined ...
Measurement by Diffraction
X-ray diffraction: Principle:




The basic principle is the usage of the Debye-Scherrer met...
Measurement by Diffraction


Recommended X-ray tube and {hkl} plane for some common
materials

14
Measurement by Diffraction
X-ray diffraction:
 Position

sensitive scintillation detector (PSSD) based Xray Diffractomet...
Measurement by Diffraction
Neutron diffraction:
 Neutron

sources:

 Fission

• predominantly employed in steady-state ...
Measurement by Diffraction
Neutron diffraction:
 Principle:






When a monochromatic radiations fall on a sample, ...
Measurement by Diffraction
Neutron diffraction:
 This

technique is capable of measuring internal stress
without destroy...
Measurement by Ultrasonic method
Ultrasonic method
 Ultrasonic

stress measurement techniques are based
on the acoustic-...
Measurement by Ultrasonic method
 Ultrasonic

Equipment and Software for Residual
Stress Measurement.



The Ultrasonic ...
Measurement by Ultrasonic method
Ultrasonic method
 This

technique is effective for the analysis of residual
stresses i...
Measurement by stress relaxation

22
Measurement of Residual Stresses in weldments
 References

:

1. AWS Residual stress and Distortion.
2. N.S.Rossini, M.Da...
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Measurement of residual stresses in weldments

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Measurement of residual stresses in weldments

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Measurement of residual stresses in weldments

  1. 1. MEASUREMENT OF RESIDUAL STESS IN WELDMENTS N PRAKASAN ME METALLURGY 1
  2. 2. Measurement of Residual Stress in weldments INTRODUCTION Residual Stress  Residual stress refers to the stress that exists in a weldment after all external loads have been removed.  Other terms: internal stress, initial stress, inherent stress, reaction stress and locked-in stress.  The residual stress that occurs when a structure is subjected to nonuniform temperature change is usually called thermal stress.  The main causes are • Differential plastic flow, • Differential cooling rates, • Phase transformations with volume changes, 2
  3. 3. Measurement of Residual Stresses in weldments INTRODUCTION Residual Stress  Tensile stress : Weld metal and adjacent base metal  Compressive stress: Areas further away from weld metal. Weld is stretched by plates. 3
  4. 4. Measurement of Residual Stresses in weldments INTRODUCTION  Residual Stress distribution in the weldment 4
  5. 5. Measurement of Residual Stresses in weldments Classification of Techniques Measurement of Residual Stress: Stress relaxation techniques, • • • • for the Sectioning using electric-resistance strain gauges Mathar-Soete drilling Gunnert drilling Rosenthal-Norton sectioning Diffraction techniques (NDT), • X-ray diffraction technique • Neutron diffraction technique Ultrasonic techniques (NDT), 5
  6. 6. Measurement of Residual Stresses in weldments MEASUREMENT BY STRESS RELAXATION The residual stress is determined by measuring the elastic strain release. The determination of residual stress takes places when the stress is relaxed by cutting the specimen into pieces or by removing a piece from the specimen. Electric or mechanical strain gauges are used to measure the strain release. 6
  7. 7. Measurement by stress relaxation Sectioning using electric-resistance strain gauges:   Electric-resistance strain gauges are mounted on the surface of the test specimen. A small piece of metal containing the gauges is removed from the specimen. The strain that takes place during the removal of the piece is determined.  The strain measured is elastic strain that resulted from the residual stress distribution in the specimen. 7
  8. 8. Measurement by stress relaxation Sectioning using electric-resistance strain gauges:  The Residual stresses can be determined by substituting measured values of the strain components , into the following equations: 8
  9. 9. Measurement by stress relaxation Mathar-Soete drilling technique:     When a small circular hole is drilled in a plate containing residual stress, the stress in the areas around the hole is partially relaxed. The residual stress that existed in the drilled area is determined by measuring the stress relaxation. Three strain gauges are placed at 120O from each other, and then a hole is drilled in the center. The magnitudes and directions of the principle stresses are calculated by measuring strain changes at the three gauges. 9
  10. 10. Measurement by stress relaxation  Gunnert     drilling technique: This technique involves, the drilling of four (3 mm) holes through the plate perpendicular to the surface at the measuring point in a circle 9 mm in diameter. A groove 0.63 in. (16 mm) from the measuring point is then trepanned around the holes in steps, and measurements are made. The diametrical distance between these holes at different levels below the surface of the plate is measured by means of a specially designed mechanical gauge. The perpendicular distance between the plate surface and the gauge location at different levels below the surface is also measured. The residual stress present in the interior of the specimen can be calculated based on the measurement data. 10
  11. 11. Measurement by stress relaxation Rosenthal-Norton sectioning technique:     This technique is used for determining residual stress in a thick weldment. Two narrow thin blocks, one parallel to the weld and the other transverse to the weld are sectioned with full thickness of plate. Strain gauges are mounted on the walls of the blocks and strain relaxation is measured that results from slicing the blocks into small pieces. Two blocks, one longitudinal and one transverse, must be cut in order to determine the three-dimensional stress distribution. 11
  12. 12. Measurement of Residual Stresses in weldments MEASUREMENT BY DIFFRACTION : Elastic strains in metals can be determined by measuring the strain on lattice planes using diffraction techniques. When a polycrystalline metal is placed under stress, the elastic strains in the metal are manifested in the crystal lattice of the individual grains of the metal. The diffraction techniques are capable of measuring the inter-atomic spacings, which are indicative of elastic strain. 12
  13. 13. Measurement by Diffraction X-ray diffraction: Principle:   The basic principle is the usage of the Debye-Scherrer method measuring the shift of the reflections or peaks, in the region of low or high 2θ (Bragg’s angle). The lattice strain will be measured in directions that are oblique and inclined to the surface of the specimen in a plane which includes the direction of the stress to be measured. 13
  14. 14. Measurement by Diffraction  Recommended X-ray tube and {hkl} plane for some common materials 14
  15. 15. Measurement by Diffraction X-ray diffraction:  Position sensitive scintillation detector (PSSD) based Xray Diffractometer and Stress X-ray diffractometers are widely used for residual stress measurements. techniques measure stresses from 2 µm to 50 µm into the surface, however, subsurface and internal stress cannot be measured nondestructively.  This  To measure internal stress with X-ray techniques, the weldment must be systematically sectioned, and the surfaces to be measured must be electropolished. 15
  16. 16. Measurement by Diffraction Neutron diffraction:  Neutron sources:  Fission • predominantly employed in steady-state nuclear reactors. • Continuous sources, • a monochromatic beam of neutrons is produced by using a monochromating device to select a given neutron wavelength.  Spallation • usually in pulsed sources • the neutron beam usually consists of a series of short pulses each containing a spectrum of wavelengths. 16
  17. 17. Measurement by Diffraction Neutron diffraction:  Principle:     When a monochromatic radiations fall on a sample, the diffraction from a Brag plane results in the form of a cone (Debye Scherrer cone), with angle 2θ. The diffracted beam is shaped using suitable optical devices The intensity profile is recorded as a circle on a two dimensional detector. Diffraction from polycrystalline sample in a Debye Scherrer cone : 17
  18. 18. Measurement by Diffraction Neutron diffraction:  This technique is capable of measuring internal stress without destroying the weldment.  Neutrons penetrate several inches of metal and can be diffracted from the internal volume of a metal weldment to measure internal residual stresses.  Optimal resolution and 3 Dimensional maps can be obtained.  The volume resolution of the neutron stress measurements is 10 mm3.  The equipment is expensive 18
  19. 19. Measurement by Ultrasonic method Ultrasonic method  Ultrasonic stress measurement techniques are based on the acoustic-elasticity effect, according to this, the velocity of elastic wave propagation in solids is dependent on the mechanical stress.  In this method, waves are transmitted by a transducer, propagate through a region of the material and are detected by a receiving transducer.  Ultrasonic measurement configurations: Throughthickness pulse-echo throughthickness pitch-catch surface pitchcatch 19
  20. 20. Measurement by Ultrasonic method  Ultrasonic Equipment and Software for Residual Stress Measurement.  The Ultrasonic Computerized Complex (UCC) with an Expert System (ES) software developed for analysis of the influence of residual stresses on the fatigue life of welded components. 20
  21. 21. Measurement by Ultrasonic method Ultrasonic method  This technique is effective for the analysis of residual stresses in the interior of the material.  Advantages: • • • • • Depth is higher than that obtained by X-ray method Quick method inexpensive Portable Free of radiation  Disadvantages: • Low resolution 21
  22. 22. Measurement by stress relaxation 22
  23. 23. Measurement of Residual Stresses in weldments  References : 1. AWS Residual stress and Distortion. 2. N.S.Rossini, M.Dassisti, K.Y. Benyounis and A.G.Olabi, Methods of Measuring Residual Stresses in Components. 3. Determination of Residual Stresses by X-ray Diffraction - Issue 2, National physical laboratory. 4. Y. Kudryavtsev and J. Kleiman, Measurement of Residual Stresses in Welded Elements and Structures by Ultrasonic Method, IIW Document XIII-2339-10 5. Structural and Residual Stress Analysis by Non-destructive Methods, Evaluation, Application, Assessment. Viktor Hauk, Elsevier, 1997. 6. CEN TC 138, Non Destructive testing – Test Method for Residual Stress by X-Ray Diffraction. 7. Ceramic Data Supplied by Stresstech, Tikkutehtaantie 1, FIN40800, VAAJAKOSKI, Finland. 8. IAEA-TECDOC-1457, Measurement of residual stress in materials using neutrons 23

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