This document discusses using magnetic methods for non-destructive evaluation of micro residual stresses. It introduces different types of materials and their magnetic properties. Micro residual stresses of the first, second, and third order are described. Experimental setups using magnetic domains, Bloch walls, and Barkhausen noise are presented. Advantages include testing any size or shape without part preparation. Applications include inspection of raw materials and in-service components in industries like power plants and aircraft. The conclusion states that a testing method was developed to quantitatively measure micro residual stresses of the third order without reference methods.

1. Non-destructive evaluation of the micro
residual stresses of 3rd order by using micro
magnetic methods
JINSON JOSEPH
S7 ME, 31

2. Contents
 Introduction
 Types of Materials
 Micro Residual Stresses
 Advantages & Disadvantages
 Applications
 Conclusion
 References
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3. Introduction
 Today we discuss about the method of magnetic inspection
used for Non Destructive testing.
 Magnetic methods can detect both production discontinuities
(seams, laps, grinding cracks and quenching cracks) and in-service
damage (fatigue and overload cracks).
 Magnetism is the ability of matter to attract other matter to
itself. Objects that possess the property of magnetism are said
to be magnetic or magnetized and magnetic lines of force can
be found in and around the objects.
 A magnetic pole is a point where the a magnetic line of force
exits or enters a material.
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4. Introduction
 Residual stresses are self-equilibrating stresses existing in
materials under uniform temperature conditions and without
external loading.
 Magnetic Residual Stresses(MRS) in superimposition with load
induced stresses have advantages when they compensate. MRS
change under the influence of the temperature/time
conditions.
 Due to their capability to detect the change in the interaction
between the magnetic structure and the lattice defects liked is
location, precipitates, grain boundaries or residual stress fields,
the micro magnetic ND techniques are suitable for the
characterization of the residual stress state of the component.
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5. Types of Materials
Diamagnetic metals: Very weak and negative susceptibility to
magnetic fields. Diamagnetic materials are slightly repelled by a
magnetic field and the material does not retain the magnetic
properties when the external field is removed.
Paramagnetic metals: Small and positive susceptibility to
magnetic fields. These materials are slightly attracted by a
magnetic field and the material does not retain the magnetic
properties when the external field is removed.
Ferromagnetic materials: Large and positive susceptibility to an
external magnetic field. They exhibit a strong attraction to
magnetic fields and are able to retain their magnetic properties
after the external field has been removed.
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6. Ferromagnetic materials
• A material is considered ferromagnetic if it can be magnetized.
Materials with a significant Iron, nickel or cobalt content are
generally ferromagnetic.
• Ferromagnetic materials are made up of many regions in which
the magnetic fields of atoms are aligned. These regions are
call magnetic domains.
• Magnetic domains point randomly in demagnetized material,
but can be aligned using electrical current or an external
magnetic field to magnetize the material.
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Demagnetized Magnetized
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7. Crack detection using magnetic method
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8. Micro residual stresses(MRS) in
multiphase materials
• Residual Stress of First Order
• MRS of Second Order
• MRS of Third Order
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9. Residual stresses of First Order
Residual stresses of first order can arise :
• due to forming under applied mechanical stress
• due to the different cooling rates of different cross sections
of homogeneous materials
• due to the different cooling rates of different cross sections
of compounds of materials
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10. Micro residual stresses(MRS) of
Second Order
MRS of second order can occur :
• due to the different thermal expansion coefficient at the
interface between different material compounds
• due to in homogeneous and/or time dependent phase
transformations in the microstructure.
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11. Micro residual stresses(MRS) of Third
Order
MRS of the third order appear :
• when the lattice parameter of the second phase particles
embedded coherently in the matrix and the lattice
parameter of the matrix are different.
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12. Magnetic Domain In Single Crystal
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13. Bloch Walls
• Walls which separate the magnetic domains.
• Two kinds are observed in ferromagnetic materials :- 90◦ &
180◦
• The indicated angle is the angle between the magnetization
vectors in two adjacent domains.
• 90◦ Bloch wall have long range stress fields.
• 180◦ Bloch wall have short range fields.
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14. Barkhausen Noise
The pulsed eddy currents induce electrical voltage pulses,
detected by an induction coil surrounding the magnetized
specimen, the so called Barkhausen noise.
14
o Magnetic Barkhausen Noise
o Accoustic Barkhausen Noise
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15. 15
Hysterisis curve
Magnetic Barkhausen noise profile curve
B
M
Ht’
HC
MMAX MR
HCM Ht
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16. Deviation of Tensile load-stress dependence of the
maximum Barkhausen noise amplitude
For higher tensile
residual state -> Grey
curve
For higher compressive
residual state -> Dotted
grey curve
16
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17. Experimental Setup
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18. Fe-1%Cu alloy
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19. Advantages
• Virtually any size or shape of component can be inspected.
• Indications are easy to interpret.
• The indications formed by the particles closely represent the
shape and type of the discontinuity.
• Test part surface preparation is less critical than with
penetrant testing.
• Training and experience requirements prior to becoming
certified are significantly less stringent than for UT, RT, or ET.
• Inservice test is possible
• Very little preparation is sufficient
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20. Disadvantages
• It is only effective for the examination of ferromagnetic
materials.
• Discontinuity detection is limited to those at or near the
surface.
• Demagnetization may be required before, between, and
after inspections.
• Paint and/or coating removal is necessary from localized
areas on the part to facilitate good electrical contact when
using direct magnetization techniques.
• Uniform, predictable flux flow through the parts being tested
may not be possible due to complex shapes
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21. Applications
o Inspection of Raw Products
o Inspection Following Secondary Processing
o Inspection For In-Service Damage
o Power Plant Inspection
o Wire Rope Inspection
o Aircraft Inspection
o Pipeline Inspection
o Rail Inspection
o Brigde Inspection
o Pressure vessel Inspection
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22. Conclusions
• A testing method based on micro-magnetic measurement
techniques was developed to determine quantitatively MRS of
third order.
• Measurement of MRS in materials is of increasing interest.
• The developed test method allows a quantitative
determination of RS without the need for a reference method
such as the X-ray RS measurement.
• Therefore, this testing technique opens a wide range of
possible industrial applications provided that loading can be
performed.
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23. References
• M.Rabungn, I.Altpeter, C.Boller, G.Dobmann, H.G.Herrmann
_”Non-destructive evaluation of the micro residual stresses of
IIIrd order by using micro magnetic methods”.
• Baldev Raj_”Non Destructive Testing”
• Charles J. Hellier_”Handbook for Non destructive Evaluation”.
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24. THANK YOU