Non-destructive evaluation of the micro

residual stresses of 3rd order by using micro

magnetic methods

JINSON JOSEPH

S7 ME, 31

Contents

Introduction

Types of Materials

Micro Residual Stresses

Advantages & Disadvantages

Applications

Conclusion

References

2jinsonjsh@gmail.com

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.

3jinsonjsh@gmail.com

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.

4jinsonjsh@gmail.com

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.

5jinsonjsh@gmail.com

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.

6

Demagnetized Magnetizedjinsonjsh@gmail.com

Crack detection using magnetic method

7jinsonjsh@gmail.com

Micro residual stresses(MRS) in

multiphase materials

• Residual Stress of First Order

• MRS of Second Order

• MRS of Third Order

8jinsonjsh@gmail.com

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

9jinsonjsh@gmail.com

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.

10jinsonjsh@gmail.com

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.

11jinsonjsh@gmail.com

Magnetic Domain In Single Crystal

12jinsonjsh@gmail.com

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.

13jinsonjsh@gmail.com

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

jinsonjsh@gmail.com

15

Hysterisis curve

Magnetic Barkhausen noise profile curve

B

M

Ht’

HC

HtHCM

MMAXMR

jinsonjsh@gmail.com

Deviation of Tensile load-stress dependence of the

maximum Barkhausen noise amplitude

16

For higher tensile residual state -> Grey curve

For higher compressive residual state -> Dotted grey curve

jinsonjsh@gmail.com

Experimental Setup

17jinsonjsh@gmail.com

Fe-1%Cu alloy

18jinsonjsh@gmail.com

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

19jinsonjsh@gmail.com

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

20jinsonjsh@gmail.com

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

21jinsonjsh@gmail.com

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.

22jinsonjsh@gmail.com

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”.

23jinsonjsh@gmail.com

THANK YOU