Magnetostriction

Source: Wikipedia, the free encyclopedia.

Magnetostriction is a property of

James Joule when observing a sample of iron.[1]

Magnetostriction applies to magnetic fields, while electrostriction applies to electric fields.

Magnetostriction causes energy loss due to frictional heating in susceptible ferromagnetic cores, and is also responsible for the low-pitched humming sound that can be heard coming from transformers, where alternating currents produce a changing magnetic field.[2]

Explanation

Internally, ferromagnetic materials have a structure that is divided into

strain in the material.[3]

The reciprocal effect, the change of the magnetic susceptibility (response to an applied field) of a material when subjected to a mechanical stress, is called the

Villari effect. Two other effects are related to magnetostriction: the Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a torque and the Wiedemann effect
is the twisting of these materials when a helical magnetic field is applied to them.

The Villari reversal is the change in sign of the magnetostriction of

kA/m
.

On magnetization, a magnetic material undergoes changes in volume which are small: of the order 10−6.

Magnetostrictive hysteresis loop

Magnetostrictive hysteresis loop of Mn-Zn ferrite for power applications measured by semiconductor strain gauges

Like

Jiles-Atherton model.[4]

Magnetostrictive materials

Cut-away of a transducer comprising: magnetostrictive material (inside), magnetising coil, and magnetic enclosure completing the magnetic circuit (outside)

Magnetostrictive materials can convert magnetic energy into kinetic energy, or the reverse, and are used to build actuators and sensors. The property can be quantified by the magnetostrictive coefficient, λ, which may be positive or negative and is defined as the fractional change in length as the magnetization of the material increases from zero to the saturation value. The effect is responsible for the familiar "electric hum" (Listenⓘ) which can be heard near transformers and high power electrical devices.

Cobalt exhibits the largest room-temperature magnetostriction of a pure element at 60

Alfer, FexAl1−x, are newer alloys that exhibit 200-400 microstrains at lower applied fields (~200 Oe) and have enhanced mechanical properties from the brittle Terfenol-D. Both of these alloys have <100> easy axes for magnetostriction and demonstrate sufficient ductility for sensor and actuator applications.[6]

Schematic of a whisker flow sensor developed using thin-sheet magnetostrictive alloys.

Another very common magnetostrictive composite is the amorphous alloy

MEMS.[citation needed
]

Cobalt

rare-earth elements, it is a good substitute for Terfenol-D.[8] Moreover, its magnetostrictive properties can be tuned by inducing a magnetic uniaxial anisotropy.[9] This can be done by magnetic annealing,[10] magnetic field assisted compaction,[11] or reaction under uniaxial pressure.[12] This last solution has the advantage of being ultrafast (20 min), thanks to the use of spark plasma sintering
.

In early sonar transducers during World War II, nickel was used as a magnetostrictive material. To alleviate the shortage of nickel, the Japanese navy used an iron-aluminium alloy from the Alperm family.

Mechanical behaviors of magnetostrictive alloys

Effect of microstructure on elastic strain alloys

polycrystalline alloys with a high area coverage of preferential grains for microstrain, the mechanical properties (ductility) of magnetostrictive alloys can be significantly improved. Targeted metallurgical processing steps promote abnormal grain growth of {011} grains in galfenol and alfenol thin sheets, which contain two easy axes for magnetic domain alignment during magnetostriction. This can be accomplished by adding particles such as boride species [13] and niobium carbide (NbC) [14] during initial chill casting of the ingot
.

For a polycrystalline alloy, an established formula for the magnetostriction, λ, from known directional microstrain measurements is:[15]

λs = 1/5(2λ100+3λ111)

Magnetostrictive alloy deformed to fracture

During subsequent

strain gauges.[16] These surface textures can be visualized using electron backscatter diffraction
(EBSD) or related diffraction techniques.

Compressive stress to induce domain alignment

For actuator applications, maximum rotation of magnetic moments leads to the highest possible magnetostriction output. This can be achieved by processing techniques such as stress annealing and field annealing. However, mechanical pre-stresses can also be applied to thin sheets to induce alignment perpendicular to actuation as long as the stress is below the buckling limit. For example, it has been demonstrated that applied compressive pre-stress of up to ~50 MPa can result in an increase of magnetostriction by ~90%. This is hypothesized to be due to a "jump" in initial alignment of domains perpendicular to applied stress and improved final alignment parallel to applied stress.[17]

Constitutive behavior of magnetostrictive materials

These materials generally show non-linear behavior with a change in applied magnetic field or stress. For small magnetic fields, linear piezomagnetic constitutive[18] behavior is enough. Non-linear magnetic behavior is captured using a classical macroscopic model such as the Preisach model[19] and Jiles-Atherton model.[20] For capturing magneto-mechanical behavior, Armstrong[21] proposed an "energy average" approach. More recently, Wahi et al.[22] have proposed a computationally efficient constitutive model wherein constitutive behavior is captured using a "locally linearizing" scheme.

Applications

See also

References

  1. ^ Joule, J.P. (1847). "On the Effects of Magnetism upon the Dimensions of Iron and Steel Bars". The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. 30, Third Series: 76–87, 225–241. Retrieved 2009-07-19. Joule observed in this paper that he first reported the measurements in a "conversazione" in Manchester, England, in Joule, James (1842). "On a new class of magnetic forces". Annals of Electricity, Magnetism, and Chemistry. 8: 219–224.
  2. ^ Questions & answers on everyday scientific phenomena. Sctritonscience.com. Retrieved on 2012-08-11.
  3. doi:10.1080/01418619808214252
    .
  4. S2CID 59468247
    .
  5. UCLA. Archived from the original
    on 2006-02-02.
  6. doi:10.1063/1.4944772
    .
  7. doi:10.1016/j.matdes.2006.12.016
    .
  8. doi:10.1088/1757-899X/60/1/012020
    .
  9. doi:10.1103/PhysRev.110.1341
    .
  10. S2CID 45873667
    .
  11. doi:10.1016/j.jmmm.2015.10.073
    .
  12. S2CID 118914808
    .
  13. doi:10.1016/j.intermet.2012.02.019
    .
  14. S2CID 136709323
    .
  15. doi:10.1088/1757-899X/60/1/012002
    .
  16. S2CID 136709323
    .
  17. ^ Downing, J; Na, S-M;
    doi:10.1063/1.4974064
    . 056420.
  18. ^ Isaak D, Mayergoyz (1999). Handbook of giant magnetostrictive materials. Elsevier.
  19. S2CID 122409841
    .
  20. ISSN 0021-8979
    .
  21. ISSN 0021-8979
    .
  22. S2CID 189954942
    .

External links
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