THE APPLICABILITY OF MAGNETIC DAMPING ALLOYS IN GEARS FOR NOISE CONTROL CONSIDERING SERVICE LOADING

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THE APPLICABILITY OF MAGNETIC DAMPING ALLOYS IN GEARS FOR NOISE CONTROL

CONSIDERING SERVICE LOADING

D. Aberle

To cite this version:

D. Aberle. THE APPLICABILITY OF MAGNETIC DAMPING ALLOYS IN GEARS FOR NOISE CONTROL CONSIDERING SERVICE LOADING. Journal de Physique Colloques, 1983, 44 (C9), pp.C9-297-C9-302. �10.1051/jphyscol:1983941�. �jpa-00223388�

JOURNAL DE PHYSIQUE

Colloque C9, suppl6ment au n012, Tome 44, d k e m b r e 1983 page C9-297

THE APPLICABILITY OF MAGNETIC DAMPING ALLOYS IN GEARS FOR NOISE CONTROL CONSIDERING SERVICE LOADING

D. Aberle

HochschuZe der Bundeswehr Hamburg, Laboratorim far Maschinenelernente und Getriebetechnik, 0-2000 Hamburg 70, F.R. G .

R&sum& - L1influence des conditions de service sur la capacitg

dl amortissement d1al 1 iages dlamortissement ferromagn6tiques a 6t6 examin6e dans le but de la rgduction du bruit des engrenages.

Abstract - The influence of service conditions on the damping capacity of ferromagnetic damping alloys has been investigated in order to apply these materials in gears for noise control.

Introduction.- Noise and vibration control is winning more and more importance. An enormous technical effort is required to satisfy the environmental and occupational noise restrictions which have been concluded in order to avoid harm to people. In some cases it is not yet to be realized.

A primary noise control in the noise source region should generally be possible with high damping a1 loys such as ferromagnetic damping a1 loys. Furthermore, the transmis- sion of body noise to neighbouring machine parts can be decreased by these a1Ioys.

The application of damping alloys in gears and other machines, however, is

basically problematic, because the silencing depends on a series of service conditio- ned parameters. Especially service loadings have an important influence on the damping of ferromagnetic alloys, which has been studied in this investigation.

Experimental procedure. - A servohydraul ic testing machine was used for tension- compression fatigue testing of damping alloys.

Table 1 shows the alloying contributions and the heat treatment of the investigated materials. All specimens and machine elements were annealed in argon-atmosphere and afterwards furnace-cooled to avoid residual stresses.

I

alloying contributions in %

I

Table 1 - Alloying contributions and heat treatment of the investigated alloys System

FeCrAl FeCo

In order to study the influence of service loading on the damping a specimen shape and a damping measuring method had to be selected which are compatible to both, fatigue testing and damping measurement.

Fig. la shows the specimen shape for this investigation. The stress concentration factor of thesespecimens is less than 1.01 /I/. The notch effect can be neglected.

The specific damping capacity was measured with strain gauges, which were applied at heat treatment annealed lh, 1100~

annealed 2h, 800' C

0,03-0,05 0,04

c

r 11,4-11,8

-

-

A1 2,2-2,4

-

-

Co -- 23-23,5

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1983941

C9-298 JOURNAL DE PHYSIQUE

the thinnest diameter of the specimen. The specimen was excited to a decaying flexural vibration, which was automatical 1 y registered and analyzed by a process computer. The specific damping capacity was calculated from the amplitudes of the decaying vibra- tion 161. By the continuous registration of all vibration amplitudes the specific damping capacity can be plotted out as a function of stress amplitude.

The influence of service loading on the damping can be registered by interrupting the fatigue test after special numbers of cycles, opening the specimen fixture on the one side, and measuring the damping.

According to the same method the influence of plastic deformation on the damping capacity was determined.

By means of a torsional pendulum the dependence of the damping on static stresses was measured. The pre-stress in the specimen was applied axially by weights. The decaying torsional vibration was registered by strain gauges. Fig. Ib shows the specimen shape for this test. All damping measurements were made at room temperature.

To prove the suitability of ferromagnetic damping alloys for noise control a 20 kW gear was developed (Fig. 2). The adjusting springs and gear hubs of this gear were substituted by those of damping alloys and the reduction of the noise emission by these measures was registered.

The gear was driven and loaded by two direct current electrical machines, which were encapsuled in order to guaranty that the noise level emitted by the gear was higher than the noise level emitted by the machines. In this case the noise emission of the gear was so high that the noise emission of the machines could be neglected.

Results.- Fig. 3 shows the fatigue-strength-diagrams of the tested alloys. The W b a b i l i t y of failure for a number of 107 cycles is plotted. These diagrams

are similar to those of low carbon steels 121.

The damping measurements showed the expected damping maxima of ferromagnetic alloys at medium stresses (Fig. 4). The torsional pendulum measurements with negligible pre- stresses gave a result similar to the analysis of the flexural vibrations.

A direct comparison, however, is limited, because different states of stress exist in both test types. The damping capacity of ferromagnetic alloys rapidly decreased as the mean stress increased (Fig. 5).

The quasistatic load of the FeCrAl-specimen was followed by a rapid decrease of the damping even at hardly measurable plastic deformations that the material became useless for vibration control (Fig. 6). The damping mechanism of FeCo proved a bit more resistant to plastic deformations 131.

During the fatigue tests it was found out that the load amplitude and the number of cycles have only a low influence on the damping. High mean stresses, however, cause a rapid damage of the damping mechanism.

At an alterning stress of 5 260 Nlmd the damping of FeCrAl decreased slowly (Fig. 7).

The specimen failed by breaking, because the fatigue limit was exceeded.

At a pulsating stress of 260 N/mrif the damping already decreased within the first 1100 cycles to about one third of the initial value while no crack occured until 10 cycles. On principle FeCo showed the same behaviour, but a lower decrease of the damping was registered.

The use of adjusting springs of FeCrAl caused a decrease of the noise level of 1-2 dB(A) (Fig. 8). It is not possible to decrease the noise even more by this measure, because the low damping gear material ist immediately in contact with the shaft. For this reason flexural vibrations, which are also caused by the mesh of

tooth, cannot be damped.

The decrease of flexural vibrations requires the use of high damping hubs. This measure caused a reduction of the noise level of about 4 dB(A) (Fig. 9). The application of adjusting springs and gear hubs made of FeCo did only entail a very low decrease of the noise level /3/.

Discussion.- The working or failing of the damping mechanism of FeCrAl and FeCo has to be regarded in connection with magnetic properties of these alloys. As a good magnetic domain wall mobility is necessary for the realization of an optimum damping capacity, only soft magnetic materials can be used for this purpose.

A soft magnetic material is characterized by the fact that only a minimum of obstac- les for the Bloch-wall shifting like non-metallic inclusions, foreign atoms, dis- locations, and grain boundaries are in its structure.

The dislocation density rapidly increases by plastic deformation /4/ and so it prevents the domain wall movement. The same explanation is true of the rapid decrease of the damping under cyclic loading with high pulsating stresses. Metallic materials including the steels can start to creep under high pulsating stresses below the fatigue limit /5/.

High pulsating stresses cause the failure of ferromagnetic damping alloys by the decrease of the damping while no damages of strength properties occur. The lower decrease of the damping by alterning stresses is less important for technical applications, because the damage of strength properties predominates.

Because of the strength properties ferromagnetic damping alloys are suitable for all machine elements which are generally made of mild steel. But it is inconvenient to produce gear-tooth systems of FeCrAl or FeCo, because the hardness is low /6/.

The size of such gears would be much bigger than the size of gears made of surface hardened materials. This would not be acceptable from the economical and in most cases from the technical point of view.

Because of the serious influence of static stress on the damping a design has to be chosen which guaranties low mean stresses in the machine parts made of damping alloys. For this reason positive couplings should be preferred to compression joints.

References :

/1/ Peterson, R,E. Stress Concentration Factors, New York 1974

Taschenbuch fur den Maschinenbau, Berlin 1981

/3/ Aberle, D. Dissertation, HSBw Hamburg 1983 /4/ Ilschner, B. Werkstoffwissenschaften,

Berlin 1982

/5/ Mayr,P., DVM-Symposium Low-Cycle Fatigue, Macherauch, E. Stuttgart 1979

/6/ Schneider, W. et al. ICIFUAS 7, Lausanne 1981

JOURNAL DE PHYSIQUE

Fig. 1

-

Specimen shapes for fatigue Fig. 2 - Experimental gear with conic tests (a) and torsional pendulum hubs

measurements (b)

Fig. 3 - Fatigue-strength-diagram of Fig. 4 - Influence of stress amplitude FeCrAl and FeCo on the damping (PRNR = number

o f specimen)

C9-301

Fig. 5 - Influence of pre-stress on the damping (PRNR = n u m5e r 0f specimen, ov = static stress)

Fig. 6 - Influence of high single loads and the corresponding plastic defor- mations on the damping of FeCrAl (LSP = number of cycles)

J O U R N A L DE PHYSIQUE

Fig. 7

-

Influence of cyclic stressing on the damping (LSP = number of cycles):

a) FeCrAl , alterning stress b) FeCrAl , pulsating stress c) FeCo, alterning stress d) FeCo, pulsating stress

- ^LSP

-

^{0. - - LSP}

-

^1000000. - ^LSP

-

^0.

LSP

-

^{4000. LSP}

-

^1100.

- - 40 ^LSP

-

^{100000. -} _{4 0} ^{- LSP}

-

^1000000.

a b

30 30

Y N

5 ^{20 20}

U U 0

* ¹⁰ * ¹⁰

0 0

0. 0 1 0. I 0 0

SIGMA I N N/MM-*2 SIGMA I N N/MM--2

-

^LSP

-

^{0. - LSP}

-

^{0. - - LSP}

-

^10000Ei0.

- ^LSP

-

^1000. _{- -} ^LSP

-

^1000.

4 0 40 LSP

-

^40000.

-

9

%

5

-r'

o C 4 5 o d ~ o s t i n g s p r i n g s o F e C r A l a d j u s t i n g s p r i n g s

Fig. 8

-

Decrease of noise emission by high damping adjusting Springs (TI = driving torque)

c d

Fig. 9 - Decrease of noise emission by high damping gear hubs

0.01 0. 1 1 10 100 1000 0.01 0 . 1 1 10 100 1000

SIGMA I N N/MM--2 SIGMA I N N/MM*-2

w ^{O M}

~ 2 6 O ~ l m . d

30 30

h. Y .

20 5 ^{2 0 '}

U U

* ¹⁰ * ^{1 0 '}

0 0 -

(T, = driving torque)

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-

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