AECL-8845

ATOMIC ENERGY F - S T 3 L'ENERGIEATOMIQUE

OF CANADA LIMITED T ^ & J r DU CANADA LIMITEE

THE SIGNIFICANCE OF SHEAR AND NORMAL FORCECOMPONENTS ON TUBE WEAR DUE TO FRETTING

AND PERIODIC IMPACTING

Importance des forces normales et de cisaillementsur I'usure des tubes causee par

le frottement et des chocs repetitifs

PS KO

Paper Prepared for the Institute of Mechanical Engineers Tribology Group Seminaron Fretting Wear held in Nottingham, England, 1985 April 2-3

Chalk River Nuclear Laboratories Laboratoires nucleates de Chalk River

Chalk River, Ontario

October 1985 octobre

ATOMIC ENERGY OF CANADA LIMITED

THE SIGNIFICANCE OF SHEAR AND NORMAL FORCE COMPONENTS ONTUBE WEAR DUE TO FRETTING AND PERIODIC IMPACTING*

by

P.L. KoDivision of Mechanical Engineering

National Research CouncilWestern Laboratory

*Paper prepared for the Institute of Mechanical Engineers Tribology GroupSeminar on Fretting Wear held in Nottingham, England, 1985 April 2-3.

Engineering Research BranchChalk River Nuclear Laboratories

CHALK RIVER, OntarioCanada KOJ 1J0

1985 October

AECL-8845

L'ENERGIE ATOMIQUE DU CANADA LIMITEE

"IMPORTANCE DES FORCES NORMALES ET DE CISAILLEMENT SUR L'USUREDES TUBES CAUSÉE PAR LE FROTTEMENT ET LES CHOCS REPETITIFS"

P.L. KoDivision du Génie MécaniqueConseil National de Recherches

Laboratoire de l'Ouest

Sommaire

Des techniques bien particulières pour prédire l'usure des tubesd'échangeurs de chaleur et d'autres composantes mécaniques semblablessoumises à des mouvements aléatoires sont nécessaires afin d'estimer leurdurée de vie et une limite acceptable du niveau de vibration.

Il a été trouvé que l'usure des tubes par frottement est une fonction del'interaction dynamique (force d'impact) entre le tube et son support.Les forces de réaction instantanées au support ont été décomposées en unecomposante normale et une composante de cisaillement. Les fonctionsdynamiques dérivées des composantes de cisaillement représentent bien lestaux d'usure.

Les résultats montrent que l'usure des tubes par frottement estessentiellement une fonction de la force d'impact et de l'angle d'impact.De plus, le taux d'usure demeure faible lorsque la composante decisaillement est absente.

Division de recherche en ingénierieLaboratoires nucléaires de

Chalk River, OntarioCanada KOJ 1J0

1985 Octobre

AECL-88H5

ATOMIC ENERGY OF CANADA LIMITED

THE SIGNIFICANCE OF SHEAR AND NORMAL FORCE COMPONENTS ONTUBE WEAR DUE TO FRETTING AND PERIODIC IMPACTING

by

P.L. Ko

Division of Mechanical Engineering

National Research CouncilWestern Laboratory

Abstract

To estimate the working life or the acceptable vibration limit for heat exchang-er tubes and similar types of engineering components that are subjected torandom motions, special wear prediction techniques are needed.

Tube fretting wear was found to relate to the dynamic interaction, or impactforce, between the tube and its support. The instantaneous reaction forces atthe support were resolved into shear and normal components. Force functionsderived from the shear force components were found to correlate well with thewear rates.

The results show that tube fretting wear is mainly a function of the impactforce and the angle of impact. Without the sliding (or shear) component, thewear rate remains low.

Engineering Research Branch

Chalk River Nuclear LaboratoriesCHALK RIVER, Ontario

Canada KOJ 1J0

1985 October

AECL-8845

1• INTRODUCTION

The working life and reliability of many engineering components is often deter-mined by the wear of parts that are subjected to reciprocating sliding, impact-ing or a combination of these motions. For example, in heat exchangers, tubevibration caused by fluid flow may result in wear damage due to dynamic inter-actions between the tube and its supports. To estimate the working life or theacceptable vibration limit for these heat exchangers, reliable wear predictiontechniques are needed. Assessments of this nature are complex because wear rateis a function of several factors, including material compatibility, environment-al conditions, loading and contacting conditions, and the type of tube motion.

Among the quantitative theories of metallic wear, those of Archardfl], Holm[21.and Burwell and Strang[3] are the most widely referred to. Theories predictthat the volume of wear will be a linear function of rubbing distance at con-stant sliding speed and that the volume-rate of wear will be proportional to theapplied load.

In heat exchangers, due to the clearance between the tube and its support, thevibrating tube can repeatedly make and break contact with the support. Depend-ing on the flow conditions, a tube may be rubbing and impacting against the tubesupport or against adjacent tubes. Alternatively, there may be simply recipro-cating rubbing with no separation, as in classical fretting. Therefore, in tubefretting, an impacting component in addition to the sliding or reciprocatingrubbing is often involved. The term "compound impact" is used to indicate thatthe normal impact velocity is accompanied by a sliding component. Under thesecircumstances, the physics of deformation, the surface and subsurface stressesmust be considered.

Tube wear prediction techniques, therefore, need to consider the plastic deform-ation, the shear stresses and the complex interrelationship of many parameters,such as tube/support clearance and type of tube motion. Several tube failureprediction techniques have been described in an earlier paper[4]. Many of thesewere based on Archard's wear theory. However, the mechanisms involved inimpact-fretting wear appear to relate better to the delamination theory intro-duced by Suh[5] and his co-workers. Their experimental studies showed thatinitially subsurface plastic deformation causes the nucleation of voids. As theformation continues, these voids elongate and link up to form long cracks in adirection nearly parallel to the wear surface. These cracks will shear to thesurface when a critical length is reached, yielding a wear particle in the formof a long thin sheet.

In earlier work, Ko[6] has shown that tube fretting wear was related to thedynamic interaction, or impact force, between the tube and its support. Theresultant force signal was statistically analysed and transformed to a forcefunction that was correlated to the wear rate. In this work, the measured orcomputer predicted forces for different types of tube motion are statisticallyanalysed using histograms of force level and frequency of occurrence. Thesehistograms not only characterize the type of tube motion, they also revealchanges in excitation or in tube/support clearance. However, the resultantforce signal does not differentiate the significance of the shear and the normalcomponents on wear. Arbitrary weighting coefficients had to be assigned to thedifferent levels of the resultant force in order to obtain a good wear-forcecorrelation.

2.

2. EXPERIMENTAL SET-UP

A single-span tube fretting rig, as that shown in Figure 1, was used for all thetests. A length of tubing clamped rigidly at its upper end Is used to hold thetube specimen mounted near its lower end. The tube support specimen, either inthe form of an annular ring or a rectangular block, is located on a transducerplatform that can be adjusted to be level with the tube specimen. As shown inFigure 2, the tube support specimen is held by four miniature quartz forcetransducers that are preloaded and positioned at 90° intervals around the cir-cumference. The support ring with its force transducer assembly can be posi-tioned either concentrically or offset with respect to the tube specimen, usingposition signals from a pair of displacement transducers, mounted on the plat-form.

Attached to the free end of the tube is a vibration generator consisting of twostepper motors driving two eccentric masses. A variety of motions can beobtained by different eccentric mass combinations, e.g., normal impacting,circular orbital, elliptical orbital and reciprocating. Ideallstically, thecircular orbital motion is primarily a sliding wear cycle; the normal impactingmotion is an impact wear cycle; the elliptical orbital motion has both obliqueand normal impact as well as some sliding motion; and the reciprocating motionsimulates fretting. In practice, both shear and impact components exist in allmotions excepting, perhaps, the reciprocating one. The ratio of these compon-ents depend on the type and level of excitation, and the tube/support clear-ance.

The four force transducers mounted around the tube support specimen measure thedynamic Interaction between the tube and the support. Their output signals areindividually amplified and then the signals from diametrically opposed trans-ducers are added after one signal is inverted. Inversion is required to main-tain the 'sense' of the signals when they are subsequently resolved into normaland tangential components. Thus, a pair of signals corresponding to 'x' and 'y'forces are obtained. These two force signals, together with the signals corre-sponding to 'x' and 'y-' displacements, are simultaneously recorded on a memorystorage device for later computer analysis.

The annular ring assembly may be replaced by a flat specimen for impacting andreciprocating rubbing tests between a cylinder (tube) and a flat specimen tosimulate other support configurations. One arrangement shown in Figure 3consists of a rectangular bar specimen, 9 x 8 x 14 mm, and four force trans-ducers. The specimen is held by two transducers, one on each side, and support-ed by two other transducers at the back. During oblique impacting or recipro-cating sliding, the tangential (or shear) force component is measured by the twoside-transducers while the normal force component is monitored by the two trans-ducers at the back.

3. DATA ACQUISITION AND DATA ANALYSIS

In an earlier study[6], the pairs of opposite force signals were first summedand then the two orthogonal components were summed vectorially to obtain theimpact force magnitude used in subsequent computation. Thus, only the resultantforce signal was analysed in this earlier technique.

3.

In the present approach, the four contact force signals are added in pairs toproduce two orthogonal force signals. These, together with the x-y displacementsignals of the tube motion, are recorded on magnetic tape. Figure 4 shows aschematic diagram of the data acquisition system for the new approach.

For analysis, the recorded analog signals are converted to digital and stored ina computer. In order to locate the instantaneous tube trajectory and its corre-sponding impact forces, the process requires a system that has a high samplingrate to minimize the delay time between signals within a sample set (two forcesand two displacement signals). The analog-to-digital converter used has simul-taneous sample/hold capability to eliminate data time-skew. The four channelsare sampled every 500 ys and held for 200 ys while analog-to-digital conversiontakes place, resulting in approximately 70 sample points per tube vibrationcycle, when the excitation frequency is around 30 Hz.

The data is now ready for processing. The computer program calculates thenormal and shear force functions and contact time. It also produces tables offorces, graphical plots of displacements and forces; and histograms of shear andnormal forces.

The actual manipulation involves several steps. First, the digitized force dataare scanned and a real datum is defined through signal averaging. This step isnecessary because the force signal is often slightly biased due to some extra-neous signals from either the transducer cables or charge amplifiers. If thisbiased signal, although very small, is not corrected, the calculation of per-centage contact time becomes meaningless as a contact is counted whenever theabsolute value of either one of the force signals exceeds 1 N. The correctedx-y force signals and the calculated contact time are stored in a file.

Once a contact is established, the x-y displacement signals at that point areused to determine the angle between the point of contact and the origin. Thisangle is Chen used to project the x-y force signals into the normal and shearcomponents as illustrated in Figure 5. Then the occurrence of the normal andshear components within designated force levels are counted and summed separate-ly. These are plotted as percentage of the total sample time. Contact time isdetermined by counting until the contact is broken, as indicated by the absenceof a force signal. Histograms for the normal and shear forces are computed anda force function is calculated.

The wear rates for the corresponding tests are also entered into the computerfor subsequent correlation with the force functions.

Figures 6 to 8 show sample histograms and their corresponding tube trajectoriesfor different tube motions. In tube fretting studies the tube may impact orslide against the tube support. There may also be fretting as the tube is pres-sed against the support due to fluid flow and/or tube/support eccentricity. Theeffect of the type of tube motion on tube wear has been discussed in severalprevious papers, e.g., [7]. They identified that impact motion alone generallycaused little wear. Later, it was further revealed that tube wear was primarilycaused by the shear component of the impact force[8]. Figure 6 shows that innormal impact motion the shear force component is very small.

4.

4. TEST PROGRAM AND TEST RESULTS

Two series of tests were performed. The first consisted of 22 tests coveringdifferent levels of excitation, frequencies, excitation force ratios in the x-ydirections, and diametral clearances. As the primary objective of this serieswas to investigate a specific wear prediction technique by correlating wear ratewith tube motion parameters, only one material combination was tested. Thesecond series of tests consisted of short duration tests to study the relation-ship between the shear and normal force components. The test matrix covereddifferent material combinations, tube/support configurations, flow media, typesof tube motion and angles of approach.

The materials used in the first series of tests were Incoloy 800 and Inconel600*. These are nickel alloys frequently used for steam generator tubing innuclear power plants. The wear rates of these tubing materials against varioussupport materials have been studied and reported elsewhere[4]. In this series,which lasted 48 to 72 hours per test, specimens were weighed before and after todetermine their weight losses. Table 1 gives a summary of the weight lossresults and the averaged normal and shear forces for each test.

The tests in the second series were run for one hour each. This was deemedsufficient for the force and displacement signals to be recorded under a steadystate test condition. However, owing to the short test duration, the wear rateswere not measured.

5. FORCE-WEAR CORRELATION

5.1 Correlation Based on Resultant Force

In [6], where only the resultant force signal was analysed, the force functionswere of the form,

nF = V (force), x (probability), x (weight).

i=l x 1 1

where (force)^ = average resultant force level in the ith band or interval.

Ni Cr Fe_

*Incoloy 800 32-35% 20-23% BalanceInconel 600 72% min. 14-17% 6-10%

5.

(probability) = number of counts In interval iI total number of counts

(weight)^ = an estimated weighting factor assigned to ith band force level toimprove correlation

When unity is assigned to (weight)|, the force function represents the inte-grated area under the absolute value curve of force signals. Fairly good corre-lations were obtained when normal-impacting data points were excluded. Forthese points, the calculated force function was consistently too high forexperimental wear rates. Subsequently, the use of different weighting for thevarious force intervals improved the correlations significantly, however, theweighting values assigned were based on too small a set of data to give repeat-able results. In this approach, smaller weighting factors were applied to thehigher force levels to reduce the contributions from the large peak forcesusually associated with pure normal impacting, but causing little wear.

For comparison purposes, the results from the first series of tests were corre-lated as shown in Figures 9 and 10, using this earlier approach. In Figure 9,(weight)^ were equal to unity and all data, including those due to normalimpacting, were included. The correlation in Figure 10 excludes the normalimpacting points. These graphs clearly show that the approach, based on result-ant force signals, only has a reasonable correlation coefficient when applied towear data that excludes normal impacting motion.

5.2 Correlation Base on Shear and Normal Components

In the present approach, the instantaneous force signal was resolved into shear(tangential) and normal components. Thus, a force function can be based oneither the shear component only, or the sum of both shear and normal compon-ents.

F = ^2 (shear), x (prob) + q X/ (normal), x (prob).

i=l 1 X 1=1 i 1

where (shear)^ = average shear force level in the ith band or interval

(normal)^ = average normal force level in the ith band or interval

. , . number of counts in the ith intervali total number of counts

q = an estimated weighing factor assigned to the normal component of theforce function, q could be varied from zero to one.

When q is assigned a value of one, the force function is somewhat similar to theone used in the previous approach. Indeed the correlation, as shown in Figure11 is rather poor, primarily due to the normal-impacting data points which fallwell below the correlation line. As shown in Figure 12, the correlation improv-ed significantly when these points were removed.

6.

By assigning a zero value to q, only the shear component is used in calculatingthe force function. This is more realistic as shear is the primary cause ofwear. Using this equation, the values of force functions for the impactingpoints are very low. This is expected, as normal forces dominate the impactingmotion. The correlation for all the data, as shown in Figure 13, is very goodhaving a correlation coefficient of 0.928. It should be recalled that the weardata are from tests covering a variety of parameters, including tube/supportclearance, type of tube motion, excitation frequency and force level.

Although wear is mainly due to shear forces, normal forces also play a role inhypothesized wear mechanisms. The higher the normal force component, the deeperthe subsurface layers that are affected by shear. With the separation of theforces into shear and normal components, it will be possible to construct newforce functions, in which the contribution of both components can be properlyidentified, and thus, separately weighed.

6. EFFECT OF TEST PARAMETERS ON FORCE COMPONENTS

6.1 Material Combination and Flow Medium

Included in the second series of tests were four material combinations and threeflow media. For each test, the tube was excited with the same excitation forcegiving a circular tube motion. The results given in Table 2 show that the nor-mal force component is about the same for the different material combinationsand flow media tested. The mean value being 16.2 N with a standard deviation of0.65. The shear force component, however, varies substantially. As expected,the Teflon/Teflon combination has the lowest shear force component followed byTeflon rubbing against Inconel 600 or Incoloy 800.

With engine oil as a lubricant, the shear force component of the Incoloy 800/Inconel 600 pair was reduced to about the same level as those of Teflon/nickelalloy pairs- Indeed the force signals and tube trajectory plot, reveal that thelubricant greatly reduces the level of secondary impact, resulting in smoothersliding. This is also the case with the Teflon/Teflon pair, as shown in theplots of Figure 14.

Interestingly, the shear force component is higher in water than in air for allthe tests involving these flow media. This would suggest that impact and fret-ting results from tube wear tests performed in water may be used for componentevaluation where air is the actual flow medium. The results would have beenslightly conservative.

6.2 Excitation Force

The effect of excitation force on the normal and shear components is shown inFigures 15 and 16. In one case, the excitation was increased by raising theexcitation frequency. In the other case, the eccentric masses on the vibrationgenerator were increased. The excitation force is proportional to the eccentricmasses and to the square of the excitation frequency (i.e., the rotational speedof the eccentric masses). Also, shown on these figures is the dynamic coeffici-ent of friction, \i, calculated as y= Fg/F(j«

In both cases studied, the two components of force increased linearly withexcitation level. For the case of increasing eccentric masses (frequency

7.

remained constant), the normal and shear components increased at approximatelythe same rate. However, for the case of increasing excitation frequency, therate of increase of the normal force was higher than that of the shear force.There are two plausible explanations. One is that the coefficient of frictiondecreases as the excitation frequency is increased, i.e., the impact velocity isincreased. For many unlubricated metal pairs, the dynamic coefficient of fric-tion is known to decrease with increasing sliding velocity. The other explana-tion for the low tangential force coefficient, (Fg/F^j), is that the tubemotion is sensitive to the excitation frequency. Here, the mode of tube vibra-tion may change as the excitation frequency is changed. If the latter is true,wear data taken under these conditions should be interpreted with care.

6.3 Impact Angle

The effect of impact angle en the two force components was studied using aZircaloy tube specimen impacting on a flat surface also of Zircaloy. Figure 17shows a plot of <)>, the ratio of the shear force component to the normal forcecomponent, against a, the angle of impact. The angles were varied from 0° to+ 90° from the vertical. When sliding occurs, the tangential force coefficient,<p, equals M, the coefficient of friction. Thus the value of <j> at a=90°, wherereciprocating sliding occurs, is taken as the nominal coefficient of friction.

Figure 18 shows five different tube trajectories. At impact angles less than30° (from the vertical), the tube trajectory appears to have rebounded in almostthe same direction of impact, suggesting that the tangential component of theimpact force is not sufficient to cause gross sliding; the average tangentialforce coefficient is less than ]j. On the other hand, at impact angles around70°, the trajectory appears to be both sliding and bouncing as shown in Figure18(d), resulting in a f value higher than that of U• It would appear that theploughing component that forms part of the frictional force becomes significantunder these oblique impact-sliding conditions. One would expect the wear rateto be higher under these conditions due to the larger shear force component.

7. DISCUSSIONS

The problem of developing a forcing function is one of deciding how the contactforces caused by tube-support collisions will affect the surface and subsurfacestresses that lead to wear. Results from the first series of tests describedimply a linear relationship between the force level and its damaging effect, thehigher the force level the higher the stress. However, the force-wear correla-tion from earlier tests[6] actually reveal a power relationship indicating thatthe impact fretting wear rate follows a power (e.g., cube) law as a function ofimpact force. Under fretting conditions Goodman[9] showed that the slip regionincreased in size roughly in direct proportion to the amplitude of vibration.Johnson[10] postulated that since the energy loss per cycle is proportional tothe cube of the amplitude, the fretting wear rate might follow a similar cubelaw. Although the actual mechanisms involved are not the same as those in theimpact-fretting cases, the analog is worth noting.

A comparison of Figure 9-13 inclusive, clearly shows the Improvement in correla-tion when only the shear (tangential) force component is used. The correlationsare reasonably good using the resultant force signal or the combined normal andtangential force components as long as the data due to normal impacting areomitted. This Is understandable since the Fg/Fjj ratios are normally around

0.43 with the exception of the impacting ones where the ratios are much lower.Thus, when the impacting points are omitted, the correlations (not the absolutevalues) are more or less the same whether only the shear-component or thecombined shear and normal components are used. Furthermore, the shear forcecomponent is related to the normal component by the angle of impact and by thecoefficient of friction. It, therefore; reflects the changes of the normal com-ponent. Ideally, the force function buould distinguish between the normalcomponents associated with static loads, e.g., flow drag, cube bow, for the rub-bing motion (characterized by a continuous normal force) and those associatedwith impacting motion (characterized by high, sharp normal peaks).

In tube fretting studies, high wear is usually associated with tube motions ofcircular or elliptical mode. Normally, the circular mode causes a higher wearrate than the elliptical mode does. However, occasionally, due to the combinedeffects of tube/support clearance, eccentricity and magnitude of excitation, thetube trajectory of a supposedly circular mode may approach the support with anearly normal impact angle, resulting in a low shear force component and lowwear rate.

In dynamic systems subjected to random motions, such as those of flow-inducedtube vibration in heat exchangers, the parameters, e.g., normal load, distancetravelled, that are needed to predict wear losses are usually not known.Indeed, nor do the type of tube motion and tube/support clearance remain con-stant as in an idealistic test case. On the other hand, results from thepresent study clearly show that the shear force component alone can provide agood account of the dynamic interaction between an impacting tube and its sup-port. This tube support impact force can be monitored with force transducers orpredicted using a computer model. The present technique for predicting tubefretting is, therefore, well suited for the dynamic systems discussed.

8. CONCLUSIONS

A technique based on tube/support impact forces was developed to predict impactfretting wear.

Experimental results show that impact fretting wear is mainly a function of theimpact force and the angle of impact. Without the sliding component, the wearrate remains low.

Low friction pairs such as Teflon/Teflon result in very small shear force com-ponents despite the fact that the excitation was primarily rubbing. Obliqueimpacting at angles around 65° from the vertical results in tangential forcecoefficient, Fs^N' n i S h e r than the nominal coefficient of friction. Thiscan be significant in terms of tube fretting wear.

ACKNOWLEDGEMENT

The author would like to thank R. Meijer-Drees and R. Dutton, both University ofWaterloo students, for their contributions in developing the computer programs,and in performing the experimental tests and data analyses. He would also liketo acknowledge the significant contribution of P.C.H. Cheng, an UKAEA sponsoredstudent at the University of London, while on attachment to the Chalk River

9.

Nuclear Laboratories. Finally, the author is grateful to Atomic Energy ofCanada Limited for permission to publish this work.

REFERENCES

[1] Archard, J.F. and Hirst, W., "The Wear of Metals Under UnlubricatedConditions", Proc. Royal Society, London, A236 (1956) 397.

[2] Holm, R., Electric Contact Handbook, Springer-Verlag, Berlin, 1958.

[3] Burwell, J.T. and Strang, CD., "On the Empirical Law of AdhesiveWear", J. of Applied Physics, 23 (1952) 18.

[4] Ko, P.L., "Heat Exchanger Tube Fretting Wear: Review and Applicationto Design", J. of Tribology, (1985).

[5] Suh, N.P., "The Delamination Theory of Wear", Wear, 25 (1973) 111.

[6] Ko, P.L. and Basista, H., "Correlation of Support/Impact Force andFretting-Wear for a Heat Exchanger Tube", J. of Pressure VesselTechnology, 106-1 (1984) 69.

[7] Ko, P.L., "Experimental Studies of Tube Fretting in Steam Generatorsand Heat Exchangers", J. of Pressure Vessel Technology, 101 May (1979)125-133.

[8] Ko, P.L., Tromp, J.H. and Weckwerth, M.K., "Heat Exchanger Tube Fret-ting Wear: Correlation of Tube Motion and Wear, ASTM SpecialPublication, STP-780 (1982) 86-105.

[9] Goodman, J.E., "A Review of Progress in Analysis of Interfacial SlipDamping", J.E. Ruzicha (ed.), Structural Damping, American Society ofMechanical Engineers, (1959).

[10] Johnson, K.L. and O'Connor, J.J., "Mechanics of Fretting", Procs.,Institution of Mechanical Engineers, London 179 (1963-64) pt. 3F, paper11.

10.

TABLE 1

Test Results

1

2

3

4

5

6

7

8*

9*

10

11

12*

13

14

15

16

17

18

19

20

21

22

V N

20.20

15.56

8.80

17.52

13.99

17.23

16.70

20.91

26.00

19.40

16.25

19.80

15.95

21.58

14.51

22.76

19.07

30.29

19.52

16.49

29.19

29.17

Fs, N

9.68

5.54

4.18

7.15

5.23

6.82

3.30

1.69

2.27

10.5

7.13

5.33

8.1

7.6

5.02

11.96

7.04

12.61

9.68

8.13

10.62

13.33

V* XH2»»

25.11

19.59

9.91

21.43

18.49

21.23

20.14

25.59

29.65

24.43

22.23

23.12

21.33

26.36

17.70

29.85

21.93

36.06

26.73

20.94

33.50

34.67

Ratio =5.r „N

0.48

0.36

0.48

0.41

0.37

0.40

0.20

0.08

0.09

0.54

0.44

0.27

0.51

0.35

0.35

0.53

0.37

0.42

0.50

0.49

0.36

0.46

Combined Tubeto Support Wear

rate mg/10cycles

21.29

3.4

0.58

8.09

2.46

6.81

1.14

0.24

1.07

14.75

4.21

1.98

10.11

16.87

3.89

14.25

8.90

25.09

14.51

11.29

58.34

25.61

*Normal Impacting

TABLE 2

Comparison of Force Components for Different Material Combinations and Flow Media

Circular tube motion at 26.5 Hz

Tube

Incoloy 800

Incoloy 800

Incoloy 800

Incoloy 800

Incoloy 800

Incoloy 800

Teflon

Teflon

Teflon

Teflon

SupportRing

Inconel 600

Inconel 600

Inconel 600

Inconel 600(flats onopposite

sides)

Teflon

Teflon

Inconel 600

Inconel 600

Teflon

Teflon

Flow Medium

Air

Water

Oil

Water

Water

Air

Water

Air

Water

Air

Water

Shear Force

VN

6.58

7.20

3.76

7.3

8.0

2.89

3.87

3.31

3.71

2.57

3.25

Normal ForceFN> N

15.9

15.7

17.1

17.2

16.2

17.2

16.6

16.3

16.0

15.8

15.3

Tangential ForceCoefficient, F,/F

b N

0.41

0.46

0.22

0.42

0.49

0.17

0.23

0.2

0.23

0.16

0.21

12.

FIGURE 1: Room Temperature Tube Fretting Rig

13.

FIGURE 2: Force-Ring Assembly and Transducer Platform

14.

^ " I O 20 30 -10 rso no TO so i>u

11111111111111.11... Ijj.i ij. J1LLU.I.L.JJ LLUJ.IJ! 1 i 111 > 1111111111111111111111 u. 1. \ 1.1, u. i

FIGURE 3: Flat Specimen and Force Transducer Assembly

FORCETRANSDUCERS

SUPPORTSAMPLE

OSCILLOSCOPE

DISPLACEMENTTRANSDUCERS

CHARGEAMPLIFIERS

TAPE

RECORDER

TUBE SAMPLE

DISPLACEMENT

TRANSDUCERS

ARITHMATIC SUM

OF OPPOSINGFORCE SIGNALS

TAPE

RECORDER

PDP 11/55

HYBRID COMPUTER &

PROGRAM DEVELOPMENT SYSTEMS

FIGURE 4: Schematic Diagram of the Data Acquisition System

16.

YCLEARANCECIRCLE

Fs =|Fy C o s 0 - FX S in0 [

Fn =|Fy Sin0 Fx Cos0 |

(b) TUBE TRAJECTORY

FIGURE 5: Force Components at the Tube/Support Clear-ance Circle

17.

wo

go

o

z

P"

12S-

i

100-

75 -

50-

25 j -

20 40 60 BO

NORMAL FORCE COMPONENT (Newtons )100

10.0

SHEAR FORCE COMPONENT INewtons)

FIGURE 6: Force Histograms and x-y Plot of Tube Trajectory fora Normal Impacting Case

18.

70

60

40

30

20

10 20 30

NORMAL FORCE COMPONENT (Newfons)

50

10.0

5.0

UJ£ 0.0

a

*" -5.0

-10.0-10.0 -5.0 0.0 5.0

X DISPLACEMENT (mm)

10.C

5 10 15 20

SHEAR FORCE COMPONENT (Newfonsl

25

FIGURE 7: Force Histograms and x-y Plot of Tube Trajectoryfor a Circular Rubbing Case

19.

70

60

w .50S3

3

oo

40

30

20

20 40 60 80

NORMAL FORCE COMPONENT (Newtons)

-10.0-10.0

100

-5 .0 0.0 s

X DISPLACEMENT (mm)10.0

5 10 15 20 25

SHEAR FORCE COMPONENT (Newtons)30 35

FIGURE 8: Force Histograms and x-y Plot of Tube Trajectory for aCombined Rubbing and Impacting Case

20.

IS)

o

100

50

01 10

RA

TE

Q :

QUJ

Eno

1.0

0.5

0.1

Coef. of Corr. = 0.56 + /

I8.0 10.0 15.0 20.0

FORCE FUNCTION F, N

30.0 40.0

FIGURE 9: Force-Wear Correlation using the Resultant Force - All Data

21.

100-

50

o

enE

TE W

.

DC

LU

a• . •

OMBI

NE

10

5

1.0

0.5

0.1

Coef.

—

—

/

S 1

of Corr. = 0.88

/

/

1

+ A +

+ / +

+

i i i i i

8.0 10.0 15.0 20.0

FORCE FUNCTION F, N30.0 40.0

FIGURE 10: Force-Wear Correlation using the Resultant Force - Omitting theNormal Impacting Points

22.

I/)UJ_J

CYC

mg/

10°

RATE

WEA

R

aUJ

COMB

If

50

10

5

1

0.5

0.1

_

Coef. of Con. = 0.735

I;

• i

++ + /

1

+

1 i 110 15 20 30

FORCE FUNCTION F, N50

FIGURE 11: Force-Wear Correlation using the Sum of Normal and Shear ComponentsAll Data

23.

l/l100

50

E 10

1 -

Z 0.5GO2:o

0.1

Coef. of Corr. = 0.92 /

i I10. 15. 20. 30.

FORCE FUNCTiON Fs+N, N

40. 50.

FIGURE 12: Force-Wear Correlation using the Sum of Normal and ShearComponents - Omitting the Normal Impacting Points.

100-

i/l 50 -

O

\

en10

<ccac< 1

0.5

0.1

Coef. of Com. = 0.928

j L I I I L

1.6 2.0 3.0 4.0 5.0

FORCE FUNCTION F,, N10.0 15.0

FIGURE 13: Force Wear Correlation using the Shear Force Only - All Data

25.

QOO 0O4TIME (SECONDS)

004 ~ 008 01271MC (SECONOS)

£30

28

100

TO

SO

19

i 9SHEAR FORCE COMPONENT (NEWTONS)

NORMAL FORCE COMFONEHT (NmrtONS)

FIGURE 14: Force Signals and Tube Trajectory from a Low Friction Pair(Teflon/Teflon)

o

CD H i.a n>C og no o

**3 Hi

MO

rt

O

o

NORMAL & SHEAR FORCE COMPONENTS, N- • - • K> )O

01 © 01 O U>

S1

l-joreno

ao

CoCOH3

TO

D

INM

XOM

HO

r-1

w

o

P P P P o(jj * A Ol Oi

COEFFICIENT<OF FRICTION,M

•9Z

27.

Z 14in(JU

o

I"10"

m

ui

O

OoetHI

O 4

-Fn NORMAL COMPONENT

0

COEFFICIENT OF FRICTION,

s , SHEAR COMPONENT

_L JL _LO.8 l.O 1.2 1.4 1.6 1.8

NORMALIZED EXCITATION LEVEL

2.0 2.2

FIGURE 16: Effect of Excitation Level on the Impact Force Components - byIncreasing Excitation Rotating Masses.

a3

TANGENTIAL FORCE COEFFICIENT

i

c

9u

9 9in 9

+4

\

\

wHiHi0>aft

•Iort

n>

I

31

o

roDrt

f

>

©

1°

Uo

s

I

•8Z

Y DISPLACEMENT (tnm|

(D

0

ortento

Oc

toft

(DCD

O

DISPLACEMENT (mm)

PII"O

Oo

Y DISPLACEMENT (mm)

Y DISPLACEMENT (mm)

PII

O

Y DISPLACEMENT (mm)

ISSN 0067-0367 ISSN 0067-0367

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