Friction and wear properties of black oxide surfaces in rollingsliding contacts

Friction and wear properties of black oxide surfaces in rolling/sliding

contacts

Carl H.Hager Jr.n,Ryan D.Evans

The Timken Company,North Canton,OH44720,USA

a r t i c l e i n f o

Article history:

Received23March2015

Received in revised form

24June2015

Accepted25June2015

Available online3July2015

Keywords:

Black oxide

Black oxidizing

Friction

Wear

a b s t r a c t

Black oxide chemical conversion treatment of steel surfaces was originally developed as a low-cost

method to improve the corrosion resistance of the base material.Over time,this surface treatment was

introduced on tribological components amid claims that it improved galling and smearing resistance.In

rolling element bearings,smearing damage can occur during high transient slip events between roller

bodies and raceways,and black oxide surface treatments have recently been prescribed as a solution for

this mode of adhesive wear damage.Therefore,fundamental friction and wear experiments using uni-

directional sliding and rolling/sliding contacts were conducted to explore the performance of black oxide

surfaces in tribological contacts.

From this work,it was concluded that mated black oxide surfaces yield similar or lower friction as

compared to mated steel surfaces(in lubricated contacts),exhibit high wear in lowλconditions,and can

mitigate adhesive wear damage as long as the oxide layer remains intact.

&2015Elsevier B.V.All rights reserved.

1.Introduction

The service life of a rolling element bearing is often limited or

reduced by component damage or material https://www.sodocs.net/doc/0718169851.html,ponent

damage can result from wear,external contaminant ingress,severe

application conditions,neglect,or misuse.One particular type of

life-limiting bearing damage is called“smearing”.Smearing is a

term that is often used to describe adhesive wear damage in

rolling/sliding contacts when sliding is substantial and the lubri-

cant?lm thickness is insuf?cient to adequately separate the con-

tacting surfaces[1].Damage associated with smearing may occur

when rolling elements slide along the raceway surface as they

enter or exit the loaded zone[2].In some cases,this type of

damage can be mitigated through component and/or system

design.However,there are some instances where the damage

cannot be avoided without modifying the tribological contact

surfaces.

If smearing damage cannot be avoided from a component or

system design approach,another way to mitigate adhesive wear

damage is to change the chemical composition of one or both of

the surfaces in contact.In1978,Gregory wrote a paper providing a

brief summary of conversion coatings available to improve adhe-

sive wear resistance[3].Gregory suggests that black oxide surfaces

(when oiled or waxed)can yield low friction and resistance to

adhesive wear damage.In1998,Philstr?m and Str?m published a

master’s thesis where black oxidizing was applied to spherical

roller bearings(Part number22222E/C3–110mm bore diameter

–200mm outer diameter)[4].In their work,the authors con-

ducted smearing tests in bearings by periodically stopping the

rollers while the shaft was still rotating.This was done for a total

of100cycles at eight different shaft speeds(100,200,400,800,

1600,2400,3200,and4500rpm).If no smearing damage was

found on the bearings after each shaft speed,the shaft speed was

raised to the next level.Upon the completion of this testing with

and without black oxidized rollers,Philstr?m and Str?m found

that black oxidized rollers yielded a small improvement in

smearing resistance as compared to uncoated rollers[4].

A few years later,Scherb and Zech developed a smearing test

using cylindrical bearings from which the authors concluded that

black oxide can prevent smearing damage and reduce frictional

torque by up to20%[5].In2010,Mihailidis et al.conducted

smearing tests with a two-disc machine where the entrainment

velocity was held constant and the slide-to-roll ratio was increased

until severe adhesive wear occurred between the mated samples

[6].These tests demonstrated that the black oxidized discs could

survive higher levels of slide-to-roll ratio compared to the

untreated discs.In addition,tests were also conducted with a

constant slide-to-roll ratio and demonstrated that the black oxi-

dized discs exhibit higher wear rate and lower friction as com-

pared to the untreated discs during a wear-in cycle.

Although the aforementioned work found that black oxide

surfaces yield some bene?t in reducing adhesive wear or smearing

Contents lists available at ScienceDirect

journal homepage:https://www.sodocs.net/doc/0718169851.html,/locate/wear

Wear

https://www.sodocs.net/doc/0718169851.html,/10.1016/j.wear.2015.06.013

0043-1648/&2015Elsevier B.V.All rights

reserved.

n Corresponding author.Tel.:t12342622077;fax:t12342622282.

E-mail address:carl.hager@https://www.sodocs.net/doc/0718169851.html,(C.H.Hager Jr.).

Wear338-339(2015)221–231

damage compared to untreated surfaces,in2013Evans et al. concluded that black oxide treatment of rollers and raceways did not provide additional smearing protection in cylindrical roller bearing tests conducted under severe conditions[7].In this work, the authors conducted bearing tests where the load zone was shifted180°every15s.In three separate tests,the bearings with black oxidized raceways and rollers exhibited smearing damage after just one load cycle.Bearings that were untreated with ground raceways exhibited smearing after just one load cycle as well.This conclusion seems contrary to the previous bearing tests by Scherb and Zech[5]and the two-disc experiments by Mihailidis et al.[6], but seems to agree with the spherical bearing tests conducted by Philstr?m and Str?m[4].

Although there are con?icting results in the literature(which may be due to the severity of the testing),black oxide surface treatments have recently been prescribed as a solution to mitigate various types of damage in rolling element bearings[8].In addi-tion,the literature also suggests that there may be other bene?ts to using black oxide such as low friction and high wear rates during break-in[5,6].Therefore,the focus of this work was to conduct bench-level tribological experiments to determine the friction and wear properties of black oxide surfaces in rolling/ sliding contacts.Several different experimental techniques and results are described in sequence and then drawn together with discussion and general conclusions.

2.Black oxide

Although black oxide or black oxidizing can be used to describe a number of surface coatings on steel,the term“black oxide”in this work refers to the conversion of a steel surface to Fe3O4or magnetite using a hot alkaline bath.This type of black oxide sur-face is created using a process that was developed in Germany in the early1900s and has been used to produce an attractive black ?nish,impart moderate corrosion resistance(with the addition of secondary oil impregnation or wax),enhance lubricity,and resist galling[9].It should be noted that the extent of these claimed bene?ts rely on a secondary process of oil or wax impregnation.In fact,many vendors state that the anti-galling properties of black oxide surfaces allow for the outer layer to be sacri?ced during initial contact.Therefore,the black oxide layer is galling resistant in that it wears away without adhesive wear damage to the mated surfaces.

The black oxide layer is generated by placing the steel com-ponents into a hot aqueous alkaline nitrate bath.The concentra-tion of the bath is controlled by boiling the solution at a desired temperature between285°F(141°C)and310°F(154°C)[10].This can be done using either a single-bath or double-bath process.The single-bath process typically uses one tank with a temperature range from285°F(141°C)to290°F(143°C)[10].The double-bath process typically uses a second tank with a temperature range from305°F(152°C)to310°F(154°C)[10].Depending on the process,the black oxide layer thickness can range from0.5to 3m m.A common standard for de?ning black oxide surface treat-ments on ferrous materials is DIN50938.

Although the black oxide process is well documented,there is comparatively less data published on the properties and micro-structure of the black oxide surface layer.In this work,a through hardened AISI52100steel disk(HRC58-62)was metallo-graphically polished and then black oxidized using a double-bath process.The microstructure of the black oxide surface layer was analyzed using a focused ion beam to mill a trench followed by inspection of the cross section with a high-resolution scanning electron microscope(SEM).Fig.1shows a secondary electron SEM The oxide layer itself is dense,but there are pre-existing carbide

particles contained within the microstructure that exhibit voids at

the boundaries between the carbide and oxide materials.Mea-

surements of the coating thickness varied from$1.4to2.2μm for this sample.In comparison,Evans et al.[11]published a trans-

mission electron micrograph of a single-bath black oxide surface

cross section.The view shown has a thinner(200–500nm)black

oxide layer that did not exhibit voids at the carbide/oxide interface

like those observed for the double-bath layer in Fig.1.

The mechanical properties of the black oxide layer were mea-

sured with a nanoindenter using the continuous stiffness techni-

que[12]and a Berkovich tip.The indentation parameters included

a depth limit of2500nm,a strain rate of0.1sà1,a harmonic

displacement target of1nm,a frequency of45Hz,and an assumed

Poisson’s ratios for black oxide(0.25)and untreated steel(0.3).

Fifteen replicate tests were performed on each sample.In addition

to measurements on the black oxide surface,a second through

hardened AISI52100steel disk was metallographically polished

and analyzed along with the black oxidized sample.The mea-

surement results from both surfaces are summarized in Table1.

Based on these measurements,the black oxide surface layer has

approximately25%of the hardness and27%of the modulus of the

base steel surface.These results were also published by Evans et al.

in2014[11].

3.Experimental details

All sliding and rolling sliding wear experiments were con-

ducted using a Wedeven Associates Inc.manufactured WAMsc4

test machine.This machine is able to run block-on-ring experi-

ments with a stationary block and a rotating cylinder,and can also

perform rotating cylinder-on-cylinder or rotating ball-on-cylinder

rolling/sliding wear experiments.The machine has two opposing

spindles that can be controlled independently.One of the spindles

is mounted on three load cells and an actuator that allows for it to

move toward the opposing spindle in the contact plane.Moving

one spindle toward the?xed second spindle allows for a normal

Fig.1.High-resolution scanning electron microscope image of black oxide surface layer.

Table1

Nanoindentation mechanical property comparison for untreated AISI52100steel and black oxide layer[11].

Sample Avg.hard-

ness(GPa)

Depth range

for avg.hard-

ness(nm)

Avg.elastic

modulus

(GPa)

Depth range

for avg.mod-

ulus(nm) Untreated AISI

52100steel

10.670.5100–200230710100–200

Double-bath

black oxide

2.670.3200–300617580–100

C.H.Hager Jr.,R.

D.Evans/Wear338-339(2015)221–231 222

rotating.The friction between the test samples was measured by the vertical load cells mounted underneath the test spindle,with the actuator system,and/or by a torque sensor on the same spindle.

All of the cylinder,block,and ball geometry test samples used for this work were manufactured from hardened AISI52100steel (HRC58-62).The cylinders were fabricated with a35mm outside diameter and a25.4mm width.All the cylinders were ground to yield a457–558nm Ra surface?nish.The block test samples were 19.05mm squares with a7.874mm thickness.The edges of the blocks were chamfered so that the block-on-ring test con?guration yielded a6.5mm contact width.The test surfaces of the blocks were ground to yield a356–457nm Ra surface?nish.The ball samples were20.6375mm diameter ABMA Grade25balls with a 6.5mm diameter hole in the center.The center hole permitted the balls to be bolted into a collet and driven by a spindle for rolling/ sliding wear experiments.The cylinder samples had a taper on the inner diameter so that they could be held onto a spindle nosepiece with a tapered outer diameter.All black oxidized test samples were manufactured similarly to the untreated samples,and then conversion coated using the double-bath process.

3.1.Sliding friction test description

Simple lubricated sliding wear experiments were conducted to compare the lubricated sliding friction of the black oxidized sur-faces to that of the base steel material.For these experiments, 35mm diameter through hardened AISI52100steel cylinders were loaded against a through hardened AISI52100steel block with a contact width of6.5mm.The sliding experiments were conducted with a linear sliding velocity of0.5m/s and a contact stress of200MPa.The friction force was measured with three vertical load cells that support the stationary block sample.The tests were lubricated with an ISO VG68poly-alpha-ole?n(PAO) oil,without extreme pressure(EP)or anti-wear(AW)additives,

and an inlet temperature of40°C.Fig.2shows a picture of the samples in contact.

Three experiments were conducted with untreated steel rings mated with untreated steel blocks,and three experiments were conducted with a steel ring that was black oxidized and mated with an untreated steel block.The test duration was20min to establish a steady-state friction measurement.The resolution on the normal load and friction force measurements allowed for the friction coef?cient to be measured within70.009.

3.2.Sliding friction test results

Fig.3shows a picture of the black oxidized test ring after all three sliding wear tests were completed.The picture shows that the black oxide surface was still intact after each sliding wear test. Fig.4shows a plot of the measured friction coef?cients from all six experiments.Interestingly,the untreated steel surfaces yielded more variation in measured friction as compared to the black oxide/untreated steel surfaces.Due to the larger error bars from the untreated steel experiments,the data suggest that the lubri-cated sliding of a black oxide surface against an untreated steel surface will yield sliding friction similar to that of two untreated steel surfaces.

3.3.Rolling/sliding friction test description

Although the black oxide and ground steel surfaces yielded similar friction in simple sliding wear experiments,friction in rolling element bearings results from rolling/sliding contact at various entrainment velocity levels.For this work,entrainment velocity is de?ned as the mean of the linear velocities at the sur-faces of two contacting bodies.The sliding velocity is de?ned as the difference between the linear velocities of two contacting bodies.Therefore,the slide-to-roll ratio(SRR)is de?ned as the ratio of the sliding velocity to the entrainment velocity(as de?ned above).

In order to accomplish the task of measuring the lubricated rolling/sliding coef?cient of friction between mated black oxide surfaces and mated steel surfaces,a ball-on-ring contact geometry was utilized,as shown in Fig.5.The tests were lubricated by continuously pumping ISO VG220PAO oil without EP or AW additives into the contact between the ball and the cylinder with a 60°C inlet temperature.The Hertzian contact pressure between the samples was maintained at a constant1.95GPa(283ksi)for

Fig.3.Black oxidized test ring after all three sliding wear tests were

completed.

Fig.4.Measured friction from ring-on-block sliding wear experiments.

C.H.Hager Jr.,R.

D.Evans/Wear338-339(2015)221–231223

ball and cylinder test samples were accelerated to the same sur-face speed (SRR ?0%)such that the entrainment velocity was 9m/s.

Once the samples reached the initial test speed,with oil ?owing between the contacts to create a fully ?ooded condition,the samples were brought into contact and loaded to 200N.After the test load was achieved,the slide-to-roll ratio was ramped to 5%by slightly slowing down the cylinder and speeding up the ball while maintaining the 9m/s entrainment velocity.Finally,the entrainment velocity was decreased from 9m/s to 0.1m/s over a period of 150s,while maintaining a constant 5%SRR.The friction force between the ball and cylinder surfaces was measured by a torque sensor on the shaft that was rotating the test cylinder.The resolution on the normal load and torque measurements allowed for the friction coef ?cient to be measured within 70.01.

Two experiments were conducted with untreated steel test samples,and two experiments were conducted with mated black oxide balls and black oxide cylinders.Prior to conducting each test,the ball surface roughness was measured in 10random locations around the circumference with a white light interferometric microscope.Similarly,the cylinder surfaces were measured in 15random locations around the circumference.After conducting each test,the surface roughness within the wear track on the ball sur-faces and the cylinder surfaces was measured at 10and 15random locations,respectively,around the circumference of the wear track.The pre-test and post-test measurements were then used to calculate the root mean square (RMS)composite surface rough-ness by ?rst calculating all the possible combinations of the 25measurements from each surface (150combinations in total).The mean and standard deviations from the RMS composite roughness after a short duration test,the mated black oxide samples exhib-ited a signi ?cant reduction in composite surface roughness.The untreated steel samples did not yield a statistically signi ?cant reduction in composite surface roughness.

The post-test RMS composite surface roughness from each pair of test samples was used to plot the measured friction coef ?cient with respect to the non-dimensional ?lm thickness (λ),as shown in Fig.7.In this work,λis de ?ned as the ratio of the calculated isothermal elastohydrodynamic central lubricant ?lm thickness [13]to the RMS composite surface roughness.This allows for the friction coef ?cient to be associated with the appropriate λvalue so that the effect of surface roughness and oil ?lm thickness on the measured friction can be analyzed.

3.4.Rolling/sliding friction test results

Fig.7shows that both the mated black oxide samples and the untreated steel samples yielded similar coef ?cients of friction when λr 0.4.When λ40.4,the mated black oxide samples yiel-ded a friction coef ?cient that was $0.01lower than that of the untreated steel samples.Although 0.01is the calculated resolution of the experiment,the replicate experiments show repeatability that is better than the calculated uncertainty.Therefore,it is possible that the mated black oxide friction coef ?cient in the mixed lubrication regime is signi ?cantly lower than the untreated steel pair.One explanation for this reduction could be associated with the fact that the mated black oxide surfaces yielded a smoother surface ?nish at the end of the test,as compared to the mated steel samples.Kang et al.[14]found that in similar rolling/sliding experiments,the measured friction in the mixed regime can be reduced due to a lower composite surface roughness without reducing the measured friction in the boundary lubrica-tion regime.

3.5.Rolling/sliding wear test description

After conducting sliding wear and rolling/sliding friction tests,it became apparent that lubrication conditions govern black oxide surface wear.Evidence of this was demonstrated by the signi ?cant reduction in surface roughness after short duration (150s)rolling/sliding wear tests.Because the tests were conducted by measuring the friction at various λconditions,it is impossible to determine which factors had the most in ?uence on the wear of the black oxide surfaces.Therefore,a full factorial design of experiments was used to determine the effect of Hertzian contact pressure,slide-to-roll ratio and λon the wear rate of mated black oxide surfaces.

Tables 2and 3summarize the variables and experimental test

Fig.5.Black oxide ball-on-black oxide ring test con ?

guration.

Fig. 6.Measured surface roughness from ball-on-ring rolling/sliding wear

experiments.

Fig.7.Measured friction from ball-on-ring rolling/sliding wear experiments.

C.H.Hager Jr.,R.

D.Evans /Wear 338-339(2015)221–231

224

with a repeated center point for improved error estimation.The tables describe a total of 10tests that can be modeled by Eq.(1).The test lubricant was a fully formulated ISO VG 320PAO gear oil with EP and AW additives and an oil inlet temperature of 80°C.The ?rst 10tests were run until the mated surfaces had been subjected to a total of 1000m of total sliding distance.Upon the completion of these experiments,each of the tests was repeated (except Test 2)with increased sliding duration.The repeat experiments were run until the black oxide appeared to be visually removed,or until a maximum of 10,000m of total sliding distance had been accumulated.

Wear Rate B1SRR B2Hertz B3B4SRR Hertz B5

SRR B6Hertz 1λλλ

=*+*+*+**+**+**()

Wear analysis of each experiment focused on the ball wear track only.This was due to the relative ease of identifying the wear scars on the smooth Grade 25balls compared to the rougher cylinders.The wear volume was calculated from three-dimen-sional interferometric microscope surface measurements made on each ball surface.The ?rst step in the calculation required making a measurement on the nominal ball surface (outside of the wear track),followed by a measurement in the wear track.This allowed for the nominal ball surface geometry to be subtracted from the ball wear track measurement,as shown in Fig.8.Once the wear track was ?attened,the data set was leveled and the wear track was isolated from the surface roughness by identifying the area below à3.3*Sq (Sq is the RMS surface roughness of the nominal ball surface with the spherical radius removed).

Fig.9shows an example of the isolated wear area in a two-dimensional view.The isolated wear area was integrated and then multiplied by the circumference of the ball to get an approximate wear volume.The wear rate was determined by dividing the measured wear volume by the total sliding distance from the test.3.6.Rolling/sliding wear test results

Table 4lists the calculated wear volumes,wear depths,and wear rates from each of the rolling/sliding wear tests.Linear least squares regression [15]was used to solve for the coef ?cients from Eq.(1)using the wear rate values in Table 4.Once the coef ?cients were calculated,the signi ?cance of each variable and each variable interaction was determined using an analysis of variance (ANOVA)for the regression components [15].Table 5lists the calculated

Table 2

Design of experiments variable de ?nitions.Parameter x

y

z Level SRR (%)Hertz pressure (GPa)λà150.820.30055 1.240.871

105

1.66

1.44

Table 3

Experimental test conditions.Test #x (SRR)y (GPa)z (λ)SRR (%)Load (N)Ue (m/s)Us (m/s)1à1à1à15150.40.0221à1à1105150.40.423à11à151230.50.03411à11051230.50.535à1à11515 4.250.2161à1110515 4.25 4.467à1115123 5.310.278111105123 5.31 5.5890005552 2.3 1.2710

55

52

2.3

1.27

Fig.9.Method for ?attening the determining wear area from a 2D slice of the 3D measurement.

Table 4

Calculated wear volume and wear rate from each experiment.Test Wear

volume (mm 3)Depth (mm)Sliding speed (m/s)Sliding dis-tance (m)

Wear rate

(mm 3)/m

19.9*10à3 1.0*10à30.0210009.9*10à62 2.4*10à2 1.5*10à30.421000 2.4*10à53 1.4*10à29.0*10à40.031000 1.4*10à54 2.4*10-2 1.1*10à30.531000 2.4*10à55 2.9*10à5 4.0*10à40.211000 2.9*10à86 2.1*10à4 5.0*10à4 4.461000 2.1*10à77 1.5*10à37.0*10à40.271000 1.5*10à68 2.0*10à37.0*10à4 5.581000 2.0*10à69 1.3*10à2 1.2*10à3 1.271000 1.3*10à5109.1*10à48.0*10à4 1.2710009.1*10à711 1.8*10à2 1.2*10à30.0225007.3*10à612 1.7*10à2 1.0*10à30.035000 3.4*10à613 2.0*10à2 1.1*10à30.535000 4.1*10à614 1.5*10à3 1.1*10à30.2110,000 1.5*10à715 3.2*10à4 5.0*10à4 4.4610,000 3.2*10à816 1.7*10à3 1.0*10à30.2710,000 1.7*10à717 1.5*10à2 1.4*10à3 5.5810,000 1.5*10à618 6.1*10à3 1.2*10à3 1.275000 1.2*10à619

2.4*10à2

2.5*10à2

1.2710,000

2.4*10à6

C.H.Hager Jr.,R.

D.Evans /Wear 338-339(2015)221–231225

coef ?cients,the regression sum of squares values,and the residual sum of squares (error).It should be noted that there is a total of only 19°of freedom because Test 2was not replicated.The regression sum of squares for each coef ?cient,the residual sum of squares,and the residual degrees of freedom can be used to cal-culate the F value (which is also listed in Table 4).

In order for a variable or interaction to be considered statisti-cally signi ?cant with 95%con ?dence,the F value must be greater than F 1,13?4.67.Based on these experiments and the analysis of the wear surfaces,only the λvalue had a statistically signi ?cant effect on the wear rate of the black oxide surfaces.Fig.10shows images of the wear on black oxidized balls from tests 1through 6.These images show the impact that λhad on the black oxide wear.Although neither is statistically signi ?cant,the slide-to-roll ratio had the next highest impact,followed by the interaction between λand the slide-to-roll ratio.The Hertzian contact pressure had almost no impact on the wear rates in these experiments.

3.7.Rolling/sliding adhesive wear test description

As stated in the introduction,smearing is a term that is often used to describe adhesive wear damage in contacts when sliding is

Table 5

Linear least squares regression analysis of wear rate test data.Variables

B

Coef ?cient value (1e à5)Degrees of freedom Regression sum of squares (1e à9)F

SRR B10.183410.05050.5766Hertz B2à0.006410.00010.0007λ

B3à0.573010.4925 5.6285SRR*hertz B4à0.030710.00140.0161SRR*λB5à0.160010.03840.4386Hertz*λB60.065510.00640.0736Error ––13 1.1375–Total ––

19

1.7268

–

Table 6

Calculated λvalues based on pre-test surface roughness measurements.Contacts Entrainment velocity (m/s)λMated steel

30.23Mated black oxide 30.30Mated steel

70.41Mated

black oxide

7

0.45

Fig.11.Measured friction from ball-on-ring rolling/sliding wear experiments with 3m/s entrainment velocity and increased slide-to-roll ratio (scaling in %).

C.H.Hager Jr.,R.

D.Evans /Wear 338-339(2015)221–231

226

substantial and the lubricant?lm thickness is insuf?cient to ade-quately separate the contacting surfaces[1].With respect to black oxide and smearing,the literature must be interpreted with respect to the severity of the test methods.Evans et al.[7]and Philstr?m and Str?m[4]concluded that black oxide treatments in bearings provided minimal or no additional smearing protection under severe contact conditions.Scherb and Zech[5]and Mihai-lidis et al.[6]suggest that there is a bene?t to applying black oxide to bearing surfaces for smearing protection under milder test conditions.In an attempt to clarify these varied results and con-clusions,ball-on-cylinder rolling/sliding wear experiments were conducted with mated steel and mated black oxide surfaces.

The tests were lubricated by continuously pumping an ISO VG 68PAO oil without EP or AW additives into the contact between the ball and the cylinder with an inlet temperature of80°C.The Hertzian contact pressure between the samples was maintained at a constant1.95GPa(283ksi)for the duration of the test.Tests were conducted at two different entrainment velocities,3m/s and 7m/https://www.sodocs.net/doc/0718169851.html,ing the composite RMS roughness from pre-test surface roughness measurements and the calculated isothermal elasto-hydrodynamic central lubricant?lm thickness[13],the pre-testλvalues were calculated and are listed in Table6.

Each test was conducted by initially loading the samples in a pure rolling condition(SRR?0%).Once the samples reached the test load of200N,the slide-to-roll ratio was increased to10%, maintaining the entrainment velocity at either3m/s or7m/s. Then every150s,the slide-to-roll ratio was increased an addi-tional10%(while keeping the entrainment velocity constant),until the samples exhibited severe adhesive wear or a maximum of 170%slide-to-roll ratio was reached.As soon as either of these conditions was met,the test was suspended.

A minimum of two tests were conducted for the mated steel and mated black oxide samples at each entrainment velocity.The friction force between the ball and cylinder surfaces was measured by a torque sensor on the shaft that was rotating the test cylinder. The resolution on the normal load and torque measurements allowed for the friction coef?cient to be measured within70.01.

3.8.Rolling/sliding adhesive wear test results

Fig.11shows the measured friction coef?cient from the experiments conducted with3m/s entrainment velocity.In the background of the plot is a stepped curve that is associated with the y-axis on the right,and shows the slide-to-roll ratio at that point in the test.Both of the untreated steel tests exhibited excessive friction and adhesive wear damage at the very beginning of the140%and130%slide-to-roll ratio stages,respectively.

The

Fig.13.Measured friction from ball-on-ring rolling/sliding wear experiments with

7m/s entrainment velocity and increased slide-to-roll ratio(scaling in%).

C.H.Hager Jr.,R.

D.Evans/Wear338-339(2015)221–231227

adhesive wear damage on the ball surfaces from these tests is shown in Fig.12.Three mated black oxide tests were conducted, and all three tests were suspended after completing the170% slide-to-roll ratio stage.Fig.12shows the wear tracks on the balls from these experiments,and shows that the mated black oxide samples did not yield any adhesive wear damage.

Fig.13shows the measured friction coef?cient from the experiments conducted with7m/s entrainment velocity.Similar to Fig.11,the slide-to-roll ratio is also plotted with the coef?cient of friction from the tribological experiments.With the increased entrainment velocity,both of the untreated steel tests exhibited excessive friction and adhesive wear damage at the very beginning of the90%and80%slide-to-roll ratio stages,respectively.The mated black oxide samples also exhibited excessive friction and adhesive wear damage.However,the mated black oxide samples exhibited this type of damage at the start of the150%and120% slide-to-roll stages.Fig.14shows the adhesive wear damage on the ball surfaces from all four tests.

The tests conducted with both3m/s and7m/s entrainment velocities and stepped slide-to-roll ratios suggest that the black oxide surfaces will mitigate adhesive wear damage when high amounts of sliding occur.Although the black oxide surfaces pre-vented adhesive wear damage at the conditions where the mated steel samples were damaged,the black oxide layers exhibited signi?cant wear.Upon completion of the3m/s entrainment velocity experiments,the roughness within the wear track on the black oxide ball and cylinder samples was measured with a white light interferometric microscope(similar to the way the samples were measured in the rolling/sliding friction section of this paper). The individual measurements were used to calculate a distribution of RMS composite roughness values within the mated wear tracks. The pre-test and post-test RMS composite roughnesses are plotted in Fig.15,and show that the mated black oxide surfaces exhibited a signi?cant reduction in RMS composite surface roughness.In addition,there is an extra data point from a mated black oxide experiment that was conducted with3m/s entrainment velocity and suspended after reaching the140%slide-to-roll ratio stage. This reduction in surface roughness yielded an increase inλfrom a pre-test value of0.3to a post-test value of0.55.

In order to determine the role that the decreased RMS com-posite surface roughness and increasedλplayed in the improved adhesive wear performance of the mated black oxide samples,a second set of experiments was conducted with a constant3m/s entrainment velocity.Because the mated black oxide samples exhibited a signi?cant reduction in composite surface roughness at the140%slide-to-roll ratio stage(where the mated steel samples exhibited severe adhesive wear),the second set of experiments was conducted with a constant slide-to-roll ratio of140%.As expected from the previous experiments,the untreated steel test samples yielded excessive friction and severe adhesive wear damage within15s of running with an entrainment velocity of 3m/s and a constant slide-to-roll ratio of140%.However,the mated black oxide samples also exhibited excessive friction and severe adhesive wear.Fig.16shows the severe adhesive wear damage on the ball surfaces from these tests.

Similar experiments were also conducted with a7m/s entrainment velocity and a constant slide-to-roll ratio of90%.Just like the previous experiments,the untreated steel samples exhibited excessive friction and severe adhesive wear damage with100s of running.However,the mated black oxide ran for the total duration of the test(26.67min).Fig.17shows the measured friction from the constant slide-to-roll ratio experiments.Fig.18 shows the wear tracks on the ball surfaces after these experi-ments.Although the black oxide surfaces were still present within the ball wear tracks,the black oxide surfaces exhibited signi?cant wear.Fig.19shows measured and calculated RMS composite roughness values for these experiments,and shows that the mated black oxide surfaces became signi?cantly smoother even

though

Fig.15.Measured surface roughness from black oxided ball-on-ring rolling/sliding

wear experiments with3m/s entrainment velocity and increased slide-to-roll ratio.

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D.Evans/Wear338-339(2015)221–231

228

the black oxide exhibited signi?cant wear.The reduction in surface roughness was such thatλincreased from0.45(pre-test)to0.75 (post-test).

The previous section of this paper demonstrated that the factor with the most in?uence on the wear rate of mated black oxide surfaces wasλ.The tests conducted with3m/s entrainment velocity started atλ?0.3.Although this low lambda value should have led to increased wear of the black oxide surface,the wear-in of the surfaces(while the slide-to-roll ratio was incrementally increased)led to an increase inλsuch that the black oxide surface was able to survive the test.When the test was conducted with a 3m/s entrainment velocity and a constant140%slide-to-roll ratio, the black oxide surface wore off before it could in-to a higherλvalue.Once the black oxide surface layer was removed,the sam-ples exhibited severe adhesive wear in the same manner as untreated surfaces.When the entrainment velocity was increased to7m/s,the initial lambda level was increased toλ?0.45.This value is similar to theλvalue that allowed the black oxide surfaces to survive the stepped slide-to-roll ratio tests with3m/s entrainment velocity.That is why the black oxide surfaces sur-vived and were able to in-to yield an even higherλvalue.

In addition to providing some adhesive wear protection in the stepped slide-to-roll ratio experiments,the mated black oxide surfaces also yielded lower friction in all the experiments.This is friction experiments.This plot shows that the black oxide surfaces yielded lower friction in the mixed regime whenλ40.4.This is approximately the range ofλfrom these experiments,if the wear-in from the3m/s entrainment velocity experiments is considered.

A similar reduction in friction was also found by Evans et al.[11]in the mixed regime while the black oxide surfaces were wearing in. However,the reduction in friction was not apparent once the black oxide layer wore away.

4.Discussion

There is literature that suggests that black oxide surfaces can reduce friction,decrease the time associated with wear-in,and improve smearing(adhesive wear)resistance[5,6,11].However, there also is some literature that questions the ability of black oxide to protect bearing surfaces against smearing damage under severe application conditions[4,7].In this work,a series of experiments was conducted to con?rm or refute the friction and wear-in conclusions while exploring the con?icting smearing protection conclusions.

Simple lubricated sliding wear experiments indicated that black oxide does not provide any reduction in friction compared to untreated steel samples.A similar conclusion could be made for the rolling/sliding wear experiments that were conducted with λo0.4.However,all of the experiments comparing mated black oxide surfaces to untreated steel surfaces in the mixed lubrication regime withλ40.4showed that the black oxide surfaces yielded lower friction.It is dif?cult to determine if this is due to wear-in and surface smoothening,or the shearing of the black oxide sur-face.Either way,it is safe to conclude that black oxide may reduce friction in some contacts based on the lubrication conditions.This work also suggests that black oxide does not increase friction in lubricated rolling/sliding contacts.

The experiments conducted with increased slide-to-roll ratios suggest that mated black oxide surfaces can mitigate smearing (adhesive wear)damage as long as the oxide surface remains intact.If the black oxide surface layer wears away,its wear pro-tection is lost.Therefore,the smearing protection of a black oxide surface is controlled by its wear rate.

A full factorial design of experiments was used to determine

Fig.16.Wear on ball surfaces from ball-on-ring rolling/sliding wear experiments with3m/s entrainment velocity and constant140%slide-to-roll

ratio.

Fig.17.Measured friction from ball-on-ring rolling/sliding wear experiments with

7m/s entrainment velocity and constant90%slide-to-roll ratio.

C.H.Hager Jr.,R.

D.Evans/Wear338-339(2015)221–231229

oxide surface layers in rolling/sliding contacts.This may explain why different publications reach different conclusions with respect to the smearing protection of black oxide surfaces.When the surfaces are worn in and the λlevel is suf ?ciently high,the black oxide surfaces provide suf ?cient protection.However,severe sliding in low λconditions will promote surface wear and can prevent the black oxide surface from protecting the steel substrate.

5.Conclusions

In this work,a series of experiments was conducted to deter-mine the friction and wear properties of black oxide surface layers in rolling/sliding contacts.Based on these experiments,it is con-cluded that:

1.Mated black oxide surfaces yield similar or lower friction coef ?cients compared to untreated steel surfaces in oil-lubri-cated rolling/sliding contacts.

https://www.sodocs.net/doc/0718169851.html,pared to untreated steel surfaces in lubricated rolling sliding/contacts,mated black oxide surfaces exhibit increased wear in low λconditions such that in-to a smoother composite surface roughness can be achieved in a shorter period of time.

3.The wear rate of mated black oxide surfaces in lubricated rolling/sliding contacts is more signi ?cantly affected by λthan

4.Mated black oxide surfaces can prevent smearing (adhesive wear)damage as long as the oxide surface layers are intact.

5.Improved smearing (adhesive wear)resistance with black oxide surfaces is dependent on the wear-in of the surfaces and the lubrication conditions.

Acknowledgments

The Timken Company is acknowledged for support of this work and permission to publish.S.P.Johnson from Timken is thanked for support and facilitation of these efforts.G.Richter and https://www.sodocs.net/doc/0718169851.html,llathin from Timken are acknowledged for their assistance with conducting the friction and wear experiments described in this paper.

References

[1]T.A.Harris,Friction and wear of rolling-element bearings,ASM Handbook,in:

T.Zorc,D.Levicki,J.Davis,K.Ferjutz,https://www.sodocs.net/doc/0718169851.html,mpman,https://www.sodocs.net/doc/0718169851.html,ls,N.Wheaton,M.Woods (Eds.),Friction Lubrication and Wear Technology,18,ASM Inter-national,1992,p.511.

[2]J.Hamer,R.Sayles,E.Ioannides,An experimental investigation into the

boundaries of smearing failure in roller bearings,J.Tribol.113(1991)102–109.[3]J.C.Gregory,Chemical conversion coatings of metals to resist scuf ?ng and

wear,Tribol.Int.11(1978)105–112.

[4]L.Philstr?m,E.Str?m,Smearing Protection and Smearing Physics,Department

of Mechanical and Vehicular Engineering,Chalmers University of Technology,G?teborg,Sweden,1998.

[5]B.J.Scherb,J.Zech,A study on the smearing and slip behaviour of radial

cylindrical roller bearings,Sonderdruck/Schriftenreihe der Georg-Simon-Ohm-Fachhochschule Nürnberg,(2001)1–20.

[6]A.Mihailidis,C.Salpistis,K.Panagiotidis,C.Sachanas,S.Gatsios,C.Hof ?nger,

V.Bakolas,Wear and smearing resistance of black iron mixed oxide coated steels,Int.J.Surf.Sci.Eng.4(2010)337–359,Nos.4/5/6.

[7]R.Evans,T.Barr,L.Houpert,S.Boyd,Prevention of smearing damage in

cylindrical roller bearings,Tribol.Trans.56(2013)703–716.

[8]K.Stadler,How Black Oxide Coated Bearings can Make an Impact on Cutting

O&M Costs for Wind Turbines,Windpower Engineering &Development,United States (2014),p.46–50.

[9]R.Farrell Jr.,Blackening of ferrous metals,Met.Finish.105(10)(2007)

390–396.

Fig.18.Wear on ball surfaces from ball-on-ring rolling/sliding wear experiments with 7m/s entrainment velocity and constant 90%slide-to-roll

ratio.

Fig.19.Measured surface roughness from black oxided ball-on-ring rolling/sliding wear experiments with 7m/s entrainment velocity and constant 90%slide-to-roll ratio.

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[11]R.Evans,C.Hager,Y.Kang,G.Doll,Comparison of black oxide and tungsten

carbide reinforced diamond-like carbon(WC/a-C:H)surface treatments for rolling element bearings,Tribol.Trans.58(2015)444–453.

[12]W.C.Oliver,G.M.Pharr,An improved technique for determining hardness and

elastic modulus using load and displacement sensing indentation experi-

ments,J.Mater.Res.7(6)(1992)1564–1583.

[13]B.Hamrock,D.Dowson,Isothermal elastohydrodynamic lubrication of point

contacts part III–fully?ooded results,J.Tribol.99(1977)264–275.[14]Y.Kang,C.Hager,R.Evans,Effects of skewed surface textures on lubricant?lm

thickness and traction,Tribol.Trans.58(2015)397–406.

[15]G.Box,J.Hunter,W.Hunter,Second Edition,Statistics for Experimenters

Design and Discovery,363–423,John Wiley&Sons,Inc.,United States(2005), p.616.

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D.Evans/Wear338-339(2015)221–231231

wear-put-on--dress---in---with用法

wear/dress/put on/in/with的区别 put on，动词短语着重于“穿”这一动作，即由没穿到穿这一动作的完成，意为“穿上、戴上””后接衣服、鞋帽等。例如： I want you to put on this coat and this hat. 我要你穿这件外套，戴这顶帽子。 Put on your heavy winter coat if you are going out. 如果你要出去，穿上你的厚冬衣。 wear 动词，“穿着；戴着”，表示状态，宾语可以是衣帽，也可以是饰物、奖章等。而dress, put on 一般不这样用。如： He seldom wears a watch. 他很少戴表。 He wears red T-shirt today. You’d better wear blue or bla ck pants with blown shoes. 穿棕色鞋子的时候, 最好要穿蓝色或黑色裤子。 Why does he often wear dark sunglasses? 他为什么经常戴着深色的太阳镜？ He was wearing a new jacket. 他当时穿着一件新夹克。

Such clothes are not often worn nowadays. 现在那样的衣服很少有人穿了。 dress 动词，常用人作宾语，不接“衣”作宾语，意为“给……穿衣服”。在表示“自己穿衣”时可说get dressed （= dress oneself）。当dress表示状态时，一般要用be dressed in形式。dress up强调着意打扮，意为“穿上盛装、乔装打扮”。例如： My son is now able to dress himself. 我儿子现在自己会穿衣服了。 It’s time to wake up and get dressed! 该起床穿衣服了。 She is dressed in a fur coat. 她穿着毛皮大衣。 She always dresses well. 她总是打扮得很漂亮 注：dress 还通常用于被动语态。如： The girl was poorly dressed. 这女孩衣着寒酸。 in是介词，表示“穿着、戴着”之意，后接表示衣服或颜色的词，着重于服装的款式或颜色。 它所构成的短语只能作表语或定语。 He was in a new black coat. 他穿着黑色的新外套。 The girl in red is my sister. 那个穿红衣服的女孩是我妹妹。 练习： It’s very cold outside. You’d bett er____________ your coat. He ____________ his coat and went out. Mr Black often ____________ white trousers. Lucy’s mother often ____________ a pair of glasses. Could you please help me ____________ the children? She was ____________ in a red coat. Do we have to ____________ up to visit her birthday party? Please ____________ your new coat.。 He’s ____________ a white shirt.。 He is ____________ on his blue hat. Could you ____________ the child for me? He cannot get ____________ (=dress himself). She was ____________ in a red coat. She ____________ the baby.

操作系统文件管理_答案

第六部分文件管理 1、文件系统的主要目的就是( )。 A、实现对文件的按名存取 B、实现虚拟存储 C、提供外存的读写速度 D、用于存储系统文件 2、文件系统就是指( )。 A、文件的集合 B、文件的目录集合 C、实现文件管理的一组软件 D、文件、管理文件的软件及数据结构的总体 3、文件管理实际上就是管理( )。 A、主存空间 B、辅助存储空间 C、逻辑地址空间 D、物理地址空间 4、下列文件的物理结构中,不利于文件长度动态增长的文件物理结构就是( )。 A、顺序文件 B、链接文件 C、索引文件 D、系统文件 5、下列描述不就是文件系统功能的就是( )。 A、建立文件目录 B、提供一组文件操作 C、实现对磁盘的驱动调度 D、实现从逻辑文件到物理文件间的转换 6、文件系统在创建一个文件时,为它建立一个( )。 A、文件目录 B、目录文件 C、逻辑结构 D、逻辑空间 7、索引式(随机)文件组织的一个主要优点就是( )。 A、不需要链接指针 B、能实现物理块的动态分配 C、回收实现比较简单 D、用户存取方便 8、面向用户的文件组织机构属于( )。 A、虚拟结构 B、实际结构 C、逻辑结构 D、物理结构 9、按文件用途来分,编译程序就是( )。 A、用户文件 B、档案文件 C、系统文件 D、库文件 10、将信息加工形成具有保留价值的文件就是( )。 A、库文件 B、档案文件 C、系统文件 D、临时文件 11、文件目录的主要作用就是( )。 A、按名存取 B、提高速度 C、节省空间 D、提高外存利用率 12、如果文件系统中有两个文件重名,不应采用( )。 A、一级目录结构 B、树型目录结构 C、二级目录结构 D、A与C 13、文件系统采用树型目录结构后,对于不同用户的文件,其文件名( )。 A、应该相同 B、应该不同 C、可以不同,也可以相同 D、受系统约束 14、文件系统采用二级文件目录可以( )。 A、缩短访问存储器的时间 B、实现文件共享 C、节省内存空间 D、解决不同用户间的文件命名冲突

智能化系统建设方案

精品文档 一.背景描述： 江南海岸总体规划和设计均体现了传统中国居家理想和现代生 活方式的有机融合，是依照21世纪人居标准精心打造的高级住宅小区。 整个小区无不营造一个舒适休闲的生活空间，是一所环境优雅，闹中 取静的花园式住宅小区，满足住户对高品质生活的追求。 二.工程说明： 江南海岸位于三明市列东区，由14栋高层住宅小区组成，总建 筑面积29.7627万平方米，其中包括4栋27层，6栋25层，4栋29 层，会所1间，负一层，一层。住户总数为1182户。 项目要求: 江南海岸，是集住宅、花园、会所于一体的高级住宅小区。小区智能化系统的工程建设具有投资大、工程复杂、专业性强等特点。小区要求建设成具有国内先进水平的，既具有自身特点，又具有时代潮流特色的高尚住宅楼宇。 整个工程规划、设计、实施上要求充分体现技术的先进性、系统的复杂性、严密的安防集控管理。注重整体功能强大，中心设备完善，系统配置科学合 理，真正体现高技术、高标准、高水平的现代化智能小区。 四.需求分析: 4.1分析与评估：

本方案以江南海岸小区住宅智能化管理及安全防范为设计目标为将力求建设成为高水平、高质量、高标准的信息化智能小区。我方提出以下见解，请发包方领导参考。 ①小区建设要求基于系统可靠、稳定、先进的基础上，既能满足用户住宅 的实际需求，同时又力求经济、实用、合理。 ②整个系统的结构要求清晰合理，小区实现全封闭管理，各个子系统既 相互关联又相对独立，形成一个全方位智能安防管理系统。 ③要求考虑未来系统扩展的需求，为小区以后系统功能的增加、升级，提 供良好的环境空间。 因此，考虑江南海岸属于大型的综合住宅小区，建筑规模庞大、结构复杂，小区各项功能模块齐备，因此在智能化建设方面，产品的集成度、统一化、高效管理方面尤为重要，同时，还必须考虑小区规模的不断扩大，智能化产品必须具备高度的扩展及冗余，顺应小区的发展。 我方进行多项分析与评估，结合小区建筑结构的分布特点、规模发展，以及对小区各功能模块的深层了解，建议江南海岸智能化系统工

dress, wear, put on, have on的用法小结

dress, wear, put on, have on, in的用法小结 都含有“穿、戴”之意，但用法不同。 in是介词，后接表示衣服或颜色的词，着重于服装的款式或颜色。它所构成的短语只能作表语或定语。例如： This is a picture of a young man in a black coat. 这是一张穿着黑色外套的年轻人的照片。这里in a black coat是young man的定语。 He is in a black nylon jacket today. 今天他穿着黑色尼龙夹克。 In a black nylon jacket在这个句子里作表语。 put on “穿上、戴上”，强调“穿”“戴”的动作，后接衣服、鞋帽等。例如： I want you to put on this coat and this hat. 我要你穿这件外套，戴这顶帽子。 Put on your heavy winter coat if you are going out. 如果你要出去，穿上你的厚冬衣。 pull on的意思也是“穿上”，带有“匆忙”的意思： It’s the weekend. I know you’re free. So pull on your jeans and come out with me. 现在是周末，我知道你有空。所以穿上你的牛仔裤，和我一起出去吧。 You’re late! Quickly pull on your clothes and leave! 你迟到了！快穿上衣服走吧！

wear “穿着；戴着”，表示状态，宾语可以是衣帽，也可以是饰物、奖章等。例如： You’d better wear blue or black pants with blown shoes. 穿棕色鞋子的时候, 最好要穿蓝色或黑色裤子。 Why does he often wear dark sunglasses? 他为什么经常戴着深色的太阳镜？ dress的宾语通常是人，意思是“给……穿衣服”。dress oneself 或get dressed表示给自己穿衣服。例如： My son is now able to dress himself. 我儿子现在自己会穿衣服了。 It’s time to wake up and get dressed! 该起床穿衣服了。 be dressed in 的意思是“穿着”，表示状态。 She is dressed in a fur coat. 她穿着毛皮大衣。 dress up的意思是“盛装打扮、乔装打扮”。 I’d like you to dress up for my birthday party tonight. 今晚我希望你为我的生日派对打扮打扮。 Young kids often dress up and have fun at Halloween. 万圣节前夜，小孩子通常都乔装打扮，玩得很开心。have on的意思是“穿着，戴着”，例如： If you're wearing black pants you should have on black shoes and a black belt. 如果你穿着黑色长裤的话，你应该要穿黑色的鞋子，配

linux下各目录作用和功能

/bin:是binary的缩写,这个目录是对Unix系统习惯的沿袭,存放着使用者最经常使用的命令。如:ls,cp,cat等。 /boot:这里存放的是启动Linux时使用的一些核心文档。 /dev:是device的缩写.这个目录下是任何Linux的外部设备,其功能类似Dos下的.sys 和Win下的.vxd。在Linux中设备和文档是用同种方法访问的。例如:/dev/hda代表第一个物理IDE硬盘。 /etc:这个目录用来存放任何的系统管理所需要的配置文档和子目录。 /home:用户主目录,比如说有个用户叫sina,那他的主目录就是/home/sina，说到这里打个岔.您现在应该明白，在我们访问一些个人网页。如:https://www.sodocs.net/doc/0718169851.html,/sina的时候,sina就是表示访问 https://www.sodocs.net/doc/0718169851.html, 站点中的用户sina的用户主目录.假如这个网站的操作系统是Linux,那就是表示/home/sina。 /lib:这个目录里存放着系统最基本的动态链接共享库,其作用类似于Windows里的.dll文档。几乎任何的应用程式都需要用到这些共享库。 /lost+found:这个目录平时是空的,当系统不正常关机后,这里就成了一些无家可归的文档的避难所。对了,有点类似于Dos下的.chk文档。 /mnt:这个目录是空的,系统提供这个目录是让用户临时挂载别的文档系统。 /proc:这个目录是个虚拟的目录,他是系统内存的映射,我们能够通过直接访问这个目录来获取系统信息。也就是说，这个目录的内容不在硬盘上而是在内存里啊。 /root:系统管理员,也叫终极权限者的用户主目录。当然系统的拥有者,总要有些特权啊。/sbin:s就是Super User的意思,也就是说这里存放的是一些系统管理员使用的系统管理程式。 /tmp:这个目录不用说,一定是用来存放一些临时文档的地方了。 /usr:这是个最庞大的目录,我们要用到的很多应用程式和文档几乎都存放在这个目录了。具体来说: /usr/X11R6:存放X-Windows的目录。 /usr/bin:存放着许多应用程式. /usr/sbin:给终极用户使用的一些管理程式就放在这. /usr/doc:这就是Linux文档的大本营. /usr/include:Linux下研发和编译应用程式需要的头文档在这里找. /usr/lib:存放一些常用的动态链接共享库和静态档案库. /usr/local:这是提供给一般用户的/usr目录,在这安装软件最适合. /usr/man:是帮助文档目录. /usr/src:Linux开放的源代码,就存在这个目录,爱好者们别放过哦! /var:这个目录中存放着那些不断在扩充着的东西,为了保持/usr的相对稳定,那些经常被修改的目录能够放在这个目录下,实际上许多系统管理员都是这样干的.顺便说一下,系统的日志文档就在/var/log目录中. /usr/local/bin 本地增加的命令 /usr/local/lib 本地增加的库根文件系统 通常情况下，根文件系统所占空间一般应该比较小，因为其中的绝大部分文件都不需要, 经常改动，而且包括严格的文件和一个小的不经常改变的文件系统不容易损坏。 除了可能的一个叫/ v m l i n u z标准的系统引导映像之外，根目录一般不含任何文件。所有其他文件在根文件系统的子目录中。

fun 用法详解

fun 用法详解 1. It’s fun后接不定式或动名词均可,意思基本相同. Eg;：It’s great fun sailing a boat.= It’s great fun to sail a boat. 扬帆驾舟十分有趣. 2. 表示做某事很开心,可用have (there is) fun (in) doing sth. Eg：We had fun riding our bicycles to the beach today. 我们今天骑自行车去海滨玩得很开心. There’s no fun in spending the evening doing nothing. 晚上无事可干,很无聊. 3. 以下各例中的fun虽用作表语,但仍为名词,而非形容词,故可用great, much, a lot of等形容词修饰,而不用very等副词修饰. 如：She’s great fun to be with. 同她在一起很有意思. Why don’t you come with us? It’ll be great fun. 干吗不同我们一起去呢?很有趣的. 下面一例中fun前的more为much的比较级.如：It is more fun to go with someone than to go alone. 偕伴同去比自己独自去好玩. 4. 注意for fun（为了高兴,为了好玩）与in fun（不是当真的,闹着玩的,开玩笑地）意不同.比较： I am not saying it for fun. 我说这话并不是在开玩笑. He said so only in fun. 他这样说只是开开玩笑. 实用词汇： dress,?wear,?put?on,?have?on,?in的用法小结 dress,?wear,?put?on,?have?on,?in?都含有“穿、戴”之意，但用法不同。? 1.in是介词，后接表示衣服或颜色的词，着重于服装的款式或颜色。它所构成的短语只能作表语或定语。例如：? This?is?a?picture?of?a?young?man?in?a?black?coat.? 这是一张穿着黑色外套的年轻人的照片。这里in?a?black?coat是young?man的定语。He?is?in?a?black?nylon?jacket?today.? 今天他穿着黑色尼龙夹克。? In?a?black?nylon?jacket在这个句子里作表语。? 2.put?on??“穿上、戴上”，强调“穿”“戴”的动作，后接衣服、鞋帽等。例如： I?want?you?to?put?on?this?coat?and?this?hat.? 我要你穿这件外套，戴这顶帽子。 Put?on?your?heavy?winter?coat?if?you?are?going?out.? 如果你要出去，穿上你的厚冬衣。 3.wear?“穿着；戴着”，表示状态，宾语可以是衣帽，也可以是饰物、奖章等。例如：You’d?better?wear?blue?or?black?pants?with?blown?shoes.?穿棕色鞋子的时候,?最好要穿蓝色或黑色裤子。? Why?does?he?often?wear?dark?sunglasses?? 他为什么经常戴着深色的太阳镜？ 4.dress的宾语通常是人，意思是“给……穿衣服”。 dress?oneself?或?get?dressed表示给自己穿衣服。例如：? My?son?is?now?able?to?dress?himself.? 我儿子现在自己会穿衣服了。 ?It’s?time?to?wake?up?and?get?dressed!?

告诉你C盘里面每个文件夹是什么作用

Documents and Settings是什么文件？ 答案： 是系统用户设置文件夹，包括各个用户的文档、收藏夹、上网浏览信息、配置文件等。补：这里面的东西不要随便删除，这保存着所有用户的文档和账户设置，如果删除就会重新启动不能登陆的情况，尤其是里面的default user、all users、administrator和以你当前登陆用户名的文件夹。 Favorites是什么文件？ 答案： 是收藏夹，存放你喜欢的网址。可以在其中放网址快捷方式和文件夹快捷方式，可以新建类别（文件夹）。 Program Files是什么文件？ 答案： 应用软件文件夹装软件的默认路径一般是这里！当然里面也有些系统自身的一些应用程序Common Files是什么文件？ 答案： Common Files. 这个文件夹中包含了应用程序用来共享的文件,很重要，不能乱删除Co mmon Files这个文件是操作系统包扩系统程序和应用程序Common Files是应用程序运行库文件数据库覆盖了大约1000多个最流行的应用程序的插件,补丁等等文件夹com mon files里很多都是系统文件，不能随意删除，除非确定知道是干什么用的，没用的可以删掉。不过就算删掉了有用的东西，也没大的关系，顶多是某些软件用不了，不会造成系统崩溃。 ComPlus Applications是什么文件？ 答案： ComPlus Applications：微软COM+ 组件使用的文件夹，删除后可能引起COM+ 组件不能运行 DIFX是什么文件？ 答案： 不可以删除，已有的XML数据索引方法从实现思想上可分为两类:结构归纳法和节点定位法.这两种方法都存在一定的问题,结构归纳法的缺点是索引规模较大而且难以有效支持较复杂的查询,而节点定位法的主要缺点是容易形成过多的连接操作.针对这些问题,提出了一种新的动态的XML索引体系DifX,它扩展了已有的动态索引方法,采用一种动态的Bisimil arity的概念,可以根据实际查询需求以及最优化的要求动态决定索引中保存的结构信息,以实现对各种形式的查询最有效的支持.实验结果证明DifX是一种有效而且高效的XML索引方法,其可以获得比已有的XML索引方法更高的查询执行效率. Internet Explorer是什么文件？ 答案： 不用说了，肯定不能删除，IE，浏览网页的！ Kaspersky Lab是什么文件？ 答案：卡巴斯基的文件包，这个是卡巴的报告，在C:\Documents and Settings\All Users\Application Data\Kaspersky Lab\AVP6\Report 的更新文件中有很多repor t文件很占地

智能化系统配置项目及要求

智能化系统初步配置方案 一、设计原则 1、智能化系统设计，应综合考虑项目投资额度的可控性、设备选型的灵活性、工程施工的可行性、系统功能的可扩展性、系统运行维护的便利性和物业管理 的规范性等要求。 2、智能化系统的设计应参照本要求，其配置标准不得低于”初步配置方案” 的要求，同时应有一定的升级和扩展能力，并预留相应的接口。 3、智能化系统设计除了满足国家标准与规范的相关规定，以及本标准基本配 置要求外，还应满足建筑、结构以及与智能化系统存在设计相关联的其他专业 的设计规范和要求，特别需要注意符合项目当地现行有关标准和规范的特殊要求。 4、智能化系统设计与工程项目建设地点的实际情况相适应。 5、智能化系统所采用的设备及线路材料等均应符合国家现行的规定，并具有 产品合格证、质量检验证书和产品须通过国家的CCC认证。 二、智能化系统基本配置要求 1、安全防范系统 a、安全防范系统包括闭路电视监控、防盗报警系统、门禁系统、电子巡更系统及无线对讲系统。 b、闭路电视监控系统主要设置重要出入口，如公共场所、重要房间、楼梯通道、楼层电梯通道、电梯轿厢、室外主干道及交叉路口等处，电梯轿厢安装电 梯专用监控镜头并加装抗干扰器，户外监控镜头须带有红外夜视功能。所有的 监控镜头全部采用网络彩色摄像机，采用矩阵主机切换至电视墙，录像以全天 实时高清图像质量保存至少30天（具体保存时间可按照当地派出所要求确定）。 c、防盗报警系统主要设置在财务室、档案室等重要房间，并设置手动报警开关或脚挑报警开关，要求闭路电视监控系统同时显示出报警地点画面。 d、重要设备机房、财务室、档案室等重要房间设置门禁系统。 e、电子巡更系统要求采用离线式，设置于重要机房、楼层楼梯口、电梯厅。 f、无线对讲系统要求具有可进行信道改写和信道加密功能，满足内部通讯需要。 g、各系统设备品牌须选用技术成熟，性能稳定可靠的产品。 2、通讯网络系统

文件夹的作用

All Users文件夹： 『Win9x/ME』所有用户文件夹，里面里面包括系统缺省登录时的桌面文件和开始菜单的内容。『Win2000』在Win2000的系统目录中没有这个文件夹，Win2000将用户的信息放在根目录下的Documents and Settings文件夹中，每个用户对应一个目录，包括开始菜单、桌面、收藏夹、我的文档等等。 Application Data文件夹： 『Win9x/ME』应用程序数据任务栏中的快捷方式，输入法的一些文件等等。根据你系统中使用不同的软件，该目录中的内容也有所不同。 『Win2000』在Documents and Settings文件夹中，每个用户都对应一个Application Data 文件夹，同样每个用户由于使用的软件不同，目录内容也相同。 Applog文件夹： 『Win9x/ME』应用程序逻辑文件目录。逻辑文件是用来记录应用软件在运行时，需要调用的文件、使用的地址等信息的文件。要查看这些文件，用记事本打开即可。 Catroot文件夹： 『Win9x』计算机启动测试信息目录，目录中包括的文件大多是关于计算机启动时检测的硬软件信息。 『WinME』该文件夹位于系统目录的system目录中。 『Win2000』该文件夹位于系统目录的system32目录中。 Command文件夹： 『Win9x/ME』DOS命令目录。包括很多DOS下的外部命令，虽说都是些小工具，但真的很好用，特别是对于系统崩溃时。 『Win2000』这些DOS命令位于系统目录的system32目录中。 Config文件夹： 『Win9x/ME/2000』配置文件夹，目录中包括一些MIDI乐器的定义文件。 Cookies文件夹： 『Win9x/ME』Cookies又叫小甜饼，是你在浏览某些网站时，留在你硬盘上的一些资料，包括用户名、用户资料、网址等等。 『Win2000』每个用户都有一个Cookies文件夹，位于Documents and Settings文件夹的每个用户目录中。 Cursors文件夹： 『Win9x/ME/2000』鼠标动画文件夹。目录中包括鼠标在不同状态下的动画文件。 Desktop文件夹： 『Win9x/ME』桌面文件夹。包括桌面上的一些图标。 『Win2000』这个文件夹在系统目录中也存在，同时在Documents and Settings文件夹的每个用户目录中还有“桌面”文件夹。

put on pull on wear 用法

put on, pull on, wear, have on , dress的用法区别(1)put on 和pull on 穿上；戴上。相当于及物动词，以衣物作宾语，着重于穿、戴的动作。put on 为普通用语；pull on多用于穿袜子、戴手套或比较随便地穿上。 ①It’s cold outside.You’d better put on your hat.外面很冷，你最好戴上帽子。 ②She put /pulled on her coat and went out of the room hurri edly.她穿上大衣，匆忙地走了。 (2)wear 和have on 穿着；戴着。相当于及物动词，有衣物作宾语，着重于穿、戴的状态。have on不用于进行时态。 ①He always wears/has on black shoes.她一直穿着黑鞋。 ②She is wearing/has on a red coat她穿着红大衣。 (3)dress 穿；戴。可用作及物动词，以人作宾语，即dress sb.（给某人穿衣）；也可用作不及物动词。既可强调动作，又可表示状态，表示状态时常用be dressed in 结构。此外dress还可用作名词。 ①Mary is dressing her daughter.玛丽正给她女儿穿衣服。 ②She usually dresses well.她总是穿得很好。 ③He is dressed in a black jacket.他穿着黑上衣。

(4)in 穿着；戴着。是介词，以衣物或表示颜色的名词作宾语，表示状态。构成的介词短词可作表语或定语。 ①My brother is in a blue jacket.我弟弟穿着蓝上衣。 ②The boy in a blue jacket is my brother.穿蓝上衣的孩子是我弟弟。 ③My brother is in blue.我弟弟穿着蓝衣服。

linux下各文件夹的结构说明及用途详细介绍解析

linux下各文件夹的结构说明及用途介绍: /bin:二进制可执行命令。 /dev:设备特殊文件。 /etc:系统管理和配置文件。 /etc/rc.d:启动的配置文件和脚本。 /home:用户主目录的基点,比如用户user的主目录就是/home/user,可以用~user 表示。 /lib:标准程序设计库,又叫动态链接共享库,作用类似windows里的.dll文件。 /sbin:系统管理命令,这里存放的是系统管理员使用的管理程序。 /tmp:公用的临时文件存储点。 /root:系统管理员的主目录。 /mnt:系统提供这个目录是让用户临时挂载其他的文件系统。 /lost+found:这个目录平时是空的,系统非正常关机而留下“无家可归”的文件就在这里。 /proc:虚拟的目录,是系统内存的映射。可直接访问这个目录来获取系统信息。 /var:某些大文件的溢出区,比方说各种服务的日志文件。 /usr:最庞大的目录,要用到的应用程序和文件几乎都在这个目录。其中包含: /usr/x11r6:存放x window的目录。 /usr/bin:众多的应用程序。

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