鈦合金輕質(zhì)、耐高溫、耐腐蝕、生物相容性好且無(wú)磁性，在航空、航天、兵器、艦船、醫(yī)療等領(lǐng)域得到了廣泛的應(yīng)用[1,2] 但是，鈦合金的導(dǎo)熱系數(shù)低、高溫化學(xué)活性高和彈性模量小，在切削加工過(guò)程中工件與刀具的粘連使其磨損嚴(yán)重、加工后的工件表面質(zhì)量較差、加工成本提高，限制了鈦合金的應(yīng)用[3~5] 提高鈦合金切削性能的關(guān)鍵，在于改善切削界面摩擦狀態(tài)，實(shí)現(xiàn)高效潤(rùn)滑 但是，鈦合金獨(dú)特的摩擦學(xué)特性使傳統(tǒng)金屬加工潤(rùn)滑液難以在鈦合金表面有效潤(rùn)滑 在基礎(chǔ)液中添加納米材料，是提高潤(rùn)滑介質(zhì)加工性的主要手段[6~8] 石墨烯(Graphene)是一種典型的二維材料，層與層之間依靠弱范德華力連接，具有較弱的剪切力、優(yōu)異的機(jī)械性能、大比表面積和較高的熱導(dǎo)率，在潤(rùn)滑領(lǐng)域受到了極大的關(guān)注[9,10] Ming等[11]在植物油中添加石墨烯用于TC4合金切削加工潤(rùn)滑，可增強(qiáng)銑削區(qū)域油膜的潤(rùn)滑性能 Ning等[12]將Graphene、磷酸鹽、納米ZrO2等按一定比例混合制備石墨烯水基潤(rùn)滑劑應(yīng)用于鈦合金熱軋，降低了熱軋過(guò)程的摩擦磨損和氧化 Ibrahim等[13]將石墨烯加入棕櫚油中，摩擦系數(shù)和切削能耗比Acculube LB2000商用潤(rùn)滑油大幅降低 但是，結(jié)構(gòu)完整的Graphene因化學(xué)穩(wěn)定性高而難以在溶劑中穩(wěn)定分散，容易產(chǎn)生不可逆團(tuán)聚使摩擦過(guò)程中難以進(jìn)入工況表面，無(wú)法發(fā)揮抗磨減磨的作用[14,15]

納米復(fù)合材料在基礎(chǔ)液中的分散性高，且不同納米材料之間的協(xié)同作用可進(jìn)一步提高潤(rùn)滑性能 Meng[16,17]等在氧化石墨烯(GO)表面沉積Au或Cu，降低了石墨烯片層間的π-π鍵的相互作用減少了團(tuán)聚 與單一納米材料(GO、Au和Cu)相比，復(fù)合材料之間的協(xié)同作用使其具有更優(yōu)異的潤(rùn)滑性能 Li等[18]用激光輻射制備的Ag/Graphene復(fù)合材料可穩(wěn)定在油中懸浮60 d以上，這種潤(rùn)滑添加劑不會(huì)產(chǎn)生金屬腐蝕和環(huán)境污染 Graphene與金屬納米材料復(fù)合的成本高，回收難，因此難以推廣 SiO2中的Si-O親水性和耐磨性較好，且成本較低[19,20] Na等[21]用原位引發(fā)聚合法制備的PTFE/SiO2復(fù)合材料，提高了PTFE在純水中的分散性和摩擦性能 Zhang等[22]用溶膠-凝膠法制備Fe3O4@SiO2納米復(fù)合材料，提高了Fe3O4在環(huán)氧樹脂中的分散性 在Graphene表面原位生成SiO2制備Graphene/SiO2納米復(fù)合材料，可提高Graphene在超純水中的分散性且降低成本 鑒于此，本文用溶膠凝膠法在Graphene表面原位生成SiO2制備Graphene/SiO2納米復(fù)合材料，以提高Graphene在超純水中的分散性且降低成本，并將其作為水基潤(rùn)滑添加劑研究GCr15/TC4接觸下的摩擦學(xué)性能并揭示其潤(rùn)滑機(jī)理

1 實(shí)驗(yàn)方法1.1 實(shí)驗(yàn)用材料

無(wú)水乙醇(C2H5OH，分析純)，氨水(NH3·H2O，分析純)，石油醚(PE)和正硅酸乙酯(TEOS)，Graphene和工業(yè)SiO2

1.2 納米復(fù)合材料Graphene/SiO2 的制備

使用溶膠-凝膠法中的St?ber法制備Graphene/SiO2[23]，其工藝示意圖如圖1所示 將0.2 g的Graphene添加到50 mL無(wú)水乙醇和50 mL超純水的混合溶液中，使用超聲波破碎30 min 然后加入1 mL氨水和2 mL TEOS并對(duì)混合溶液磁力攪拌12 h 對(duì)產(chǎn)物進(jìn)行離心分離后收集膠狀固體產(chǎn)物，用無(wú)水乙醇多次清洗以除去氨水和未反應(yīng)的TEOS 將所得膠狀固體在75℃真空環(huán)境干燥12 h后達(dá)到納米復(fù)合材料Graphene/SiO2

圖1



圖1制備Graphene/SiO2納米復(fù)合材料的示意圖

Fig.1Schematic diagram of preparation of Graphene/SiO2 composite nanomaterials

1.3 摩擦磨損實(shí)驗(yàn)

使用旋轉(zhuǎn)式摩擦磨損試驗(yàn)儀(UMT-5)測(cè)試試樣的摩擦磨損性能，上試樣是直徑為6 mm的GCr15鋼球，下試樣是厚度為8 mm直徑為25 mm的TC4圓盤 摩擦實(shí)驗(yàn)中的潤(rùn)滑劑，是超純水中添加不同質(zhì)量分?jǐn)?shù)的Graphene/SiO2 實(shí)驗(yàn)的線速度為0.047 m/s，載荷為8~15 N，時(shí)間為30 min，根據(jù)赫茲理論計(jì)算赫茲接觸壓力

πP=4Fπa2

(1)

a=2(23×FRE')3

(2)

1E'=12(1-μ12E1+1-μ22E2)

(3)

其中P為赫茲接觸應(yīng)力，a為接觸直徑、F為摩擦試驗(yàn)機(jī)施加載荷(8~15 N)、R為GCr15球半徑、E'為有效彈性模量[24,25] E1(TC4 113 GPa)和E2(GCr15 207 GPa)為摩擦試樣的彈性模量，μ1(0.34)和μ2(0.30)為泊松比 最大接觸應(yīng)力范圍為1.04~1.29 GPa GCr15球的磨損率為[26,27]

h=r-r2-d24

(4)

V=πl(wèi)63d24+h2

(5)

WB=VPS

(6)

式中d為等效圓的直徑，r為GCr15球的直徑，P為載荷，S為總滑動(dòng)距離 實(shí)驗(yàn)前用無(wú)水乙醇超聲清洗GCr15球和TC4圓盤30 min以去除污染，摩擦實(shí)驗(yàn)開(kāi)始前滴加80 μL的潤(rùn)滑劑 實(shí)驗(yàn)結(jié)束后用棉球擦拭表面，干燥后保存

1.4 性能表征

用沉降法評(píng)估Graphene/SiO2在超純水中的分散穩(wěn)定性[35] 將0.2%(質(zhì)量分?jǐn)?shù))的Graphene和Graphene/SiO2分別加到超純水中，超聲1 h靜置適當(dāng)時(shí)間后拍攝光學(xué)圖像

用X射線衍射儀(XRD，D/MAX-RB)測(cè)試Graphene/SiO2納米材料的晶體結(jié)構(gòu) 用掃描電子顯微鏡(SEM，JSM-5610LV)觀察Graphene/SiO2復(fù)合材料的微觀組織形貌，用SEM附帶的EDS分析復(fù)合材料和磨損表面元素的成分 用拉曼光譜儀(LabRam HR Evolution)測(cè)試Graphene和Graphene/SiO2納米復(fù)合材料的拉曼光譜 用金相顯微鏡(OM，GX51) 測(cè)量鋼球磨斑的直徑，用三維白光掃描儀(TDWS，MicroXAM-800)測(cè)量TC4圓盤磨損體積 用掃描電鏡分析實(shí)驗(yàn)后TC4圓盤磨痕的微觀組織形貌和元素的分布 用X射線光電子能譜儀(XPS，PHI 5000) 分析磨損表面的特征元素

2 結(jié)果和討論2.1 Graphene/SiO2 納米復(fù)合材料的形貌與表征

圖2給出了Graphene和SiO2的掃描電鏡照片，可見(jiàn)片層之間褶皺，邊緣處卷曲，SiO2球狀顆粒的直徑約為300 nm 圖2c給出了Graphene/SiO2納米復(fù)合材料的掃面電鏡照片，可見(jiàn)Graphene的卷曲結(jié)構(gòu)，表面均為小球顆粒，能譜分析表明主要元素為Si、O和C，即Graphene表面生成了SiO2納米顆粒 與單一的納米SiO2相比，Graphene表面的SiO2顆粒尺寸差異較大(圖2b和c) 其原因是，在TEOS發(fā)生化學(xué)反應(yīng)形成SiO2的過(guò)程中Graphene和部分SiO2顆粒都是形核位點(diǎn)，生成了較大的SiO2顆粒[28]

圖2



圖2不同試樣的SEM照片、Graphene/SiO2的能譜、以及Graphene/SiO2、Graphene、Amorphous SiO2和SiO2的XRD譜

Fig.2SEM images of different samples (a) graphene, (b) SiO2, (c) graphene/SiO2; (d) energy spectrum of Graphene/SiO2;(e) XRD patterns of Graphene/SiO2, Graphene, Amorphous SiO2 and SiO2

圖2e給出了XRD譜 可以看出，Graphene在譜中的26.34°和42.68°出現(xiàn)了兩個(gè)特征衍射峰[29]，低矮的衍射峰對(duì)應(yīng)非晶態(tài)SiO2，明顯的衍射峰對(duì)應(yīng)晶體SiO2[30] Graphene/SiO2納米復(fù)合材料的衍射峰與非晶SiO2一致，沒(méi)有出現(xiàn)Graphene的衍射峰特征

圖3給出了Graphene和Graphene/SiO2的拉曼光譜，可見(jiàn)Graphene的衍射峰位于1333.2 cm-1、1567.1 cm-1和2671.8 cm-1處，分別對(duì)應(yīng)D峰、G峰和2D峰 G峰的強(qiáng)度高于2D峰，表明材料具有多層結(jié)構(gòu)[31,32] 與Graphene的特征峰相比Graphene/SiO2的特征峰正向偏移，表明Graphene表面原位生成了SiO2[33,34] 以上結(jié)果表明，已制備出Graphene/SiO2納米復(fù)合材料

圖3



圖3Graphene/SiO2和Graphene的Raman譜

Fig.3Raman spectra of Graphene/SiO2 and Graphene

2.2 Graphene/SiO2 的分散性

圖4給出了不同潤(rùn)滑劑放置不同時(shí)間的光學(xué)圖像 Graphene在超純水中分散性差，放置24 h就完全分層 而含有Graphene/SiO2的超純水溶液的分散較為穩(wěn)定，靜止48 h后開(kāi)始出現(xiàn)沉淀，上層溶液變淺，表明其分散性優(yōu)于Graphene

圖4



圖4不同潤(rùn)滑劑在不同時(shí)間的光學(xué)圖像

Fig.4Optical images of different lubricants at different time:(a) 0.2% Graphene; (b) 0.2% Graphene/SiO2

2.3 Graphene/SiO2 納米復(fù)合材料作為水基潤(rùn)滑添加劑的摩擦學(xué)性能

圖5給出了不同含量的Graphene/SiO2的平均摩擦系數(shù)和磨損率曲線 可以看出，平均摩擦系數(shù)和磨損率均呈現(xiàn)先下降后上升，0.2%(質(zhì)量分?jǐn)?shù))的Graphene/SiO2摩擦系數(shù)最低，比超純水工況降低17.9%，鋼球磨損率降低61.7% 添加劑含量超過(guò)0.2%(質(zhì)量分?jǐn)?shù))，則摩擦性能開(kāi)始降低

圖5



圖5不同含量的Graphene/SiO2的平均摩擦系數(shù)和磨損率曲線

Fig.5Curves of average coefficient of friction and wear rate of Graphene/SiO2 with different contents

圖6給出了在不同載荷下0.2%(質(zhì)量分?jǐn)?shù))Graphene/SiO2潤(rùn)滑劑的摩擦系數(shù) 從圖6可見(jiàn)，在相同的載荷下超純水的摩擦系數(shù)曲線均在潤(rùn)滑添加劑上方 在8 N載荷工況下超純水的摩擦系數(shù)先上升到0.36然后降到0.28，最終在0.29~0.32之間波動(dòng)，而Graphene/SiO2的摩擦系數(shù)明顯降低 在12 N載荷工況下，超純水和Graphene/SiO2的摩擦系數(shù)接近，而Graphene/SiO2的摩擦曲線有升高的趨勢(shì) 在15 N載荷工況下5 min后超純水的摩擦系數(shù)保持在0.29，而Graphene/SiO2的摩擦系數(shù)保持在0.24 在總體上，在載荷相同的工況下Graphene/SiO2的摩擦系數(shù)曲線始終在超純水之下

圖6



圖6超純水和Graphene/SiO2在不同載荷條件下的摩擦系數(shù)

Fig.6Coefficient of friction curve of water and Graphene/SiO2 under different loads (a) 8 N, (b) 10 N, (c) 12 N, (d) 15 N

圖7給出了超純水和含量為0.2%(質(zhì)量分?jǐn)?shù))的Graphene/SiO2在不同載荷下的平均摩擦系數(shù)和磨損率 可以看出，載荷由8 N增大到12 N時(shí)Graphene/SiO2的摩擦系數(shù)和磨損率均增大，而超純水的摩擦系數(shù)降低、磨損率提高 載荷為10 N時(shí)Graphene/SiO2的平均摩擦系數(shù)比超純水的平均摩擦系數(shù)降低了5.9%而磨損率降低了34.4% 載荷從12 N增大到15 N，Graphene/SiO2和超純水的平均摩擦系數(shù)和磨損率都降低 在載荷相同條件下，Graphene/SiO2的平均摩擦系數(shù)和磨損率均低于超純水 在15 N載荷工況下Graphene/SiO2的摩擦系數(shù)和磨損率最低，摩擦系數(shù)為0.2399，磨損率為3.75×10-8 mm3/N·m 與超純水相比，摩擦系數(shù)降低17.9%，磨損率降低了61.7%

圖7



圖7超純水和Graphene/SiO2不同載荷條件下的摩擦系數(shù)和磨損率

Fig.7Coefficient of Friction(a) and wear rates of water and Graphene/SiO2 (b) under various load conditions

圖8給出了三維白光測(cè)量數(shù)據(jù) 計(jì)算結(jié)果表明，超純水和0.2%(質(zhì)量分?jǐn)?shù))潤(rùn)滑添加劑的磨痕磨損體積分別為0.017 mm3和0.019 mm3，但0.2%(質(zhì)量分?jǐn)?shù))潤(rùn)滑添加劑的摩擦系數(shù)和鋼球磨損率的實(shí)驗(yàn)結(jié)果均低于超純水 其原因是，較高載荷產(chǎn)生更多的磨屑，使TC4盤磨損體積增大 同時(shí)，磨屑和SiO2顆粒對(duì)磨損表面共同修復(fù)提高了耐磨性，使摩擦系數(shù)降低[36]

圖8



圖8TC4圓盤的三維白光和磨痕剖面

Fig.83D Micrographs and profiles of wear tracks of TC4 discs (a) Ultra-pure water (b) Graphene/SiO2

2.4 磨損表面

圖9給出了超純水和Graphene/SiO2潤(rùn)滑下磨痕表面的OM圖 可以看出，GCr15鋼球磨痕均為橢圓狀，在載荷作用下接觸區(qū)域不是理想狀態(tài)的剛體，因此使局部變形成橢圓狀的接觸區(qū)(圖10)[37,38] 用超純水潤(rùn)滑(圖9a~d)則鋼球表面沿滑動(dòng)方向有深而寬的磨痕，劃痕和凹坑較多，磨損量大 在超純水中加入Graphene/SiO2潤(rùn)滑劑(圖9e~h)使磨痕變淺變窄，磨斑明顯變小

圖9



圖9不同載荷下GCr15的磨痕OM圖

Fig.9OM images of GCr15 wear scars at different loads (a~d) Ultra-pure water (e~h) 0.2% Graphene/SiO2

圖10



圖10Hertz球盤接觸模型

Fig.10Hertz contact model of sphere-on-disc

圖11a~d給出了經(jīng)超純水潤(rùn)滑的TC4圓盤磨痕的SEM照片和EDS譜 可以看出，超純水潤(rùn)滑的磨損表面有明顯的脫屑且出現(xiàn)細(xì)小顆粒磨損 表面上的元素主要是TC4的主要元素而未發(fā)現(xiàn)氧元素，表明未發(fā)生氧化 在15 N載荷工況下表面出現(xiàn)片層狀脫落、磨屑和犁溝，表明磨損機(jī)制為磨粒磨損和黏著磨損 圖11e~h給出了經(jīng)Graphene/SiO2潤(rùn)滑后的表面 可以看出，在8 N和10 N載荷下磨損表面上的殘留物質(zhì)較多 圖12給出了對(duì)殘留物質(zhì)的能譜分析，可見(jiàn)磨損表面的物質(zhì)主要為TC4和Graphene/SiO2 Fe元素來(lái)自于GCr15小球，表明發(fā)生了材料轉(zhuǎn)移 在15 N載荷工況下磨損表面出現(xiàn)坑洞和裂縫，還出現(xiàn)顆粒和脫屑，表明磨損形式主要為疲勞磨損、磨粒磨損和黏著磨損 圖11g~h給出了12 N和15 N載荷工況表面的EDS分析結(jié)果 可以看出，磨損表面出現(xiàn)Si元素，C元素的含量較低 這表明，在高載荷下潤(rùn)滑劑難以進(jìn)入摩擦表面 圖13給出了在15 N載荷工況下的面掃描結(jié)果 可以看出，表面出現(xiàn)均勻的Si元素，高分辨SEM圖像證明磨損表面有SiO2顆粒

圖11



圖11不同載荷下TC4盤的磨痕SEM照片

Fig.11SEM images of wear scars of TC4 discs under different loads: (a~d) Ultra-pure water, (e~h) 0.2% Graphene/SiO2 lubricant

圖12



圖1210 N載荷下0.2%Graphene/SiO2潤(rùn)滑添加劑的TC4盤磨痕能譜

Fig.12EDS spectra of the wear scar of the TC4 disc lubricated by 0.2%Graphene/SiO2 lubrication additive under 10 N load (a) high resolution SEM image (b) area I EDS (c) area II EDS

圖13



圖1315N載荷下0.2% Graphene/SiO2潤(rùn)滑添加劑的 TC4盤磨痕能譜

Fig.13EDS spectra of the wear scar of the TC4 disc lubricated by 0.2%Graphene/SiO2 lubrication additive under 15 N load (a) The high resolution SEM image, (b) the spectra, (c~e) the distribution of Ti, C, Si elements

圖14給出了對(duì)磨損表面特征元素的XPS分析，以揭示Graphene/SiO2添加劑的潤(rùn)滑機(jī)理 由圖14a中的C1s譜峰對(duì)應(yīng)磨損表面的C-C、C-O、C=O鍵可見(jiàn)，磨損表面存在Graphene，而SiC是切割圓盤制取XPS試樣時(shí)引入的 Si2p的譜峰(圖14c)也證實(shí)了SiC的存在[39] 從圖14b中的O1s譜峰可知，Ti和Al金屬在空氣中易生成一層致密的氧化薄膜，磨損表面出現(xiàn)TiO2和Al2O3[40,41] 而SiO2的存在，證明磨損表面Graphene/SiO2潤(rùn)滑添加劑的存在 磨損表面并未發(fā)生復(fù)雜的化學(xué)反應(yīng)，而在15 N載荷條件下Si元素在磨損表面均勻分布，表明在摩擦過(guò)程中Graphene/SiO2水基潤(rùn)滑劑在摩擦界面生成了一定厚度的物理吸附膜

圖14



圖14Graphene/SiO2潤(rùn)滑的TC4圓盤磨損表面的XPS分析

Fig.14XPS analysis of worn surface of TC4 disc lubricated by Graphene/SiO2: (a) C1s (b) O1s (c) Si2p (d) Al2p (e) Ti2p

根據(jù)潤(rùn)滑理論，潤(rùn)滑的狀態(tài)可用潤(rùn)滑狀態(tài)圖中的兩個(gè)分量

gV=GW3u2

(7)

gE=W8/3u2

(8)

表示 其中u=ηV/E'R，G=αE'，W=F/E'R2，R為GCr15球的半徑(3 mm)，V為摩擦過(guò)程中的摩擦副的相對(duì)線速度(47.1 mm/s)，η為潤(rùn)滑劑的粘度，α為粘度-壓力系數(shù)，E'(163 GPa)為有效彈性模量，F(xiàn)(8~15 N)施加的載荷，k(≈1.03)為橢圓參數(shù) 根據(jù)hamrock-dowson理論，薄膜的最小理論厚度和比率分別為[42]

hmin=2.69G0.53U0.67W0.067(1-0.61e-0.73k)

(9)

和

λ=hminσ12+σ22

(10)

其中σ1和σ2分別為球和盤的粗糙度(σ1=20 nm，σ2=40 nm) 計(jì)算結(jié)果表明，hmin約為8.08 nm，λ約為0.18，表明潤(rùn)滑狀態(tài)處于邊界潤(rùn)滑[43]

根據(jù)計(jì)算出的邊界潤(rùn)滑狀態(tài)提出相應(yīng)的磨損機(jī)理(圖15)：添加在超純水中的Graphene/SiO2吸附或沉積在摩擦表面生成潤(rùn)滑膜，將摩擦副和磨損表面凹凸點(diǎn)接觸轉(zhuǎn)變?yōu)槟Σ粮?潤(rùn)滑膜-磨損面的接觸，減少了磨損[44~46] 由圖11h和圖13可見(jiàn)，在摩擦實(shí)驗(yàn)過(guò)程中從Graphene表面脫落的SiO2修補(bǔ)了磨損表面，部分SiO2在接觸面產(chǎn)生微軸承作用，將滑動(dòng)摩擦轉(zhuǎn)變?yōu)闈L動(dòng)摩擦[47] 在高載荷情況下摩擦副表面上的凸峰折斷產(chǎn)生了更多的細(xì)小磨屑，磨屑與部分潤(rùn)滑添加劑相結(jié)合修復(fù)了磨損表面[48] 因此，與其他載荷相比15 N載荷情況下的摩擦系數(shù)更低 另一方面，Graphene片層間依靠范德華力結(jié)合，在滑動(dòng)過(guò)程中摩擦副之間的低剪切力使片層產(chǎn)生相對(duì)滑動(dòng)，Graphene給接觸區(qū)域補(bǔ)充水而避免了直接接觸[49] 這表明，Graphene/SiO2潤(rùn)滑添加劑的加入提高了超純水的摩擦學(xué)性能

圖15



圖15Graphene/SiO2的潤(rùn)滑機(jī)理示意圖

Fig.15Schematic diagram of lubrication mechanism of Graphene/SiO2

3 結(jié)論

(1) 使用溶膠-凝膠St?ber法制備的Graphene/SiO2復(fù)合材料，Graphene為軟質(zhì)內(nèi)核，SiO2在其表面形成一層硬質(zhì)外殼，外殼粒子的直徑約為100 nm并能在水中穩(wěn)定分散

(2) 在15 N載荷工況下，0.2% Graphene/SiO2水基潤(rùn)滑劑摩擦系數(shù)比超純水降低17.9%，鋼球磨損率降低了61.7%

(3) 在高載荷作用下Graphene/SiO2潤(rùn)滑劑的潤(rùn)滑效果更好，主要原因是Graphene/SiO2納米復(fù)合材料在磨損表面生成了物理吸附膜、Graphene的層狀剪切作用以及SiO2對(duì)磨損表面的修復(fù)和滾珠軸承作用

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Hip arthroplasty can be considered one of the major successes of orthopedic surgery, with more than 350000 replacements performed every year in the United States with a constantly increasing rate. The main limitations to the lifespan of these devices are due to tribological aspects, in particular the wear of mating surfaces, which implies a loss of matter and modification of surface geometry. However, wear is a complex phenomenon, also involving lubrication and friction. The present paper deals with the tribological performance of hip implants and is organized in to three main sections. Firstly, the basic elements of tribology are presented, from contact mechanics of ball-in-socket joints to ultra high molecular weight polyethylene wear laws. Some fundamental equations are also reported, with the aim of providing the reader with some simple tools for tribological investigations. In the second section, the focus moves to artificial hip joints, defining materials and geometrical properties and discussing their friction, lubrication and wear characteristics. In particular, the features of different couplings, from metal-on-plastic to metal-on-metal and ceramic-on-ceramic, are discussed as well as the role of the head radius and clearance. How friction, lubrication and wear are interconnected and most of all how they are specific for each loading and kinematic condition is highlighted. Thus, the significant differences in patients and their lifestyles account for the high dispersion of clinical data. Furthermore, such consideration has raised a new discussion on the most suitable in vitro tests for hip implants as simplified gait cycles can be too far from effective implant working conditions. In the third section, the trends of hip implants in the years from 2003 to 2012 provided by the National Joint Registry of England, Wales and Northern Ireland are summarized and commented on in a discussion.

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Utilizing the theory developed by the authors in an earlier publication, the influence of the ellipticity parameter, the dimensionless speed, load, and material parameters on minimum film thickness was investigated. The ellipticity parameter was varied from one (a ball on a plate configuration) to eight (a configuration approaching a line contact). The dimensionless speed parameter was varied over a range of nearly two orders of magnitude. The dimensionless load parameter was varied over a range of one order of magnitude. Conditions corresponding to the use of solid materials of bronze, steel, and silicon nitride and lubricants of paraffinic and naphthenic mineral oils were considered in obtaining the exponent in the dimensionless material parameter. Thirty-four different cases were used in obtaining the minimum film thickness formula given below as Hˉmin=3.63U0.68G0.49W?0.073(1?e?0.68k) A simplified expression for the ellipticity parameter was found where k=1.03RyRx0.64 Contour plots were also shown which indicate in detail the pressure spike and two side lobes in which the minimum film thickness occurs. These theoretical solutions of film thickness have all the essential features of the previously reported experimental observations based upon optical interferometry.

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Application of titanium alloy in airplane

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