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Friction between single aramid fibres under pre-tension load

2019, Tribology International

Understanding the friction mechanism at microscale of fibrous material is important as it is one of the key roles in governing the behaviour of fibre assemblies at meso and macroscale. However, mechanical stress such as tension may also influence the frictional behaviour. In this study the frictional behaviour between fibres under pretension is explored. A new experimental setup was successfully developed to measure the friction force between two single aramid fibres at perpendicular contact. Although pre-tension influences the bending stiffness of the fibre, the results show that the effect of pre-tension on the contact length is relatively small. The elastic deformation of the contact dominates over the 'wrapping effect', generating the contact area over which the interfacial shear takes place.

Accepted Manuscript Friction between single aramid fibres under pre-tension load Nurhidayah Ismail, Matthijn B. de Rooij, Erik G. de Vries, Nurul Hilwa Mohd Zini, Dik J. Schipper PII: S0301-679X(19)30207-5 DOI: https://doi.org/10.1016/j.triboint.2019.04.013 Reference: JTRI 5729 To appear in: Tribology International Received Date: 23 November 2018 Revised Date: 26 March 2019 Accepted Date: 4 April 2019 Please cite this article as: Ismail N, de Rooij MB, de Vries EG, Hilwa Mohd Zini N, Schipper DJ, Friction between single aramid fibres under pre-tension load, Tribology International (2019), doi: https:// doi.org/10.1016/j.triboint.2019.04.013. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT 1 Friction between single aramid fibres under pre-tension load Nurhidayah ISMAIL 1 1 , Matthijn B. de ROOIJ , Erik G. de VRIES , Nurul Hilwa MOHD ZINI J. SCHIPPER 1 5 6 7 1,2,3 ,and Dik 1 Laboratory for Surface Technology and Tribology, Department Mechanics of Solids, Surfaces and Systems (MS3), Faculty of Engineering Technology, University of Twente, Drienerlolaan 5, 7522 NB, Enschede, The Netherlands. 2 8 9 10 11 1,2,3* Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia. M AN US C 3 4 RI PT 2 3 Centre for Advanced Research on Energy, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia. 12 13 Abstract 15 Understanding the friction mechanism at microscale of fibrous material is important as it 16 is one of the key roles in governing the behaviour of fibre assemblies at meso and 17 macroscale. However, mechanical stress such as tension may also influence the 18 frictional behaviour. In this study the frictional behaviour between fibres under pre- 19 tension is explored. A new experimental setup was successfully developed to measure 20 the friction force between two single aramid fibres at perpendicular contact. Although 21 pre-tension influences the bending stiffness of the fibre, the results show that the effect 22 of pre-tension on the contact length is relatively small. The elastic deformation of the 23 contact dominates over the ‘wrapping effect’, generating the contact area over which the 24 interfacial shear takes place. 25 AC C EP TE D 14 26 1 Introduction 27 Aramid fibres are often found in high-performance applications such as in some 28 composites, ballistics, aerospace, protective clothing, ropes and cables applications. 29 This is due to its combination of high strength and high stiffness properties as well as ACCEPTED MANUSCRIPT the high strength-to-weight ratio, about five times higher than steel. Unfortunately, the 31 fibre may expose to a series of mechanical stresses for instance friction during 32 processing or handling stages, which lead to its structural deformation and deteriorate 33 the physical and mechanical performance of a final product. 34 In general, the fibre is produced in the form of individual continuous filaments which are 35 bundled together forming the tows. These yarns are then interlaced to form a woven 36 fabric. The processes show that the individual continuous filaments, are basically the 37 contacting and interacting bodies and subjected to frictional effects. Therefore, a 38 thorough understanding of the frictional behaviour between fibres at filament level is 39 necessary, especially for the complex structures like woven fabrics. 40 It is important to note that, the friction plays a dual role. An excessive frictional force, 41 either fibre against fibre or fibre against tool, can deteriorate the physical characteristics 42 of the fibre itself, e.g., defibrillation that lead to fibre breakage. This breakage is crucial 43 as it influences the strength properties of the fibre yarns and fabric [1-3]. On the 44 contrary, for the spun yarn, a higher inter-fibre friction will increase the yarn strength, 45 but if the tension exceeds the friction level, a high possibility of rupturing and slipping of 46 fibres exists. For example, in some dynamically loaded applications such as in mooring 47 lines, the friction between fibres may cause a premature failure of the fibre ropes and 48 hence influence the mechanical properties and the ropes lifespan [4,5]. Vertical tension 49 because of the rope weight as well as a dynamic response which is excited by 50 longitudinal oscillation due to wave motion will generate the internal friction in fibres 51 ropes. Thus, understanding the friction and tension between fibres at microscale level is 52 needed as it has a great influence on the structural and properties of a final product 53 such as a rope and a woven fabric. 54 Many researchers have developed various methods to study the friction between fibres 55 and have been reviewed by several authors [6,7]. One of the fundamental methods is to 56 measure friction based on the principle of rubbing fibre against another fibre in linear 57 motion [8-12]. This method is commonly used for concentrated point, line and disperse 58 contacts between fibres, yarns (tows) and fabrics. For example, this method has been 59 adapted in measuring the friction force between single fibres of different materials such AC C EP TE D M AN US C RI PT 30 ACCEPTED MANUSCRIPT as carbon [13], polyamide [14], polyester [14] and polyethylene [15], and tow against 61 tow or metal contact [16,17]. Meanwhile, Gralen, Olofsson and Lindberg [18-20] have 62 used a twist method to study the frictional behaviour in textile materials. In their 63 experiments, two fibres were twisted together by a certain number of turns, and the 64 friction force would be only measured during slippage. If measuring at high velocities or 65 when a lubricant is present at the fibre interface, a capstan method is the most common 66 way to measure friction between fibres. In this method, a fibre is wrapped over a 67 cylindrical body and the frictional force that is developed is calculated based on a 68 normal force generated by the tension exerted at both fibres end. Roselman and Tabor 69 [21] have used this method to study friction behaviour at microscale level, while 70 Cornelissen et al. [22] and Chakladar et al. [23] used this method to study at mesoscale 71 level. Other factors that affecting the friction such as surface roughness [22], tow angle 72 and tow size [23] have been also investigated through this method. 73 There are many papers on the friction between fibres, however, to the best of the 74 author’s knowledge, the effect of pre-tension loads on the frictional behaviour at 75 microscale has not yet been discussed in detail even though it is a relevant issue in 76 many applications. For example, in a continuous composite manufacturing process, low 77 and high pre-tension during winding may result in poor mechanical properties and 78 catastrophic failure, respectively. Therefore, this study aims at investigating the frictional 79 behaviour between single fibres in contact with the influence of pre-tension. The ‘fibre- 80 on-fibre’ term that will be used hereafter is representing the interactions between two 81 single fibres. A new experimental setup has been developed to measure the dynamic 82 friction of two single fibres sliding onto each other at 90° (perpendicular) contact under 83 the influence of pre-tension and other parameter conditions such as normal load and 84 elastic modulus. 85 2 Material and Method 86 2.1 Materials used 87 Two types of aramid fibres used in this study was provided by Teijin Aramid B.V. The 88 properties of the fibres are listed in Table 1. In this study, a low Young’s modulus fibre AC C EP TE D M AN US C RI PT 60 ACCEPTED MANUSCRIPT type and a high Young’s modulus fibre type are called as LM and HM, respectively. 90 Initially, the fibres were in the form of tow bundle (see Figure 1(a)), with each tow 91 consists of thousand single filaments. Then, the fibres were manually separated into a 92 single filament with its Scanning Electron Microscope (SEM) image is shown in Figure 93 1(b). 94 2.2 95 The surface texture of the Twaron aramid fibres was examined using atomic force 96 microscopy (AFM). The FlexAFM from Nanosurf was used to observe the surface 97 topography and measure the roughness of the fibre surface. The ACTA cantilever form 98 AppNano was used with a stiffness in the range of 13-77 N/m. The scanning area was 99 set at a size of 3 µm x 3 µm. RI PT 89 M AN US C Surface characterization 2.3 Experimental setup 101 An experimental setup has been developed to measure friction between two single 102 fibres crossing each other at angle of 90°. Figure 2 shows the schematic description of 103 the experimental setup. The setup consists of fibre holder (one to hold top fibre and 104 the other one is to hold bottom fibre), an XY linear stage and a set of two capacitive 105 sensors mounted and a force measuring mechanism (FMM). The resolution of the 106 capacitive sensor is 1 nm with a measuring range up to 50 µm. Using this setup the 107 forces (normal and friction) are calculated based on the spring stiffness concept, in 108 which the deflection of the FMM is measured in x and z direction. A detailed explanation 109 of the FMM can be found in Yaqoob [24]. With this load controlled setup, the maximum 110 normal load can be applied is 100 mN with an accuracy of 8 µN. 111 In this study, the tension of the fibre during gluing is only controlled at the bottom fibre, 112 while for the top fibre a minimal pre-tension is applied just to prevent the fibre from 113 slacking.. A low viscosity glue type, Loctite 401 was used for gluing the fibre at fibre 114 holders. For bottom fibre, the first end of the fibre is initially glued to a holder, then the 115 other end is connected to a cable lug. The function of the cable lug is to clamp the end 116 of the fibre into a loop shape so that the dead weight can be hooked to it to induce the AC C EP TE D 100 ACCEPTED MANUSCRIPT pre-tension to the fibre. Once the dead weight is loaded to the fibre , the other end is 118 then glued. The dead weight is removed after the glue at both ends is cured. 119 To conduct the friction measurement, both fibres need to be brought into an initial 120 contact. The top fibre is moved downwards approaching the bottom fibre at two different 121 speeds; v = 0.01 mm s-1 to find the contact and v = 0.001 mm s-1 to find a few microns 122 before the contact. During this procedure, no initial load is applied (Figure 3(a)). 123 Therefore, the normal and friction forces are assumed zero just before contact is made. 124 As there is no deformation in the FMM system before contact, the measured normal 125 load is close to represent the true value. Once the final normal load is applied to the 126 contact, the fibres start to bend as shown in Figure 3(b). The friction force measurement 127 is taken as the bottom fibre is sliding against the top fibre in x direction with the help of 128 the stage. Multi-pass friction loops are executed to determine the repeatability and 129 running-in effects. Table 2 shows the parameters that are used for the friction force 130 measurements. The measurements are repeated five times for data producibility and 131 repeatability. M AN US C RI PT 117 132 3 Results and discussion 134 3.1 Surface roughness 135 AFM measurements were performed to obtain the roughness of the fibre surface in 136 three-dimensional (3D) analysis. The Sq parameter, represents the root mean square of 137 the roughness within the measured area and is calculated using the following formula 138 [25]: TE EP AC C 139 D 133 = 1 ( , ) (1) 140 141 where is the roughness measured area and is the height surface profile. To observe 142 the effect of the pre-tension on the fibre surface, a roughness measurement is 143 performed before and after applying the pre-tension load on the fibre. The fibre sample ACCEPTED MANUSCRIPT that has been confronted with pre-tension is prepared separately from the sample for 145 friction tests. The pre-tension fibre sample has the same length as for the friction test 146 sample, which is cut, stretched with load for about 2 hours. Then, the load is released 147 from the fibre and a roughness measurement is carried out using the AFM. Here, it is 148 assumed that at a very small length, the pre-tension load would play a role on the 149 roughness surface. Then, the fibre is placed vertically parallel to the AFM tip (see Figure 150 4). The fibre is scanned along the x direction within the scan size are of 3 µm x 3 µm 151 with a resolution of 512 x 512 points and thus the influence of fibre orientation on the 152 roughness measurement is therefore eliminated. 153 Figure 5 shows the AFM images of HM fibre type before and after applying pre-tension 154 loads. The lines and treated particles on the surface prove that at microscale level, the 155 fibre surface is quite rough with Sq ≈ 15.1 nm as in Fig. 5(a). With 50 mN of pre-tension 156 load, the surface roughness is found to be reduced to Sq ≈ 11.3 nm, the AFM image is 157 shown in Figure 5(b). By increasing the pre-tension load to 100 mN, the fibre surface 158 changes to be even smoother, as shown in Figure 5(c) with Sq ≈ 5.6 nm. Note that the 159 Sq value decreases asymptotic when the pre-tension load is more than 50% of the fibre 160 breaking strength. For each pre-tension load, the roughness measurements are 161 performed at three different locations. Figure 6 shows the overall results of the Sq value 162 of the fibre surface measured at different pre-tension loads. The result shows that the 163 Sq values reduced as the pre-tension increases. Note that, in one single fibre consists 164 hundreds of fibrils. With pre-tension this fibril elongates and hence reduce the contour 165 peaks. AC C 166 EP TE D M AN US C RI PT 144 167 3.2 Friction measurements 168 Figure 7 shows the friction force measurement signal, which measured on the HM fibre 169 type under 10 mN normal load and a pre-tension load of 50 mN. The fibre is set to slide 170 with a stroke of 100 µm both in forward and backward direction to complete one friction 171 cycle. At the first 10 µm of sliding distance, the friction force signal shows a transient 172 response when the normal load is applied to the contacting fibres. This is due to the 173 lateral stiffness of the friction force mechanism (FFM) and the deformation of the ACCEPTED MANUSCRIPT contact. After reaching the desired normal load, the fibre starts sliding and the friction 175 signal becomes stable. The pattern of the friction curve during forward and backward 176 direction is similar, showing that a same value of the force is measured in both 177 directions. Also, it is observed that the friction force values for the first cycle is slightly 178 different from the other four cycles. This may be explained by the presence of the 179 impurities on the fibre surface and these impurities are removed as the fibre slides. To 180 complete one friction experiment, the friction cycle is repeated five times. The same 181 trends can be observed in all friction tests. The friction force is calculated based on the 182 average value of the friction force of five cycles both during forward and backward 183 sliding. It is also can be seen from Figure 7, that the variation between each cycle is 184 very small showing a good reproducibility, with a standard deviation, SD ≤ 0.1 mN. M AN US C RI PT 174 185 186 3.2.1 Geometrical analysis on the contact length due to pre-tension and the effect on 187 friction 188 The contact length between the fibres is totally governed by the fibre deflection. The 190 theory of taut wire [26] was used to have a clear view on the relationship between 191 deflection, D 189 TE and pre-tension load, T. The taut wire equation is given by: 192 193 . + − 4 =0 (2) AC C EP 2( ) 194 where is the fibre deflection (m), L is the fibre length (m), A is the fibre cross-sectional 195 area (m2), E is the Young’s modulus (Pa), T is the pre-tension load (N) and N is the 196 normal load (N). There are two assumptions that were made in the analysis; (a) the 197 contact length could be influenced by the deflection of the fibre and (b) the contact 198 geometry is triangular as shown in Figure 8. This latter assumption is due to the very 199 small contact length as compared to the fibre diameter. Also, note that a higher pre- 200 tension will result in a lower deflection, which reduces the contact length. By using the ACCEPTED MANUSCRIPT taut wire equation (Eq. 2), the length of the contact could be determined by solving the 202 equations in the half-plane axis that represents the fibres in the system (see Figure 8). 203 Due to the normal load, both fibres that are in contact start to deform at certain 204 deflection . Thus, the behaviour of the bottom fibre can be mathematically expressed 205 as; = − (3) and the circumference of the top fibre that touch the bottom fibre is represented by; 207 ( − !) M AN US C 206 RI PT 201 +( − 208 !) =" ! ! 209 where m is the line gradient, 210 of the top fibre and R is the fibre radius. By solving both equations (3) and (4), the half- 211 plane axis of the crossing point in coordinates x and z between two fibres can be 212 determined. If it is assumed that the contact geometry is triangular and the negative 213 sign represent the direction of the fibre deflection moving downward (see Figure 8), the 215 is the centre coordinates D load can be calculated as; 216 +( & − ) (5) AC C EP #$ = % 217 and wrapping length #$ between two fibres in contact at a certain pre-tension and normal TE 214 is the fibre deflection, (4) 218 From the calculation using the geometrical analysis above, the results of HM and LM 219 fibre deflection (of the bottom fibre) under the influence of pre-tension and normal loads 220 are plotted in Figure 9 (a) and (b) respectively. The calculation (theoretical model) are 221 validated by comparing the results with the experiment data. The results of HM and LM 222 fibres show a similar trend where the deflection of the fibre decreases with the pre- 223 tension load. However, it is must be noted that the experimental values represent the 224 total deflection of both top and bottom fibre, meanwhile the theoretical value only ACCEPTED MANUSCRIPT represent the deflection of the bottom fibre. Therefore, the deflection of the top fibre is 226 the difference between the experimental and theoretical values. Interestingly, the 227 difference between the experimental and theoretical values are found to be in the same 228 range at least for the high normal loads at N = 5 mN and 10 mN, regardless of the fibre 229 types. This result shows that the pre-tension of the top fibre is constant. From equation 230 (2), we know that if the pre-tension is constant, the only factor that contribute to the 231 deflection is the fibre length. Moreover, as the top fibre length is only 2 mm, so it is 232 considered as stiff, which resulting in lower values of deflection than for the bottom fibre. 233 Figure 10 shows the experimental results of the friction force as a function of the pre- 234 tension load for both the LM and HM fibre type. It can be observed that there is a 235 gradual decrease in friction as the pre-tension load is increased, regardless of the 236 normal load. A high pre-tension load could reduce the conformability and intimacy of the 237 contact, which results in the decrease of the contact size and the friction force. 238 Assuming the contact behaviour between fibres follows the Hertzian theory [27], the 239 radius of the elastic contact deformation is compared with the calculated contact length 240 (taut wire model). The contact radius between fibre-fibre at perpendicular contact is 241 calculated using the equation as follows: D M AN US C RI PT 225 TE 242 EP 243 #' = * 3 "∗ 4 ∗ (6) where N is the normal load, R* is the effective radius and E* is the contact modulus. 245 The contact modulus is calculated from the elastic modulus of the fibre, 246 AC C 244 Poisson ratios ,+ and , [27]; 1 ∗ = 1 − ,+ + + + and 1−, 247 248 and the effective radius is calculated from the radius of the fibre, R1 and R2 [27]; and (7) ACCEPTED MANUSCRIPT 249 "∗ = "+ " "+ + " (8) RI PT 250 From calculations, at 1 mN, 5 mN and 10 mN normal loads, the contact radius is about 252 1.3 µm, 2.3 µm and 2.9 µm, respectively. Obviously, this contact radius is larger than 253 the contact length that is due to the ‘wrapping effect’ between fibres which are found 254 only 0.1 µm, 0.5 µm, 0.8 µm, respectively. Thus, in this case, the elastic deformation in 255 fibre-fibre contact is found more significant over the ‘wrapping effect’ in influencing the 256 contact area and friction force (see Figure 11). However, the role of pre-tension cannot 257 be neglected as our result (see Figure 6) shows that the Sq values could be reduced by 258 increasing the pre-tension load. This shown that although the influences of pre-tension 259 on the fibre ‘wrapping effect’ is small, it does play a small role in changing the physical 260 surface of the fibres and indirectly influences the size of the elastic deformation of the 261 contact area. M AN US C 251 D 262 3.2.2 Effect of elastic modulus on friction 264 Figure 12 shows the friction force of the low and high modulus fibre with similar sizing 265 under 50 mN pre-tension at varying normal load. The friction force of low modulus (LM) 266 fibre type is found to be slightly higher than the high modulus (HM) fibre type under 267 similar conditions. The fibre with low elastic modulus has a low bending stiffness and 268 therefore during loading, the LM fibre have a higher deflection and generate a larger 269 contact length between the fibres that increase the friction force as shown in Figure 12 270 (a). With respect to the elastic modulus values, one would expect that the friction force 271 of LM fibre will be two times higher than the HM fibre. However, according to Gupta, the 272 resistance to bending is determined by [7]: 273 AC C EP TE 263 ACCEPTED MANUSCRIPT "-./.0#12- 03 4-1 /15 = 6 1 ; : 4789 < (9) 274 276 where ; is the shape factor, E is the modulus, d is linear density, < is the density and 89 is a constant which depend on the units in which , RI PT 275 and < are expressed. So, although the elastic modulus of the LM fibre is half of the HM fibre, the size of the fibre 278 in terms of linear density also need to be considered in influencing the contact intimacy 279 and friction between fibres. Due to this effect the friction forces are found to differ by 280 34%. 281 282 M AN US C 277 3.2.3 Effect of normal load on friction 284 In order to study the effect of normal load on friction, the friction forces are also 285 measured for the HM fibre with varying normal load in the range of 1 to 10 mN at 286 various pre-tension loads. The same normal load range has been used by Tourlonias et 287 al. [13] in tests with single carbon fibres. The friction force as a function of normal load 288 is shown in Figure 13. In the range of normal load tested, the friction force is found to be 289 proportional with the normal load. These results are in agreement with [13], as the 290 friction force is found to approximately follow the Coulomb’s law. 291 292 4 293 The frictional behaviour between two single aramid fibres in contact under the influence 294 of pre-tension loads have been successfully studied. An experimental setup was 295 developed to measure the friction force of single fibres sliding perpendicular against 296 each other in linear reciprocating motion. The friction measurements data of the single 297 aramid fibres obtained show a good reproducibility. Also, the friction force obtained 298 using this experimental setup and the contact length model are in agreement. As a high 299 pre-tension load is induced to the fibre, the friction force decreases as a result of high 300 resistance to bending of the fibre and as a consequence a reducing contact length AC C Conclusions EP TE D 283 ACCEPTED MANUSCRIPT 301 between the fibres. However, this contact length is found to be very small compared to 302 the contact radius of the elastic deformation of the fibre-fibre contact. It can be 303 concluded that the elastic deformation in contact dominates the contact area and friction 304 force significantly. On average, for normal loads ranging from 1 to 10 mN, the friction 306 force increased ~ 34% as the elastic modulus of the fibre increased.Also,the friction RI PT 305 force increases linear with the normal load. Knowing that at tow and fabric level the contact configuration is in complex 308 arrangement, therefore understanding the friction mechanism at the microscale level 309 enables the engineers to predict the friction and contact model of the fibre assemblies at 310 meso (tow level) and macroscale (fabric level). 311 Acknowledgement 312 The authors would like to thank Universiti Teknikal Malaysia Melaka and Ministry of 313 Education Malaysia for providing financial support of the first author and Teijin Aramid 314 B.V, The Netherlands for supplying the material. M AN US C 307 316 References 317 [1] D 315 318 advanced 319 2003;34(10):963–70. 321 322 [3] [4] [5] Appl Sci Manuf Lee B, Leong KH, Herszberg I. Effect of weaving on the tensile properties of carbon fibre Decrette M, Mourad S, Osselin J-F, Drean J-Y. Jacquard UNIVAL 100 parameters study Leech M. The modelling of friction in polymer fibre ropes. Int J Mech Sci 2002; 44: 621Humeau C, Davies P, Engles TAP, Govaert LE, Vlasblom M, Jacquein F. Tension fatigue failure prediction for HMPE ropes. Poly Test 2018; 65:497-504. [6] 329 330 A 643. 327 328 Compos for high-density weaving optimization. J Ind Text 2015. 325 326 composites. tows and woven composites. J Reinf Plast Compos 2001; 20:652–70. 323 324 woven EP [2] three-dimensional AC C 320 TE Rudov-Clark S, Mouritz AP, Lee L, Bannister MK. Fibre damage in the manufacture of Yusekkaya ME. More about friction and its measurements. Textile Progress 2009; 41(3):141–193. [7] Gupta BS. Friction in textile materials. Woodhead Publishing Limited, 2008. ACCEPTED MANUSCRIPT [8] 332 333 London A 1939; A169; 371–391. [9] 334 335 Pascoe MW, Tabor D. The friction and deformation of polymers. Proc R Soc London A 1956; 235(1201); 210–24. [10] 336 337 Bowden FP, Leben L. The nature of sliding and the analysis of friction. Proc R Soc Roselman IC, Tabor D. The friction of carbon fibres. J Phys D Appl Phys 1976; 9 (17):2517. [11] 338 RI PT 331 Mercer EH, Makinson KR. The frictional properties of wool and other textile fibres. J Textile Inst Trans 1947; 38(5): T227–40. [12] Howell HG. Inter-fibre friction. J Textile Inst Trans 1951; 42(12): T521–33. 340 [13] Tourlinas M, Bueno M-A, Poquillon D. Friction of carbon tows and fine single fibers. 341 342 Compos Part A: Appl Sci Manuf. 2017; 98: 116-123. [14] 343 344 [15] Briscoe BJ, Kremnitzer SL. A study of the friction and adhesion of Polyethylene terephthalate monofilaments. J Phys D: App Phys 1979; 5:505-516. [16] 347 348 Houssem EG, Barbier G, Kocher CW, Sinoimeri A, Pumo B. Experimental evaluation of transverse friction between fibers. Trib Int 2018; 119:112-122. 345 346 M AN US C 339 Mulvihil D, Smerdova O, Sutcliffe M. Friction of carbon fibre tows. Compos Part A: Appl Sci Manuf 2016; 93:185–198. [17] Mulvihil D, Sutcliffe M. Effect of tool surface topography on friction with carbon fibre tows for composite fabric forming Friction of carbon fibre tows. Compos Part A: Appl Sci 350 Manuf 2017; 93:199-206.[18] Lincoln B. Frictional and elastic properties of high 351 polymeric materials. Brit J Appl Phys 1952; (3):60. 353 354 Gralen N, Olofsson B. Measurement of friction between single fibers. Text Res J 1947; 17(9): 488–496. [20] TE [19] EP 352 D 349 Lindberg J, Gralén N. Measurement of friction between single fibers: II. Frictional properties of wool fibers measured by the fiber-twist method. Text Res J 1948; 356 18(5):287–301. 357 [21] 358 359 362 Roselman IC, Tabor D. The friction and wear of individual of carbon fibres. J Phys D Appl Phys 1977; 10: 1181-1194. [22] 360 361 AC C 355 Cornelissen B, Rietman B, Akkerman R. Frictional behaviour of high performance fibrous tows: friction experiments. Compos Part A: Appl Sci Manuf 2013; 44:95–104. [23 Chakladar ND, Mandal P, Potluri P. Effects of inter-tow angle and tow size on carbon fibre friction. Compos Part A: Appl Sci Manuf 2014; 65; 115–124. ACCEPTED MANUSCRIPT 363 [24] Yaqoob MA, de Rooij MB, Schipper DJ. Design of a vacuum based test rig for 364 measuring micro adhesion and friction force. WTT Transaction and Built Environment, 365 2012 ;( 14):261–274. [25] ASME B46-1. Surface texture, surface roughness, waviness and lay. 2002. 367 [26] Charles I. Applied mechanics for engineers. The Syndic of the Cambridge Uni Press 368 369 1951:54-66. [27] Johnson KL. Contact mechanics. Cambridge Uni Press. 1985. 370 AC C EP TE D M AN US C 371 RI PT 366 ACCEPTED MANUSCRIPT Table 1 Manufacturer data of the material properties of the aramid fibres used in the friction experiments. HM Elongation at break [%] 4.4 2.9 Linear density [dtex] 1.2 1.6 Young’s modulus [GPa] 60 115 Tensile stress [GPa] 3.2 Breaking strength [N] 0.26 Fibre diameter [µm] 10.8 alkyl-phosphate salt EP TE D Finishing material AC C RI PT LM 3.5 0.4 M AN US C Description [unit] 11.9 alkyl-phosphate salt ACCEPTED MANUSCRIPT Table 2 Parameters for friction measurements. symbol value units Normal load N 1- 10 mN Pre-tension load T 50 - 200 mN Sliding speed v 0.002 mm/s Crossing angle θ 90 degree Sliding distance d 100 Fibre length Top fibre: 2 D TE EP AC C µm mm Bottom fibre: 6 mm 5 - M AN US C Number of friction cycles RI PT Description RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN US C Figure 1 Aramid fibres (a) Scanning electron microscope (SEM) images of the fibre tow bundle , (b) close-up image of the fibre surface. RI PT ACCEPTED MANUSCRIPT (b) AC C EP TE D M AN US C (a) (c) Figure 2 (a) Schematic description of friction experiment between fibres, (b) Schematic of the fibreon-fibre contact, and (c) Experimental setup. RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN US C Figure 3 (a) Finding initial contact between the fibres, and (b) Fibres under loading. M AN US C RI PT ACCEPTED MANUSCRIPT AC C EP TE D Figure 4 Illustration of the roughness measurement using AFM. AC C EP TE D M AN US C RI PT ACCEPTED MANUSCRIPT Figure 5 AFM images of HM fibre type (a) without pre-tension, (b) 50 mN pre-tension load, (c) 100 mN pre-tension load, and (d) 200 mN pre-tension load. ACCEPTED MANUSCRIPT 18 16 14 8 6 4 2 0 After applying pretension (T= 50 mN) After applying pretension (T= 100mN) After applying pretension (T= 200 mN) M AN US C Before applying pretension RI PT 10 EP TE D Figure 6 The effect of pre-tension on the Sq value of the fibre surface, scan area 3 µm x 3 µm. AC C Sq [nm] 12 M AN US C RI PT ACCEPTED MANUSCRIPT AC C EP TE D Figure 7 Typical friction force measured, N = 10 mN and T = 50 mN. M AN US C RI PT ACCEPTED MANUSCRIPT AC C EP TE D Figure 8 Fibre deflection due to the presence of pre-tension and normal load. ACCEPTED MANUSCRIPT (a) 300 Experiment, N = 1 mN Experiment, N = 5 mN Experiment, N = 10 mN Model, N = 1 mN Model , N = 5 mN Model , N = 10 mN RI PT 200 150 100 50 0 0 50 100 M AN US C deflection, δ (µm) 250 150 200 250 pre-tension load, T (mN) (b) 300 D 200 TE 150 100 EP deflection, δ (µm) 250 AC C 50 0 Experiment, N = 1 mN Experiment, N = 5 mN Experiment, N = 10 mN Model, N = 1 mN Model , N = 5 mN Model , N = 10 mN 0 50 100 150 200 250 pre-tension load, T (mN) Figure 9 Comparison of the theoretical and experimental results on fibre deflection: (a) HM fibre, and (b) LM fibre. ACCEPTED MANUSCRIPT (a) 3.00 N = 5 mN 2.50 N = 10 mN 2.00 1.50 RI PT Friction force, F [mN] N= 1 mN 1.00 0.50 0 M AN US C 0.00 50 100 150 200 250 Pre-tension load, T [mN] (b) 2.50 N = 5 mN N = 10 mN D 2.00 N= 1 mN 1.50 TE Friction force, F [mN] 3.00 1.00 0.00 AC C 0 EP 0.50 50 100 150 200 250 Pre-tension load, T [mN] Figure 10 Friction force as a function of pre-tension load: (a) LM fibre type, and (b) HM fibre type. M AN US C RI PT ACCEPTED MANUSCRIPT AC C EP TE D Figure 11 Illustration of the contact length due to ‘wrapping effect’ and elastic deformation in fibrefibre contacts. ACCEPTED MANUSCRIPT LM fibre type with E = 60 GPa 2.00 HM fibre type with E = 115 GPa 1.50 1.00 0.50 0.00 N= 5 mN (b) [um] 1.20 LM fibre type with E = 60 GPa 1.00 HM fibre type with E = 115 GPa 0.80 0.60 0.40 0.20 0.00 TE N= 1 mN D Contact length, N= 10 mN M AN US C N= 1 mN RI PT Friction force, F [mN] (a) 2.50 N= 5 mN N= 10 mN AC C EP Figure 12 The effect of elastic modulus on (a) Friction force, and (b) Contact length two different fibre types under 50 mN pre-tension load. 2.2 2 1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 1 2 3 4 M AN US C RI PT Pre-tension load, T= 50 mN Pre-tension load, T= 80 mN Pre-tension load, T= 100 mN Pre-tension load, T= 200 mN 5 6 7 8 9 10 Normal load, N [mN] EP TE D Figure 13 Friction force as a function of normal load for the HM fibre type. AC C Friction force, F [mN] ACCEPTED MANUSCRIPT 11 ACCEPTED MANUSCRIPT Highlights: RI PT M AN US C D TE • EP • The frictional behaviour between two single aramid fibres in contact under the influence of pre-tension loads. A newly developed experimental setup to measure friction force in contact at microscale level. The effect of pre-tension load on the fibre bending stiffness, contact intimacy and friction force. AC C •