 Advances in Technology Innovation , vol. 1, no. 2, 2016, pp. 41 - 45 41 Copyright © TAETI Experimental Investigation into Mechanical Properties of Nanomaterial-reinforced Table Tennis Rubber Yu-Fen Chen 1,* , Jian-Hong Wu 2 , Chen-Chih Huang 3 1 Office of Physical Education, National Formosa University, Yunlin, Taiwan. 2 Taiwan Semiconductor Manufacturing Company Limited, Hsinchu, Taiwan. 3 Department of Sport, Health & Leisure, Wufeng University, Chiayi County, Taiwan . Received 02 February 2016; received in revised form 28 March 2016; accept ed 02 April 2016 Abstract A new table tennis rubber is prepared consisting of carbon nanotubes, zinc o xide and titanium o xide added to a mixture of natural and synthesized rubber. The Nano-re inforced rubber is attached to wooden table tennis blades and patterned with four diffe rent surface structures, name ly flat, long pimp les, short pimp les and med iu m pimp les. The results show that of the five rubbers, the Nano-reinforced rubber with a flat surface offe rs a significantly imp roved elastic and mechanical performance. Keywor ds : table tennis rubber, surface modification, carbon nanotube, zinc oxide, titanium oxide 1. Introduction Poly mer co mpound materials have many advantages over traditional engineering metals and alloys, including a high strength, a low weight, good resilience, a low cost, and superior chemical resistance. Consequently, the synthesis and characterization of poly mer co mposites has attracted significant attention in the literature [1-3]. Furthermore, with the advancement of nanotechnology, nanometer-scale materia ls are now used widely throughout the text iles, biomed ical, agricultural, industrial, e lectronics and energy generation fields. Many studies have shown that nanoparticle addition provides an effective means of altering the mechanica l properties of compound materia ls, thereby improving the performance of e xisting products or paving the way for the develop ment of ne w ones [4-5]. Poly mer co mpound mate rials have found e xtensive use in the sports equip ment fie ld. Fo r e xa mp le , the rac kets used by table tennis players were orig inally made simp ly o f wood, and hence games we re played at slo w speed with a lac k of spin. In the 1920s, h o wever, Eu ropean manufacturers attached a rubber skin to the bat; thereby enabling players to strike the ball with a far greater velocity and to e xert a higher degree of control over the ball trajectory [6-7]. In later years, Japanese manufacturers replaced the rubber skin with innovative polymer co mpound materia ls; lead ing to a further significant imp rove ment in p layer performance [8-10]. The literature conta ins many investigat ions into poly mer co mpound materia ls and rubber mod ificat ion. Ho wever, the modif ication o f poly mer co mposite materia ls fo r sporting applicat ions has thus far attracted relat ive ly little attention. Accord ingly , the present study develops a new rubber materia l for table tennis rackets consisting of a mixture of carbon nanotubes (CNTs), zinc oxide (ZnO) and titanium o xide (TiO2) added to natural and synthesized rubber. The Nano-re inforced rubber is attached to wooden table tennis paddles and patterned with four different surface structures, na me ly flat , long pimples, short pimp les and med iu m pimp les. The restitut ion coeffic ient and mechanica l prope rties (y ie ld stress, elastic modu lus and shear modulus) o f the four Nano-reinforced rubbers are then investigated and compared with those of a flat non-reinforced rubber skin. * Corresponding aut hor, Email: yvonne@nfu.edu.tw Advances in Technology Innovation , vol. 1, no. 2, 2016, pp. 41 - 45 42 Copyright © TAETI 2. Experimental Process 0.035 g CNTs, 0.105 g TiO2 and 0.175 g ZnO were added to a 35-g mixture of natural and synthesized rubber. The Nano-re inforced rubber was glued to wooden table tennis blades and patterned with four diffe rent surface structures, name ly flat, short pimples, long pimp les and med iu m pimp les, as shown in Figs. 1(a )~(d), respectively. (a) flat (b) short pimples (c) long pimples (d) medium pimples Fig. 1 The different surface structures of Nano- reinforced rubber 2.1. Restitution Coefficient The restitution coefficients of the Nano-rein forced rubber skins were evaluated in a wind-less environ ment using the e xperimental setup shown in Fig. 2. In each test, a table tennis ball was placed at a height of 300 mm above the racket and was then dropped vertically onto the racket surface. The rebound height of the ball was recorded using a high-speed camera and the restitution coeffic ient of the rubber was then computed as height drop height rebound e . For each rubber, the restitution coeffic ient was calculated in three separate tests and then averaged to obtain a final representative value. Fig. 2 Experimental setup used for restitution coefficient testing 2.2. Mechanical Properties The mechanica l prope rties of the Nano-rein forced rubber skins we re eva luated using the Material Testing System (M TS 810) shown in Fig. 3. Test specimens with dimensions of 150 mm x 3 mm x 1 mm (length x width x th ickness) we re p repared . Each specimen was e xtended at a constant rate of 10 -1 s -1 until the point of fracture . The load and d isp lac e me nt v a lues we re me as u re d continuously during the test, and were then used to compute the elastic modulus and shear modulus of the rubber in accordance with basic engineering theory. The MT S system co mprised three components, namely: Power unit: a hydraulic power system used to actuate the system. Load unit: a stand-alone testing unit consisting of a load fra me , c rosshead lifts and locks, actuators, servo-valves, transducers and grip controls. Advances in Technology Innovation , vol. 1, no. 2, 2016, pp. 41 - 45 43 Copyright © TAETI Contr ol uni t: a control system used to coordinate and control the power unit and load unit. Fig. 3 MT S system used for mechanica l p roperty testing 3. Results and Discussion 3.1. Restitution Coefficient Fig. 4 shows the restitution coeffic ients of the four Nano-re inforced rubbers. As e xpected, the restitution coefficient has a value of less than 1 for all five skins; indicating a non -fully -elastic collision between the ball and the racket. Notably, the Nano-re inforced rubbers all yie ld a slightly higher reinstitution coeffic ient than the non-reinforced skin. In other words, all four rubbers have a higher elasticity than the original skin. The performance imp rovement is particularly apparent for the three re inforced rubbers with pimples -out surface patterns. Fig. 4 Restitution coefficients of Nano- reinforced rubbers and non-reinforced rubber 3.2. Stress-bearing Capability Fig. 5 shows the yield stress values of the Nano-rein forced and non-reinforced rubbers. (Note that the stress values indicate the ma ximu m stress recorded in the tensile tests, i.e., the stress at which specimen fa ilure occurred.) As shown, the flat Nano-reinforced rubber has a ma ximu m stress of approximately 8.03 MPa. By contrast, the non-reinforced rubber has a ma ximu m stress of around 7.04MPa. In other words, the re inforced rubber has an imp roved stress -bearing capability, and thus provides a better wear resistance. Notably, however, the pimples -out rubbers all have a lowe r stress -bearing capability than the non -reinforced rubber. The loss in strength is particularly apparent in the rubber with a long -pimp le structure. Fig. 5 Stress -bearing capabilities of Nano- reinforced rubbers and non-reinforced rubber 3.3. Elastic Modulus For each rubber, the elastic modulus was computed as Ε = Slope = ∆𝜎 ∆𝜖 = (𝜎2 − 𝜎1) (𝜖2 𝜖1⁄ )⁄⁄ . The corresponding results are shown in Fig . 6. It is seen that the flat Nano-re inforced rubber has an elastic modulus of approximate ly 1.8. For the non-reinforced flat rubber, the elastic modulus is equal to approximately 1.09. In other words, the addition of CNTs, ZnO and TiO2 is beneficia l in improving the stiffness of the rubber skin. However, the use of a pimp les -out surface pattern greatly reduces the rubber stiffness. For e xa mple , the Nano-reinfo rced rubber with a long-pimple structure has an elastic modulus of just 0.13, i.e., a round 8 times lower than that of the non-reinforced flat rubber skin. Advances in Technology Innovation , vol. 1, no. 2, 2016, pp. 41 - 45 44 Copyright © TAETI Fig. 6 Elastic modulus values of Nano-reinforced rubbers and non-reinforced rubber 3.4. Shear Modulus For each rubber, the shear modulus was computed as G=E/2(1+v), where v is the Poisson ratio (the values of the Poisson ratio for the present rubbers is 0.45). As shown in Fig. 7, the shear modulus of the flat Nano-re inforced rubber (0.6) is around 50% higher than that of the flat non-reinforced rubber (0.4). In other words, the reinforced rubber has a significantly improved shear resistance. However, for all the pimples -out rubbers, the shear modulus is lowe r than that of the non-reinforced rubber. Consequently, these skins are more prone to shear damage, and therefore fa il at a lowe r maximu m stress (see Fig. 4). Fig. 7 Shear modulus values of Nano- reinforced rubbers and non-reinforced rubber 4. Conclusions This study has synthesized a new table tennis rubber consisting of natural and synthesized rubber reinforced with a mixture of ca rbon nanotubes (CNTs), zinc o xide (ZnO) and titanium o xide (T iO2). Re inforced rubber skins have been attached to wooden table tennis paddles and patterned with four different surface structures, namely flat, long-pimple, short-pimple and medium-pimple. The restitution performance and mechanical properties of the various rubbers have been evaluated and compared with those of a flat non-re inforced rubber skin. The e xperimental results have shown th at the flat Nano-rein forced rubber outperforms the non-reinforced rubber in terms of a higher restitution coeffic ient, a superior stress -bearing capability, and an improved stiffness. As a result, it provides several impo rtant practical advantages over the non-reinforced rubber, including a superior e lasticity and an imp roved wear resistance (i.e., a longer service life). The pimples -out reinforced rubbers provide a slightly higher elasticity than either of the two flat rubbers. However, the elasticity improve ment is obtained at the e xpense of significantly lowe r mechanica l properties. As a result, the pimp le-based coatings are less practical for real-world table tennis applications. Acknowledgement The authors gratefully ac knowledge the e xperimental assistance provided to this study by Professor S.C. Lin of the Depart ment of Power Mechanical Engineering at Nat ional Formosa University, Ta iwan. Furthermo re, the preparation of the rubbers used in the present study by Training Co. Ltd, Taiwan, is also greatly appreciated. References [1] N. R. Park, I. Y. Ko, J. M. Doh, W. Y. Kong, J. K. Yoon, and I.J. 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