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of Jabbouri F.S.T.T, nica, January 1 September During the clutch engagement manoeuvre, sliding contact occurs between the pair of clutch facings mounted on the friction disk and the counter faces belonging to the flywheel and the pressure plate. The transmitted torque is proportional to the overall coecient of primary shaft (motor) to the secondary shaft (gear box) for belonging to the flywheel and the pressure plate. Through- ments. Good performances of the clutch facings material complex and non reproducible. Their eects could be, in practice, globally taken into account through the coe- cient of friction tolerances. To characterize the tribological behaviour of clutch fac- ings, a lot of standard laboratory tests are usually per- formed by the manufacturers: Raybestos tests in case of * Corresponding author. Address: 33, Residence Al Ismalia, Avenue des F.A.R., Appt. 15B, Tetouan, Morocco. Tel.: +212 67 79 50 68; fax: +212 39 35 07 02. E-mail address: (A. Khamlichi). Materials and Design 28 (2007) Materials intermittent periods only. To achieve that, a clutch is required between these two components. The function of the clutch is to produce a soft gradual increase in the angu- lar velocity of the driven shaft until full coupling between the motor and the gear box is achieved. Then, the clutch must act as a permanent coupling transmitting, from the driving shaft to the vehicle wheels, the entire mechanical power without subsequent slip 1. During dry clutch engagement manoeuvre, a transient sliding contact situation occurs between the pair of clutch facings mounted on the friction disk and the counter faces such as a stable and suciently high coecient of friction are required in order to operate engagements in an ecient and regular way. Fading phenomenon which is due to a sudden decrease of the friction coecient as function of temperature must be avoided. Variations in time of the fric- tion coecient during the running in phase or due to mate- rial wear must also remain limited. Other factors in addition to temperature might influence the coecient of friction level. They are related to hetero- geneities of the contact surfaces, chemical reactions or physical transformations. But, these mechanisms are both friction which depends essentially on temperature, normal pressure load and relative sliding velocity. In this work, performance of the friction coecient is investigated experimentally. Samples of a commercial clutch facings material have been tested using a Pin- on-disk apparatus. When the previous three parameters are preset constant, this machine provides automatic acquisition of friction coef- ficient and wear measurements. The obtained results are compared with the classical SAE J661a standard test. It is found that the actual clutch facings material has good fading resistance and a rather stable coecient of friction once running in phase is achieved. C211 2006 Elsevier Ltd. All rights reserved. Keywords: Composites; Thermal; Mechanical; Friction behaviour; Clutch facings 1. Introduction In a vehicle rotary motion is to be transmitted from the out this engagement process, heat is generated at the con- tact surface yielding temperature to rise 2. Temperature rise may be very important in case of repetitive engage- Experimental characterization facings using Pin-on-disk M. Bezzazi a , A. Khamlichi a, * , A. a LMMS, Departement de Physique, b Departamento de Engenharia Meca Received 24 Available online Abstract 0261-3069/$ - see front matter C211 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2006.07.001 frictional behaviour of clutch machine a , P. Reis b , J.P. Davim b B.P. 416, Tangier, Morocco Universidade do Aveiro, Portugal 2006 2006 21482153 v = 1 m/s; P = 51 N. (b) T = 100 C176C; v = 1 m/s; P = 53 N. (c) T = 100 C176C; v = 3 m/s; P = 56 N. (d) T = 200 C176C; v = 1 m/s; P = 58 N. (e) T = 200 C176C; v = 3 m/s; P =51N. 2152 M. Bezzazi et al. / Materials and Design 28 (2007) 21482153 was verified during Pin-on-disk testing by means of a ther- mocouple which was set on the wear path. 6. Conclusions For the friction material of clutch facings considered in this experimental work the mean conclusions found could be stated as follows: after running in, the friction coecient is essentially sta- ble at a level which depends on both the sliding velocity and temperature; the friction coecient decreases with increasing temper- ature and with increasing sliding velocity. Comparison of Pin-on-disk results with those obtained through SAE J661a standard test, which was performed 50 100 150 200 250 300 350 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 TemperatureC Friction coefficient 1 2 3 5 6 7 4 Fig. 5. SAE J661a coecient of friction results for clutch facings material. on the same clutch facing material, shows that the usual features regarding the coecient of friction behaviour are identical if dierences of temperature are incorporated. Using the clutch facing material as the disk in the Pin- on-disk machine enables to eliminate glazing eect which is frequently observed on other tests where the friction material is reduced to a small sample which is bonded on the pin like for example the FAST test. The tests carried out in the present study have assessed that the most desired performances of clutch facings are confirmed for the actual material since a stable a su- ciently high coecient of friction is obtained. References 1 Williams JA. Engineering tribology. New York: Oxford University Press; 1994. 2 Khamlichi A, Bezzazi M, Parron Vera MA. Optimizing the thermal properties of clutch facings. J Mater Process Technol 2003;634:142. 3 RIP Test programs. R + D Department, Raybestos, Morbach, Ger- many, 1996. 4 JIS D-4311: Clutch facings for automobiles. Tokyo: Japanese Stan- dards Association, 1995. 5 Nicholson G. Facts about friction. Winchester, Virginia: Gedoran America Limited; 2000. 6 Davim JP. An experimental study of tribological behaviour of the brass/steel pair. J Mater Process Technol 2000;273:100. 7 Davim JP, Cardoso R. Thermo-mechanical model to predict the tribological behaviour of the composite PEEK-CF30/steel pair in dry sliding using multiple regression analysis. Ind Lubricat Tribol 2005;57(5):1816. 8 Davim JP, Cardoso R. Tribological behaviour of the composite PEEK-CF30 at dry sliding against steel using statistical techniques. Mater Des 2006;27:33842. 9 Mahieux CA. A systematic stiness Temperature model for polymers and application to the prediction of composite behaviour. PhD dissertation, Faculty of Virginia Tech., Blacksburg, Virginia, 1999. M. Bezzazi et al. / Materials and Design 28 (2007) 21482153 2153