I N D U S T R I A L R E S E A R C H
1 5 0 H I G H L I G H T S 2 0 2 2 I
Investigating the coefficient of thermal expansion of clutch facings
Car clutch facings are orthotropic, fibre-reinforced composites that only exist as non-planar annular discs. The coefficient of thermal expansion (CTE) of the composite is one of its main thermal properties, and affects the dry clutch engagement process due to heat associated with friction. X-ray tomography and numerical procedures were used to identify the CTE distributions on the entire part.
An experimental technique based on digital stereo image correlation (DSIC) was developed, allowing the measurement of the free expansion of the clutch facing under homogeneous thermal loading in the temperature range of usage (30 - 300°C). The strain fields were measured at thermal equilibrium (Figure 138b) and used to obtain the experimental CTE distribution of the material. Two numerical approaches were proposed to predict the coefficient of thermal expansion distribution of the clutch facing.
Using the knowledge of fibre organisation obtained from X-ray tomography images at beamline BM05 (Figure 138a) and an inverse identification of the properties of the composite constituents by comparing experimental and numerical strain fields, the classical laminate theory (CLT) allowed a fast prediction, with a good order of magnitude, of the thermal coefficients and strain fields of clutch facings. For a more accurate identification of the thermal expansion tensor, the finite element method combined with a Levenberg-Marquardt algorithm  considers the structure effect on the deformation fields and gives better results.
PRINCIPAL PUBLICATION AND AUTHORS
Characterization of the Thermal Behavior of a Complex Composite (Clutch Facing) Combining Digital Image Stereo Correlation and Numerical Approach, C. Flament (a,b), B. Berthel (a), M. Salvia (a), G. Grosland (b), I. Alix (b), Materials 15, 2582 (2022); https:/doi.org/10.3390/ma15072582 (a) Laboratoire de Tribologie et Dynamique des Systèmes, UMR CNRS 5513, Ecole Centrale de Lyon, Ecully (France) (b) Valeo Matériaux de Friction, Limoges (France)
 M.I. Lourakis, Found. Res. Technol. 4, 1-6 (2005).
Fig. 138: a) Annular clutch facing and network of reinforcement fibres (copper wires) obtained using X-ray tomography. b) Normed radial and tangential strain fields of a clutch facing as a function of the temperature using DSIC.