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By suming up over a unit volum, we obtain i— 1 / (1) F(l) ~ nc(0E)1/2 j| Vf r(2)(7/4)=0.782 nc(lH) 3 - The assumption of non elastic contacts hetween halls turns out to be very demanding, since it directly goveras the behaviour of F(l) near the origin. If we replace the cusp in C (Fig. 1) by an angle, the power of 1 in (1) becomes ,one instead of 0.5. More precisely, let us assume now that the two balls pénétrate in each other with a depth 26 (Fig. 2 b). When test plane n varies by a) b) Fig. 2a : a) cross section X n in case of non elastic contacts b) section normal to n. translations, the contribution of (Xi,Xo) to F(l)) iff : « 0 when h ^ d cos X = 2d cosx[(1+(1/2ô)cos\)1/2-1]1/2-1 when h > d cos X therefore rel.(1) has to be replaced by %/2 (2) F(l) = nc d f [1+^j; cos\]1/2-1] cos2 X d X J C\