Dynamic coefficients in impact mechanics

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tested (Fig. 5b). An interesting effect can be noticed when the dependence of k on the initial impact velocity of the particle is studied (Fig. 6). It should be mentioned that similar effect of initial increase of k has been observed when composite targets were impacted with glass beads of much larger size of 650 µm in diameter (Fig. 6b). Some increase in the coefficient of restitution can be explained by the compression of the target material. Impacting particle squeezes out the plastic binder and plunges hard carbide grains into a soft substratum without any failure. Carbide grains loose their protective binder, forming a thin subsurface transition layer with strength parameters differing from the bulk body 0.940 0.930 Restitution coefficient 0.920 0.910 0.900 0.890 0.880 0.870 0.860 W15 C20 C20S 0.850 5 10 15 20 25 30 Particle velocity, m/s (a) 0.98 Restitution coefficient 0.96 0.94 0.92 0.90 0.88 W15 TiC-40% steel TiC-40% Ni 0.86 5 15 25 35 45 55 Particle velocity, m/s (b) Fig. 6. Coefficient of velocity restitution vs particle velocity: (a) present study; (b) [ 7 ]. 33
0.140 Coefficient of dynamic friction 0.130 0.120 0.110 0.100 0.090 W15 C20 C20 0.080 5 10 15 20 25 30 Initial velocity, m/s (a) 0.140 Coefficient of dynamic friction 0.120 0.100 0.080 0.060 0.040 W15 C20S C20 0.020 25 35 45 55 65 75 85 Impact angle, deg (b) Fig. 7. Coefficient of dynamic friction: (a) vs particle velocity; (b) vs impact angle. parameters. In all probability, some energy is accumulated by interphases up to the velocity when tensile stresses both in the target surface and particle initiate crack propagation [ 9 ]. As it was expected, f is a function of both impact angle and initial velocity of the particle (Fig. 7). Moreover, the coefficient of friction depends on the relative sliding velocity between the particle and the target and may be estimated 34
Page 1 and 2: Proc. Estonian Acad. Sci. Eng., 200
Page 3 and 4: The appropriate equations are well
Page 5 and 6: to illuminate the working area [ 5,
Page 7: where α 1 is the impact angle. The
Page 11 and 12: This reveals that the energy loss a
Page 13 and 14: velocity restitution, k , and the d

Dynamic coefficients in impact mechanics

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