Interparticle Contact Behavior and Wave Propagation
byGiovanni Cascante And J. Carlos Santamarina
Cascante, G. and Santamarina, J. C. (1996). "Interparticle Contact Behavior and Wave Propagation." ASCE Geotechnical Journal, Vol. 122, No. 10, pp. 831-839
The low-strain stiffness and energy dissipation in particular materials is strongly determined by the behavior of contacts. This paper presents results of a test program designed to study the effects of contact response on the propagation of waves. Wave velocity and attenuation were measured during isotropic loading using a resonant column devΚice at shear strains varying from γ = 10-5 to γ = -10. Elastic, viscoplastic and brittle contact behaviors were studied with steel spheres, lead shot, and silica-kaolinite pellets. All measured velocity-stress exponents were b/2 > ≈ 1/6, which is the theoretical value for spherical contacts. High-tolerance steel spheres approximated this value. Contact crushing showed the highest exponent. Theoretical analyses confirmed that several phenomena conduce to a velocity-stress exponent b/2 – 0.25: buckling of particle chains and increase in coordination number, elastoplastic behavior, and cone-plane contacts. Load and unload data for viscoplastic lead shot showed that contact deformation is the governing parameter for low-strain stiffness, regardless whether the causing mechanism was elastic deformation, creep, or yield. All measured damping-stress exponents were between κ ≈ -0.45 for steel and κ ≈ -0.11 for the brittle pellets, while the theoretical value from frictional Mindlin contacts is κ ≈ -2/3. Damping showed higher sensitivity than velocity to stress and time.