CONTACT LAWS FOR CEMENTED GRAINS - IMPLICATIONS FOR GRAIN AND CEMENT FAILURE

Analytical solutions are presented to predict the intergranular contac t load transfer in cemented granular media where both grain material a nd cement are elastic. The grains can be separated, have a direct poin t contact, or be compacted prior to cement deposition. For all these c ases contact stress distributions are obtained for normal, tangential and torsional deformation of two cemented deformable grains. An import ant result is that intergranular cement: even if very soft, is load-be aring. Thus cementation reduces contact stress concentration (as compa red with direct Hertzian interaction). Contact stresses are maximum ne ar the center of the contact region when the cement is soft relative t o the grains, and are maximum at the periphery of the contact region w hen the cement is stiff. These results allow us to predict the Followi ng modes of static and dynamic failure of the grains and intergranular bonds in a particulate material. (1) Uncemented grains will tend to s hatter whereas cemented grains will stay intact, and the cement will f ail. (This conclusion is supported by hydrostatic loading experiments where intensive crushing of uncemented glass beads was observed at abo ut 50 MPa, whereas grains cemented at their contacts with small amount s of epoxy stayed intact.) (2) Where intergranular cementation is pres ent, grain failure may still be expected if the cement is strong and s tiff. In this case, grain damage will be initiated at the periphery of the cement layer. (3) Yielding of a cement material that is soft (as compared with the grain material) will initiate at the center of the c ontact region, whereas stiff cement will yield at the periphery.