Project Summary: It is difficult to assess the stability of a granular material, or to determine whether failure is imminent. The ability to non-invasively characterize changes in the mechanical state of a granular material would aid our understanding of the transition to failure. In both ordinary atomic/molecular systems and idealized jammed systems, the density of states provides a wealth of information about the state of the system. Acoustic measurements are a promising route to a similar characterization for granular materials, due to their ability to transmit vibrational energy into the bulk of the material, and to gather information in return. We will develop such techniques in both static and sheared systems where internal stresses are visible, as well as in more realistic three-dimensional materials which are of natural and industrial importance. Objectives are: (1) Simulations and analytics predict that an increased abundance of low-frequency modes is associated with an impending loss of rigidity. Do real granular materials exhibit this feature as a universal hallmark of incipient failure, e.g. under shear? (2) Simulated jammed materials with different shapes (circles vs. ellipses vs. dimers) each have a characteristic density of states. Do real granular materials, for instance those with corners, exhibit similar shape-dependent features? (3) The properties of force and contact networks may depend on the dimensionality of the system. Results from shear experiments may improve our understanding of earthquake nucleation and rupture. Connections to geophysics are possible by analyzing results in light of current ideas about foreshocks, tremors, triggering, and monitoring fault damage.
This research position could be filled by either a graduate student or a postdoc. To apply as a graduate student, applications to the PhD program in the physics department proceed through a central office. More information about the graduate program and application process are available here. To apply as a postdoc, application materials should be uploaded to the NC State central job website. In both cases, applicants should also contact Karen Daniels directly.