Some problems pertaining to the mechanics of accreted planetary bodies.

This dissertation addresses problems pertaining to the mechanics of accreted planetary bodies. Roughly 4.6 billion years ago, all mass was in form of dust and gas that orbited the sun in a large cloud called the solar nebula. The growth of kilometer-sized objects from sub-micron sized dust grains occurred by the collisional and/or gravitational evolution of a swarm of particles. Growth in this manner, or growth by the continual deposition of material onto an object's surface, is known as a process of accretion. An explicit, closed form solution for the stress field of an accreted, triaxial ellipsoid is derived using the linear, small deformation theory of elasticity. It is found that that this stress field is qualitatively different from the typical elastic solution, which is equivalent to building the body to its final dimensions and then endowing it with mass and angular momentum. On a related topic, a discrete element method is used to simulate growth as the head-on collision between a particle and a pack of particles that are all spherical, smooth, and rigid. It is found that energy can be dissipated amongst these constitutively simple particles by a rise of the system's granular temperature, which allows growth to occur even when the accreting particle's velocity is larger than its escape velocity. This phenomena may have played an important role during growth in the early solar system.PhDApplied SciencesAstronomyMechanical engineeringPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126458/2/3253305.pd