The ThermoMechanical Behavior of Cometary Nuclei.
Abstract
The thermomechanical behavior of cometary nuclei is investigated in terms of the properties of the porous ice composing them. The timedependent thermal gradients and the material properties dictate the thermal stress response and possible fracture. Thermal conductivity, specific heat, coefficient of thermal expansion, Young's modulus, and Poisson's ratio are studied analytically as functions of porosity and composition. More extensive numerical calculations, employing the method of finite elements, yield the thermal conductivity as a function of porosity, pore shape, pore size, ice composition, pore vapor composition, pore orientation with respect to heat flow, pore size distribution, pore packing geometry, grain grain interface size and heat transport mechanism. Numerical techniques are employed to simulate the largescale thermal and stress response of twodimensional, planar comet surface layers. The thermal and stress profiles are calculated as functions of porosity, pore shape and presence of pore space vapor. The numerical results are compared with analytical results for the development of thermal stress in a sphere under the same conditions. Fracture mechanics calculations of Griffith crack propagation are employed to investigate the occurrence of catastrophic fracture.
 Publication:

Ph.D. Thesis
 Pub Date:
 1989
 Bibcode:
 1989PhDT.........3G
 Keywords:

 Physics: Astronomy and Astrophysics;
 Comet Nuclei;
 Finite Element Method;
 Fracture Mechanics;
 Fracturing;
 Specific Heat;
 Thermal Conductivity;
 Thermal Expansion;
 Thermal Stresses;
 Thermodynamics;
 Crack Propagation;
 Flow Distribution;
 Griffith Crack;
 Heat Transfer;
 Heat Transmission;
 Modulus Of Elasticity;
 Spheres;
 Stress Distribution;
 Surface Layers;
 Temperature Gradients;
 Time Dependence;
 Astrophysics