The chemical stresses in solids

• Main Authors: Wei-Long Wang, 王偉龍
• Other Authors: Sanboh Lee
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/84682743560846722771

博士 === 國立清華大學 === 材料科學工程學系 === 87 === The main purpose of this research is to investiage the chemical stress induced by diffusion. There are tow general diffusion processes of constant surface concentration source and instantaneous surface concentration source are applied to diffusion process. After the initial and boundary conditions are obtained, we utilize the Laplace or Fourier-Lapalce transform skill to solve the partial differential equation of diffusion. The derivation of stress distribution arising from the solute diffusion is similar to the thermal stresses arising from the heat transfer. Some important results in this thesis are concluded as following: (1) If the concentration for instantaneous surface source is equal to that for constant surface concentration, the chemical stress for instantaneous is greater than that for constant surface concentration. (2) The concentration or chemical stress distributions are similar to that of thin plate when the ratio of outer radius to inner is near 1. For instantaneous surface source, the The concentration or chemical stress distributions are similar to that of solid cylinder when the outer radius of hollow cylinder is much greater than that inner radius. (3) There exists a time dependent function of surface concentration which control the stress under the threshold value to induce plastic deformation, i.e, it is the fast diffusion process without plastic deformation. (4) For composite hollow cylinder, only radial stress apply on the surface of interface. The magnitude of the radial stress depends on the diffusion time, Young''s modulus, the ratio of diffusion coefficient, partial molal volume and chemical potential of media. (5) The chemical stress will enlarge the diffusion coefficient and speed up the diffusion. (6) In a grain boundary diffusion of thin film, the chemical stress in grain boundary increase with increasing film thickness. When the film thickness is large enough, the stress or concentration distribution in the grain boundary can be simplified as semi-infinite model. (7) In the mass transport of glassy polymer, the maximum stress occurs at the absorption surface and in the initial diffusion time. The value of the maximum stress is $-E\overline{V}C_0/3(1- \nu )$。 For given time and thickness of polymer, the displacement of two side absoprtion is the same as the one side absorption. Comparing the threotical and experimental displacement curves, we can obtain the solvent of partial molal volume in polymer. (8) In the mass transport of glassy polymer, the chemical stress for viscoelastic model is smaller than that for elastic model. The same trend is also for the strain energy.