Effects of absorption and desorption on the chemical stress field

Abstract

The present work studies the effects of absorption and desorption on the chemical stress field in a membrane during permeation or both-side charging of a diffusing species. The permeation and both-side charging processes are analyzed with the consideration of the absorption and desorption processes, wherein the flux continuity boundary conditions are adopted. The results show that the chemical stresses are compressive near the surfaces and tensile in the center of the membrane. The maximum magnitude of stress occurs at the entry surface for the permeation process and at both surfaces for the both-side charging process. For the permeation process, the compressive stress at the entry surface increases with time to a maximum and then decreases with time gradually to zero. A similar phenomenon is found at both surfaces in the both-side charging process. In both processes, the stress magnitude depends upon the ratio of the drift velocity through surface to the drift velocity through bulk. When this ratio approaches infinity, the flux continuity boundary conditions reduce to the concentration boundary condition and the highest chemical stress field will be produced. Therefore, reducing the drift velocity through surface would be an efficient means to reduce the strength of the chemical stress. In general, designed surface alloying can introduce diffusing species traps at the surfaces of a membrane, which may efficiently decrease the drift velocity through surface.

Coupling effects of chemical stresses and external mechanical stresses on diffusion

“…For the one-side charging process, the external stress will increase the chemical stress compared with that with lower external stress gradient or without external stress at a given time, as shown in figures 3(a)-(c). For the both-side charging process, asymmetric distribution of chemical stresses occurs through the thickness of plate due to the coupling effect of asymmetrically distributed external stress, as shown in figures 3(d)-(f ), in contrast to the result of effects of absorption and desorption on the chemical stress field given by Zhang et al [7]. The curves are concave for a short time and gradually become straight when steady state is reached.…”

“…The coupling effects of chemical stresses and external mechanical stresses on diffusion are analysed. A selfconsistent diffusion equation including the chemical stress and the external mechanical stress gradient has been developed based on Zhang et al's [7,29] work by using thermodynamic theory and Fick's law.…”

“…Substituting the chemical stress equation ( 8) and external stress equation (9) in equation (7) yields…”

“…in specimens of different geometries such as thin plates, solid cylinders, hollow cylinders and solid spheres. Zhang et al [7] studied the effects of absorption and desorption on the chemical stress field in a membrane during permeation or both-side charging of a diffusing specimen, wherein the flux continuity (FC) boundary conditions were adopted. Recently, Ko et al [8] investigated the chemical stresses in a square sandwich composite with two different diffusion processes by the numerical method.…”

Insertion-induced breakage of materials

“…21 Li 18 studied the diffusion-induced stress in elastic materials of simple geometries. Lee and co-workers 22,23 analyzed the effect of diffusion on the stress evolution in composite materials. Yang and Li 20 considered the effect of chemical stress on the bending of beam/plate structure.…”