Shrinkage driving forces

During pressure sintering, interiDarticle compressive stress, approximated by the externally applied stress and nonnalized by the relative density of the compact p, supplements the surface tension driving force for pore shrinkage ... 

The flux is therefore directed toward the outer interface, causing the spherical shell to shrink toward its center under the driving force supplied by the decrease in interfacial energy that occurs as a result of the shrinkage. (Note that ultimately the shell will shrink to form a solid sphere of a phase at the origin.)... 

Based on the authors experience, membrane fracture frequently occurs during events when membrane is dried out the in-plane hygrothermal stress is a critical driving force in membrane mechanical failure. The in-plane hygrothermal stress can be lowered by reducing the swelling/shrinkage ratio of the membrane, i.e., the dimensional instability of the membrane. 

These results indicate that the solvent removal process in poly(amic acid) film formation is dependent on the residual stress level. Solvent evaporation creates volume changes which in turn generate shrinkage stresses ( 8 MPa at room temperature). This will continue until there is a balance between the internal stress and the driving forces for solvent removal. Further solvent may be removed if this balance is altered by a change in stress or temperature. 

Thermosets are often used in intimate contact with materials of much lower coefficient of linear thermal expansion p. A thermoset film may be coated on a surface, or sandwiched between two surfaces as an adhesive. A thermoset matrix may be filled with high-modulus fibers in aerospace structural materials and in other composite materials. A residual stress other material(s) to changes in temperature. The value of or typically reflects the balance between the driving force to produce residual stresses due to differential shrinkage upon cooling and the temperature-dependent capacity to relax these stresses. The worst such effects... 

Polymerization continues both between monomers or polymers and the spanning network and within the network itself as reactive terminal groups diffuse into close proximity. This process appears to promote syneresis (sometimes called macrosyneresis) (63), the shrinkage of the gel network, resulting in expulsion of liquid from the pores. Scherer (64) states that the kinetics of syneresis depend on the driving force (polymerization), the mobility of the gel network, and the rate of fluid flow through the contracting network. 

Because the liquid wets and spreads over the solid surfaces, pores will be formed in the liquid. The reduction of the liquid-vapor interfacial area provides the driving force for shrinkage or densification of the compact. If the pore in the liquid is assumed to be spherical with radius of r, the pressure difference across the curved surface is given by the Young and Laplace equation ... 

According to the pore filling theory, the shrinkage of a compact occurs by a successive accommodation and recovery of grain shape. Explain the process of sample shrinkage in detail and its related driving force. 

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