Stress relaxation

About: Stress relaxation is a research topic. Over the lifetime, 12959 publications have been published within this topic receiving 270815 citations.

Catalyst Selection, Creep, and Stress Relaxation in High-Performance Epoxy Vitrimers

Abstract: Vitrimers were created from a commercial high-performance anhydride-cured epoxy in the presence of various metal transesterification catalysts. Compressive creep strains greater than 50% were observed in samples containing dibutyltin diacetate or dibutyltin bis(2,4-pentanedionate) via a compression set experiment. Stress relaxation experiments were carried out in a parallel plate geometry and analyzed with a newly modified exponential model proposed to better describe the relaxation process. The results demonstrate that it is not only possible to realize reworkability on relatively short time scales (hundreds of seconds) without compromising the mechanical properties of these networks at elevated temperatures but that, with proper catalyst selection, this may be accomplished with negligible activity under curing conditions. This effort also highlights differences in the behavior of different transesterification catalysts in this context. The approach to the selection and analysis of the materials reported...

A model of threading dislocation density in strain-relaxed Ge and GaAs epitaxial films on Si (100)

Abstract: Strain relaxation in large lattice-mismatched epitaxial films, such as Ge and III-V materials on Si, introduces high threading dislocation densities (TDDs). A thermodynamic model of TDD dependence on film thickness is developed. According to this model, the quasiequilibrium TDD of a given strain-relaxed film scales down with the inverse square of its thickness. The quasiequilibrium TDDs in both Ge and GaAs films follow this model consistently. Our model predicts the lowest possible TDD of a large lattice-mismatched film on Si (100), which is determined by the dislocation glide activation energy and the film thickness.

Diffusion‐controlled stress relaxation in polymers. III. Stress relaxation in a swelling polymer

Abstract: An approximate theory of the relaxation of stress in amorphous linear polymers accompanying sorption of a low molecular weight penetrant is worked out on the assumption that the relaxation time of each Maxwellian relaxation mechanism involved is changed in the presence of penetrant by a factor dependent on penetrant concentration. A method is derived from the theory which permits approximate evaluation of the integral diffusion coefficient D of the penetrant in the polymer from stress-relaxation data on swelling systems. The theory is checked on experimental data for the systems polymethyl acrylate-water and polymethyl acrylate-methanol at 40°C., and it is found that, for both systems studied, the values of D computed from mechanical data agree reasonably with those evaluated directly from usual sorption experiments. The theory described presents only a first attempt to the quantitative interpretation of the phenomenon discussed. Further improvement and modification of it is apparently desirable, in view of some drastic approximations incorporated in its mathematical development.

Strain relaxation due to V-pit formation in InxGa1−xN∕GaN epilayers grown on sapphire

Abstract: Strain relaxation in semiconductor heterostructures generally occurs through the motion of dislocations that generates misfit dislocations above a critical thickness. However, majority of the threading dislocations in GaN-related materials have no driving force to glide, and those with a driving force are kinetically impeded even at a temperature of 1000 °C. In spite of this, the strain in InxGa1−xN∕GaN epilayers grown on c-plane sapphire substrates was observed to decrease as the InxGa1−xN layer becomes thicker. We have explored the possibility of V-pit formation at terminated dislocations as the predominant relaxation mechanism in highly mismatched systems such as InxGa1−xN∕GaN. We demonstrate that a driving force exists to nucleate V pits for strain relief. The formation of V pits was modeled through the energy balance between the strain energy in the InxGa1−xN epilayer, the destruction of dislocation energy to form V pits and the strain that is relieved due to the formation of edges during the process...