Viscoelastic response of sonic band-gap materials

A brief report is presented on the effect of viscoelastic losses in a high density contrast sonic band-gap material of close-packed rubber spheres in air. The scattering properties of such a material are computed with an on-shell multiple scattering method, properties which are compared with the lossless case. The existence of an appreciable omnidirectional gap in the transmission spectrum, when losses are present, is also reported.Comment: 5 pages, 4 figures, submitted to PR

High-speed machining of martensitic stainless steel using PcBN

The performance of PcBN cutting tool during its application in the mass production of components made from AISI 440B stainless steel has been considered. The experimental tests have been performed at cutting speed ranging between 350–500 m/min at dry cutting conditions. The machining operations that have been explored included facing, turning, grooving and boring and the 3D topography of the machined surface presented. The results show that good surface finish similar to grinding and dimensional accuracy can be achieved with PcBN tools.Рассмотрены рабочие характеристики режущего инструмента, оснащенного поликристаллическим кубическим нитридом бора (КНБ), используемого в массовом производстве изделий из нержавеющей стали AISI 440B. Экспериментальные испытания проводили при скорости резания в диапазоне от 350 до 500 м/мин в условиях сухого резания. Представлены операции обработки, включающие обточку торца, точение, прорезание канавок и сверление, а также 3D-топография обработанной поверхности. Результаты показывают, что, применяя в инструментах поликристаллический КНБ, можно достичь хорошего качества обработки поверхности и точности размеров, таких же как при шлифовании.Розглянуто робочі характеристики ріжучого інструменту, оснащеного полікристалічним кубічним нітридом бору (КНБ), що використовують в масовому виробництві виробів з нержавіючої сталі AISI 440B. Експериментальні випробування проводили при швидкості різання в діапазоні від 350 до 500 м/хв в умовах сухого різання. Представлено операції обробки, що включають обточування торця, точіння, прорізання канавок і свердління, а також 3D-топографія обробленої поверхні. Результати показують, що, застосовуючи в інструментах полікристалічний КНБ, можна досягти хорошої якості обробки поверхні і точності розмірів, таких же як при шліфуванні

Effect of Temperature on Flow-Induced Crystallization of Isotactic Polypropylene:A Molecular-Dynamics Study

Molecular-dynamics simulations are employed in order to study the flow-induced crystallization (FIC) of isotactic polypropylene from a supercooled state at different temperatures. The study found that FIC displayed the highest rate at a temperature range of Tmax = 330-360 K. By applying the mean first passage time method, the pre-nucleation, nucleation, and growth stages were successfully identified. The pre-nucleation stage was thoroughly examined, and multiple phenomena were observed, including unexpected strain hardening in the vicinity of Tmax and the formation of high ordering areas that acted as nuclei precursors with limited motion along the tensile direction. Additionally, a non-uniformly slowed segmental relaxation was noted, which suggested the existence of cooperative rearranging regions, the percolation of which could potentially explain the strain hardening effect. Furthermore, the size of the critical clusters at the nucleation point was independent of temperature. Finally, stable clusters grew and merged, resulting in the formation of a shish network.</p

Effect of Temperature on Flow-Induced Crystallization of Isotactic Polypropylene:A Molecular-Dynamics Study

Molecular-dynamics simulations are employed in order to study the flow-induced crystallization (FIC) of isotactic polypropylene from a supercooled state at different temperatures. The study found that FIC displayed the highest rate at a temperature range of Tmax = 330-360 K. By applying the mean first passage time method, the pre-nucleation, nucleation, and growth stages were successfully identified. The pre-nucleation stage was thoroughly examined, and multiple phenomena were observed, including unexpected strain hardening in the vicinity of Tmax and the formation of high ordering areas that acted as nuclei precursors with limited motion along the tensile direction. Additionally, a non-uniformly slowed segmental relaxation was noted, which suggested the existence of cooperative rearranging regions, the percolation of which could potentially explain the strain hardening effect. Furthermore, the size of the critical clusters at the nucleation point was independent of temperature. Finally, stable clusters grew and merged, resulting in the formation of a shish network.</p

Nonlocal electrodynamics of two-dimensional wire mesh photonic crystals

We calculate analytically the spectra of plasma waves and electromagnetic waves (EMW) in metallic photonic crystal consisting of the parallel thin infinite metallic cylinders embedded in the dielectric media. The axes of metallic cylinders form a regular square lattice in a plane perpendicular to them. The metal inside the cylinders is assumed to be in the high frequency regime $\omega \tau >> 1$, where $\tau$ is the relaxation time. The proposed analytical theory is based upon small parameters $f << 1$, where $f$ is the volume fraction of the metal, and $kR << 1$, where $k$ is the wave vector and $R$ is the radius of the cylinder. It is shown that there are five different branches of the EMW that cover all frequency range under consideration except one very small omnidirectional gap in the vicinity of the frequency of the surface plasmon. However, at some directions of propagation and polarizations the gap may be much larger. The reflection and refraction of the EMW is also considered. The general theory of refraction is proposed which is complicated by the spatial dispersion of the dielectric constant, and one particular geometry of the incident EMW is considered.Comment: 14 pages, 8 figure

Acoustic properties of colloidal crystals

We present a systematic study of the frequency band structure of acoustic waves in crystals consisting of nonoverlapping solid spheres in a fluid. We consider colloidal crystals consisting of polystyrene spheres in water, and an opal consisting of close-packed silica spheres in air. The opal exhibits an omnidirectional frequency gap of considerable width; the colloidal crystals do not. The physical origin of the bands are discussed for each case in some detail. We present also results on the transmittance of finite slabs of the above crystals.Comment: 7 pages, 9 figures, prb approve

Scattering of elastic waves by periodic arrays of spherical bodies

We develop a formalism for the calculation of the frequency band structure of a phononic crystal consisting of non-overlapping elastic spheres, characterized by Lam\'e coefficients which may be complex and frequency dependent, arranged periodically in a host medium with different mass density and Lam\'e coefficients. We view the crystal as a sequence of planes of spheres, parallel to and having the two dimensional periodicity of a given crystallographic plane, and obtain the complex band structure of the infinite crystal associated with this plane. The method allows one to calculate, also, the transmission, reflection, and absorption coefficients for an elastic wave (longitudinal or transverse) incident, at any angle, on a slab of the crystal of finite thickness. We demonstrate the efficiency of the method by applying it to a specific example.Comment: 19 pages, 5 figures, Phys. Rev. B (in press