Stress-strain analysis of pipelines laid in permafrost

Increasing reliability of pipelines becomes a real challenge at all stages: design, construction and operation of pipeline systems. It is very important to determine the behaviour of the constructed pipeline under the operational and environmental loads using the design model in accordance with that one adopted in the rules and regulations. This article presents the simulation of pipeline in permafrost. The evaluation of the stress-strain state is given herein and the areas of the stress concentration are detected with the account for different loads occurred during the pipeline operation. Information obtained from the assessment of the stress-strain state of the pipeline allows determining sections in pre-emergency state (even before damages) and take all the necessary measures for eliminating them, thus increasing the pipeline system reliability. It is shown that the most critical pipeline cross-section is observed at the point of transition from one environment to another. The maximum strains decrease the level of the pipeline reliability. The finite element model is presented to determine the pipeline sections in pre-emergency state

ИДЕНТИФИКАЦИЯ ПАРАМЕТРОВ СЛОЖНОЙ МЕХАНИЧЕСКОЙ СИСТЕМЫ ПРИ ТЕРМОСИЛОВЫХ ВОЗДЕЙСТВИЯХ

Empirical dependences for calculating reliability and mass of an aviation engine are obtained with the help of a regression analysis method and test of the obtained expression adequacy has been carried as well.A model for degradation of the effective, elastic and heat-conducting material properties of engine parts due to spreading growth in physical and mechanical properties in comparison with data-sheet values in the process of operation without continuity violation has been developed and described in the paper. The paper also presents a model for emergence and accumulation of such damages as micro-pores, micro-cracks. The paper evaluates a critical concentration of damages with due account of a percolation theory at which a cluster-crack is formed in some local space.Получены эмпирические зависимости для расчета надежности и массы авиационного двигателя с помощью метода регрессионного анализа, и выполнена проверка адекватности полученных выражений.Разработаны и описаны модель деградации эффективных упругих и теплопроводных свойств материалов деталей двигателя за счет роста разброса физико-механических свойств от номинальных (проектных) значений в процессе эксплуатации без нарушения сплошности и модель возникновения и накопления повреждений типа микропор, микротрещин, с учетом теории перколяции дана оценка критической концентрации повреждений, при которой образуется кластер-трещина в некотором локальном объеме

Non-thermal transport of energy driven by photoexcited carriers in switchable solid states of GeTe

Phase change alloys have seen widespread use from rewritable optical discs to the present day interest in their use in emerging neuromorphic computing architectures. In spite of this enormous commercial interest, the physics of carriers in these materials is still not fully understood. Here, we describe the time and space dependence of the coupling between photoexcited carriers and the lattice in both the amorphous and crystalline states of one phase change material, GeTe. We study this using a time-resolved optical technique called picosecond acoustic method to investigate the \textit{in situ} thermally assisted amorphous to crystalline phase transformation in GeTe. Our work reveals a clear evolution of the electron-phonon coupling during the phase transformation as the spectra of photoexcited acoustic phonons in the amorphous ($a$-GeTe) and crystalline ($\alpha$-GeTe) phases are different. In particular and surprisingly, our analysis of the photoinduced acoustic pulse duration in crystalline GeTe suggests that a part of the energy deposited during the photoexcitation process takes place over a distance that clearly exceeds that defined by the pump light skin depth. In the opposite, the lattice photoexcitation process remains localized within that skin depth in the amorphous state. We then demonstrate that this is due to supersonic diffusion of photoexcited electron-hole plasma in the crystalline state. Consequently these findings prove the existence of a non-thermal transport of energy which is much faster than lattice heat diffusion

Chaos in wave front propagation in heterogeneous media = Хаос распространения волнового фронта в неоднородных средах

The appearing of the determined chaos at propagation of nonstationary volume and surface waves in heterogeneous media is investigation. The conditions which satisfy distributions of the determined heterogeneity and appear stochastic states in behaviour of rays are obtained. Исследуется возникновение детерминированного хаоса при распространении нестационарных объемных и поверхностных волн в гетерогенных средах. Получены условия, которые удовлетворяют распределениям детерминированной неоднородности и проявляются стохастическими состояниями в поведении лучей

Diffraction of picosecond bulk longitudinal and shear waves in micron thick films

Investigation of thin metallic film properties by means of picosecond ultrasonics [C. Thomsen et al., Phys. Rev. Lett. 53, 989 (1984)] has been under the scope of several studies. Generation of longitudinal and shear waves [T. Pézeril et al., Phys. Rev. B 73, 132301 (2006); O. Matsuda et al., Phys. Rev. Lett. 93, 095501 (2004)] with a wave vector normal to the film free surface has been demonstrated. Such measurements cannot provide complete information about properties of anisotropic films. Extreme focusing of a laser pump beam (≈0.5 μm) on the sample surface has recently allowed us to provide evidence of picosecond acoustic diffraction in thin metallic films (≈1 μm) [C. Rossignol et al., Phys. Rev. Lett. 94, 166106 (2005)]. The resulting longitudinal and shear wavefronts propagate at group velocity through the bulk of the film. To interpret the received signals, source directivity diagrams are calculated taking into account material anisotropy, optical penetration, and laser beam width on the sample surface. It is shown that acoustic diffraction increases with optical penetration, so competing with the increasing of directivity caused by beam width. Reflection with mode conversion at the film-substrate interface is discussed

Optical reflectometric detection of a three-dimensional acoustic field

In laser ultrasonics, when focusing strongly the pump beam, a three-dimensional (3D) diffracted acoustic field can be generated. Considering weakly absorbing materials, the 3D interaction of this elastic perturbation with the optical detection beam must be taken into account. A semi-analytical model is proposed to describe such phenomena in reflectometric measurements. Once the acoustooptic interaction has been partially linearized, the resulting inhomogeneous differential system is solved using the matricant method. Good agreement is found comparing the calculated results with the experimental data in an aluminum film

Theory and illustration of the three-dimensional elasto-optic interaction in picosecond ultrasonics

The three-dimensional (3D) photoelastic interaction involved in the detection mechanism of picosecond ultrasonics is investigated in micrometric metallic films. In pump-probe experiments, the laser source beam is focused to a spot size less than 1 µm. A 3D diffracted acoustic field is generated at high frequencies of several tens of gigahertz, containing longitudinal and shear waves altogether. Their propagation changes the dielectric permittivity tensor and the material becomes optically heterogeneous. Consequently, the detection process is modeled through the propagation of the laser probe beam in a material with dielectric properties varying in all directions. Thus, the solving of Maxwell equations leads to a differential system, the source term of which is proportional to the acoustic field itself. The scattered electromagnetic field is described using the matricant and the ensuing analytical solution allows then analyzing the 3D photoelastic interaction. Good agreement with experiments performed in a 1 µm thick aluminum film is found