柴油机曲轴整体结构的三维有限元分析

本文采用子结构方法对柴油机曲轴整体结构进行了三维有限元分析，对曲轴这种复杂的工程结构问题通过分成子结构进行求解可以建立更加灵活合理的结构模型，也可降低方程组的阶数，节省大量的重复计算工作，使我们能够在没有大机器的情况下，用很少的内存容量解算大自由度数的题目。     

Coupling of the phase-field and CALPHAD methods for predicting multicomponent,solid-state phase transformations

The development of an effective microstructure design method for multicomponent alloys is of considerable importance for improving both the design of alloys and the design of processes for producing alloys with unique properties. The coupling of the phase-field method and the calculation of phase diagrams (CALPHAD) method can be used for predicting the evolution of microstructures in multicomponent alloys. Such predictions make use of CALPHAD thermodynamic information with the chemical free energy function in the phase-field method. This article reviews several of these coupling methods, focusing on solid-state phase transformations in multicomponent systems, such as phase separation and disordered or ordered phase precipitation from a matrix. When calculating disordered phase transformations, the Gibbs energy function derived from the CALPHAD database can be used directly in the phase-field method. On the other hand, when dealing with an order/disorder transition, the degrees of freedom of the element site fraction for an ordered phase in the CALPHAD method can be reduced using the Gibbs energy single formalism for constituent phases, by using a database that stores the Gibbs energy and chemical equilibrium conditions, or by obtaining the driving force calculated using the Thermo-Calc software. The current status and future directions for further development of these coupled methods are discussed.     

Basal slip localization in zinc single crystals. The Considère analyses

The tensile and compression tests were performed on zinc single crystals oriented for slip in the basal slip system. During the first stage of the stress–strain curve, the localized necking was typical of strain localization in the tensile specimens. Single or multiple necks were formed along the specimen length. The range of temperatures and the strain rates for single necking of the sample was determined. The formation of such necking depends on strain hardening characteristics and can be predicted by the Considère criterion. On the other hand, propagation of the necked area along the sample length was not predictable by this criterion. Localized sliding and specimen kinking was indicative of the strain localization observed for different specimens compressed under the same conditions, i.e. temperature and strain rate. A decrease in the compression force and in the cross-sectional area with anvil displacements produced localized sliding. On the other hand, a continuous increase in the compression force was representative of tests leading to specimen kinking.     

Low-temperature elastic constants and piezoelectric coefficients of langasite (La3Ga5SiO14)

A complete set of elastic constants C _ij and piezoelectric coefficients e _ij of a La₃Ga₅SiO₁₄ (langasite) single crystal was determined from 5.5 to 275.5?K by resonant ultrasound spectroscopy. Unlike a conventional crystal, the elastic constants C _ij of the langasite crystal showed three types of temperature dependence: (i) monotonic elastic stiffening upon cooling (C ₄₄ and C ₁₄); (ii) monotonic elastic softening (C ₆₆); and (iii) a stiffening-to-softening transition below 150?K (C ₁₁, C ₁₂, C ₁₃ and C ₃₃). In addition, a strong correlation between C ₆₆ and the piezoelectric coefficient e ₁₁ was confirmed. Group theoretical lattice dynamics analysis revealed that the novel phenomena of elastic softening and strong correlation are explained on the basis of two types of optical mode internal displacements which have the totally symmetric A ₁ and doubly degenerated E symmetries in the point group D ₃.     

Thermodynamics of elastic strength of the metal surface layer

This paper presents a physicochemical model that establishes a connection between the elastic strength of the surface layer (SL) of metal and its surface Gibbs energy. The elastic limit of SL along the low-index face of the metal single crystal under stress during the transition from elastic to plastic deformation was calculated. Calculation shows that the elastic limit of metal SL with fcc and bcc structures is approximately three orders of magnitude higher than the yield strength of these metals in bulk and close to nanohardness of the metals, in particular; for Cu(111) и Al(111), it is 5.3 and 2.8?GPa, respectively. In the light of the proposed model, the effect of lowering the elastic strength of metal SL due to adsorption of surfactant is formulated.     

Electron channelling contrast imaging of dislocations in a conventional SEM

Abstract

Dislocations in shock loaded tantalum single crystals were imaged using both transmission electron microscope (TEM) and electron channelling contrast image (ECCI) in a scanning electron microscope with a conventional backscattered electron detector. The results were compared with backscattered electron intensity profiles across dislocations calculated via the dynamic theory of electron diffraction. A one-to-one correspondence between ECCI and TEM is established. High voltage and low index reflections should be used to obtain the highest dislocation contrast and greatest imaging depth.     

Stable single longitudinal mode erbium-doped silica fiber laser based on an asymmetric linear three-cavity structure

We present a stable linear-cavity single longitudinal mode (SLM) erbium-doped silica fiber laser. It consists of four fiber Bragg gratings (FBGs) directly written in a section of photosensitive erbium-doped fiber (EDF) to form an asymmetric three-cavity structure. The stable SLM operation at a wavelength of 1545.112 nm with a 3-dB bandwidth of 0.012 nm and an optical signal-to-noise ratio (OSNR) of about 60 dB is verified experimentally. Under laboratory conditions, the performance of a power fluctuation of less than 0.05 dB observed from the power meter for 6 h and a wavelength variation of less than 0.01 nm obtained from the optical spectrum analyzer (OSA) for about 1.5 h are demonstrated. The gain fiber length is no longer limited to only several centimeters for SLM operation because of the excellent mode-selecting ability of the asymmetric three-cavity structure. The proposed scheme provides a simple and cost-effective approach to realizing a stable SLM fiber laser.