固体火箭推进剂燃烧微粒场的激光全息诊断

大幅度提高金属燃料的含量是实现高能高效推进剂配方的一个发展方向。现针对含铝量2／%,粒度及含铝量6%,粒度15±2μm的两种推进剂展开了一系列的研究工作。应用离轴4F全息技术,进行了固体火箭推进剂燃烧流场的粒子分布研究。在常压、2MPa和4MPa实验工况下,获得了清晰的全息图。     

Bayesian reassessment of the number of flaws in a pipeline

A practical method for correcting an estimate of the true number of defects in a pipeline after performing in-tube flaw detection and subsequent verification of measurement results by a second independent verifying instrument is presented. A direct correction method was initially proposed by one of the authors [1]. A more precise method, which is based on the Bayesian procedure, is considered in this study. The problem of predicting the most probable number of true flaws in each interval of changes in the flaw parameters (hereinafter, the flaw depth is considered) is solved on the basis of data from the inspection of detected and actual flaws in a pipeline. These results can be used for the evaluation of the quality of a performed in-tube inspection and the quality of in-tube and verifying instruments, when solving appropriate problems of pipeline reliability (as the input data), and when planning inspections on the basis of risk assessment.     

固体自润滑涂层摩擦磨损特性研究

随着机械加工技术和空间技术的发展,固体润滑涂层在比较恶劣的润滑环境下能起到独特的润滑效果,得到高速发展和广泛应用.在综合国内外研究和报道的基础上,对一般固体润滑涂层和纳米固体润滑涂层的摩擦磨损特性的研究现状进行归纳,指出固体润滑涂层摩擦磨损研究的发展方向.     

Wear resistant solid lubricant coating made from PTFE and epoxy

A composite coating of polytetrafluoroethylene and epoxy shows 100 × improvements in wear resistance as compared to either of its constituents alone and reduced friction coefficient under testing on a pin-on-disk tribometer. This coating is made by impregnating an expanded PTFE film with epoxy, which provides three unique functions: (1) the epoxy compartmentalizes the PTFE nodes, which is believed to reduce the wear of the PTFE, (2) the epoxy increases the mechanical properties such as elastic modulus and hardness, and (3) the epoxy provides a ready interface to bond the films onto a wide variety of substrates easily and securely. The experimental matrix had normal loads of 1–3 N, sliding speeds from 0.25 to 2.5 m/s, and used a 2.4 mm radius low carbon steel pin in a rotating pin-on-disk tribometer. The skived PTFE films had wear rates on the order of K=10^–3 mm³/Nm and friction coefficients around =0.2. Both the high density films (70 wt%PTFE) and low density films (50 wt% PTFE) had wear rates on the order of K=10^–6 mm³/Nm and friction coefficients around =0.15. The neat epoxy films showed significant scatter in the tribological measurements with wear-rates on the order of K=10^–4 mm³/Nm and friction coefficients around =0.40. The enhanced tribological behavior of these composites is believed to stem from the coatings ability to draw thin PTFE transfer films into the contact from the nodes of PTFE, which act like reservoirs. Nanoindentation mapping of the coatings and the transfer films supports this hypothesis, and accompanies scanning electron microscopy observations of the worn and unworn coatings.     

The maximum tensile stres on a hard coating under sliding friction

In the friction of a hard coating the maximum tensile stress in the sliding direction generated at the friction surface is important for predicting crack propagation in the coating. The finite element method is employed to evaluate the stress field in the hard coating and the substrate under frictional loads, and the ratio between the values of maximum tensile stress and the maximum contact pressure is calculated under various contact conditions. Finally, a simple equation is introduced for the calculation of the maximum tensile stress at the friction surface. This equation is a function of friction coefficient, maximum contact pressure, coating thickness, contact width and elastic moduli of coating and substrate, and gives the value of the maximum tensile stress which is affected by the existence of the substrate.     

The detection of flaws in optoelectronic systems

Potentially dangerous spots (PDSs), for example, leaks in product pipelines (oil and gas pipelines), are revealed using optoelectronic systems (OESs) that are usually mounted on airborne vehicles (e.g., helicopters). Earlier, a relevant problem consisted of revealing the onset of leaks in PDSs; however, today it is necessary to detect the PDSs of leaks in order to prevent their development. The complexity of the problem is related to the fact that product pipelines are most often located near densely populated areas and near reservoirs with drinking water. The appearance of PDSs is usually characterized by deviations in the temperature and other physical parameters from standard values in small areas. The detection of such spots necessitates decreasing the flying height of an OES carrier. As a rule, this yields a deterioration of imaging quality and OES overheating, which decreases the efficiency of this PDS detection method. Conservative OES developers believe that a low imaging quality and OES overheating result from random flaws in the OES assembly. Contrary to this, it is shown that failures occur due to a deterministic flaw at the stage of designing drives for an OES platform.     

Tribotechnical characteristics of cast iron with a steel coating in lubrication medium under unsteady modes

The effect of the lubrication, antifriction, and rheological characteristics of transmission oil exerted on the wear resistance of a sprayed 30KhGSA steel coating on cast iron under the conditions of a stepwise load increase has been studied. An increase in serviceability with increasing thickness of the coating due to the formation of screening boundary lubricating layers characterized by low shear stress and the stabilization of the specific frictional work in the contact area has been revealed.     

Analysis of coating delamination under extreme contact loading

This paper investigates the catastrophic failure due to wear of protective coatings when face-milling the Titanium alloy Ti-6242S in dry mode. The study employs a synergetic approach that teams finite element-based simulations to experimental observations in order examine the wear mechanisms for two groups of alloyed carbide inserts, (coated and uncoated). The results presented in this study pertain to cutting experiments performed at cutting speeds of 100–125 m/min and feed rates of 0.15–0.20 mm/tooth. Post experimental SEM micro-graphical analysis reveal that delamination is the primary wear mechanism for different cutting conditions, and that the major portion of delamination takes place at the very initial moments of cutting (first few seconds). Consequences of delamination on wear and the implications on the dry machining process of titanium and titanium based alloys are discussed.     

The role of a stressed state in the formation of stress-corrosion flaws in pipelines

In recent years, as a result of performance of intensive in-tube flaw detection, the integrity and reliable operation of trunk pipelines have been achieved. However, because of an unpredictable development of such tube flaws as stress corrosion, the probability of occurrence of emergencies in pipelines substantially increases. An analysis of the stressed state in pipelines exposed to their main load—the operating pressure—and various types of additional forces is presented. As a result, it is shown that the obtained direction, value, and location of the effective maximum stresses in the tube wall fully correspond to the pattern of statistical formation of stress-corrosion flaws in pipelines. It can be concluded from the data of this study that the standardized tube-strength margin is insufficient; during tube operation, this circumstance may lead to the formation of stresses at the level of the metal yield stress and initiation and growth of stress-corrosion cracks.     

The method of prediction of the life of the dry friction bearing unit with a solid grease coating

The method is considered of prediction of wear of full-scale friction units by the temperature dependence of the integral parameter (Φ, the factor of wear) governed by the conditions of operation derived from the respective type of interactions. The temperature dependence of this parameter can be found from the results of laboratory tests of a model random-configured pair. It is shown that the calculated life of the bush-shaft coupling with the solid-grease VNIINP-212 determined from the factor of wear of this coating obtained with end-to-end tests is 4–45% different from the actual life.     

Classification of flaws in ultrasonic and X-ray testing

Classification of flaws in welded joints during X-ray and ultrasonic nondestructive testing are considered. The consideration is focused on the parameters of flaws that affect the reliability of the tested item. Recommendations are made to improve identification of a flaw’s shape and type via relationships between test signatures and to assess parameters involved in calculations of the strength and service life of a tested item.     

Detection of flaws in the railhead by the mirror method under the condition of multiple reflection of ultrasonic oscillations

Issues of detection of flaws in the railhead by the echo and mirror methods are considered. The influence of the degree of rail wear on the path of propagating ultrasonic beams has been studied. It has been shown that, owing to multiple reflection of ultrasonic beams inside the railhead, transverse cracks can be reliably detected on both the working and nonworking faces of the railhead. Computer-simulation-based calculations are confirmed by data on detection of actual flaws in the railhead. The results are used in the development of sounding systems for AVIKON-type multichannel demountable ultrasonic flaw detectors for total inspection of rails.     

Effect of the number of surface flaws in a group on their magnetic field

The effect of the number of surface flaws in a group on the value of their magnetic field in air above a ferromagnetic article is considered.Translated from Defektoskopiya, Vol. 40, No. 8, 2004, pp. 3–9. Original Russian Text Copyright © 2004 by Zagidulin, Muzhitskii, Bizyulev.     

Effect of coating layer for spheres under Hertzian contact

A model is constructed to analyze the effects of layer hardness and thickness upon contact stresses for the coated elastic sphere under normal loading. It is assumed that the layer is perfectly bonded to the elastic substrate and the radius of contact is very small compared to the radius of indenter. By following a linear theory of elasticity, Fredholm integral equation is developed and it is solved numerically. The resulting contact stresses are calculated at the layer surface as well as the layer-substrate interface. Also, the second invariant of the deviatoric stress tensor, are calculated for various layer substrate combinations and for several layer thickness.     

Tribological behavior of tungsten-doped DLC coating under oil lubrication

Diamond-like carbon (DLC) protective films have received considerable attention in recent years. Beside tools and dies, diamond-like and related coatings are starting to find application in some highly stressed mechanical components, including bearings and gears. Several different gear tests show an increase in carrying load capacity or prolonged lifetime with tungsten carbide-doped DLC (W-DLC)-coated gears. The lubricants have been mostly commercially available gear oils that were primarily developed or tailored for ferrous materials and are probably far from optimal for amorphous W-DLC layers.In the present work, the influence of lubricant chemistry on the friction and wear in W-DLC-coated contacts was investigated using a reciprocating test device. The first six test lubricants were conventional non-inhibited API/ATIEL base stocks followed by selected test blends in combination with different surface-active single additives. Experimental results in coated contact have shown that for friction reduction performance, additives are not necessary, while wear resistance is related with the chemistry of the lubricant. It may be concluded at this stage that different mechanisms of friction-induced interaction between lubricants and W-DLC-coated layers are possible.     

Development of the technique of laser diagnostics of solids under pulsed optical irradiation

A technique based on the recording of a Fraunhofer diffraction pattern and allowing studies of structural and phase transitions in an ion-implantion-doped semiconductor layer with a high time resolution simultaneously with sample-temperature measurements is described. For this purpose, two measuring diffraction gratings—phase and amplitude—are preliminarily formed on the surface of a silicon plate. Solid-phase recrystallization and melting processes were studied using the kinetics of disappearance and appearance of diffraction peaks from the amplitude grating. The sample temperature was monitored by the deviation of the diffraction angle of a probing laser beam from the phase diffraction grating caused by a change in the grating period resulting from its thermal expansion.     

Diffractometry of wire-drawing dies with local flaws

The problem of measurement of flaw dimensions in diamond wire-drawing dies is discussed. An analytical expression for the modulation depth of diffraction rings as a function of the flaw dimension is given, and analytical calculations are compared to numerical calculations for various types of flaws. Changes in the symmetry of the diffraction pattern due to a local flaw on the hole surface are described.     

Detection of internal flaws in highly refractive crystals with the help of a holographic microscope

Feasibility of contactless investigations of internal structure of transparent crystals with high refraction indices, in particular, diamonds, using the technique of scanning a real reconstructed image of an object has been studied. Investigations were performed using an in-house designed small holographic interference microscope.     

Wear resistance of coating materials under the frictional heating conditions

The problem of the wear of an elastic coating due to a rigid body sliding over the coating surface and heating due to contact friction has been considered. The solution of the quasi-static problem has been constructed in the form of a series over eigenvalues. The area of unstable solutions of the problem, where the thermoelastic instability of a sliding contact takes place, has been determined in the dimensionless parameter space. The wear resistance of a coating has been studied for different kinds of materials depending on the following parameters: the relative sliding velocity of contact surfaces, the mode of the contact interaction of the friction surfaces, the coating thickness, etc. taking into account the temperature and stresses developing at the contact interface.