Showing papers by "Beihang University published in 1994"

Study on the drill skidding motion in ultrasonic vibration microdrilling

Abstract: In this paper, a new axial ultrasonic vibration microdrilling technology has been developed which restrains the skidding motion of miniature drills at the beginning of penetration. The causes and mechanisms of the initial skidding motion of the drill in conventional drilling have been analyzed. The mechanisms of intermittent cutting and initial penetration of the chisel edge, and the dynamic stability of the drilling machine have been investigated analytically. An experimental study on the influence of the amplitude of ultrasonic vibration on the radial deflection of drill point at the start of drilling and its effect on hole accuracy and drill life have been conducted. Finally a new variable amplitude vibration drilling method is presented.

Effect of the Interfacial Interleaf to the Interlaminar Fracture and Intralaminar Fracture of a New BMI Matrix Composites System

Abstract: Systematic studies were conducted to investigate the effect of the introduc tion of a soft thermoset adhesive layer at appropriate interface to the interlaminar fracture and intralaminar fracture o...

A Logical Framework for Evolution of Specifications

Abstract: A logical framework of software evolution is built The concepts of sequence of specifications and the limit of a sequence are established Some concepts used in the development of specifications, such as new laws, user's rejections, and reconstructions of a specification are defined; the related theorems are proved A procedure is given using transition systems It generates sequences of specifications from a given user's model and an initial specification It is proved that all sequences produced by the procedure are convergent, and their limit is the truth of the model Some computational aspects of reconstructions are studied; an R-calculus is given to deduce a reconstruction when a specification meets a rejection An editor called Specreviser is introduced It is used to develop specifications The main functions of the editor are given; some techniques used in its implementation are also discussed Finally, the theory is compared with AGM's theory of belief revision

An expenditure‐based bilateral comparison of gross domestic product between china and the united states

Abstract: This paper presents a detailed bilateral comparison of GDP between China and the U.S. with 1986 as a reference date, using the purchasing power parity (PPP) approach formulated by the United Nations International Comparison Program (ICP). An estimate of PPP over GDP made for Chinese currency in this study was used t o estimate China's dollar per capita GDP in 1986 and 1991. The specific issues in the comparisons of the housing and the comparison-resistant services categories were discussed and an approach similar to the estimation of shadow rent was exercised. The possible errors in the bilateral comparison were analyzed.

Fracture toughness of single crystal alumina in air and a simulated body environment

Abstract: The critical intensity factor KIC of a single crystal alumina (1100)-plane in air and in a simulated body environment was measured. Based on these measurements, the estimated durability of a single crystal alumina disk in a ceramic heart valve was determined. Standard single-edge notched beam specimens were prepared. The specimens were classified into three groups: (a) stored in air (n = 10), (b) immersed in Ringer's solution for 2 months (n = 11), and (c) immersed in Ringer' solution for 4 months (n = 6). KIC was 2.345 ± 0.072 MPam½ for specimens stored in air, 2.141 ± 0.147 in Ringer's solution for 2 months, and 2.005 ± 0.153 in Ringer's solution for 4 months. The KIC decreased for specimens stored in Ringer's solution (P < .01), but it did not differ significantly between 2 and 4 months. The decrease of KIC is the stress corrosion effect of Ringer's solution at the crack tip, and is not associated with an over all deterioration of strength. The stress intensity factor for possible cracks (length: 0.4 mm) in the single crystal alumina was calculated. Maximum stress was assumed 2.668 MPa ( = 40 × 500 mm Hg). The stress intensity factor calculated was far less than the KIC. The single crystal alumina disk can endure a static pressure of 500 mm Hg. © 1994 John Wiley & Sons, Inc.

Global well-posedness of the initial value problem for the Hirota-Satsuma system

Abstract: This paper discusses the global well-posedness of the initial value problem for a mathematical model proposed by Hirota and Satsuma. In order to derive the global well-posedness we employ Kato's theory for abstract evolution equations together with some delicate a priori estimates obtained by using harmonic analysis techniques.

Preparation of Metal-Coated Carbon Fiber Reinforced Composites and Their Electromagnetic Properties

Abstract: Medium temperature curing by infrared radiation was used to prepare electromagnetic wave absorbing multilayered plastic matrix composite materials containing metal-coated carbon fibers (MCFs). The electromagnetic properties of the materials were investigated by frequency scanning tests with microwave vector network analyzer. It is found that the electromagnetic parameters, mainly permittivity of the composites increase significantly with the addition of MCFs, which gives the composites good designability as thin, light-weight EM wave absorbers. It is also shown that MCFs can improve on the EM wave energy attenuating property of the composites by widening the work frequency band width and raising the absorptive peak

Simulators as a tool for rapid manufacturing simulation

Abstract: This paper discusses the use of two simulators for the design and analysis of manufacturing modules. Included in the paper is a brief discussion of the simulators, the application of the simulators in solving a real world problem, and the lessons learned in using simulators.

Chirp scaling algorithm for processing SAR data with high squint angle and motion error

Abstract: This paper proposes a modified chirp scaling algorithm which is suitable for the processing of highly squinted data with motion errors. By means of azimuth subaperture processing with extended spectral length, the vanations of the Doppler centroid in range and azimuth can be accommodated without using block processing with overlap. The new approach, denoted as extended chirp scaling (ECS), is considered to be a generalized algonthm suitable for the high resolution processing of most airborne SAR systems.

Sloshing dynamics modulated cryogenic helium fluids driven by gravity gradient or jitter accelerations associated with slew motion in microgravity

Abstract: The mathematical formulation of the Dewar container sloshing dynamics for a partially filled liquid of cryogenic superfluid helium II driven by the gravity gradient or jitter accelerations associated with slew motion in a microgravity environment are studied. The numerical computation of sloshing dynamics is based on the non-inertia container bounded frame and the solution of time-dependent, three-dimensional partial differential equations subjected to the initial and boundary conditions. This study discloses that the capillary effect of sloshing dynamics governs the liquid-vapor interface fluctuations driven by the gravity gradient or jitter accelerations associated with slew motion in a microgravity environment. The peculiar behavior of superfluid helium in response to sloshing dynamics is also investigated.

The feasibility study of the waste heat air-conditioning system for automobile

Abstract: In this paper, the feasibility of application of a solid-absorption system using ammonia and chlorides as working pair to automobile air-conditioning system is investigated. This system has the advantages of minimum environmental problem and utilizing waste heat from the automobile engine as thermal energy input. Analyses show that the main problem associated with the application of solid-absorption system is the size of the reactors. Techniques to solve this problem are discussed.

Stochastic analysis of fatigue crack growth for metallic structures

Abstract: In order to estimate the statistical variability of fatigue crack growth in metallic structures, a stochastic model is proposed by combining stochastic theory with experimental results. A stochastic differential equation is derived from the stochastic model for fatigue crack growth. By using the solution of the stochastic differential equation, some distribution functions related to fatigue crack growth were derived. Sample functions of fatigue crack growth time histories have been simulated as random processes.

A Note on Tableaux of Logic of Paradox

Abstract: The logic of paradox LP proposed by Priest [1979] is one of paraconsistent logics. One of the motivations behind paraconsistent logic, namely LP, is that it should not be the case that everything follows from a single contradiction. It must pay a price, however, that some classical inferences would be invalid in LP. In Priest's recent invention, the logic of minimal paradox LPm can overcome the drawback, such that paraconsistent logic would be equivalent to classical logic when there is not direct effect of a contradiction. Although some proof theories for LP were introduced, there has not yet been a satisfactory proof theory for LPm. We will propose a sound and complete tableaux for LPm in this article.

Numerical Analysis for Design of Composite Specimens for Through-the-Thickness Tensile Measurements

Abstract: The research reported in this paper was motivated by the need for measuring through-the-thickness tensile properties of composite panels. Such measurements are especially necessary for three-dimensional textile structural composites, in which the rein-forcement effect in the thickness direction is significant. A multi-section specimen design which includes gauge section, transition section and grip section is proposed. The two-dimensional boundary element technique has been adopted for analyzing the characteristics of the stress distribution in the specimen. A general singular boundary element with arbitrary order of the stress singularity has been formulated. Verification studies show good accuracy of the analytical method. The geometric and material factors affecting the stress distribution and stress singularity have been identified. Finally, recommendations have been made for multi-section specimen design in achieving high uniformity of stress distribution within the gauge section and low intensity of...

Mode II delamination behavior of carbon/epoxy composites

Abstract: The end-notched flexure (ENF) test was employed in an investigation of the interlaminar fracture behavior in mode II static and fatigue loading for carbon/epoxy composites T300/M10 and HTA/6376. The mode II interlaminar fracture toughness was determined by a compliance calibration method. The tests were performed in the range of the a/L ratio from 0.5 to 0.9. Both composites, T300/M10 and HTA/6376, exhibited brittle unstable and brittle stable behavior of crack growth. Stable mode II crack growth was observed during fatigue loading with R = 0.1 in a large range of cyclic strain energy release rate. A consistent relation of the crack growth rate to the cyclic strain energy release rate was obtained for both T300/M10 and HTA/6376 composites. Within the range of moderate crack growth rate, the data of mode II fatigue crack growth for the composites obeyed a power law. The trend of reduction in the crack growth rate data with degradation in the cyclic strain energy release rate suggests the presence of a thre...

Vibration Control of a Rotor System Utilizing a Bearing Housing With Controllable Spring Nonlinearity

Abstract: On the basis of characteristics of vibration in the rotor system with spring nonlinearity, a new method for vibration control has been developed. In the method, the spring characteristics of a bearing housing are controlled to be of softening nonlinearity when the rotor supported on it is accelerated and to be of hardening one when it is decelerated. So vibratory amplitudes of the rotor system always vary along the smallest solution curve in the whole operating process. A model of vibration of the rotor system supported on the controllable hearing housing is derived. Its dynamic behaviour is predicted and verified by experiments. Both theoretical and experimental results show that not only vibratory amplitudes and transmitted forces are suppressed significantly but also nonlinear vibration performance of the rotor supported on squeeze film dampers, such as “lock up” at rotor pin-pin critical speeds and asynchronous vibration, can be avoided.Copyright © 1994 by ASME

Tempering rapidly solidified ductile cast iron by pulsed laser beam reprocessing

Abstract: During laser surface rapid remelting of cast irons, the melt pool solidifies rapidly and metastably (i.e. according to the metastable Fe-Fe[sub 3]C system) producing an ultra-fine ledeburite hard surface which is much more abrasion resistant than the original substrate. Previous literature mainly focused on remelting various grey and ductile irons with high power CO[sub 2] lasers for improved wear resistance and other surface properties, and on studying the physical metallurgy of laser remelted surfaces. Unfortunately, the unstable nature and rapid tempering behavior of the rapidly solidified ledeburite were generally neglected, although some publications mentioned the tempering phenomenon during successive overlap remelting. In this paper, a laser remelted ductile case iron surface was tempered by rapid pulsed laser beam reprocessing. The rapidly solidified ductile iron was found to be rapidly graphitized, as a result, a layer of Fe-base alloy containing ultra-fine graphite particles was produced. The unusual rapid graphitization phenomenon was preliminarily discussed.

Stability of lamellar structure in a Ti-47.8at%Al alloy

Abstract: The stability of the lamellar structure is known to be highly structure sensitive. Although some reports have investigated the stability of lamellae in lower aluminum content alloys, few reports have studied the stability of lamellae in near gamma titanium aluminide alloys. The purpose of this paper is to investigate the stability of lamellar structure with different features in Ti-47.8at%Al alloy. The following conclusions were reached: (1) A lamellar structure was obtained in furnace cooled (FC), air cooled (AC) and oil quenched (OQ) samples. As the cooling rate increased, the interlamellar spacing decreased. Thus, the stability of lamellae decreased. The coarsening rate increased with increasing temperature. (2) An {alpha}{sup 2} single phase was obtained in the water quenched (WQ) samples. The lamellae transformed from the {alpha}{sub 2} phase are less stable, and hence have a faster coarsening rate and finer coarse structure compared with the lamellar formed during cooling. (3) Since coarse lamellae nucleate in the {alpha}{sub 2} and {gamma} matrices, more than one habit plane exists, so that the alignment of coarse lamellae is complex. Parallel coarse lamellae with same close-packed plane index form a packet.

Modal Analysis of Blades With Densely Distributed Small Holes

Abstract: At present, when numerical methods are used to analyze the dynamic characteristics of blades with densely distributed small holes, it is difficult to consider the influence of small holes accurately. A new method is presented regarding air-cooled turbine rotor blades of gas turbine engines. To investigate the topic, a series of experimental rules are simulated effectively by theoretical formulae. The method is developed by combining the experimental results and finite element analysis. To include the effects of small holes on dynamic behaviors of blades, the equivalent concept is employed. In a generalized eigen-equation, the modified stiffness matrix and mass matrix are used to perform an accurate modal analysis of the blades. When making comparison between the analytical results obtained by using the method of this paper and the experimental data, a good agreement is seen. Accuracy, reliability, and practicality of the method presented in this paper are verified.Copyright © 1994 by ASME

Formalizing computational river networks

Abstract: We present a simple framework, called computational network, for formalizing river networks to provide a computer-based solution to problems of simulating concentrations of water quality constituents in river networks. The method was applied on a river network in Beijing-Tianjin area. The framework is developed by an object-oriented approach integrating the modelling of the static structure of river networks with that of the dynamic behavior of water quality constituents in them. Similar to artificial neural networks, computational networks can be used for learning, problem solving and controlling.

Bifurcation analysis of absorption and reflection effects in electromagnetic wave absorbing composites with multi-layered structure

Abstract: Static bifurcation of electromagnetic wave transmission differential equation for multilayered structural composite materials has been studied to explain the transformation effect of absorption and reflection. Experimental result is given to illustrate the absorption and reflection transformation caused by variation of inherent impedance of the composite.

Damage Tolerance Analysis of Compressor Blade

Abstract: In this paper, we apply damage tolerance analysis to a certain compressor blade by finite element and fracture mechanics methods. The blade is analysed by using the isoparametric finite element with 20 nodes, its stress and displacement fields are determined, and the critical position where the crack probably initiates is located. Then the value of J–integral with different crack sizes in the critical position are computed using the 3-D J-integral program. On the basis of the fracture toughness of blade material, Je, the blade extension limit δe, and the deviation of natural frequency, Δfe, the failure criterion of the blade is discussed and the critical crack size, ae, is determined. Then according to the crack growth rate obtained from the testing, the residual life of the blade with different crack sizes is evaluated. The maximum allowable crack size, a0*, is determined using the condition that the crack would not grow to critical crack size during double overhaul periods. This value can be used to design the structure of compressor blade or to establish the criterion to judge whether a compressor blade with a crack can be used. In this way the safety and reliability of airplanes is maintained and the costs are reduced. So the damage tolerance analysis of compressor blades is practical and economical.Copyright © 1994 by ASME