Gifford-McMahon cycle — a theoretical analysis

A theoretical analysis of the Gifford-McMahon cycle is presented. Expressions for the ideal refrigeration produced and the figure of merit are developed. Various losses occurring in a real machine are considered and equations to account for these losses are derived. Results are presented in graphical form.     

Transient analysis of the DSIFs and dynamic T-stress for particulate composite materials—Numerical vs. experimental results

The fracture behavior of particulate composite materials when subjected to dynamic loading has been a great concern for many industrial applications as these materials are particularly susceptible to impact loading conditions. As a result, many numerical and experimental techniques have been developed to deal with this class of problems. In this work, the fracture behavior of particulate composites under impact loading conditions is numerically studied via the two most important fracture parameters: dynamic stress intensity factors (DSIFs) and dynamic T-stress (DTS), and the results are compared with the experimental data obtained in Refs. [1,2]. Here, micromechanics models (self-consistent, Mori–Tanaka, …) or experimental techniques need to be employed first to determine the effective material properties of particulate composites. Then, the symmetric-Galerkin boundary element method for elastodynamics in the Fourier-space frequency domain is used in conjunction with displacement correlation technique to evaluate the DSIFs and stress correlation technique to determine the DTS. To obtain transient responses of the fracture parameters, fast Fourier transform (FFT) and inverse FFT are subsequently used to convert the DSIFs and DTS from the frequency domain to the time domain. Test examples involving free–free beams made of particulate composites are considered in this study. The numerical results are found to agree very well with the experimental ones.     

Process capability analysis—a robustness study

The robustness of two popular process capability ratios, C_p and C_pk, when the random process being observed departs from normality is analysed. The distributions of estimated process capability ratios are derived and used as a basis for validation of large-scale simulation studies in an examination of departures from normality. The simulation studies and analytical results provide a basis for recommended procedures. It is recommended that the impact of process distributions be considered before using popular process capability indexes, due to the lack of robustness when departures from normality are ecountered. As an extension of our findings, we consider the Taguchi loss function as a generalization to process capability analysis regardless of the underlying population distribution.     

Patent analysis using online databases—I. Technological trend analysis

Patent analysis has been the subject of academic interest for some thirty years or more, because of its potential as an econometric measure. For industrial information units, which lack the manpower to carry out the extensive and time-consuming calculations involved, it can nevertheless be a valuable aid to decision-making in such areas as acquisitions and divestitures, R&D planning and new product development. Access to online patents databases and simple analytical software allows the information specialist to obtain measures of technological and competitive activity which, if not always statistically verifiable, may help focus attention on underlying trends. This paper lists a number of suitable techniques, accompanied by examples, which may be used to study technological trends. A second paper will be devoted to competitor activity monitoring.     

Failure analysis of adhesively-bonded skin-to-stiffener joints: Metal–metal vs. composite–metal

The purpose of this research is to evaluate the performance of two adhesively bonded skin-to-stiffener connections: composite stiffener bonded to a Fiber Metal Laminate (FML) skin, representing a hybrid joint, and an Aluminium stiffener bonded to a FML skin, representative for a metal joint. The bonded joints were tested using Stiffener Pull-Off Tests (SPOT), which is a typical set-up used to simulate the structural behavior of full-scale components subject to out-of-plane loading, such as internal pressure of a fuselage or leading edge low pressure zone. In the hybrid joint, the damage initiates at the central noodle of the composite stiffener. Unstable delamination then propagates from the noodle to the tip of the stiffener foot, preferably through the stiffener foot plies (>90% of inter/intra-laminar failure) and, in limited areas, through the adhesive bond line (<10% of cohesive failure). In the metal joint, the failure starts at the tip of the stiffener foot at the adhesive bond line. Unstable debonding then propagates along the stiffeners foot. The complete failure occurs in the adhesive bond line (100% cohesive failure). The loads associated with >90% of inter/intra laminar failure of the composite stiffener (hybrid joint) are 40–60% lower than the ones associated with 100% cohesive failure (metal joint). This research identifies that in order to use the full capacity of adhesively bonded hybrid joints, the adhesion between carbon fibers of the composite laminate, ie intralaminar strength, must be improved. Otherwise, Aluminium stringers are still very competitive.     

(Y vs. X) or (log Y vs. X)?

The problem of choosing between the models Y = α + βX and log Y = α + βX is considered. The maximum likelihood method of Box and Cox is compared with the method of using correlation coefficients to make the choice between the two models. The methods are applied to some data from the field of metallurgy. Operating characteristics of the two methods are estimated by simulation. Over a wide range of parameters there is not much difference between the two methods, although there are parameter values for which the correlation method appears markedly inferior to the likelihood method. The likelihood method seems preferable in that it is based on a probability model; this enables the statistician to make a confidence statement about the choice of model.     

Exploration–exploitation trade-off features a saltatory search behaviour

Searching experiments conducted in different virtual environments over a gender-balanced group of people revealed a gender irrelevant scale-free spread of searching activity on large spatio-temporal scales. We have suggested and solved analytically a simple statistical model of the coherent-noise type describing the exploration–exploitation trade-off in humans (‘should I stay’ or ‘should I go’). The model exhibits a variety of saltatory behaviours, ranging from Lévy flights occurring under uncertainty to Brownian walks performed by a treasure hunter confident of the eventual success.     

外包vs.自主研发方案

金属涂层技术让干散固料处理行业的领导者保持领先优势     

Safety analysis in design—Evaluation of a case study

Safety analysis was applied in the design of a section at a paper mill. The case study involved analysis of layout, transport system, machines, and a number of different activities. The purpose of the analysis was to find measures to decrease occupational accidents. Three years after the installation was finished the occurrence of accidents was investigated. There was a 56% decrease in the number of accidents; the number of working days lost due to accidents was diminished by 75% as compared to 4 years preceding. The results of the safety analysis were also evaluated with respect to the accidents which had occurred. The methods for safety analysis seem to have been efficient in identifying hazards. The general conclusion of the study is that safety analysis can be an effective tool to decrease occupational accident risks.     

Application of a dynamic numerical solution to high speed fracture experiments—I. analysis of experimental geometries

The application of a dynamic, generation mode, finite element program to the analysis of experimental geometries is reported. Particular attention is given to the DCB specimen, which is widely used in high speed fracture studies despite strong inertia effects, which are described. Finite strip and infinite plate results are also considered. Here, idealised cases are discussed, while in Part II the application of the analysis to experimental measurements, to derive propagating crack fracture resistance data, is reported.     

Patent analysis using online databases — II. Competitor activity monitoring

Patent analysis has been the subject of academic interest for some 30 years or more, because of its potential as an econometric measure. For industrial information units, which lack the manpower to carry out the extensive and time-consuming calculations involved, it can nevertheless be a valuable aid to decision-making in such areas as acquisitions and divestitures, R&D planning and new product development. Access to online patents databases and simple analytical software allows the information specialist to obtain measures of technological and competitive activity which, if not always statistically verifiable, may help focus attention on underlying trends.This is the second of two papers on the subject, listing techniques, accompanied by examples, which may be used for competitor activity monitoring. Technological trend analysis was covered in the previous paper (part I, World Patent Information Vol. 9, No. 1).     

Mechanics of crack curving and branching — a dynamic fracture analysis

A comparative study on crack curving and branching criteria in dynamic fracture mechanics shows that the criteria based on advanced cracking concept correlated best with available experimental data. The crack branching criterion requires as a necessary condition, a critical dynamic stress intensity factor, K _Ib, and a sufficient condition involving the crack curving criterion. The criteria are used to predict crack curving and crack branching in dynamic photoelastic experiments involving Homalite-100 and polycarbonate fracture specimens, as well as bursting steel and aluminum pipes.

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Résumé Une étude comparative sur les eritères d'incurvation et d'arborescence d'une fissure en mécanique de rupture dynamique montre qu'un critère basé sur le concept de fissuration avancée présente la meilleure corrélation avec les données expérimentales disponibles. Le critère d'arborescence d'une fissure requiert comme condition nécessaire un facteur d'intensité de contrainte dynamique critique, K _Ib, et comme condition suffisante un critère tenant compte de l'incurvation de la fissure. Les critères sont utilisés pour prédire l'incurvation et l'arborescence d'une fissure au cours d'expériences photo-élastiques en condition dynamique mettant en oeuvre de l'Homalite 100 et du polycarbonate ainsi que des tubes d'acier et d'aluminium en cours d'explosion.

     

Fracture mechanics as a tool in failure analysis — Prospects and limitations

Although fatigue crack propagation and fracture cause a large part of failure events in industrial practice, fracture mechanics in failure analysis seems to be still a side issue. Starting from an introduction into important basic questions of failure analysis and fracture mechanics, the authors specify what kind of questions in failure analysis can be effectively solved by fracture mechanics (and which can't). They illustrate their discussion with a number of 13 case studies from the literature. Much more pronounced than in the design stage the benefit of fracture mechanics in failure analysis depends on its accuracy. This is limited by both, intrinsic factors of the method and the availability and quality of the input information. The authors discuss the various aspects and provide the reader with some background information which, as they believe, will be helpful for better understanding the prospects and limitations of fracture mechanics in failure analysis and the conditions of its application.     

二维Kaplan—Meier估计a.s.一致收敛速度

设(T_(11),T_(21)),…,(T_(1n),T_(2n))和(Y_(11),Y_(21)),…,(Y_(1n),Y_(2n))都是i.i.d.的非负r.v.F(s,t)=P(T_(11)>s,T_(21)>t)和G(s,t)=P(Y_(11)>s,T_(21)>t)都是未知的连续函数.文[3]给出了基于观察Z_(if),=min(T_(if),T_(if))和δ_(if)=I(T_(if)≤Y_(if)),i=1,2,i=1,…,n估计F的二维Kaplan-Meier估计_n.本文在一定条件下证明了_n a.s.一致收敛于F的速度为,即     

Shadowing vs. distality for actions of ℝ n

This article introduces the notion of weakly parametrized (wp) shadowing for actions of groups ? ^m ?×?? ⁿ , where m,?n?≥?0 and m?+?n?>?0. The possibility of coexistence of distality and shadowing for actions of ? ⁿ is discussed. It is proven that an equicontinuous action of ? ⁿ on a compact connected space possessing wp-shadowing is actually minimal. Moreover, distal real flows (?-actions) on one-dimensional compact metric spaces are characterized as constant-one suspensions over adding machines.     

Effects of kanban withdrawal policies and other factors on the performance of JIT systems—a simulation study

This paper presents the results of a simulation study of a just–in–time (JIT) production control system and its performance under different operational conditions. In particular, the effects of two different kanban withdrawal policies on such performance measures as throughput rate, station utilizations and total work in process levels are investigated. Also, simulation experiments are carried out to determine the effects of processing time variability, number of different types of kanbans allowed at each station and production line length on the mentioned performance measures of JIT production control method. The simulation experiments were carried out for production lines in which processing times of stations were assumed to follow gamma and Erlang distributions.     

Failure of planetary pinions in earth moving equipment—a failure analysis approach

A series of failures of planetary pinions occurred in the final drive epicyclic gearbox of large trucks used in underground mining. A metallurgical analysis indicated that failure had occurred by internal rupture of the gear. This was attributed to poor heat treatment procedures used in case hardening the gear. This had induced high residual stresses just below the case/core interface, leading to the internal rupture of the gear.     

Hybrids — a review: Part 2. Physical properties

The second section of a review, commenced in the previous issue, is presented, covering the subject of carbon fibre and glass fibre hybrid reinforced plastics (cghrp). The existence of a ‘hybrid effect’ is still the subject of some controversy, although a negative synergism has been reported in fracture at high interdispersion of the two fibres. Some attempts to quantify the residual thermal stresses from curing have been made, but these do not correlate well with the observed hybrid effect. A discrete burst of acoustic emission has been reported on the transfer of load to the glass fibres, coincident with the load drop associated with failure of the carbon fibres. The conclusions of the previous review would appear to be still valid. An outline of the areas of ignorance is included.