Multiscale aggregating discontinuities method for micro–macro failure of composites

The application of a multiscale method, called the multiscale aggregating discontinuities (MAD) method, to the failure analysis of composites is described. Two distinct features of the MAD method are the use of perforated unit cells, and the extraction of coarse-grained failure information. In the perforated unit cell, all subdomains of the unit cell that are not strictly elliptic are excluded, which enables the decomposition of its stable and unstable material. By means of these concepts, it is possible to compute an equivalent discontinuity at the macroscale, including both the direction and the magnitude of the discontinuity. This equivalent discontinuity is then passed to the macroscale along with the computed stress from the unit cell. The macroscale discontinuity is injected into the macro model by the extended finite element method (XFEM) procedure. In this paper, the method is improved by adding hourglass modes to the unit cell deformations, which better model growing cracks. Several examples comparing the MAD method with direct numerical simulations are presented.     

Dynamic analysis of bridge–vehicle system with uncertainties based on the finite element model

A new method of dynamic analysis on the bridge–vehicle interaction problem considering uncertainties is proposed in this paper. The bridge is modeled as a simply supported Euler–Bernoulli beam with Gaussian random elastic modulus and mass density of material with moving forces on top. These forces are time varying with a coefficient of variation at each time instance and they are considered as Gaussian random processes. The mathematical model of the bridge–vehicle system is established based on the finite element model in which the Gaussian random processes are represented by the Karhunen–Loéve expansion and the equations will be solved by the Newmark  -β$\beta$ method. The proposed method is compared with the Monte Carlo method in numerical simulations with good agreements for cases with different vehicle speed and level of uncertainties in the excitation and system parameters. The mean value and variance of the structural responses are found to be very accurate even with large uncertainties in the excitation forces. The proposed method is also found to have superior performance in the computational efficiency compared with the Monte Carlo method.     

Cost–volume–profit analysis under uncertainty: a model with fuzzy estimators based on confidence intervals

In this paper we express the uncertainty existing in cost–volume–profit analysis via a new method that constructs fuzzy estimators for the parameters of a given probability distribution function using statistical data. First we present a fuzzy function for the cost and we search for the optimal solution among alternatives as Finch and Gavirneni [2006, International Journal of Production Research, 44 (20), 4329–4342] do, but here we use fuzzy estimators for the variable costs. As a consequence, we formulate a fuzzy number that represents the difference between the costs of the alternatives. Furthermore, we consider conditions of ‘complete’ uncertainty when a company needs to choose between two products and we express the profits and the risk via fuzzy estimators. Finally, under the same conditions of uncertainty we express the breakeven point when the income equals the total cost.     

Product low-carbon innovative design based on the carbon footprint information model北大核心CSCD

Aiming at further alleviating global warming and reducing carbon emission in product life cycle from source, low-carbon design has increasingly becoming an important direction of product design. Based on exploring the composition of decision making information and corresponding choice of design strategy in low-carbon design process, a carbon emission integrated product low-carbon design information model was established. Based on the analysis of information connotation within low-carbon design decision making, a double progressive positioning method of carbon footprint source features which was based on product structural tree and detailed design parameters was proposed, in which streamlined life cycle assessment (SLCA) using qualitative/semi-quantitative matrix approach was used to preliminarily screen the key structural units with high emission, then the key design features and parameters were stepwisely positioned by weight assigned relation digraph. With regard to design parameters related conflicts, TRIZ conflict resolution theory was used. Finally, a handled vacuum cleaner was used as an example to prove the feasibility and effectiveness of the method.     

On two micromechanics theories for determining micro–macro relations in heterogeneous solids

The average-field theory and the homogenization theory are briefly reviewed and compared. These theories are often used to determine the effective moduli of heterogeneous materials from their microscopic structure in such a manner that boundary-value problems for the macroscopic response can be formulated. While these two theories are based on different modeling concepts, it is shown that they can yield essentially the same effective moduli and boundary-value problems. A hybrid micromechanics theory is proposed in view of this correspondence. This theory leads to a more accurate computation of the effective moduli, and applies to a broader class of microstructural models. Hence, the resulting macroscopic boundary-value problem gives better estimates of the macroscopic response of the material. In particular, the hybrid theory can account for the effects of the macrostrain gradient on the macrostress in a natural manner.     

Evolving collaboration networks in Scientometrics in 1978–2010: a micro–macro analysis

This paper reports first results on the interplay of different levels of the science system. Specifically, we would like to understand if and how collaborations at the author (micro) level impact collaboration patterns among institutions (meso) and countries (macro). All 2,541 papers (articles, proceedings papers, and reviews) published in the international journal Scientometrics from 1978–2010 are analyzed and visualized across the different levels and the evolving collaboration networks are animated over time. Studying the three levels in isolation we gain a number of insights: (1) USA, Belgium, and England dominated the publications in Scientometrics throughout the 33-year period, while the Netherlands and Spain were the subdominant countries; (2) the number of institutions and authors increased over time, yet the average number of papers per institution grew slowly and the average number of papers per author decreased in recent years; (3) a few key institutions, including Univ Sussex, KHBO, Katholieke Univ Leuven, Hungarian Acad Sci, and Leiden Univ, have a high centrality and betweenness, acting as gatekeepers in the collaboration network; (4) early key authors (Lancaster FW, Braun T, Courtial JP, Narin F, or VanRaan AFJ) have been replaced by current prolific authors (such as Rousseau R or Moed HF). Comparing results across the three levels reveals that results from one level might propagate to the next level, e.g., top rankings of a few key single authors can not only have a major impact on the ranking of their institution but also lead to a dominance of their country at the country level; movement of prolific authors among institutions can lead to major structural changes in the institution networks. To our knowledge, this is the most comprehensive and the only multi-level study of Scientometrics conducted to date.     

Micro–macro homogenization of granular materials based on the average-field theory of Cosserat continuum

This paper performs further study on the micro–macro homogenization approach of granular materials (Li et al., 2010) based on the advancement of Hill’s lemma for Cosserat continuum (Liu, 2013). Firstly, the average couple stress tensor, expressed as the volume integration of quantities over the representative volume element (RVE) in the average-field theory of Cosserat continuum, is further deduced and expressed in terms of discrete quantities on the discrete particle assembly RVE of granular materials. The expression is also discussed and compared with other typical definitions of the effective couple stress tensor for granular materials in the literature. Then, rate forms of micromechanically based constitutive models consistent with different types of RVE boundary conditions are derived and discussed. Since the presented micro–macro homogenization approach is used, not only the micro–macro energy equivalence is satisfied, but also the microstructure and its evolution can be taken into account in the constitutive formulation with no need of specifying macroscopic phenomenological constitutive model.     

Effect of cannibalism on a predator–prey system with nutritional value: a model based study

Enrichment of a simple predator–prey system results in the destruction of stable steady state and further enrichment leads to the extinction of the species, which is a classical problem in ecology and known as the paradox of enrichment. The Paradox of enrichment is a controversial issue. Most theoretical studies show the destabilization of predator–prey system due to enrichment, but there is a discrepancy between the empirical evidence and theoretical predictions. In spite of the debate and cross-debate, research is still being carried out on the paradox of enrichment (16 papers and nearly 500 citations in 2008), which in general does not include the effect of cannibalism. Here we present a simple predator–prey system in the presence of cannibalism among predators and offer a novel resolution to the paradox of enrichment. The concept of nutritional value is introduced by many authors to resolve the issue. It is observed that even in the face of sufficient enrichment the system remains stable in the vicinity of critical nutritional value. In the case of a lower cannibalism rate we also observe similar kinds of behaviour, but for a higher cannibalism rate, the system remains always stable and does not depend upon the nutritional value of prey, i.e. paradox of enrichment does not hold at all in such a situation. We also observe that cannibalism can have a positive as well as a negative effect on population abundance, depending on the cannibalism rate.     

An investigation on electroless Cu–P composite coatings with micro and nano-SiC particles

Cu–P/micro-SiC and Cu–P/nano-SiC composite coatings were deposited by electroless plating and their composition and microstructure were observed by EDX (energy-dispersive analysis), SEM (scanning electron microscope) and XRD (X-ray diffraction). The corrosion resistance, microhardness and the wear resistance of the Cu–P/nano-SiC composite coatings were measured and the comparison with those of Cu coatings and Cu–P/micro-SiC coatings were given. The anti-corrosion properties of Cu coatings were investigated in 3.5% NaCl solution by the potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. Among three kinds of Cu–P based coatings, the corrosion resistance, hardness and wear resistance of Cu–P/nano-SiC coatings were the largest. This indicates that the precipitation of nano-SiC particles would improve the corrosion resistance, hardness and wear resistance of the Cu–P coatings significantly.     

Study of hydrodynamic characteristics of particles in liquid–solid fluidized bed with modified drag model based on EMMS

Flow behavior of solid phases is simulated by means of Eulerian–Eulerian in a liquid–solid fluidized bed with modified drag model based on energy-minimization multi-scale (EMMS) method. The modified EMMS drag coefficient is characterized by the treatment of the particle-rich dense phase and the liquid-rich dilute phase as the two interpenetrating continua. It was shown that the modified EMMS drag coefficient can predict reasonably the solid concentration profiles in a liquid–solid fluidized bed. The distributions of solid velocity, granular temperature and granular pressure are predicted. The phenomenon of back-mixing near the wall is found in the liquid–solids fluidized beds.     

A weighted min–max model for balanced freight train routing problem with fuzzy information

A multi-objective freight train routing problem with fuzzy information is investigated in this article. To handle the fuzziness in the railway transportation system, the measure ?_λ (i.e. the convex combination of a possibility measure and a necessity measure) is first introduced. Then, a min–max chance-constrained programming model is constructed to obtain optimal train routing plans. In order to solve the model, a potential route algorithm, fuzzy simulation and tabu search algorithm are integrated as a hybrid algorithm. Finally, some numerical experiments are performed to show the applications of the model and the algorithm.     

Controlling information access in workflow management systems using RBAC‐based model

Abstract

We developed an RBAC‐based model RBAC/WF (RBAC‐based workflow information access control) to control information access in workflow management systems. Primary features offered by the model are preventing workflow information leakage and adapting to dynamic role association change. This paper presents RBAC/ WF and proves that the model offers the mentioned features.     

Analysis of water drop erosion on turbine blades based on a nonlinear liquid–solid impact model

Water drop erosion is regarded as one of the most serious reliability concerns in the wet steam stage of a steam turbine. One of the most challenging aspects of this problem involves the fundamental solution of the transient pressure field in the liquid drop and stress field in the metal substrate, which are coupled with each other. In this paper, we first solve the fundamental problem of high-speed liquid–solid impact, both analytically and numerically, based on a nonlinear wave model. The transient pressure distribution in liquid (include shock wave) and transient stress distribution in solid are obtained for representative water drop-1Cr13 impacts, with impact speed varying from 10 m/s to 500 m/s. The relationship between the most important parameters characterizing impact and incident speed is established. With the statistics of water drop impact on the blade, a simple fatigue model is employed in this paper to obtain the lifetime map on a blade surface under typical working conditions, in terms of both impact times and operation hours. The most dangerous water drop erosion regions and operating conditions of the steam turbine blade are deduced. These results are useful for evaluating the water drop erosion mechanisms based on the fundamental solution of liquid–solid impact.     

Fracture analysis of epoxy/SWCNT nanocomposite based on global–local finite element model

A global–local multiscale finite element method (FEM) is proposed to study the interaction of nanotubes and matrix at the nanoscale near a crack tip. A 3D FE model of a representative volume element (RVE) in crack tip is built. The effects of the length and chirality of single walled carbon nanotube (SWCNT) in a polymer matrix on the fracture behavior were studied in the presence of van der Waals (vdW) interaction as inter-phase region. Detailed results show that with increasing the weight percentage of SWCNT, fracture toughness improves. Three situations of nanotube directions with respect to crack are considered. Results show that bridging condition has minimum stress intensity factor. In addition, it can be seen that the crack resistance improves by increasing the length and chirality for all kinds of nanotubes. Finally, epoxy/SWCNT 10 wt.% has lower stress intensity factor compared to epoxy/halloysite 10 wt.% in similar loading state.     

Plasmonic refractive index sensor based on metal–insulator-metal waveguides with high sensitivity

A plasmonic square ring resonator sensor design based on metal–insulator-metal waveguide is proposed. The transmission spectra and electric field distribution of the resonator are simulated using the finite element method (FEM). The numerical simulation results achieved from the transmission spectra are used to investigate the sensing characteristics of the structure. The effect of structural parameters on the spectral characteristics and sensing performance are investigated in detail. The sensitivity is obtained to a value as high as 1367?nm/RIU with a figure of merit of ～25. The suggested design can possibly be applied in optical network-on-chip and on-chip nanosensors.     

A label‐based information flow control model for object‐oriented systems

Abstract

This paper proposes a label‐based information flow control model to prevent information leakage within object‐oriented systems. It offers the features of: (a) adapting to dynamic object state change, (b) adapting to dynamic role change, (c) preventing indirect information leakage, (d) detailing the control granularity to variables, (e) allowing purpose‐oriented method invocation, (f) controlling method invocation through argument sensitivity, (g) allowing declassification, and (h) allowing only trusted sources to write a variable.     

A novel constitutive model for Ti–6Al–4V alloy based on dislocation pile-up theory

The mechanical properties of the titanium alloy Ti–6Al–4V, which vary with the specimen size under different temperatures, are studied through the Split Hopkinson Pressure Bar (SHPB) test and the quasi-static tensile test to determine the parameters for the classical Johnson-Cook (JC) constitutive model. Based on the dislocation pile-up theory, the classical JC constitutive model is modified by adding a grain strain term Δσ to consider the influence of grain size. The SHPB and tensile tests are analysed using a finite element method simulation. Compared with the experimental results, the simulation results based on the modified JC model exhibit a much higher calculation accuracy than that of the classical JC model.