Dynamic ductile crack growth and transition to cleavage – a cell model approach

The fracture behavior of ferritic steel in the transition regime is controlled by the competition between ductile tearing and cleavage. Many test specimens that failed by catastrophic cleavage showed significant amounts of ductile tearing prior to cleavage fracture. The transition from ductile tearing to cleavage has been attributed to the increase in constraint and sampling volume associated with ductile crack growth. This work examines the role of dynamic ductile crack growth on the fracture mode transition by way of a cell model of the material. The cell model incorporates the effects of stress triaxiality and strain rate on material failure characteristics of hole growth and coalescence. Loading rate and microstructure effects on the stress fields that evolve with rapid (ductile) crack growth are systematically studied. The stress fields are employed to compute the Weibull stress which provides probability estimates for the susceptibility to cleavage fracture. A center-cracked panel subjected to remote tension is the model problem under study. The computational model uses an elastic-viscoplastic constitutive relation which incorporates enhanced strain rate hardening at high strain rates. Adiabatic heating due to plastic dissipation and the resulting thermal softening are also accounted for. Under dynamically high loading rate, our model shows the crack speed achieves its peak value soon after crack initiation and quickly falls off to slower speeds with further crack growth. Remarkably, the Weibull stress follows a similar pattern which suggests that the transition to the cleavage fracture is most likely to occur, if at all, at the peak speed of ductile crack growth. Key words: Dynamic fracture, ductile tearing, crack growth, transition regime, cleavage fracture, cell model, finite element.     

Tabu search‐based approach to multi‐objective machine‐part cell formation

The machine‐part cell formation with respect to multiple objectives has been an attractive search topic since 1990 and many methodologies have been applied to consider simultaneously more than one objective. However, the majority of these works unify the various objectives into a single objective. The final result of such an approach is a compromise solution, whose non‐dominance is not guaranteed. A Pareto‐optimality‐based multi‐objective tabu search (MOTS) algorithm is presented for the machine‐part grouping problems with multiple objectives: it minimizes the total cost, which includes intra‐ and inter‐cell transportation cost and machine investment cost, minimizing the intra‐cell loading unbalance and minimizing the inter‐cell loading unbalance. A new approach is developed to maintain the archive storing non‐dominated solutions produced by the tabu search. The comparisons and analysis show that the proposed algorithm has considerable promise in multi‐objective cell design.     

Synergy of cell–cell repulsion and vacuolation in a computational model of lumen formation

A key step in blood vessel development (angiogenesis) is lumen formation: the hollowing of vessels for blood perfusion. Two alternative lumen formation mechanisms are suggested to function in different types of blood vessels. The vacuolation mechanism is suggested for lumen formation in small vessels by coalescence of intracellular vacuoles, a view that was extended to extracellular lumen formation by exocytosis of vacuoles. The cell–cell repulsion mechanism is suggested to initiate extracellular lumen formation in large vessels by active repulsion of adjacent cells, and active cell shape changes extend the lumen. We used an agent-based computer model, based on the cellular Potts model, to compare and study both mechanisms separately and combined. An extensive sensitivity analysis shows that each of the mechanisms on its own can produce lumens in a narrow region of parameter space. However, combining both mechanisms makes lumen formation much more robust to the values of the parameters, suggesting that the mechanisms may work synergistically and operate in parallel, rather than in different vessel types.     

Assessing the actual Gamma process quality – a curve-fitting approach for modifying the non-normal flexible index

Process capability indices (PCIs) have been widely adopted for quality assurance activities. By analysing PCIs, a production department can trace and improve a poor process to enhance product quality level and satisfy customer requirements. Among these indices, C_pk remains the most prevalent for facilitating managerial decisions because it can provide bounds on the process yield for normally distributed processes. However, processes are often non-normal in practice, and C_pk may quite likely misrepresent the actual product quality. Hence, the flexible index C_jkp, which considers possible differences in the variability above and below the target value, has been developed for practical use. However, C_jkp continues to suffer from serious bias in assessing actual capability, especially when the process distribution is highly skewed. In this paper, we modify C_jkp for assessing the actual process quality of a Gamma process. A correction factor is obtained by the curve-fitting method. The results show that our proposed method can significantly reduce the bias for calculation of actual nonconformities. Moreover, we introduce a sample estimator for our modified index. The ratio of this estimator’s average value and the modified index is approximately 1. This implies that our proposed estimator can provide an appropriate estimation for assessing the actual Gamma process quality.     

How to design a dynamic feed-in tariffs mechanism for renewables – a real options approach

Feed-in tariffs (FITs) are among the most favoured policies with which to drive the deployment of renewable energy. This paper offers insights into quantifying dynamic FITs to realise the expected installed capacity target with minimum policy cost under uncertainties of renewable intermittence and technology learning. We incorporate real options and use stochastic dynamic programming to model the strategic behaviour between policy-maker and investor and extend the one-time investment decision described by Farrell et al. [2017. ‘Specifying an Efficient Renewable Energy Feed-in Tariff.’ The Energy Journal 38: 53–75] to multiple-period decisions. An approach that combines binary tree scenario generation and a least squares Monte Carlo method is used to numerically identify the optimal FITs plan in practice. China’s offshore wind power investment is used as a case study to investigate the relationships among the optimal dynamic FITs level, the total policy cost, the expected capacity target, and the learning effect. The simulation results demonstrate that our proposed dynamic FITs can track the changes in technology learning well and that they can avoid the inefficiency of fixed FITs in stimulating technology adoption in the initial periods, along with overpayment by the policy-maker.     

A nonlinear meso–macro approach to modelling delayed ettringite formation and concrete degradation

We show how a two-scales FE model—within a sequential approach—leads to consistently simulate the DEF macroscopic consequences: cracks pattern and opening, residual modulus decrease. The mesoscopic part of this model is adapted to heterogeneous materials and is based on two kinematics enrichments. The first one leads to a very fast meshing process along the randomly chosen set of aggregates and, the second leads to directly compute the cracks openings. Assuming DEF is driving to a progressive and homogeneous mortar expansion, we show how the macroscopic—concrete—expansion as well the cracks pattern are consistent with the experiments. For the latter we are interested in the characterization of the aggregates effect on the amplitude of DEF swelling, so that we focus on parameters such as the size and the volume fraction of granular inclusions.     

An air to water bridge: air sampling and analysis using tetraglyme

A water-soluble organic liquid is shown to scrub a wide variety of volatile organic compounds from air and gas streams. Gas pulled through impingers containing chilled tetraglyme (an organic solvent utilized in USEPA methods 3050A and 8240) is found to efficiently trap volatile Priority Pollutant, Hazardous Substance List and other organic species. A portion of the tetraglyme is subsequently dispersed into water and analyzed using conventional water analysis methodology. Practical quantitation limits of 100 ppbv have been demonstrated, and a potential to achieve lower limits of detection is clear. The method offers advantages over canister, adsorption tube, or Tedlar bag air-sampling techniques. Attributes include broad applicability, preservation of sample integrity ("plating out" of analytes is eliminated), freedom from water vapor interference, ready inclusion into water analysis methodology, simplicity, and low cost. Environmental laboratories with ordinary water/volatile organic analysis equipment are enabled to perform air-monitoring analyses without specialized hardware or expertise.     

A robust nano-mechanics approach for tensile and modal analysis using atomistic–continuum mechanics method

Nanoscale engineering has been developing rapidly. However, experimental investigations at the nanoscale level are very difficult to conduct. This research seeks to employ the same model to investigate an atomic-scale structure for tensile and modal analyses, based on atomistic–continuum mechanics (ACM) and a finite element method (FEM). The ACM transfers an originally discrete atomic structure into an equilibrium continuum model using atomistic–continuum transfer elements. All interatomic forces, described by the empirical potential functions, can be transferred into springs to form the atomic structure. The spring network models were also widely utilized in FEM based nano-structure studies. Thus, this paper attempts to explore ACM using three examples including silicon, carbon nanotube, and copper. All of the results are validated by bulk properties or literature.     

Structural approach to nanoscience: a case study of complex and cluster formation in ZnBr2–ZnCl2 melts

Although the melt structure of glass-forming ZnCl₂ has so far been well studied, there exists quite little information on the structural change due to anion-substitution. In the present work, the short-range structure of ZnCl₂–ZnBr₂ mixture melts was analyzed systematically by time-of-flight pulsed neutron diffraction techniques, Raman spectroscopy, molecular orbital calculations, and molecular dynamics simulations. According to radial distribution analysis, it was found that there were tetrahedral structural units of ligand-substituted [ZnCl_nBr_4–n]^2– (n=0–4) in these melts, not implying the simple mixing of [ZnCl₄]^2– and [ZnBr₄]^2– units. Further detailed estimation indicated that the ligand-substituted complex anions were linked with each other by sharing a common anion.     

Buckling analysis of Reissner–Mindlin plates subjected to in-plane edge loads using a shear-locking-free and meshfree method

Buckling study of plates subjected to uniformly uniaxial, biaxial in-plane compression and pure shear loads using an efficient novel meshfree method is presented in this paper. The moving Kriging (MK) interpolation technique satisfying the Kronecker delta function property is employed to construct the shape functions. To allow for the effect of transverse shear deformation on thick plates, the first-order Reissner–Mindlin plate theory (FSDT) is adopted. The new formulation enables us to eliminate shear-locking demonstrated by various numerical examples involving both thin and moderately thick plates. It is found that the results achieved by the present approach match well with those obtained by other existing numerical approaches and analytical solutions, which illustrates the applicability, the effectiveness and the accuracy of the method.     

From research to cost-effective directional solidification and single-crystal production – an integrated approach

Abstract

This approach has required work in the three broad areas of process development, material development, and quality assurance. The first has led to the development of an automated casting facility, and the adoption of the technically more difficult seeding technique, as a result of its greater process and design flexibility. The second has been met by the development of a series of three alloys to meet specific turbine applications and the economies necessary to make the complex shapes to the required precision. The third has been met by the development of SCORPIO, a real-time rapid-orientation measurement system for the production environment, and the understanding and development of the process controls necessary to control wall section measurements and heat treatment. By the involvement of multidisciplined teams, this approach has led to a demonstrated technology with little or no cost penalty.

MST/244     

Formulation of H2 and H8 optimal control problems – a variational approach

Abstract

In this paper, the full state and output feedback controllers with gains determined using either an H₂ or an H₈ – norm optimality criterion are presented. The problem is approached by transforming the frequency domain optimality criteria to the corresponding variational forms in the time domain. The variational approach allows formulation of the H₈ – optimal control problem without the limitations placed by the orthogonality assumptions. The state feedback gains and the observer gains are determined by solving two special Riccati equations. The tracking and the regulation problems are presented, and a computer algorithm is proposed for determining both the controller gains and the observer gains. The theoretical developments are applied to two examples for illustrative purposes.     

Some insights into Malakooti et al . ‘Integrated group technology,cell formation and process planning’ approach

Rajagopalan and Irani (Some comments on Malakooti et al. ‘Integrated group technology, cell formation, process planning, and production planning with application to the emergency room’. Int. J. Prod. Res., 2006, 44, 2265--2276.) provide a critique of Malakooti et al. (Integrated group technology, cell formation, process and production planning with application to the emergency room. Int. J. Prod. Res., 2004, 42, 1769–1786.) integrated cell/process/capacity formation (ICPCF) approach and suggest an improved method for solving the ICPCF problem. Rajagopalan and Irani (2006 Rajagopalan, RIrani, SA. 2006. Integrated group technology, cell formation, process planning, and production planning with application to the emergency room. Int. J. Prod. Res., 44: 2265–2276. Some comments on Malakooti[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) attempt to solve the emergency room layout problem presented in Malakooti et al. (2004) and claim to have obtained an improved solution from their approach (hybrid flowshop layout). Although there are certain advantages of considering Rajagopalan and Irani's (2006 Rajagopalan, RIrani, SA. 2006. Integrated group technology, cell formation, process planning, and production planning with application to the emergency room. Int. J. Prod. Res., 44: 2265–2276. Some comments on Malakooti[Taylor &; Francis Online], [Web of Science ®] , [Google Scholar]) approach, we believe that their approach for solving ICPCF problems have significant shortcomings.     

Modal analysis of delaminated plates and shells using Carrera Unified Formulation – MITC9 shell element

The present paper considers the modal analysis of delaminated composite shell structures with double-curvature geometry. The finite element for shell with variable through-the-thickness kinematic is adopted for the analysis. The refined models are grouped in the Unified Formulation by Carrera (CUF) and they permit the distribution of displacements along the thickness of the multilayered shell to be accurately described. The shell element has nine nodes and the Mixed Interpolation of Tensorial Components (MITC) method is used to alleviate the membrane and shear locking phenomenon. The governing equations are derived from the Principle of Virtual Displacement (PVD) and the Finite Element Method (FEM) is employed to solve them. From the analysis, one can conclude that the shell element based on the CUF is very efficient and the results obtained match closely with three-dimensional finite element simulations. The effect of delamination size, curvature, stacking sequence, and boundary conditions is studied. The results from different ordered theories are tabulated and compared. It is observed that there is reduction in frequencies in the presence of delamination; however, for a given size of delamination, stacking sequence, and boundary conditions, the effect of delamination on shell structure is more predominant in comparison with respect to the plates structures.     

Phase shift calibration in speckle photography—a first step to practical real-time analysis of speckle correlation fringes

Abstract

The paper is focused on the implemention of phase shift calibration in speckle photography with a view to introducing the possibility of realtime analysis of displacement data obtained by the method. Phase reversal is accomplished by varying pressure within an air-filled quartz cell inserted in the pump beam in a conventional two-beam coupling arrangement. It is shown that phase reversal is achieved when a π-shifted speckle pattern overlaps on an unshifted speckle pattern at the observation plane. This phenomenon is exploited for calibration of the phase shift. Experimental results show good agreement with the theory.     

Exploring inventory systems sensitive to shrinkage – analysis of a periodic review inventory under a service level constraint

Motivated by empirical evidence, this article focuses on the behaviour of a store inventory exposed to inventory record inaccuracy. The inventory, controlled by an infinite horizon, single-stage, single-product periodic-review policy, is subject to shrinkage errors that cause a difference between the physical and information system inventory levels. We model a set of scenarios depending on the technology available to track shrinkage in the store. In scenarios where a technology such as Radio Frequency IDentification (RFID) is not used, inventory is controlled by estimating the expected shrinkage rate. We assume that an inspection process is performed at a regular frequency of N selling periods. We analyse two situations that permit management of the joint ordering and inspection policy based on the information the inventory manager has on shrinkage errors. A comparison between these two situations permits us to analyse the impact of shrinkage errors and the value of taking into account the inventory inaccuracy issue when optimising the inventory and inspection policies. The deployment of the RFID technology produces two benefits: total visibility of the shrinkage rate and the elimination of shrinkage errors. A comparison of the scenarios enables us to evaluate the economic impact of inventory record inaccuracies, which can be significant, particularly in systems with a poor estimation of the error parameter as well as with a high inspection cost.     

Nano-morphology of a polymer electrolyte fuel cell catalyst layer—imaging, reconstruction and analysis

The oxygen reduction reaction (ORR) in the cathode catalyst layer (CCL) of polymer electrolyte fuel cells (PEFC) is one of the major causes of performance loss during operation. In addition, the CCL is the most expensive component due to the use of a Pt catalyst. Apart from the ORR itself, the species transport to and from the reactive sites determines the performance of the PEFC. The effective transport properties of the species in the CCL depend on its nanostructure. Therefore a three-dimensional reconstruction of the CCL is required. A series of two-dimensional images was obtained from focused ion beam — scanning electron microscope (FIB-SEM) imaging and a segmentation method for the two-dimensional images has been developed. The pore size distribution (PSD) was calculated for the three-dimensional geometry. The influence of the alignment and the anisotropic pixel size on the PSD has been investigated. Pores were found in the range between 5 nm and 205 nm. Evaluation of the Knudsen number showed that gas transport in the CCL is governed by the transition flow regime. The liquid water transport can be described within continuum hydrodynamics by including suitable slip flow boundary conditions.      

Discussion A note on ‘Similarity of a new greedy heuristic for facility layout by graph theory to an existing approach’

A recent paper by Boswell claims the development of a new greedy heuristic for constructing a maximal planar weighted graph. This paper points out that Boswell's procedure is not actually new since it has similiarity to an approach introduced earlier by Hassan and Hogg. The paper also points out the advantages of the Hassan and Hogg approach over Boswell's procedure.     

Assessment of patentability by means of semantic patent analysis – A mathematical-logical approach

To obtain patent protection, a patent must fulfill statutory patentability requirements examined by a patent office. Such examinations are mostly performed manually and are quite time-consuming. Therefore, we suggest a computer-based process for the assessment of patentability by means of a mathematical-logical approach comparing patents with semantic structures. In order to make such an assessment, we compare the feature combinations of patent claims with the pertinent prior art. For proof of concept, the process has been tested successfully on an US-application claiming a method for raising a crane boom which can be categorized as non-patentable with regard to the requirement of non-obviousness. The result is consistent with that of a USPTO patent examiner, which underpins that at least under certain conditions not only patent examiners but also applicants and third parties can assess the chance and scope of protection for claimed inventions and patent applications with regard to patentability by our process.