Hole Expansion of Dual‐phase and Complex‐phase AHS Steels ‐ Effect of Edge Conditions

Hole expansion is one of the most important properties describing the formability of steel sheets, especially those used in automotive industry. In order to determine and emphasize the influence of hole edge conditions and hole surface quality on the results of standardized hole expansion tests, different hole preparation methods such as hole punching, hole drilling and wire cutting were applied to the industrially produced dual–phase and complex–phase steel grades DP800 and CP800. Results of hole expansion testing were discussed with respect to the impact of deformation introduced into the material during the hole preparation and to the material microstructure and mechanical properties. The damage characteristics of every method as well as the fracture surfaces were investigated in detail via light optical microscopy (LOM) as well as scanning electron microscopy (SEM). Qualitative and quantitative analyses of microstructure combined with microhardness measurements were used for the interpretation of the results and are correlated with the mechanical properties and the formability characteristics of the investigated steel grades.     

Efficient algorithms for checking the atomicity of a run of read and write operations

LetX ₁,...,X _c be variables shared by a number of processorsP ₁,...,P _q that operate in a totally asynchronous and wait-free manner. An operation by a processor is either a write to one of the variables or a read of the values ofall variables. Operations arenot assumed to be instantaneous and may arbitrarily overlap in time. A succession of possibly overlapping operationsa ₁,...,a _n (i.e., a run) is said to be atomic, if these operations can be serialized in a way compatible with any existing precedences among them and so that any read operation returns for each variable the value of the most recent — with respect to the serialization — write operation on this variable. This paper examines the complexity of the combinatorial problem of testing a run for atomicity. First, it is pointed out that when there is only one shared variable or when only one processor is allowed to write to each variable, known theorems lead to polynomial-time algorithms for checking the atomicity of a run (the variable of the time-complexity function is the number of operations in the run). It is then proved that checking atomicity has polynomial-time complexity in the general case of more than one variables and with all processors allowed to read and write each variable. For the proof, the atomicity problem is reduced to the problem of consecutive 1s in matrices. The reduction entails showing a combinatorial result that might be interesting on its own.The research of the first author was partially supported by the European Union ESPRIT Basic Research Projects ALCOM II (contract no. 7141) and Insight II (contract no. 6019).The research of the second author was carried out while he was a student at the University of Patras and also during subsequent visits of his to Patras.     

Constraint-based deductive model checking

We show that constraint logic programming (CLP) can serve as a conceptual basis and as a practical implementation platform for the model checking of infinite-state systems. CLP programs are logical formulas (built up from constraints) that have both a logical interpretation and an operational semantics. Our contributions are: (1) a translation of concurrent systems (imperative programs) into CLP programs with the same operational semantics; and (2) a deductive method for verifying safety and liveness properties of the systems which is based on the logical interpretation of the CLP programs produced by the translation. We have implemented the method in a CLP system and verified well-known examples of infinite-state programs over integers, using linear constraints here as opposed to Presburger arithmetic as in previous solutions. Published online: 18 July 2001     

Analyses of structurally modified quasi‐solid‐state electrolytes using electrochemical impedance spectroscopy for dye‐sensitized solar cells

Electrochemical properties of structurally modified quasi‐solid‐state electrolytes were examined using porous substrates (PSs). The PS was prepared into two categories by a phase inversion method with a brominated poly(phenylene oxide) (BPPO): the sponge and finger types. Effects of the humidification and cosolvent compositions on the morphology of the PS were analyzed by scanning electron microscopy. In all cases of the PSs, a higher V_OC was observed of about 0.1 V than that of a liquid electrolyte owing to a suppressed back electron charge transfer. In addition, the PS prepared by the polymer solution of 1 : 4 : 1 (BPPO : N‐methyl‐2‐pyrrolidone : butyl alcohol) with the humidification process showed better photovoltaic properties in terms of the current density and conversion efficiency owing to the appropriate combinations of pore size, tortuosity, and interconnectivity. Effects of the pore structures were intensively examined using electrochemical impedance spectroscopy. The impedance results revealed that large pores at the surface layers are advantageous for a lower R_S and R_TiO2. Meanwhile, the straight inner structure is beneficial for the facile I^?/I₃^? diffusion, thus lowering R_Pt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39739.     

ForceArc双面焊熔池流场与温度场的数值模拟

基于超威弧(ForceArc)焊接时电弧的形态特征,及超短电弧下实现强制熔滴喷射过渡的特点,采用双椭圆分布热源模型及峰值指数熔滴热焓衰减分布模型. 通过分析工件坡口形貌对ForceArc焊接物理过程的影响,建立贴体坐标系下的ForceArc焊接过程三维瞬态数值分析模型. 模拟了不同预热温度及层间温度对焊接过程的影响,分析了工件上下坡口形貌对熔池传热、传质的影响,并与试验结果进行了对比. 结果表明,文中所建模型能够较好地模拟ForceArc焊接过程,对优化其焊接工艺参数具有一定的指导意义.     

Transformation of the EFQM approach from business towards operations excellence

The purpose of this paper is to provide an enabler-based approach for a supervised self-assessment of operations excellence (OsE). Based on the latest approaches of excellence in operations from the literature as well as on the philosophy of the EFQM model, an OsE working definition was developed. In contrast to operational excellence (OE), which deals exclusively with the optimization of result driven processes, OsE promotes the enhancement of operation-specific enablers and linked results. The evaluation of crucial cause–effect relationships of relevant enabler and result criteria supports the determination of a company’s capability to achieve sustainability and excellence in terms of its operations. To foster a methodical integration of OsE in organizations, a phase model for a systematic assessment process was designed and verified with 24 companies in the Austrian machinery and metalware industries.     

Numerical microstructure prediction for an aluminium casting and its experimental validation

Virtual manufacturing based on through-process modelling becomes an evolving research area which aims at integrating diverse simulation tools to realize computer-aided design, analysis, prototyping and manufacturing. Numerical prediction of the as-cast microstructure is an initial and critical step in the whole through-process modelling chain for engineering components. A commercial software package with the capability of calculating important microstructure features for aluminium alloys is used to simulate a G-AlSi7MgCu0.5 laboratory casting. The simulated microstructure, namely grain size, secondary dendrite arm spacing and diverse phase fractions are verified experimentally. Correspondence and discrepancies are reported and discussed.     

A Comparison of Different Nitinol Material Data Sources for Finite Element Analysis

Nitinol (NiTi) is widely used for minimal invasive vascular implants due to its superelastic material behavior. Today computerized finite element analysis (FEA) modeling is a standard tool for the development of medical devices and an essential part of the product design and device approval process (X. Gong and A.R. Pelton, ABAQUS Analysis on Nitinol Medical Applications, Proceedings of ABAQUS User??s Conference, New Port, Rhode Island, 2001, p 1; N. Rebelo and M. Perry, Finite Element Analysis for the Design of Nitinol Medical Devices, Min. Invas. Ther. Allied Technol., 2000, 9(2), p 75). Quality of simulation depends on a multitude of parameters such as the mathematical material model and FE model generation (meshing). As such, a superior material data input is crucial in order to calculate the correct stress and strain conditions. In this study, we used different sources for material data input for our FE simulations. We compared simulated output versus the experimental results using a stent-like structure after various heat treatments. We used NiTi literature data, tensile data from raw as-supplied NiTi tubes as well as tensile and compression data from microtest samples which underwent stent-like processing for our FEA modeling. A FEA model of the diamond shape (DS) was constructed to quantify and visualize the force and motion response after applying different loading conditions similar to physiologic stress and strain. Force-deflection response of the virtual model was compared against the differently processed DS specimen. All results were put into a matrix in order to evaluate the quality of the different inputs for the FEA. The goal of this study was to demonstrate the importance of selecting and applying the correct material parameter inputs and to further show the importance of not just using given parameter, but also calibrating the values to get accurate results of FE simulations.