Relationships between process, microstructure and properties of molded zirconia micro specimens

Due to size effects the mechanical behavior of micro-components with dimensions in the range of some 100 μm and structure details of about 10 μm differs markedly from those of larger components. This is a crucial aspect for the design of micro-components for applications where demands for high strength are critical. The present study, which was performed in the frame of the Collaborative Research Centre 499 (SFB 499), approaches this issue by investigating the relationship between production process, microstructure and the mechanical properties of micro-specimens made from zirconia using two different feedstocks. The specimens were produced by a sintering process. The sintering temperature was varied between 1,300 and 1,500°C. Mechanical and tribological behavior of the specimens was determined by three-point bending tests as well as static and sliding friction tests, respectively. Properties derived from these tests were then correlated to the surface states in the specimens such as porosity, edge radius and roughness. The strength of the micro-specimens was found to be significantly influenced by these surface features. Whilst low porosity alone is not sufficient for high strength, notch effects resulting from pores as well as surface roughness can lower the strength. With increasing edge radius the strength of the material also increases. The porosity, edge radius and surface roughness were mathematically correlated with the strength to allow for a forecast. Within the SFB 499 feedstocks with specific properties were designed and reliable processes were developed to guarantee desirable surface roughness and porosity in the specimens. A characteristic bending strength of about 2,000 MPa is realizable in the micro-specimens within a good statistical reliability. The tribological tests revealed that the wear properties of the zirconia micro-components are strongly dependent on the quality of the feedstock.     

Determination of mechanical properties of slip cast, micro powder injection moulded and microcast high aspect ratio microspecimens

In a project of the German Research Council (DFG) Collaborative Research Centre (SFB) 499 Development, production and quality assurance of moulded micro-components made of metallic and ceramic materials [SFB03] three-point bending-specimens (dimension: 1.2 × 0.2 × 0.2 mm) made of slip cast [BAU02] or micro powder injection moulded ZrO₂ [RUP03] as well as tensile specimens (dimension of the gauge length: 0.78 × 0.26 × 0.13 mm) made of the micro-cast AuAgCu-alloy Stabilor G [BAU03] were investigated with respect to their behaviour under quasi-static loading.The support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged. The authors appreciate the co-operation of all the project partners within the SFB 499.     

Fuzzy optimization of slab production from mechanical stone properties

This paper aims to conduct slab production optimization by a flexible tool, which is fuzzy linear programming. There is a direct relationship between slab production and mechanical stone characteristics. In this process, the goal and its tolerance cannot be specified firstly due to a lack of knowledge. Therefore, the optimal system design problem for optimal slab production under soft constraints is constructed and solved in a fuzzy environment. The results show that fuzzy linear optimization is a convenient tool for optimizing slab production.     

Modeling of mechanical properties and bond relationship using data mining process

Reinforced concrete is a widely used construction material. Its properties depend on the bond between the reinforcing bar and concrete as much as the compressive strength or properties of the reinforcing bar because of component of construction expose to both flexural and bond together compressive loads. In this paper, the bond properties of concretes with different mix designs were investigated according to the results of compressive, flexural, bond, and flexural-bond tests. The data mining (DM) process was used to determine relationships among the test results and DM algorithms. Seventeen modeling techniques within WEKA were applied to the experimental data for the prediction of bond properties.The results show that the implemented models were good at predicting the bond properties. The best results were obtained from the RepTree algorithm for bond strength, the Multilayer Perceptron algorithm for flexural-bond strength, the MedSq algorithm for bond slippage, and the Pace Regression for flexural-bond deformation. Bond and flexural-bond can be easily predicted using the compressive strength, flexural strength and tensile stress of the rebar. Although a relationship is also existent between these and bond slippage and flexural-bond deformation, these relationships are weaker than the others.These results suggested that the DM algorithms can be used as an alternative approach to predict the bond strength using the results of compressive, flexural, bond, and flexural-bond tests as input parameters. The predictions of the bond slippage and flexural-bond deformation models poorly agreed with the experimental results. It can be obtained more successful results for these variables, when DM models with different inputs like the rebar-concrete interface stress together the measured parameters are used.     

Mechanical strength and microstructure of Stabilor-G® and ZrO2 microspecimens

For a safe design of micromechanical components reliable data of mechanical properties at static and cyclic loadings are of vital interest. Such data together with a detailed analysis of the microstructure are also useful for a straight forward optimization of the manufacturing process. Therefore, in the present study the mechanical behavior of microcast Stabilor-G^® microspecimens under quasistatic and cyclic loadings and of slip cast and micro powder injection molded ZrO₂ microspecimens under quasistatic loadings was determined. Together with a microscopic characterization of the specimens it could be shown that the elastic-plastic behavior of Stabilor-G^® microspecimens is strongly determined by grain anisotropy. In fatigue tests cyclic hardening occurs. The scatter of the lifetimes is not larger than observed at cast macrospecimens. The failure behavior of ZrO₂ microspecimens under quasistatic bending is mainly determined by surface roughness and near surface porosities as well as by the edge geometry. The highest characteristic bending strength which currently can be reached is nearly 3,200 Mpa.     

Correlations between bugginess and time-based commit characteristics

Modern software is often developed over many years with hundreds of thousands of commits. Commit metadata is a rich source of time-based characteristics, including the commit’s time of day and the commit frequency and seniority of its author. The “bugginess” of a commit is also a critical property of that commit. In this paper, we investigate the correlation between a commit’s time-based characteristics and its “bugginess”; such results can be useful for software developers and software engineering researchers. For instance, developers or code reviewers might be well-advised to thoroughly verify commits that are more likely to be buggy. In this paper, we study the correlation between a commit’s bugginess and the time of day of the commit, the day of week of the commit, the commit frequency and seniority of the commit authors, and whether or not the developers have marked a commit as a “stable” commit. We survey three widely-used open source projects: the Linux kernel, PostgreSQL, and the Xorg server. Our main findings include: (1) commits between midnight and 4 AM (referred to as late-night commits) are significantly buggier and commits between 8 AM and noon are less buggy, implying that developers may want to double-check their own late-night commits; (2) daily-committing developers produce less-buggy commits, indicating that we may want to promote the practice of daily-committing developers reviewing other developers’ commits; (3) the bugginess of commits versus day-of-week varies for different software projects; and (4) stable commits are significantly less buggy than commits in general.     

Microstructure and mechanical properties of micro tensile specimens made of CuAl10Ni5Fe4 produced by micro casting

In this paper the results of micro tensile tests of specimens produced by vacuum pressure casting (VPC) and centrifugal casting (CC) with varied mould temperatures are described. The microstructure of VPC-micro specimens is clearly different from CC-micro specimens. Due to the large tolerance range of the chemical composition of the aluminum bronze CuAl10Ni5Fe4 and process instabilities the microstructure of batches of VPC-micro specimens can be very fine grained as well as very coarse grained even if the process parameters were nominally the same. As a consequence the mechanical properties of micro specimen show a wide range, e.g. the ultimate tensile strength (VPC, mould temperature T _m = 1,000°C) is between 670 and 1,000 MPa. Within one batch (ca. 15 specimens) the scatter of microstructure and mechanical properties is clearly smaller. If the chemical composition of the material is nearly constant for a larger number of batches, then the production process of vacuum pressure casting leads reproducibly to nearly identical microstructure and mechanical properties.     

芳烃生产流程模拟与研究

根据某石化企业芳烃生产数据,运用Petro-SIM软件建立了包括芳烃歧化和烷基转移、芳烃异构化反应模型的流程模型,经校正后,对模型计算值与实际测量值进行对比,验证了模型的准确性。利用软件中的Databook功能,对建立的模型进行了单装置反应条件和原料组成对产品产率影响的研究,结果表明,甲苯歧化及烷基转移反应中,产物的选择性主要受原料中T/C9A的比值的影响;芳烃异构化单元中,提高反应温度,有利于二甲苯达到热力学平衡,增加反应压力,乙苯转化率增加,原料中乙苯和C8环烷烃的含量对乙苯转化率和对二甲苯收率影响较为显著。     

Stress engineering and mechanical properties of SU-8-layers for mechanical applications

SU-8 is an essential material for manufacturing micromechanical components with high demands in aspect ratio and toughness in the area of micro-system technologies. For reproducible production of SU-8 components, e.g. polymeric AFM-cantilevers and chip carriers, a characterization sequence for the material in its raw state and in all subsequent processing steps was developed. Included in these tests were differential scanning calorimetry of the unprocessed resist, in situ monitoring of the solid content during soft bake, measurement of the stress behaviour during and after post-exposure bake as well as determination of micro-hardness and Young’s modulus at different baking and exposure conditions. The results are promising with respect to definition of a novel procedure for reproducible preparation of micromechanical components from SU-8.     

Extremal properties of conditional entropy and quantum discord for XXZ,symmetric quantum states

For the XXZ subclass of symmetric two-qubit X states, we study the behavior of quantum conditional entropy \(S_{cond}\) as a function of measurement angle \(\theta \in [0,\pi /2]\). Numerical calculations show that the function \(S_{cond}(\theta )\) for X states can have at most one local extremum in the open interval from zero to \(\pi /2\) (unimodality property). If the extremum is a minimum, the quantum discord displays region with variable (state-dependent) optimal measurement angle \(\theta ^*\). Such \(\theta \)-regions (phases, fractions) are very tiny in the space of X-state parameters. We also discover the cases when the conditional entropy has a local maximum inside the interval \((0,\pi /2)\). It is remarkable that the maxima exist in surprisingly wide regions, and the boundaries for such regions are defined by the same bifurcation conditions as for those with a minimum.     

Biped robots: Correlations between technological design and dynamic behavior

The authors of the paper have collaborated in a joint project involving four French control, mechanics and computer-science laboratories. In the paper, various mechanical architectures of biped robots are examined in detail, showing that their walking capabilities are closely linked to the kinematic characteristics of the mechanical structure. Then, it is shown that the geometrical and inertial parameters of the mechanical systems strongly affect the gait. In particular, the influence of the biped inertia on the lateral stability of the system, as well as the conditions of the existence of passive pendular gaits during the swing phase, are computationally analyzed. Extending the ideas previously developed, some characteristics of the mechanical architecture and design of the BIP project can be clearly justified. It turns out that a kinematic structure with 15 degrees of freedom is necessary in order for the biped robot to develop anthropomorphic gaits. Furthermore, as an anthropometric mass distribution can improve the walking abilities of the robot, special transmitters have been designed in order to help to fulfil this requirement.     

Interdiffusion behaviors and mechanical properties of Cu-Zr system

In this work, solid-to-solid diffusion couples were assembled and annealed to investigate diffusion behavior and mechanical properties of the Cu-Zr system in temperatures range from 1043 K to 1113 K. Six intermetallic compounds (IMCs) Cu₉Zr₂, Cu₅₁Zr₁₄, Cu₈Zr₃, Cu₁₀Zr₇, CuZr, and CuZr₂ were observed in the diffusion zone. Composition-dependent interdiffusion coefficients of IMCs have been calculated based on the measured composition Cu profiles of the diffusion zones by using Sauer–Freise method. And the average effective interdiffusion coefficients for each phase were also calculated by using Wagner method. The activation energies of diffusion are evaluated according to the average effective interdiffusion coefficient. Finally, the load-displacement curves measured by nano-indentation are obtained to characterize mechanical properties of Cu₉Zr₂ and Cu₅₁Zr₁₄, which have similar hardness and elastic moduli.     

Quasi-optimal integrated production, inventory and maintenance policies for a single-vendor single-buyer system with imperfect production process

In this paper we deal with the integrated supply chain management problem in the context of a single vendor-single buyer system for which the production unit is assumed to randomly shift from an in-control to an out-of-control state. At the end of each production cycle, a corrective or preventive maintenance action is performed, depending on the state of the production unit, and a new setup is carried out. Two different integrated production, shipment and maintenance strategies are proposed to satisfy the buyer’s demand at minimum total cost. The first one suggests that the buyer orders batches of size nQ and the vendor produces nQ and makes equal shipments of size Q. The second policy proposes that to satisfy the same ordered quantity, the vendor produces separately smaller batches of size Q, n times. The total integrated average cost per time unit corresponding to each strategy is considered as the performance criterion allowing choosing the best policy for any given situation.     

Correlations between Horn fractions, satisfiability and solver performance for fixed density random 3-CNF instances

An enhanced concept of sub-optimal reverse Horn fraction of a CNF-formula was introduced in [18]. It was shown that this fraction is very useful in effectively (almost) separating 3-colorable random graphs with fixed node-edge density from the non-3-colorable ones. A correlation between this enhanced sub-optimal reverse Horn fraction and satisfiability of random 3-SAT instances with a fixed density was observed. In this paper, we present experimental evidence that this correlation scales to larger-sized instances and that it extends to solver performances as well, both of complete and incomplete solvers. Furthermore, we give a motivation for various phases in the algorithm aHS, establishing the enhanced sub-optimal reverse Horn fraction, and we present clear evidence for the fact that the observed correlations are stronger than correlations between satisfiability and sub-optimal MAXSAT-fractions established similarly to the enhanced sub-optimal reverse Horn fraction. The latter observation is noteworthy because the correlation between satisfiability and the optimal MAXSAT-fraction is obviously 100%. AMS subject classification 90C05, 03B99, 68Q01, 68W01     

Explaining Disease: Correlations,Causes, and Mechanisms

Minds and Machines - Why do people get sick? I argue that a disease explanation is best thought of as causal network instantiation, where a causal network describes the interrelations among...     

基于组件的机械仿真架构及流程控制技术研究

为了协同实现仿真作业的真正流程化,在分析典型工作流应用系统框架基础上,建立了CSE体系框架.结合组件开发思想,提出了仿真组件的概念;根据机械仿真的特点,引入虚拟网络计算(Virtual Network Computing,VNC)技术.项目开发进度表明,该框架对于机械仿真需求变化有强大的适应能力,整体结构清晰,组件化的方法明显提高了系统的适应性和灵活性.     

Evaluating the learning process of mechanical CAD students

There is little theoretical or experimental research on how beginner-level trainees learn CAD skills in formal training sessions. This work presents findings on how trainees develop their skills in utilizing a solid mechanical CAD tool (Pro/Engineer version 2000i² and later version Wildfire). Exercises at the beginner and intermediate levels were designed so that several variations of a solid object are built by non-experienced trainees as they accumulate training time. In this case, trainees are fourth year mechanical engineering seniors and as such, they were of a similar technical and gender make-up. This assessment was conducted over the duration of training (16-week long semester). The test exercises were used to assess the trainees’ speed and proficiency in the use of CAD by (1) measuring their performance time and (2) feature count (number of features-of-size used to build the test parts). Using performance time data, empirical learning curves are generated. Breaking these curves into declarative and procedural components provides insight into how fast the trainees develop cognitive and motor CAD skills. In order to confirm that this methodology can be extended to other CAD platforms, a follow-up study was performed on a different set of beginner-level trainees with similar make-up while using the same beginner-level parts but with a more recent version of Pro/Engineer: Wildfire. One significant result of this study is that the procedural and declarative components of CAD learning are largely cognitive.     

Methodologies for Measuring the Correlations between Post-Editing Effort and Machine Translatability

Against the background of a wider research project that aims to investigate the correlation, if any, between post-editing effort and the presence of negative translatability indicators in source texts submitted to Machine Translation (MT), this paper sets out to assess the potential of two methods for measuring the effort involved in post-editing MT output. The first is based on the use of the keyboard-monitoring program Translog; the second on Choice Network Analysis (CNA). The paper reviews relevant research in both machine translatability and MT post-editing, and appraises, in particular, the suitability of think-aloud protocols in assessing post-editing effort. The combined use of Translog and CNA is proposed as a way of overcoming some of the difficulties presented by the use of think-aloud protocols in the current context. Initial results from a study conducted at Dublin City University confirm that triangulating data from Translog and CNA can cast light on the temporal, cognitive and technical aspects of post-editing effort.