A forecast‐based monitoring methodology for process transitions

Nonconforming parts are often produced when a process moves from one level to another due to transition events. Control charting, when applied to a stable state process, is an effective monitoring tool to continuously check for process shifts or upsets. However, the presence of transition events can impede the normal performance of traditional control chart with increased false alarms. The presence of autocorrelation also requires modification to the control charting procedure. We present a methodology for characterizing the process transition which involves a tracking signal statistic, based on the forecast‐based exponentially weighted moving average (EWMA). This test will supplement the forecast‐based EWMA control charting as a means of detecting when the transition event is complete. Such a procedure facilitates smooth application of the appropriate control chart by knowing when the transition is over. The transition characterization methodology also carries benefits in cost and material savings. We use a color transition process in plastic extrusion to illustrate a transition event and demonstrate our proposed methodology. Simulation is employed to evaluate the performance of the methodology. Copyright © 2001 John Wiley & Sons, Ltd.     

High temperature deformation of a submicron grained Al-12 wt% Ti alloy

Compressive deformation behavior of a MA Al-12wt%Ti alloy has been studied at 623–773 K with strain rates from 4 × 10⁻⁵ to 1 × 10⁻¹s⁻¹. A high stress exponent was observed in the stress dependence of strain rate. By assuming that the presence of a threshold stress is the cause of the high stress exponent, the experimental data were analyzed and compared with existing models. The creep behavior of this alloy is found similar to the dispersion strengthened Al-Al₂O₃ alloys. It is suggested that the high temperature deformation of this alloy is mainly governed by the fine carbide and oxide strengthened aluminum matrix, which can be described by lattice-diffusion controlled creep with a “constant structure” [11]. In addition, a strong temperature dependence of the threshold stress was observed. It might be related to certain grain boundary processes and/or thermally activated deformation of strengthening particles.     

Efficient optimization of integrated aerodynamic–structural design

The introduction of composite materials is having a profound effect on the design process. Because these materials permit the designer to tailor material properties to improve structural, aerodynamic and acoustic performance, they require a more integrated multidisciplinary design process. Because of the complexity of the design process numerical optimization methods are required. The present paper is focused on a major difficulty associated with the multidisciplinary design optimization process—its enormous computational cost. We consider two approaches for reducing this computational burden: (i)development of efficient methods for cross-sensitivity calculation using perturbation methods; and (ii) the use of approximate numerical optimization procedures. Our efforts are concentrated upon combined aerodynamic-structural optimization. Results are presented for the integrated design of a sailplane wing. The impact of our computational procedures on the computational costs of integrated designs is discussed.     

Effect of carbon on the oxidation of Fe-5.5 Al-0.55 C alloy

An alloy with the chemical composition Fe-5.5 wt% Al-0.55 wt% C is employed to investigate the effect of carbon on the oxidation at 600, 800 and 1000° C in dry air. Kinetic curves were determined by thermogravimetry analyses. Optical metallography and electron probe microanalysis were used to examine the oxide scales formed on the alloy surfaces. The kinetic curves observed at 600, 800 and 1000° C had simple, three-stage and two-stage parabolic rate laws, respectively. No carbide-free layer could be observed in the alloy which was oxidized at 600° C. In contrast, a carbide-free zone was found in specimens of the alloy after oxidizing at 800 and 1000°C.     

轨道交通盾构双线隧道穿越建筑群的沉降影响分析

目前,城市轨道交通建设中往往需要穿越大量的建(构)筑物群,施工时必须采取措施确保这些建筑物的正常使用。以武汉轨道交通L2中山公园站—循礼门站区间轨道交通隧道为依托,系统介绍轨道交通盾构隧道在穿越小高层建筑物群所采取的相关保障技术,综合考虑隧道各项设计参数、合理调整穿越施工参数、严密监控建筑物沉降。该工程在充分考虑各种因素后,盾构顺利穿越建筑群且建筑物未出现有害裂缝,其中建筑物最大累计沉降为62.78 mm,最大差异沉降43.69 mm,且在建筑物脱出盾构影响范围后3~7 d沉降即出现明显的稳定趋势。     

GDKAT: A goal-driven knowledge acquisition tool for knowledge base development

While knowledge-based systems are being used extensively to assist in making decisions, a critical factor that affects their performance and reliability is the quantity and quality of the knowledge bases. Knowledge acquisition requires the design and development of an in-depth comprehension of knowledge modeling and of applicable domain. Many knowledge acquisition tools have been developed to support knowledge base development. However, a weakness that is revealed in these tools is the domain-dependent and complex acquisition process. Domain dependence limits the applicable areas and the complex acquisition process makes the tool difficult to use. In this paper, we present a goal-driven knowledge acquisition tool (GDKAT) that helps elicit and store experts' declarative and procedural knowledge in knowledge bases for a user-defined domain. The designed tool is implemented using the object-oriented design methodology under C++ Windows environment. An example that is used to demonstrate the GDKAT is also delineated. While the application domain for the example presented is reflow soldering in surface mount printed circuit board assembly, the GDKAT can be used to develop knowledge bases for other domains also.     

Minimum variance hedging with bivariate regime-switching model for WTI crude oil

This paper proposes a four-regime bivariate Markov regime-switching model to estimate the daily time-varying minimum variance hedge ratios for West Texas Intermediate (WTI) crude oil, and evaluates its in- and out-of-sample hedging performances with two-regime model, CC-GARCH, TVC-GARCH, and OLS models. Empirical results reveal that the four-regime Markov switching model outperforms the other models for both in- and out-of-sample hedging performance. Based on Hansen’s SPA test (2005), the four-regime model significantly outperforms the other models for only in-sample hedging.     

Investigation of growth behavior of Al-Cu intermetallic compounds in Cu wire bonding

In this work, we investigate the intermetallic compound formation in Cu wire bonded device. Voids near the Cu side at the bond interface are clearly seen. Nevertheless, these voids do not seem to interfere with the function of the unit. High temperature storage test (HTST) results show that there are Al₂Cu and AlCu in the damaged unit while Al₂Cu and Al₄Cu₉ appear in the good unit. The results clearly show that the Al layer is exhausted in the damaged unit while those with Al₄Cu₉ on the Cu side pass HTST with unconsumed Al. Theoretical calculations indicate that AlCu and Al₄Cu₉ are energetically more favorable than Al₂Cu, which is consistent with the reported IMC forming sequence. Formation energy of AlCu is compatible but slightly lower to that of Al₄Cu₉, suggesting AlCu tends to be the most stable phase among all. The reason why the Al layer is completely consumed in one case and some Al layer remains in the other is due to the fact that the formation of AlCu requires more than twice the amount of Al than Al₄Cu₉ for the same amount of Cu consumed. The complete consumption of Al is proposed as the reason responsible for the failure of the damaged unit.     

A polyethylene glycol-assisted carbothermal reduction method to synthesize LiFePO4 using industrial raw materials

Olivine LiFePO₄ is synthesized by a carbothermal reduction method (CTR) using industrial raw materials with polyethylene glycol (PEG) as a reductive agent and carbon source. A required amount of acetone is added to the starting materials for the ball milling process and the precursor is sintered at 973 K for 8 h to form crystalline phase LiFePO₄. The structure and morphology of the LiFePO₄/C composite samples have been characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, differential scanning calorimetry and magnetic susceptibility. Electrochemical measurements show that the LiFePO₄/C composite cathode delivers an initial discharge capacity of 150 mAh g⁻¹ at a 0.2C-rate between 4.0 and 2.8 V, and almost no capacity loss is observed for up to 50 cycles. Remarkably, the cell can sustain a 30C-rate between 4.6 and 2.0 V, and this rate capability is equivalent to charge or discharge in 2 min. The simple technique, low-cost starting materials, and excellent electrochemical performance make this process easier to commercialize than other synthesized methods.     

Deformation Structure of Unidirectionally Compressed Ultrafine-Grained Mg-3Al-1Zn Alloy

Ultrafine-grained (UFG) Mg-3Al-1Zn (AZ31) alloys with gain sizes ranging from 0.46 to 3.22 μm were prepared by equal channel angular pressing (ECAP) and annealing. The deformation structure of UFG AZ31 alloy resulting from uniaxial compression was studied by optical and electron microscopy. The deformation was noted to proceed with the development of shear bands (SBs), which has not been reported in an UFG hcp metal. Characterization of these SBs was performed, and comparison with the SBs formed in UFG bcc and fcc metals was given. { 10[`1]2} \{ 10\bar{1}2\} tension twins inside SBs were found in all specimens compressed, irrespective of the grain size. Discussion on the limiting grain size of twinning in the UFG AZ31 alloy is also given.