Fracture mechanisms and failure processes at stiffener run-outs in polymer matrix composite stiffened elements

This paper describes the fractographic analyses of three stringer run-out designs which had been loaded to failure in tension. The main aims of the investigation were to deduce the failure processes in the elements, and to characterise the effect of local geometry of the stringer run-out on the failure process. The analysis showed that the critical failure mechanism in the elements was the development of +45° ply splitting at the skin surface, initially under mode I dominated intralaminar fracture. However, as these splits grew beneath the stringer foot, the mode II component increased. This led to mixed-mode delamination growth, extending parallel to the +45° ply, at the skin/adhesive interface. Subsequently, the delamination migrated through the skin via ply splits, ultimately reaching the interface between the second and third (−45°/0°) plies, in which it remained until catastrophic failure.

Extending and tapering the stringer foot led to shifting of the site of the +45° ply splitting; this was attributed to in-plane tensile stresses in the skin being inhibited in the modified designs. The reduced out-of-plane support on the stiffener foot in the modified designs led to an increase in the mode I component at the delamination from the stringer tip. It also led to an increase in the degree of multi-plane delamination growth. Based on the fractographic observations, recommendations for modelling the elements were suggested.     

Development of an Active Thermoplastic Film with Oxygen Scavengers Made of Activated Carbon and Sodium Erythorbate

An active thermoplastic film made of low‐density polyethylene (LDPE) filled with oxygen scavengers made of powdered activated carbon (PAC) impregnated with sodium erythorbate (SE) was developed for packaging applications. Initial tests indicated that the impregnation of PAC with SE enhanced the heat resistance of SE, thereby allowing processing at temperatures typical of LDPE manufacturing. Subsequently, LDPE films with PAC/SE particles were manufactured in coupons that represented a typical juice package, and experiments indicated that these films absorbed 3.57 mg of oxygen in 11 days. This amount corresponded to 80% the concentration of oxygen in the headspace of the package. Furthermore, findings indicated that active particles alone have 10 times higher oxygen absorption capacity than the active LDPE film. Finally, the physical properties of the film were characterized by microscopy where oxygen scavengers showed a good dispersion within the matrix. However, 20 wt.% of these active particles decreased tensile strength of the film by 53%. Copyright © 2014 John Wiley & Sons, Ltd.     

The State‐of‐the‐Art in Predictive Visual Analytics

Predictive analytics embraces an extensive range of techniques including statistical modeling, machine learning, and data mining and is applied in business intelligence, public health, disaster management and response, and many other fields. To date, visualization has been broadly used to support tasks in the predictive analytics pipeline. Primary uses have been in data cleaning, exploratory analysis, and diagnostics. For example, scatterplots and bar charts are used to illustrate class distributions and responses. More recently, extensive visual analytics systems for feature selection, incremental learning, and various prediction tasks have been proposed to support the growing use of complex models, agent‐specific optimization, and comprehensive model comparison and result exploration. Such work is being driven by advances in interactive machine learning and the desire of end‐users to understand and engage with the modeling process. In this state‐of‐the‐art report, we catalogue recent advances in the visualization community for supporting predictive analytics. First, we define the scope of predictive analytics discussed in this article and describe how visual analytics can support predictive analytics tasks in a predictive visual analytics (PVA) pipeline. We then survey the literature and categorize the research with respect to the proposed PVA pipeline. Systems and techniques are evaluated in terms of their supported interactions, and interactions specific to predictive analytics are discussed. We end this report with a discussion of challenges and opportunities for future research in predictive visual analytics.     

Ligand‐Free Synthesis of Aluminum‐Doped Zinc Oxide Nanocrystals and their Use as Optical Spacers in Color‐Tuned Highly Efficient Organic Solar Cells

The color of polymer solar cells using an opaque electrode is given by the reflected light, which depends on the composition and thickness of each layer of the device. Metal‐oxide‐based optical spacers are intensively studied in polymer solar cells aiming to optimize the light absorption. However, the low conductivity of materials such as ZnO and TiO₂ limits the thickness of such optical spacers to tenths of nanometers. A novel synthesis route of cluster‐free Al‐doped ZnO (AZO) nanocrystals (NCs) is presented for solution processing of highly conductive layers without the need of temperature annealing, including thick optical spacers on top of polymer blends. The processing of 80 nm thick optical spacers based on AZO nanocrystal solutions on top of 200 nm thick polymer blend layer is demonstrated leading to improved photocurrent density of 17% compared to solar cells using standard active layers of 90 nm in combination with thin ZnO‐based optical spacers. These AZO NCs also open new opportunities for the processing of high‐efficiency color tuned solar cells. For the first time, it is shown that applying solution‐processed thick optical spacer with polymer blends of different thicknesses can process solar cells of similar efficiency over 7% but of different colors.     

Localized Ligand Induced Electroless Plating (LIEP) Process for the Fabrication of Copper Patterns Onto Flexible Polymer Substrates

The “ligand induced electroless plating (LIEP) process” is a simple process to obtain localized metal plating onto flexible polymers such as poly(ethylene terephtalate) and polyvinylidene fluoride sheets. This generic and cost‐effective process, efficient on any common polymer surface, is based on the covalent grafting by the GraftFast process of a thin chelating polymer film, such as poly(acrylic acid), which can complex copper ions. The entrapped copper ions are then chemically reduced in situ and the resulting Cu⁰ species act as a seed layer for the electroless copper growth which, thus, starts inside the host polymer. The present work focuses on the application of the LIEP process to the patterning of localized metallic tracks via two simple lithographic methods. The first is based on a standard photolithography process using a positive photoresist masking to prevent the covalent grafting of PAA in designated areas of the polymer substrate. In the second, the patterning is performed by direct printing of the mask with a commercial laser printer. In both cases, the mask was lifted off before the copper electroless plating step, which provides ecological benefits, since only the amount of copper necessary for the metallic patterning is used.     

A diagnoser algorithm for anomaly detection in DEDS under partial and unreliable observations: characterization and inclusion in sensor configuration optimization

Complex engineering systems have to be carefully monitored to meet demanding performance requirements, including detecting anomalies in their operations. There are two major monitoring challenges for these systems. The first challenge is that information collected from the monitored system is often partial and/or unreliable, in the sense that some occurred events may not be reported and/or may be reported incorrectly (e.g., reported as another event). The second is that anomalies often consist of sequences of event patterns separated in space and time. This paper introduces and analyzes a diagnoser algorithm that meets these challenges for detecting and counting occurrences of anomalies in engineering systems. The proposed diagnoser algorithm assumes that models are available for characterizing plant operations (via stochastic automata) and sensors (via probabilistic mappings) used for reporting partial and unreliable information. Methods for analyzing the effects of model uncertainties on the diagnoser performance are also discussed. In order to select configurations that reduce sensor costs, while satisfying diagnoser performance requirements, a sensor configuration selection algorithm developed in previous work is then extended for the proposed diagnoser algorithm. The proposed algorithms and methods are then applied to a multi-unit-operation system, which is derived from an actual facility application. Results show that the proposed diagnoser algorithm is able to detect and count occurrences of anomalies accurately and that its performance is robust to model uncertainties. Furthermore, the sensor configuration selection algorithm is able to suggest optimal sensor configurations with significantly reduced costs, while still yielding acceptable performance for counting the occurrences of anomalies.     

Pretreatment predictors of dropout from cognitive behavioral therapy for PTSD in Iraq and Afghanistan war veterans.

Cognitive–behavioral therapies (CBTs) can be effective treatments for posttraumatic stress disorder (PTSD) but their effectiveness is limited by high rates of premature dropout. Few studies have compared pretreatment characteristics of treatment completers and dropouts, and only one has examined these factors in Operations Iraqi Freedom and Enduring Freedom (OIF/OEF) Veterans. This study analyzed archival clinical data from 117 OEF/OIF Veterans evaluated and treated through a Veterans Affairs PTSD clinic. High numbers dropped out of treatment (68%). Treatment dropouts (n = 79) and completers (n = 38) differed significantly on Minnesota Multiphasic Personality Inventory-2 (MMPI-2) scales, PTSD symptom severity, and age. Regression analyses identified one MMPI-2 scale, TRT (negative treatment indicators), and age as unique but modest predictors of dropout. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Phase transition characteristics and dielectric properties of rare-earth (La,Pr, Nd,Gd) doped Ba(Zr0.09Ti0.91)O3 ceramics

A-site deficient rare-earth doped barium zirconate titanate (BZT) ceramics (Ba_1−yLn_2y/3)Zr_0.09Ti_0.91O₃ (Ln = La, Pr, Nd, Gd) are obtained by a modified solid-state reaction method. Perovskite-like single-phase compounds were confirmed from X-ray diffraction data. Morphological analysis on sintered samples shows that the addition of rare-earth ions inhibits the growth of the grain and remarkably changes the grain morphology. The effect of rare-earth addition to BZT on phase transition and dielectric properties is analyzed. A dramatic fall in the transition temperature occurs when BZT ceramic is doped with rare-earths. Moreover, diffusivity degree of the phase transition increases and a relaxor-type behaviour is induced due to both the increment of the lanthanide content and the increase of the ionic radius of the dopant element. High values of dielectric tunability are obtained for lanthanum doped BZT. A direct relation between transition temperature and tunability is discussed. Conclusively, low permittivity and high tunability materials can be obtained by the adequate substitution of rare-earths into BZT ceramics.     

Erosion of glacial till from the St. Clair River (Great Lakes basin)

Variations in water level observed in Lakes Michigan and Huron during the last few decades have motivated a comprehensive study involving climatic, hydrologic and hydraulic factors organized by International Joint Commission of the Great Lakes. It has been submitted, among other possible causes, that changes in conveyance in the St. Clair River could be contributing to the lowering of the upper Great Lakes water level. Sediment transport processes, in particular bed scour and erosion, can affect significantly a river's conveyance, thus creating the need to assess the erodibility properties of the river bed. To this end, laboratory tests were performed in order to obtain the value of the critical shear stress needed to erode the cohesive fraction of the bed sediment material, known as glacial till, from the St. Clair River. Different flows with increasing velocities were run up to the point where initial sediment erosion could be observed. Through detailed near-bed velocity measurements using a laser Doppler velocimetry (LDV) system, a value of 4.2 N/m² was obtained as the critical shear stress for the erosion of glacial till. A threshold for the critical shear stress for erosion of similar cohesive sediments was also found and expressed in dimensionless form. These results could be used in combination with mathematical models to estimate the risk of scour and erosion at locations where the glacial till is exposed to both strong currents and flow forces induced by the large navigation vessels commonly observed along the course of the St. Clair River.     

Stator Windings Fault Diagnostics of Induction Machines Operated From Inverters and Soft-Starters Using High-Frequency Negative-Sequence Currents

This paper studies the application of high-frequency voltage excitation-based stator winding diagnostic methods to three-phase ac machines operated from power converters that create the necessary high-frequency excitation as part of their normal operation. This paper focuses on two specific operating modes: 1) machines operated from inverters in the overmodulation region and 2) machines operated from soft-starters during startup. In both cases, high-frequency (in the range of the hundred hertz) voltage components at well-defined frequencies are created. The negative-sequence currents induced from these high-frequency voltages are shown to contain accurate information on the level of asymmetry (fault) in the machine. This information is significantly richer than exists in other modes of operation, i.e., inverters working in the linear modulation region or soft-starters in the steady state, and provides interesting opportunities to complement other diagnostic methods.