High temperature fatigue behavior of tungsten copper composites

The high temperature fatigue behavior of a 9 vol percent, tungsten fiber reinforced copper matrix composite was investigated. Load-controlled isothermal fatigue experiments at 260 and 560 C and thermomechanical fatigue (TMF) experiments, both in phase and out of phase between 260 and 560 C, were performed. The stress-strain response displayed considerable inelasticity under all conditions. Also, strain ratcheting was observed during all the fatigue experiments. For the isothermal fatigue and in-phase TMF tests, the ratcheting was always in a tensile direction, continuing until failure. The ratcheting during the out-of-phase TMF test shifted from a tensile direction to a compressive direction. This behavior was thought to be associated with the observed bulging and the extensive cracking of the out-of-phase specimen. For all cases, the fatigue lives were found to be controlled by damage to the copper matrix. Grain boundary cavitation was the dominant damage mechanism of the matrix. On a stress basis, TMF loading reduced lives substantially, relative to isothermal cycling. In-phase cycling resulted in the shortest lives, and isothermal fatigue at 260 C, the longest

Characterization of failure processes in tungsten copper composites under fatigue loading conditions

A fractographic and metallographic investigation was performed on specimens of a tungsten fiber reinforced copper matrix composite (9 vol percent), which had experienced fatigue failures at elevated temperatures. Major failure modes and possible failure mechanisms, with an emphasis placed on characterizing fatigue damage accumulation, were determined. Metallography of specimens fatigued under isothermal cyclic loading suggested that fatigue damage initiates in the matrix. Cracks nucleated within the copper matrix at grain boundaries, and they propagated through cavity coalescence. The growing cracks subsequently interacted with the reinforcing tungsten fibers, producing a localized ductile fiber failure. Examinations of interrupted tests before final failure confirmed the suggested fatigue damage processes

Noise Source Identification of Small Fan-BLDC Motor System for Refrigerators

Noise levels in household appliances are increasingly attracting attention from manufacturers and customers. Legislation is becoming more severe on acceptable noise levels and low noise is a major marketing point for many products. The latest trend in the refrigerator manufacturing industry is to use brushless DC (BLDC) motors instead of induction motors in order to reduce energy consumption and noise radiation. However, cogging torque from BLDC motor is an undesirable effect that prevents the smooth rotation of the rotor and results in noise. This paper presents a practical approach for identifying the source of excessive noise in the small fan-motor system for household refrigerators. The source is presumed to a mechanical resonance excited by torque ripple of the BLDC motor. By using finite element analysis, natural frequencies and mode shapes of the rotating part of the system are obtained and they are compared with experimental mode shapes obtained by electronic torsional excitation test which uses BLDC motor itself as an exciter. Two experimental validations are carried out to confirm the reduction of excessive noise

Physical and Radiobiological Evaluation of Radiotherapy Treatment Plan

Radiation treatment planning plays an important role in modern radiation therapy; it could simulate to plan the geometric, radiobiological, and dosimetric aspects of the therapy using radiation transport simulations and optimization. In this chapter, we have reviewed several quantitative methods used for evaluating radiation treatment plans and discussed some important considering points. For the purpose of quantitative plan evaluation, we reviewed dosimetrical indexes like PITV, CI, TCI, HI, MHI, CN, COSI, and QF. Furthermore, radiobiological indexes like Niemierko’s EUD-based TCP and NTCP were included for the purpose of radiobiological outcome modeling. Additionally, we have reviewed dose tolerance for critical organs including RTOG clinical trial results, QUENTEC data, Emami data, and Milano clinical trial results. For the purpose of clinical evaluation of radiation-induced organ toxicity, we have reviewed RTOG and EORTC toxicity criteria. Several programs could help for the easy calculation and analysis of dosimetrical plan indexes and biological results. We have reviewed the recent trend in this field and proposed further clinical use of such programs. Along this line, we have proposed clinically optimized plan comparison protocols and indicated further directions of such studies

A decomposition-based approach for the integration of product development and manufacturing system design

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.Includes bibliographical references (p. 354-364).Using a structured approach to understand the interaction between product design decisions and manufacturing system design is critical to reflect manufacturing system issues early in the product development process. Early consideration of manufacturing system issues prevents product design iterations due to manufacturing system constraints or unnecessary manufacturing system design modification to accommodate new product designs. However, in academia and industry, few frameworks are available to capture the interaction between manufacturing system design and product design decisions. This thesis presents an approach to capture the interaction between manufacturing system design and product design decisions, which is called manufacturability evaluation process. The manufacturability evaluation process aims to guide product development teams to see the effects of their design decisions on manufacturing systems and thus, to make the right decision from the early stage of product development. The manufacturability evaluation process satisfies four objectives: 1) to describe the objectives of manufacturing systems clearly separated from the means of achievement, 2) to present the impact of various design decisions on the achievement of the objectives of manufacturing systems, 3) to provide a common platform to effectively communicate the impact across the organization, and 4) to provide a framework to put existing tools together to integrate manufacturing system design and product design. The manufacturability evaluation process is based on a recently developed Manufacturing System Design Decomposition (MSDD).(cont.) This thesis describes three groups of case studies to identify industry practices and provide application examples of the proposed manufacturability evaluation process. The manufacturability evaluation process has been successfully applied to the cases. In addition, the interaction between manufacturing system design and product design decisions are discussed with industry case study examples in the automotive industry. An evaluation tool is developed to evaluate the general practices of a company ensuring the manufacturability of product designs. Furthermore, this thesis provides a basis for future research to extend the scope of the MSDD into product development areas.by Yong-Suk Kim.Ph.D

Graph Anomaly Detection with Graph Neural Networks: Current Status and Challenges

Graphs are used widely to model complex systems, and detecting anomalies in a graph is an important task in the analysis of complex systems. Graph anomalies are patterns in a graph that do not conform to normal patterns expected of the attributes and/or structures of the graph. In recent years, graph neural networks (GNNs) have been studied extensively and have successfully performed difficult machine learning tasks in node classification, link prediction, and graph classification thanks to the highly expressive capability via message passing in effectively learning graph representations. To solve the graph anomaly detection problem, GNN-based methods leverage information about the graph attributes (or features) and/or structures to learn to score anomalies appropriately. In this survey, we review the recent advances made in detecting graph anomalies using GNN models. Specifically, we summarize GNN-based methods according to the graph type (i.e., static and dynamic), the anomaly type (i.e., node, edge, subgraph, and whole graph), and the network architecture (e.g., graph autoencoder, graph convolutional network). To the best of our knowledge, this survey is the first comprehensive review of graph anomaly detection methods based on GNNs.Comment: 9 pages, 2 figures, 1 tables; to appear in the IEEE Access (Please cite our journal version.

In-silico based redesign of CO-dehydrogenase catalyzing the oxidation of toxic waste CO gas for improved O2 resistance and mediator affinity

Carbon monoxide (CO) harmful to most creatures, is largely discharged by industrial processes in steel mill and thermal power plant. Conversion of toxic waste CO gas to safe gas or more valuable chemicals will be a great worth at this point. Interestingly, carbons and high potential electrons from CO-oxidation can be resourced as essential core parts for the chemical products by using CO-dehydrogenase (CODH) and artificial mediator. For industrial application of the enzymatic CO-oxidation, however, key issues remain that most CODHs show oxygen (O2) sensitivity and low-affinity for artificial mediator. Because steel mill waste gas such as blast furnace gas (BFG) commonly contains a little O2 and higher affinity is required to achieve higher reaction rate. In this research, in-silico based approach was used to redesign Carboxydothermus hydrogenoformans CODH (ChCODH) II, capable of increasing O2 resistance and affinity to ethyl viologen (EV) mediator. ChCODHs belong to a group of Ni-Fe containing CODH. Among five known ChCODHs (ChCODH I-V), ChCODH II shows the highest activity toward CO but more O2 sensitive than ChCODH IV. The artificial mediator of EV functions as an electron acceptor for ChCODH II but the affinity of ChCODH II to EV mediator is known poor. As our result, more than 10 folds increase of O2 resistance was achieved for the redesigned ChCODH II enzyme, which will be definitely a working horse in the conversion of waste CO gas into value-added chemicals