http://dspace.cityu.edu.hk:80/handle/2031/3808 Tue, 30 Apr 2013 07:48:33 GMT 2013-04-30T07:48:33Z http://dspace.cityu.edu.hk:80/handle/2031/6653 Title: A study on the mechanical properties and performance of selected thermoplastic and thermosetting composites for engineering applications Authors: Yeung, Kai Kin ( 楊啟健) Abstract: Fibre reinforced composites, a combination of reinforcing fibre and matrix, offer many advantages over traditional materials and therefore found wide application in the aerospace and construction industry. Among the advantages that traditional thermosetting composites offer, the most citied are weight saving, high modulus, high strength-to weight ratio, corrosion and fatigue resistance. Recently, the development of high performance thermoplastics composites has been accountable for increasing their demand. Whereas the developed thermosetting composites have created environmental concerns because of hazardous fumes generated during fabrication of composites and, most importantly, they are non-recyclable. Lack of previous experience on the durability of thermoplastic composites and the demand for more understanding of their properties in the planning and design stage is increasing. Such advances have created in inescapable need for establishing an understanding and comparison of the mechanical behaviour of thermoplastic and thermosetting composites. The main aim of this research is to investigate and explore the potential advantages and feasibility of thermoplastic composites in typical applications that are traditionally deploying thermosetting composites. In addition, the study also widens the scope of designing composites in a simple and direct way by industry persons, without the need for complex mathematical analysis. This study also covers issues of environmental aging, durability and cost analysis for thermoplastic and thermosetting composites that can serve as a ready reference for the industry. The objectives of this research are: 1) to develop a class of thermoplastic-based Boron, Kelvar-49 and Carbon reinforced fibre composite laminates; 2) to study the mechanical behaviour of the developed composites and explore the application of theoretical models for predicting the mechanical behaviour of these composites, and 3) to study the value, benefit and potential application of thermoplastic composites for the industry. The selection of fibres for this study was based on an initial study using some simple theoretical models for predicting the mechanical properties of a large number of fibres with combination of several thermoplastic and thermosetting matrixes. The fibre and matrix combinations are chosen such that low, medium and high strength composites are developed for further study. The three types of fibres selected (Boron, Kevlar-49 and Carbon) are combined with three types of thermoplastics (Styrene Acrylonitrile (SAN), Acrylonitrile Butadiene Styrene (ABS) and Polyethylene (PE)) and two types of thermosetting matrices (Polyimide (PI) and Low Modulus Polyester). Firstly, the prediction of mechanical behaviour of composites with these chosen combinations of constituents has been made. Theoretical prediction of mechanical properties of thermoplastic and thermosetting composites from their constituent's properties has been made by using the following micromechanical models: (1) Rule of Mixtures (ROM), Halpin-Tsai, Eshelby's Inclusion model, Modified Rule of Mixtures (Modified ROM) and Self-Consistent model for uniaxial longitudinal tensile strength; (2) Rosen - extensional mode, Rosen - shear mode and Xu-Reifsnider Model for longitudinal compressive strength and; (3) Inverse Rule of Mixture (IROM) and Modified Inverse Rule of Mixtures (Modified IROM) for transverse strength. All the tested specimens were prepared in sheet form by modified pultrusion process which is being widely used in the manufacture of thermosetting composites. The fibre volume fraction was maintained at 61% which is commonly used for most structural composites. The experimental work to evaluate the mechanical properties of the developed composites included uniaxial tension test following British Standards BS 2782 Part 3 Method 321:1994, compression test based on BS 2782 Part 3 Method 345A:1993 standard, and three-point bending test following BS 2782 Part 3 Method 335A:1993 standard. The consolidated results indicate that all experimentally obtained strength values are the highest for Boron composites when compared with Carbon and Kevlar-49 thermoplastic and thermosetting composites. The tensile strengths are nearly the same for all composites prepared with the same fibre but with different matrix materials, indicating that they are fibre dominated. Their respective compressive strengths are lower than tensile strengths as they appear to be matrix dependent. The flexural strengths are between the tensile and compressive values, whereas the flexural modulus values are the lowest among the three types of loading, except Boron-Polyimide composite having its flexural strength higher than tensile strength. In assessing the standing of theoretical models which predict the mechanical properties of Boron, Carbon and Kevlar-49 thermoplastic and thermosetting composites in terms of their constituents, it is often difficult to discriminate between the validity of assumptions made in the models and constructional imperfections within the specimens. Results indicate the theoretically estimated tensile strengths using ROM model are dramatically higher by an order of magnitude than the experimentally obtained tensile strengths. The tensile strengths are controlled and dominated by fibre alone and the matrix contribution to their strengths is negligible. From the compression tests, it is found that micro-buckling approach has made little success in predicting the compressive strength by Rosen's model whereas Xu-Reifsnider model has shown good agreement with the experimental values which are only about 10% lower than theoretically obtained compressive strengths. The matrix properties seem to be the major contributors of the prepared composites. It is found that the flexural strength values obtained from the three-point flexural tests are about 14-17% lower than the corresponding theoretical values using IROM models. These properties have more complex dependency with respect to the properties of participating fibre, matrix and manufacturing. Systematic and numerical costing analysis of respective thermoplastic and thermosetting composites has been made for managing their application. The total product cost is established based on factors such as material, labour, overhead, selling expenses, general administrative expenses, taxes as well as net profit. The results indicate that the production cost is highest for Boron based thermoplastic composites among all the selected composites whereas thermosetting composites with Carbon are the lowest. From the comparison of cost per unit strength analysis, it is found that Boron-Polyethylene, Carbon-Polyimide and Boron-SAN gave the best results in tensile properties, flexural properties and compressive properties, respectively. The outcomes can assist the fabricator to choose suitable composites in order to suit their specific loading requirement during design stage. In conclusion, the micromechanical models can hardly be used for exact practical analysis of composite materials and structures because even the most vigorous models cannot describe adequately the real composites evolved during manufacturing. Many features such as voids, microcracks, and randomly damaged and misaligned fibres cannot be formally reflected in mathematical models. In such circumstances, micromechanical models may be used for initial qualitative analysis, providing an understanding of how the constituent parameters affect the mechanical properties followed by experimental determination of these properties. Unintentional variations in fibre alignments provide unforeseeable complications and variations to the experimental results and the problems are enhanced in fabric reinforced blocks. Even with these reservations and complications, the results obtained in the present investigation fall into a clearly identified pattern and the results obtained are readily applicable in the composites industry. Notes: CityU Call Number: TA418.9.C6 Y48 2011; xvii, 202 leaves : ill. 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2011.; Includes bibliographical references (leaves 153-161) Sat, 01 Jan 2011 00:00:00 GMT http://dspace.cityu.edu.hk:80/handle/2031/6653 2011-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6649 Title: Improving technical quality in repair service to achieve customer satisfaction in automotive after-sales service Authors: Tong, Kwok Kei ( 湯國基) Abstract: Hong Kong has gone through a rapid change in her economy from industrial to service base during the last two decades. The service industry has played a major role in determining the Gross Domestic Product (GDP) of the city and the growth trend can be well explained from the figures of 85.7% in 1998 to 92.3% in 2007. In order to run a service business successfully, it is essential to provide excellent service quality so as to satisfy the customers' need. For the after-sales service of the motor industry, there are keen competitions among the various number of after-sales service dealers. Generally, the after-sales service is linked up with parts supply and vehicle repair or maintenance service (conclusively named as after-sales repair service). Such a relationship has always been considered as one of the major factors in affecting the customers' decision when buying a new vehicle. After from the high expectation from customers, the car manufacturers shall also demand seriously a high standard of after-sales service from their dealers. Apart from these two parties, the dealers also have to encounter the competition from small garages which tend to attract customers with aged vehicles by offering service at a highly competitive price. Therefore, the service dealers nowadays have to meet the challenge of not only providing the best service to the customers but also maintaining the business in a sustainable manner. There are lots of service dimensions that contribute to service quality and customer satisfaction. Through literature review and interviews with professional of the industry, the technical quality in after-sales repair service, i.e. to fix it right the first time (F-1) in order to avert repeated repair is regarded as the principal factor of the overall quality level in automotive after-sales repair service. When customers are satisfied with the service, the business will sustain. This project proposes a framework on how to improve the technical quality in repair service with adoption of knowledge sharing and transfer in automotive after-sales service industry. The project uses the action research method and applies to one of Hong Kong's leading automotive after-sales dealers, Dah Chong Hong (MSC) Ltd., hereafter called DCHMSC, for illustration. A general customer satisfaction survey conducted in year 2005 revealed that the Company had a low customer satisfaction score among the market. At last, the Company was able to improve the overall service quality through the improvement of technical quality in after-sales repair service. Apart from taking into account of the non-technical aspects like the attitude of the service personnel in order to narrow down the project scope to the improvement of technical quality in repair service of after-sales service, the project aims at exploring the critical steps within the overall after-sales service process. Based on customer complaints, feedbacks and commended cases on repeated repair or dissatisfaction with the workmanship in service, investigation is carried out into these cases to differentiate the types of quality problems so as to conclude the most common causes that have led to non F-1 (fix it right the first time) or repeated repairs. The two major results are identified as: 1) Previous repair is not effective, and 2) Problems occurred after periodical maintenance is done. An in-depth analysis is conducted to identify the possible causes to these deficiencies. The latter part of the project suggests and establishes the roadmap for implementation of improvement / remedial actions with the emphasis being put on knowledge sharing and transfer among the workshop mechanics, and service process enhancements. This is because knowledge assets play an important role in sustaining the competitive advantage of the companies in business environment nowadays. More importantly, knowledge and skills are the indispensable elements in performing vehicle repair and maintenance service. A knowledge map is then used for analysis on the knowledge needs and requirements by service people within the after-sales service process. Another social network analysis tool, named Applied Graphic and Network Analysis (AGNA), is adopted to identify the role of individuals within the service network. AGNA also helps to determinate on how knowledge should be transferred and shared among the service network in order to achieve the best and effective result in improving the technical quality in repair services. Finally, the enhancements in service process help to minimize any human mistake and service inconsistency. The effectiveness of the improvement actions is then measured by two different approaches, 1) quality of repair / maintenance through customer's feedback, and survey measurements; and 2) feedback from the workshop mechanics as being the end users on the efficacy of improvement actions implemented. The innovation of this EngD project aims at exploring / analyzing knowledge application and sharing in a systematic approach called AS-QiKi with the result of improving the technical quality in repair service and eventually the overall after-sales service quality of motor industry. As long as the research nature of the project is of industrial base, the framework delivered shall contribute to the motor industry by means of providing solutions to similar problems encountered by service dealers and workshops of similar scale or capacity. Notes: CityU Call Number: TL152 .T66 2011; xx, 246 leaves : col. ill. 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2011.; Includes bibliographical references (leaves 212-224) Sat, 01 Jan 2011 00:00:00 GMT http://dspace.cityu.edu.hk:80/handle/2031/6649 2011-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6648 Title: A survey of contact wire wear parameters and the development of a model to predict wire wear by using the artifical neural network Authors: Shing, Wai Chung ( 盛偉忠) Abstract: To provide energy for the running of electric trains the overhead conductor system (OCS) is one that is commonly used. The OCS is fixed over the railway tracks with the contact wire above for the collection of electricity by the pantographs which are mounted on the roof of trains. The interaction of the pantograph collector strips and the contact wires is maintained by the pressure applied by the pantographs. This friction inevitably leads to the wear and tear of both the interfacing materials. Replacement of the pantograph collector strips is performed in the train maintenance facility whereas the replacement of the contact wires can be done during the limited non train running periods normally at night or planned system shutdowns. The railway operator has to plan in advance the replacement of the contact wire, before the cross-sectional area is worn below the point where, it infringes on either the electrical or mechanical limits. If the contact wire is worn below its limit then the electrical resistance may result in a voltage drop becoming too high and train motors may stall and burn out. If the contact wire fails mechanically i.e. below the minimum tensile strength, then it may break due to tension on the wire. Without a creditable method of predicting the condition of the contact wire then it would eventually reach the threshold and place the system at risk of a failure. The railway operator needs to be proactive and prudent in the planning and executing a wire replacement program, well before the wire reaches its engineering limits or a failure that can drain resources unnecessarily. With the scarcity in resources, the railway operators needs tools to predict the 'when' contact wire replacement needs to take place prior to its useful life expiring. A statistical approach using historical data is therefore proposed. The success of this statistical approach relies on a large quantity of data collected. In the past decade or two, advances in on-line measurement to collect the primary data on wear and contact force has provided far more information than a railway operator can assimilate. In this research, a review of the analytical and other approaches to predict contact wire wear was conducted. A comprehensive review of the possible contributing factors to the rate of wear for the contact wire and its pantograph counterpart is summarized. This includes as far fetching as the effect of humidity on the rate of wear of pantograph collector strips. Then, a statistical approach together with an artificial neural network (ANN) model is proposed to make the wear projection. Based on the data obtained from the 33-km double tracked Airport Express Line (AEL) taken over a two-year period, an attempt is to establish a feed-forward neural network to correlate the wire wear (as output/target pairs) with the contributing factors (i.e. input parameters corresponding to the output/target). Thus the ANN model, if successfully created, can predict when the wires in segments will need just-in-time replacement. The potential input parameters are wire height, wire stagger, train speed, contact force, traction mode, span length and pantograph passes. Due to the measurement of these parameters with data records taken from different train runs and devices, the data records are combined as input-target pairs to explore the correlation between output and target by the ANN model. A reasonable degree of correlation between wire wear and track topology is found. Following this, an attempt is to check the wire wear for different measurement runs over the two-year period to include the time as an input. However a sanity check of the wear data across datasets found that the average cross-sectional area of contact wires in segments increases with time. The increase in wire cross-sectional area is physically improper and this anomaly is attributed to calibration inconsistency in the measurement equipment. The calibration accuracy and consistency of the measuring equipment between runs needs improvement to predict wear rate over time as proposed research works for future study. The proposed method using ANN model has demonstrated the methodology for wire wear projection and the correlation of selected parameters to the contact wire wear even without the time factor. The methodology establishes the need to use statistical mean and variance of every data in a section as a form of abstraction of wire wear states by segments. This has the advantage over the analysis point-by-point using the raw data and makes it suitable for the training of the feed-forward ANN model and helps in the visualization of contact wire deterioration due to wear as well as the improvement if there is any modification works such as maintenance and renewal activities. In conclusion, this research involves using data obtained from a real railway network to build an ANN model which is able to correlate the wire wear using known operating parameters such as height, stagger, train speed, contact force etc. This prediction method can be refined periodically when new data is collected and integrated as target/input pairs to improve the model every year until the contact wire is finally replaced. Notes: CityU Call Number: TK3231 .S54 2011; 164 leaves : col. ill. 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2011.; Includes bibliographical references (leaves 138-144) Sat, 01 Jan 2011 00:00:00 GMT http://dspace.cityu.edu.hk:80/handle/2031/6648 2011-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6644 Title: A strategic assessment model of brand extensions of consumer electronics brands : an integrated quantitative and qualitative study Authors: Ho, Alvin Felix ( 郝廣仁) Abstract: The aim of this research is to formulate a consumer electronics brand extension assessment model (C-BEAM) that captures the key factors of brand extension success (i.e., original brand attitude, perceived quality of the original brand, and the perceived fit between the original brand and extension product in different dimensions). The C-BEAM is intended to serve primarily for an US-based consumer electronics firm, namely Maxpower, which has sponsored and supported this research. An integrated approach of mixing both quantitative and qualitative research methods had been used in the current study. In this research, quantitative study had included data collection via extensive structured surveys. The collected quantitative data was analyzed by using multiple regression analysis in order to examine any relationships that could provide justification to the hypotheses generated. Concerning qualitative works, they consisted of: 1) focus group study under a real brand extension scenario as principle source of qualitative data; and 2) in-depth interviews with interviewees with different backgrounds in the consumer electronics field as the second source. Qualitative findings acquired from the focus group study and in-depth interviews had been used as supplementary support to the quantitative findings. The following findings are drawn from this integrated quantitative and qualitative research: 1. The direct effects of original brand attitude, perceived quality of the original brand, and perceived fit between the original and new products positively affect the consumers' evaluations of brand extensions. 2. Brand familiarity has no specific sign of direct effect on the overall evaluation of the extension products. 3. Perceived fit between the original and new products is the most important factor contributing to favorable evaluations on brand extensions. 4. Feature and know-how are the two brand extension dimensions that are more likely to drive brand extension success. Based on the overall research findings of this study, the C-BEAM has then been developed. After the development of the C-BEAM, a pilot application of the C-BEAM in real brand extension cases of Maxpower was undertaken as part of this research in order to validate the model. Having referred to the model developed, the product/brand managers of Maxpower are able to evaluate the relative extendibility of their brand name by taking their existing brand characteristics and value into account. Therefore, they are given certain references to decide on the kinds of new products their brand should extend to during the opportunity identification phase of the new product development process. A "go" or "no go" decision can then be made by the product/brand managers of the firm according to what have been indicated by the model. Notes: CityU Call Number: HD69.B7 H6 2011; xiii, 163 leaves : col. ill. 30 cm.; Thesis (Eng.D.)--City University of Hong Kong, 2011.; Includes bibliographical references (leaves 107-115) Sat, 01 Jan 2011 00:00:00 GMT http://dspace.cityu.edu.hk:80/handle/2031/6644 2011-01-01T00:00:00Z