Microstructural Parameters for Modelling of Superconducting Foams

Superconducting YBa2Cu3Oy (YBCO) foams were prepared using commercial open-cell, polyurethane foams as starting material to form ceramic Y2BaCuO5 foams which are then converted into superconducting YBCO by using the infiltration growth process. For modelling the superconducting and mechanical properties of the foam samples, a Kelvin-type cell may be employed as a first approach as reported in the literature for pure polyurethane foams. The results of a first modelling attempt in this direction are presented concerning an estimation of the possible trapped fields (TFs) and are compared to experimental results at 77 K. This simple modelling revealed already useful information concerning the best suited foam structure to realize large TF values, but it also became obvious that for various other parameters like magnetostriction, mechanical strength, percolative current flow and the details of the TF distribution, a refined model of a superconducting foam sample incorporating the real sample structure must be considered. Thus, a proper description of the specific microstructure of the superconducting YBCO foams is required. To obtain a set of reliable data, YBCO foam samples were investigated using optical microscopy, scanning electron microscopy and electron backscatter diffraction (EBSD). A variety of parameters including the size and shape of the cells and windows, the length and shape of the foam struts or ligaments and the respective intersection angles were determined to better describe the real foam structure. The investigation of the foam microstructures revealed not only the differences to the original polymer foams used as base material, but also provided further insights to the infiltration growth process via the large amount of internal surface in a foam sample

Joining Technologies for Cardiovascular Implants

Nitinol (NiTi) is widely used in the medical field, due to its unique superelastic and shape memory properties. Nitinol undergoes thermo-mechanical processing, such as thermosetting, laser-cutting and joining for medical application, however these processes can alter these properties. The Temperature-dependant characteristics of nitinol can work as a disadvantage to fully exploit this alloy for biomedical applications. Three different themes are explored in this thesis, a) the properties of nitinol-nitinol bonds compared to base metal b) understanding how welding method affects bond properties and joint strength and c) investigating the optimum method for bonding nitinol to non-metal such as biopolymers. In order to overcome the above-mentioned limitations, different joining techniques for nitinol was investigated in this study. Initially, the effect of different joining techniques on nitinol properties, in comparison to base metal was investigated. Experimental results mainly focus on the nitinol to nitinol joining techniques, including laser micro welding (Ytterbium-fiber laser and quansi continuous wave laser), capacitor discharge welding, percussive arc welding, adhesive bonding, PEEK shrink tubes and crimping. The effects of these joining techniques on the microstructure, superelastic properties and strength of a joint are analysed and compared. The mechanical tests and analytical results suggest that the use of laser welding should be employed for the development of new and improved medical implants. However, long-term studies are required which are currently underway to further develop this technique. For various medical applications, metal components are mainly used to provide the strength and stiffness whereas polymeric biomaterials can provide unique chemical properties and manufacturing, benefits as they can be moulded and shaped into complex designs depending on the application. However, due to the massive difference in physical and chemical properties of metal and polymers, joining them generates new challenges. Hence, the third part of the thesis explores different approaches to join nitinol to polymeric biomaterials including Polyetheretherketone (PEEK), and polyethylene terephthalate (PET) fabric, commercially known as Dacron®. Due to the difference in chemical and physical properties of nitinol to PET, it was difficult to join them without using an interlayer. Thus, a polyurethane coating was used as an interlayer to bond nitinol to PET fabric. This study also provides an insight into different surface treatments used to improve the bonding between nitinol and polyurethane coating including chemical etching and cold atmospheric plasma treatment. The study shows how an appropriate selection of the joining technique can enhance the exploitation of properties of nitinol alloy in the clinical area, resulting in improvements in the safety and durability of medical devices

Nanoporous-gold-based composites : toward tensile ductility

We report on mechanical tests on interpenetrating-phase nanocomposite materials made by vacuum impregnation of nanoscale metal networks with a polymer. The metal component is nanoporous gold made by dealloying, whereas two epoxy resins and polyurethane are explored as the polymer component. The composites are strong and deformable in compression. Although previous observations invariably indicate tensile brittleness for nanoporous gold, composite samples made from cm-sized nanoporous samples enable macroscopic tensile and four-point bending tests that show ductility. This implies that the high strength of individual metal objects such as nanowires can now be incorporated into a strong and ductile material from which macroscopic things can be formed. In fact, a rule-of-mixture-type analysis of the stresses carried by the metal phase suggests quantitative agreement with data reported from separate experiments on small-scale gold nanostructures

The Effects of Material and Configuration on the Acoustic Response of an Impact Stop

The noise levels on factory floors have been a historical concern with respect to worker health. The sponsor utilizes impact stops throughout their production facilities; each stop is hit hundreds of times per minute contributing to high decibel levels. The goal of this project was to identify alternative materials and configurations of the stop to minimize the noise output upon impact. This was accomplished by researching alternative materials, constructing a testing apparatus, and the construction and testing of prototype stops

Do the Mechanical and Chemical Properties of Invisalign\u3csup\u3eTM\u3c/sup\u3e Appliances Change After Use? A Retrieval Analysis

Aim: To investigate the mechanical and chemical alterations of Invisalign appliances after intraoral aging. Materials and methods: Samples of Invisalign appliances (Align Technology, San Jose, California, USA) were collected following routine treatment for a mean period of 44±15 days (group INV), whereas unused aligners of the same brand were used as reference (group REF). A small sample from the central incisors region was cut from each appliance and the buccal surface was analysed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (n = 5). Then the appliances were cut (n = 25) and embedded in acrylic resin, ground/polished in a grinding polishing machine, and the prepared surfaces were subjected to Instrumented Indentation Testing under 4.9 N load. Force-indentation depth curves were recorded for each group and the following parameters were calculated according to ISO 14577-1; 2002 specification: indentation modulus (E IT), elastic to total work ratio also known as elastic index (ηIT), Martens Hardness (HM), and indentation creep (C IT) The mean values of the mechanical properties were statistically analysed by unpaired t-test (a = 0.05). Results: ATR-FTIR analysis confirmed the urethane based structure of the appliances, without important chemical differences attributed to the aging process. INV group showed significantly lower E IT (REF: 2466±20, INV: 2216±168MPa), HM (REF: 119±1, INV: 110±6 N mm−2) and higher ηIT (REF: 40.0±0.3, INV: 41.5±1.2%), and C IT (REF: 3.7±0.2 INV: 4.0±0.1%). The increase in ηIT indicates that INV is a more brittle than REF, whereas the increase in C IT, a decrease in creep resistance. Conclusion: Despite the lack of detectable chemical changes, intraoral aging adversely affected the mechanical properties of the Invisalign appliance

The study on the integration of Activity Based Costing (ABC) system and six-sigma principle

Manufacturing organizations are facing much more challenges as compared to the earlier years. The important and crucial decisions have to be taken by the management in continuous basis in order to ensure the survival and competitiveness of company throughout the journey to become a successful organization. In order to make these decisions fast and correct, they need more accurate information related to financial and non-financial aspects. The conventional cost management systems, which were developed decades ago are unable to provide all information required to make right decision, justify the cost reduction and process improvements (Chen, 1996). This is because they were based on labor-intensive production system while today’s production processes are more sophisticated and faces constant changes. An alternative costing system, Activity Based Costing (ABC) has emerged to the new solution to costing system. It provides financial and non-financial information not only for product costing but also for each activity of manufacturing process. It can list and measure the cost of each activity individually in production and in supporting activities to deliver of a product or service right to customers (Sohal & Chung, 1998). ABC focuses on the activities performed to produce the products throughout the manufacturing process (Gunasekaran et al., 1999). By assigning other costs, such as marketing and administrative to cost object, ABC able to provide more accurate product costs. It helps to improve the operational performance by allocating overhead costs correctly. It provides cost information based on the actual consumption of the resources by each particular activity. The goal of ABC is to reveal cost allocation information by tracing the production costs accurately to activities and product (Gunasekaran et al., 1999). The implementation of ABC has provided many benefits, such as more accurate product costing, providing of cost behavior information and tracing resources consumptions. Realizing many benefits gain from implementation of ABC, many companies have embarked in applying ABC system. However, there are many problems and barriers they encountered during the implementation, which made some has decided to abort this system and not be able to exploit its advantages. It is the objective of this study to help foster the growth of Malaysian companies by helping them to provide better understanding,knowledge and skills to take advantage of using ABC as a tool to improve their manufacturing process. The title of the project is The Study on Integration of Activity-based Costing and Six-sigma Principle. The specific objective of the study is to determine success factors for ABC implementation in manufacturing companies based on Six-sigma process improvement principle. The focus of the study is to identify and understand the critical success factors in implementation of ABC, to identify and specified the problems and barriers and to understand their relationship with the ABC success. In order to identify, understand and formulate the proposed solution, this study will use a survey approach to get required data for further analysis. The survey will be based on mailed questionnaires to selected manufacturing industries in Malaysia. In order to formulate a comprehensive and relevant set of questionnaires, a comprehensive review of literature will be studied, followed by validation and verification process,which involved expert opinions and a pilot study. The next phase is where data from the study will be analyzed to identify areas related to the level of acceptance of ABC,the critical success factors and also to determine the relationship between the organization’s factors and the success of implementation of ABC system. The tangible outcome of this project is to provide a set of proposed guidelines and support tools for manufacturing organizations in applying Activity-based Costing for process improvement efforts as suggested by Six-sigma improvement principle

The Armaments of the Hundred Years\u27 War and Their Effects on Western Europe

This project investigates the development of weaponry during the late medieval period, specifically focusing on the Hundred Years\u27 War, fought between England and France between 1337 and 1453. This report will explore the historical background of this conflict and the changes to army organization, military technology, and tactics that resulted from it. Additionally, it will describe the construction of a warhammer, a staple of the conflict, and explore its material properties in an attempt to classify the general armaments of the time. Finally, it describes the changes made to WPI\u27s Historical Evolution of Arms and Armors website with respect to adding content related to the project, as well as improving the inner workings of the site and providing a better user experience

Microstructure-Based Multistage Fatigue Characterization And Modeling Of An Acrylonitrile Butadiene Styrene Copolymer

In this work, fatigue experiments and observations are used to experimentally and computationally quantify fatigue structure-property relationships and then capture these effects through a microstructure-based MultiStage Fatigue (MSF) model for a thermoplastic Acrylonitrile Butadiene Styrene copolymer. Completely reversed fatigue experiments were conducted over a range of strain amplitudes at two frequencies (1 Hz and 10 Hz). Scanning electron microscopy of fatigue fracture surfaces was used to quantify the microstructural notch root or initiating particle size for structure-property relations. Results were then processed in an MSF model sensitive to microstructural effects to capture the fatigue lifetimes for the thermoplastic ABS copolymer

Microstructure-Based Multistage Fatigue Characterization And Modeling Of An Acrylonitrile Butadiene Styrene Copolymer

In this work, fatigue experiments and observations are used to experimentally and computationally quantify fatigue structure-property relationships and then capture these effects through a microstructure-based MultiStage Fatigue (MSF) model for a thermoplastic Acrylonitrile Butadiene Styrene copolymer. Completely reversed fatigue experiments were conducted over a range of strain amplitudes at two frequencies (1 Hz and 10 Hz). Scanning electron microscopy of fatigue fracture surfaces was used to quantify the microstructural notch root or initiating particle size for structure-property relations. Results were then processed in an MSF model sensitive to microstructural effects to capture the fatigue lifetimes for the thermoplastic ABS copolymer