Dissertations / Theses on the topic 'Aerospace defence'
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Tsolakidis, Stefanos K. "Foresight of aerospace and defence technologies in Greece up to 2020." Thesis, Middlesex University, 2006. http://eprints.mdx.ac.uk/13552/.
Full textJohn, Ryan Nichols. "Impact detection techniques using fibre-optic sensors for aerospace & defence." Thesis, Heriot-Watt University, 2015. http://hdl.handle.net/10399/2970.
Full textLatham, Michael John. "Restructuring the West European defence aerospace industry : a "domestic filtration" approach." Thesis, University of Sheffield, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.521958.
Full textDarling, Eric J. (Eric John) Carleton University Dissertation Management Studies. "A study of government-business partnerships in the aerospace/defence electronics industry." Ottawa, 1990.
Find full textDelmonte, Tiina. "Studies into the potential uses for microstructured fibres in aerospace and defence applications." Thesis, Heriot-Watt University, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493515.
Full textBarnett, Neil John. "A proposed model for servitization based collaboration in the UK Aerospace Defence industry." Thesis, University of the West of England, Bristol, 2016. http://eprints.uwe.ac.uk/27696/.
Full textIakovaki, Antigoni. "Service supply chain integration in multi-organisation networks : findings from the defence aerospace sector." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610686.
Full textMiah, Abdul. "Product-based environmental metrics for use within aerospace, defence, space and security industries (ADS)." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/845983/.
Full textAli, Usman. "Configuration management process maturity : definition and maturation of configuration management for aerospace and defence industries." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/configuration-management-process-maturity-definition-and-maturation-of-configuration-management-for-aerospace-and-defence-industries(63343e6b-9f51-4492-b934-00394ef2720c).html.
Full textCullen, Penny-Anne. "Contractual and working relations in the aerospace industry: A comparison of the Civil and defence sectors." Thesis, University of Warwick, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500586.
Full textJackson, Ian. "The economics of the UK aerospace industry : a transaction cost analysis of defence and civilian firms." Thesis, University of York, 2004. http://etheses.whiterose.ac.uk/10976/.
Full textRaja, Sandeep. "The systematic development of Direct Write (DW) technology for the fabrication of printed antennas for the aerospace and defence industry." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14930.
Full textJenvald, Mattias, and Mikael Hovmöller. "Reducing Delays for Unplanned Maintenance of Service Parts in MRO Workshops : A case study at an aerospace and defence company." Thesis, Linköpings universitet, Produktionsekonomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-167203.
Full textVenditti, Sara. "New Wings for Europe : Western European Strategic Cooperation and Integration in the Aerospace Field : Ariane and Eurofighter, 1973–1985." Doctoral thesis, Luiss Guido Carli, 2020. http://hdl.handle.net/11385/203542.
Full textCollison, Kurt Ryan. "The South African military aerospace industry: An overview of the special defence account more commmonly known as 'The South African Arms Deal'." Thesis, University of the Western Cape, 2007. http://etd.uwc.ac.za/index.php?module=etd&action=viewtitle&id=gen8Srv25Nme4_5741_1256300601.
Full textThe paper focuses specifically on the South African Military Aerospace Industry as most of the weapons procured under the arms deal were military aircraft. Taking into account the numerous social needs of South Africa, the purpose of this paper is to inter alia try to establish the rationale behind the South African government's decision to to purchase an array of military weapons from foreign suppliers at an initial cost of almost thirty billion rand. In order to gain a better undrstanding of the topic, the author gives a brief overview and history of the South African Aerospace industry.Furthermore, an examination of the politics of the transition from apartheid to democracy and how this affected the aeropace industry is given.
Gartzke, Ulf. "The Boeing / McDonnell Douglas and EADS mergers : ethnocentric vs. regiocentric consolidation in the aerospace and defence industry and the implications for international relations." Thesis, London School of Economics and Political Science (University of London), 2010. http://etheses.lse.ac.uk/266/.
Full textBergstedt, Malin. "Sales and Operations Planning Framework : How to balance demand and supply for a project-oriented and complex organization operating inthe aerospace and defence industry." Thesis, Linköpings universitet, Produktionsekonomi, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-156501.
Full textFabbri, Riccardo. "Conceptualization, design & simulation of a small asteroid probe." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textLungu, Sorin. "European defense market integration : the aerospace sector in 1987-1999 /." Thesis, Connect to Dissertations & Theses @ Tufts University, 2005.
Find full textChair: Robert L. Pfaltzgraff, Jr. Submitted to the Fletcher School of Law and Diplomacy. Includes bibliographical references (leaves 358-398). Access restricted to members of the Tufts University community. Also available via the World Wide Web;
Arsenault, Reginald W. "Creation of a CRM selection methodology for the aerospace & defense industry." [Denver, Colo.] : Regis University, 2006. http://165.236.235.140/lib/rarsenault2006.pdf.
Full textDonovan, Mark H. "The French Aerospace and Defense Industries: changing dynamics of procurement and consolidation." Thesis, Monterey, California. Naval Postgraduate School, 1998. http://hdl.handle.net/10945/8427.
Full textFrance's traditions of national sovereignty and its global status as a "great power" help to explain its investments in an independent and autonomous armaments industry. The resulting capabilities, ranging from fighter aircraft to nuclear weapons, have helped to ensure the position of France as a leading nation during the latter half of the twentieth century. Overcoming the inherent problems associated with state control and oversight of the means of production, France has developed a robust manufacturing capability and has produced, among other systems, technologically advanced designs in combat aircraft (the Rafale fighter), space rocket launchers (the Ariane 5 launcher), and remote sensing satellites (the Helios military satellite). However, the need to continue incorporating modem, expensive technology into French systems in the face of budgetary cutbacks has brought the future viability of autonomous and French-led programs into question. As a result, France and other major European nations have tried to find a common solution to consolidate each country's aerospace and defense firms into one corporate entity that could compete effectively against the United States. However, problems rooted in maintaining national capabilities, especially in France, have kept this design from becoming a reality
Johnstone, Jeffrey Carl, and Patrick Daniel Keavney. "Pricing Strategy, Pricing Stability and Financial Condition in the Defense Aerospace Industry." Thesis, Monterey, California. Naval Postgraduate School, 1987. http://hdl.handle.net/10945/41618.
Full textAll original copies missing. Best digital copy available.
The purpose of this research is to determine if pricing strategy and pricing stability for products in the defense aerospace industry can be predicted based on a firm's financial condition. The sample for this research includes 17 contractors and 52 missile and aircraft programs. Two separate issues are addressed. The first issue concerns the relationship between financial condition and contractor pricing strategy. The second concerns the relationship between organizational slack and pricing stability. The overall findings are: 1) That a limited amount of variation in pricing strategy can be explained through the use of a linear regression model using financial ratios; and 2) That no apparent relationship exists between organizational slack and pricing stability.
Gianzina-Kassotaki, Olga. "Ambidexterity and leadership : a multilevel analysis of the aerospace and defense organizations." Thesis, University of Warwick, 2017. http://wrap.warwick.ac.uk/95904/.
Full textWu, Marcus Shihong. "Design for affordability in defense and aerospace systems using tradespace-based methods." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/89937.
Full textThesis: S.M. in Technology and Policy, Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 262-270).
Program failures have plagued the defense and aerospace industry for decades, as unanticipated cost and schedule overruns have rendered the development of systems ineffective in terms of time and cost considerations. This raises the need to holistically include performance, cost and schedule considerations during the early-phase design of systems to perform valuable tradeoffs that derive more feasible and affordable solutions. This paradigm is the design for affordability. This design for affordability conundrum is targeted at defense and aerospace systems, which have complex mission requirements and stakeholder involvement that are susceptible to changes and perturbations over time. Without a systematic framework, the design for affordability process can potentially become cognitively challenging to system architects and lead to unsatisfactory results. To resolve affordability, it can first be defined as the property of becoming or remaining feasible relative to resource needs and resource constraints over time. Affordability can then be treated as an ility that drives the design of more affordable yet technically sound architectures. Tradespace-based methods are introduced to drive affordability and incorporate these holistic considerations into the design process. They facilitate the systematic and disciplined search for affordable solutions to the system, program and portfolio of interest. Multi-Attribute Tradespace Exploration (MATE), Epoch-Era Analysis (EEA) and the Multi-Attribute Expense (MAE) function were modified for affordability analysis. Their feasibility was demonstrated through application to two design case studies. Results from both case studies demonstrated the dynamic tradeoffs among performance, cost and schedule parameters. Tradespace-based methods can thus be applied to the progressive design of systems, programs and portfolios using either a bottom-up or top-down approach to deliver affordable solutions in these cases. Affordability is not only an engineering problem; it is also a policy and management problem. Therefore, affordability can be approached through perspectives beyond engineering design. New policies and refined management practices can be used alongside tradespace-based methods for affordability analysis to ensure the continued delivery of affordable systems for the future.
by Marcus Shihong Wu.
S.M.
S.M. in Technology and Policy
Vaughn, Amanda F. (Amanda Faith) 1977. "A holistic approach to manufacturing system design in the defense aerospace industry." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/82236.
Full textShaw, Thomas E., Alexander Lengyel, and Greg Ferre. "An Assessment of the Degree of Implementation of the Lean Aerospace Initiative Principles and Practices within the US Aerospace and Defense Industry." Defense Contract Management Agency, 2004. http://hdl.handle.net/1721.1/7320.
Full textMyers, Kevin Michael. "Building flexibility in the volatile aftermarket parts : supply chains of the defense aerospace industry." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39695.
Full textIncludes bibliographical references (p. 89-90).
Within the Integrated Defense Systems of The Boeing Company, aftermarket support of military aircraft serves as an increasingly large source of revenue. One of the newest contracts between Boeing and the U.S. Government created such a supply partnership at the Army Rotorcraft Repair Depot in Corpus Christi, Texas. At this depot, all Army helicopters, including Boeing's AH-64 Apache Attack helicopter and CH-47 Chinook Cargo helicopter undergo major repair and overhaul. In 2004, Boeing entered an agreement with the U.S. Government to assume responsibility of the repair depot's supply chain for aftermarket parts for Boeing rotorcraft. Over the last two years, Boeing has been creating and refining Corpus Christi's support structure to ensure that the required repair parts arrive when demanded. In establishing this new supply chain, Boeing has identified numerous inefficiencies as a result of inaccurate and highly volatile forecasts. This thesis examines the impact of volatility within the new support structure and creates flexible solutions to mitigate its negative effects on lead times, multiple sources of supply and inventory management.
(cont.) Efforts to increase communication flow across the supply chain are used to capitalize on economies of scale for cost reduction while safety stock recommendations are made for critical end-items. Monte Carlo simulations are employed to justify and validate the solutions. The results of the thesis reveal that a strategic selection of raw material safety stock can reduce procurement lead times by an average 61% for a subset of parts while maintaining financial responsibility. Additionally, by leveraging cost reduction techniques, an average increase of 11% in Boeing's income from sales can be achieved while eliminating inefficient administrative delays and increasing customer fulfillment rates. These two recommendations demonstrate specific solutions for mitigating the effects of demand volatility and inaccurate forecasting.
by Kevin Michael Myers.
S.M.
M.B.A.
Wood, David J. H. "Corporate consolidation an event study of historic stock prices in the defense aerospace industry." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FWood.pdf.
Full textThesis Advisor(s): Laverson, Alan. Second Reader: Gates, William. "December 2009." Description based on title screen as viewed on January 27, 2010. Author(s) subject terms: Defense industry, Consolidations, Mergers, Acquisitions, Event study, Boeing, Lockheed Martin, Northrop Grumman, Raytheon. Includes bibliographical references (p. 55-58). Also available in print.
Melin, Peter B. "The impact of accounting methods on cost reduction rates in defense aerospace weapons system programs." Thesis, Monterey, California. Naval Postgraduate School, 1988. http://hdl.handle.net/10945/23256.
Full textPomponi, Renata Alma. "Control of manufacturing processes with MRP II : benefits and barriers in the defense aerospace industry." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11167.
Full textRose, William B. (William Burford). "The Introduction of Robotic Technology: Perceptions of the Work Force of an Aerospace Defense Company." Thesis, University of North Texas, 1988. https://digital.library.unt.edu/ark:/67531/metadc330596/.
Full textHughes, Robert Rhys. "High-sensitivity eddy-current testing technology for defect detection in aerospace superalloys." Thesis, University of Warwick, 2015. http://wrap.warwick.ac.uk/79695/.
Full textPlace, David S. Grubbs Gregory A. "Empirical evaluation of a model of team collaboration using selected transcripts from September 11, 2001." Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Jun/09Jun%5FPlace.pdf.
Full textThesis Advisor(s): Hutchins, Susan G. "June 2009." Description based on title screen as viewed on July 13, 2009. Author(s) subject terms: Team Collaboration, Team Communication, NORAD, NEADS, September 11, 2001, Cognition, Macro-cognition, Model of Team Collaboration. Includes bibliographical references (p. 193-198). Also available in print.
Nishizaki, Santor. "Work environment preferences of Los Angeles Generation Y contract managers in the defense and aerospace industry." Thesis, Pepperdine University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3631046.
Full textThere are currently 4 different generations in the workplace, and the newest generation, Generation Y, has caused leaders within organizations to rethink their management and workplace cultural approach to leading this emerging generation. This qualitative phenomenological dissertation examines the work environment preferences of Generation Y contract managers who work in the Los Angeles area in the defense and aerospace industry by interviewing 11 participants from both the public and private sectors. The research indicates that this new generation, Generation Y or Millennials, prefer to have autonomy over their workload and schedule, but prefer to have their direct manager active in a mentoring and coaching role, rather than acting as a task-master. In addition, the participants in this study preferred a healthy amount of pressure, but not too much of a workload that would cause them to fail. Lastly, this dissertation found that Millennials have a high preference for innovation and using innovative technology in the workplace to increase efficiency.
Eady, Levern. "Job embeddedness and intention of voluntary turnover in the aerospace and defense industry| A quantitative study." Thesis, Capella University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3643057.
Full textEmployee turnover is one of the greatest problems facing top management teams. The general problem is that employee undesirable voluntary turnover regularly occurs in organizations. This study of job embeddedness is unprecedented and is the first scholarly work using a sample from the Aerospace and Defense Industry. The purpose of this quantitative study was to evaluate the primary data collected to examine the linear association between job (organization and community) embeddedness at the sub-dimension (fit, links, and sacrifice) level and voluntary turnover in the Aerospace and Defense Industry subpopulation System Engineering and Technical Assistance (SETA) support contract workforce. The sample (n = 185) included full-time working adults age 18 to 65 in the United States. The respondents, for two weeks in mid-Spring 2014, self-reported and completed a Likert scale survey as the primary data collection instrument. Three research questions were investigated. Research question 1 determined the relationship between on-the-job embeddedness and voluntary turnover amongst defense SETA support contract employees. The study findings revealed there is a significant relationship between on-the-job embeddedness and intention to voluntary turnover. Research question 2 determined the relationship between off-the-job embeddedness and voluntary turnover amongst defense SETA support contract employees. The study findings revealed there is a significant relationship between off-the-job embeddedness and intention to voluntary turnover. Research question 3 asked, "What is the difference between age, job embeddedness, and voluntary turnover amongst defense SETA support contract employees?" This research question was eliminated because of data skew. In addition, significant gender statistical analysis differences exist.
Bakkila, Michelle Vivian. "A system dynamics analysis of the interaction between the U.S. government and the defense aerospace industry." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/47560.
Full textChristian, William J. R. "The development of a strain-based defect assessment technique for composite aerospace structures." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3010051/.
Full textStalker, Joshua D. "A Reading Preference and Risk Taxonomy for Printed Proprietary Information Compromise in the Aerospace and Defense Industry." NSUWorks, 2012. http://nsuworks.nova.edu/gscis_etd/314.
Full textMitchell, A'Shawn Lora. "Corporate Image Branding Strategies to Attract Engineering Talent." ScholarWorks, 2019. https://scholarworks.waldenu.edu/dissertations/7561.
Full textSinclair, Armond E. "Achieving Program Success with Productive Outcomes: Lessons from Concurrent Engineering for United States Department of Defense Major Defense Acquisition." University of Toledo / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1494593155068787.
Full textHallander, Per. "Towards defect free forming of multi-stacked composite aerospace components using tailored interlayer properties." Doctoral thesis, KTH, Lättkonstruktioner, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-185694.
Full textQC 20160425
Holland, Marcia Annette. "Aerospace and Defense Industries Online Recruiting of College and University Graduates: Strategies Toward Defining a Comprehensive Informational Benchmark." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc84219/.
Full textGerona, Leovigildo Mahon. "Vibration excitation of aerospace composite materials for defect determination using optical NDT techniques (ESPI/Shearography)." Master's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/13432.
Full textThis project investigates the detection of structural damage in aerospace composite materials using ESPI and/or Shearography. ESPI and shearography are both laser based digital interferometric techniques used to non-destructively identify defects in small and large structures. Vibration excitation is proposed to be used as the excitation method for the above Non-Destructive Testing (NDT) techniques. The material may or may not contain any defects, in which case the flaws are to be artificially induced.
Wheeler, Benjamin (Benjamin Ray). "Reducing enterprise IT fragmentation through standard metrics and decision tools : a case study in the aerospace and defense industry." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/66041.
Full textCataloged from PDF version of thesis.
Includes bibliographical references (p. 60-61).
Over the last several decades, manufacturing companies around the world have embraced new and powerful business tools made possible with Information Technology. Major investments are frequently made in enterprise-wide systems, such as Enterprise Resource Planning (ERP) solutions to take advantage of cost saving opportunities. While promising in concept, system implementations can grow to be expensive and complicated during execution, commonly resulting in project de-scoping and sacrifices in functionality and integration. If not carefully managed, this can ultimately lead to an environment of costly custom workaround solutions for years to follow, subverting the central goal of the original investment. This thesis presents a case study examining Raytheon's initiative to launch an enterprise ERP system (SAP PRISM) in an effort to standardize and modernize supply chain operations. Within the SAP implementation, the repair and retrofit, or depot, business had major integration components de-scoped due to cost constraints. As a result numerous systems have been developed to manage the business, leading to difficulties in process alignment across manufacturing programs. This work introduces a pilot project with the objective of re-aligning business processes by delivering a portal of common metrics and decision tools to the manufacturing and operations community. With the common portal, the user community gains access to existing centralized data, reducing the need for isolated application development and enabling richer capability.
by Benjamin Wheeler.
S.M.
M.B.A.
Riwes, Mina (Mina Diaa). "The "+Add" Model : a proposed strategic framework to create agile high performance aerospace and defense product support supply chains." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81105.
Full textCataloged from PDF version of thesis.
Includes bibliographical references.
The U.S. Aerospace and Defense industry is a vital organ for national security and humanitarian disaster response as well as an economic powerhouse creating jobs and driving exports. News headlines often stop at the sale of complex, hi-tech and expensive defense systems short of capturing the critical aftersales support. However, it is the aftersales support that enables the mission to be accomplished. Without a well-functioning product support supply chain, even the most advanced fleet of fighter jets is rendered useless. This paper looks in-depth at such support supply chains within top industry companies. The investigation spans the current and desired states, and gaps the difference. It also establishes a visionary roadmap to get to the desired state and ensure optimum performance. The research proposes the "+Add Model", an easy to understand 5-level framework to achieve Global Optimization. The +Add Model acronyms stand for Aggregate Dynamic Derivatives, which are key elements in the framework. Aggregate refers to enabling a one integrated supply chain approach at the prime-integrator to benefit from economies of scale elements such as risk pooling and large discount buys. Dynamic refers to enabling a continuously improving supply chain through feedback loops making the supply chain agile. Derivatives refer to the realization that the supply chain is full of hidden derivatives (or levers). As in calculus, the derivative is a measure of how a function changes as its input changes. The +Add model identifies those main supply chain derivative functions and inputs, and then aims to fine-tune them to drive performance. By adopting the +Add Model a prime-integrator is able to improve demand forecast accuracy (Level-1), system planning lead times (Level-2) and increase collaboration with the supplier (Level-3). In turn, levels 1 through 3 enable significantly reduced supplier lead times (Level-4). Finally, as various programs apply the +Add Model approach, Aggregation (Level-5) provides additional benefits such as increased forecast accuracy, discount buys, and lower safety stock inventory through centralization. The +Add Model has a significant impact to the button line, analysis reveals substantial improvements to earnings, economic profit and cash flow while maximizing performance and reducing risk.
by Mina Riwes.
M.Eng.in Logistics
Donaldson, Catherine W. Johnson David A. "Validating a model of team collaboration at the North American Aerospace Defense Command using selected transcripts from September 11, 2001." Monterey, Calif. : Naval Postgraduate School, 2008. http://bosun.nps.edu/uhtbin/hyperion-image.exe/08Jun%5FDonaldson.pdf.
Full textThesis Advisor(s): Hutchins, Susan G. ; Kendall, Anthony. "June 2008." Description based on title screen as viewed on August 25, 2008. Includes bibliographical references (p. 181-185). Also available in print.
Johnson, David A. "Validating a model of team collaboration at the North American Aerospace Defense Command using selected transcripts from September 11, 2001." Thesis, Monterey, California. Naval Postgraduate School, 2008. http://hdl.handle.net/10945/4069.
Full textIthier, Jan P. "Synchronizing federal operational planning for national catastrophes." Thesis, Monterey, California : Naval Postgraduate School, 2010. http://edocs.nps.edu/npspubs/scholarly/theses/2010/Mar/10Mar%5FIthier.pdf.
Full textThesis Advisor(s): Supinski, Stanley ; Morag, Nadav. "March 2010." Description based on title screen as viewed on April 28, 2010. Author(s) subject terms: Operational Planning, Synchronization Of Plans, Federal Planning, Planning for Catastrophes, Catastrophe Planning, Integrated Planning, Multi-Sector Planning, Federal Operational Plans, Agency Operational Plans, Department Operational Plans. Includes bibliographical references (p. 111-121). Also available in print.
Reents, Mark J. "Operation Noble Eagle and the use of combat air patrols for homeland defense." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Dec/08Dec%5FReents.pdf.
Full textThesis Advisor(s): Moran, Daniel. "December 2008." Description based on title screen as viewed on February 2, 2009. Includes bibliographical references (p. 87-97). Also available in print.
Serrano, Munoz Itziar. "Influence of casting defects on the fatigue behaviour of an A357-T6 aerospace alloy." Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0117/document.
Full textThe excellent castability, relatively low production costs, and high strength to weight ratios make Al-Si-Mg cast alloys an attractive choice for use in cheaper and lighter engineering components, in both automotive and aerospace industries. However, it is well known that High Cycle Fatigue (HCF) lives (105 < Nf < 107 cycles) of cast components are severely reduced when casting defects (notably pores and oxides) are present at the free surface or subsurface. They act as stress raisers which can considerably reduce the crack incubation period depending on their size, shape and the microstructural features of the surrounding material. Internal casting defects are of special interest to this work. The application of safety coefficients considers that all casting defects present in a component have the same deleterious effect and no attention is paid, for example, to their distance to the free surface. In other words, internal defects (corresponding to the case where the depth of the defect allows crack nucleation and propagation to essentially occur without interaction with the air environment) are considered as damaging to fatigue life as surface defects (those placed at the free surface and in contact with the air environment). Surface crack monitoring performed on uniaxial fatigue specimens indicates that the presence of a surface microshrinkage exceeding the size of microstructurally small cracks (√A ≈ 500 μm, controlled by the SDAS) readily nucleates a fatigue cracks producing steady crack propagation and remarkable reduction in the expected fatigue life. A smaller surface defect (√A ≈ 300 μm) nucleated a crack that did not reduced the expected fatigue life as in this case early stages of propagation are still nfluenced by the SDAS. Pure torsional cycling reveals that the morphology of fracture surfaces is highly influenced by the stress level. In general, torsional fatigue behaviour is described by having reduced (with respect to uniaxial testing) and multisite crack nucleation periods. Several dominant cracks can evolve simultaneously and the final failure occurs by the linkage of some of those cracks. Crack propagation is controlled by the crystallography and pores do not appear to be preferential nucleation sites. S-N curves show that macroscopic specimens containing Øeq ≈ 2 mm internal artificial defect produce similar fatigue lives to those obtained with a defect-free material. Internal crack nucleation was rarely observed during synchrotron tomography experiments; instead the fatal cracks initiated from much smaller surface defects. Tomographic images show that, in the case of internal propagation, crystallographic paths are formed while surface cracks propagate in mode I. The crack growth rate of internal cracks is much smaller than that of cracks propagating from the free surface