DEMI_PhD http://hdl.handle.net/10362/1041 2013-06-19T23:07:08Z 2013-06-19T23:07:08Z Pinto, Abel Fernando do Nascimento http://hdl.handle.net/10362/9681 2013-05-23T09:52:39Z 2012-01-01T00:00:00Z

Title: Development of a fuzzy qualitative risk assessment model applied to construction industry Authors: Pinto, Abel Fernando do Nascimento Abstract: The construction industry is plagued by occupational risky situations and poor working conditions. Risk Assessment for Occupational Safety (RAOS) is the first and key step to achieve adequate safety levels, particularly to support decision-making in safety programs. Most construction safety efforts are applied informally under the premise that simply allocating more resources to safety management will improve safety on site. Moreover, there are many traditional methods to address RAOS, but few have been adapted and validated for use in the construction industry, thus producing poor results. The contribution of this dissertation is a qualitative fuzzy RAOS model, tailored for the construction industry, named QRAM (Qualitative Risk Assessment Model). QRAM is based on four dimensions: Safety Climate Adequacy, (work accidents) Severity Factors, (work accidents) Possibility Factors and Safety Barriers Effectiveness. The risk assessment is based on real data collected by observation of reality, interviews with workers, foreman and engineers and consultation of site documents (working procedures, reports of work accident investigation, etc.), avoiding the use of data obtained by statistical tecnhiques. To rating each parameter it was defined qualitative evaluators - linguistic variables - which allow to perform a user-friendly knowledge elicitation. QRAM was, firstly evaluated by “peer” review, with 12 safety experts from Brazil (2), Bulgaria (1), Greece (3), Turkey (3) and Portugal (3), and then, evaluated by comparing QRAM with other RAOS tecnhiques and methods. The safety experts , concluded that: a) QRAM is a versatile tool for occupational safety risk assessment on construction sites; b) the specific checklists for knowledge elicitation are a good decision aid and, c) the use of linguistic variables is a better way to make the risk assessments process more objective and reliable. Description: Dissertação para obtenção do Grau de Doutor em Engenharia Industrial

2012-01-01T00:00:00Z Machado, Carla Maria Moreira http://hdl.handle.net/10362/9058 2013-02-27T15:55:32Z 2012-01-01T00:00:00Z

Title: Empirical models for quantification of machining damage in composite materials Authors: Machado, Carla Maria Moreira Abstract: The tremendous growth which occurs at a global level of demand and use of composite materials brings with the need to develop new manufacturing tools and methodologies. One of the major uses of such materials, in particular plastics reinforced with carbon fibres, is their application in structural components for the aircraft industry with low weight and high stiffness. These components are produced in near-final form but the so-called secondary processes such as machining are often unavoidable. In this type of industry, drilling is the most frequent operation due to the need to obtain holes for riveting and fastening bolt assembly of structures. However, the problems arising from drilling, particularly the damage caused during the operation, may lead to rejection of components because it is an origin of lack of resistance. The delamination is the most important damage, as it causes a decrease of the mechanical properties of the components of an assembly and, irrefutably, a reduction of its reliability in use. It can also raise problems with regard to the tolerances of the assemblies. Moreover, the high speed machining is increasingly recognized to be a manufacturing technology that promotes productivity by reducing production times. However, the investigation whose focus is in high speed drilling is quite limited, and few studies on this subject have been found in the literature review. Thus, this thesis aims to investigate the effects of process variables in high speed drilling on the damage produced. The empirical models that relate the delamination damage, the thrust force and the torque with the process parameters were established using Response Surface Methodology. The process parameters considered as input factors were the spindle speed, the feed per tooth, the tool diameter and the workpiece thickness. A new method for fixing the workpiece was developed and tested. The results proved to be very promising since in the same cutting conditions and with this new methodology, it was observed a significant reduction of the delamination damage. Finally, it has been found that is possible to use high speed drilling, using conventional twist drills, to produce holes with good quality, minimizing the damage. Description: Dissertação para obtenção do Grau de Doutor em Engenharia Mecânica

2012-01-01T00:00:00Z Remigio, Helena Maria Lourenço Carvalho http://hdl.handle.net/10362/8949 2013-02-22T14:36:19Z 2012-01-01T00:00:00Z

Title: Modelling resilience in supply chain Authors: Remigio, Helena Maria Lourenço Carvalho Abstract: Global supply chains are vulnerable to a number of disturbances that may affect negatively company’s operational and financial performance. The company’s ability to cope with supply chain disturbances, i.e. the ability to be resilient, is vital to sustain the company and respective supply chain competitiveness. The aim of this thesis is modelling resilience in a supply chain context. More specifically, it is intended to develop an explanatory framework of the supply chain resilience phenomena and to model supply chain resilience indices to be deployed at individual company level. These indices intend to measure the companies’ ability to be resilient in a supply chain context. Using a theory building approach, a case study was conducted in seven companies’belonging to the Portuguese automotive upstream supply chain. It was found that managers do not associate supply chain disturbances to a particular type of events, but with the negative effects that events provoke. When companies experience a disturbance, its ability to deliver on-time may be compromised. The resilient practices, adopted by companies, depend on the type of supply chain disturbances and their negative effects. The main failure modes arising from the case study are “capacity shortage” and “material shortage”. Eight propositions were derived from the case study empirical findings. They were used to develop the supply chain resilience explanatory framework,to provide additional understanding regarding the relationships between supply chain disturbances, supply chain failure modes and resilient practices. To support the assessment of companies’ resilience, two resilience indices were modelled and developed. These indices intend to measure the companies’ ability to sustain its performance in terms of “on-time delivery” when a “capacity shortage” or “material shortage” occur. Finally, the indices were tested in companies belonging to the Portuguese automotive upstream supply chain. The dissertation contributes to the existing literature by empirically investigating the main effects of supply chain disturbances and how companies can increase supply chain resilience. It suggests an approach to assess companies’ resilience and identifies a set of supply chain state variables that companies may control to improve supply chain resilience. Description: Dissertação para obtenção do Grau de Doutor em Engenharia Industrial

2012-01-01T00:00:00Z Santos, António Gabriel Marques Duarte dos http://hdl.handle.net/10362/6096 2011-09-12T09:58:41Z 2010-01-01T00:00:00Z

Title: O projecto de produtos únicos desenvolvidos em empresas de pequena dimensão Authors: Santos, António Gabriel Marques Duarte dos Abstract: O projecto de máquinas novas, desenvolvido em Pequenas e Médias Empresas Industriais, nos casos em que as quantidades de produtos produzidos, a partir do mesmo projecto, são muito pequenas, apresenta as características do projecto de protótipos, sendo cada projecto desenvolvido caso a caso e em função das necessidades particulares de cada cliente. Por outro lado, os factores de escala dessas empresas e os prazos de entrega impostos pelo mercado inviabilizam a obtenção e utilização de dados rigorosos, sendo o desenvolvimento dos projectos realizado sob condições de grande incerteza, de diversos tipos e origens,acabando o produto final, que será entregue ao cliente, por ser um protótipo, cujos ensaios são feitos, muitas vezes, em condições reais de utilização. Dada a inviabilidade de se reduzir por via experimental essas incertezas, foi desenvolvida uma metodologia para o processo de projecto de produtos únicos, de modo a torná-los insensíveis, dentro de limites razoáveis, às incertezas presentes na fase inicial do processo de projectar. Com esta metodologia, que foi desenvolvida de acordo com as mais recentes teorias e métodos existentes no âmbito da actividade de projecto, pretende-se minimizar o esforço necessário para a redução daquelas incertezas, sendo os produtos resultantes desses projectos capazes de se adaptar às diversas condições a que possam vir a estar sujeitos. Na metodologia criada, são utilizadas técnicas de projecto que incorporam soluções passíveis de serem adaptadas a diferentes situações, quer por modificação dos seus componentes, quer por intermutabilidade de componentes, em concepções modulares, cuja arquitectura é baseada em estruturas do tipo “plataforma”, as quais constituem a base comum a vários tipos de produtos, consoante os módulos que sejam adicionados à referida plataforma. A metodologia proposta proporciona uma base lógica para uma estratégia do projecto de engenharia, que leva em conta os modelos do processo de projecto mais adequados ao projecto de produtos únicos, e que procura integrar, na medida do possível, as práticas de projecto seguidas na indústria. Faz-se, assim, a ligação entre a teoria e a prática do projecto de produtos únicos. Description: Dissertação apresentada para obtenção do Grau de Doutor em Engenharia Mecânica na especialidade de Projecto de Máquinas pela Universidade Nova de Lisboa,Faculdade de Ciências e Tecnologia

2010-01-01T00:00:00Z