| 1. |
- Azizoğlu, Yağız, 1986-
(författare)
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Modeling of Cold Pilgering of Tubes
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cold pilgering is a challenging tube forming process in terms of modeling due to the complexity in kinematic of tools, friction condition and material behavior. The process development has mostly been based on simple formulas and costly full-scale tryouts. The aim in this study is to develop validated Finite element models of cold pilgering to increase the understanding of influence of the process parameters on the produced tubes.In the course of this thesis, three-dimensional mechanical and thermo-mechanical Finite element models of cold pilgering were developed. The commercial code MSC.Marc was used in the simulations. General 3D models are needed to be able to capture asymmetric deformation in cold pilgering. It was found that tool deflections together with elastic deformation of roll dies have considerable influence on the rolling force. Furthermore, the strain rate and temperature effects on the response of the material and thereby on the rolling force were evaluated.
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| 2. |
- Loukil, Mohamed Sahbi, 1984-
(författare)
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Microcracking in fiber composites and degradation of thermo-elastic properties of laminates
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The macroscopic failure of composite laminates subjected to tensile increasing load is preceded by initiation and evolution of several microdamage modes. The most common damage mode and the one examined in this thesis is intralaminar cracking in layers. Due to this kind of microdamage the laminate undergoes stiffness reduction when loaded in tension. For example, the elastic modulus in the loading direction and the corresponding Poisson’s ratio will decrease.The degradation of the elastic properties of these materials is caused by reduced stress in the damaged layer which is mainly due to two parameters: crack opening displacement (COD) and crack sliding displacement (CSD). At fixed applied load these parameters depend on the properties of the damaged and surrounding layers, on layer orientation and on thickness. When the number of cracks per unit length is high (high crack density in the layer) the COD and CSD are reduced because of to crack interaction.The main objective of the first paper is to investigate the effect of crack interaction on COD using FEM and to describe the identified dependence on crack density in a simple and accurate form by introducing an interaction function dependent on crack density. This interaction function together with COD of non-interactive crack gives accurate predictions of the damaged laminate thermo-elastic properties. The application of this function to more complex laminate lay-ups is demonstrated. All these calculations are performed assuming that cracks are equidistant.However, the crack distribution in the damaged layer is very non-uniform, especially in the initial stage of multiple cracking. In the second paper, the earlier developed model for general symmetric laminates is generalized to account for non-uniform crack distribution. This model is used to calculate the axial modulus of cross-ply laminates with cracks in internal and surface layers. In parametric analysis the COD and CSD are calculated using FEM, considering the smallest versus the average crack spacing ratio as non-uniformity parameter. It is shown that assuming uniform distribution we obtain lower bond to elastic modulus. A “double-periodic” approach presented to calculate the COD of a crack in a non-uniform case as the average of two solutions for periodic crack systems is very accurate for cracks in internal layers, whereas for high crack density in surface layers it underestimates the modulus reduction.In the third paper, the thermo-elastic constants of damaged laminates were calculated using shear lag models and variational models in a general calculation approach (GLOB-LOC) for symmetric laminates with transverse cracks in 90° layer. The comparison of these two models with FEM was presented for cross-ply and quasi-isotropic laminates.
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| 3. |
- Bäckström, Ingela, 1963-
(författare)
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Quality Management for Sustainable Health : Methodologies, Values and Practices taken from Swedish Organizations
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In many Western countries today, not least in Sweden, there are a lot of organizations that have great problems with sickness absence. The costs connected to the high rates of sickness absence have also risen to alarming levels. Healthy co-workers and healthy organizations are obvious goals for many leaders, but this is not always so easy to establish. Work practices and leadership that are beneficial to co-worker health are thus vital to identify. Studies have shown relationships between company-wide implementation of quality programs and improved co-worker satisfaction along with low co-worker turn over; in other words, co-worker health along with improved customer satisfaction and financial results. Despite the great problems concerning sickness absence, there are organizations that have been awarded prizes for excellence in leadership, internal partnership, working environment, and profitability. The overall purposes of the research described in this thesis are to examine and describe how management and leadership can establish sustainable health among the co-workers and examine how the leadership for sustainable health is related to Quality Management. The in-depth purpose is to examine which aspects within the values derived from the quality movement are those that primarily influence the co-workers’ perceived health. The results presented can be described in three parts and are results from four case studies carried out in five different organizations. Three of the organizations have received awards for establishing good working environment, good financial results, and low sick leaves among their co-workers; the fourth received an award for the successful implementation of quality programs. The first part consists of results from case studies in three different organizations and describes how organizations can work to achieve sustainable health among their co-workers, with practical examples. The results are methodologies, values and organizational structure, which it is considered possible for other organizations to adopt in their efforts to achieve good working conditions resulting in fewer sick leaves. The second part is an attempt to investigate if leadership for sustainable health is related to Quality Management. Methodologies, leadership values, organizational structure, and general values found in organizations which have achieved sustainable health are analyzed in the light of Deming’s 14 points, and a correlation is indicated. There is also correlation found between the TQM values and the co-workers’ perception of their health. The third part examines which of the aspects within the values grown from the quality movement are those that influence the co-workers perceived health. The results show significant correlation between the values and the co-workers’ perception of their health. Aspects found within the value “Top management commitment” were named; Empathy, Presence and Communication, Integrity, and Continuity. Within the value “Let everybody be committed” the aspects; Development, Influence and Being informed were found. These aspects are described in more detail and also in one model per value. The result implies that the TQM values; “Top management commitment”, “Improve continuously” “Let everybody be Committed” and “Focus on customers” are important for achieving healthy organizations and sustainable health among co-workers.
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| 6. |
- Rundquist, Jonas, 1964-
(författare)
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Outsourcing of New Product Development - A decision framework
- 2007
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis is the outsourcing of activities in the New Product Development (NPD) process. Outsourcing of NPD refers to the outsourcing of development activities for the developing of new products (goods and/or service), where all or just the innovative part of the NPD process is purchased externally based on a contract with organizational units separate from the outsourcing firm. This definition implies that (A) the activity should be an innovative part of the NPD process, (B) the activity should have previously been conducted internally, and (C) the activity should be purchased under a contractual agreement between the organizations.This thesis focuses on the outsourcing of NPD in medium sized firms. Although the framework is probably also useful for small and large firms, the three empirical studies in the thesis explored samples of medium sized firms. NPD is a knowledge intensive activity that requires the ability to handle uncertainties and is very dependent on the individuals involved in the process. In this way it differs from production, which (especially when producing standard items on a large scale) is easier to control, monitor and to evaluate the costs. Therefore, some considerations connected to knowledge acquisition and uncertainty needs to be addressed.A literature review reveals that research on outsourcing often focuses on A) Large firms and B) outsourcing of production activities. In addition, research on NPD usually involves large firms, despite the fact that the interest in product development in small and medium sized firms has grown rapidly in recent years. Since outsourcing of NPD is a method frequently used to access competence, and reduce costs and/or uncertainty, it seems motivated to study the outsourcing of NPD in medium sized firms.The thesis presents a decision framework that is based on three empirical studies (two survey studies and one case study) and a theoretical framework. The theoretical framework presented in the thesis is commonly used to understand outsourcing questions in general. In the present thesis the framework is applied in the specific situation of outsourcing a knowledge intensive activity (such as NPD) in the context of medium sized firms. Transactions cost, resource based, resource dependency, knowledge based, agency cost, and institutional theories are revisited in the thesis.Outsourcing can lead to advantages in form of lower costs, access to knowledge or other resources, as well as access to markets, but it can also result in a knowledge drain, lower motivation among in-house staff, or an increased level of dependency on external organizations. Therefore the decision to outsource is not always a good one, and the pros and cons must be carefully evaluated. The result of the thesis is a decision framework that maps factors affecting the decisions that need to be made when outsourcing NPD. The implications can be of value to the outsourcing firm as well as to the potential outsourcing partner. The framework has been presented to the firms in the studies and thus has already proved its value to some extent.The framework will also be used for the design of the studies that will hopefully take me towards my PhD degree, including a new survey study as well as a case study focusing on knowledge integration.
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| 7. |
- Charles, Corinne, 1979-
(författare)
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Modelling microstructure evolution of weld deposited Ti-6Al-4V
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process.Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment.The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure.
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| 9. |
- Larsson, Tobias
(författare)
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Effective development of dynamic systems : a structured approach
- 1999
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This licentiate thesis deals with effective simulation of multibody dynamic systems in the product development process. Previous work to make simulation more effective has concentrated on developing faster calculation methods. Instead, this approach is to make the process of multibody dynamics simulation more effective by structuring of products, simulation models and their usage. Efforts have been made to clarify how computer tools are used in product development in industry today. Insight into the two domains of product development and multibody dynamics is given. These domains have traditionally been separated but the introduction of concurrent engineering and faster computers puts new demands on the integration of computer support and analysis in the development process. A proposal for performing the multibody dynamics methodology in a modular way in the product development process is given based on the performed work.
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