| 1. |
- Alfredsson, Svante
(författare)
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Constitutive Behaviour and Fracture of Adhesive Layers : Inverse Methods and Energetic Balance
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the automobile industry, current demands on reduced emissions with maintained or even increased crash worthiness, forces the industry to seek weight-reducing designs. The possibility to use lightweight materials is obviously attractive. At joints, these lightweight materials have to be connected to high-strength or low-cost materials. In this context adhesive joining can provide a flexible solution. The method adds little weight to the structure, it allows for material combinations that are not possible to weld, and it provides increased stiffness to the structure as compared to the conventional spot-welding procedure. Moreover, electrolytic isolation of the multi-material joints is achieved. In this thesis, experimental methods are developed to determine the complete stress-deformation relation for an adhesive layer loaded in shear. Generally, the stress distribution is non-uniform in the test geometries used. Evaluation of experiments is performed using an inverse method. The idea is to measure the energy release rate as a function of the crack tip deformation. The stress-deformation relation is obtained by a subsequent differentiation. The method is shown to be capable of capturing the complete stress-deformation relation under stable loading conditions. A method to accurately determine the energy release rate is needed for the inverse method to be successful. A closed form expression for the energy release rate of the end-notch flexure adhesive joint specimen (ENF) is derived in this thesis. An approximate formula containing measurable quantities is also given. It is shown that both the applied load and the crack tip deformation are needed to determine the instantaneous value of the energy release rate of the ENF-specimen. Experimental results show that the influence of the crack tip deformation can be substantial. An alternative specimen is also analysed theoretically. An initial theoretical study on mixed mode fracture of adhesive layers is also given in this thesis. A detailed comparison is made of the mode-mixity obtained using two different, frequently used mechanical models; the beam/adhesive layer model, and the continuum model, i.e. a model neglecting the presence of the adhesive layer. It is tempting to assume that the two methods would produce similar results for the case of a thin adhesive layer. However, this is only the case for geometries which are materially and geometrically symmetric with respect to the adhesive layer. For asymmetric joints, on the other hand, the two models are found to predict fundamentally different values of the mode-mixity. Moreover, the mode-mixity of the beam/adhesive layer model is found to depend highly on the relative stiffness of the adherends and the adhesive layer. This dependency is found to be quantified through two parameters.
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| 2. |
- Lagerberg, Adam, 1967
(författare)
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Control and Estimation of Automotive Powertrains with Backlash
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In automotive powertrains, backlash causes problems with vehicle driveability, specifically at so called tip-in and tip-out maneuvers. These maneuvers may trigger phenomena known in the automotive industry as shunt and shuffle, which are partially caused by the backlash. These phenomena are considered difficult to cope with, and until recently, only relatively simple controllers have been used to reduce the discomfort. Also, the tuning of these controllers is made quite subjectively. A number of approaches to the control of systems with backlash are reported in the literature. Most of these approaches assume another system structure around the backlash than what is the case in automotive powertrains. Very few approaches are therefore directly applicable to the control of automotive powertrains. The first part of this thesis gives an overview of available control strategies for backlash control. The strategies can be divided into active and passive strategies, depending on the way the controller handles the backlash. An active controller compensates the backlash nonlinearity by a more active control signal, while the passive controller becomes more cautious when the backlash gap is entered. Some of the strategies, e.g. switched linear controllers and model predictive controllers, are evaluated in the powertrain application by means of simulation. The results show that active nonlinear controllers have a potential for improved backlash control. However, the robustness of these controllers needs further investigation. Open-loop optimal control is used in this thesis as a way to find theoretical limits on backlash compensation performance. High-performance controllers for backlash compensation require high-quality measurements of the current state of the powertrain. Information about the size of the backlash is also needed. These problems are addressed in the second part of this thesis. Two nonlinear estimators based on Kalman filtering theory have been developed, one for state estimation and one for the estimation of backlash size. Simulation and experimental results show that the resulting estimates are of high quality.
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| 3. |
- Linder, Astrid
(författare)
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Neck injuries in rear impacts : Dummy neck development, dummy evaluation and test condition specifications
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of the work underlying this thesis was firstly to develop a neck for a new rear impact dummy, to evaluate the complete dummy and to specify test conditions for a consumer test with attention to AIS 1 neck injuries in rear impacts. In the development of the dummy neck, a mathematical neck model was developed and evaluated. Furthermore, impact severity and seat designs were also investigated.Rear collisions can result in AIS 1 neck injuries. These injuries, which are becoming more frequent, occur mostly at low changes of velocity (less than 30km/h). Since AIS 1 neck injuries can result in long-term symptoms, it is of major importance to devise protection from these injuries. When testing the safety performance of seats and head restraints, an essential tool is the crash test dummy. However, the standard crash dummy of today, the Hybrid III, has had limitations in its interaction with the seat and head restraint.The new dummy neck developed was evaluated by using data from crash tests involving volunteers as well as post mortem human subjects. For comparison, the Hybrid III frontal impact dummy was also tested under the same conditions. The new neck was found to have more human-like motion than that of the Hybrid III in low velocity rear tests when compared to both volunteers and post mortem human subjects. This was found to be the case for the head relative to upper torso horizontal and angular displacement. The new dummy neck became a fundamental part of the new, low-velocity rear impact crash dummy, the BioRID. The BioRID was found to have more human-like motion than that of the Hybrid III in low velocity rear impact tests when compared to both volunteers and post mortem human subjects. This result was observed for angular, vertical and horizontal displacement of the upper torso.The variations in acceleration pulse characteristics in different vehicle models in identical impact conditions was shown to be substantial. A similar delta-V could be generated in a large variety of ways in terms of mean acceleration and acceleration pulse shape in a rear impact. The variation in crash pulse characteristics for the same car model from different real-world crashes of similar delta-Vs was also shown to be significant. This served as a background for the specifications of the test conditions for a proposed consumer test.Real-world rear impact collisions with crash recorder-equipped vehicles, were reconstructed on a sled reproducing the real-world crash pulse. The results illustrate the risk of sub-optimisation when using only a single test in assessing neck injury protection. Further, five different seat configurations were evaluated in a series of sled tests at four impact severities. Identical vehicle seats were found to perform differently in tests with of different severities. Changing the mean acceleration (from 4.2g to 7.6g) influenced key dummy readings more than changing the delta-V (from 15km/h to 25km/h). Therefore, it should be expected that different real-world rear collisions at similar delta-Vs imply highly differing loading conditions to the occupants. As a consequence, the test conditions for the proposed consumer test program included specifications for several levels of change of velocity and mean acceleration.The results of this thesis are expected to become important input in the definition of future rear impact test procedures for neck injury risk assessment.
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| 4. |
- Linderholt, Andreas, 1968-
(författare)
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Test Design for Finite Element Model Updating - Identifiable Parameters and Informative Test Data
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- It is important to predict structural phenomena, such as noise and fatigue, stemming from vibrations. To do this, reliable structural dynamic models are needed. To be useful the models have to compare well with reality in the validation against test data; if not, the models should be modified. The thesis research is in the field of computational model updating, which is, more often than not, the updating of uncertain parameters of a finite element model to better correlate to test data. This is a specialization that started to grow in the 1970s, and since then much research has been done. The work presented here concerns the design of tests for model updating, which is one of several model updating sub-tasks. For a test to be useful for model updating, the test data set must be such that the model parameters are sufficiently well identifiable. The dynamic properties of a structure to be compared with test data may under certain conditions change similarly when one parameter or a set of other parameters is changed. When this happens, there is lack of identifiability and, before a meaningful model updating can take place, either complementary test data have to be added or a re-parameterization of the model must be made. An index was developed, the Orthogonality-Co-linearity Index (OCI), that helps to find the best way to reduce the number of parameters when there is low identifiability. For the model updating, test data also need to be informative with respect to the parameters to be tuned. The data informativeness depends on the test design, i.e. the choice of stimuli and the placement of the actuators and sensors. A data informativeness index that supports the design of an informative test is proposed. Procedures were also worked out to make the test design robust with respect to parameter uncertainties. The study is limited to linear and time-invariant systems.
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| 5. |
- Tell, Joakim, 1967-
(författare)
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Organising University-Led Learning Networks Among Small-Enterprise Managers
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis elaborates upon the use of a university-led approach to facilitated learning through organised networks of small-enterprise managers and researchers. The opportunity for universities to take on an interactive role in initiating development processes, and even regional change in a wider respect, has been explored through an action research (AR) approach. One of the aims of the University-Led Learning Network (ULLN) is to develop the knowledge and managerial skills required by small-enterprise managers in order to cope better with an economic and social reality that is difficult to survey and to predict. This was done through the ongoing review and evaluation of actions carried out within as well as between the participating companies. Different management perspectives were scrutinised in an environment of close co-operation, with the intention of generating new ideas for action. ULLN is also an approach that enables the university to fulfil the task of co-operating with the external world, which in Sweden is referred to as "the third task", and to reach out to small enterprises, creating a common learning partnership. Earlier studies of networks focusing on an exchange of knowledge and learning demonstrate, above all, the power of innovation that come from a close relationship between companies and universities and the importance of dialogue. The analysis of this study shows similar results. However, there has in the past been a lack of long-term studies which monitored and investigated the effects of co-operation from within. This study aims to rectify that deficiency.In this thesis, it is argued that ULLN has unique advantages, such as the initiation and support of important processes of change, which are not equally matched by other approaches, such as those which depend on consultants, traditional education or purely industrial networks. ULLN should therefore be seen as an important complement to the development support structure for managers of small traditional manufacturing enterprises. This study contributes an understanding of the process of organising these networks, and an analysis of the type of learning developed through such lengthy co-operation over six years.The results of the study can be divided into three categories, namely:1. Implications of organising ULLNs for universities and researchers, by providing an understanding of the advantages of using the university as a platform for initiating development processes for small-enterprise managers in networks.Considerable knowledge and experience were gained during the study of the organisational requirements of continuous development processes, in order to generate and extend learning between small-enterprise managers and university representatives in a ULLN. Results from the study acknowledge the importance of the university adopting different roles during the process, in order to build the trust and commitment necessary for facilitating innovative and creative dialogue within the networks. Another important point that is highlighted in the study is the importance of the university and small traditional manufacturing enterprises meeting halfway in interdependent relations. For the university, this means taking on new roles, and for the small companies, a willingness to learn and to co-operate with other companies and organisations in networks rather than acting alone.This type of close interaction with companies gives university representatives a better knowledge base of small traditional manufacturing enterprises (which make up the majority of the small-business community in Sweden) and their special needs, which in turn contributes to a deeper understanding and makes it possible for the university to introduce research projects that are more relevant and draw small enterprises into a co-operative partnership with the university. The networks are a way of increasing mutual knowledge processes by enabling managers and researchers to examine a variety of development issues and solutions in the company of others who have different frames of reference and perspectives.2. A description of the effects of the ULLN in the participating companies in terms of development projects initiated.The thesis further supports the conclusion that learning in small enterprises is stimulated by interaction with other organisations. New ideas and the inspiration for development work are created in meetings between different actors. As a result of this partnership, projects have been developed internally within individual companies and between the participating companies - for instance in issues related to IT, improved working practices, employee exchanges, ISO 14 001, and so on. Practical lessons have been learnt about different ways of handling various company-related problems, as well as theoretical knowledge about the processes of change themselves. Thus the ULLNs have both initiated important changes and acted as a bridge between the university and SMEs during development work. Through this medium, the university has been able to establish links even with the traditional manufacturing small-enterprise community.3. A description and analysis of the learning process that is created by using the network concept as a development tool.The trustful relationships established between managers and researchers have proved to be an effective medium for sharing experience and enhancing mutual learning. It has been particularly effective in providing a basis for the sharing of explicit and tacit knowledge that is required to support the implementation of different development projects. The ULLN approach has also facilitated a more reflective type of learning (double-loop learning) and created new management perspectives, which have inspired further development. Managers have also become more "secure" in their management role (as a result of the frank and confidential dialogue with different actors in and through the network) and have, for example, experienced a greater ease in delegating and contributing to the empowerment of their employees.
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| 6. |
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| 7. |
- Fridh, Kristina, 1961-
(författare)
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Japanska rum – en diskussion kring tomhet och föränderlighet i traditionell och nutida japansk arkitektur
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Traditional and contemporary Japanese architecture is examined, with focus on the characteristics of emptiness and changeability, the point of departure being Japanese conceptions of space which are interpreted and described from a Western perspective. According to Japanese cultural tradition space is conceived as a subjective perception, a physical experience and a changeable process. A description and analysis of how these conceptions of space are expressed and perceived in architectonic forms, both in traditional sukiya architecture and in a selection of contemporary works of architecture, is then presented. The buildings discussed in the thesis are, among others, the Katsura villa, the pavilions Rinun-tei and Kyusui-ken in Shugaku-in, Shisen-do, Hillside Terrace, Church with the Light, Villa in Shimo-gamo, Gifu Kitagata Apartment Building and Tofu. The contemporary works of architecture have been designed by Fumihiko Maki, Tadao Ando, Waro Kishi, Kazuyo Sejima and Jun Tamaki. Besides visiting the buildings, articles written by these architects have been studied which convey their views on architecture. These texts reflect both Japanese and Western influences in a global debate about architecture. This thesis is based on a direct experience of various buildings together with a personal Western interpretation. In this way the subjective experience is put into focus and leads to a discussion about architecture based on concepts or perceptions. The strong Japanese architectural tradition lives on in the reinterpretations of contemporary architecture, the study of which creates a deeper understanding of the tradition. In this foreign world of architecture there is room for dimensions which could become an architectonic challenge in designing new buildings and environment.
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| 8. |
- Kaestner, Anders
(författare)
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Non-Invasive Multidimensional Imaging Applied on Biological Substances
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents the research and development of a microwave in-strument to capture tomographic information from the inner structure ofthe biological sample. The principle of the instrument is based on theanisotropy introduced by the fibres in materials such as wood and musclesin terms of information regarding changes in the fibre structure. The in-formation is presented as images representing the state of polarization us-ing Stokes parameters, the complex polarization ratio, and the ellipticityand the linear tilt angles. The theory of wave propagation in anisotropicmedia is discussed and related to the dielectric properties of wood. Ex-periments have shown that the developed instrument can be utilized invarious applications such as localizing knots and cavities in wood andto detect mechanical contamination of meat. A second instrument hasbeen improved by introducing a new signal analysis step to estimate therelative shrinkage profile of paper. The estimator is based on trackingfrequency variations in the joint time frequency spectrum and follows thelower bound of the problem for the relevant noise levels.
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| 9. |
- Lundberg, Magnus
(författare)
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Land Mine Detection using Dual-Band Electro-Optical Sensing
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses the detection of buried and partially occluded land mines using electro-optical sensing. According to the Red Cross approximately 10000 people are killed and another 30000 are injured each year in mine related accidents. In addition, the mine situation often prohibits economic growth in countries affected, as agricultural areas cannot be used and infrastructure cannot be developed. Detection of buried land mines using electro-optical sensing is possible mainly by exploiting the infrared wavelengths. The buried mine disturbs the natural heat and mass transfer in the surrounding soil and leads to a thermal signature at the surface that might be possible to detect with an infrared camera. However, it is problematic to design a detector as the signature is weak and distorted by noise and clutter stemming from irregularities in the soil and at the surface. It is identified that the surface clutter, which is the prime concern, is highly correlated to the reflected surface illumination. By using an additional sensor operating in the visual wavelengths, the dual-band data can be exploited to enhance the detection performance. Deriving detectors for such a scenario implies two main problems. Neither the mine signature nor the statistics of the background noise/clutter are known a-priori. The main theme of the thesis is to consider both parametric and non-parametric solutions to these problems. Specifically, a Bayesian perspective is promoted. Considering the problem of an unknown signature, the Bayesian approach can be used to incorporate prior knowledge regarding physical properties, such as recent weather and time of burial, into the detector. The Bayesian perspective is also studied in order to handle the problem of an unknown noise covariance matrix. By properly take into account the uncertainties regarding the noise color, an enhanced ability to describe the desired signal is obtained. Finally the problem of detecting partially occluded surface-laid mines is considered. In such a scenario, the traditional additive clutter model is no longer applicable. Instead a more realistic model is presented and detectors are derived. The methods proposed in this thesis are evaluated both on synthetic data and real measurements and show promising results.
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| 10. |
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