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- Broberg, Patrik, 1983-
(författare)
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Towards Automation of Non-Destructive Testing of Welds
- 2011
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All welding processes can give rise to defects that will weaken the joint and can lead to failure of the welded structure. Because of this, non-destructive testing (NDT) of welds have become increasingly important to ensure the structural integrity when the material becomes thinner and stronger and welds become smaller; all to reduce weight in order to save material and reduce emissions due to lighter constructions.Several NDT methods exists for testing welds and they all have their advantages and disadvantages when it comes to the types and sizes of defects that are detectable, but also in the ability to automate the method. Several methods were compared using common weld defects to determine which method or methods were best suited for automated NDT of welds. The methods compared were radiography, phased array ultrasound, eddy current, thermography and shearography. Phased array ultrasound was deemed most suitable for detecting the weld defects used in the comparison and for automation and was therefore chosen to be used in the continuation of this work. Thermography was shown to be useful for detecting surface defects; something not easily detected using ultrasound. A combination of these techniques will be able to find most weld defects of interest.Automation of NDT can be split into two separate areas; mechanisation of the testing and automation of the analysis, both presenting their own difficulties. The problem of mechanising the testing has been solved for simple geometries but for more general welds it will require a more advance system using an industrial robot or similar. Automation of the analysis of phased array ultrasound data consists of detection, sizing, positioning and classification of defects. There are several problems to solve before a completely automatic analysis can be made, including positioning of the data, improving signal quality, segmenting the images and classifying the defects. As a step on the way towards positioning of the data, and thereby easing the analysis, the phase of the signal was studied. It was shown that the phase can be used for finding corners in the image and will also improve the ability to position the corner as compared to using the amplitude of the signal. Further work will have to be done to improve the signal in order to reliably analyse the data automatically.
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| 2. |
- Edstorp, Marcus, 1980-
(författare)
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Weld Pool Simulations
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This investigation is devoted to the study of welding and its effect on the workpiece, focusing on the thermo and fluid dynamical phenomena occuring during a autogenous or nonautogenous arc fusion welding process. Its aim is to simulate the behaviour of the weld pool and analyze the consequence of the solid-liquid phase change, thus obtaining a methodology for predicting the appearance of weld defects related to solidification and cooling. In order to accomplish this, we solve equations governing a number of continuum mechanical and electromagnetical quantities, as well as consider the motion of the freely moving boundary of the weld pool. Since the state of these quantities is strongly influenced by phenomena such as arc and droplet impingement, non-isothermal phase change, surface tension, Marangoni forces and Lorentz forces, much effort is necessarily devoted to the modelling of the corresponding fluxes and sources, as well as to the implementation of computationally efficient techniques for simulating the geometrical deformation of the workpiece, which in our setting is entirely determined by the motion of the weld pool surface.Common to all arc fusion welding processes is the employment of a welding arc. Many techniques rely on the arc to clean and shield the workpiece during the process, however in this study we consider it to be its main purpose to cause the local increase of thermal energy that is required for the establishment of the weld pool, and also to exert the mechanical forces that provoke the subsequent fluid flow which enhances heat transfer and facilitates weld penetration. The physics of the welding arc itself is quite intricate, and although the modelling of the arc is not the prime objective of this research project, we conclude that arc forces act on the pool surface, and that the investigation of the arc behaviour is important insofar that it provides input to the pool model and thus enables a more accurate prediction of the quality of the weldment that is created once the pool has solidified
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| 3. |
- Köhler, Veronica, 1974-
(författare)
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Co-Creators of Scope of Action : An exploration of the dynamic relationship between people, IT, and work in a nursing context
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Information Technology (IT) is today widespread in our work places, in our spare time and in our society overall. Implementations of IT in organizations come with high expectations on effectiveness, revenue, smoother work processes and so on. However, this simplified view on IT ignores the fact that it is the IT usage rather than the IT artifact per se that in the end decides the effect of an implementation of IT. Although the IT artifact certainly has been designed to support certain tasks and processes, the success or failure of the Information System (IS) in the end depends on the individuals' actions, which ultimately depend on their perceptions and interpretations of the IS. Thus, when technology is being implemented and becomes an IS in use, it becomes a part of work, and as such more of a social system than a technological one.The actual result of a design process does not solely consist of things or artifacts, but above all changed action patterns for the users. From this follows that we must consider design of artifacts as something more than merely the constructing of actual objects with functions and properties that are easily measured. Rather, a large part of all design activities has to do with design of conceivable social milieus, not artifacts. Thus, design may be defined as the suggesting and establishing of scope of action. The concept scope of action aims at describing the fact that the design of, and consequently the implementation of, a specific IT artifact always aims at creating a certain scope of action; some actions are made easier, others are made more difficult or even impossible. This scope of action has to some extent been deliberately designed, but these changes may on the other hand also be undesired and not predicted in advance. The complexity of this phenomenon is great and hard to grasp in advance. However, this does not mean that we can allow ourselves to ignore exploring this phenomenon more deeply. On the contrary, with a usage perspective on IS success or failure, scope of action becomes very important.Although the term scope of action may seem a rather intuitive concept, we need more concrete knowledge about its character in order to be able to understand IT usage, both when designing a new IT artifact and when studying or evaluating IT. Thus, our intuitive understanding of the concept needs to be complemented with theory on the ‘constituents’ and effects of this phenomenon. For this purpose, in this thesis nurses’ use of the Electronic Patient record (EPR) is being explored in order to gain an empirically derived understanding of the character of scope of action.The research findings highlight the emergent character of scope of action. It is obvious that an individual’s scope of action is not being created on one occasion, and above all not only by the IT artifact. Various co- creators such as the IT artifact, the usage and the social context create and re-create scope of action. Also, how the individual interprets and understands the IT artifact in IT usage will influence her scope of action. This since sensemaking and learning processes on both a personal and organizational level take place that are co-creators of the individual’s scope of action, at the same time as the individual’s knowledge and previous sensemaking and learning influences her use of the IT artifact.Thus, reasoning, thinking, learning, and the IT artifact co-evolve over time in adaptation and appropriation processes. This means that IT as a mediational means constitutes an important co-creator of scope of action. From this also follows that work integrated learning is an important co- creator of scope of action when using IT in a work setting, at the same time as work integrated learning is being influenced by the individual’s scope of action.Finally, in order to understand how scope of action emerges in use, merely focusing on structures is insufficient. Scope of action emerges as a product of interplay between complex processes involving artifacts, usage and context. This means that the user’s scope of action is co-created by both static structures as well as dynamic processes relating to the IT artifact, the organization, and the work practice. Thus, the IT artifact, and subsequently scope of action, must be must be understood in relation to the multi-aspectual context of which it is a part instead of merely in relation to the properties of the IT artifact per se.
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| 4. |
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| 5. |
- Nilsson, Stefan, 1975-
(författare)
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Exploring the relationship between awareness information and user activities online
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis contributes to the domain of awareness information. Awareness information can be viewed as a fundamental building-block of social media, visualizing people and their activities in an online setting. With life becoming more and more influenced by social media such as Facebook, Flickr, Twitter, Linkedin and Digg, it becomes important for designers of social media to have an understanding of how users respond to awareness information. An online gallery of pictures was developed and equipped with a chat and a basic awareness information system. Usage data was collected by the system and analyzed combining qualitative as well as quantitative approaches aiming to explore the influence awareness information have on the usage of the system. The analysis reveals that awareness information is a powerful tool triggering social behaviour. It is, at the same time, challenging to implement in a way that it provides a sound environment for social interaction. This was manifested by co-present users both stayed longer in the system and also was inclined to take a different path through the gallery than the solitary user. However, the interaction that took place in the gallery was characterized by frequent conversational break-downs and irritation among users. Results indicate that this is, in part, due to the lack of built-in social norms guiding users in their activities in the system. Subsequently, it is important to facilitate the creation, recreation and reinforcement of social norms when designing social systems.
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| 6. |
- Tano, Ingrid
(författare)
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Contributions to multivariate process capability indices
- 2012
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work presented in this thesis considers multivariate process capability indices (MPCIs) with focus on confidence intervals and tests for MPCIs. It also includes a case study, where multivariate statistical analysis and MPCIs are applied to data from a thermal spraying process at Volvo Aero Corporation. A process capability index measures the ability of a process to satisfy customers’ demands. Since the knowledge about the process performance is based on a random sample, it is important to be able to handle the uncertainty this implies. If the uncertainty is not dealt with and the estimated index is used directly without considering, e.g. a confidence interval, an erroneous conclusion may be drawn about the process capability.The thesis consists of a summary and of three papers, one of which has been presented at an international conference, one has been accepted for publication in an international journal, and the third has been submitted for publication.In Paper I, multivariate statistical analysis is used for screening and tentative model building to describe the relationship between the porosity and the heat conductivity in the thermal spraying process. Object-oriented finite element analysis (OOF) is subsequently used for verification of the statistical model. The new approach functions well and confirms the findings from the statistical model.Paper II reviews and compares four different MPCIs with confidence intervals, requiring multivariate normal distribution. MPCIs are needed when the quality characteristic of interest is multivariate, i.e. when the quality characteristic consists of several correlated variables. The review shows that more research is needed to obtain an MPCI with a confidence interval or a test that works properly. In particular, it is required that a stated value of the MPCI at least limits the probability of non-conformance in a known way. A drawback is also elucidated with existing MPCIs based on principal component analysis.Paper III presents some method development with the purpose of meeting the deficiencies identified in Paper II. A new index together with a confidence interval and a decision procedure is developed that converts a multivariate situation into a familiar univariate situation. Well-known statistical theory for univariate process capability indices can then be used. Properties, like significance level and power, of the pro¬posed deci¬sion procedure is evaluated through a simulation study in the two-dimen¬sional case. A comparative simulation study between our new MPCI and an MPCI pre¬viously suggested in the literature is also done. These studies show that our proposed MPCI with accompanying decision procedure has desirable properties and is worth to study further.
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