| 11. |
- Broberg, Patrik, 1983-
(författare)
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Imaging and analysis methods for automated weld inspection
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- All welding processes can give rise to defects, which weakens the joint and can eventually lead to the failure of the welded structure. In order to inspect welds for detects, without affecting the usability of the product, non-destructive testing (NDT) is needed. NDT includes a wide range of different techniques, based on different physical principles, each with its advantages and disadvantages. The testing is often performed manually by a skilled operator and in many cases only as spot-checks. Today the trend in industry is to move towards thinner material, in order to save weight for cost and for environmental reasons. The need for inspection of a larger portion of welds therefore increases and there is an increasing demand for fully automated inspection, including both the mechanised testing and the automatic analysis of the result. Compared to manual inspection, an automated solution has advantages when it comes to speed, cost and reliability. A comparison of several NDT methods was therefore first performed in order to determine which methods have most potential for automated weld inspection. Automated analysis of NDT data poses several difficulties compared to manual data evaluation. It is often possible for an operator to detect defects even in noisy data, through experience and knowledge about the part being tested. Automatic analysis algorithms on the other hand suffer greatly from both random noise as well as indications that originate from geometrical variations. The solution to this problem is not always obvious. Some NDT techniques might not be suitable for automated inspection and will have to be replaced by other, better adapted methods. One such method that has been developed during this work is thermography for the detection of surface cracks. This technique offers several advantages, in terms of automation, compared to existing methods. Some techniques on the other hand cannot be easily replaced. Here the focus is instead to prepare the data for automated analysis, using various pre-processing algorithms, in order to reduce noise and remove indications from sources other than defects. One such method is ultrasonic testing, which has a good ability for detecting internal defects but suffers from noisy signals with low spatial resolution. Work was here done in order to separate indications from corners from other indications. This can also help to improve positioning of the data and thereby classification of defects. The problem of low resolution was handled by using a deconvolution algorithm in order to reduce the effect of the spread of the beam.The next step in an automated analysis system is to go beyond just detection and start characterising defects. Using knowledge of the physical principles behind the NDT method in question and how the properties of a defect affect the measurement, it is sometimes possible to develop methods for determining properties such as the size and shape of a defect. This kind of characterisation of a defect is often difficult to do in the raw data, and is therefore an area where automated analysis can go beyond what is possible for an operator during manual inspection. This was shown for flash thermography, where an analysis method was developed that could determine the size, shape and depth of a defect. Similarly for laser ultrasound, a method was developed for determining the size of a defect.
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| 12. |
- Charles Murgau, Corinne
(författare)
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Microstructure model for Ti-6Al-4V used in simulation of additive manufacturing
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to microstructure modelling of Ti-6Al-4V. The microstructure and the mechanical properties of titanium alloys are highly dependent on the temperature history experienced by the material. The developed microstructure model accounts for thermaldriving forces and is applicable for general temperature histories. It has been applied to study wire feed additive manufacturing processes that induce repetitive heating and cooling cycles.The microstructure model adopts internal state variables to represent the microstructure through microstructure constituents' fractions in finite element simulation. This makes it possible to apply the model efficiently for large computational models of general thermomechanical processes. The model is calibrated and validated versus literature data. It is applied to Gas Tungsten Arc Welding -also known as Tungsten Inert Gas welding-wire feed additive manufacturing process.Four quantities are calculated in the model: the volume fraction of phase, consisting of Widmanstätten, grain boundary, and martensite. The phase transformations during cooling are modelled based on diffusional theory described by a Johnson-Mehl-Avrami-Kolmogorov formulation, except for diffusionless martensite formation where the Koistinen-Marburger equation is used. A parabolic growth rate equation is used for the to transformation upon heating. An added variable, structure size indicator of Widmanstätten, has also been implemented and calibrated. It is written in a simple Arrhenius format.The microstructure model is applied to in finite element simulation of wire feed additive manufacturing. Finally, coupling with a physically based constitutive model enables a comprehensive and predictive model of the properties that evolve during processing.
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| 13. |
- Dagbro, Ola
(författare)
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Studies on Industrial-Scale Thermal Modification of Wood
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood as a raw material is useful for many purposes even though some properties are less than optimal, for example, dimensional stability and durability. These characteristics can however be improved by different treatment methods. Environmental awareness has led to an increased demand for environmentally friendly processes like thermal modification that does not add any chemicals to the wood in contrast to, for example, CCA-impregnated wood.This thesis mainly focuses on thermally modified wood from species such as pine, spruce and birch. The thesis present studies of physical attributes such as color, and chemical analysis of water-soluble compounds and degradation products. Treatment intensity is compared between two different industrial processes referred as Thermowood and WTT, which use respectively superheated steam and pressurized steam as heating media.Thermal modification processes darken the color of wood throughout its cross-section. The formation of darker color is related to a degradation processes that takes place during thermal modification. During thermal modification wood is exposed to temperatures between 160 - 220°C, and the temperature causes physical and chemical transformations that change some of the wood properties. Dimensional stability and durability are typically improved, but mechanical strength properties are usually negatively affected by the treatment.The studied wood species were Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies L.) and Birch (Betula pendula L.). Treatments using pressurized steam were carried out under temperatures of 160°C, 170°C and 180°C, and treatments using superheated steam at normal air pressure were carried out at temperatures of 190°C and 212°C. Results showed that similar L* (lightness) can be reached at lower temperatures using pressurized steam compared to superheated steam. The residual moisture content after completed thermal modification was approximately 10% higher in wood treated with the pressurized steam process. It was found that despite an approximately 25°C lower treatment temperature, birch modified in pressurized steam was more acidic compared to birch modified in superheated steam. This will likely have further consequences, requiring more research concerning surface treatment and fixation.The thesis also includes the development of an industrial-quality control procedure based on nondestructive color measurements verified in industrial environment. Treatment intensity in industry is today certified by inspection of documented process schedule and measuring the temperature and time of the process. Quality control in this context refers to the measurement of wood color as an indirect measure of treatment intensity. The color in our study was measured using L*C*H color space. The study shows that it is possible for quality control purposes to measure the color of thermally modified wood from the surfaces of planed boards instead of sawdust or board cross sections that have been used in other studies.The thesis has a final section about academia-industry collaboration that describes how trust building was established through a fruitful relationship involving academia and regional wood products industry in northern Sweden. The study presents an example of a successful research and development alliance between university and a group of small- and medium-sized enterprises (SMEs). This alliance has been a great example on international collaboration involving researchers originating from Finland, China, Bangladesh, Spain, Russia and Sweden. Through an in-depth multi-year study of how the research cooperation developed, the paper describes how the involved companies successfully entered into a new segment of the market.
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| 14. |
- Gama, Fabio, 1980-
(författare)
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Managing the Collaborative Front End of Innovation in Manufacturing Firms : Requirements, Capabilities, and Conditions
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The front end of innovation is critical to innovative efforts in firms yet it remains to be poorly understood. This especially important since innovation efforts in the front end are becoming increasingly open in line with the era of open innovation. Although the literature on the front end of innovation is well developed, prior studies have largely focused on bilateral agreements and have overlooked conditions for collaborations with science-based partners (universities and research institutes). This is especially true for manufacturing firms, for which a continuous stream of new product ideas are a key source of competitiveness. To make things worse, the front end of innovation in this setting is often characterized by incongruent practices by partners, different magnitudes of fuzziness, and high risks in revealing new ideas. Developing new product definitions with different partners is thus a risky endeavor that may seriously compromise competitive advantages if mishandled. Therefore, there is a need for greater knowledge to facilitate the collaborative front end with different types of partners. Accordingly, the purpose of this dissertation is to understand how to manage the collaborative front end in manufacturing firms, with a particular focus on requirements, capabilities, and conditions.To fulfill this research purpose, data on manufacturing firms were collected through four case studies and one survey. In total, this dissertation is based on empirical data from 81 interviews with R&D members across 10 medium-sized and large manufacturing firms, as well as a survey of 146 small and medium-sized manufacturing firms. Respondents were based in Brazil or Sweden. The key theories and literatures covered in this dissertation include coordination modes, control mechanisms, organizational routines, the resource-based view, and appropriability mechanisms.This dissertation makes numerous theoretical contributions to the front-end literature. First, it extends the front-end literature by presenting the concepts of systematic idea generation and fuzziness assessment as a prerequisite for improving front-end performance. Second, this dissertation extends the front-end literature by listing the collaboration conditions that help firms cooperate with science-based partners. By collaborating with science-based partners, firms can access (unpublished) codified and tacit scientific knowledge, enabling them to rapidly build on the latest research findings. The findings suggest particular practices that can be applied to reduce cultural differences and diminish goal divergence among project members. Third, the findings in this dissertation enrich the front-end literature by describing a set of detailed practices to streamline the involvement of different types of partners using diverse protective practices. Fourth, it suggests a theoretical framework that describes how to manage the collaborative front end of innovation. The theoretical framework explains how manufacturing firms can use their organizational capabilities to develop new product ideas efficiently and safely. In particular, the framework discerns the capabilities that are necessary to explore mechanisms, practices, and routines in terms of divergent thinking, external expertise, and multiple opinions. Altogether, these contributions assist firms to better manage collaborative front end.
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| 15. |
- Ghasemi, Yahya, 1982-
(författare)
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Flowability and proportioning of cementitious mixtures
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding the role of constituents of cementitious mixtures as the most globally used human-made material and their effect on the flowability of the blends is of great importance. A comprehensive understanding of the ingredients of mixtures allows for optimized proportioning of constituents and can lead to a reduction in cement and water demand of the blends.The thesis focuses on relating the flow of mixtures to the specific surface area of the particles through the concepts of excess water layer theory by assuming that the particles are enveloped by a thin film layer that separates the grains and lubricates their surfaces. However, in order to study the film thickness, it is inevitable to consider packing density and specific surface area of the particles. Both of the mentioned parameters and their influence on water requirement of mixtures were investigated as a part of the project.The theoretical part of the thesis includes background and explanation of the concepts and theories used in conducting the research including particle packing theory, specific surface area, and excess layer theories. In addition, the thesis attempts at defining and formulating terms and parameters such as representative shape, mixer efficiency, and optimal packing.The experimental part of the thesis consists of laboratory measurements of packing density in the loose state, estimation of specific surface area using microtomography and slump tests for mortar and concrete.The results of the thesis indicate that the available packing models can estimate the packing density with acceptable accuracy. In addition, it was shown that it is possible to estimate flowability of mixtures based on information about the specific surface area of the constituents. A mix design approach is introduced which predicts flow spread of slump test, a measure that is often used in laboratories and at the building sites.Moreover, the research revealed that the estimation of the specific surface area of particles can be improved by assuming a platonic solid shape for the particles instead of spheres. Furthermore, the mixer efficiency was quantified and optimization of mixtures against packing density and water requirement was explained.The finding of the project lays a foundation for a simple workability based mix design approach.
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| 16. |
- Gustafsson, Emil
(författare)
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Design and application of experimental methods for steel sheet shearing
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Shearing is the process where sheet metal is mechanically cut between two tools. Various shearing technologies are commonly used in the sheet metal industry, for example, in cut to length lines, slitting lines, end cropping etc. Shearing has speed and cost advantages over competing cutting methods like laser and plasma cutting, but involves large forces on the equipment and large strains in the sheet material. The constant development of sheet metals toward higher strength and formability leads to increased forces on the shearing equipment and tools.Shearing of new sheet materials imply new suitable shearing parameters. Investigations of the shearing parameters through live tests in the production are expensive and separate experiments are time consuming and requires specialized equipment. Studies involving a large number of parameters and coupled effects are therefore preferably performed by finite element based simulations. Accurate experimental data is still a prerequisite to validate such simulations. There is, however, a shortage of accurate experimental data to validate such simulations.In industrial shearing processes, measured forces are always larger than the actual forces acting on the sheet, due to friction losses. Shearing also generates a force that attempts to separate the two tools with changed shearing conditions through increased clearance between the tools as result. Tool clearance is also the most common shearing parameter to adjust, depending on material grade and sheet thickness, to moderate the required force and to control the final sheared edge geometry.In this work, an experimental procedure that provides a stable tool clearance together with accurate measurements of tool forces and tool displacements, was designed, built and evaluated. Important shearing parameters and demands on the experimental set-up were identified in a sensitivity analysis performed with finite element simulations under the assumption of plane strain. With respect to large tool clearance stability and accurate force measurements, a symmetric experiment with two simultaneous shears and internal balancing of forces attempting to separate the tools was constructed.Steel sheets of different strength levels were sheared using the above mentioned experimental set-up, with various tool clearances, sheet clamping and rake angles. Results showed that tool penetration before fracture decreased with increased material strength. When one side of the sheet was left unclamped and free to move, the required shearing force decreased but instead the force attempting to separate the two tools increased. Further, the maximum shearing force decreased and the rollover increased with increased tool clearance.Digital image correlation was applied to measure strains on the sheet surface. The obtained strain fields, together with a material model, were used to compute the stress state in the sheet. A comparison, up to crack initiation, of these experimental results with corresponding results from finite element simulations in three dimensions and at a plane strain approximation showed that effective strains on the surface are representative also for the bulk material.A simple model was successfully applied to calculate the tool forces in shearing with angled tools from forces measured with parallel tools. These results suggest that, with respect to tool forces, a plane strain approximation is valid also at angled tools, at least for small rake angles.In general terms, this study provide a stable symmetric experimental set-up with internal balancing of lateral forces, for accurate measurements of tool forces, tool displacements, and sheet deformations, to study the effects of important shearing parameters. The results give further insight to the strain and stress conditions at crack initiation during shearing, and can also be used to validate models of the shearing process.
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| 17. |
- Holmquist, Mats, 1954-
(författare)
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Lärande nätverk : En social oas i utvecklingsprocessen
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intresset för nätverk mellan organisationer växer i arbetslivet. Fler och fler chefer, ledare och ansvariga går med i nätverk för att få stöd i sitt utvecklingsarbete. Varför? Vad är det för speciellt med lärande i nätverk? Vad får individen och organisationen ut? Mina egna och kollegors erfarenheter från tio års praktiskt arbete i fem nätverk i Halland, har gett mig en unik tillgång till data för att söka svar på frågorna.Med hjälp av flervetenskaplig teori och tidigare empirisk forskning har jag skapat en modell över nätverk som stöd i utvecklingsprocessen. Modellen har jag använt till att analysera mina data för att förstå lärprocessen i nätverk, vilka förutsättningar och organiseringsformer som är viktiga för att stimulera det kollektiva lärande som uppstår i samverkan mellan olika individer och organisationer. Jag har även undersökt vad deltagandet ger i utbyte och vad som stödjer respektive hindrar en transformering till organisatorisk nytta och förändring.Resultaten visar att nätverk fungerar som en social oas för chefer och ledare, som kan vara ganska ensamma och osäkra i sitt arbete. De uppskattar en plats där de kan möta andra i en liknande situation, för att under tillitsfulla former utbyta erfarenheter och reflektera över sina handlingsalternativ. Deltagarnas olikheter tillför variationer som stimulerar ett kreativt lärande och genererar innovativa idéer.I stort sett alla deltagare är mycket positiva till nätverkformen. Utbytet är huvudsakligen personliga insikter och kunskaper i form av ökat självförtroende, reducerad osäkerhet och stärkt förändringskompetens. Deltagandet ger även inspiration, idéer och organisatoriska förändringsförslag. När dessa sedan ska föras över från nätverket till organisationen möter dock deltagarna ofta svårigheter och hinder.Organisationernas förmåga att absorbera nätverksresultaten brister. De har många gånger svårt att ta tillvara nya kunskaper och idéer, att integrera nätverkslärande med organisatoriskt lärande och därmed svårt att utnyttja den utvecklingspotential som nätverk rymmer. Viktiga hinder är strategi- och förankringsbrist på ledningsnivån.Nätverkets styrka som en stödjande social oas för deltagaren i utvecklingsprocessen rymmer också en svaghet. Utbytet riskerar att begränsas till personlig bekräftelse och bidra till få organisatoriska förändringar. För att undvika detta behöver deltagarens, organisationens och nätverkets utvecklingssyfte tydliggöras från början.Analysen leder fram till en idealmodell av en utvecklingsprocess med stöd av nätverk. I modellen stimulerar gemensamma reflektionen över praktiska erfarenheter ett kreativt lärande som ger nya kunskaper och idéer i utbyte. När dessa ska överföras och tillämpas i verksamheten behövs en utvecklingsorganisation med en ledning som kan ta ett strategiskt helhetsgrepp över förändringsprocessen.Slutsatserna talar för lärande nätverk som ett stöd i utvecklingsprocessen. De talar för fortsatt forskning för att pröva idealmodellen och för att fördjupa kunskaperna om absorberingssvårigheten och strategibristen.
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| 18. |
- Homayoun, Saeid
(författare)
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Internet corporate reporting disclosure and transparency
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The recent wave of well-publicized global corporate accounting scandals has highlighted the importance of the enhanced adoption of Internet technology and hence the increased transparency resulting from the enhanced disclosure of firm information. The objective of this study is to explore and identify Internet corporate reporting (ICR) disclosure in a context of publically listed firms. On a descriptive level, this thesis show that a considerable portion of publically listed firms have relativity high quality in their ICR disclosure, which is indicated by results showing that publically listed firms publish reasonably well-developed Internet-based reporting. In line with the Financial Accounting Standards Board, this thesis depicts characteristics of ICR disclosure practice by outlining the extent of content and presentation. As an indication of the quality of ICR, on average, the frequency of the identified items disclosed by the firms for the content of their websites was higher than for the presentation of information. One of the characteristics of presentation format is extensible business reporting language (XBRL). Consequently, the thesis also seeks to identify the important factors that drive publically listed firms to adopt of XBRL by conducting open-ended interviews. At the explanatory level, the results in this thesis indicate that among firm characteristics and the variables identified as important determinants for the disclosure of firm information in general, only profitability (proxy by return of equity) shows significant association with the extent of ICR disclosure. In addition, the thesis results show that among corporate governance mechanisms, only board size influences the ICR disclosure of firms. The thesis offers an integrated model for ICR disclosure and transparency anchored in multiple theoretical lenses and contributes to the field of corporate Internet reporting. The integrated model is based on four complementary theories: agency theory, stakeholder theory, signaling theory and legitimacy theory. Accordingly, the framework offers the potential for a rich understanding of the phenomena of internet corporate reporting disclosure practice and determinants.
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| 19. |
- Jahncke, Helena
(författare)
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Cognitive performance and restoration in open-plan office noise
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation presents four experimental studies (in four papers) with the overall aim to investigate the effects of office noise on cognitive performance and restoration. In the first two papers the focus was on the effects of different sound levels (i.e., the mean level from all sound sources at an office, such as speech, phones, people walking) on performance, fatigue and stress. In the last two papers the focus was on the effects of background speech, as this has previously been shown to be the most disturbing noise source in open-plan offices. Paper I demonstrated decreased word memory performance, increased fatigue and motivational deficits when the background sound level increased by 12 dB, from 39 to 51 dB LAeq. Paper II showed that the sound level effects were more pronounced for individuals with a hearing impairment. Unexpectedly, no effects were found of acute noise exposure on the participant´s stress hormone levels (Paper I and Paper II).Regarding effects of irrelevant speech, Paper III showed that cognitive performance decreased as a function of background speech intelligibility, the higher the intelligibility depicted by the Speech Transmission Index (STI), the worse the performance. The results indicated that the STI-value must be less than 0.50, to avoid a negative influence on performance. Further, both Paper III and IV showed that performance is more impaired by background speech if the focal task requires episodic memory and rehearsal—such as word memory and information search. Interestingly, some tasks were insensitive for speech.The restorative effects of a break were addressed in Paper I and II (i.e., directly after the work sessions in noise). The break period differed in content between the participants. Paper I showed that a break with a nature movie with corresponding sound increased energy ratings compared to just listening to river sounds or office noise. Continued exposure to office noise gave the lowest ratings of motivation after the break. Paper II showed improved arithmetic performance and motivation after the break with a nature movie and decreased performance and motivation after continued noise exposure. For the hearing impaired participants, however, continued noise during the break increased motivation and performance, while the movie did not.Taken together, the current thesis demonstrates that open-plan office noise can have a negative impact on fatigue, motivation and performance. How much performance is impaired varies with the cognitive processes required by the tasks performed and hearing status. Moreover, continued noise exposure during a short break can further decrease motivation and subsequent performance.
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| 20. |
- Khodadad, Davood
(författare)
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Multiplexed Digital Holography incorporating Speckle Correlation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In manufacturing industry there is a high demand for on line quality control to minimize the risk of incorrectly produced objects. Conventional contact measurement methods are usually slow and invasive, meaning that they cannot be used for soft materials and for complex shapes without influencing the controlled parts. In contrast, interferometry and digital holography in combination with computers become faster, more reliable and highly accurateas an alternative non-contact technique for industrial shape evaluation. For example in digital holography, access to the complex wave field and the possibility to numerically reconstruct holograms in different planes introduce a new degree of flexibility to optical metrology. With digital holography high resolution and precise three dimensional (3D) images of the manufactured parts can be generated. This technique can also be used to capture data in asingle exposure, which is important when doing measurements in a disturbed environment. The aim of this thesis is devoted to the theoretical and experimental development of shape and deformation measurements. To perform online process control of free-form manufactured objects, the measured shape is compared with the CAD-model to obtain deviations. To do this, a new technique to measure surface gradients and shape based onsingle-shot multiplexed dual-wavelength digital holography and image correlation of speckle displacements is demonstrated. Based on an analytical relation between phase gradients and speckle displacements it is shown that an object is retrieved uniquely to shape, position and deformation without the unwrapping problems that usually appear in dual-wavelength holography. The method is first demonstrated using continues-wave laser light from twotemperature controlled laser diodes operating at 640 nm. Then a specially designed dual core diode pumped fiber laser that produces pulsed light with wavelengths close to 1030 nm is used. In addition, a Nd:YAG laser with the wavelength of 532 nm is used for 3D deformation measurements. One significant problem when using the dual-wavelength single-shot approach is that phase ambiguities are built in to the system that needs to be corrected. An automatic calibration scheme is therefore required. The intrinsic flexibility of digital holography gives a possibility to compensate these aberrations and to remove errors, fully numerically without mechanical movements. In this thesis I present a calibration method which allows multiplexed singleshotonline shape evaluation in a disturbed environment. It is shown that phase maps and speckle displacements can be recovered free of chromatic aberrations. This is the first time that a multiplexed single-shot dual-wavelength calibration is reported by defining a criteria tomake an automatic procedure. Further, Digital Speckle Photography (DSP) is used for the full field measurement of 3D deformations. In order to do 3D deformation measurement, usually multi-cameras and intricate set-up are required. In this thesis I demonstrate the use of only one single camera torecord four sets of speckle patterns recorded by illuminating the object from four different directions. In this manner, meanwhile 3D speckle displacement is calculated and used for the measurement of the 3D deformations, wrapping problems are also avoided. Further, the same scale of speckle images of the surface for all four images is guaranteed. Furthermore, a need for calibration of the 3D deformation measurement that occurs in the multi-camera methods,is removed. By the results of the presented work, it is experimentally verified that the multiplexed singleshot dual wavelength digital holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve and evaluate the object shape. Usingmultidirectional illumination, the 3D deformation measurements can also be obtained. The proposed method is robust to large phase gradients and large movements within the intensity patterns. The advantage of the approach is that, using speckle displacements, shape and deformation measurements can be performed even though the synthetic wavelength is out of the dynamic range of the object deformation and/or height variation.
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