A stereo camera system together with a single projected fringe pattern and one image recording is used to measure 3D-shape. The idea is to make the measurement quick enough to be able to use the method when testing quality on-line in manufacturing industry. For this to be possible the digital master (e.g. the CAD model) of the object is used to find homologous points, i.e. points corresponding to the same object point, in the cameras. Given the homologous points the shape can be calculated using optical triangulation. In the results of the shape measurement it can be seen that as long as the object has approximately the same shape as expected (the same shape as the digital master) the method works. For the setup used in these measurements the accuracy was ≈± 40 µm. However, large deviation from the digital master will be incorrectly detected due to the fact that the phase in the images is wrapped. An analytical expression for the maximum detectable deviation is calculated and for the setup used it became ≈± 1.6 mm. Since the accuracy in the shape measurement depends on the phase error an analytical expression for this is derived. It is seen that the phase error becomes large if the fringe modulation is low and the speckle contrast in the fringe pattern is high. The phase in the fringes is determined using a Fourier filter method which gives that the phase error also depends on the size of the filter in the Fourier spectrum. To reduce the phase error focus has been put on suppressing the speckles by moving the aperture. It is verified by simulations and experiments that this method reduces both the speckle contrast and the phase error by 60 % for a movement of three aperture diameters. / För att mäta 3D-form används ett stereokamerasystem tillsammans med ett projicerat fransmönster och en avbildning. Tanken är att göra mätningen tillräckligt snabb för att den ska kunna användas till att testa kvalitet on-line i tillverkningsindustrin. För att detta ska vara möjligt används objektets digitala master (t ex. CAD modellen) för att hitta de homologa punkterna, dvs. de punkter som motsvarar samma objektpunkter, i kamerorna. Givet de homologa punkterna kan formen beräknas med optisk triangulering. Resultaten från formmätningarna visar att så länge som objektet har ungefär samma form som förväntat (dvs. samma form som den digitala mastern) så fungerar metoden. Stora avvikelser från den digitala mastern kommer dock att detekteras inkorrekt eftersom att fasen i bilderna är vikt. Ett analytiskt uttryck är beräknat för den maximala detekterbara avvikelsen och för denna uppställning blir den ≈± 1.6 mm. Noggrannheten i mätningarna blir med samma uppställning ≈± 40 µm. Då noggrannheten i formmätningen beror på fasfelet har ett analytiskt uttryck härletts för detta. Detta visar att fasfelet blir stort om fransmodulationen är låg och specklekontrasten i fransmönstret är hög. Då fasen i fransarna bestäms med en Fourierfiltermetod kommer fasfelet även att bero på filtrets storlek i Fourierspektrumet. För att minska fasfelet har fokus lagts på att reducera specklerna genom att förflytta aperturen. Simuleringar och experiment har använts för att verifiera att denna metod reducerar både specklekontrasten och fasfelet med 60 % för en förflyttning på tre aperturdiametrar.

Digital holographic interferometry is an optical measurement technique that is capable of measuring the movement/deformation of an object surface with extremely high accuracy, spatial resolution and temporal resolution. But, because it is very sensitive to disturbances, it is mostly used in well controlled laboratory environments. An exciting new application of the method could be for process supervision in the manufacturing industry. But before it can be used in such an environment it must be made more insensitive to disturbances. The work in this thesis deals with post processing of data from holographic interferometry measurements to reduce the effects of mechanical vibrations and random refractive index fluctuations in the surrounding air. The first approach of using a purely temporal interference filter was successful in reducing the noise due to vibrations, but the noise from the air disturbance was only reduced over a very limited spatial region. A more complete spatio-temporal filter that is not of the interference type requires that the spatio-temporal statistics of the noise from the air can be measured. Therefore the rest of the work is devoted to this problem. The method developed is applied to the relatively simple case of locally homogenous/isotropic refractive index fluctuations generated in a small wind tunnel. There is a simple theory for these types of fluctuations for which the method was successfully verified.

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.

In recent decades, the use of high- and ultra high strength steels in modern car bodies has increased drastically. This is due to both severe legislation of passenger passive safety and the recent year's effort to reduce fuel consumption to decrease environmental harmful emissions. Many new materials and technologies have been developed to meet these new demands, where press hardening, or also called hot stamping, has been one of the most successful technologies to produce complex components with superior mechanical properties. In the product development process, thermo-mechanical coupled forming simulations are used to predict the final components properties. In order to obtain accurate results, correct models of the physics involved in the simultaneous forming and quenching is needed. The objective of current work is to investigate the heat transfer between the hot blank and the cold tools in the press hardening process. The transfer of heat is the key process that affects the products formability, final geometry, residual stresses and the development of mechanical properties. The two most important contact criteria are investigated in this thesis, heat transfer at a thin contact gap and heat transfer at mechanical contact under an applied contact pressure. An experimental setup to investigate these two contact criteria is developed. It consists of an upper and lower cylindrically shaped tool were the hot blank is quenched between cold tool surfaces. The results from experiments consist of measured temperature histories in the tools. A finite element model of the experiments in combination with an inverse simulation algorithm is used to predict the heat transfer at each contact condition. The inverse technique called improved advance retreat and golden section method is used to solve the ill conditioned inverse heat conduction problem that arise when solving for the heat transfer at the contact interface. The result from inverse simulations in combination with regression analysis is used to develop a general model of the heat transfer coefficient. The outcome is two regression models, one for each contact criterion, were the parameters affecting the heat transfer coefficient are identified. It is found, that a heat transfer coefficient depending on contact pressure or contact gap as well as contacting surface temperatures provide a good match between experimental and simulated temperature response in the tools. The regression model captures the main characteristics of the heat transfer coefficient and has been implemented as a subroutine in the finite element code LS-DYNA.

No description available.

In the past decade, there has been an increasing demand from governments for high level protections for military vehicles against explosives. However, designing and validation of protection is a time consuming and expensive process, where previous experience plays an important role. Development time and weight are the driving factors, where the weight influences vehicle performance. Numerical simulations are used as a tool in the design process, in order to reduce development time and optimise the protection. The explosive load acting on a structure is sometimes described with analytical functions, with limitations to shape and type of the explosive, confinement conditions etc. An alternative way to describe the blast load is to use numerical simulations based on continuum mechanics. The blast load is determined by modelling the actual type and shape of the explosive in air or sand, where the explosive force transfers to the structure of interest. However, accuracy of the solution must be considered, were methods and models should be validated against reliable experimental data. Within this work, tests with explosive placed in air, sand or a steel pot has been performed. For all tests, the dynamic and residual deformation of steel plates was measured, while the impulse transfer was measured for some tests. This thesis focuses on continuum based numerical simulations for describing the blast load, with validation against data from the experiments. The main conclusion of this work is that numerical simulations of air blast loading in the near-field can be described with sufficient accuracy.

Over recent years the demand of press hardened ultra-high strength steel for safety structures in automobiles has increased and continuation of this trend is expected.Components with tailored material properties can be manufactured using a thermo-mechanical process with heated and cooled areas in a tool. In industry the cooling rate of the blank is controlled this utilizes the formation of different microstructures with varying mechanical properties within a single component.The structural response in a crash situation can be altered by the design of the component with formation of different material grades based on the microstructure in designated areas of the component.Material models used in finite element analysis are required by the automotive industry and its suppliers. These models contribute to the improvement and quality of press hardened components.In this work a set of tensile test specimens with different volume fractions of phases are produced. As material is the boron steel 22MnB5 chosen which is a common material used in press hardening due to its good hardenability. The specimens are austenitized before starting the heat treatment at different temperatures and holding times. In total fourteen different microstructures are produced. Reference material grades for pure phases are ferrite, bainite and martensite. The produced samples consist of ferrite-bainite, ferrite-martensite and bainite-martensite with different volume fractions, additionally a microstructure consisting of three phases, ferrite-bainite and martensite, is available. Using measured mechanical properties of pure phases and the volume fraction of formed phases different homogenization methods are compared in their ability to represent the mechanical response of mixed microstructures. The homogenization methods account for elastic deformation and the hardening of the material. The onset of necking is seen as the last valid point for all homogenization methods. After this point a localization and damage function for the prediction of softening and fracture is applied. Strain localization and fracture are mesh dependent, therefore an analysis length scale is introduced to account for different element sizes. A weakest link criterion is used for fracture. This means failure of the composite is assumed to occur if one phase fails. The material model for homogenization of mixed microstructures including damage is implemented in the commercial available finite element code LS-Dyna and validated by comparison to experimental results.

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 thecontrolled parts. In contrast, interferometry and digital holography in combination with computers become faster, more reliable and highly accurate as an alternative non-contact technique for industrial shape evaluation. In digital holography, access to the complex wave field and the possibility tonumerically 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 a single exposure,which is important when doing measurements in a disturbed environment.The aim of this thesis is to perform online process control of free-form manufactured objects by measuring the shape and compare it to the CAD-model. To do this, a new technique to measure surface gradients and shape based on single-shot 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 and position without the unwrapping problems that usually appear in dual wavelength holography. The method is firstdemonstrated using continues wave laser light from two temperature controlled laser diodes operating at 640 nm. Further a specially designed dual core diode pumped fiber laser that produces pulsed light with wavelengths close to 1030 nm is used. 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 single-shot online 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 single-shot dual wavelength calibration is reported by defining a criteria to make an automatic procedure.By the results of the presented work, it is experimentally verified that the single-shot dual wavelength digital holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve and evaluate the object shape. The proposed method is also robust to large phasegradients and large movements within the intensity patterns. The advantage of the approach is that, using speckle displacements, the shape measurement can be done even though the synthetic wavelength is out of the dynamic range of the height variation of the object.

Growing demands for passenger safety, vehicle performance and fueleconomy is a continuous driving force for the increase in use of advancedhigh strength steels (AHSS) in the automotive industry. Thesesteels area characterised by improved formability and crash worthinesscompared to conventional steel grades. An important prerequisite of theapplication of new material grades is the characterization of its mechanicalproperties. Post-localization and fracture predictive technologiesgreatly facilitate the design of components which make optimal use ofthese steel grades. In this thesis, press hardened boron alloyed steelsubjected to differential thermo-mechanical processing is characterized.Fracture properties in relation to the different microstructures obtainedis studied. Furthermore a dual phase (DP) cold forming steel is chosenfor evaluation of ductility limit in shear loading. throughout thiswork a strategy for modelling post-localization response and predictingductility limit using shell elements larger then the typical width of thelocalized neck is used. The studied material is assumed to be in a stateof plane stress. Mesh dependency is alleviated by the introduction of aelement size dependent parameter into the constitutive description. Thisparameter acts as a hardening parameter, controlling the evolution ofthe yield surface depending on loading, strain history and shell elementsize. Model calibration relies on a full field measurement technique, DigitalSpeckle Photography (DSP), to record the plane deformation field oftensile specimens. Quantitative measurements of the severely localizeddeformation preceding crack initiation are feasible. With the proposedstrategy, mesh sensitivity in terms of post localization load responseand fracture elongation predictions is reduced significantly compared toresults obtained without the element size dependent parameter. It wasfound that high strain hardening favours strain localization of shear band type, and accelerates the formation of a localized neck. The hardeningcharacteristics is determinant to which deformation mode dissipates theminimum energy. For the DP steel, the Tresca yield surface more accuratelydescribes the yielding point compared to the von Mises planestress elipse. Furthermore, the exponential ductility function dependenton the stress triaxiality parameter agrees well with experimental fracturedata in the ductile loading regime for both DP and boron steel.In shear loading, the maximum shear (MS) stress criterion successfullydescribes the ductility limit. Due to the significantly different ductilityof the various microstructures obtainable by the thermo-mechanicalprocessing of boron alloyed steel, a modelling strategy is needed. It wasfound that in ductile loading, local equivalent fracture strain can be relatedto the hardness of that material point. An exponential decrease inductility with increased hardness describes experimental data collectedfor five different microstructures.

Rotary kilns are important in a variety of different manufacturing areas for e.g. calcination and sintering of materials. In fact, two of the most produced materials in the world, cement and iron, are likely to start their journey in a rotary kiln.A rotary kiln is a large cylinder-formed furnace which rotates about its axis and where certain chemical and physical reactions take place by the influence of heat. The slope and the rotation make the material inside to move through the kiln from feed to discharge end. Due to high process temperatures the casing of the kiln is insulated by a refractory lining. Service conditions inside the kiln are rough and the lining is continuously degrading, especially pronounced in the hot zone of the kiln. If the lining is significantly deteriorated and can no longer protect the casing from the heat − the production is shut-down − leading to very high production losses.Despite many improvements of rotary kilns in the past decades there is still a gap in the knowledge regarding refractory linings during usage. Many assumptions are based on practical knowledge. One explanation to this could be the difficulty to study and observe the lining due to kiln size and high operating temperatures. Today, computer programs are of a great help for studying various issues without causing production delays or risking failures. However, the field of rotary kilns has stagnated on this matter and very little documentation can be found regarding numerical simulations of the lining, especially of the thermomechanical character.Purpose of this licentiate work is to study the mechanical behaviour of the lining by means of the finite element method (FEM). For this, a simplified model of a kiln was created and various fundamental cases were studied. The commercial FE-software LS-DYNA is used for the FE-calculations. The main work is based on cases of the kiln in cold condition. However, an initial study in warm condition is presented as well.The studied lining was a brick lining used in a kiln of dimensions typical for iron-ore pelletizing. Additionally, this licentiate thesis gives an overview of some of the most fundamental issues encountered in a refractory brick lining of a rotary kiln in general. Some material tests are presented as well.Model’s geometry was based on a section at the position of the support wheels, having a thickness of one brick. Some simplifications, such as choice of the material model and a rigid riding tyre, were done and a three-fold faster computational time was achieved. Response of the created model was partly verified analytically, by available in-house data and data from literature. It was confirmed that the model gives a good response.One of the important findings is that despite variation of conditions in cold state, e.g. rotational speed and relative ovality of the kiln, the induced stresses in the lining remained harmless. This challenges traditional believes which imply that ovality is of considerable importance for stress generation in the lining. On the other hand, by continuously tracing gaps between the bricks and the casing, it was found that integrity of the lining was significantly affected by rotational speed and ovality. Gaps as large as 80 mm could be observed between bricks and casing in a worst case scenario.An initial study on the kiln in hot state was made. Thermal expansion of a perfectly lined and an disordered brick lining were performed. The results indicate that stresses due to thermal expansion are rising slightly but are harmless in both cases. Additionally, expansion of the kiln stabilizes the lining and the effect of rotation compared to rotation in cold state is small.Analytical and numerical calculations were compared, indicating that analytical assumptions are often coarse and misleading from the reality.