Högskolan i Skövde

The compensation of large in-plane motions in digital speckle-pattern interferometry (DSPI) with the use of digital speckle photography (DSP) is demonstrated. Ordinary recordings of DSPI are recombined and analyzed with DSP. The DSP result is used to compensate for the bulk speckle motion prior to calculation of the phase map. This results in a high fringe contrast even for deformations of several speckle diameters. In addition, for the case of an in-plane deformation, it is shown that the absolute phase change in each pixel may be unwrapped by use of the DSP result as an initial guess. The principles of this method and experiments showing the in-plane rotation of a plate and the encounter of two rounded plates are presented.

In the battery pack assembly, it is essential to ensure that the cell-to-busbar joints can be produced with high quality and with minimal impact on the individual battery cells. This study examines the influence of process parameters on the joint quality for nickel-plated copper and steel plates, laser welded in an overlap configuration. Artificial neural network-based meta models, trained on numerical results from computational fluid dynamics simulations of the laser welding process, are used to predict and evaluate the joint quality. A set of optimized process parameters is identified, in order to simultaneously maximize the interface width for the joints, and minimize the formation of undercuts and in-process temperatures. In an meta model-based multi-objective optimization approach, the non-dominated sorting genetic algorithm II (NSGA-II) is used to efficiently search for trade-off solutions and the meta models are used for objective approximation. As a result, the objective evaluation time is decreased from around 9 h, when evaluated directly from numerical simulations, to only tenths of a second. From the Pareto-optimal front of trade-off solutions, three optimal solutions are selected for validation. The selected solutions are validated through laser welding experiments and numerical simulations, resulting in joints with large interface widths and low in-process temperatures without a full penetration.

For battery pack assemblies, it is crucial that the laser welded cell-to-busbar joints demonstrate both high mechanical strength and minimal electrical resistance. The present study investigates the effect of different laser welding parameters, on the mechanical strength, electrical resistance, porosity formation and joint microstructure, for dissimilar material cell-to-busbar joints. Laser welding experiments are performed, on thin nickel-plated copper and steel plates. The plates are joined in an overlap configuration, using laser beam wobbling and power modulation. Both circular and sinusoidal laser beam wobbling are used as selected strategies to increase the interface width of the joints, where also a comparison is made between the two methods. The joint quality is evaluated using joint geometry analysis, shear strength tests, computed tomography scanning and electrical resistance measurements. The results show that circular laser beam wobbling gives a larger joint shear strength compared with sinusoidal laser beam wobbling. In addition, it is observed that both the total pore volume and material mixing are significantly increased with increasing laser power and wobbling frequency for circular laser beam wobbling. However, for the sinusoidal laser beam wobbling the wobbling frequency does not show a significant impact on the total pore volume.

Static form errors due to in-process deflections is a major concern in flank milling of thin-walled parts. To increase both productivity and part geometric accuracy, there is a need to predict and control these form errors. In this work, a modelling framework for prediction of the cutting force-induced form errors, or thickness errors, during flank milling of a thin-walled workpiece is proposed. The modelled workpiece geometry is continuously updated to account for material removal and the reduced stiffness matrix is calculated for nodes in the engagement zone. The proposed modelling framework is able to predict the resulting thickness errors for a thin-walled plate which is cut on both sides. Several cutting strategies and cut patterns using constant z-level finishing are studied. The modelling framework is used to investigate the effect of different cut patterns, machining allowance, cutting tools and cutting parameters on the resulting thickness errors. The framework is experimentally validated for various cutting sequences and cutting parameters. The predicted thickness errors closely correspond to the experimental results. It is shown from numerical evaluations that the selection of an appropriate cut pattern is crucial in order to reduce the thickness error. Furthermore, it is shown that an increased machining allowance gives a decreased thickness error for thin-walled plates.

In machining, the heat flow into the workpiece during the cutting process is often a major concern. The temperature rise can lead to substantial residual stresses or elastic in-process deformations which may result in the dimensional tolerance requirements being violated. In the present study a modelling strategy is developed for determination of the heat load during indexable drilling. The heat load on the workpiece is determined from 3D thermomechanical Coupled Eulerian Lagrangian analyses of orthogonal turning for various chip thicknesses and cutting speeds. The determined heat load is then transferred to a 3D transient heat transfer analysis of the indexable drilling process for the determination of the temperature field. Thereby, this modelling technique avoids the complex cutting process that is performed in real cutting simulations and thereby reducing the computational complexity of the problem considerably. The simulated temperatures are compared with experimentally measured temperatures and some conclusions are drawn regarding the modelling approach.

For adhesive tapes, the strain before fracture often exceeds 500%. Although the maximum stresses are quite modest the high strains to fracture result in impressive fracture energy. Due to hydrostatic stress the fracture process often starts by nucleation of microscopic cracks inside the layer. The final crack path is usually close to one of the adherends.

Repeated experiments are performed both with DCB-specimens and butt-joints. The used adhesive tape is an acrylic foam tape with a thickness of 1.1 mm and a width of 19 mm. The geometry of the specimen is adapted to the properties of the soft layer. For the DCB-specimen this implies that the length of the specimen is about 1 m. The evaluated cohesive laws from the DCB- specimens give a fracture energy of 2 kN/m and a maximum stress about 0.5 MPa. For the butt-joints, the evaluated cohesive law corresponds well to the results from the DCB-experiments. However, the strain to fracture is slightly smaller. The stress in these specimens is distributed over a larger area and a nucleated crack rapidly crosses the load bearing area and fails the joint prematurely. For both kinds of experiments the evaluated cohesive laws show a small linear part. After this part there is an almost linear strain-hardening phase until fracture.

The stress-deformation relation i.e. cohesive law representing the fracture process in an almost incompressible adhesive tape is measured using the double cantilever beam specimen. As in many ductile materials, the fracture process of the tape involves nucleation, growth and coalesce of cavities. This process is studied carefully by exploiting the transparency of the used materials and the inherent stability of the specimen configuration. Utilising the path independence of the J -integral, the cohesive law is measured. The law is compared to the results of butt-joint tests. The law contains two stress peaks—the first is associated with nucleation of cavities at a stress level conforming to predictions of void nucleation in rubber elasticity. The second stress peak is associated with fracture of stretched walls between fully-grown cavities. After this second peak, a macroscopic crack is formed. The tape suffers at this stage an engineering strain of about 800%. A numerical analysis with the determined cohesive law recreates the global specimen behaviour.

High-quality simulation methods demand accurate material models. In simulations an adhesive can be represented by a cohesive layer. A cohesive layer model utilizes a cohesive law to represent the homogenized mechanical behaviour of a layer with a thickness. In the current paper we use three experimental methods to measure the cohesive law in shear using the ENF-specimen; one of the methods is novel and is also useful for evaluation of experiments with the ELS-specimen. Two sets of experiments are performed, one with elastic substrates and one with plastically deforming substrates. Each experiment is evaluated using all three methods. The evaluation shows that all methods provide reasonable data; the results are similar if the substrates are elastic. With smaller specimens, the substrates deform plastically and one of the methods is identified as the most accurate.

Confined layers may fracture in shear. This occurs, for example in adhesive joints and composite materials. A common mechanism for shear fracture is the formation of shear hackles associated with an expansion of the layer. This makes shear toughness and strength depend on the constraint of the expansion. By constraining the expansion using external loading in experiments, the expansion is reduced but not totally inhibited. The experiments are evaluated using the path independent properties of the J-integral. It is shown that the shear toughness increases for the more constrained case. Thus, from a strength analysis perspective, ignoring the expansion leads to a conservative estimate of the fracture properties. Extrapolation of the evaluated properties to totally inhibited expansions gives the traction separation relation and the fracture toughness for a layer in simple shear.

In comparison with other adhesives e.g. epoxies, polyurethane adhesives (PUR) are soft. In automotive applications, the thickness of PUR-adhesive layers is between about 2 to 5 mm. Since these adhesives cure by moisture, the width of the joints is limited. Often, the width is only marginally larger than the thickness of the layer. In numerical FE-simulations it is now common to represent epoxy adhesive layers by cohesive elements. With this model, both stress distribution and fracture can be modelled using mesh sizes that allows for large-scale analyses. Material properties are usually the result from experiments with coupon type specimens, e.g. the double cantilever beam specimen (DCB). With PUR-adhesives this approach is problematic. The adhesive is very flexible and effects from the edge-boundaries cannot be ignored. In order to study the influence of the edge-boundaries in peel loading, experiments with the DCB-specimens are performed. Specimens with a layer thickness of 3 mm and three different widths between 10.6 mm to 40.6 mm are studied. The PUR-adhesive SikaFlex-UHM is used. All the experiments are performed at a constant loading rate. The cohesive law is measured. The experimental results show that the maximum peel stress is increasing with an increasing width of the specimen, i.e. when the influences from the edges decrease. When the width increases from 10.6 mm to 40.6 mm, the maximum evaluated peak stress increases from about 5 MPa to about 7 MPa. From visual inspections during the experiments it is conjectured that crack growth starts with voids initiating inside the adhesive. At a critical point, the voids rapidly reach the surface and crack growth starts.

Residual stress (RS) within titanium alloy structural components is the primary factor contributing to machining deformation. It comprises initial residual stress （IRS） and machined surface residual stress (MSRS), resulting from the interplay between IRS and high-level machining-induced residual stress MIRS). Machining deformation of components poses a significant challenge in the aerospace industry，and accurately assessing RS is crucial for precise prediction and control. However, current RS prediction methods struggle to account for various uncertainties in the component manufacturing process，leading to limited prediction accuracy. Furthermore, existing measurement methods can only gauge local RS in samples，which proves inefficient and unreliable for measuring RS fields in large components. Addressing these challenges, this paper introduces a method for simultaneously estimating IRS and MSRS within titanium alloy aircraft components using a Bayesian framework. This approach treats IRS and MSRS as unobservable fields modeled by Gaussian processes. It leverages observable deformation force data to estimate IRS and MSRS while incorporating prior correlations between MSRS fields. In this context，the prior correlation between MSRS fields is represented as a latent Gaussian process with a shared covariance function. The proposed method offers an effective means of estimating the RS field using deformation force data from a probabilistic perspective. It serves as a dependable foundation for optimizing subsequent deformation control strategies. 

Sustainable engineering within product development is becoming increasingly important with the ever-growing amounts of resources used to sustain the human way of life in modern times. An effective way of helping to deal with this problem is to reduce the resources used in products and components across the world.

This thesis explores the effectiveness of the topology optimization method in achieving significant material reductions whilst maintaining structural strength and integrity when designing an aircraft component. The part is an engine handling mounting bracket which will be optimized to be produced by additive manufacturing, and so restrictions imposed by traditional manufacturing methods are not considered, allowing for larger material reductions to be achieved.

The original bracket part was provided by GE Electric, and the computer software Abaqus computer aided engineering with integrated TOSCA was used to solve the problem.

Two trials were conducted, with the first being used to gain knowledge and understanding of the optimization features of the software. The basic requirements for the optimized design were that it should be able to withstand four given static load cases without undergoing plastic deformation, and these load cases were applied separately in trial 1 for simplicity.

The second trial was conducted with a higher complexity, utilising multi-objective topology optimization which allowed the load cases to be weighted individually whilst being applied simultaneously during optimization. The resulting bracket part that was created with the help of the optimized topology from trial 2 reduced the volume of the original part by over 75%. This also left potential for further material reductions as the optimized part did not undergo plastic deformation when subject to any of the four load cases of the study.

In conclusion, topology optimization seems to be extremely helpful when designing components that have clearly defined load cases, producing results that designers and engineers can have confidence in. The method does however have its flaws, such as difficulties in utilising the optimized topology directly to create a computer aided design part file. The post-processing process needed to achieve such a part is also time-consuming although it must be implemented to create a digital part that can be analysed and verified by FEA.

The royal warship Vasa sank on its maiden voyage outside Stockholm and was salvaged more than 300 years later in 1961. Nowadays the vessel lies in its eponymous museum in Stockholm on a dry dock. However, it was determined that the ship cannot handle its own weight in a satisfactory manner with the current support system. Measurements during the past ten years have ascertained that the upper structure components of the hull are slowly deforming, mostly due to creep behavior.

A new support system for the ship needs to be designed in the near future and therefore, the mechanical behavior of its structural members and the stresses they are subjected to have to be determined. Factors that complicate a stress analysis include both inhomogeneity of the oak’s mechanical properties and limited opportunities for experimental testing. Furthermore, contamination, microbial degradation and preservation agents have significantly changed the integrity of the oak.

In this project a section of the Vasa’s bottom structure is studied through Finite Element Analysis in order to determine the stresses and deformations originated by the support system and to have a better understanding of these effects on the ship’s structure. Due to the considerable deterioration of the oak, especially on the external structural members, several assumptions are considered in order to perform analytical calculations to determine appropriate material properties for the FE-Models. 

After performing the computational simulations, the obtained results indicate that the bottom structure exhibits sufficient mechanical integrity to endure the stresses generated by the support system. Even by assuming the possibility of several damaged structural connections, only a minor difference of the effects of the reaction forces on the structure members was determined.

The thesis work ends with further conclusions from the performed analysis and suggested future work.

Constrained optimization is a computationally difficult task, particularly if the constraint functions are nonlinear and non-convex. As a generic classical approach, the penalty function approach is a popular methodology which degrades the objective function value by adding a penalty proportional to the constraint violation. However, the penalty function approach has been criticized for its sensitivity to the associated penalty parameters. Since its inception, evolutionary algorithms have been modified in various ways to solve constrained optimization problems. Of them, the recent use of a bi-objective evolutionary algorithm in which the minimization of the constraint violation is included as an additional objective has received significant attention. In this article, a combination of a bi-objective evolutionary approach with the classical penalty function methodology is proposed, in a manner complementary to each other. The evolutionary approach provides an appropriate estimate of the penalty parameter, while the solution of an unconstrained penalized function by a classical method induces a convergence property to the overall hybrid algorithm. The working of the procedure on a number of standard numerical test problems and an engineering design problem is demonstrated. In most cases, the proposed hybrid methodology is observed to take one or more orders of magnitude fewer function evaluations to find the constrained minimum solution accurately than some of the best reported existing methodologies.

The capability to predict high cycle fatigue properties of adhesive joints is important for cost-efficient and rapid product development in the modern automotive industry. Here, the adaptability of adhesives facilitates green technology through the widening of options of choosing and joining optimal materials. In the present paper a continuum damage mechanics model is developed based on the adhesive layer theory. In this theory, through-thickness averaged variables for the adhesive layer are used to characterise the deformation, damage and local loading on the adhesive layer. In FE-simulations, cohesive elements can thereby be used to model the adhesive layer. This simplifies simulations of large scale complex built-up structures. The model is adapted to experimental results for two very different adhesive systems; one relatively stiff rubber based adhesive and one soft polyurethane based adhesive. The model is able to reproduce the experimental results with good accuracy except for the early stage of crack propagation when the loads are relatively large. The model also predicts a threshold value for fatigue crack growth below which no crack growth occurs. The properties of the model are also compared with the properties of Paris’ law. The relations between the parameters of the continuum damage mechanics law and the parameters of Paris’ law are used to adapt the new law. It also shows that the properties of a joined structure influence the Paris’ law properties of the adhesive layer. Thus, the Paris’ law properties of an adhesive layer are not expected to be transferable to joints with adherends having different mechanical properties.

Chatter vibrations encountered in machining can degrade surface finish and damage the machining hardware. Since chatter originates from unstable interaction of the machining process and the machining structure, information about vibration parameters of the machining structure should be used to predict combinations of cutting parameters that allow stable machining. While modal test methods, for example those with impact hammers, are widely used to identify structural parameters; the need for sophisticated test equipment is prohibitive in their use. Furthermore, dynamic properties of critical components of a machine tool may change as they get affected by cutting loads, material removal and spindle rotation. Recently few algorithms have been proposed that identify the in-process dynamic parameters by frequency measurements, thus avoiding these problems. In this paper, some of these algorithms are reviewed and their capabilities and limitations in processing am experimental data set are compared and discussed. © 2018 The Authors. Published by Elsevier Ltd.

In this paper, we propose a stabilized augmented Lagrange multiplier method for the finite element solution of small deformation elastic contact problems. We limit ourselves to friction-free contact with a rigid obstacle, but the formulation is readily extendable to more complex situations. © 2016 Elsevier B.V.

We propose a discontinuous finite element method for small strain elasticity allowing for cohesive zone modeling. The method yields a seamless transition between the discontinuous Galerkin method and classical cohesive zone modeling. Some relevant numerical examples are presented. © 2015 Elsevier B.V.

For a flexible linear adhesive, the mode mixety of a single-layer adhesive joint is directly related to the deformation of the adhesive layer at the crack tip. The governing equations for linear elastic singe-layer adhesive joints show that the mode mixety depends on the exteranl loads, the properties of the adherends and often on the flexibility of the adhesive layer. This implies some fundemantal problems that has to be adressed before an experimental method can be established. Requirements for the design of a specimen configuration for a mixed mode testing of adhesive layers are given. A new specimen configuration is proposed and some preliminary experimental results are given.

The purpose of this work is to develop a flexible cohesive law to simulate the constitutive behaviour of an adhesive layer under mixed mode loading. A mixed mode cohesive law that captures the linear elastic and softening behaviour before fracture is presented. This simple model uses a coupled formulation to describe the mixed mode cohesive behaviour. It also allows for different fracture parameters, such as fracture energy, strength and critical separation in different mode mixities. Thus, the fracture process in mode I (peel), in mode II (shear) or in mixed mode (a combination of peel and shear) can be modelled without the usual constraint of a common fracture energy in peel and shear. Examples are given of FE-implementation of the normalised cohesive law, namely for the Unsymmetric Double Cantilever Beam (UDCB) specimen and the Mixed-mode double Cantilever Beam (MCB) specimen. Both specimens are adhesively bonded and loaded in mixed-mode.

The Double Cantilever Beam (DCB) specimen is a common test geometry for testing of mode I fracture properties of adhesive joints. However, when unbalances are introduced to the adherends, the adhesive layer is loaded in a combination of peel (mode I) and shear (mode II). In this work the unbalanced DCB-specimen is studied by the use of the beam/adhesive layer (B/A) model, in which the adherends are considered as beams and the adhesive layer as a generalised spring media. The effect of the thickness of adhesive layer together with the effect of the geometrical and material unbalances is analysed. The result of the B/A model is compared to the continuum model through FE-simulations. Finally, an unsymmetric DCB-specimen is dimensioned for mixed mode testing of adhesive layer.

Experiments show that enclosed air in a thin walled structure affects some modes of vibration significantly. Air coupling between vibrating sides of the structure cannot (always) be neglected and frequencies cannot be predicted if calculations are performed as if in a vacuum. As a first attempt to include the enclosed air in a FE model of a violin body, the elastic properties of the air are modelled as a set of one dimensional non-interacting elastic members (columns of air) connecting opposite sides of the orthotropic shell structure. This admittedly oversimplified (but easy to formulate) model must be used with great care, since it neglects the three-dimensional wave behaviour of the enclosed air. A lower limit of allowed frequencies is that which corresponds to a wavelength in air which is much greater than a characteristic length of the object. For the violin this lower limit is less than about 600 Hz. Optical modal analysis of the real, physical, violin model has been performed by using electronic holography. Calculated modes of vibration are compared with experimental ones. For the lowest eigenmodes a good agreement between measured and calculated frequencies is reached despite the simple air model used. Modal shapes remain surprisingly unaffected. For some engineering calculations the simple one-dimensional model might be used.

Large displacement peel was studied for cases where a compliant substrate leads to a large value of the root rotation. An existing simplified beam model to calculate the peel fracture energy was modified to allow for a kinematic hardening beam model of the foil. The steady-state peel force and the root rotation were used as input data to the resulting analytical beam model. Test results from the literature were analysed. A more elaborate finite element model was also studied, using cohesive elements for the interface layer between the foil and the substrate. The cohesive zone parameters used were the fracture energy, the cohesive strength and a shape parameter. An optimization scheme for the cohesive zone parameters was developed and optimized against experimental steady-state peel force and root rotation. The optimization scheme was effective to characterize the cohesive parameters. The method yields similar values of fracture energy for the two peel angles, with the one for being slightly higher than for . The difference in fracture energies for different peel angles suggests that the fracture energy can be mode dependent.

In this paper we present a semi-multiscale methodology, where a micrograph is split into multiple independent numerical model subdomains. The purpose of this approach is to enable a controlled reduction in model fidelity at the microscale, while providing more detailed material data for component level- or more advanced finite element models. The effective anisotropic elastic properties of each subdomain are computed using periodic boundary conditions, and are subsequently mapped back to a reduced mesh of the original micrograph. Alternatively, effective isotropic properties are generated using a semi-analytical method, based on averaged Hashin–Shtrikman bounds with fractions determined via pixel summation. The chosen discretization strategy (pixelwise or partially smoothed) is shown to introduce an uncertainty in effective properties lower than 2% for the edge-case of a finite plate containing a circular hole. The methodology is applied to a aluminium alloy micrograph. It is shown that the number of elements in the aluminium model can be reduced by 99.89 % while not deviating from the reference model effective material properties by more than 0.65 % , while also retaining some of the characteristics of the stress-field. The computational time of the semi-analytical method is shown to be several orders of magnitude lower than the numerical one. © 2021, The Author(s).

This project analyses the impact in the mechanical properties of Polyoxymethylene (POM) of three different blends of biodiesels: B0 with 0% of Rapeseed Methyl-ester (RME), B20 with 20% of RME and B100 with 100% of RME. Polyoxymethylene specimens have been subjected to an accelerated aging during 1600 hours at 85ºC. This is the equivalent to 20 years of life time. In addition, a thermal oxidation in air at the same temperature has been performed to check the impact of the temperature in the final degradation.Three different methods have been performed to calculate the diffusion rate, however and one of them has been selected for its reliable results. The second Fick´s law have been chosen to model the diffusion. The diffusion rate has been calculated for the B20 and B100 blend due to the B0 blend has a non-constant diffusion rate. B20 shows also some divergence while B100 fits the Fickian behaviour.A Finite Different approximation method has been used to predict the concentration profiles of the diffusion process of B20 blend. They have been compared with the results of the IR Microscope, with a clear misalignment between the expected and the actual values.Tensile tests have been done in different stages of the test to check the stress-strain behaviour of the specimens for each aging type. The most relevant parameter of degradation is the Elongation At Break (EAB), which decrease considerably a cause of the embrittlement. A study of the real stress-strain has been also done to assure the real behaviour of the material.A fracture surface study through Scanning Electron Microscope (SEM) and Light Microscope has been done to assure the brittle behaviour with the aging and the changes in the structure of the material.The swelling behaviour has been also modelled, and the bases for a future FEM analysis have been exposed.

The design and analysis of drop test to investigate the behaviour of adhesive joints in automotive structures is performed. The drop test is simulated by FE software. The specimen geometry is based on Volvo Car Corp. drop test standard.

In the drop test machine, a general beam structure is supporting all the parts. The machine includes a lifting system. The test is applied to a pre designed specimen, which will provide the information about adhesive joint strength.

Adhesively bonded T-Peel specimens are loaded in a rotary impact device to investigate the behaviour of adhesive joints under high-strain rates. To gain a better understanding of that kind of tests and their results, the deformation of the samples as well as the movement of specimen support during the test is analyzed. A three-dimensional optical measurement system is used in combination with two synchronized high-speed cameras to obtain the deformations. The paper explains the experimental challenges and discusses the results of the analyses with respect to a planned usage of the experimental results in a finite element crash simulation. As main results of the investigations it can be summarized that the compliant clamping leads to an inadvertent out-of-plane-movement of the load introduction point. Based on finite element calculations it can be concluded that the measured out-of-plane-movement possesses a negligible influence on the obtained force signal, which is of primary interest in a T-Peel test.

The keyhole depth is a key measurement characteristic in the laser welding of busbar to battery tabs in battery packs for electric vehicles (EV), as it directly affects the quality of the weld. In this work, experiments are carried out with controlled and adjusted laser power and feed rate parameters to investigate the influence on the keyhole width, keyhole depth and porosities. A 3D numerical model of laser keyhole welding of an aluminum alloy (A1050) has been developed to describe the porosity formation and the keyhole depth variation. A new integration model of the recoil pressure and the rate of evaporation model is implemented which is closer to the natural phenomena as compared to the conventional methods. Additionally, major physical forces are employed including plume formation, upward vapor pressure and multiple reflection in the keyhole. The results show that keyhole depth is lower at higher feed rate, while lower feed rates result in increased keyhole depth. This study reveals that low energy densities result in an unstable keyhole with high spattering, exacerbated by increased laser power. Mitigating incomplete fusion is achieved by elevating laser energy density. The findings emphasize the critical role of keyhole depth in optimizing laser welding processes for applications like busbar-to-battery tab welding.

After 333 years under depths of the Baltic Sea, the warship Vasa was salvaged and nowadayslies in a dry dock inside the Vasa Museum in Stockholm. Its current support system, which consists on eighteen cradle-stanchions pairs of steel, is not able to handle the present loads in a satisfactory manner. Experimental tests showed that the Vasa's hull is gradually deforming mainly due to creep behavior.

Thus, in order to preserve the Vasa for future generations, a new support system has to be implemented in a foreseeable future. There are several factors to take into consideration for its construction, which are: the degradation of the oak, its current mechanical properties and its inhomogeneity in addition to the climatic conditions of the Museum and the impossibility of taking unlimited specimens for its analysis. Hence, it is crucial to investigate the areas where the stresses and deformations are critical in the ship and how affected is the stiffness of the hull, its most important component.

In this dissertation work two Finite Element Analyses are accomplished. The first study consists on the creation of a superelement of a section of Vasa's hull with the intention of investigating the influence of the dowels on the stiffness of the hull. In the second analysis a simplied model of the entire warship Vasa is created in order to analyze it and locate possible critical areas on the hull due to its own weight and the stresses originated by the support system. The software selected for these simulations are Abaqus and CreoSimulate 2.0.

From the first study it is concluded that that the dowels do not have a signicant influence in the stiffness coeffcients of the hull. The second analysis determines that the maximum stresses are located on the bottom part of the hull. This dissertation work concludes with a suggested future work.

The mechanical behaviour and performance of a ductile iron component is highly dependent on the local variations in solidification conditions during the casting process. Here we show a framework which combine a previously developed closed chain of simulations for cast components with a micro-scale Finite Element Method (FEM) simulation of the behaviour and performance of the microstructure. A casting process simulation, including modelling of solidification and mechanical material characterization, provides the basis for a macro-scale FEM analysis of the component. A critical region is identified to which the micro-scale FEM simulation of a representative microstructure, generated using X-ray tomography, is applied. The mechanical behaviour of the different microstructural phases are determined using a surrogate model based optimisation routine and experimental data. It is discussed that the approach enables a link between solidification- and microstructure-models and simulations of as well component as microstructural behaviour, and can contribute with new understanding regarding the behaviour and performance of different microstructural phases and morphologies in industrial ductile iron components in service.

The industrial use of Virtual Reality, Augmented Reality, Mixed Reality and all the eXpanded Realities is rapidly increasing over the last few years. This thesis aims to provide with a standardised method to measure calibration alignment error for augmented reality devices. A literature review was conducted on different SLAM and calibration methods to achieve this goal. The device selected for this thesis was HoloLens2, as it has a considerably better performance than its competitors. For the experiment, the first step needed was to create a digital replica of a small robot on RobotStudio.This study proposes a method to measure alignment calibration error based on projecting the hologram of a cube against a physical calibrated board to measure error on each axis. The deviation of the hologram from its calibrated position can be calculated directly setting the hologram to locate it at the 0,0,0 of the real calibrated board. Validation is done by doing only one calibration, using several holograms set at known distances which will cover a wide range of positions. For the validation to be successful, the initial condition is that the orientation error needs to be close to cero or relatively negligible in comparison with the linear alignment error, as the proposed method it is not able to measure orientation error and alignment error simultaneously. If validation is successful, the calibration alignment error of any calibration method can be measured with this method by projecting a hologram against the calibrated board and repeating the experiment several times to perform a statistical analysis of the error measured. Finally, this study suggests some calibration methods which may give better results than the one evaluated. It discusses that automatic calibration methods will very likely be the future for calibration. Still, there is a precise manual method which may be an excellent fit to calibrate the devices when used to display safety areas, which is also suggested. As the experiment could not be carried out due to several limitations, there are not results of the calibration alignment error. However, this thesis gives a detailed guideline on this thesis to be able to replicate the experiment at any time for future work.

This thesis refers to a simulation of an adhesive joint used to bond two metal sheets of a component of the side skirt bracket implemented in trucks. The adhesive joint must support fatigue and mixed-mode loading. The principal goal is the implementation of a novel material model, which governs the damage produced by a mixed-mode fatigue loading in a rubber adhesive layer.

Two approaches to define the material model are implemented: the filament model and the principal strain model. The models are fitted against experiments, which have been performed parallel to the development of this thesis by the Mechanics of Materials (MoM) research group of the University of Skövde. The models incorporate fitting parameters with the aim of adjusting the models against experimental results. Simulations are performed using the Finite Element (FE) software, ABAQUS, and the material models are implemented using UMAT subroutines.

The filament model is inaccurate and it is considered unable to model the mixed-mode behaviour of the adhesive joint. The principal strain model is considered a well-established method to define the damage and to predict the fatigue life of the adhesive under fatigue in mixed-mode loading.

Child restraint systems (CRS) are used for protection of the child in case of car accident. These systems have been found to have a difficult installation process that in many cases can cause greater loads on the child and as a consequence can lead to an increased risk of injury and a reduction in safety. The problems are even more significant in cases of families with two or more children and in small cars with lack of available space. Misuse and its causes are identified from literature as well as from surveys and market research. The design guidelines are gathered from existing CRS designs. Currently available automotive and CRS fastening systems are studied. A specific methodological approach is used for project development. A new concept for a child restraint system is introduced. The main aims are the design proposal of a double ISOFIX base for two children, reduction in the misuse of the CRS, improving the user experience and achieving technological, societal and environmental contributions. The second aspect is to verify the structure of the double base by means of preliminary finite-element analysis using the case of a frontal collision in accordance to current approval testing procedures. Al 2024 is chosen for design by the material selection performed in order to optimize the structure in relation to strength and weight. The finite-element preliminary static analysis is performed employing shell elements. The results are analysed with respect to the mesh convergence. In addition a linearized buckling check is carried out. Finally, the achieved results are discussed in comparison with initial assumptions and goals and future work is suggested.

Horseshoes are manufactured metal plates developed in an extensive assortment of materials and shapes and their main function is to protect the horse’s hooves and legs against abrasion and rupture. After a certain period of time the horseshoes are lost, worn out, or the hoof needs to be treated. Horseshoeing is a repetitive time consuming process for the farrier who has to heat the horseshoe inside a forge until it reaches the required temperature and shape it with a hammer until it fits perfectly to the horses’ hoof. The main goal of this project is to develop a horseshoe bending machine able to shape the horseshoe so its shape fits perfectly the horse’s hoof. The calculation of the bending force needed to be applied to the horseshoe in order to provoke a plastic deformation will be done with Euler-Bernoulli beam theory. The bending force is then used to design and dimension each element of the bending mechanism so that it may be able to resist the stresses and prevent the parts from collapsing during its working life span. A study of the springback effect will be done followed by the analysis of the hertzian contact stresses between the rollers and the horseshoe. In addition, a clamping system is selected to constrain the movements of the horseshoe during the bending process. This machine will reduce the final user’s horse maintenance costs at the same time that makes the fitting process easier and less demanding, which will improve the farrier’s working life span and quality.

Modern synthetic structural adhesives are finding a place in the drive to improve the fuel efficiencyof automobiles through weight reduction of the structure. One of the most important properties ofthe adhesives used in this type of joining is the fracture energy.A literature study is carried out to gain a broader understanding of the methods used for thedetermination of the fracture energy of adhesives. One of the most common experimental methodsrelies on the use of the Double Cantilever Beam (DCB) test specimen. International standards for theDCB test are studied. Prediction of the fracture energy using Linear Elastic Fracture Mechanics andthe J-integral approach, a closed form solution and finite element methods are also seen. Differencesin these methods are attributed in part to the nonlinear behaviour of the adhesive being studied. It isdecided to use the results of a non-standard DCB test and the 40% error calculated by a theoreticalstandard method as a point of reference.A comprehensive comparison of the American Society for Testing Materials (ASTM) and BritishStandard Institution (BSI) standards for the determination of the fracture energy of adhesives isundertaken. Limitations and overlaps in the standards are identified. A DCB specimen isrecommended and an experimental procedure that satisfies elements one or both standards issuggested along with several small additions such as using a wire to assist in the application of theadhesive and the use of cameras to track the crack growth. In addition, a new fixture to allow testingof the recommended DCB specimen according to the standards is designed and manufactured.Materials for the preparation of tests specimens are ordered and, based on available laboratorytime, a single DCB test specimen is made for the purposes of testing a rubber-based automotivestructural adhesive. The specimen is tested using the recommended experimental procedure usingthe new fixture. The data produced during the test are collected and interpreted using themethodology proposed in the BSI standard for the calculation of the fracture energy of the selectedrubber-based adhesive. Several challenges found during this process are identified. The fractureenergy determined from the standard-based experiment ranges from 140 J/m2 to 1380 J/m2depending on the methodology used.The values of the fracture energy determined from the standard-based DCB experiment are thencompared to the fracture energy seen with the nonstandard-based experiment and to the standardbasednumerical test seen in the literature. It is shown that when simple beam theory method isused the difference in the results found in the standard-based experiment and nonstandard-basedexperiment can be confirmed to lie within the 40% error observed in the literature.Finally, the contributions of the project are summarized and recommendations for future work aremade. In particular, the lack of information given in the BSI standard when calculating the fractureenergy and the need for multiple test specimens are required by the standard, must be addressed inorder to support the obtained results and conclusions.

A simple but informative whole-field method to visualize standing waves in air enclosures is presented. The integrated sound pressure field distribution of standing-wave patterns inside a rectangular, air-filled transparent box is measured using ordinary TV holography (also called ESPI or DSPI). The phase distribution of the sound pressure is measured by using the more complicated, phase-modulated TV holography technique. Standing waves in the box are excited by a loudspeaker. The structural vibration amplitude distribution of the walls of the same box (operational deflection shapes, ODSs) are measured at the same frequencies as the standing waves with the same optical technique. The pressure maps obtained and the corresponding structural ODSs are of great pedagogical value and can be used to verify numerical models, etc. Standing-wave patterns in non-rectangular enclosures, as the sound box of a guitar, illustrates the usefulness of the method.

Phase modulated TV holography is used to measure sound pressure variations of standing waves of the air inside cavities of transparent models of a violin and a guitar. The accompanying motions, the Operating Deflection Shapes (ODSs) of the now white painted walls of the enclosures are measured using TV holography. Experimental measurements of the ODSs are compared to finite element calculations of the coupled air cavity and plate motion.

Earlier investigations have assumed only "out-of-plane" vibrations of the plates of the violin. The violin body can, however, be described as a thin-walled, double-arched shell structure and as such it may very well elongate in one direction as it contracts in another. Therefore, at least two orthogonal vibration components have to be included to describe the vibrations. The operating deflection shapes (ODSs) of a good, professionally made and carefully selected violin were therefore measured in several directions by TV holography to determine both "in-plane" and out-of-plane vibration components of the ODSs. The observations were limited to the frequency range 400-600 Hz, as this interval includes two most-prominent resonance peaks of bridge mobility and sound radiation as well as a third poorly radiating resonance. These three peaks clearly showed orthogonal vibration components in the ODSs. The vibration behavior of the violin body, sectioned in the bridge plane, was interpreted as the vibrations of an "elliptical tube" with nodal diameters. The number of nodal diameters increases from two to three in the selected frequency range. The TV holography measurements were supported by electrodynamical point measurements of bridge mobility, of air volume resonances, and by reciprocity, of radiation properties. Furthermore, a fourth mode, the air mode, A1, is involved indirectly in the sound radiation via influence on the body vibrations.

How do the walls of an open organ pipe vibrate when blown? Two geometrically similar open organ pipes are made of different alloys and tooled in different ways. Using a scanning laser Doppler vibrometer the operational deflection shapes (forced modes of vibration) for the first three harmonic partials of the blown pipes are measured. The upper lip is further investigated for the five first harmonic partials. The results are compared and related to the sound intensity distribution from the pipes. This comparison shows that the vibration modes of the structure are dependent upon the material of the pipes. Both the amplitude and the shape of the vibration differ between the pipes. It is found that the vibration amplitude is low for the fifth harmonic partial. For this partial the sound intensity emitted from the mouth also is low.

This work aims at providing a numerical tool for the efficient design of the multidirectional carbon fiber reinforced composite material by means of finite element simulations. Abaqus/ CAE v 6.9-1 software has been used to establish a 3D model for simulation of the tensile test on the composite specimen. The aim of this analysis of multidirectional carbon fiber reinforced composite is to predict the strain and stress distribution in different plies through thickness. Tensile test experiment was carried out and the result was analyzed by ARAMIS to calculate the young’s modulus, stress, loads and strain of the composite specimen. The numerical model was compared against the result obtained from tensile test experiment to arrive at meaningful results for validation. This is done in order to understand the mechanical strength and strain at failure of the composite material. In this work three types of CFRP composite specimens are used, all have same 15 no. of ply but stacked in different orientation. It is found out that mechanical strength, failure load and strain differ slightly depending on this different ply orientation. A series of different modeling technique has also been done to verify the best modeling technique.

The micromechanics of composite material is complex and the experimental predictions are time consuming and expensive. Though using FEM frequently solves the problem.

A detailed model of experiments with the double cantilever beam specimen is set up. Analysis of the model shows that an experimentally deduced apparent increase of fracture energy with severely deforming adherends is due to contributions of in-plane straining of the adhesive layer to the fracture energy. An analysis with the J-integral confirms the result.

A finite element analysis of a complex assembly was made. The material description used was a physically based material model with dislocation density as an internal state variable. This analysis showed the importance of the materials’ behavior in the process as there is discrepancy between the bolt head contact pressure and the internals state of the materials where the assembly process allows for recovery. The end state is governed by both the tightening process and the thermal history and strongly influenced by the thermal expansion of the AZ91D alloy.

This thesis work is based on the analysis of a fan blade attachment whereby a complete 3D model is presented by a partner company. The acceptability of a new design regarding the mechanical loads consisting of dividing the hub into two parts instead of using a solid hub is studied. From the model some critical parameters for the attachment of the blade with respect to the stresses are chosen such as the rotational speed, fillet size of the blade and the neck size of the blade. Parametric studies of these parameters are carried out in order to suggest the new design. Bearing in mind that a safety factor of 2 is the prerequisite, based on the analysis performed on ANSYS Workbench, it is suggested from the preliminary design that the axial fan can operate in two specific scenarios consisting of a rotational speed of 1771 rpm and a rotational speed of 1594 rpm. Using this set of parameters, a suggestion is drawn up on the blade fillet which will give lower stress. Blade fillet size of 30 to 35mm is recommended while a size of 45mm is recommended on the neck of the blade. A modal analysis is performed in order to find at what frequency will the model be vibrating and a lowest and critical frequency of 16.8 Hz is obtained. Finally, a fatigue analysis of some interesting areas is performed in order to determine the numbers of cycles before fatigue failure occur. It is recommended to use the rotational speed since these speeds have offered a High Cycle Fatigue results.

A methodology to develop experimental methods to measure cohesive laws is introduced. This methodology is based on the property of all configurational forces equilibrium acting on a specimen to be in equilibrium. Two applications are given. The first shows a method to measure the cohesive law for shear representing the mechanical behaviour of an adhesive layer. The second application is a method to measure the cohesive law for the formation of a kink-band in a unidirectional composite. It is concluded that the methodology is critically dependent on the ability to associate a pseudopotential to the inelastic properties of the deforming material where the fracture process takes place. The importance to clearly identify the material that is modelled with the cohesive zone is also stressed.

This paper gives a short review of two different methods for life prediction at high temperature; namely continuum damage mechanics (CDM) and the linear life-fraction rule (LFR). It is well known that the class of CDM theories with a separable evolution law gives a life prediction in accordance with the LFR. However, it appears to be an open question if this is a necessary condition. It is here shown that in order for a CDM theory to comply with the LFR it must have a separable evolution law. That is, if we can assume that a material follows the LFR, it is necessary to chose a separable evolution law for this material. The reverse is also true, to get a life-fraction different from unity, we must chose a nonseparable evolution law.

Pressure sensitive adhesives provide high toughness at low stress and stiffness. These properties are beneficial for bimaterial bonding. In the present study the tape is modelled with a cohesive layer characterized by a cohesive law. This is suitable for FE-analysis of bonded structures. The cohesive law is measured using a method based on the path independent property of the J-integral. Complementing an earlier study, we here focus on influences of loading rate on the properties of the pressure sensitive adhesive. Transparent PMMA substrates are used with the transparent tape in Double Cantilever Beam specimens. The transparency of both the tape and the substrates provides the possibility of in-situ studies of the fracture process. The results indicate that the fracture energy levels off at about 1 kN/m for small loading rates. Moreover, the cohesive law also appears to level off below an engineering strain rate of about 2 s-1. The cohesive law contains two peak stresses. The first is associated with the nucleation of cavities in the tape. This occurs at a stress level comparable to the critical stress associated with an unbonded growth rate of a spherical cavity in rubber. The second peak stress is associated to the breaking down of walls formed between the fully developed cavities. This process precedes the final fracture of the tape. It also appears as nucleation of cavities is influenced by the strain rate where slower rates give more time for cavities to nucleate. This results in larger cavity density at smaller loading rates. The results also indicate a similarity of the effects of loading rate and ageing of the macroscopic properties of the present pressure sensitive adhesive.

Adhesive joints are designed to transfer load in shear since both the fracture energy and the fracture stress are larger in shear than in peel. Shear deformation is isochoric, however, the fracture process involves nucleation and growth of a multitude of slanted microcracks. In order to grow, these microcracks open up. Thus, adhesive layers show a tendency to deform in peel during shear fracture. This opening is localized to the fracture process zone and the adherends have to separate locally over the process zone to allow for the adhesive to swell. Depending on the stiffness of the adherends, the opening mode is more or less prohibited. With stiffer adherends, the opening is obstructed more efficiently than with softer adherends. Micromechanical studies indicate that the constraints of the peel deformation during shear loading have a profound influence on the strength of the joint. In the present study, we compress the process zone during experiments. Repeated experiments with ENF-specimens are performed. A compressive force is applied on the first part of the adhesive layer by use of a pneumatic cylinder. The experiments are evaluated using the path independent J-integral. Together with measurements of the shear and peel deformation of the adhesive layer at the start of the layer, the complete shear stress vs shear deformation relations are evaluated. It is shown that the inhibited peel deformation gives a substantial increase of the fracture energy

Cracks normally propagate in the opening mode associated with a state of local symmetry at a crack tip. However, the micro- or macrostructure of a material or structure sometimes forces cracks to propagate in a shearing mode. Irrespective of the actual material studied, fracture in shear is frequently asso- ciated with the formation of a large number smaller sigmoidal-shaped cracks in the propagation direction of the major crack. Propagation of the major shear crack is accomplished by coalescing the sigmoidal-shaped cracks. Ex- periments show that the formation of sigmoidal cracks due to shear loading leads to a normal separation of the joined substrates. Theoretical studies show that constraining the local opening of the sigmoidal cracks increases the frac- ture resistance for the propagation of the major crack. In the present study, experiments with a ductile adhesive loaded in shear and where the normal sep- aration is constrained are presented. The experiments are evaluated using the path independent J-integral. The associated cohesive law shows that consid- erable normal compressive stress develops in the adhesive during macroscopic shear loading. It is also concluded that by ignoring the normal separation in the evaluation of the experiments, the strength of the adhesive is underesti- mated. Thus, the procedure developed in earlier studies is conservative from a strength analysis perspective. The present technique might be possible to extend to other materials to reveal their properties in shear fracture.