Motor vehicle-traffic accidents are a common cause of traumatic brain injuries, resulting in severe and sustaining disabilities, or even fatality. In an effort to mitigate injuries related to vehicle crashes, various safety systems such as the occupant airbag has been implemented. In angled impacts, occupant interaction with the airbags can lead to head rotation, and during recent years head rotation has been emphasized as an important contributor to head injury risk. Therefore, for prediction of head injury risk in crash simulations it is important to correctly model the friction force which arises in the contact between occupants and the car interior. The aim of this thesis is therefore to study the friction within such a system. More specifically, the analysis is focusing on dummy head to airbag interaction and to correlate a three parameter friction model for this contact pair, as well as a one parameter model currently used by Volvo Car Group, with measured laboratory test data in the software LS-DYNA.A preliminary study in LS-DYNA was conducted to determine the configuration of the laboratory setup consisting of a statically inflated customized driver airbag and a crash dummy head being launched to impact the airbag. The laboratory test data was analyzed using linear regression and Students T-test to identify the influence of parameters on the measured responses. The simulation model was then modified to represent the laboratory setup, prior to an optimization study performed to correlate simulation and laboratory test data responses. Lastly, an evaluation study was made to test whether or not the proposed friction model could improve occupant crash simulations.It was found in the thesis study that the friction force had a large effect on the rotation of the head around the vertical axis (z−axis in the anatomical coordinate system of the head). The experimental data showed that the internal pressure of the airbag had little effect on the response. This was likely due to the studied pressures being large enough for the airbag to be so stiff that no plowing effect of the dummy head moving through the airbag fabric could be seen. Furthermore, results from the optimization study indicated that the model correlation was improved when a three parameter friction model with velocity dependence was used. This implies that the friction coefficient is dependent on the velocity. It was also shown that material properties affecting friction behavior vary between different crash dummy heads, as well as different surface coating. Both dummy T-shirt fabric and grease paint resulted in significantly lower surface friction.Due to the difference in friction for different dummy heads, a single set of friction model parameter values that describes the friction behavior of all crash dummy heads does not exist. The study finds that when sliding is present in a contact, a three parameter model for describing the friction improves the correlation, as it can account for the velocity dependence of the friction in the contact. In contrast, when sliding is not present the one parameter and the three parameter model give similar results.Keywords: friction, velocity dependent friction coefficient, finite element analysis, car crash simulation, Volvo Cars, crash test dummy head, driver airbag, LS-DYNA, laboratory testing, optimization study.

Based on the customers' increasing demands on the precision of the preload in a screw joint Atlas Copco is investigating the opportunity to integrate ultrasonic technologies in their industrial tools in order to be able to measure the screw elongation and thereby preload. The preload in a screw joint is important when trying to optimize the joint in terms of weight and life time. The ultrasonic technology for preload measurements has two large advantages; the technique requires only access to the screw head and it is completely independent of the friction in the joint which enables more accurate measurements of the preload. In ultrasonic preload measurements the time of flight is measured (i.e. time for ultrasonic waves to travel through the screw). The time can be transformed into length and elongation by use of the sound velocity. Of importance in this calculation is to take the so called acoustoelastic effect into account which predicts a lower longitudinal wave velocity with increasing tensile stress. The purpose of this master thesis is to develop a method that can predict screw elongations from ultrasonic measurements. Finite element simulations showed that the acoustoelastic ultrasonic constant only depend on the ratio between the clamp length and the screw diameter up to a certain degree of accuracy. A function of type =∙ ∙ where a, b and c are real-valued constants and = is the clamp length () divided by the screw diameter () fits the data well. However, the ultrasonic measurements showed some deviations from the theoretical predictions.

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Aeronautical companies face well-known engineering challenges, suchas finding the best trade-off between weight and strength of planes.Numerical simulations have become a key tool to design lighter andstronger structures. The apparition of distributed computing has openednew possibilities for numerical computations. This master thesis aimsto improve methods that study crack propagation. Domain decompositionof the structure is used to take maximum advantage of parallelcomputing. This requires unusual solving methods, such as Schurcomplements methods, to correctly solve a given problem.

Additive manufacturing enables a simplified production process of components with complex geometry based on computer aided three-dimensional design. The technology of creating components layer-by-layer allows an efficient process with the ability to design parts with specific properties which can be difficult to obtain when conventional manufacturing methods are used. In this master thesis, an EMI shield was analyzed where the choice of manufacturing process was of interest. Producing the shield with additive manufacturing, instead of conventional methods, and how to integrate different materials in the process were investigated. The possibility to produce the shield and its components in the same process would result in a shorter production process with less process steps and would be an effective approach for future applications. In the current EMI shield, each component has a specific function with high demands in terms of temperature resistance, weight and EMC. These requirements must be taken into account when choosing manufacturing method and suitable materials in order to obtain desired characteristics of the shield.In the analysis of creating an electromagnetic interference (EMI) shield with multi-materials, a comprehensive literature study was conducted where different AM methods and available materials were investigated. Based on the literature research, possible concepts were generated and 3 different concepts were suggested for the final solution. A Finite Element Method software was used to verify these concepts in terms of solid mechanics, where the final design of the shield was determined based on the choice of materials in addition to optimization of the geometry.To evaluate the function and electromagnetic compatibility of the final concepts, prototypes were manufactured and tested in an experimental setup. These results were compared to the results of the original shield in order to determine whether the concepts met the given requirements or not. Concept E showed similar EMI results as the current shielding solution, whereas concept C and D resulted in a decrease of shielding effectiveness.

Brown bears go into hibernation for several months during the winter period,but regain all bodily functions shortly after waking up, such as the strength ofbones. The aim of this thesis has been to characterise the material of activebear’s bones (tibiae) by destructive testing and then fitting a damage modelby the use of finite element simulations. Standard beam theory was used tocompare with the simulated results and supplemental compression testing wasconducted to verify elastic parameters. Examination of results show quite alarge distribution in both material parameters and determined stresses for thetested bones, with elastic moduli varying 3-10 GPa, Poisson’s ratio 0.3-0.45,strain for onset of damage 1-2%, damage rate factor of 25-40 and fracturestresses varying proportionally with stiffness between 50-190 MPa.

In order to keep up with the increasing demand of fuel-efficiency in the transportationindustry, the interest of making the vehicles as lightweight as possible is steadilyincreasing. One of the ways of reducing the weight is to introduce an anisotropicmaterial as Short Fibre Reinforced Polymers (SFRP) as a replacement for structuralparts made out of metals. To meet the modern vehicle design process which strivestowards a more simulation driven workflow, the need for accurate simulations offibre reinforced composites is of importance.This thesis aims to evaluate and find a working process for fatigue analysis of injectionmoulded SFRP components. To evaluate the fatigue analysis procedure anexisting SFRP component has been studied. The component is the front bracket thatmounts the roof air deflector to the roof on Scania trucks. To correlate the fatigue lifeestimation from the fatigue analysis, experiments were performed at ÅF Test Centerin Borlänge.The anisotropic behaviour is modelled using the commercial software Digimat togetherwith an injection simulation provided by Scania, to estimate the fibre orientationand thereby the material behaviour of the SFRP component. The fatigue analysiswas conducted by performing a coupled structural analysis between Digimat-Abaqus and then import the resulting stress- and strain-fields into the fatigue postprocessornCode DesignLife. The stress is then cyclic tested towards experimentallydetermined S-N curves determined in Digimat.Due to restriction of available fatigue data for the plastic in the front bracket, a fatiguematerial model for a plastic containing the same fibres and matrix but witha different fibre amount was implemented. The fatigue data were scaled using theUTS method to get a good characterisation of the real-life material behaviour of theplastic of the front bracket component.From the correlation between the fatigue analysis and performed experiments, itwas shown that the simulated fatigue life was conservative compared to the fatiguelife determined from the experiments. However, the correlation between the fatigueanalysis and experiments is not fully captured but gives a better estimation of thefatigue life compared to performing the fatigue analysis using an isotropic materialmodel.

Additive Manufacturing (AM), also known as 3D-printing, is the process of joining materials layer by layerfrom a 3D-model data and has several advantages over traditional manufacturing techniques. AM is destinedto change the way products are designed and manufactured in the future. In recent years, the process hasrapidly gained interest in all industry segments due to its ability to create customized and complex geometriesfor no added costs. This study focuses on a rather unexplored area of application of AM, namely of a vehiclecomponent that traditionally is manufactured with conventional manufacturing methods. The purpose ofthis study is to investigate the potential of AM of a PTO-shaft used in Scania's trucks. With the help oftopology optimization and a developed cost estimation model, dierent design cases are compared to eachother. Three areas are investigated: design, mechanical performance, and cost. The study found that adesign with roughly 25 % weight reduction is realizable, and would today cost about 15 times the cost forseries production using traditional manufacturing methods. This have clearly suggested that the PTO-shaftis not suitable for AM. However, by forecasting the cost into the future, the study found that printing thePTO-shaft are likely to be cost eective in terms of prototype production in the future, with up to about200 e in cost savings per part.

A method to evaluate technical solutions to handle external loads on subsea wellheadshas been developed. The solutions, or concepts, are compared with respect to load relief,cost and operation. As a basis, a Pugh matrix was used. It is well proven and commonlyused amongst engineers to evaluate concepts. However, it has some major cons due toits simplicity.Two more layers were added trying to solve or minimize these cons. This made up a totalof three layers.I. Evaluation - gather concept data, answer questions with valuesII. Transformation - transforms gathered values to a [1-5] scalingIII. Comparison - scaled values are presented in a Pugh matrixIn layer I, questions are to be answered by analyses and expert knowledge, carried outby developers.As for layer II, a value-scaling relationship should be set by developers and decisionmakers. They decide what is a good difference compared with a reference, and what isnot. The values for layer I can then be translated to layer III.Lastly, in layer III the performances of concepts with respect to different criteria are statedin a Pugh matrix. A scaling [1-5] is used for this. The decision maker decides what criteriaare most important by weighting them.Besides that, everything could be made automated. So when the method was carried outon two concepts, a winner could be decided immediately in layer III when the questionsin layer I had been answered.A simple and straightforward method to compare concepts have been done. Visualizingthe concept evaluation process and the connection between developers and decisionmakers. Making it easier for them to understand one another.The method can continuously be improved over time and might have the potential to makethe development process in many companies leaner.

The aim of this thesis is to estimate the high cycle fatigue life of welds using finite element methods and liner elastic fracture mechanics (LEFM). Develop a new method of calculating the fatigue life that can replace the old method in use today at GKN Driveline. This is a continuation of an earlier master thesis1. When gears have been subjected to high cycle fatigue testes, cracks have been observed propagating though the welds and resulted in component failure. The current method of estimating the welds fatigue life has a tendency to overestimate the life and thus a new method with better accuracy is sought after.The crack propagation is simulated by starting with an initial crack in the weld which is then incrementally increased in a pre-determined direction. The energy release rate for each node at the crack tip is calculated using virtual crack closure technique (VCCT). Due to multiaxial loads on the weld, an effective stress intensity factor is used together with a Paris Law type equation to estimate the propagation speed. The total amount of cycles it takes the crack to propagate between each of the increments is then estimated.The results show a good correlation to experimental data and takes approximately 40% longer time compared to the old method. The new method has a high dependency on good material parameters and thus important that these are chosen accurately, which can be especially hard for welds. The results can also be linearized which means that the life can be estimated for different load levels from one single simulation. / Målet med detta arbete har varit att uppskatta utmattningslivslängden för svetsar genom finita elementmetoder och linjär elastisk brottmekanik (LEFM). Skapa en ny metod för att uppskatta livslängden som ska ersätta den nuvarande metoden som just nu används hos GKN Driveline. Detta arbete bygger vidare på ett tidigare examensarbete2 som gjorde hos GKN. I högcykel utmattningsprov har det observerats att sprickor bildas i svetsen som sedan växer tills det ger upphov till ett haveri. Den nuvarande metoden för att uppskatta svetsarnas livslängd har en tendens att överskatta livslängden, vilket har gjort att GKN söker efter en ny metod för att räkna livslängden på deras svetsar.Sprickpropageringen simuleras genom att börja med en startspricka i svetsen som sedan stegvis ökas i storlekt i en förutbestämd riktning. Energi frigörelsen för varje nod längs sprickspetsen beräknas med hjälp av virtuell sprickförslutningsteknik (VCCT). Svetsarna utsätts för fleraxliga laster vilket gör det nödvändigt att använda en effektiv spänningsintensitetsfaktor tillsammans med en Paris Lag liknande ekvation. Med hjälp av detta kan sedan sprickhastigheten mellan de olika stegen beräknas.Resultaten visar god korrelation mot gjorda test samt att den nya metoden tar cirka 40% längre tid än den nuvarande metoden. Den nya metoden är också väldigt beroende på att materialparametrarna, vilket kan vara svåra att erhålla för svetsat gods. Resultaten kan linjäriseras, vilket betyder att olika last nivåer kan undersökas från en simulering.