ABSTRACT The rapid development of structural materials and their successful applications in various sectors of industry have led to increasing demands for assessing their mechanical properties in small volumes. If the size dimensions are below micron, it is difficult to perform traditional tensile and compression tests at such small scales. Indentation testing as one of the advanced technologies to characterize the mechanical properties of material has already been widely employed since indentation technology has emerged as a cost-effective, convenient and non-destructive method to solve this problem at micro- and nanoscales. In spite of the advances in indentation testing, the theory and development on indentation testing are still not completely mature. Many factors affect the accuracy and reliability of identified material parameters. For instance, when the material properties are determined utilizing the inverse analysis relying on numerical modelling, the procedures often suffer from a strong material parameter correlation, which leads to a non-uniqueness of the solution or high errors in parameter identification. In order to overcome that problem, an approach is proposed to reduce the material parameter correlation by designing appropriate indenter tip shapes able to sense indentation piling-up or sinking-in occurring in non-linear materials. In the present thesis, the effect of indenter tip geometry on parameter correlation in material parameter identification is investigated. It may be helpful to design indenter tip shapes producing a minimal material parameter correlation, which may help to improve the reliability of material parameter identification procedures based on indentation testing combined with inverse methods. First, a method to assess the effect of indenter tip geometry on the identification of material parameters is proposed, which contains a gradient-based numerical optimization method with sensitivity analysis. The sensitivities of objective function computed by finite difference method and by direct differentiation method are compared. Subsequently, the direct differentiation method is selected to use because it is more reliable, accurate and versatile for computing the sensitivities of the objective function. Second, the residual imprint mappings produced by different indenters are investigated. In common indentation experiments, the imprint data are not available because the indenter tip itself shields that region from access by measurement devices during loading and unloading. However, they include information about sinking-in and piling-up, which may be valuable to reduce the correlation of material parameter. Therefore, the effect of the imprint data on identification of material parameters is investigated. Finally, some strategies for improvement of the identifiability of material parameter are proposed. Indenters with special tip shapes and different loading histories are investigated. The sensitivities of material parameters toward indenter tip geometries are evaluated on the materials with elasto-plastic and elasto-visoplastic constitutive laws. The results of this thesis have shown that first, the correlations of material parameters are related to the geometries of indenter tip shapes. The abilities of different indenters for determining material parameters are significantly different. Second, residual imprint mapping data are proved to be important for identification of material parameters, because they contain the additional information about plastic material behaviour. Third, different loading histories are helpful to evaluate the material parameters of time-dependent materials. Particularly, a holding cycle is necessary to determine the material properties of time-dependent materials. These results may be useful to enable a more reliable material parameter identification.

The stretch forming process is frequently used in the automotive industry (outer pan- els, inner panels, stiffeners etc.), the packaging industry and household appliances sector, to manufacture complicated shapes and curvatures. However it requires accurate prediction of tool geometries and manufacturing parameters to avoid the currently used trial and error approach. Metal forming is also associated with cer- tain defects like local thinning, wrinkling, tearing etc. Avoiding such defects and prediction of spring back presumably requires a thorough understanding of the de- formation mechanics and material behavior beyond the elastic range. In the stretch forming operation, material essentially passes through the elastic, yield point and plastic states. Elastic behavior can be explained based on classical theory of elasticity wherein linear trend of infinitesimal deformation is expressed by generalized Hooke’s law. In the plastic range, the theory is based on certain exper- imental observations of the macroscopic behavior of metals in the uniform state of combined stresses. Experimentally observed results are idealized into mathematical formulation to describe the complex behavior of metals under combined state of stress. These formulations are based on some assumptions like material behavior is time independent, strain rate effects could be neglected, hysteresis loop and Bauschinger effects which arise from the non-uniformity of the microscopic scale could be disregarded etc. The thermal effects are neglected and material is assumed to be isotropic. Supposedly because of these assumptions existing theory of plastic- ity does not accurately predict the phenomenon of stretch forming occurring during plastic deformation. Theories are being developed like that of Rao and Shrinivasa [2002], which consider stresses during deformation as resistance due to shape change, volume change, rate of shape change and rate of volume change. Such theories need variation of material parameters like bulk modulus (K), shear modulus (G), bulk viscosity (µ’) and shear viscosity (µ) as deformation progreses. Therefore uni-axial tension exper- iments have been conducted to find out the strains at the corresponding loads. Mild steel and aluminum have been chosen for the experiments. Chemical and physical properties of the materials are chosen such that they are very similar to those used in the automotive industry for stretch forming. A procedure is developed using uni-axial tension test results to calculate the material parameters for the entire range of material deformation. For mild steel, bulk modulus and shear modulus decrease and become almost zero as the material deforms from elastic to transition region. After transition zone, both moduli increase and then decrease as material deforms in the strain-hardening region. For aluminum both bulk and shear moduli decrease non-linearly as material deforms from elastic to plastic region. The behavior of bulk modulus and shear modulus are consistent with the stress-strain behavior of the materials. For mild steel as well as aluminum, the bulk and shear viscosities are positive in the elastic region and in the large deformation region the values are small compared to elastic region. We can separate the various stresses, hydrostatic, deviatoric and viscous stresses, associated with (µ) and (µ’) and contribution of each to the total stresses can be obtained. It is observed that contribution from the viscous stresses is as high as 5 % when the material is subjected to large strain rate tests. The strain rate in stretch forming operation may be different from the strain rate at which the material parameters are calculated. Knowing the material para- meters at one strain rate, the stress-strain curves at different strain rates can be predicted. The repeatability of computation of the material parameters and contributions from the viscous and non-viscous stresses for large deformation has been ascertained by using different test samples. The material parameters obtained from one set of samples have been applied to different samples and experimental versus predicted stresses have been found to match fairly well. A lot more work needs to be done to reach the goal of accurately predicting the behavior during stretch forming. Test data on different materials need to be generated and the new theories need to be validated for compression as well as loading and unloading cases.

Use of weight-saving materials to produce lightweight components with enhanced dimensional control is important to the automotive industry. This has increased the need to understand the material behavior with respect to the forming process at the microstructural level. A test matrix was developed based on the orthogonal array of Taguchi design of experiment (DOE) approach. Experiments were conducted for the V-bending process using 6022-T4 AA to study the variation of springback due to both process and material parameters such as bend radius, sheet thickness, grain size, plastic anisotropy, heat treatment, punching speeds, and time. The design of experiments was used to evaluate the predominate parameters for a specific lot of sheet metal. It was observed that bend radius had greatest effect on springback. Next, finite element simulation of springback using ANSYS implicit code was conducted to explore the limits regarding process control by boundary values versus material parameters. 2-D finite element modeling was considered in the springback simulations. A multilinear isotropic material model was used where the true stress-strain material description was input in discrete form. Experimental results compare well with the simulated predictions. It was found that the microstructure of the material used in this study was processed for sheet metal forming process.

Abstract Primary hallmark of osteoarthritis (OA) is the progressive degeneration of articular cartilage. An accurate estimation of cartilage mechanics is important when analyzing the subject-specific function of the knee joint and risks for the onset and development of OA due to cartilage damage. Finite element (FE) modeling can help to estimate peak joint stresses and strains and explain how they could lead to OA. FE models of the knee joint during simplified gait were developed to define the level of material complexity required for 3D FE modeling of the knee joint in estimation of reliable tissue stresses and strains within articular cartilage of the knee joint; and to investigate the predictive value of FE modeling of the knee joint on the development and progression of radiographic OA within obese and normal weight subjects. It was found that maximum principal stresses and strains within articular cartilage in the knee joint during walking are highly sensitive to the material parameters of cartilage. It was not possible to match simultaneously stresses, strains and contact pressures between simplified (non-fibrillar) and advanced (fibrillar) models. Though, it was possible to find parameters for transversely isotropic models that enable the estimation of stresses and strains throughout the depth of cartilage similarly to more advanced fibril reinforced models. Locations of peak cumulative stresses in obese subjects at the baseline without radiographic OA showed a good agreement with the locations of cartilage loss and magnetic resonance imaging (MRI) based scoring in four year follow-up when they had developed OA. Simulated weight loss in obese subjects significantly reduced the highest cumulative stresses in cartilage to the level of normal weight subjects. The cartilage degeneration algorithm was able to predict subject-specific progression of OA similarly with MRI follow-up data and separate subjects with radiographic OA from healthy subjects. The computational FE models developed in this thesis represent useful tools to identify possible risk locations within the knee joint and how they relate to OA onset and progression. The presented methods have clinical potential in the diagnostics of knee joint OA in a subject-specific manner and in simulating the effect of interventions on the progression of OA thus helping with an effective treatment planning. / Tiivistelmä Nivelrikon tunnusomaisin piirre on nivelrustokudoksen rappeutuminen ja kuluminen. Nivelruston tehtävänä on tasata niveliin kohdistuvaa kuormitusta. Rustokudoksen mekaanisten ominaisuuksien määrittäminen on tärkeässä roolissa, kun halutaan arvioida tarkemmin polvinivelen toimintakykyä sekä rustokudoksen rappeutumista. Magneettikuvantamisen pohjalta tehtävä polvinivelen biomekaaninen tietokonemallinnus mahdollistaa rustokudoksen jännitys- ja puristusjakauman arvioinnin simuloidun kuormituksen aikana, mikä edelleen voi antaa vastauksia siihen, kehittyykö niveleen tulevaisuudessa nivelrikko, tai miten tietyn nivelrikkopotilaan sairaus etenee. Tämän tutkimuksen päätavoitteena oli kehittää kolmiulotteisia polvinivelen biomekaanisia tietokonemalleja, joiden perusteella simuloitiin normaalia kävelyä. Polvinivelen kolmiulotteinen geometria luotiin terveiden koehenkilöiden sekä nivelrikkopotilaiden magneettikuvista. Malleilla selvitettiin aluksi, miten monimutkaisena materiaalina nivelrusto tulee mallintaa, jotta mallin ennustama jännitys- ja puristusjakauma on silti realistinen. Tämän jälkeen tutkittiin, miten hyvin tietokonemallinnus ennustaa polvinivelrikon kehittymistä ja etenemistä sekä nivelruston rappeutumista ylipainoisilla potilailla. Tutkimuksessa havaittiin, että tietokonemallin ennustamat jännitys- ja puristusjakaumat nivelrustossa kävelyn aikana riippuvat merkittävästi nivelrustolle valitusta materiaalimallista ja sen parametreista. Tietokonemallien ennustamat nivelruston jännityskeskittymien sekä ruston rappeutumisen sijainnit vastasivat erittäin hyvin nivelrustokudoksen todellisen kulumisen sijainteja magneettikuvasta arvioituna neljän vuoden seuranta-ajan jälkeen. Tietokonemalleilla oli myös mahdollista simuloida painon pudotuksen vaikutusta, jolloin nivelrustokudoksen jännitys- ja puristusjakaumat palautuivat normaalien koehenkilöiden tasolle. Tässä tutkimuksessa kehitetyt polvinivelen tietokonemallit tarjoavat tutkijoille uuden työkalun paikallistaa sellaiset kohdat nivelpinnalta, joissa kuormituksen aiheuttama mekaaninen jännitys on suurta; nämä kohdat ovat kaikista riskialtteimpia nivelrikon kehittymiselle. Kehitettyjä malleja voidaan perustutkimuksen lisäksi jatkokehittää edelleen kohti kliinistä sovellusta, jolloin niitä voitaisiin hyödyntää esimerkiksi simuloitaessa erilaisten hoitojen vaikutusta kuormitusjakaumiin ja rustokudoksen rappeutumiseen.

The constantly tightening emission regulations demand the engines to be moreefficient, to get more power out of smaller engines. Higher engine loads andcomponent temperatures are causing more stresses to engine components. Therefore,a company that produces engines wanted to study if it would be possible to increasethe capabilities of the components by optimising the used material. In this final project work, a cylinder head will be studied. The cylinder heads for theengines are made of ductile cast iron. The limits of that material are near safety limits,and therefore a better material is needed. In this work are some previous studiesanalysed and tried to find how to optimise the used material. The optimised materialshould have better thermal conductivity properties combined with sufficient strengthproperties. Previous studies were analysed to gather knowledge of the elements that affect thematerial parameters. Those studies showed that copper, silicon, pearlite fraction, andthe use of chills are the elements to be optimised. Silicon and pearlite fraction waschosen as optimisation parameters because of their effect on the thermal conductivityand strength properties. Copper was chosen as an optimisation variable due to its effecton the pearlite formation. Chills were used to affect the cooling rate and thereby thepearlite formation. The work was made using MAGMASOFT™ simulation software to simulate cylinderhead casting. The simulated cylinder head was divided into 4 parts for the simulations.For those sections were then set targets for pearlite fraction according to previousstudies. The silicon content was kept constant in the simulation, based on the studiespresented in this work. Copper content was simulated with variations from 0 to 0.7weight-%, and chill heights were simulated from 20 to 60 mm and without chills. After simulating the different variables, the results were analysed. Then the selectedcasting simulation result was mapped to finite element simulation mesh to include thelocal material parameters to finite element simulation. With the finite elementsimulation, the estimated lifetime of the component was simulated. By analysing the casting simulation results, an optimal combination was found. Theoptimal material parameters for a cylinder head casting would be copper 0.5weight-%, silicon 1.9 weight-% and chills thicker than 40 mm on the flame plate. Theoptimised material gives more possibilities to develop engines even further when thecomponent demands are growing.

Os biopolímeros surgem como materiais alternativos no atendimento aos requisitos de desempenho que a área médica tem exigido para implantes ósseos. Nesse contexto o polímero poliuretano derivado de óleo de mamona (Ricinus communis) tem obtido lugar de destaque. Mesmo assim, esse material, considerado um biopolímero regenerador ósseo, ainda necessita de investigação mecânica consistente para uma aplicação de forma confiável. No entanto, há uma grande dificuldade em se prever o comportamento mecânico das estruturas fabricadas por biopolímeros. Diante desse fato, o presente projeto de pesquisa visa através de ensaios experimentais em amostras padronizadas para ensaios de tração e compressão, bem como, ensaios normalizados para próteses de quadril, adquirir propriedades de material adequadas para a implementação dos modelos computacionais, assim como dados de comportamento mecânico sob solicitação. De posse desses dados, através do método dos elementos finitos, são realizadas simulações computacionais com o objetivo de verificar a capacidade do modelo de material de Drucker-Prager representar o comportamento mecânico do biopolímero. Este modelo é aplicado inicialmente na simulação dos ensaios de tração e compressão e posteriormente nas simulações das próteses em biopolímero, onde carregamentos mais complexos estão presentes. Os resultados obtidos nas simulações são analisados e discutidos para fins de validação do uso deste modelo de material em estruturas fabricadas com o biopolímero. / Biopolymers have been widely used as alternative materials to attend the performance requirements that medical area has demanded to bone implants. In this way, the Castor Oil Polyurethane (Ricinus communis) has taken a distinct place. Nevertheless, this material, considered bone constructive, still needs a consisting mechanical investigation for a reliable application, despite the great difficulty to predict the mechanical behavior of biopolymer structures. Face this fact, this work intends through experiments in normalized specimens for tensile and compressive tests, as well as normalized tests for hip implants, to obtain material properties and mechanical behavior data required to implement computational models of the hip prosthesis. Using the finite element method, computational simulations are carried out to verify the capability of Drucker-Prager material model to represent the biopolymer mechanical behavior. This model is first applied in tensile and compressive tests simulations, and further in prosthesis biopolymer simulations, where more complex loadings are present. The results of these simulations are analyzed and discussed in order to validate the use of this material model in biopolymers structures.

Os biopolímeros surgem como materiais alternativos no atendimento aos requisitos de desempenho que a área médica tem exigido para implantes ósseos. Nesse contexto o polímero poliuretano derivado de óleo de mamona (Ricinus communis) tem obtido lugar de destaque. Mesmo assim, esse material, considerado um biopolímero regenerador ósseo, ainda necessita de investigação mecânica consistente para uma aplicação de forma confiável. No entanto, há uma grande dificuldade em se prever o comportamento mecânico das estruturas fabricadas por biopolímeros. Diante desse fato, o presente projeto de pesquisa visa através de ensaios experimentais em amostras padronizadas para ensaios de tração e compressão, bem como, ensaios normalizados para próteses de quadril, adquirir propriedades de material adequadas para a implementação dos modelos computacionais, assim como dados de comportamento mecânico sob solicitação. De posse desses dados, através do método dos elementos finitos, são realizadas simulações computacionais com o objetivo de verificar a capacidade do modelo de material de Drucker-Prager representar o comportamento mecânico do biopolímero. Este modelo é aplicado inicialmente na simulação dos ensaios de tração e compressão e posteriormente nas simulações das próteses em biopolímero, onde carregamentos mais complexos estão presentes. Os resultados obtidos nas simulações são analisados e discutidos para fins de validação do uso deste modelo de material em estruturas fabricadas com o biopolímero. / Biopolymers have been widely used as alternative materials to attend the performance requirements that medical area has demanded to bone implants. In this way, the Castor Oil Polyurethane (Ricinus communis) has taken a distinct place. Nevertheless, this material, considered bone constructive, still needs a consisting mechanical investigation for a reliable application, despite the great difficulty to predict the mechanical behavior of biopolymer structures. Face this fact, this work intends through experiments in normalized specimens for tensile and compressive tests, as well as normalized tests for hip implants, to obtain material properties and mechanical behavior data required to implement computational models of the hip prosthesis. Using the finite element method, computational simulations are carried out to verify the capability of Drucker-Prager material model to represent the biopolymer mechanical behavior. This model is first applied in tensile and compressive tests simulations, and further in prosthesis biopolymer simulations, where more complex loadings are present. The results of these simulations are analyzed and discussed in order to validate the use of this material model in biopolymers structures.

For modeling of particulate materials, discrete element method (DEM) is commonly used. It perceives every particle like a single body. A railway ballast loading by trains is a typical example of a particulate discrete material. By a passing train, static and dynamic forces act on a track bed. Cycling loading results in pernament changes in the railway ballast. Cavity creation, agglomeration and ballast cracking lead to damages in rail traffic. Usage of the discrete element method may reveal the real issues of the railway ballast and it may leads to a reduction of costs associated with a design and repairs. This thesis is focused on the ballast modeling and identification of the discrete model parameters. Obtained results are compared with real experiments from Nottingham University.

In 2017, the Swedish Parliament stated a new climate law with the goal that Sweden should be climate neutral by 2045. The concrete industry has developed a roadmap on how the goal for 2045 can be achieved, where one way to reduce the carbon emissions from concrete is by replacing a part of the cement clinker with alternative binders in the concrete mix. Ground granulated blast furnace slag (GGBS), fly ash, silica fume and trass are alternative binders that are possible to use in concrete mixes to reduce the amount of ordinary Portland cement (OPC). GGBS, fly ash and silica fume are by-products from other industries, while trass is volcanic ash that can be extracted. Besides the positive environmental impact that comes from using alternative binders and reducing the amount of cement clinker, the alternative binders have other properties, both positive and negative, that affect the concrete. The aim of this thesis was to investigate whether concrete with alternative binders does fulfill the regulations set by Swedish standards and how concrete with alternative binders does affect the material parameters. The concrete mixes were divided into three different types of concrete: concrete for bridges (w/c ratio 0.4), hydropower structures (w/c ratio 0.45) and wind powerplant foundations (w/c ratio 0.55). A total of seven concrete mixes were cast in a laboratory and the concrete mixes were investigated in the three hardening stages of concrete: fresh, young and hardened. The analyzed material parameters were compressive strength, shrinkage, frost resistance, workability, air voids and temperature development. Beyond the experimental testing, a global warming potential (GWP) comparison was made to compare the reduction of GWP for each concrete mix compared to a reference concrete for each usage area. The mix containing a CEM II/A-V fly ash cement and 15% GGBS showed great potential regarding the different material parameters. This mix, however, is according to Swedish standards not possible to certify for structures in exposure class XF4, such as bridges, but is possible to certify for structures in exposure class XF3, such as wind powerplant foundations. The mix containing 30% GGBS and 5% silica fume also showed beneficiary properties, but superplasticizers are required in this mix to ensure good workability. For hydropower structures, the mix containing 35% GGBS showed a great compressive strength but a high temperature development and low workability. The mix containing trass had a notably low temperature development, but with an increase in shrinkage and low workability. Moreover, all concrete mixes showed a frost resistance which, according to standard, is classified as “Very Good”. / Sveriges regering antog 2017 ett nytt klimatpolitiskt ramverk med målet att Sverige ska ha noll nettoutsläpp av växthusgaser år 2045. Betongindustrin har tagit fram en färdplan för hur betong kan bli klimatneutralt, där ett sätt att reducera klimatpåverkan från betong är att byta ut en del av cementklinkern mot alternativa bindemedel. Mald granulerad masugnsslagg (GGBS), flygaska, silikastoft och trass är alternativa bindemedel som är möjliga att använda i betongblandningar för att reducera mängden Portlandcement. GGBS, flygaska och silikastoft är restprodukter från andra industrier medan trass är en vulkanisk aska som kan utvinnas. Utöver den positiva miljöeffekten som erhålls när alternativa bindemedel ersätter cementklinker, så har de alternativa bindemedlen andra egenskaper, både positiva och negativa, som påverkar betongen. Målet med denna studie var att undersöka och jämföra om betongblandningar där en del av cementklinkern har ersatts med alternativa bindemedel når upp till de krav som ställs i nuvarande regelverk. Utöver det så undersöktes även hur betongblandningarnas materialparametrar påverkades av alternativa bindemedel. Betongblandningarna delades in i tre olika typer av betong: betong för broar (vct 0.4), vattenbyggnader (vct 0.45) och vindkraftverksfundament (vct 0.55), där totalt sju betongblandningar tillverkades i ett laboratorium. Betongblandningarna undersöktes i de tre olika faserna för hårdnande av betong, vilka är färsk, ung och hårdnad betong. De materialparametrar som analyserades var tryckhållfasthet, krympning, frostresistens, arbetbarhet, luftporhalt och temperaturutveckling. Förutom de experimentella testerna gjordes en jämförelse kring hur mycket koldioxid som kan reduceras för varje betongblandning, jämfört med en referensbetong för varje användningsområde. Betongblandningen med ett CEM II/A-V flygaska-cement och 15% GGBS visade stor potential med avseende på de olika materialparametrarna. Denna blandning är dock enligt svensk standard inte möjlig att certifiera för betongbyggnad i exponeringsklass XF4, exempelvis broar, men kan certifieras för betongbyggnad i exponeringsklass XF3, exempelvis fundament för vindkraftverk. Blandningen med 30% GGBS och 5% silikastoft visade även positiva egenskaper, men flyttillsatsmedel måste användas i denna blandning för att erhålla en god arbetbarhet. För vattenbyggnadsbetong så visade blandningen med 35% GGBS en hög tryckhållfasthet, men samtidigt en hög temperaturutveckling och en låg arbetbarhet. Blandningen med trass hade en noterbart låg temperaturutveckling, men med ökad krympning samt låg arbetbarhet. Avslutningsvis så uppvisade alla blandningar en frostresistens som enligt standard klassificeras som ”Mycket bra”.