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Europa, the smallest of the Galilean satellites, is characterized by a young water-ice surface showing a rich structure of cracks, ridges and chaotic terrain. Below the ice shell a subsurface water-ocean might exist, which in Europa’s case would be in direct contact with the silicate mantle. This direct contact is important from an astrobiological perspective, as living organisms might have developed at places where a hot part of the mantle contacts the ocean. As a consequence, many scientists consider Europa as the planetary body with the largest probability to harbor life within our solar system. It is therefore of utmost importance to find out whether a subsurface ocean exists underneath the ice shell. One plausible method to determine the existence of an ocean is based on the measurement of the radial deformation induced by the eccentricity-tide acting on Europa. If an ocean is present in the interior, the radial deformation at the surface will be one to two orders of magnitude larger than in the case that an ocean is absent. Such a large difference in deformation can be detected from measurements performed by a dedicated orbiter. As a result, a mission to the Jovian system would be required. An alternative method to determine whether there is a subsurface ocean underneath the ice shell is based on establishing a connection between the shape of the lineaments observed on the surface and the acting stress fields. Stresses at the surface might be induced by several different mechanisms, from which only the two most important will be analyzed in this research: the eccentricity-tide acting on Europa and non-synchronous rotation (NSR) of the ice shell. The first mechanism, i.e. the eccentricity-tide, induces a highly variable stress field that explains the formation of cycloidal features even without taking into account NSR stresses. The second mechanism, i.e. NSR, induces a nearly static stress field that explains the formation of slightly-curved or global lineaments. As both types of lineaments exist on Europa’s surface, the strength of NSR stresses should have changed throughout the geological history of Europa. Such a change can be driven by a variable rate of non-synchronous rotation, which can be the result of thickness variations in the ice shell. One important result obtained in this research is that tensile stresses at the surface of models without a subsurface ocean are too small to originate a crack at the surface if NSR is not taken into account. If NSR stresses are added to the modeling of the stress field, tensile stresses only become large enough to break ice when the stress field is practically static. As a result, the existence of cycloidal features strongly suggests the existence of a subsurface ocean underneath the ice shell of Europa.

In dit proefschrift wordt een algemene oplossingsmethode voor een bepaalde klasse van problemen uit de twee-dimensionale elasticiteitstheorie aangegeven. Het betreft hier problemen die als gemeenschappelijk kenmerk hebben dat het elastische lichaam de vorm heeft van een beneden-halfvlak met een iets gewijzigde bovenrand, waarop als belasting uitsluitend het eigen gewicht van het materiaal werkt. Deze klasse van problemen omvat onder meer het probleem van een dijk, bestaande uit elastisch materiaal, gebouwd op een elastisch halfvlak, en ook de problemen van een ontgraving of een ontgronding in een lichaam dat oorspronkelijk een halfvlak innam. Na een beschrijving van het algemene probleem in hoofdstuk 2, en de wiskundige formulering ervan in hoofdstuk 3, wordt in de hoofdstukken 4 en 5 de eigenlijke oplossingsmethode behandeld. Deze valt uiteen in twee gedeelten. In de eerste plaats wordt in hoofdstuk 4 beschreven hoe de conforme afbeelding van het gebied, ingenomen door het elastische lichaam, op het inwendige van de eenheidscirkel in standaardvorm kan worden gebracht. Deze standaardvorm bestaat uit een singulier gedeelte, dat er voor zorgt dat op het oneindige het gebied een halfvlak benadert, en een regulier gedeelte, dat geschreven kan worden in de vorm van een reeks van Taylor. Bewezen wordt dat deze Taylor-reeks in het algemeen convergeert, niet alleen binnen, maar ook op de eenheidscirkel, mits keerpunten in de contour worden uitgesloten. Ook wordt aangegeven hoe de coefficienten van de termen uit de Taylor-reeks kunnen worden berekend. Daarbij wordt gebruik gemaakt van een methode van Pilon voor de numerieke berekening van trigonometrische integralen. Van de Taylor-reeks worden vervolgens alleen de eerste n termeo in aanmerking genomen. Dit betekent dat niet het oorspronkelijke probleem wordt opgelost, maar een probleem met een iets afwijkende vorm van de rand. Door voldoende termen van de Taylor-reeks in aanmerking te nemen kan de afwijking kleiner gemaakt worden dan elke willekeurig kleine maat. Afgezien van deze benadering van de rand is de oplossingsmethode exact. De oplossing van het randvoorwaarde-probleem wordt, in een algemene vorm, gegeven in hoofdstuk 5. Deze oplossing wijkt alleen af van de bekende technieken (zoals ontwikkeld door Muskhelishvili) doordat de afbeeldingsfunctie een singulariteit, namelijk een pool van de eerste orde, heeft op de rand van de eenheidscirkel. Dit leidt tot enige complicaties, maar verhindert niet dat een algemene oplossing kan worden gegeven. Uitwerking van de oplossing voor een specifiek geval vereist alleen algebraïsche bewerkingen. Daarbij is de meest gecompliceerde bewerking het oplossen van een stelsel van 2 n lineaire vergelijkingen met 2 n onbekenden (n is het aantal termen van de afgebroken reeks van Taylor). In hoofdstuk 6 zijn de uit te voeren bewerkingen verzameld. Bij wijze van voorbeeld wordt vervolgens in hoofdstuk 7 beschouwd het geval van een halfvlak met een uitsnijding in de vorm van een cirkelboog. Enige numerieke resultaten worden gegeven. Voor een speciaal geval blijkt een exacte oplossing te bestaan, en dit maakt een toetsing van de benaderingsmethode mogelijk. Een goede overeenstemming met de exacte oplossing toont aan dat de methode tot vrij nauwkeurige resultaten leidt, behalve voor punten juist op (of zeer dicht bij) de rand gelegen. In paragraaf 7.2 wordt ook verklaard waarom de methode onnauwkeurig is voor randpunten. In paragraaf 7.3 worden de resultaten van de benaderde complexe berekeningsmethode nog vergeleken met enige resultaten verkregen met een (exacte) methode die gebruik maakt van Fourier-integralen. Ook daar blijkt de overeenstemming uitstekend te zijn in punten in het inwendige van het gebied. Als een tweede type van voorbeelden wordt in hoofdstuk 8 het probleem van een dijk op een halfvlak beschouwd. Ook voor dit geval worden enige numerieke resultaten gegeven. In hoofdstuk 9 tenslotte wordt een generalisatie hiervan, namelijk het geval van een halfvlak met een kerf in de vorm van een willekeurige veelhoek, behandeld. Het blijkt mogelijk te zijn een keten van procedures samen te stellen waarbij, uitgaande van de coordinaten van de hoekpunten van de rand, als resultaat de spanningen in het inwendige worden verkregen.

In skew bridges torsion occurs. This leads to a substantial amount of reinforcement stirrups. Minalu already did research to torsion in bridge decks with different types of finite element models. The question when torsion cracks will really occur is still unanswered. This question is the main subject of this research. The focus of the research is on a skew bridge with a skew angle of 45 degrees. In that bridge the largest torsional moments will occur. Beside that also a straight bridge is analysed, the torsional moments in a straight bridge are always lower than in a skew one under the same loading. The loads of Eurocode 1991-2 are used. Two important load configurations governing for torsional moments and shear force are used: a configuration which is used in daily practice at Spanbeton and a configuration developed by Minalu. An attempt is made to model the whole bridge including physically non-linear behaviour with the program ATENA 3D to analyse the torsion effects. With the current state-of-the-art modelling technology that appeared to be impossible. For that reason a simplified model is developed to simulate the stress state and cracking in one ZIP girder. It was concluded that it is important to use more quadratic elements over the thickness of the web to obtain correct torsion shear stresses. From the simplified model it is concluded that, despite some shortcomings, clearly a substantial length at the ends of the girder is uncracked. To be sure that the computer model is correct a calculation of the principal stresses is carried out at the ultimate limit state. The stresses due to prestressing, own weight and the weight of the fresh poured concrete can be calculated by hand. The calculation of the force distribution of the loads on the deck can be carried out using finite element methods. Scia Engineer (orthotropic plate model) and ATENA 3D (volume elements) are used for this calculation. Especially the determination of the torsional moments from ATENA by using an analysis of the rotations is interesting. This calculation results in the torsional moments, bending moments en shear forces acting on the ends of the girder. The main conclusion of this research is that in ultimate limit state no cracking will occur in the end of the considered girder in the skew bridge. This means that only the minimal shear reinforcement must be applied and the full torsional stiffness can be used in finite element calculations. A practical method to check this for other bridges using ZIP-girders is proposed.

Non-homogenous cooling rates and solidification conditions during DC-casting of high strength aluminum alloys result in the formation and accumulation of residual thermal stresses with different signs and magnitudes in different locations of the billet. Rapid propagation of microcracks in the presence of thermal stresses can lead to catastrophic failure in the solid state, which is called cold cracking. Numerical models can simulate the thermomechanical behavior of an ingot during casting and after solidification and reveal the critical cooling conditions that result in catastrophic failure, provided that the constitutive parameters of the material represent genuine ascast properties. Simulation of residual thermal stresses of an AA7050 alloy during DC-casting by means of ALSIM5 showed that in the steady-state conditions large compressive stresses formed near the surface of the billet in the circumferential direction. Stresses changed sign on moving towards the centre of the billet and became tensile with high magnitudes in radial and transverse directions, which made the alloy prone to hot and cold cracking.

Reinforcement in a concrete structure is often determined based on linear elastic stresses. This paper considers computation of the required reinforcement when these stresses have been determined by the finite element method with volume elements. Included are both tension reinforcement and compression reinforcement, multiple load combinations and crack control in the serviceability limit state. Results are presented of seventeen stress state examples.

Thin films on substrates are usually in a stressed state. An important, but trivial, contribution to that stress stems from the difference in thermal expansion coefficient of substrate and film. Much more interesting are the intrinsic stresses, resulting from the growth and/or microstructure of the film. Intrinsic compressive stress was explained by d’Heurle in 1970. Intrinsic tensile stress for recrystallizing metal films was treated succesfully by Doljack and Hoffman in 1972. In the present letter we explain the occurrence of tensile stress in nonrecrystallizing metal films. The explanation is based on modern grain growth models and accurate stress measurements. The key ingredient to the explanation is the proof of the existence of a stress gradient in nonrecrystallizing metal films.

We report the effects of biaxial strain on the charge ordering temperature Tco of the mixed-valent manganite perovskite oxide Pr0.5Ca0.5MnO3. Thin films were grown on SrTiO3, which has a 1.3% larger in-plane lattice parameter. Other substrates were used for comparison. Transport measurements combined with data from electron microscopy show that Tco is considerably enhanced. At thicknesses of the order of 10 nm, where the films are fully strained, Tco is above 320 K, more than 70 K above the bulk value of 250 K, while around 50 nm, where relaxation has set in, the enhancement is around 40 K. The bulk value is only reached at a thickness of about 150 nm.

Tungsten carbide-diamond like carbon (WC-DLC) multilayer coatings have been prepared by sputter deposition from a tungsten-carbide target and periodic switching on and off of the reactive acetylene gas flow. The stress in the resulting WC-DLC multilayers has been studied by substrate curvature. Periodicity and microstructure have been studied by transmission electron microscopy. It has been observed that compressive stress in the multilayers decreases when the bilayer thickness is reduced. Results show a minimum compressive stress for bilayer thickness of around 5 nm. This behavior is discussed in terms of interface stress and mixing between layers.

A magnetic field, imposed on turbulent flow of an electrically conductive fluid, is known to cause preferential damping of the velocity and its fluctuations in the direction of Lorentz force, thus leading to an increase in stress anisotropy. Based on direct numerical simulations (DNS), we have developed a model of magnetohydrodynamic (MHD) interactions within the framework of the second-moment turbulence closure. The MHD effects are accounted for in the transport equations for the turbulent stress tensor and energy dissipation rate—both incorporating also viscous and wall-vicinity nonviscous modifications. The validation of the model in plane channel flows with different orientation of the imposed magnetic field against the available DNS (Re = 4600,Ha = 6), large eddy simulation (Re = 2.9×104,Ha = 52.5,125) and experimental data (Re = 5.05×104 and Re = 9×104, 0 ⩽ Ha ⩽ 400), show good agreement for all considered situations.

Stress in hard films is the net sum of tensile stress generated at the grain boundaries, compressive stress due to ion peening, and thermal stress due to the difference in thermal expansion of the coating and substrate. The tensile part due to grain boundaries is thickness dependent. The other two contributions are not thickness dependent. Summation of the three components leads to a stress gradient in the coating. In the present paper it is demonstrated that adding the three contributions mentioned above yields a good description of the observed dependence of stress on thickness in CrN coatings.

Two-dimensional (2D) discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect (BE) in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.

In this paper, we present a systematic investigation of the influence of the deposition parameters on the deposition rate, etch rate, and mechanical stress of SiC films prepared by plasma-enhanced chemical vapor deposition (PECVD) technique. Among the relevant deposition parameters, the SiH4 gas flow rate, the main parameter to determine the Si to C ratio, plays a crucial role in controlling the properties of SiC films. By combining a design of experiments with a mathematical technique, an empirical model to control the stress of the PECVD SiC films is obtained. Using this empirical model taking into account the interaction between parameters, the stress of the SiC film can be reduced down to only 22.5 MPa.

In the absence of thermal stress, tensile stress in hard metal films is caused by grain boundary shrinkage and compressive stress is caused by ion peening. It is shown that the two contributions are additive. Moreover tensile stress generated at the grain boundaries does not relax by ion bombardment. In polycrystalline hard metal films the grain structure evolves during growth, leading to wider grains higher up in the film. The tensile component of the stress in the film is generated at the grain boundaries and therefore depends on film thickness. The effect of ion bombardment is independent of grain size, therefore compressive stress does not depend on film thickness. As a result in polycrystalline films deposited under a bias voltage a stress gradient exists from tensile at the interface to compressive at the top of the film.

Data on chloride penetration into concrete exposed to a simulated aggressive marine environment are presented. Concrete specimens, large beams and small cubes, are subjected to 90 complete exposure cycles of wetting and drying plus heating and cooling. The applied exposure condition consists of a drying period of 42 hrs followed by a wetting phase of 6 hrs with salt water containing 5% NaCl. The drying phase itself is a thermal regime characterised by a temperature swing from 20°C to 60°C within a period of 12 hrs. This simulates, with some accelerations, the aggressive marine environmental condition in hot regions with varying daily temperature including direct solar radiation. Totally 315 temperature cycles and 90 cycles of wetting/drying were applied to specimens in this experiment. It was observed that temperature and humidity variations promote chloride penetration into marine concrete significantly. This particular study shows that thermally-induced microcracks increase, but slightly, the permeability of concrete in "restrained" beams compared to the relatively "stress free" small specimens. Effect of two other significant parameters, i.e. type of curing and type of cement, on chloride ingress rate is also investigated.

We studied the tensile stress and grain-width evolution in sputter-deposited Cr films with thickness from 20 nm to 2.7 μm. Films were deposited in an industrial Hauzer 750 physical vapor deposition machine at 50–80 °C. The films exhibited a columnar microstructure. A power law behavior of the tensile stress as well as of the average grain width with thickness was observed. Both power exponents were strongly dependent on the Ar pressure during deposition. The power exponent α for stress varied from 0.26 to 0.79 for the range of Ar pressures used (5×10−3–2×10−2 mbar). The mechanism of tensile stress generation is the shrinkage of the grain boundaries. Assuming the same shrinkage of the grain boundaries all through the layer, the stress and the grain width would be inversely proportional. Indeed, the grain width followed the same power law as the stress at low Ar pressure [α = 0.3(1)], but not at high Ar pressure [α = 0.58(3)]. Transmission electron microscopy showed the formation of numerous voids. At higher Ar pressure the void fraction is significantly higher than at low pressure, thereby diminishing stress generation.