This study was performed to investigate how pressure, glue amount, dowel penetration depth and wood grain orientation affect direct withdrawal resistances of dowel pin joints both experimentally and numerically, and develop FE (finite element) models to simulate tensile strength, contact pressure, and shear stress occurred in dowel pin joints. Results indicated that the direct withdrawal resistance load of a dowel pin joints can be predicted based on knowing the glue bonding shear strength between dowel and joint member materials and the pressure between the contact surfaces of the dowel and hole of a connected joint member. The FE contact element model developed in this study was verified as an effective tool to analyze and predict the pressure between the contact surface of dowel and hole of a dowel-pin joint.

Because of an eventual ban of creosote-impregnated products, alternative materials for poles used in the electrical grid are needed. Concrete is one alternative and spun concrete poles have been manufactured for the Swedish grid before. These poles are still in use since the high strength and good functioning. However, they weigh too much in terms of the way that poles are assembled on the grid today. Therefore, a study comparing the capacity of different geometries, resulting in lower weight, is of interest.  In this Master’s Thesis, crack initiation and compressive failure in concrete poles are examined by creating FE-models in the software BRIGADE/Plus, using concrete damage plasticity. Thus, guidance is provided about how thin the concrete walls can be made without risking failure – which also means how low the weight of such a pole can be. The failure most likely to occur is a compressive failure in the concrete with a ductile behavior. The result shows that a geometry change, which implies a thinner concrete wall, is possible. This means a weight reduction between 30-75 % or even more, depending on which network the poles are designed for.

During aircraft development, the impact of vibrations is examined and how this affects the aircraft structure under different conditions. Those vibrations can damage electronic equipment that are installed within the fuselage and can even lead to material fatigue within the structure. To reduce vibrations there are two approaches that are preferred to use, installing vibration insulators attached between the structure and the electrical component or change the design of the structure to a stiffer one. Those methods are easiest to implement in an early stage of the development but in later stages, when vibration problems usually are detected, it is too difficult and expensive to do major changes of the structure and there is lack of space to implement vibration insulators. A third method is then to apply passive damping in form of damper mats to surfaces on structures where critical vibrations occurs.    The effects on the structural behavior when damper mats are applied to a certain structure are studied in this thesis work. The purpose is to get deeper knowledge about how damper mats can be used to reduce vibrations in aircraft structures. The type of damper mat that is studied is known as Constrained Layer Damping, CLD, which is a sandwich of a visco-elastic material layer and a stiffer constraining material layer. Modelling and simulation methods that are based on commercial FE-software have been developed. The analysis method is based on doing a modal analysis with structural damping taken into account. This makes it possible to predict the overall global damping at each structural mode. The models for damper mats have in this project been verified with experimental testing using typical damper mats. The methodology can be used to predict the behavior of damped structures in order to obtain an effective and lightweight passive damping solution. / Under utvecklingen av flygplan undersöks hur vibrationer påverkar flygplansstrukturen under olika förutsättningar. Dessa vibrationer kan skada elektronisk utrustning som är monterad i flygplanskroppen och kan även göra så att materialutmattning uppstår i flygplansstrukturen. För att motverka vibrationer finns det två metoder som är att föredra, antingen att montera vibrationsisolatorer mellan de elektroniska utrustningarna och strukturen eller att ändra designen på strukturer till en styvare. Dessa metoder är enkla att implementera i ett tidigt steg i utvecklingsprocessen men i senare steg, då vibrationsproblem ofta upptäcks, så är det för komplicerat och för dyrt att göra större ändringar på strukturen och så är det ont om plats för att kunna installera vibrations isolatorer. En tredje metod är istället att implementera passiv dämpning i form av dämpningsmattor på ytor av strukturen där kritiska vibrationer uppstår. Effekterna av det strukturella uppförandet när dämpningsmattor är applicerade på en viss struktur har studerats i det här examensarbetet. Syftet är att få en fördjupad kunskap om hur dämpningsmattor kan användas för att reducera vibrationer i flygplan strukturer. Den typ av dämpningsmatta som har studerats är känd som Constrained Layer Damping, CLD, vilken är en sandwich av ett visko-elastiskt lager samt ett styvare lager.  Modellerings och simuleringsmetoder som är baserade på kommersiella FE-mjukvaror har utvecklats. Analysmetoderna är baserade på att utföra modalanalys tillsammans med strukturell dämpning. Detta möjliggör att förutse den övergripande dämpningen vid varje strukturell mod. Modellerna för dämpningsmattorna har i det här projektet verifierats med experimental testning av typiska dämpningsmattor. Metodiken kan användas till att prediktera beteendet av dämpade strukturer för att uppnå en effektiv och lättviktig passiv dämpningslösning.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第20760号 / 工博第4412号 / 新制||工||1686(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 杉浦 邦征, 教授 白土 博通, 教授 清野 純史 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

The focus of this thesis was to increase the knowledge in the area of "dynamic friction" during oblique helmet impacts, both experimentally and numerically. Physical experiments have been performed with multiple helmets, different angles of the anvil and different surface materials, with results of impact forces from the anvil and accelerations of the head. By the use of the Coulomb friction model the friction, over time, during the impact of the head and helmet has been calculated. Finite element method has then been used in LS-DYNA to try and replicate the physical results with the goal of creating an accurate friction model. There has been previous work done where the commonly used abrasive paper has been compared to asphalt as ground material in the drop tests. A similar study has been performed in this project which has been compared to the previous work. The results when comparing asphalt to abrasive paper and stainless steel shows that abrasive paper has a higher friction and rotational acceleration of the head compared to asphalt. Stainless steel however displays similar characteristics as asphalt in both friction and accelerations. The load cell used during the experimental testing has been examined carefully since the value of the friction coefficient has differed depending on the angle and the impact location on the anvil. There are still uncertainties surrounding the reliability of the results from the load cell. LS-DYNA has two different ways of modelling friction, one where LS-DYNA uses a modified equation of the Coulomb friction model and another one where the user can insert a table of values on coefficient of friction and relative velocity. Both methods have been used, however the latter method has proven to be more suitable for the kind of tests used in this project. / Fokuset för denna rapport var att öka förståelsen inom området ”dynamisk friktion” under sneda hjälmislag, både experimentellt och numeriskt. Fysiska experiment har genomförts med flertalet hjälmar och olika vinklar samt underlag på städet, med resultat på både krafter från städet samt accelerationer från huvudet. Genom användandet av Coulombs friktionsmodell har friktionen, över tid, under islag med en hjälm beräknats. Finita elementmetoden har använts i LS-DYNA för att försöka efterlikna resultaten från de fysiska experimenten med målet att kunna skapa en friktionsmodell. Det har gjorts liknande arbete tidigare där sandpapper har jämförts mot asfalt som underlagsmaterial i falltesterna. En liknande studie har genomförts i detta projekt vilket har jämförts med den tidigare gjorda studien. Resultaten när asfalt jämförs mot sandpapper och rostfritt stål visar att sandpapper har en högre friktion samt rotations acceleration av huvudet jämfört med asfalt. Rostfritt stål uppvisar dock liknande egenskaper som asfalt när det kommer till både friktion och acceleration. Lastcellen som har använts har undersökts noggrant, då värdet på friktionskoefficienten har förändrats beroende på vinkeln och träffpunkten på städet. Osäkerheter kring trovärdigheten på resultatet från lastcellen kvarstår. LS-DYNA har två olika sätt att modellera friktionen på, antingen så används en modifierad ekvation av Coulombs friktionsmodell eller så skapar användaren en tabell med värden på friktionskoefficienten och den relativa hastigheten. Båda metoderna har använts men det har visat sig att den senare metoden är bättre anpassad för de test som har utförts i detta projekt.

Initial forms of analytical models created to simulate real engineering structures may generally yield dynamic response predictions different than those obtained from experimental tests. Since testing a real structure under every possible excitation is not practical, it is essential to transform the initial mathematical model to a model which reflects the characteristics of the actual structure in a better way. By using structural model updating techniques, the initial mathematical model is adjusted so that it simulates the experimental measurements more closely. In this study, a sensitivity-based finite element (FE) model updating method using experimental frequency response (FRF) data is presented. This study bases on a technique developed in an earlier study on the computation of the so-called Mis-correlation Index (MCI) used for identifying the system matrices which require updating. MCI values are calculated for each required coordinate, and non-zero numerical values indicate coordinates carrying error. In this work a new model updating procedure based on the minimization of this index is developed. The method uses sensitivity approach. FE models are iteratively updated by minimizing MCI values using sensitivities. The validation of the method is realized through some case studies. In order to demonstrate the application of the method for real systems, a real test data obtained from the modal test of a scaled aircraft model (GARTEUR SM-AG19) is used. In the application, the FE model of the scaled aircraft is updated. In the case studies the generic software developed in this study is used along with some commercial programs.

The course of polymer film functioning has been a crucial concern in the advent of packaging technology. The thesis project aims towards obtaining an understanding of mechanical properties for a class of these materials, namely LDPE and PET. A constitutive understanding of this behavior in the case of LDPE is acquired through incorporating a plastic stress strain relationship in an iterative approach with focus put on the sensitivity of a few parameters by following a simple linear curve-fit technique in a way that the global as well as the local response are predictable. FE-models also developed in this way are validated with experimental data. An inverse analysis testing validity or usefulness of DIC technique in identifying a material model is done and some discussions are drawn towards this area. A relative numerical study with respect to experimentally obtained global response for tearing of these polymers is done through use of a similar material model developed from tensile tests and the challenges faced in this area have been addressed.

Mobile Miner 40V is a machine used for rock excavation and developed by Epiroc. This machine is equipped with a large cutter wheel to perform the excavation. After a test run, some surfaces associated with bearings within the cutter wheel were found to be damaged due to scuffing - severe sliding wear. There is a static load applied to the surfaces due to gravity. However, the reason for this damaged issue was believed that there is a large dynamic load applied to the surfaces during the excavation. This dynamic load was not found in a previous FE model used to verify safety issues. Therefore, a new FE model that is more in line with reality, and a failure analysis were required. Additionally, a feasibility study for a cutter wheel with a larger dimension was also needed since a larger cutter wheel is desirable. Firstly, wear mechanisms were reviewed, and some theories were chosen to analyze the damaged issue. Since it was unknown whether the surfaces were well-lubricated or not, both cases were investigated. The Archard wear equation was used to analyze the poor-lubricated situation, while the lubrication number and the Reynolds equation were used to analyze the well-lubricated case. Secondly, contact mechanisms between the surfaces were also investigated. The investigation of the contact mechanisms involved several theories, such as the Hertzian contact theory and the impact load factor. Besides these theoretical analyses, a numerical analysis was performed. Lastly, a new FE model was established in Ansys. Both the cutter wheel which was subjected to scuffing(existing cutter wheel), and the cutter wheel with a larger dimension(larger cutter wheel) were analyzed by the use of the new FE model. The maximum and minimum wear rates obtained by the Archard wear equation are approximately 1.9・10-2mm3/m and 4.8・10-3mm3/m, which are considered as a completely unacceptable level in engineering applications. The maximum and minimum critical loads obtained by the Reynold equation are approximately 1.8kN and 24.8kN, which both are larger than the static load applied to the surfaces. The maximum and minimum critical mean contact pressures obtained by the lubrication number are approximately 65MPa and 240MPa, which both are larger than the mean contact pressure generated by the static load. No evidence shows that there is a large dynamic load applied to the surfaces during the excavation. The largest possible contact pressure on the bearings in the existing cutter wheel is very close to the limit of severely damaged. The largest possible contact pressure on the bearings in the larger cutter wheel is believed to exceed the limit of severely damaged. The previous assumption that the surfaces were damaged due to a large dynamic load was wrong. The obtained results support that the surfaces were only subjected to a static load and were damaged due to inadequate lubrication. The existing cutter wheel is operated safely with the current load cases. However, the forward thrust force is suggested to decrease when the cutting angle is large. There is a high risk if the larger cutter wheel is operated with the current load cases.

For intermediate floors in residential and office buildings, as well as in parking garages and malls, there is a wide use of hollow core concrete slabs in Sweden today. Hollow core slabs are precast and prestressed concrete elements with cylindrical-shaped voids extending along the length of the slab. These structural elements have the advantage compared to cast-in-situ concrete slabs that they have a high strength, due to the prestressing, and that the voids allow for a lower self-weight. Additionally, the voids allow for a reduction in the use of concrete material. These characteristics offer possibilities to build long-span floors with slender designs. However, a consequence of the slenderness of the slabs is that such floors have an increased sensitivity to vibrations induced by various dynamic loads. In residential and office buildings vibrations are primarily caused by human activity, and therefore concerns related to the serviceability of such floors are raised. These vibrations are often not related to problems with structural integrity, but rather to different aspects of comfort of the residents or workers. The aim of this thesis is to provide additional information regarding the dynamic behavior of hollow core floors. An experimental modal analysis has been performed on an existing floor in an office building. The dynamic properties in the form of natural frequencies, mode shapes, damping ratios and frequency response functions were derived and analyzed from these measurements. Subsequently, several finite element models were developed, aiming to reproduce the experimental dynamic behavior of the studied floor. The measurements initially showed some unexpected dynamic responses of the floor. For this reason, more advanced methods of signal analyses were applied to the data. The analyses showed that the slab has some closely spaced modes and that the modes of the floor are complex to a certain degree. The finite element models were studied with different configurations. In particular, the effect the model size, boundary conditions, material properties and potential structural discontinuities have on the dynamic response of the slab was studied. Sufficiently good agreement has been achieved between the experimental and numerical results in terms of natural frequencies and mode shapes. The acceleration amplitude responses of the numerical models were generally higher than the ones obtained from the measurements, which leads to difficulties in matching of the frequency response functions. / Håldäck i betong används idag i stor utsträckning som bjälklag i bostads- och kontorsbyggnader, liksom i parkeringsgarage och köpcentra. Håldäcksbjälklag består av prefabricerade och förspända betongelement, med cylindriska hål som sträcker sig i plattans längsriktning. Dessa konstruktionselement har fördelen, jämfört med platsgjutna betongplattor, att de har en hög hållfasthet på grund av förspänningen och att hålen möjliggör en lägre egenvikt. Dessutom gör hålen att en mindre mängd betongmaterial behövs. Dessa egenskaper ger möjligheter att bygga golv med långa spännvidder och slank design. En konsekvens av slankheten är emellertid att sådana golv har en ökad känslighet för vibrationer som orsakas av olika dynamiska belastningar. I bostads- och kontorsbyggnader orsakas vibrationer främst av mänsklig aktivitet, och därför finns det en del oro relaterad till sådana golvs brukbarhet. Dessa vibrationer är oftast inte relaterade till frågor om strukturell integritet, utan snarare till olika aspekter av boendes eller arbetares känsla av komfort. Syftet med detta examensarbete är att bidra till kunskapen om håldäcksbjälklags dynamiska beteende. En experimentell modalanalys har utförts på ett befintligt golv i en kontorsbyggnad. De dynamiska egenskaperna i form av egenfrekvenser, modformer, dämpning och frekvenssvarsfunktioner erhölls och analyserades med hjälp av dessa mätningar. Därefter utvecklades flera finita element modeller för att reproducera det experimentellt uppmätta dynamiska beteendet hos det studerade golvet. Mätningarna visade initialt något oväntade dynamiska responser från golvet. Av denna anledning applicerades mer avancerade signalanalysmetoder på datan. Analyserna visade att plattan har några moder inom ett litet frekvensintervall och att moderna till en viss grad är komplexa. De finita element modellerna studerades med olika konfigurationer. I synnerhet studerades effekten av modellstorleken, randvillkoren, materialegenskaperna och potentiella strukturella diskontinuiteter på golvets dynamiska respons. Tillräckligt bra överensstämmelse har uppnåtts mellan de experimentella och numeriska resultaten i form av egenfrekvenser och modformer. Accelerationsamplituderna för de numeriska modellerna var i allmänhet högre än de som erhölls under mätningarna, vilket leder till svårigheter att matcha frekvenssvarsfunktionerna.

Dagens planering och projektering av konstruktioner präglas av ett resursutnyttjande, miljömässigt och ekonomiskt tänk, där resultatet kan medföra brister med avseende på dynamiken. Därmed är det ytterst viktigt att skapa goda förutsättningar för noggranna beräkningsmodeller som i ett projekteringsskede kan representera konstruktionernas dynamiska beteende. I denna rapport utfördes en jämförelseanalys mellan en FE-modell och en fältmätning, där Folke Bernadottes bro har använts som underlag. Syftet är att presentera skillnader och likheter i naturliga frekvenser och modformer baserat på jämförelseanalysen, samt belysa några av de viktigaste faktorerna bakom dessa. Resultatet visade för en kalibrerad FE-modell 11 % genomsnittlig skillnad för de naturliga frekvenserna och 99 % överensstämmelse med avseende på modformerna, där den mest väsentliga parametern i modellen var upplagsvillkoren. / Today's planning and design of constructions is characterized by a resource utilization, environmental and economic thinking, where the result can lead to shortcomings with regard to dynamic behaviour. Thus, it is extremely important to create good conditions for accurate calculation models that in a design phase can represent the dynamic behaviour of the structures. In this report, a comparison analysis was performed between an FE-model and a field measurement, where Folke Bernadotte's bridge has been used as basis. The purpose is to present differences and similarities in natural frequencies and mode shapes based on the comparative analysis, and to highlight some of the most important factors behind these. The result showed for a calibrated FE-model an average difference of 11 % for the natural frequencies and 99 % agreement with respect to the mode shapes, where the most important parameter in the model was the support conditions.