The objective of this thesis is to investigate the progressive failure behavior of laminated fiber reinforced composite shell structures under different loading conditions. The laminates are assumed to be orthotropic and the first order shear deformation theory is applied. Three-node layered flat-shell elements are used in the analysis. To verify the numerical results obtained, experimental and analytical results found in literature are compared with the outputs of the study, and the comparison is found to have shown good agreement with the previous work. Rectangular graphite/epoxy composite laminates under transverse loading are analyzed through several boundary conditions and stacking sequences. Maximum stress criteria, Hashin&rsquo / s criteria and Tsai Wu criteria are employed to detect the failure and progressive failure methodology is be implemented according to instantaneous degradation approach. First ply failure, final failure loads, corresponding deformations and failure patterns are presented and compared.

Panel zone is one of the significant parts of beam-column connections in steel structures. Until the 1994 Northridge Earthquake, a few experimental research and parametric studies had been carried out to understand the behavior of the panel zones. However, after the Northridge Earthquake, it was observed that beam-column connections were unable to show presumed seismic performance. Therefore, current design codes needed to be revised to improve seismic performance of connections in general and panel zones in particular. In this research, panel zone deformation demands are examined using explicit three dimensional finite element models and considering different parameters. For this purpose, a frame model with two different beam-column configurations was developed in order to observe the effects of beam depth, the axial load level and the level of seismicity. The frame models were analyzed under twenty different ground motion records. Local strain demands at the panel zones as well as the global frame deformation demands are evaluated. Analysis results revealed that AISC Specification designs allowed panel zone yielding / however, panel zones designed according to FEMA 355D showed minimal yielding for both shallow and deep beam configurations. Based on the analysis results, local shear strain demands in panel zones were expressed as a function of interstory drifts and normalized panel zone thicknesses.

CFRD (Concrete Faced Rockfill Dam) construction becomes more frequent recently not only because of its secure nature, but also its economical cost where its built up material is feasible to obtain. Although CFRDs are known to be safe compared to other dam types, it is behavior during an earthquake loading still not a well-known aspect since it is mostly constructed in regions of low seismicity until now. Considering this fact, this study

<p>A research group at University of Skövde has developed an interphase element for implementation in the commercial FE-software Abaqus. The element is using the Tvergaard & Hutchinson cohesive law and is implemented in Abaqus Explicit version 6.7 using the VUEL subroutine. This bachelor degree project is referring to evaluate the interphase element and also highlight problems with the element.</p><p>The behavior of the interphase element is evaluated in mode I using Double Cantilever Beam (DCB)-specimens and in mode II using End Notch Flexure (ENF)-specimens. The results from the simulations are compared and validated to an analytical solution.</p><p>FE-simulations performed with the interphase element show very good agreement with theory when using DCB- or ENF-specimens. The only exception is when an ENF-specimen has distorted elements.</p><p>When using explicit finite element software the critical time step is of great importance for the results of the analyses. If a too long time step is used, the simulation will fail to complete or complete with errors. A feasible equation for predicting the critical time step for the interphase element has been developed by the research group and the reliability of this equation is evaluated.</p><p>The result from simulations shows an excellent agreement with the equation when the interphase element governs the critical time step. However when the adherends governs the critical time step the equation gives a time step that is too large. A modification of this equation is suggested.</p>

<p>Intensive competition on the global market puts great pressure on manufacturing companies to develop and produce products that meet requirements from customers and investors. One key factor in meeting these requirements is the efficiency of the product development and the production preparation process. Design automation is a powerful tool to increase efficiency in these two processes.</p><p>The benefits of automating the production preparation process are shortened led-time, improved product performance, and ultimately decreased cost. Further, automation is beneficial as it increases the ability to adapt products to new product specifications with production preparations done in few or in a single step. During the automation process, knowledge about the production preparation process is collected and stored in central systems, thus allowing full control over the design of production equipments.</p><p>Three main topics are addressed in this thesis: the flexibility of design automation systems, knowledge bases containing conflicting rules, and the automation of the finite element analysis process. These three topics are discussed in connection with the production preparation process of rotary draw bending.</p><p>One conclusion drawn from the research is that it is possible to apply the concept of design automation to the production preparation process at different levels of automation depending on characteristics of the implemented knowledge. In order to make design automation systems as flexible as possible, the concept of object orientation should be adapted when building the knowledge base and when building the products geometrical representations. It is possible to automate the process of setting up, running, and interpreting finite element analyses to a great extent and making the automated finite element analysis process a part of the global design automation system.</p>

<p>Composite structures can lower the weight of an airliner significantly. The increased production cost, however, requires the application of cost-effective design strategies. Hence, a comparative value is required which is used for the evaluation of a design solution in terms of cost and weight. The direct operating cost (DOC) can be used as this comparative value; it captures all costs that arise when the aircraft is flown. In this work, a cost/weight optimization framework for composite structures is proposed. It takes into account manufacturing cost, non-destructive testing cost and the lifetime fuel consumption based on the weight of the aircraft, thus using a simplified version of the DOC as the objective function.</p><p>First, the different phases in the design of an aircraft are explained. It is then focused on the advantages and drawbacks of composite structures, the design constraints and allowables, and non-destructive inspection. Further, the topics of multiobjective optimization and the combined optimization of cost and weight are addressed. Manufacturing cost can be estimated by means of different techniques; here, feature-based cost estimations and parametric cost estimations proved to be most suitable for the proposed framework. Finally, a short summary of the appended papers is given.</p><p>The first paper contains a parametric study in which a skin/stringer panel is optimized for a series of cost/weight ratios (weight penalties) and material configurations. The weight penalty, defined as the specific lifetime fuel burn, is dependent on the fuel consumption of the aircraft, the fuel price and the viewpoint of the optimizer. It is concluded that the ideal choice of the design solution is neither low-cost nor low-weight but rather a combination thereof.</p><p>The second paper proposes the inclusion of non-destructive testing cost in the design process of the component, and the adjustment of the design strength of each laminate according to the inspection parameters. Hence, the scan pitch of the ultrasonic testing is regarded as a variable, representing an index for the (guaranteed) laminate quality. It is shown that the direct operating cost can be lowered when the quality level of the laminate is assigned and adjusted in an early design stage.</p>

<p>Träbyggnandet i Sverige gick in i en ny era när myndigheterna beslutade att upphäva förbudet mot att bygga byggnader som är högre än två våningar. Denna förändring i lagstiftningen har bidragit till att utveckla träbyggandet under det senaste decenniet. Cross Laminerat Timber (CLT) har blivit erkänt som en ny teknik som använt på ett korrekt sätt ger starka och pålitliga konstruktioner. Materialet visar sig mer och mer intressant huvudsakligen beroende på den styvhet och styrka det visar i olika tester.</p><p>Ett av de projekt som använt CLT som bärande element är Limnologen i staden Växjö 500 kilometer söder om Stockholm. I detta projekt har både väggar och bjälklag med bärande delar av CLT använts. En av utmaningarna i samband med högre träbyggande är att beräkna och ta hänsyn till de vertikala förskjutningarna i stommen. Orsakerna till förskjutningen är momentana samt tidsberoende. I denna uppsats utvärderas dessa vertikala förskjutningar med två olika metoder. Den första av dessa är experimentell. Förskjutningarna mättes av en grupp forskare från Växjö universitet och utvärderas i denna rapport. Den andra är en Finit Element Modell där förskjutningarna simuleras beroende på parametrar som anses viktiga. Resultatet av simuleringen jämförs med de experimentellt erhållna värdena. Simulering är ett viktigt sätt att förutsäga förskjutningar i CLT byggnader i framtiden. Alla modeller har gjorts med hjälp av finita element programmet Abaqus.</p><p>FEM- modellen av Limnologen består av ett väggelement per våning i sex våningar. Detta element är det element där också förskjutningarna mätts på plats. På så sätt kan modell och verklighet jämföras. Förutom väggelement modelleras också bjälklagselement och kopplingen mellan vägg och bjälklag.</p><p>De experimentella resultaten har analyserats i programvaran Matlab. Resultatet blev ett antal grafer som redovisar förloppet. Det viktigaste resultatet är det som visar både den totala relativa förskjutningen samtidigt som den visar fuktkvoten i CLT- skivan. Fuktkvoten beräknades från temperatur och relativ luftfuktighet som båda mättes på plats.</p><p>Slutsatsen är att man med en simulering kan åstadkomma en acceptabel tillförlitlighet med avseende på vertikala förskjutningar. Krympningen har spelat en viktig roll för förskjutningarna. Den maximala förskjutningen som erhållits från mätningar var 21 mm medan det maximala förskjutningen fått från simuleringen baserad på tre olika antaganden var 35 mm, 33 mm och 17 mm. Skillnaden i resultaten kan delvis förklaras av de antaganden som använts för beräkning av fuktkvot och antagandet om fiberriktningen i timret. I simuleringen antogs fuktkvoten vara konstant över alla tre lager i CLT- skivan i de två första fallen. Orienteringen av fibrerna antogs radiell och tangentiell. Det tredje antagandet bygger på att fukten enbart påverkar det yttersta lagret i skivan. Detta antagande är rimligt på grund av tidsåtgången att uppnå fuktjämvikt och på grund av det limlager som skiljer lagren åt och hindrar fukt att vandra från ett lager till ett annat.</p> / <p>The history of timber buildings in Sweden entered a new era when the authorities decided to lift the ban on constructing more than two-storey timber buildings in Sweden. This change in legislations has contributed to the emergence of timber construction during the last decade. The Cross Laminated Timber (CLT) has become recognized as a new technology that used correctly in construction gives strong and reliable structures. The building material is gaining more credit day by day mainly due to the stiffness and strength it proved throughout the tests in projects where it was used.</p><p>One of the projects that used CLT as load bearing elements was Limnologen in the city of Växjö 500 kilometres south of Stockholm. In this project, a system of CLT floors as well as CLT walls has been used. One of the challenges related to medium-rise timber buildings in general is to calculate and take account of the vertical displacement of the whole building. The sources for the displacements are instantaneous elastic as well as time dependent. In this thesis we are introducing two evaluation methods for the vertical displacements in Limnologen. The first is the experimentally measured vertical displacement that was performed by a group of researchers from Växjö University, and the second is a Finite Element Model simulating the vertical displacement according to the factors and parameters thought to be important to be included in the modelling. The output of the simulation was to be compared with the experimentally obtained values. Simulation is an important way to predict the vertical displacement in future CLT buildings. All modelling were done using the finite element software Abaqus.</p><p>The Abaqus model of the Limnologen building consists of six wall elements from six storeys. The modelled wall elements are the wall elements that the vertical displacement devices were installed on. The reason for this is to get a better picture of how the results from the model would yield in comparison to the site measurements. The floor itself and the sylodyn used in the interface between wall and floor were also modelled.</p><p>The data collected from the site were processed in the software Matlab. Several graphs were attained out of the data processing. The most important graph is the one that include both the total relative displacement and the equivalent moisture content in the CLT. The equivalent moisture content was calculated from the measured temperature and relative humidity.</p><p>In this thesis it is concluded that a simulation can accomplish an acceptable reliability with respect to the vertical displacements. The shrinkage factor has played a vital role in simulation of the displacements. The maximum displacement obtained from the measurements was 21 mm while the maximum displacement gained from the simulation based on three different assumptions was 35 mm, 33 mm, and 17 mm respectively with the similar displacement pattern. The difference in the results can partly be explained by the assumptions used for the equivalent moisture content and local coordinate system of the CLT layers. In the simulation the moisture content was assumed to be equal over each layer of the CLT-panel. The first two assumptions were formulated due to the amphibolous grain of the middle layer of the CLT-panel which was considered having effect on the vertical displacement. The third assumption was formulated due to the glue layer between the wood layers of the CLT-panel which was considered having effect on preventing moisture diffuse from one layer to another layer. In reality it is questionable if the moisture content is varied in the different layers of the CLT-panel. The diffusion of the moisture content hasn't been taken into account.</p>

A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes, et al., Nature, 410, pp. 565-567, (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The nonlinear multiscale model is then utilized in a set-based hierarchical design approach to explore the design space over a wide range of inclusion geometries. Finally, prototype NS inclusions are fabricated using an additive manufacturing technique and tested to determine quasi-static inclusion stiffness which is compared with analytical predictions. / text

In this study, excavation of jet-grouted tunnels in ground with strong time-dependent behavior is analyzed. The constant growth of population has led to a constant increase in the price of lands and thus infrastructures. Underground alternatives are becoming more economical. Furthermore, advances in the construction technology have made it feasible to construct tunnels in difficult ground conditions. By providing a grouted arch ahead of the tunnel face, jet-grouting has proved effective for the stability and performance of tunnels in difficult conditions. Given the limited depth of jet-grouting into the face, the jet-grouted arch is loaded soon after installation, when the rigidity of the grouted material is growing significantly. The simultaneous loading and hardening of the jet-grouting makes the tunnel response depend on the excavation rate. Furthermore, in difficult tunneling conditions, the ground material is associated with highly viscous behavior. This behavior is synonymous with delayed deformation depending on the level and duration of the ground loading by the tunnel excavation. In order to show the importance of the time-dependent behaviors, the full-face and the sequential excavation method are compared using three-dimensional and two-dimensional finite element analyses. First, a three-dimensional model is constructed and its results are validated against available analytical solutions for time-independent behaviors. The hardening of the jet-grouting is then introduced into the model by embedding jet-grouting elements through the analysis. In order to account for the ground viscous behavior, an advanced viscoplastic constitutive model is adopted, numerically implemented in FORTRAN, and used in conjunction with finite element software ABAQUS. The excavation methods are compared for the well documented study case of Tartaiguille tunnel. The results indicate that the full-face method outperforms the sequential method in the studied case by installing the tunnel invert closer to the face. The two-dimensional analysis of the tunnel is conducted by using the convergence-confinement method. To this end, a new approach is introduced to use the method for tunnels in time-dependent conditions. The effect of the jet-grouting hardening and the ground viscous behavior is characterized within the new approach by deriving the ground convergence curves. The reverse dependency of these mechanisms on the tunnel advance rate leads to an optimum advance rate, at which minimum tunnel convergence develops. / text

Recycling of plastics always plays an important role in keeping our environment better and safe. With the rise in usage of plastics and industrialization, the need for recycling the plastics has become a big business and is getting bigger. This thesis work was done for a company called Rapid Granulator AB, which works with the recycling of plastics as a big trade in Sweden. Like all the industries across the globe are trying to be economical in every way, Rapid Granulator AB wanted to develop an economical design of their high quality granulating knife. For achieving the economical design, they wanted to study the behaviour of the rotating knife during the process of producing plastic granules. The granulator cutting process was simulated and numerical analysis was done on the rotating knife of a plastic granulator machine by using the finite element code ABAQUS with 3D stress elements to find out the critical stresses and forces acting on the rotating knife. The bolt preload was applied by Abaqus/Standard, and the results of implicit analysis were imported to Abaqus/Explicit for the impact analysis where the flow of stresses on the rotating knife during the impact with materials were simulated and studied. The study was done on knife models of different thickness to see if the thickness of the current knife model can be reduced. Analysis were done also on a knife model assembly with a double sided cutting edge knife to see if the knife model can be used to its full extent. The simulation models and analysis results were given to the company to develop a more economical knife model.