Unique features of behavior of granular materials make constitutive modeling of these materials a challenge that has not yet been answered completely. Because volume changes are so important for the type of behavior exhibited by frictional materials, it is important to correctly incorporate them in constitutive models, both in terms of their rate of development and their magnitude. In this study a number of consolidated drained triaxial tests are performed to find those features of sand behavior that can be considered "material parameters" and can be used for constitutive modeling of granular soils. Special attention is given to those features of material behavior that are related to dilatancy. A number of published experimental data are also analyzed and useful trends of soil behavior are found.

Published Article / The paper presents a critical review of the techniques that are used to cool plastic injection moulds. It examines research on cooling of injection moulds by conventional cooling, the benefits and the limitations of the method. It compares the deployment mechanisms that have been proposed by various researchers. It also examines how the various mechanisms affect the plastic cooling rate and the overall heat transfer performance of the mould and how the various deployments affect the stress distribution of the mould and mould durability. The paper also presents the possibilities that have been presented by rapid prototyping. It discusses the development of conformal cooling as an alternative to conventional cooling. It presents the state of the art on the method. The paper presents the deficiencies in the current theories on conformal cooling and suggests areas that require further work in order to fully exploit the technique.

A constitutive model based on rate-independent elastoplasticity concepts is developed and used to simulate the behavior of geologic materials under arbitrary three-dimensional stress paths. The model accounts for various factors such as friction, stress path and stress history that influence the behavior of geologic materials. A hierarchical approach is adopted whereby models of progressively increasing sophistication are developed from a basic isotropic-hardening associative model. Nonassociativeness is introduced as correction or perturbation to the basic model. Deviation of normality of the plastic strain increments to the yield surface F is captured through nonassociativeness. The plastic potential Q is obtained by applying a correction to F. This simplified approach restricts the number of extra parameters required to define the plastic potential Q. The material constants associated with the model are identified, and they are evaluated for three different sands (Leighton Buzzard, Munich and McCormick Ranch). The model is then verified by comparing predictions with laboratory tests from which the constants were found, and typical tests not used for finding the constants. The effect of varying initial density of a material on the stress-strain and volumetric response is investigated. An empirical relation is proposed, whereby one parameter is modified based on the initial density, such that improved predictions can be obtained without increasing the total number of parameters. Implementation of the nonassociative model in a finite element program to solve boundary value problems leads to a nonsymmetric stiffness matrix. Besides, using a nonsymmetric solver, three numerical schemes are investigated. The idea of the schemes is to modify the stiffness matrix such that a symmetric equation solver can be used. Prediction of stress-strain, volumetric response and CPU time for different schemes are compared with the predictions obtained using the nonsymmetric solver. The nonsymmetric equation solver used less CPU time and the solutions were more accurate. Based on the above findings, a soil-footing system is analyzed using the finite element techniques. The associative and nonassociative models are used to predict the behavior. For the nonassociative model, solution is obtained by using a nonsymmetric solver. Results obtained from both models are compared with a model footing test performed in the laboratory.

State-of-the-art solar-thermal flat-plate collectors suffer from a limited potential to decrease production costs for the necessary higher economic benefit of so-lar-thermal systems. Costly metallic materials and corresponding manufactur-ing processes prevent further cost reductions. For that issues, plastic materials can offer a promising approach. The main hurdle for the use of cost-effective plastics lies in the high thermal loads on the collector components — absorber and insulation — which were identified in a field-testing. The necessary overheating protection approaches to lower these thermal loads were investigated in a literature review. A large number of relevant concepts was evaluated related to achievable temperature reduction, influence on solar yield, additional costs and intrinsic safety. There-fore, a mathematical model was developed to determine the solar-thermal col-lector´s behaviour in a solar-thermal system for hot water and space heating. This way, the most promising overheating concepts were simulated and ana-lysed with regard to component temperatures and system performance. Omitting the selective absorber coating and reducing the backside insulation was found to be the most suitable solution for component materials with limited temperature resistance like polypropylene. In the second part of the research, collector design concepts were developed on the basis of the characteristics of plastic material processing. The identified unit costs showed savings of more than 50 % in comparison to stateof- the-art collectors. The analysis regarding temperature loads and annual solar yield by simulation proved the performance of the concepts. The collector costs and the simulation results were used to define the total costs of the solar-thermal sys-tems and to evaluate the economic benefits by means of the collector con-cepts. The benefits were similar to state-of-the-art set-ups. Thus, further adjustments at system level are necessary to lower the total costs. Therefore, the system set-up has to be harmonised with the collector requirements and investigated in detail.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

The behavior of porous media subjected to any arbitrary loading is a complex phenomenon due to the coupled nature of the problem. Proper understanding of this coupled behavior is essential in dealing with many of the geotechnical engineering problems. A very general three-dimensional formulation of such a coupled problem was first reported by Biot; however, a two-dimensional idealization of the theory is used here with extension to nonlinear material behavior. A finite element computer code is developed to analyze the response of coupled systems subjected to both static and dynamic excitations. The code can also be used to solve problems involving only solid media by suppressing the presence of fluid. The generalized anisotropic hardening model is implemented into the finite element procedure to characterize nonlinear material behavior throughout the realm of its deformation process. Both drained and undrained conditions are considered in order to verify the performance of the model in capturing material behavior. Three different materials are considered for this purpose. The predictions obtained using the anisotropic model for both drained and undrained condition yield satisfactory comparison with observed behavior. The finite element procedure is verified by solving several problems involving undrained, consolidation and dynamic responses of coupled system. Good agreements are found between numerical and analytical results. Further verification of the computer code and the material model is performed by solving two boundary value problems. For this purpose, a laboratory pressuremeter test subjected to quasi-static loading condition and a building foundation system subjected to rapid earthquake excitation were analyzed. The results of this research have provided an improved understanding of coupled behavior of porous media. The procedure developed here can be effectively used under a wide range of loading conditions varying from very slow quasi-static to very rapid earthquake excitations.

Analysis and design of structures supported by geological media pose various complexities such as nonlinear behavior of supporting media, nature of loading, irregularities in geometry and boundary condition, and the interaction effects. It is extremely difficult to find closed-form solutions for such problems. So often, numerical techniques such as finite difference, finite element and boundary integral methods are used. In this research two soil-structure interaction problems are analyzed using the finite element method involving fully three-dimensional idealizations. In order to incorporate nonlinear behavior of a soil, a nonlinear elastic (hyperbolic model), and generalized single surface plasticity model including hardening are implemented in the finite element program for analysis of a pile group foundation, and an anchor in sands, respectively. The parameters required to define these models are determined from comprehensive laboratory stress-strain data obtained by using a multiaxial testing device. Typical stress paths are back predicted using the generalized plasticity model to verify that it is capable of predicting those paths, and is found to be satisfactory. In order to include the interaction effects resulting in relative slip and debonding or crack and openings at the junction between two dissimilar materials, the thin-layer element model is implemented. Load deformation behavior, force and stress distributions in various components of pile group foundation, and the anchor-soil system are predicted by using the numerical procedure. The predictions are compared with results from a model test for the pile group and field observations for the anchor problem; the comparisons are found to be satisfactory. The effects of soil nonlinearity and interface behavior are also delineated and it is found that their inclusion, particularly in case of anchors analysis, can substantially effect the behavior of the system. Detailed analysis of the results permits an increased understanding of the stress deformation mechanisms of the three-dimensional problems.

No description available.

No description available.

No description available.