The autogenous shrinkage due to self-desiccation of high- and ultra-high performance concretes with very low water-cement ratio in case of restraint leads to considerable stresses starting from very early age. The resultant risk of cracking presently cannot be adequately investigated. Parameters that are particularly difficult to capture experimentally are the concrete temperature and the viscoelasticity. The primary objective of this work was to assess as precise as possible the autogenous shrinkage cracking propensity of representative concretes at strong restraint and constant room temperature. Test methods needed to be chosen and enhanced in a way that preferably allowed for the efficient and precise investigation of all relevant factors in the future. Ideally, a method suitable for a complete empirical modeling was provided. First the methodological requirements and the advantages and disadvantages of existing test methods were discussed. Based on this, optimized test methods were proposed. Their suitability was verified using the example of ultra-high strength concrete. The choice of concrete compositions considered the essential measures for reducing shrinkage (internal curing, shrinkage-reducing admixtures, reduction of the fraction of Portland cement in the binder). The autogenous shrinkage was measured with the shrinkage cone method. This new test method was validated by investigations of the repeatability and reproducibility and proved efficient and precise. It allows for measurements under non-isothermal conditions; no established test method exists for that purpose to date. The autogenous shrinkage of the ultra-high strength concretes at the age of 24 h, investigated under quasi-isothermal conditions (20 °C), was between 0,25 mm/m and 0,70 mm/m. It was particularly low when a shrinkage-reducing admixture was added and when superabsorbent polymers were used. The stresses due to restraint were determined with the restrained ring test. A large part of the stresses to be expected according to Hooke’s Law were eliminated by creep and relaxation. The relaxation capacity being very pronounced at very early age was the main reason that no visible cracking occurred, not even with the concretes with high autogenous shrinkage. The development of the autogenous shrinkage cracking propensity was described as ratio of restraint stress and splitting tensile strength. By means of modified ring tests, used to determine the maximum tensile stress, it could be shown that the ratio of stress to strength is an appropriate failure criterion. However, the cracking propensity can be calculated correctly only if the strongly age-dependent ratio of uniaxial to splitting tensile strength is accounted for. Besides, it needs to be considered that at very early age a plastic stress redistribution may occur in restrained ring tests. The reference concrete showed a high cracking propensity of up to 0.68. The fact that shrinkage-reducing measures led to significantly lower values reveals their relevance for the safe application of ultra-high strength concrete. However, the investigations carried out here at 20 °C do not allow for a final assessment of the cracking propensity under typical on-site conditions. To empirically model the autogenous shrinkage cracking propensity as a function of temperature and stress level in the future, an analytical stress solution for non-isothermal restrained ring tests and a new approach for investigating the residual stress and relaxation capacity by means of non-passive restrained ring tests was suggested.:1 Introduction 2 Autogenous shrinkage 5 2.1 Shrinkage and hydration 5 2.2 Definitions and research approaches 10 2.3 Metrological issues 14 2.3.1 Multitude of test methods 14 2.3.2 Time-zero 16 2.3.3 Other metrological issues 18 2.4 Corrugated tube method 19 2.5 Influencing parameters 21 2.5.1 Concrete composition 21 2.5.2 Temperature 23 2.5.3 Specific countermeasures 25 2.6 Summary and conclusions with respect to the own work 25 3 Concretes used in the own investigations 27 3.1 Preliminary remarks 27 3.2 Concrete compositions 27 3.3 Constituents 28 3.3.1 Cement 28 3.3.2 Ground-granulated blast furnace slag 28 3.3.3 Silica fume 28 3.3.4 Admixtures 29 3.3.5 Aggregates 29 3.4 Mixing 29 3.5 Basic properties 30 3.5.1 Compressive strength 30 3.5.2 Splitting tensile strength 31 3.5.3 Modulus of elasticity 33 3.5.4 Analysis of mechanical properties 35 3.5.5 Coefficient of thermal expansion 38 3.5.6 Isothermal calorimetry 39 3.6 Summary 39 4 Shrinkage cone method for measuring autogenous shrinkage 41 4.1 Introduction 41 4.2 Setup and measurement procedure 41 4.3 Temperature control 44 4.4 Precision under quasi-isothermal conditions 47 4.4.1 Repeatability 47 4.4.2 Reproducibility 49 4.4.3 Shrinkage cone method vs. corrugated tube method 49 4.5 Autogenous shrinkage of the investigated concretes at 20 °C 54 4.6 Tests under non-isothermal conditions 55 4.7 Summary 56 5 Stress and cracks due to restrained autogenous shrinkage 58 5.1 Introduction 58 5.2 Degree of restraint 58 5.3 Formation of cracks 60 5.4 Very early age and importance of stress relaxation 63 5.5 Creep and cracking - further methodological aspects 65 5.6 Autogenous shrinkage cracking propensity 69 5.7 Role of temperature history 70 5.8 Further state of knowledge 72 5.8.1 Preliminary remarks on test methods 72 5.8.2 Quantitative investigations under restraint conditions 73 5.8.3 A full-scale model for assessing the cracking risk at very early age 77 5.9 Summary 78 6 Investigation of the autogenous shrinkage cracking propensity 80 6.1 Introduction 80 6.2 Suitability of temperature-stress testing machines 80 6.2.1 Development, setup and use 80 6.2.2 Results of round robin tests 83 6.3 Restrained ring test - methodological foundations 86 6.3.1 Setup and use 86 6.3.2 Evaluation of restrained ring tests 90 6.3.3 Use of temperature changes for the investigation of creep and relaxation 96 6.4 Own investigations with the restrained ring test 97 6.4.1 Setup 97 6.4.2 Compensation of disturbing temperature effects 99 6.4.3 Repeatability 100 6.4.4 Measured steel ring strains 101 6.4.5 Simple stress analysis 102 6.4.6 Autogenous shrinkage cracking propensity - further analysis 106 6.4.7 Thermal stress component 116 6.4.8 Period of maximum cracking propensity 118 6.4.9 Restraint stress versus autogenous shrinkage 119 6.4.10 Cracking propensity versus autogenous shrinkage 120 6.4.11 Further considerations on creep 121 6.5 Summary 126 7 Summary, conclusions and outlook 128 7.1 Summary and conclusions 128 7.2 Outlook 130 8 Literature 131 9 Annex 159 / Das durch Selbstaustrocknung verursachte autogene Schwinden von besonders leistungsfähigen Betonen mit sehr niedrigem Wasserzementwert führt bei Dehnungsbehinderung bereits in sehr frühem Alter zu erheblichen Zwangsspannungen. Die Gefahr der Rissbildung, die sich daraus ergibt, lässt sich bislang nur unzureichend untersuchen. Experimentell besonders schwer zu erfassende Faktoren sind die Betontemperatur und die Viskoelastizität. Das vorrangige Ziel der Arbeit war die möglichst genaue Ermittlung der autogenen Schwindrissneigung repräsentativer Betone bei starker Dehnungsbehinderung und konstanter Raumtemperatur. Dabei waren die Prüfverfahren möglichst so zu wählen und weiterzuentwickeln, dass sich zukünftig alle relevanten Faktoren effizient und genau untersuchen lassen. Im Idealfall sollte eine Methode entstehen, die eine vollständige empirische Modellierung erlaubt. Zunächst wurden die methodischen Anforderungen und die Vor- und Nachteile existierender Prüfverfahren diskutiert. Darauf aufbauend wurden optimierte Verfahren vorgeschlagen. Ihre Eignung wurde an ultrahochfestem Beton überprüft. Bei der Auswahl der Betone wurden die wesentlichen Maßnahmen zur Schwindreduzierung berücksichtigt (innere Nachbehandlung, schwindreduzierende Zusatzmittel, Verringerung des Portlandzementanteils am Bindemittel). Das autogene Schwinden wurde mit dem Schwindkegelverfahren gemessen. Das neue Verfahren wurde durch Untersuchungen zur Wiederhol- und Vergleichsgenauigkeit validiert und erwies sich als effizient und genau. Es ermöglicht Messungen unter nicht-isothermen Bedingungen; hierfür existiert bisher kein etabliertes Verfahren. Das autogene Schwinden der untersuchten ultrahochfesten Betone unter quasi-isothermen Bedingungen (20 °C) betrug im Alter von 24 h zwischen 0,25 mm/m und 0,70 mm/m. Besonders gering war es bei Zugabe eines schwindreduzierenden Zusatzmittels bzw. Verwendung superabsorbierender Polymere. Mit dem Ring-Test wurden die bei Dehnungsbehinderung entstehenden Spannungen ermittelt. Ein großer Teil der gemäß Hooke’schem Gesetz zu erwartenden Spannungen wurde durch Kriechen und Relaxation abgebaut. Die im sehr frühen Alter stark ausgeprägte Relaxationsfähigkeit war der wesentliche Grund dafür, dass es selbst bei Betonen mit hohem autogenen Schwinden zu keiner erkennbaren Rissbildung kam. Die Entwicklung der autogenen Schwindrissneigung wurde als Verhältnis von Zwangsspannung und Spaltzugfestigkeit beschrieben. Durch modifizierte Ring-Tests, mit deren Hilfe die maximale Zugspannung ermittelt wurde, konnte gezeigt werden, dass das Verhältnis von Spannung und Festigkeit als Versagenskriterium geeignet ist. Die Rissneigung lässt sich aber nur dann korrekt berechnen, wenn das stark altersabhängige Verhältnis von einaxialer Zugfestigkeit und Spaltzugfestigkeit berücksichtigt wird. Außerdem ist zu beachten, dass es im sehr frühen Alter zu einer plastischen Spannungsumlagerung in Ring-Tests kommen kann. Der Referenzbeton wies eine hohe Rissneigung von bis zu 0,68 auf. Dass die schwindreduzierenden Maßnahmen zu deutlich geringeren Werten führten, zeigt deren Bedeutung für den sicheren Einsatz von ultrahochfestem Beton. Die hier bei 20 °C durchgeführten Untersuchungen erlauben allerdings keine abschließende Bewertung der Rissneigung unter baustellentypischen Bedingungen. Um die autogene Schwindrissneigung zukünftig als Funktion der Temperatur und des Lastniveaus empirisch modellieren zu können, wurden eine analytische Spannungslösung für nicht-isotherme Ring-Tests und ein neuer Ansatz zur Untersuchung der Resttrag- und Relaxationsfähigkeit mit Hilfe nicht-passiver Ring-Tests vorgeschlagen.:1 Introduction 2 Autogenous shrinkage 5 2.1 Shrinkage and hydration 5 2.2 Definitions and research approaches 10 2.3 Metrological issues 14 2.3.1 Multitude of test methods 14 2.3.2 Time-zero 16 2.3.3 Other metrological issues 18 2.4 Corrugated tube method 19 2.5 Influencing parameters 21 2.5.1 Concrete composition 21 2.5.2 Temperature 23 2.5.3 Specific countermeasures 25 2.6 Summary and conclusions with respect to the own work 25 3 Concretes used in the own investigations 27 3.1 Preliminary remarks 27 3.2 Concrete compositions 27 3.3 Constituents 28 3.3.1 Cement 28 3.3.2 Ground-granulated blast furnace slag 28 3.3.3 Silica fume 28 3.3.4 Admixtures 29 3.3.5 Aggregates 29 3.4 Mixing 29 3.5 Basic properties 30 3.5.1 Compressive strength 30 3.5.2 Splitting tensile strength 31 3.5.3 Modulus of elasticity 33 3.5.4 Analysis of mechanical properties 35 3.5.5 Coefficient of thermal expansion 38 3.5.6 Isothermal calorimetry 39 3.6 Summary 39 4 Shrinkage cone method for measuring autogenous shrinkage 41 4.1 Introduction 41 4.2 Setup and measurement procedure 41 4.3 Temperature control 44 4.4 Precision under quasi-isothermal conditions 47 4.4.1 Repeatability 47 4.4.2 Reproducibility 49 4.4.3 Shrinkage cone method vs. corrugated tube method 49 4.5 Autogenous shrinkage of the investigated concretes at 20 °C 54 4.6 Tests under non-isothermal conditions 55 4.7 Summary 56 5 Stress and cracks due to restrained autogenous shrinkage 58 5.1 Introduction 58 5.2 Degree of restraint 58 5.3 Formation of cracks 60 5.4 Very early age and importance of stress relaxation 63 5.5 Creep and cracking - further methodological aspects 65 5.6 Autogenous shrinkage cracking propensity 69 5.7 Role of temperature history 70 5.8 Further state of knowledge 72 5.8.1 Preliminary remarks on test methods 72 5.8.2 Quantitative investigations under restraint conditions 73 5.8.3 A full-scale model for assessing the cracking risk at very early age 77 5.9 Summary 78 6 Investigation of the autogenous shrinkage cracking propensity 80 6.1 Introduction 80 6.2 Suitability of temperature-stress testing machines 80 6.2.1 Development, setup and use 80 6.2.2 Results of round robin tests 83 6.3 Restrained ring test - methodological foundations 86 6.3.1 Setup and use 86 6.3.2 Evaluation of restrained ring tests 90 6.3.3 Use of temperature changes for the investigation of creep and relaxation 96 6.4 Own investigations with the restrained ring test 97 6.4.1 Setup 97 6.4.2 Compensation of disturbing temperature effects 99 6.4.3 Repeatability 100 6.4.4 Measured steel ring strains 101 6.4.5 Simple stress analysis 102 6.4.6 Autogenous shrinkage cracking propensity - further analysis 106 6.4.7 Thermal stress component 116 6.4.8 Period of maximum cracking propensity 118 6.4.9 Restraint stress versus autogenous shrinkage 119 6.4.10 Cracking propensity versus autogenous shrinkage 120 6.4.11 Further considerations on creep 121 6.5 Summary 126 7 Summary, conclusions and outlook 128 7.1 Summary and conclusions 128 7.2 Outlook 130 8 Literature 131 9 Annex 159

The diploma thesis aims to analyze bent FRP reinforcements. It describes the method of production of bent FRP reinforcement, examples of application of FRR reinforcement in structures and mentions aggressive influences influencing the durability of FRP reinforcement. Furthermore, an experiment is proposed to monitor changes in straight and bent FRP reinforcement stored in an aqueous environment at 20 °C and an alkaline environment at 20 °C and 40 °C. The output of the diploma thesis is the evaluation of changes in mechanical properties and durability. The condition of the FRP reinforcement is documented using optical and electron mocroscopy.

This master's thesis deals with the design of two asphalt mixtures for a wearing course containing 35 % R-material. The asphalt mixtures use a soft bitumen modified with crumb rubber (CRMB) or the unmodified soft binder itself with a penetration grade of 70/100. The work verifies the effect of crumb rubber as a bitumen modifier on the properties of the asphalt mixture with reclaimed asphalt pavement (RAP). At the same time, the work deals with the possibility of using higher amounts of reclaimed asphalt pavement only in combination with a softer binder without the use of rejuvenating additives. The properties of asphalt binders and mixtures are verified using suitable functional tests. Furthermore, the proposed mixtures and their results are compared from various perspectives. At the same time, the thesis in the theoretical part deals with the dosing of a reclaimed asphalt pavement into the asphalt mixture and describes the handling and use of reclaimed asphalt pavement in the Czech Republic and abroad

The diploma thesis deals with the use of recycled asphalt with aggregate in a hydraulically bound mixtures. The mixture is determined in the base or sub-base course of the pavement. The theoretical part of the diploma thesis describes the base course of the pavement, the production of recyclates from construction demolition waste, the acquisition and processing of recycled asphalt, the road reuse and recycling. The thesis is enriched by a contribution from the implementation of recycled asphalt laying into the base course of the communication company SKANSKA a.s. and ČNES a.s. The next chapter describes detailed experiences with recycling abroad. The thesis also contains a description of laboratory tests, which are important for evaluating the properties of mixtures with recycled asphalt. The practical part verifies the suitability of the mixture of recycled asphalt and aggregate for the road surface by testing the transverse tensile strength, compressive strength and frost and water resistance. The mixtures used are found to be suitable for pavement base course.

Thermoelectric generators (TEG) are re-emerging technology that can be used to recover heat waste from commercial and industrial processes to generate electricity, enhancing fuel utilization and lowering greenhouse gas emissions. TEG modules are solid-state heat engines that produce no noise or vibration during operation. Notably, TEG modules are also able to operate at low-temperature differences, which makes them ideal for a wide range of heat waste recovery applications. Annular thermoelectric generator (ATEG) modules are optimal in applications where either the heat source or sink are round in shape. Bi2Te3 solution-based compounds are of significant interest in the application of thermoelectric materials (TE) used in low-temperature cooling and power generation applications. The main objective of the current work is to design a mechanically reliable ring-shaped ATEG module with a predictable performance using spark plasma sintered Bi2Te3 TE material for low temperature waste heat recovery applications. In terms of structure, this work is divided into two parts. The first part investigates how the use of a powder pre-treatment technique affects the mechanical and thermoelectric properties of P- and N-type Bi2Te3. In addition, part one also presents the measurements of these materials’ mechanical and thermoelectric properties, which serve as inputs for the finite element models used to design thermoelectric modules with parallel and perpendicular configurations vis-a-vis the sintering pressing direction. The second part evaluates the thermoelectric performance and thermal stresses of a ring-shaped ATEG couple that has been integrated between hot-side and cold-side heat exchangers. To this end, two configurations are compared with respect to their heat/electrical current flow paths: one that allows for radial flow (radial configuration), and one that allows for axial flow (axial configuration). The P- and N-type Bi2Te3 powder was treated using a mechanically agitated fluidized powder reduction facility that was built in-house. The characteristic uniaxial tensile strength of the P-type Bi0.4Sb1.6Te3 increased from 13.9 MPa to 26.3 MPa parallel to the sintering pressure, and from 16.3 MPa to 30.6 MPa perpendicular to the sintering pressure following oxide reduction using 5% H2 ˗ 95% Ar at 380 ℃ for 24 h. The figure of merit, ZT, increased from 0.35 to 0.80 and from 0.42 to 1.13 at room temperature (25 ℃) in the parallel and the perpendicular directions, respectively, after the surface oxide reduction treatment. On the other hand, the annealing effects of the oxide reduction pr-treatment of the N-type (Bi0.95 Sb0.05)2(Se0.05 Te0.95)3 using 5% H2 ˗ 95% Ar at 380 ℃ for 24 h were found to be responsible for the majority of the mechanical properties and ZT enhancement. Additionally, the characteristic uniaxial tensile strengths for this material increased from 30.4 to 34.1 MPa and from 30.8 to 38 MPa in the parallel and the perpendicular directions, respectively. The ZTmax (150 ℃) increased from 0.54 to 0.63 in both the parallel and perpendicular directions due to oxide reduction, while annealing led to an increase to 0.58 and 0.62 in the parallel and the perpendicular directions, respectively. An analytical model was constructed to compare the thermoelectric performance of the two configurations under three different hot-side thermal resistances, and a 3D coupled finite element ANSYS model was constructed to study and compare the thermal stresses of the two configurations at different dimensions. The two models were then used to create 2D maps in order to investigate the effects of ATEG couple configuration and dimensions, as well as the hot-side thermal resistance, with the goal of identifying the optimum design. The optimization of module geometry requires a trade-off between performance and mechanical reliability. The results of these investigations showed that increases in the temperature difference across the ATEG couple (ΔT) led to increases in both power and thermal stresses in both configurations. When both configurations were generating the same power at ΔT = 105 ℃, the thermal stresses in the radial configuration were as much as 67 MPa higher than those in the axial configuration due to the formation of additional tensile hoop stresses. The lowest thermal stress obtained for the axial couple configuration was 67.8 MPa, which was achieved when the couple had an outer diameter of 16 mm, an axial thickness of 1 mm, a ΔT of 14.8 ℃, and power generation of 10.4 mW per couple. The maximum thermal stress values were located at the corners of the interface between the solder and the TE rings due to the mismatched coefficient of thermal expansion. This thesis makes a novel contribution to the state-of-the-art literature in ring-shaped ATEG modules, as it details a well-characterised spark plasma sintered Bi2Te3 TE material and a methodology for designing a ring-shaped ATEG module with reliable, robust, and predictable thermoelectric and mechanical performance. The details of the contribution made by this work have been disseminated in the form of three journal publications, which have been integrated into this sandwich Ph.D. thesis. / Thesis / Doctor of Science (PhD)

Much study has been carried out to determine the properties of Lamellar Graphite Iron (LGI) or grey iron and their relations to factors such as the cooling rate, the dendrite morphology, the pouring temperature, and so on. However, there hasn’t been much comprehensive study on the properties of LGI outside the generally used and accepted composition, with 1 to 3% Silicon. The scope of this study is to measure and evaluate the thermal conductivity and tensile strength of LGI, for a higher concentration of  Si and different carbon contents. The concentration of Si aimed for was 4% but the concentration obtained after spectroscopy was between 4.1% to 4.15%. There are two hypereutectic, one near-eutectic and three hypoeutectic samples considered and these six chemical compositions were cast under different cooling conditions . The cooling time has been varied by providing different molds of 30mm, 55mm, and 80mm diameter cylinders respectively, for all the six sample compositions. The microstructure analysis carried out studies the segregation of Si, the graphite morphology, primary austenite morphology. These factors are then compared to the thermal and tensile behavior measured in this study. It can be observed that the thermal conductivity studied in the present work has a direct correlation for a higher Si content and tends to be greater than the thermal conductivity values observed from other studies with lower content Of Si. However, the conductivity shows an inverse relation with the cooling rate and is maximum for the samples with the lowest cooling rate. The tensile strength, on the other hand, seems to have a lower value than that observed in previous studies for LGI with 1 to 3% Si, but shows a direct correlation with the cooling rate. The mean area fraction of dendrites obtained and the mean interdendritic hydraulic diameter is also measured and their influence on the properties are also studied. The addition of more Si has greatly favored the thermal behavior positively but has also reduced the tensile strength.

Das Ziel dieser Arbeit besteht in der Erforschung des Zusammenhangs zwischen der Struktur der Metalloberfläche und der Verbundfestigkeit von thermisch gefügten Thermoplast-Metall-Verbunden. Dazu wird für die Haftungsmechanismen Stoff-, Kraft- und Formschluss an einem Minimalbeispiel rechnerisch gezeigt, dass verschiedene Oberflächenmerkmale (wahre Oberfläche, Strukturdichte, Aspektverhältnis, Hinterschnitte, Substrukturen) mit der Verbundfestigkeit in Verbindung stehen. Basierend darauf werden Oberflächenkenngrößen (standardisierte Rauheitsparameter, fraktale Dimension) gewählt, die die haftungsfördernden Strukturmerkmale möglichst umfassend einbeziehen. Daraus werden Hypothesen abgeleitet, die die Prognostizierbarkeit der Verbundfestigkeit aus Oberflächenkenngrößen für Thermoplast-Metall-Verbunde postulieren. Die experimentelle Überprüfung erfolgt an Aluminium im Verbund mit Polyamid 6 bzw. Polypropylen in Rohrtorsions-, Rohrzug- sowie Zugscherversuchen. Die Einstellung der Oberflächenstruktur des Aluminiums erfolgt durch mechanisches Strahlen, alkalisches Ätzen, thermisches Spritzen sowie Laserstrukturieren. Die Erfassung der Oberflächenstruktur erfolgt taktil sowie aus Querschliffaufnahmen. Die Höhe der Verbundfestigkeit kann anhand der Oberflächenstruktur erklärt und teilweise mit hoher Korrelation quantitativ in Verbindung gebracht werden. Bei taktiler Messung verhindert jedoch eine unzureichende Erfassung bestimmter Strukturmerkmale eine exakte Abbildung der tatsächlichen Oberflächenstruktur. Bei der Erfassung der Oberflächenstruktur aus Querschliffaufnahmen stellt die erreichbare Bildauflösung und -qualität einen limitierenden Faktor dar. Ebenso können aus der Oberflächenstruktur keine individuellen, strukturspezifischen Versagensmechanismen abgeleitet werden.:Inhaltsverzeichnis 5 Abbildungsverzeichnis 9 Tabellenverzeichnis 14 Abkürzungsverzeichnis 16 Symbolverzeichnis 17 1 Motivation 20 2 Stand der Wissenschaft und Technik 22 2.1 Verwendete Begriffe 22 2.2 Verbundwerkstoffe und Werkstoffverbunde 22 2.2.1 Faser-Kunststoff-Verbunde 24 2.2.2 Polymer-Metall-Verbunde 25 2.3 Fügen von Polymer-Metall-Verbunden 27 2.3.1 In-Mold Assembly 28 2.3.2 Kleben 28 2.3.3 Montage 29 2.3.4 Thermisches Fügen 31 2.4 Prüfung der Verbundfestigkeit 34 2.4.1 Prüfkörpergeometrien 34 2.4.2 Beständigkeit gegen Umwelteinflüsse 36 2.5 Verfahren zur Vorbehandlung der Metalloberfläche 38 2.5.1 Mechanisches Strahlen 39 2.5.2 Laserstrukturieren 40 2.5.3 Chemische und elektrochemische Verfahren 43 2.5.4 Beschichten 43 2.5.5 Weitere Verfahren 44 3 Zusammenhang zwischen Oberflächenstruktur und Verbundfestigkeit 46 3.1 Haftungsmechanismen 47 3.1.1 Stoffschluss 48 3.1.2 Kraftschluss 50 3.1.3 Formschluss 51 3.1.4 Skalenabhängigkeit 53 3.1.5 Eigenspannungen 54 3.1.6 Folgerungen 54 3.2 Charakterisierung der Oberflächenstruktur und Korrelation mit der Verbundfestigkeit 55 3.2.1 Standardisierte Rauheitsparameter 56 3.2.2 Fraktale Dimension 58 3.2.3 Anwendungsbeispiel 59 4 Zielstellung 62 4.1 Folgerungen aus dem Stand der Wissenschaft und Technik 62 4.2 Forschungshypothesen 63 5 Experimentelle Vorgehensweise 64 5.1 Charakterisierung der Ausgangswerkstoffe 64 5.2 Vorbehandlung der Metalloberflächen 67 5.2.1 Mechanisches Strahlen und alkalisches Ätzen 67 5.2.2 Thermisches Spritzen 68 5.2.3 Laserstrukturieren 68 5.3 Charakterisierung der Oberflächenstruktur 69 5.4 Mechanische Verbundprüfung 71 5.5 Verwendeter Fügeprozess 73 5.6 Statistische Betrachtung 75 6 Ergebnisse und Diskussion 77 6.1 Verbundfestigkeit in Abhängigkeit von der Oberflächenvorbehandlung 77 6.1.1 Rohrproben 77 6.1.1.1 Oberflächencharakteristika und Benetzung 77 6.1.1.2 Verbundfestigkeit und Korrelation mit Oberflächenkennwerten 81 6.1.1.3 Bruchflächenanalyse 85 6.1.2 Zugscherproben 90 6.1.2.1 Oberflächencharakteristika und Benetzung 90 6.1.2.2 Verbundfestigkeit und Korrelation mit den Oberflächenkennwerten 91 6.1.2.3 Bruchflächenanalyse 93 6.1.3 Ergebnisdiskussion 95 6.2 Verbundfestigkeit in Abhängigkeit von der Skalierung 97 6.2.1 Oberflächencharakteristika und Benetzung 97 6.2.2 Verbundfestigkeit und Korrelation mit Oberflächenkennwerten 102 6.2.3 Bruchflächenanalyse 102 6.2.4 Ergebnissdiskussion 106 7 Zusammenfassung und Folgerungen 108 8 Ausblick 112 Literaturverzeichnis 115 Anhang 129 / The aim of this work is to investigate the relationship between the structure of the metal surface and the compound strength of thermally joined thermoplastic-metal compounds. For this purpose, equations are derived for the adhesion mechanisms of material, force and form closure using a minimal example, which link various surface characteristics (true surface, structure density, aspect ratio, undercuts, substructures) with the compound strength. Based on this, surface parameters (standardized roughness parameters, fractal dimension) are chosen that incorporate the adhesion-promoting structural features as comprehensively as possible. From this, hypotheses are derived that postulate the predictability of compound strength from surface parameters for thermoplastic-metal composites. Experimental verification is carried out on aluminum in compounds with polyamide 6 or polypropylene in hollow cylinder torsion tests, hollow cylinder tensile tests as well as tensile shear tests. The surface of the aluminum is structured by mechanical blasting, alkaline etching, thermal spraying and laser structuring. The surface structure is recorded tactilely and from transverse micrographs. The height of the compound strength can be explained on the basis of surface structure and, in part, quantitatively related with high correlation. However, in the case of tactile measurement, nondetection of certain structural features prevents accurate mapping of the actual surface structure. When recording the surface structure from cross-section images, the achievable image resolution and quality is the limiting factor. Likewise, no individual, structure-specific failure mechanisms can be derived from the surface structure.:Inhaltsverzeichnis 5 Abbildungsverzeichnis 9 Tabellenverzeichnis 14 Abkürzungsverzeichnis 16 Symbolverzeichnis 17 1 Motivation 20 2 Stand der Wissenschaft und Technik 22 2.1 Verwendete Begriffe 22 2.2 Verbundwerkstoffe und Werkstoffverbunde 22 2.2.1 Faser-Kunststoff-Verbunde 24 2.2.2 Polymer-Metall-Verbunde 25 2.3 Fügen von Polymer-Metall-Verbunden 27 2.3.1 In-Mold Assembly 28 2.3.2 Kleben 28 2.3.3 Montage 29 2.3.4 Thermisches Fügen 31 2.4 Prüfung der Verbundfestigkeit 34 2.4.1 Prüfkörpergeometrien 34 2.4.2 Beständigkeit gegen Umwelteinflüsse 36 2.5 Verfahren zur Vorbehandlung der Metalloberfläche 38 2.5.1 Mechanisches Strahlen 39 2.5.2 Laserstrukturieren 40 2.5.3 Chemische und elektrochemische Verfahren 43 2.5.4 Beschichten 43 2.5.5 Weitere Verfahren 44 3 Zusammenhang zwischen Oberflächenstruktur und Verbundfestigkeit 46 3.1 Haftungsmechanismen 47 3.1.1 Stoffschluss 48 3.1.2 Kraftschluss 50 3.1.3 Formschluss 51 3.1.4 Skalenabhängigkeit 53 3.1.5 Eigenspannungen 54 3.1.6 Folgerungen 54 3.2 Charakterisierung der Oberflächenstruktur und Korrelation mit der Verbundfestigkeit 55 3.2.1 Standardisierte Rauheitsparameter 56 3.2.2 Fraktale Dimension 58 3.2.3 Anwendungsbeispiel 59 4 Zielstellung 62 4.1 Folgerungen aus dem Stand der Wissenschaft und Technik 62 4.2 Forschungshypothesen 63 5 Experimentelle Vorgehensweise 64 5.1 Charakterisierung der Ausgangswerkstoffe 64 5.2 Vorbehandlung der Metalloberflächen 67 5.2.1 Mechanisches Strahlen und alkalisches Ätzen 67 5.2.2 Thermisches Spritzen 68 5.2.3 Laserstrukturieren 68 5.3 Charakterisierung der Oberflächenstruktur 69 5.4 Mechanische Verbundprüfung 71 5.5 Verwendeter Fügeprozess 73 5.6 Statistische Betrachtung 75 6 Ergebnisse und Diskussion 77 6.1 Verbundfestigkeit in Abhängigkeit von der Oberflächenvorbehandlung 77 6.1.1 Rohrproben 77 6.1.1.1 Oberflächencharakteristika und Benetzung 77 6.1.1.2 Verbundfestigkeit und Korrelation mit Oberflächenkennwerten 81 6.1.1.3 Bruchflächenanalyse 85 6.1.2 Zugscherproben 90 6.1.2.1 Oberflächencharakteristika und Benetzung 90 6.1.2.2 Verbundfestigkeit und Korrelation mit den Oberflächenkennwerten 91 6.1.2.3 Bruchflächenanalyse 93 6.1.3 Ergebnisdiskussion 95 6.2 Verbundfestigkeit in Abhängigkeit von der Skalierung 97 6.2.1 Oberflächencharakteristika und Benetzung 97 6.2.2 Verbundfestigkeit und Korrelation mit Oberflächenkennwerten 102 6.2.3 Bruchflächenanalyse 102 6.2.4 Ergebnissdiskussion 106 7 Zusammenfassung und Folgerungen 108 8 Ausblick 112 Literaturverzeichnis 115 Anhang 129

The rapid growth of plastic waste from food packaging around the world demands renewable substitutes, such as natural fibers and biocomposites. Wood fibers are natural fibers extracted from trees and are commonly used in packaging. In order for renewable alternatives to compete against plastics and other non-renewable materials, a better understanding of the mechanical properties of single fibers at the micro-scale are necessary. A great deal of previous research into the mechanical properties of single wood fibers has focused on their tensile behavior, however, little work has been published about their compressive behavior. It is difficult to measure the compressive strength of single fibers directly due to fiber buckling. The purpose of this study is to investigate how post-buckling of single wood pulp fibers affects the mechanical properties of fibers in tension. Two alternative hypotheses were tested through experiments in The Odqvist Laboratory for Experimental Mechanics at KTH. The major part of the thesis process has been invested in developing components called grippers, and testing methods for the Single Fiber Testing System, in order to be able to perform the experiments. The existing grippers were tested and alternative grippers were developed, as well as an alternative testing method without grippers, called the Paper frame method (PFM). PFM was used in the final experimental work to test the hypotheses. The main finding from this study is that there is not enough evidence to suggest that the tensile strength or tensile stiffness of single wood fibers are significantly reduced by post-buckling damage. This finding is mostly relevant in the research and development of fibrous material with larger distances between individual fibers, such as low-density fiber network materials. The main findings from the single fiber testing methods development were that the existing grippers cannot prevent fiber slippage. Furthermore, the alternative gripper 22A with its arc design generates higher grip force than previous grippers but lacks surface friction in the contact region in order to prevent fiber slippage. PFM has an experimental success rate of over 80 % for trained users and easy usage for the operator. The testing equipment Single Fiber Testing System displays several systematic errors occurring in the post-processing process of tests with cyclic loads. / Den snabba tillväxten av plastavfall från livsmedelsförpackningar runt om i världen kräver förnybara alternativ, såsom förpackningar gjorda av naturfibrer och biokompositer. Träfibrer är naturliga fibrer som utvinns från trä och används ofta i förpackningar. För att dessa förnybara alternativ ska kunna konkurrera mot plast och andra icke-förnybara material krävs en bättre förståelse av de mekaniska egenskaperna hos enskilda fibrer på mikronivå. Det finns en omfattande forskning om de mekaniska egenskaperna i drag hos enskilda träfibrer. Däremot existerar det lite publicerad forskning om träfibrers kompressionsegenskaper. Kompressionsegenskaperna är svåra att mäta direkt på grund av fiberknäckning. Syftet med denna studie är att undersöka hur skadan som uppstår efter knäckning av enskilda träfibrer påverkar de mekaniska egenskaperna hos fibrer i drag. Två alternativa hypoteser testades genom experiment i Odqvistlaboratoriet för experimentell mekanik vid KTH. Huvuddelen av examensarbetet har investerats i att utveckla grepparmar och testmetoder för testmaskinen Single Fiber Testing System, för att kunna utföra experiment. De befintliga grepparmarna testades och nya grepparmar utvecklades, och även en alternativ testmetod utan grepparmar som kallas Paper frame method (PFM) utvecklades. PFM användes i det sista experimentella arbetet för att pröva hypoteserna. Huvudslutsatsen från denna studie är att det inte finns tillräckligt med bevis för att stödja hypotesen att enskilda träfibrers draghållfasthet eller dragstyvhet reduceras av skada som uppstår efter knäckning. Detta resultat är mest relevant för forskning och utveckling av fibernätverks material med större avstånd mellan fibrerna, såsom fibermaterial med låg densitet. Huvudslutsatserna från utvecklingen av testmetoder var att de befintliga grepparmarna inte kunde förhindra fiberglidning. Den alternativa grepparmen 22A med sin bågkonstruktion genererade högre greppkraft än tidigare grepparmar men saknar rätt beläggning i kontaktområdet för att förhindra glidning av fiber. PFM har en hög test framgångsgrad med över 80 % för erfarna användare och den är enkel att arbeta med. Testmaskinen Single Fiber Testing System visar flera systematiska fel som blir märkbar under dataanalys av tester med cykliska belastningar.

The purpose of the work is to study the effect of fiber on the physical and mechanical characteristics of concrete and to develop recommendations for the production of dispersed reinforced structures. As a result of the research work, the principles of optimizing the structure of fiber concrete due to the influence of fiber length on the mechanical strength properties are proposed. Using graphical methods derived statistical dependence of the qualitative characteristics (prism strength, modulus of elasticity, Poisson's ratio) of fiber-reinforced concrete from prescription-technological parameters of the dispersed reinforcement, which improves the bearing capacity of concrete structures or to reduce the amount of steel reinforcement. / Цель работы - изучение влияния фибры на физико-механические характеристики бетона и разработка рекомендаций по изготовлению дисперсно-армированных конструкций. В результате проведенной исследовательской работы предложены принципы оптимизации структуры фибробетона за счет влияния длины волокон на механико-прочностные свойства. С помощью графических методов выведены статистические зависимости качественных характеристик (призменная прочность, модуль упругости, коэффициент Пуассона) фибробетонов от рецептурно-технологических параметров дисперсного армирования, что позволяет повышать несущую способность бетонных конструкций или уменьшать расход стальной арматуры.

Increasing demand for structural health monitoring in space highlights the need to make the creation of these systems more accessible. This study investigates the potential of additive manufacturing to achieve this goal by characterizing a self-sensing material made of a commercially available 3D-printed continuous carbon fibre filament. The results demonstrate the feasibility of converting the filament into a strain sensor with improved sensitivity compared to conventional foil strain gauges. Mechanical and electromechanical properties of the self-sensing material were characterized, including an ultimate tensile strength of 45.09 ± 3.45 MPa, a failure strain of 38.93 ± 3.41%, and a base resistance of 759.11Ω. The tensile gauge factor was calculated to be 467.06 ± 375.90 within the strain range of 0% to 3.8% with a linearity (R2) of 0.93. For the first time, a systematic literature review compares mechanical and electromechanical properties to enable material selection for mechanical design incorporating self-sensing material. The study highlights that the spread of material properties in a group of materials indicates how well-developed a material is for self-sensing purposes. This study advances our understanding of the feasibility of using additive manufacturing to create self-sensing materials for structural health monitoring systems and opens up new avenues for further research.