Ground Improvement by Deep Vibratory Methods

Vibro compaction and vibro stone columns are the two dynamic methods of soil improvement most commonly used worldwide. These methods have been developed over almost eighty years and are now of unrivalled importance as modern foundation measures. Vibro compaction works on granular soils by densification, and vibro stone columns are used to displace and reinforce fine-grained and cohesive soils by introducing inert material. This second edition includes also a chapter on vibro concrete columns constructed with almost identical depth vibrators. These small diameter concrete piles are increasingly used as ground improvement methods for moderately loaded large spread foundations, although the original soil characteristics are only marginally improved. This practical guide for professional geotechnical engineers and graduate students systematically covers the theoretical basis and design principles behind the methods, the equipment used during their execution, and state of the art procedures for quality assurance and data acquisition. All the chapters are updated in line with recent developments and improvements in the methods and equipment. Fresh case studies from around the world illustrate the wide range of possible applications. The book concludes with variations to methods, evaluates the economic and environmental benefits of the methods, and gives contractual guidance

Ground Improvement by Deep Vibratory Methods

Vibro compaction and vibro stone columns are the two dynamic methods of soil improvement most commonly used worldwide. These methods have been developed over almost eighty years and are now of unrivalled importance as modern foundation measures. Vibro compaction works on granular soils by densification, and vibro stone columns are used to displace and reinforce fine-grained and cohesive soils by introducing inert material. This second edition includes also a chapter on vibro concrete columns constructed with almost identical depth vibrators. These small diameter concrete piles are increasingly used as ground improvement methods for moderately loaded large spread foundations, although the original soil characteristics are only marginally improved. This practical guide for professional geotechnical engineers and graduate students systematically covers the theoretical basis and design principles behind the methods, the equipment used during their execution, and state of the art procedures for quality assurance and data acquisition. All the chapters are updated in line with recent developments and improvements in the methods and equipment. Fresh case studies from around the world illustrate the wide range of possible applications. The book concludes with variations to methods, evaluates the economic and environmental benefits of the methods, and gives contractual guidance

Design and fabrication of a tapped densification apparatus for bulk solids

Experiments are commonly used to ascertain the flow properties of bulk solids. One such property is a measurement quantity known as the tapped density. Here, a container of granular material is subjected to a long sequence of discrete taps, after which the bulk density - the total mass divided by the volume occupied –- is determined. Current technology exists to achieve the maximum tap density by subjecting a container to a user defined number of taps at a specific, predetermined amplitude and frequency. However, the final bulk density is known to be dependent on the tap parameters. It can therefore be beneficial to alter both the frequency and the amplitude during the experimental process to determine what role these two factors contribute to the tap density of a sample. Thus, the topic of this thesis is the design, fabrication and testing of a mechanical system device that allows for finite control of the tap stroke and force, as well as quantitative measurement feedback for the motion of the sample. The first phase of the work consisted of the design and fabrication of a prototype system, which was tested for the proper functioning of the mechanical components. The results of the tests suggested modifications were required. A series of revisions were preformed on the prototype in order to satisfy the updated design requirements. Final tests and calibrations were preformed on the new apparatus and the results are discussed

Synthesis, Processing, and Characterization of the Cobalt Alloys with Silicon Addition

The composition of the cobalt alloys contains only noncytotoxic elements (Cr, Si, and Mo) that ensure its biocompatibility, and consequently, the development and proliferation of cells at the implant/tissue interface. The cobalt alloy has an original composition with silicon addition and the proportion of the alloying elements was established so as to ensure a high biocompatibility and adequate physical-chemical characteristics for it to be used in various applications. Silicon is known to be a metal with a high biocompatibility; it can replace noble/non-noble metals in commercial alloys, thereby excluding the occurrence of any toxic corrosion products. We chose it as an alloying element because it confers good casting properties, has double role as hardener and oxidant, ensures an increase in the resistance to tear, and offers a proper fluidity in the liquid phase

Transparent glasses obtained by unconventional sintering

openGlasses are conventional manufactured by melting natural sand or silicon compounds at high temperatures. The traditional melting method requires high energy input to reach the melting temperature of precursors. Conventional solid-state sintering of powders is a valid alternative to reduce the processing temperature; however it requires time consuming thermal treatment to obtain densification. With the aim of reducing the environmental impact, energy, temperature and cost, the thesis project carried out in collaboration with the University of Lyon 1 aims to develop new ways of producing glass by employing unconventional sintering approaches. During the experimental work, three different strategies are explored: synthesis of nanoparticles at a low glass transition temperature, cold sintering process on commercial sub-micrometer particles borosilicate glass, the Spark Plasma sintering process on nanostructured silica nanoparticles. - Synthesis of nanoparticles with a low glass transition temperature: using a modifying Stober synthesis, including tetraethyl orthosilicate, as silicon precursor, and boron, calcium and sodium salts or alkoxides as precursors of modifier oxides, capable of lowering the glass transition temperature. Several parameters were investigated such as the type of precursor, the molar ratio of the oxide precursors to TEOS, the concentration of the solution and the calcination temperature. The results showed that particles with a diameter of about 150 nm were obtained, with a strong presence of organic residue. The glass transition temperature was about 950°C, likely due to the lack of successful incorporation of modifier oxides into the silica network. - Cold Sintering Process: a basic sodium hydroxide solution was selected as a liquid phase to promote densification at low temperatures. The main parameters investigated were the following: temperature, pressure, liquid/solid molar ratio and residence time of the powder in the mould. Density measurements by means of the Archimedes test and pycnometer revealed the following best parameter combinations: Pressure P=300MPa, temperature T=250°C, % liquid/mass =40, residence time t in the mould = 30 min; Pressure P=300MPa, temperature T=200°C, % liquid/mass =20, dwell time t in the mould = 120 min, The lack of an unit value of relative density is an indication of sintering having only partially taken place, which is confirmed by the high porosity visible through SEM characterisation analysis, and the lack of transparency. - Spark Plasma Sintering: the silicon oxide particles pre-treated at 900°C (in order to remove water and carbonate groups absorbed) were subjected to the sintering process by Spark Plasma. During the operations, the pressure and dwell time values were chosen and kept fixed (2GPa and 3 minutes respectively), allowing the effect of the key parameter of temperature to be assessed. Characterisation of the samples produced, carried out using SEM and Raman spectroscopy, revealed the following: * Crystallization occurs at 2GPa for temperature above 1000°C * Densification and transparency occur for a temperature of 800°C. In-situ measurements of the process combined with Archimedes density test show, however, that the sintering process is not complete. *An initial sintering step takes place at temperatures around 500°C; one could develop the idea of future experiments by decreasing the temperature, so as to decrease the energy consumption required to achieve densification. This thesis work shows that it is indeed possible to produce transparent glass using unconventional sintering techniques. From these preliminary investigations, it's possibile to confirm an important role of the particles dimension for the obtainment of dense and transparent glass components.Glasses are conventional manufactured by melting natural sand or silicon compounds at high temperatures. The traditional melting method requires high energy input to reach the melting temperature of precursors. Conventional solid-state sintering of powders is a valid alternative to reduce the processing temperature; however it requires time consuming thermal treatment to obtain densification. With the aim of reducing the environmental impact, energy, temperature and cost, the thesis project carried out in collaboration with the University of Lyon 1 aims to develop new ways of producing glass by employing unconventional sintering approaches. During the experimental work, three different strategies are explored: synthesis of nanoparticles at a low glass transition temperature, cold sintering process on commercial sub-micrometer particles borosilicate glass, the Spark Plasma sintering process on nanostructured silica nanoparticles. - Synthesis of nanoparticles with a low glass transition temperature: using a modifying Stober synthesis, including tetraethyl orthosilicate, as silicon precursor, and boron, calcium and sodium salts or alkoxides as precursors of modifier oxides, capable of lowering the glass transition temperature. Several parameters were investigated such as the type of precursor, the molar ratio of the oxide precursors to TEOS, the concentration of the solution and the calcination temperature. The results showed that particles with a diameter of about 150 nm were obtained, with a strong presence of organic residue. The glass transition temperature was about 950°C, likely due to the lack of successful incorporation of modifier oxides into the silica network. - Cold Sintering Process: a basic sodium hydroxide solution was selected as a liquid phase to promote densification at low temperatures. The main parameters investigated were the following: temperature, pressure, liquid/solid molar ratio and residence time of the powder in the mould. Density measurements by means of the Archimedes test and pycnometer revealed the following best parameter combinations: Pressure P=300MPa, temperature T=250°C, % liquid/mass =40, residence time t in the mould = 30 min; Pressure P=300MPa, temperature T=200°C, % liquid/mass =20, dwell time t in the mould = 120 min, The lack of an unit value of relative density is an indication of sintering having only partially taken place, which is confirmed by the high porosity visible through SEM characterisation analysis, and the lack of transparency. - Spark Plasma Sintering: the silicon oxide particles pre-treated at 900°C (in order to remove water and carbonate groups absorbed) were subjected to the sintering process by Spark Plasma. During the operations, the pressure and dwell time values were chosen and kept fixed (2GPa and 3 minutes respectively), allowing the effect of the key parameter of temperature to be assessed. Characterisation of the samples produced, carried out using SEM and Raman spectroscopy, revealed the following: * Crystallization occurs at 2GPa for temperature above 1000°C * Densification and transparency occur for a temperature of 800°C. In-situ measurements of the process combined with Archimedes density test show, however, that the sintering process is not complete. *An initial sintering step takes place at temperatures around 500°C; one could develop the idea of future experiments by decreasing the temperature, so as to decrease the energy consumption required to achieve densification. This thesis work shows that it is indeed possible to produce transparent glass using unconventional sintering techniques. From these preliminary investigations, it's possibile to confirm an important role of the particles dimension for the obtainment of dense and transparent glass components

State Limits of Peloids

State limits are states of a granular material which are asymptotically attained by proportional deformation with constant deformation rate. Peloids (Greek: muds) are mixtures of hydrophilic fine-grained minerals, water, ions, gas bubbles and additives. Well-defined aluminium oxide and laponite peloids are experimentally investigated with respect to the influence of particle interactions on the course of state limits. The transferability of the results to natural peloids is exemplarily shown

Development of Structural Steels for Powder Bed Fusion - Laser Beam

Over the past decade, powder bed fusion – laser beam (PBF-LB) has attracted noticeable attention from both academia and industry. However, there remains a scarcity of approved material for the process, as fewer than 40 alloys are commercially available. Although structural steels are some of the most commonly used materials in traditional manufacturing, they have yet to be developed for PBF-LB as their high carbon content makes them susceptible to cracking. The objective of this thesis was to develop structural steels for PBF-LB by determining the impact of various process parameters on part quality, microstructure and mechanical properties. This involved the production and analysis of various carbon (0.06 to 1.1 wt.% C) and low-alloy steels (AISI 4130, 4140, 4340 and 8620).In terms of part quality, specimen density was related to the volumetric energy density (VED) and the carbon content of the alloy. Regarding the VED, specimens produced at low VED formed lack of fusion porosity, while specimens produced at high VED formed keyhole porosity. As for the carbon content, increasing the carbon content would reduce lack of fusion porosity at low VED, while lowering the required VED to form keyhole porosity. As for cold cracking, this occurred in structural steels with ≥ 0.38 wt.% C as elevated carbon contents would increase specimen hardness. However, cracking could be mitigated by increasing the VED, laser power or build plate preheating temperature, as each enhanced the level of in situ tempering during PBF-LB. From these findings, process windows were established for each structural steel that produced defect-free and high-density specimens (> 99.8%).In terms of the microstructure, the as-built specimens were primarily composed of tempered martensite, with retained austenite also observed in alloys with ≥ 0.75 wt.% C. During PBF-LB, martensite formed during layer melting and was initially in a quenched-like state, with carbon atoms segregating to dislocations and martensite lath boundaries. Subsequent tempering of this martensite was due to micro-tempering within the heat affected zone and macro-tempering within the previously solidified material. Although both influenced martensite tempering, micro-tempering had the most significant effect as it reduced martensite hardness by up to ~380 HV. This noticeable reduction in hardness was due to the precipitation of nano-sized carbides at the previously carbon enriched regions of martensite.Lastly, mechanical testing found that structural steels produced by PBF-LB achieved a high ultimate tensile strength (4140: ∼1400 MPa, 4340: ∼1500 MPa, 8620: ∼1100 MPa), impact toughness (4140:∼90–100 J, 4340:∼60–70 J, 8620:∼150–175 J) and elongation (4140:∼14%, 4340:∼14%, 8620:∼14–15%) that met or exceeded the ASTM standards. Additionally, these specimens displayed limited directional anisotropy due to small grains with weak crystallographic texture, a homogenous microstructure and low levels of internal defects. These findings are meant to highlight that these alloys are not only suitable but actively take advantage of PBF-LB to achieve properties that meet or exceed those of conventionally produced alloys

Reciprocity in Social Networks with Capacity Constraints

Directed links -- representing asymmetric social ties or interactions (e.g., "follower-followee") -- arise naturally in many social networks and other complex networks, giving rise to directed graphs (or digraphs) as basic topological models for these networks. Reciprocity, defined for a digraph as the percentage of edges with a reciprocal edge, is a key metric that has been used in the literature to compare different directed networks and provide "hints" about their structural properties: for example, are reciprocal edges generated randomly by chance or are there other processes driving their generation? In this paper we study the problem of maximizing achievable reciprocity for an ensemble of digraphs with the same prescribed in- and out-degree sequences. We show that the maximum reciprocity hinges crucially on the in- and out-degree sequences, which may be intuitively interpreted as constraints on some "social capacities" of nodes and impose fundamental limits on achievable reciprocity. We show that it is NP-complete to decide the achievability of a simple upper bound on maximum reciprocity, and provide conditions for achieving it. We demonstrate that many real networks exhibit reciprocities surprisingly close to the upper bound, which implies that users in these social networks are in a sense more "social" than suggested by the empirical reciprocity alone in that they are more willing to reciprocate, subject to their "social capacity" constraints. We find some surprising linear relationships between empirical reciprocity and the bound. We also show that a particular type of small network motifs that we call 3-paths are the major source of loss in reciprocity for real networks