Inelastic deformation is a common but often neglected phenomenon in experimental analysis of metal deformation and in contacts. This neglect leads to degraded measurement accuracy of material properties. Therefore a need arises for material models that a priori incorporate inelasticity. These material models must be simple and comprehensive to have the highest impact in society. This thesis addresses three main sources of inelasticity, namely anelasticity and plasticity in metals and viscosity in contacts. Inelasticity is a dissipative mode of deformation that is mechanically recoverable for anelasticity and viscosity, and irrecoverable for plasticity. We connect the fundamental properties and structures of metallic and soft matter constituents with experimentally accessible measures. The presented models will aid in the development of materials with specific properties that meet the needs of industry. Chapter 2 presents an analytical model of the tensile test tangent moduli and yield points for single-crystallite metals with spatially uniform and nonuniform dislocation distributions across slip systems. The moduli and the onset of plastic flow show a notable dependence on initial dislocation character, spatial dislocation distribution, and loading direction with respect to crystallographic orientations. An improved methodology accounts for elastic compressibility and anisotropy, and the geometric structure of crystal lattices when one measures dislocation network geometry in single metallic crystallites. Chapter 3 contains a seamless, unified stress-strain treatment of dislocation-driven deformation. This treatment combines the three deformation mechanisms of elastic bond stretching, stable dislocation glide, and unstable dislocation glide. The model’s yield criterion connects the bowing out of local dislocation links and global dislocation multiplication. A semi-empirical relation is constructed for the evolution of the dislocation network structure with uniaxial loading. Chapter 4 formulates a macromechanical model of the yield point phenomenon under invariant plane conditions. The heterogeneous stress state across the Lüders front and the plastic flow inside the Lüders band are accounted for. The Lüders band orientation with respect to the tensile direction is not unique; the orientation changes with material properties and tensile specimen geometry by the stress concentration at the front. The model serves to approximate constitutive parameters independent of the test conditions. Chapter 5 elucidates the interplay between adhesion and roughness by modelling the retraction of rigid, wavy indenters from viscoelastic substrates. Viscoelasticity governs adhesive hysteresis across all loading rates, and even in the presence of roughness-induced mechanical instabilities. This confirms the central role that viscoelasticity must play in experimental measurements in the presence of adhesive interfaces in soft matter contacts. Chapter 6 examines the static, quasi-static, and dynamic trajectories of a base-excited mass-spring-damper system in the presence of friction. The differences between the dynamic and the quasi-static solution in engineering problems with viscous, static, and dry friction are assessed. The omission of inertial contributions will under-predict dissipation at both low and high excitation frequencies. This chapter is a guide for future (multi-scale) numerical modelling efforts on adhesion and interface friction, and the hysteretic deformation of metals. Chapter 7 is a general discussion on the impact of inelasticity in metals, that follows from Chapters 2 and 3, the measurement of the yield point phenomenon in Chapter 4, and numerical modelling of dissipative contacts in Chapters 5 and 6. The four models as presented in Chapters 2-6 are readily applicable in experimental measurements and future numerical models. The importance of accounting for inelasticity in experimental measurement and modelling of the yield strength in metals, and adhesive dissipation in soft matter contacts is emphasised. Finally, the state of the art in research on the three main sources of inelasticity and potential applications of the presented models are enumerated, which serve as starting points of future research.@en

The recent possibilities given by additive manufacturing in free shape design have been seen as a potential breakthrough in the design and production of structural components of a racecar and more generally their influences on the future lightweight strategies in the automotive industry is expected to influence the next generation of products. Among the emerging techniques for the production of metal products, Direct Metal Laser Sintering (DMLS) and Selective Laser Melting (SLM) technologies are becoming technically ahead of the competition: the possibility of direct production of aluminum and titanium alloys components with good surface finishing and net shape from CAD geometry is nowadays a concrete option for the mechanical designer. The purpose of the present study is to demonstrate the feasibility of thementionedAMtechniques and to exploit their potentialweight saving opportunities in the design of highly structurally optimized racing components while determining the current state-of-art of AM for metallic components. The present project reports the design and production of two car components redesigned in the perspective of the novel manufacturing techniques. The first component is the rear top wishbone bracket of the rear suspension. The production has been developed following the best practices for the design of additively manufactured structures such as complete topology optimization and a reconstruction with special focus on the design for manufacturing assessment. The bracket has been developed for DMLS manufacturing in titanium alloy Ti6Al4V. On the contrary, the second component has been developed in a novel aluminumalloy: the Scalmalloy, commercial name of a high strength aluminum alloy specifically developed for high strength to weight critical applications. For this novel material a characterization campaign has been set up comprehending tensile testing, micro-graphical analysis, tomography inspection and an X-ray analysis. Both component underwent a full scale fatigue testing. Both components proved an achievement in terms of weight saving between 7% and 10%with the same functionality and performance level of the machine counterparts. The material characterization campaign revealed the concrete maturity of the DMLS process for Ti6Al4V while the process of SLM production of Scalmalloy requires some final tuning. The tensile strength levels achieved are compliant for both materials’ specifications but the presence of localized lack of fusion in the Scalmalloy specimens reduced the final ductility of the material considerably. The obtained results are an encouraging step towards the application of the analyzed technology in structural components for the motorsport industry and possibly, in the near future, for the wider automotive industry. The limited standardization in the quality processes is addressed as well with a concrete proposal for establishing a controlled level of defects in additively manufactured components.

Microstructure-corrosion property correlation is an open question in the field of materials science. The microstructure of metals and alloys consists of several features with different individual corrosion response. The corrosion behavior of the macroscopic system is an outcome of the complex interaction of the components of microstructure. Hence, a definitive understanding of the corrosion response of the microstructural features is needed for improving the material durability and design.In the present work, the effect of grain size  on the active corrosion behavior of pure iron is investigated. Samples with different grain sizes are obtained by annealing heat-treatment. The microstructure of samples is characterized by optical microscopy, electron backscatter diffraction and X-ray diffraction. Electrochemical characterization using potentiodynamic polarization and electrochemical impedance spectroscopy are performed on the samples in deaerated 0.1 M and 0.01 M H2SO4 solutions. The surface topography of the corroded sample surface is characterized by atomic force microscopy. Following the experiments, a numerical corrosion model is attempted to replicate the observations. The results reveal an aggregate effect of grain size and crystallographic orientation of grains on the corrosion behavior of the samples.

Highly-loaded low-speed roller bearings are frequently used in equipment offshore e.g. slew bearings in crane, sheave bearings and FPSO turret bearings. Reducing maintenance costs, increasing productivity, ensuring safety of people and structural integrity and longevity assurance of equipment can be achieved by the condition monitoring of highly-loaded low-speed roller bearings. Currently, very limited research is performed in the field of condition monitoring with acoustic emission (AE) monitoring for highly-loaded low-speed (<10 rpm) bearings with naturally developed damage. Acoustic emission monitoring has shown promising results in early stage and real time identification of defects according to literature. Furthermore, contamination of wear particles in lubricant shows an increase in AE activity according to literature. In this research, the applicability of AE monitoring for damage assessment of highly-loaded low-speed roller bearings is investigated in a full scale duration test. Furthermore, the influence of contaminated lubricant with steel particles is investigated in the contamination test to study the feasibility of real-time detection of contaminated lubricant during operations and as a supporting technique for wear debris analysis in lubricant. From the results, an increase in AE activity expressed in hit-rates is observed for a wide frequency band of 40 - 580 kHz during the duration test where the basic rating lifetime (L10) is consumed from 40% to 50%. Wear development in the bearing is observed during visual inspection and has been quantified with lubrication analysis. A safety limit and a limit if the bearing is at risk for the AE activity has been defined with the results of the baseline and duration test. This research suggests that AE monitoring can be applied on highly-loaded low-speed bearings to assess the damage for representative operational conditions. From the results of the lubricant contamination test, an increased AE activity with respect to higher lubricant contamination levels were observed. Furthermore, with a proper choice of the SNR-level, there is no masking effect of acoustic emission signals due to contaminated lubricant. The results of the contamination tests, indicates the possibility of detecting contaminated lubricant with AE monitoring.

The society of Delft Aerospace Rocket Engineering (DARE) aims at launching the Stratos IV sounding rocket to an apogee of 100km; thus cementing their place as one of the few student teams that have had the unique opportunity to design and build a rocket that is capable of reaching the frontiers of space. In doing so, DARE has entered flight supersonic regimes during atmospheric entry. With the development of cryogenic engines in the pipeline, future DARE missions look at reaching the hypersonic velocity regimes resulting in the current cork and carbon fibre composite heat shield design becoming redundant. Thus, hypersonic flight brings with it the challenge of designing new a heat shield; capable of withstanding the elevated temperatures. Alginate and montmorillonite nanoclay based biopolymer nanocomposites have become a well-researched topic in recent years. This stems from the ability of the nanoclay fillers to align themselves within the suspension to mimic natural materials such as nacre (mother of pearl). The alignment of the nanoclay not only reinforces the biopolymer to provide a high storage modulus but also provides a tortuous path for transport phenomenon such as diffusion to take place; thereby making them flame retardant. In their native state, the nanocomposites are film-like and offer limited viability. But, simple production practices may be borrowed from culinary disciplines to transform the nanocomposites into foams with different relative densities. The introduction of the gaseous voids should further heighten the thermal characteristics; allowing them to function as heat shields. However, in transforming the nanocomposite to a foam, little is understood about the impact it will have on the mechanics of the native nanocomposite. As multiple analytical and numerical models have been provided over the years to estimate the mechanical properties of foams, a careful assessment of the various literature sources becomes necessary. Once a suitable model is identified, a detailed experimental campaign can be carried out to characterise the biopolymer nanocomposite foams mechanically.

The principal objective of this work is to understand the physicochemical behaviour of the ferrous raw material (pellet and/or sinter) bed mixed with nut coke under the blast furnace conditions. To investigate this behaviour, a specially designed blast furnace simulator called the Reduction Softening and Melting (RSM) apparatus is utilised (Chapter 3). In the RSM, blast furnace conditions of gas (varying profile of CO-CO2-H2-N2 gas mixture), load and temperature (20-1550 oC) were simulated for a stationary raw materials bed.@en

This thesis studies in-situ the phase transformations during heat treatment of two advanced steels: a supermartensitic stainless steels (SMSS), on which the main focus of this work is, and Fe-C-Mn-Si steels. A magnetic technique, based on the analysis of saturation magnetization, is utilized as the primary analysing tool. The scientific aim of this work is twofold: (i) to study the microstructural evolution involved in thermal processing of advanced steels based on optimising retained austenite and (ii) to optimise and extend the application of magnetic methods for these steels. For SMSS, the retained austenite fraction plays an essential role in controlling mechanical properties that often have a narrow tolerance window. Magnetic techniques are of increasing interest in the steel industry for monitoring the development of austenite on the basis of different magnetic properties of the phases in the steel. A new approach is proposed for determining the austenite fraction from in-situ thermo-magnetic measurements in SMSS. The formation of austenite during heat treatment of a SMSS is investigated and the kinetics of the martensite to austenite transformation, as well as the stability of austenite was established. The analysis of the Fe-C-Mn-Si steels provides a basis to further develop the analysis of austenite formation of multi-phase steels using thermo-magnetic techniques.@en

The different phases in the life of archaeological objects can be described by artefact biography. This dissertation defines an updated version: artefact biography 2.0, and the life phases of Early Iron Age bronze studs from Oss-Zevenbergen, the Netherlands, are elaborated. Throughout the thesis, the research revolves around information value. The bronzes have been studied from an interdisciplinary point of view, which has allowed the extraction of information that is also applicable to other corroded bronzes in general. It is argued that: - corrosion products and inclusions may reflect original microstructure
 - corrosion inhibitor BTAH binds to Sn and SnO2 - technical investigations before conservation increase the information value of an artefact.@en