For in-­situ resource utilisation start-up Maana Electric, an investigation was undertaken to determine whether a cover glass for solar panels can be produced using only desert sand as the raw material. During this investigation, the composition of desert sand, melt formation, processing temperatures, and mechanical and optical properties were considered. The composition of 18 desert sands was analysed by means of X­ray fluorescence and estimations of mineralogical composition were made, after which an attempt was made to melt the unmodified sand samples in a microwave furnace built for the purpose. Melt formation was further observed by melting binary combinations of store bought minerals that were found in the desert sands. The composition data and modelling of temperature-viscosity curves were employed to explore lowering the practical melting of the sand point by modification of the composition through benificiation. `Synthetic benificiated desert sand' was produced and melted based on the results. Glass samples produced were characterized using X­ray fluorescence, visual inspection, optical spectrometry, and fracture mirror analysis. It was found that about half of the desert sand samples assessed contain over 90 wt% silica, making it less feasible for use as raw material for glass due to high melting temperatures and/or large waste streams from benificiation, while sands containing larger fractions of carbonates and/or feldspars will form a melt at less than 1650 degrees Celsius if the SiO2 content is less than 55 wt%. Transmission of 85 % of ~550 nm wavelength light was shown to be possible for desert sand glass of 3 mm thickness if Fe2O3 content is lower than 0.1 wt%, while for the same transmission in the complete effective spectrum of silicon based solar cells the iron content needs to be lowered further. Known absorbing species such as Cr2O3, NiO and CuO were detected in desert sand in trace amounts, but were not present in the synthetic mixtures, the influence of these contaminants on transmission requires further research. Mechanical analysis was inconclusive due to a limited number and low quality of the samples produced, but a review of the literature implies that a Young's modulus of >70 GPa and flexural strength of >45 MPa are attainable in a glass produced from desert sand components.

In floors without dilation joints drying shrinkage cracking can occur. Shrinkage reducing agents (SRAs) can reduce the amount of drying shrinkage and improve the durability of the concrete structure. The mechanism of shrinkage reduction and the influences on the hydration process and development of mechanical properties of the SRA Sika Control 40 were researched. Shrinkage reducing agents lower the surface tension of water which reduces the capillary tensile stresses and ultimately reducing the drying shrinkage. Experiments were performed on cement paste samples to investigate influences on the hydration process of cement (surface tension, rate of hydration, porosity, shrinkage, flexural and compressive strength). In addition experiments were performed on concrete samples to investigate the influences of applying shrinkage reducing agents on the mechanical properties of concrete (compressive strength, shrinkage, elastic modulus). Overall, the experimental results showed that applying Sika Control 40 is an effective method for reducing drying shrinkage when concentrations of 1.56 w% and 2.61 w% are used. The shrinkage reducing agent has positive effects on the surface tension, weight loss and drying shrinkage for concentrations of 1.56 w% and 2.61 w% of cement. It has negative effects on rate and degree of hydration, porosity, pore size distribution, compressive and flexural strength for concentrations of 1.56 w% and 2.61 w%. The elastic modulus lacks adequate data to observe a trend, however the results are within the range of expected values for concrete for mixtures 156 and 261. , An SRA concentration of 0.52 w% of cement resulted in unpredictable and contradicting results.

Due to EU regulations on fuel consumption, reducing the weight of vehicles has become one of the most important goals of car manufacturers in Europe. Among them, Toyota Motor Europe is one of the worldwide leaders in the research for a sustainable future. Materials like fiber-reinforced plastics and aluminum play a significant role in the research for lightweight design, thanks to their very good strength-to-weight ratio. However, joining these materials efficiently together is still a challenge. When thermoplastic composites are used, direct joining with the metal substrate can be obtained using welding technologies which melts the thermoplastic at the interface. Ultrasonic welding is well-known for being a fast, reliable and effective technology for metal/metal or plastic/plastic joining. In this study, a collaboration between Toyota and TU Delft, ultrasonic plastic welding was investigated as candidate joining technology for aluminum/thermoplastic joints in automotive applications. The goal was to understand the main mechanisms involved in the adhesion and how they affect the performance of the joint. Initially, the technique proved to be successful, but moderate strengths were obtained. Therefore, several surface pre-treatments of the aluminum were analyzed to improve performance in terms of strength and durability of the joint; mechanical, chemical and physical treatments were carried out. With laser structuring, strengths comparable to adhesive bonded joints were obtained, but in a much shorter process time. Other treatments such as conversion coating, sandblasting and plasma led to considerable improvements as well. The encouraging results achieved represent an important step in the development of ultrasonic plastic welding for multi-material joining in the automotive industry. Additional research could help Toyota and other car manufacturers realizing a better design to further decrease weight and CO2 emissions of vehicles.

Wire and arc additive manufacturing (WAAM), a relatively new metal 3D-printing technology, allows for fabrication of shapes that were not possible to produce a few years ago. Using 6-axis industrial robots with a gas metal arc welding (GMAW)-head, Dutch start-up MX3D prints metal in every direction mid-air. By welding small parts of material at a time along a laser guided - CAD-generated path, self-supporting cross-sections of very complex shapes, such as internally reinforced non-prismatic hollow sections can be manufactured fully automatically. Unlike powder-bed based manufacturing, this technology is not bounded by size limits of a final product, which creates opportunities for fabrication of large-scale structural components and finally entire structures. It is MX3D’s aim, in collaboration with key industry partners, to 3D-print world’s first fully functional bridge spanning 12 metres, to be installed in the city centre of Amsterdam in the course of 2019. The bearing elements of the bridge consist of tubular shaped elements, together building up to a complex-shaped free-form steel structure. These tubular members mainly behave as axially compressed bearing elements, nonetheless it is yet not known how the stability of WAAM-members can be assessed. Several standards for testing (and characterisation) of additively manufactured materials are published by different national and international committees, e.g. ISO/ASTM 529 and CEN-CT 438, but a comprehensive set of international standards has not been achieved yet. It is widely recognised that there is a strong link between manufacturing process parameters and material properties, which requires special attention in this research area. So far there is a lack of sufficient test results to cover a specific manufacturing process. In this research the material properties of MX3D’s dot-by-dot and continuously printed members are studied. This pioneering research provides insight in material and geometrical properties relevant for the stability of (ER)308LSi stainless steel tubular columns. A tubular column is used as existing basic structural element to assess the stability of wire and arc additively manufactured steel members. Advanced 3D-laserscanning technology is applied to characterise and analyse geometrical imperfections. A clear understanding of bending stiffness and buckling behaviour is established by performing four-point flexural bending tests and flexural buckling tests on tubular columns, diameter 33.8mm, thickness 3.7 mm. Tensile properties of milled WAAM specimens are analysed both in - and perpendicular to - their print direction for dot-by-dot and continuously printing. It is verified whether or not the structural properties are in compliance with the existing steel standard (EC3). Additional Vickers hardness measurements and metallographical analyses are performed to examine the microstructure of column samples. Finally, a buckling design graph is proposed based on own experiments, aiming towards a safe model suitable for stability calculations of additively manufactured tubular columns. It is concluded from experiments that the material properties of 3D-printed steel differ from that of conventionally produced steel. Following the thermal gradient of the weld pool, large columnar grain structures are detected giving rise to anisotropy. Stiffness, strength and ductility prove to be dependent on the print direction. Whereas the tensile strength top expected values, the obtained stiffness is significantly lower than that of commonly applied steel grades. Inaccuracies of the printing process result in local wall thickness variations and a relatively high out-of-straightness, both negatively affecting the buckling capacity of printed tubular columns. Yet it should be acknowledged that due to rapid advancements in improving the printing process, the geometrical imperfections are soon expected to reduce drastically. It is recommended to apply active cooling during manufacturing to enhance mechanical properties even further. By combining topology optimisation and WAAM, an optimal material layout can be found ánd manufactured, consequently an excellent material efficiency can be achieved. A promising prospect for future construction projects.

In recent years, Wire and Arc Additive Manufacturing (WAAM), is gaining attractions both from academia and industry, because it has the potential to substitute or complement the traditional manufacturing methods. Traditional materials and methods are reaching their limitation when demanding and special applications are considered. The current growth in WAAM applications will boost the WAAM consumable material development in the coming future. WAAM applications mostly refer to small batch production or prototypes, which often requires special wire compositions or can benefit from tailoring the consumable composition for the desired components. On one hand, solid wire production is only economically viable when large volumes are involved. On the other hand, metal-cored wires are particularly suitable to produce tailored or small-batch consumable compositions, which is very attractive for WAAM. However, only limited research has been carried out in the use of metal-cored wires in additive manufacturing. In this research, the focus is to explore the use of metal-cored wire in WAAM applications. Two chemical compositions, one ferrous, medium carbon low steel alloy (AM-XC-45), and one non-ferrous, Stellite 6 (cobalt-based superalloy), metal-cored wires were investigated based on industrial interests at RAMLAB. The microstructure of the WAAM AM-XC-45 thin wall was characterized using optical microscopy and scanning electron microscopy. Pearlite, ferrite, bainite, and martensite are present in the deposited wall. Columnar grains are found near the fusion line. The repeated thermal cycles cause the grains to become finer from the top to bottom layers. The mechanical properties including microhardness and tensile strength were tested and compared with the traditional processing methods like casting, milling, and forging. It showed a comparable or superior microhardness and tensile strength to the traditional process whereas the relative lower elongation of the deposited AM-XC-45 thin wall indicates that further post heat treatment is needed to improve the ductility of the part. Stellite 6 is a cobalt-based superalloy, which has good wear and corrosion resistance and retains these properties at high temperatures. In this study, Stellite 6 metal-cored wire (WEARTECH® WT-6 GMAW-C, AWS A5.21 ERCCoCr-A) is selected and optimized to obtain results comparable to the commonly employed and more costly laser deposition, in terms of microstructure and mechanical properties. The optimal deposition parameters were developed using the S355 steel substrate, and then adopted on depositing on the AISI 420 stainless steel substrate. Characterization showed that Stellite 6 layer mainly contains Co-Cr-Fe solid solution with FCC crystal structure as the matrix and the Cr7C3 and Cr3C2 were identified in the microstructure through SEM, EDS, and XRD. These carbides can contribute to the strength. In addition, the identified Co4W2C carbides can contribute to the wear properties of the Stellite 6 WAAM deposits. The dilution and hardness of the WAAM deposit can reach the same level as laser deposition. Additionally, a 3D temperature distribution model is developed by adopting the moving mesh technique to numerically study the WAAM process. The model helps to gain a better understanding of the physical phenomena (heat and mass transfer) during the WAAM deposition. The AM-XC-45 was used to validate the developed model. The simulated and experimental results were compared. The dilution and HAZ of WAAM deposited single bead was used as validation criteria. The A1 line (1100K) simulation is in a good agreement with the experimental result. The fusion line (1800K) shows some deviation. Compared with laser deposition, the main differences between the two processes lie on the heat source, the boundary conditions, and the material responses to the process.

Preventing solidification cracking is an essential prerequisite for the safety of a welded structure. An undetected solidification crack has the potential to cause premature failure during service. Two conditions generated by a weld thermal cycle are responsible for the initiation of solidification cracks. The first is the presence of excessive stresses/strains imposed on the solidifying weld metal and the second is the existence of a weak solidifying microstructure. For more than five decades, weld solidification cracking has been a subject of considerable interest. Cracking has been observed in various alloys, used in a wide range of engineering applications. Despite achieving a better understanding over this period, an accurate prediction of the occurrence of solidification cracking under a specific set of conditions remains difficult. An alloy with a high susceptibility to solidification cracking can still exhibit good weldability upon selection of appropriate welding conditions. Conversely, an alloy with supposedly high resistance to cracking, can still fail when subjected to inappropriate welding conditions. The objective of the research work reported in this dissertation is to study and elucidate the solidification cracking phenomenon in two popular and commercially available automotive sheet steels, namely transformation-induced plasticity (TRIP) and dual phase (DP) steels. In particular, the effect of restraint (strain imposed), shape of the weld pool, solidification morphology, segregation, solidification temperature range, dendrite coherency and interdendritic liquid feeding on susceptibility to solidification cracking is considered.@en

The pipeline production rate and the pipeline’s superior mechanical properties are the crucial parameters for the offshore pipe laying company. Pulling on the bead, i.e. the action of moving the pipe on the firing line to the subsequent weld stall as the vessel moves forwards allows a fast and reliable pipe welding process. During this movement, the ends of the pipes are intermittently not supported and the bending moment in the weld is created as a consequence. Such operation imposes tensile loads in the welds, that are especially high for the 3 mm thick beadweld and the subsequent 3 mm thick hot pass (6mm thick in total). An important question arises whether imposing loads above the beadweld material yield capacity affects the overall fatigue performance of the girth weld. It is in the best interest of the offshore industry to assure that the pipeline welds properties during their 20-30 years operation lifetime are not adversely affected during its installation. This study investigates the effect of pulling on the bead on the weld’s fatigue behaviour. The overstressing simulation of the test coupons, Finite Element Analysis (FEA) of the loaded beadweld and the small-scale specimens comparative fatigue study were conducted to investigate the effect of straining history on the full girth weld fatigue performance. Additionally, the holistic approach was implemented to investigate the consolidated effects of other factors: local weld root misalignment (Hi-Lo), weld porosity and microstructure quality. Four test coupons were welded together and overstressed to simulate the pulling on the bead action. To assess the stress-strain state in the beadweld and hot pass during the overstressing simulation the FEA analysis was done. The FEA results allowed to quantitatively determine the exact locations of the elastically and plastically strained beadweld material. Full welds were checked against the porosity and subsequently, 46 fatigue specimens were fabricated and tested in the 4-point-bending fatigue loading setup. Additionally, the fatigue crack observation techniques were implemented in order to separate fatigue crack initiation and growth phases out of the total fatigue life. The optical observations (with the optical-digital microscope) and the Potential Drop techniques were used. Tensile and hardness tests were done to compare the strength properties of specimens with different straining and porosity histories. Finally, the microstructure and fracture surfaces of the fatigue broken specimens were studied. The research done in this study gives a good overview of the fatigue behaviour of the girth welds and provides insights into the straining history effects. Plastic straining was found not to affect the fatigue performance more than currently acceptable elastic straining does. Moreover, plasticity was found to reduce the negative effect of porosity. Additionally, the prevalent influence of Hi-Lo on the crack initiation phase was confirmed, making it the driving negative factor for the fatigue resistance.

This research focused on the question whether it is possible to predict the density of tropical hardwoods with acceptable accuracy based on drill resistance measurements. To assess the feasibility, the influence of the characteristics of the drill resistance measurement tool; the Resistograph® and the wood species have been investigated. With respect to the measurement tool, drill sharpness, feed speed and rotation rate were examined. For the wood samples, the influence of extractives, moisture content, drill direction and density were investigated. It was found that the influence of drill sharpness cannot be ignored and a calibration procedure was developed. No significant difference in drill resistance was observed between drilling in radial and tangential directions; however, drilling in the longitudinal direction resulted in a significant higher drill resistance. Moisture content influences the drill resistance; however, the effect is small and not statistically significant, it can usually be ignored. The influence of extractives on the drill resistance most likely depends not only on the mass fraction of extractives but also on the sort and the composition of the cell wall. Meranti has a typical density within the range 350 to 860 kg/m3. With an appropriate calibration procedure, it is possible to predict the density of meranti with 95% confidence to an accuracy of ± 70 kg/m3

Additive manufacturing (AM) is currently making a transition from mainly being used for prototyping to an alternative for conventional production methods. AM provides more freedom in design geometry combined with the possibility to produce (complex) products in low quantities. As a result, the need arises for printed parts with consistent mechanical properties that rival those of conventionally produced parts. Currently, the layer-by-layer process used by AM introduces weaknesses at the interlayer (weld) bonds. Polymer science suggests that raising weld bonds to temperatures above the glass transition temperature (Tg) can improve their mechanical properties up to bulk strength. This research aims to verify if fused filament fabrication (FFF) printing at elevated print room temperatures (Tenv) raises interlayer temperatures above Tg and as a result enhances mechanical properties. In order to measure the increase in interlayer properties double cantilevered beam (DCB) testing is used. Additionally, tensile testing is used to evaluate the effect of elevating Tenv on general mechanical properties. DCB and tensile testing of samples printed at elevated Tenv values has shown an increase of 109 % in interlayer energy release rate (G1c), up to 50 % in ultimate tensile strength and 106 % in tensile toughness. This has been determined by comparing samples printed at elevated Tenv with samples printed at room temperature (23 ◦C). To further understand the mechanisms behind the enhanced properties, the temperature history during printing has been determined. This has been done by running simulations and using IR imaging. The temperature history of printed parts has been related to data obtained from mechanical testing. This showed that mechanical properties increased for samples in which the interlayer bonds resided above Tg for prolonged periods of time. In addition, optical microscopy and micro CT has been used to monitor the meso-structure of printed samples. This showed that voids in the sample caused by printing defects contributed to an increased spread in measured values. Mechanical properties corrected for effective surface areas showed a roughly 10 % increase for average values. While significant this is not in the same order of magnitude as the increase in mechanical values reported for printing at higher Tenv values. Combining these results it has been found that elevating Tenv does not significantly affect the meso-structure, but it does cause bonds to spend an increased amount of time above Tg. Therefore, it has been concluded that the enhanced mechanical properties are caused by weld bond healing due to the part residing above Tg.