The Science and Technology of 3D Printing

Three-dimensional printing, or additive manufacturing, is an emerging manufacturing process. Research and development are being performed worldwide to provide a better understanding of the science and technology of 3D printing to make high-quality parts in a cost-effective and time-efficient manner. This book includes contemporary, unique, and impactful research on 3D printing from leading organizations worldwide

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells

Additive Manufacturing Research and Applications

This Special Issue book covers a wide scope in the research field of 3D-printing, including: the use of 3D printing in system design; AM with binding jetting; powder manufacturing technologies in 3D printing; fatigue performance of additively manufactured metals, such as the Ti-6Al-4V alloy; 3D-printing methods with metallic powder and a laser-based 3D printer; 3D-printed custom-made implants; laser-directed energy deposition (LDED) process of TiC-TMC coatings; Wire Arc Additive Manufacturing; cranial implant fabrication without supports in electron beam melting (EBM) additive manufacturing; the influence of material properties and characteristics in laser powder bed fusion; Design For Additive Manufacturing (DFAM); porosity evaluation of additively manufactured parts; fabrication of coatings by laser additive manufacturing; laser powder bed fusion additive manufacturing; plasma metal deposition (PMD); as-metal-arc (GMA) additive manufacturing process; and spreading process maps for powder-bed additive manufacturing derived from physics model-based machine learning

Nondestructive evaluation and in-situ monitoring for metal additive manufacturing

Powder-based additive manufacturing (AM) technologies are seeing increased use, particularly because they give greatly enhanced design flexibility and can be used to form components that cannot be formed using subtractive manufacturing. There are fundamental differences in the morphology of additively manufactured materials, when compared with, for example castings or forgings. In all cases it is necessary to ensure that parts meet required quality standards and that “allowable” anomalies can be detected and characterized. It is necessary to understanding the various types of manufacturing defects and their potential effects on the quality and performance of AM, and this is a topic of much study. In addition, it is necessary to investigate quality from powder throughout the manufacturing process from powder to the finished part. In doing so it is essential to have metrology tools for mechanical property evaluation and for appropriate anomaly detection, quality control, and monitoring. Knowledge of how and when the various types of defects appear will increase the potential for early detection of significant flaws in additively manufactured parts and offers the potential opportunity for in-process intervention and to hence decrease the time and cost of repair or rework. Because the AM process involves incremental deposition of material, it gives unique opportunities to investigate the material quality as it is deposited. Due to the AM processes sensitivity to different factors such as laser power and material properties, any changes in aspects of the process can potentially have an impact on the part quality. As a result, in-process monitoring of additive manufacturing (AM) is crucial to assure the quality, integrity, and safety of AM parts. To meet this need there are a variety of sensing methods and signals which can be measured. Among the available measurement modalities, acoustic-based methods have the advantage of potentially providing real-time, continuous in-service monitoring of manufacturing processes at relatively low cost. In this research, the various types of microstructural features or defects, their generation mechanisms, their effect on bulk properties and the capabilities of existing characterization methodologies for powder-based AM parts are discussed and methods for in-situ non-destructive evaluation are reviewed. A proof-of-concept demonstration for acoustic measurements used for monitoring both machine and material state is demonstrated. The analyses have been performed on temporal and spectral features extracted from the acoustic signals. These features are commonly related to defect formation, and acoustic noise that is generated and can potentially characterize the process. A novel application of signal processing tools is used for identification of temporal and spectral features in the acoustic signals. A new approach for a K-means statistical classification algorithm is used for classification of different process conditions, and quantitative evaluation of the classification performance in terms of cohesion and isolation of the clusters. The identified acoustic signatures demonstrate potential for in-situ monitoring and quality control of the additive manufacturing process and parts. A numerical model of the temperature field and the ultrasonic wave displacement field induced by an incident pulsed laser on additively manufactured stainless steel 17 4 PH is established which is based on thermoelastic theory. The numerical results indicate that the thermoelastic source and the ultrasonic wave features are strongly affected by the characteristics of the laser source and the thermal and mechanical properties of the material. The magnitude and temporal-spatial distributions of the pulsed laser source energy are very important factors which determine not only the wave generation mechanisms, but also the amplitude and characteristics of the resulting elastic wave signals

Development of Reactor Multiphysics framework to analyze the effect of crossflow and dynamic gHTC for Depletion and REA transient

Department of Nuclear EngineeringThe aim of this research is to create a Multiphysics coupling framework called MPCORE (Multi-Physics CORE) to analyze the behavior of nuclear reactors. This framework couples fuel performance (FP) with neutron kinetics (NK) and thermal hydraulics (TH) modules for depletion and transient analysis. Coupling the FP code allows for accurate modeling of dynamic gap heat transfer for each pin. Converging all modules together provides a more meaningful insight into the variation of reactor parameters. Depletion studies with Multiphysics parameters are essential to understand safety parameters throughout a nuclear reactor's life. The study investigates the passive response of the reactor core to reactivity insertions caused by rod ejection accidents (REA). Most coupling frameworks only couple NK with TH, but this research also includes FP and uses two-way coupling between TH and FP modules to examine the impact on critical safety parameters. The adaptive time-step feature of MPCORE reduces execution time, and the framework performs in-memory data transfer between modules. Verification and validation work for MPCORE coupled modules (RAST-K for NK, CTH1D/CTF for TH, and FRAPI for FP) has been performed for single assembly, 3x3 mini-core, and whole-core problems. The performance of the TH module is evaluated with and without crossflow for transient calculations in whole-core problems. The effect of dynamic and static gap heat transfer coefficient models on the FP module is quantified for assembly, mini-core, and whole-core transient problems. Difference between one-way and two-way coupling between FP and TH modules is quantified for whole-core depletion problems. The study compares safety parameters such as departure from nucleate boiling ratio, linear power, fuel enthalpy, fuel centerline temperature, cladding outer surface temperature, coolant temperature, and cladding hydrogen concentration for different models. A best-estimate coupling framework has been developed and tested for uncertainty quantification (UQ) studies for assembly and mini-core problems. Random sampling and Latin hypercube sampling options are available for UQ studies in MPCORE. Standard deviation of different parameters in case of dynamic gap conductance has increased due to the difference of gap heat transfer in different cases.clos

Additive manufacturing of porous ceramic structures

This doctoral thesis describes the additive manufacturing of porous structures starting from preceramic mixtures. Preceramic polymers are a class of inorganic polymers which can be converted to a ceramic with high yield. The use of a preceramic polymer has been explored in this work with the double aim of providing the desired ceramic phases and of facilitating the shaping processes. The work is divided in three parts. In a first project, the powder-based three-dimensional printing technology has been applied to a preceramic polymer powder. Complex porous structures with Kagome and octahedral geometries have been replicated. The preceramic polymer was successively converted to a unique SiOC phase upon heat treatment in inert atmosphere. This approach, in contrast to the use of a ceramic powder, allows an easier shaping and the achievement of relatively higher green densities, due to the dissolution and re-solidification of the polymer in the process. The shaping of fine porous structures is particularly suited to this material because problems related to gas release during the polymer-to-ceramic transformation are limited. In a second project, the same powder-based technology was applied to mixtures of a preceramic polymer and ceramic fillers. In this case, the preceramic polymer acts as a binder for the fillers during the printing process. Upon heat treatment in air, the polymer is converted to silica, which then can be reacted with the fillers in the mixture in order to form silicate ceramic phases. This approach is very versatile and has been used to form apatite-wollastonite bioceramic composites, which have been shaped into porous scaffolds with designed porosity and cylindrical or cubic geometries. Finally, a different technology, which is an extrusion-based printing, has been applied. In this technique, as opposite to powder-based technologies, the part is not supported during its buildup, therefore a careful tailoring of the ink rheology is necessary in order to create spanning features. In this context, mixtures of a preceramic polymer and fillers were formulated which had a suitable shear-thinning behaviour, with the help of suitable additives. A hardystonite ceramic, which is a bio-silicate phase, was formed upon heat treatment in air. Hardystonite scaffolds with orthogonal pores were successfully shaped by the deposition of fine (< 0.5 mm) filaments

Design and Application of Additive Manufacturing

Additive manufacturing (AM) is continuously improving and offering innovative alternatives to conventional manufacturing techniques. The advantages of AM (design freedom, reduction in material waste, low-cost prototyping, etc.) can be exploited in different sectors by replacing or complementing traditional manufacturing methods. For this to happen, the combination of design, materials and technology must be deeply analyzed for every specific application. Despite the continuous progress of AM, there is still a need for further investigation in terms of design and applications to boost AM's implementation in the manufacturing industry or even in other sectors where short and personalized series productions could be useful, such as the medical sector. This Special Issue gathers a variety of research articles (12 peer-reviewed papers) involving the design and application of AM, including innovative design approaches where AM is applied to improve conventional methods or currently used techniques, design and modeling methodologies for specific AM applications, design optimization and new methods for the quality control and calibration of simulation methods

Additive Manufacturing of Porous Ceramic Structures from Preceramic Polymers

This doctoral thesis describes the additive manufacturing of porous structures starting from preceramic mixtures. Preceramic polymers are a class of inorganic polymers which can be converted to a ceramic with high yield. The use of a preceramic polymer has been explored in this work with the double aim of providing the desired ceramic phases and of facilitating the shaping processes. The work is divided in three parts. In a first project, the powder-based three-dimensional printing technology has been applied to a preceramic polymer powder. Complex porous structures with Kagome and octahedral geometries have been replicated. The preceramic polymer was successively converted to a unique SiOC phase upon heat treatment in inert atmosphere. This approach, in contrast to the use of a ceramic powder, allows an easier shaping and the achievement of relatively higher green densities, due to the dissolution and re-solidification of the polymer in the process. The shaping of fine porous structures is particularly suited to this material because problems related to gas release during the polymer-to-ceramic transformation are limited. In a second project, the same powder-based technology was applied to mixtures of a preceramic polymer and ceramic fillers. In this case, the preceramic polymer acts as a binder for the fillers during the printing process. Upon heat treatment in air, the polymer is converted to silica, which then can be reacted with the fillers in the mixture in order to form silicate ceramic phases. This approach is very versatile and has been used to form apatite-wollastonite bioceramic composites, which have been shaped into porous scaffolds with designed porosity and cylindrical or cubic geometries. Finally, a different technology, which is an extrusion-based printing, has been applied. In this technique, as opposite to powder-based technologies, the part is not supported during its build-up, therefore a careful tailoring of the ink rheology is necessary in order to create spanning features. In this context, mixtures of a preceramic polymer and fillers were formulated which had a suitable shear-thinning behaviour, with the help of additives. A hardystonite ceramic, which is a bio-silicate phase, was formed upon heat treatment in air. Hardystonite scaffolds with orthogonal pores were successfully shaped by the deposition of fine (< 0.5 mm) filaments

Aeronautical engineering: A continuing bibliography with indexes (supplement 295)

This bibliography lists 581 reports, articles, and other documents introduced into the NASA Scientific and Technical Information System in Sep. 1993. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics