Development of a digital manufacturing process chain for ceramic composites

The development of ceramic matrix composites, with their increasing use in high temperature and corrosive environment applications, is still restricted to ‘trial and error’ approach in comparison to other conventional materials like metals. The main reason behind that is the lack of experimental data due to high manufacturing costs of CMCs which generally includes a chain of several complex processes. This adds to the complexity of this material class and thus, makes it a difficult task to establish a relationship between a component with desired properties and the manufacturing parameters required to realise it. In the current work, the digital aspects are investigated from two point of views to use numerical methods to support the material design process: ‘material’ and ‘manufacturing process’. The case ‘material’ is the focus of this work where, ‘process-structure-property-performance’ (PSPP) relationship is established to study the entire life cycle of a CMC component, starting from the intermediate products, such as fibre preforms or green bodies prior to siliconization process, used in the processing to the mechanical performance of the final machined component under operating conditions. Each aspect of the PSPP relationship is discussed in detail and its implementation is demonstrated with the help of a numerical example. Cohesive zone elements at micro-level and homogenous damage development at macro-level were used to define the non-linear behaviour of the material under mechanical loading. Experimental results obtained for different CMCs such as C/C-SiC, C/SiCN, SiC/SiCN and Al2O3/ Al2O3 were used to validate the results obtained for the finite element models at different scales ranging from micro to macro. With the help of data analysis techniques like image segmentation and machine learning algorithm, computationally inexpensive data-based surrogate models were generated from accurate but computationally expensive physics-based models. A detailed review of the available numerical methods to model the manufacturing process and the process monitoring techniques is given. Based on the data and information obtained from the modelling of the material and the manufacturing process, a concept is proposed for optimized development of a CMC part. The concept combines the generated data with quantified expertise in the fields of material science to realise a manufacturing process chain to facilitate the material design process for CMCs. With the implementation of such an approach, the production cost of CMCs can be reduced by knowledge-based selection of the CMC constituents and manufacturing parameters. This will open the door for new applications of CMCs which would enable the material community to extend their use to other cost-efficient high temperature applications.Die Entwicklung von Verbundwerkstoffen mit keramischer Matrix, die zunehmend bei hohen Temperaturen und in korrosiven Umgebungen zum Einsatz kommen, ist im Vergleich zu anderen herkömmlichen Werkstoffen wie Metallen noch immer auf ein "Versuch-und-Irrtum"-Konzept beschränkt. Der Hauptgrund dafür ist der Mangel an experimentellen Daten aufgrund der hohen Herstellungskosten von CMCs, die im Allgemeinen eine Prozesskette aus mehreren komplexen Verfahrensschritten umfassen. Dies trägt zur Komplexität dieser Werkstoffklasse bei und macht es somit schwierig, eine Beziehung zwischen einem Bauteil mit gewünschten Eigenschaften und den Herstellungsparametern herzustellen. In der vorliegenden Arbeit werden die digitalen Aspekte aus zwei unterschiedlichen Blickwinkeln untersucht, um numerische Methoden zur Unterstützung der Werkstoffauslegung einzusetzen: 'Werkstoff' und 'Herstellungsprozess'. Im Mittelpunkt dieser Arbeit steht der "Werkstoff", bei dem die "Process-Structure-Property-Performance"-Beziehung (PSPP) hergestellt wird, um den gesamten Lebenszyklus eines CMC-Bauteils zu untersuchen. Angefangen bei den Zwischenprodukten, wie z. B. den Faser-Vorkörpern (Preform)vor dem Silizierverfahren, die die Basis der Verarbeitung bilden, bis hin zur mechanischen Belastungsgrenze des fertig bearbeiteten Bauteils unter Betriebsbedingungen. Jeder Aspekt der PSPP-Beziehung wird im Detail untersucht und ihre Umsetzung anhand eines numerischen Beispiels demonstriert. Kohäsive Zonenelemente auf der Mikroebene und homogene Schädigungsentwicklung auf der Makroebene wurden verwendet, um das nichtlineare Verhalten des Werkstoffs unter mechanischer Belastung zu definieren. Experimentelle Ergebnisse, die für verschiedene CMCs wie C/C-SiC, C/SiCN, SiC/SiCN und Al2O3/ Al2O3 erzielt wurden, dienten zur Validierung der Ergebnisse der Finite-Elemente-Modelle auf verschiedenen Skalen von Mikro bis Makro. Mit Hilfe von Datenanalysemethoden wie Bildsegmentierung und ‚Machine-Learning-Algorithmen‘ wurden aus genauen, aber rechenintensiven physikalischen Modellen zeiteffiziente datenbasierte Ersatzmodelle erstellt. Es wird ein detaillierter Überblick über die verfügbaren numerischen Methoden zur Modellierung des Fertigungsprozesses und der Prozessüberwachungstechniken gegeben. Auf der Grundlage der Daten und Informationen, die aus der Modellierung des Materials und der Herstellungsprozesse gewonnen wurden, wird ein Konzept für die optimierte Entwicklung eines CMC-Bauteils vorgeschlagen. Das Konzept kombiniert die generierten Daten mit quantifiziertem Fachwissen in den Bereichen der Materialwissenschaft, um eine Fertigungsprozesskette zu realisieren, die die Werkstoffauslegung für CMCs erleichtert. Mit der Umsetzung eines solchen Ansatzes können die Produktionskosten von CMCs durch eine wissensbasierte Auswahl der CMC-Bestandteile und Herstellungsparameter gesenkt werden. Dies wird die Tür für neue Anwendungen von CMCs öffnen, die es der Materialgemeinschaft ermöglichen wird, ihre Verwendung auf andere kosteneffiziente Hochtemperaturanwendungen auszuweiten

Active thermography for the investigation of corrosion in steel surfaces

The present work aims at developing an experimental methodology for the analysis of corrosion phenomena of steel surfaces by means of Active Thermography (AT), in reflexion configuration (RC). The peculiarity of this AT approach consists in exciting by means of a laser source the sound surface of the specimens and acquiring the thermal signal on the same surface, instead of the corroded one: the thermal signal is then composed by the reflection of the thermal wave reflected by the corroded surface. This procedure aims at investigating internal corroded surfaces like in vessels, piping, carters etc. Thermal tests were performed in Step Heating and Lock-In conditions, by varying excitation parameters (power, time, number of pulse, ….) to improve the experimental set up. Surface thermal profiles were acquired by an IR thermocamera and means of salt spray testing; at set time intervals the specimens were investigated by means of AT. Each duration corresponded to a surface damage entity and to a variation in the thermal response. Thermal responses of corroded specimens were related to the corresponding corrosion level, referring to a reference specimen without corrosion. The entity of corrosion was also verified by a metallographic optical microscope to measure the thickness variation of the specimens

Damping mechanisms in chemically vapor deposited SiC fibers

Evaluating the damping of reinforcement fibers is important for understanding their microstructures and the vibrational response of their structural composites. In this study the damping capacities of two types of chemically vapor deposited silicon carbide fibers were measured from -200 C to as high as 800 C. Measurements were made at frequencies in the range 50 to 15000 Hz on single cantilevered fibers. At least four sources were identified which contribute to fiber damping, the most significant being thermoelastic damping and grain boundary sliding. The mechanisms controlling all sources and their potential influence on fiber and composite performance are discussed

Novel Approaches for Nondestructive Testing and Evaluation

Nondestructive testing and evaluation (NDT&E) is one of the most important techniques for determining the quality and safety of materials, components, devices, and structures. NDT&E technologies include ultrasonic testing (UT), magnetic particle testing (MT), magnetic flux leakage testing (MFLT), eddy current testing (ECT), radiation testing (RT), penetrant testing (PT), and visual testing (VT), and these are widely used throughout the modern industry. However, some NDT processes, such as those for cleaning specimens and removing paint, cause environmental pollution and must only be considered in limited environments (time, space, and sensor selection). Thus, NDT&E is classified as a typical 3D (dirty, dangerous, and difficult) job. In addition, NDT operators judge the presence of damage based on experience and subjective judgment, so in some cases, a flaw may not be detected during the test. Therefore, to obtain clearer test results, a means for the operator to determine flaws more easily should be provided. In addition, the test results should be organized systemically in order to identify the cause of the abnormality in the test specimen and to identify the progress of the damage quantitatively

Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors

In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications. A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement

Boron Nitride Nanotube Reinforced Titanium Composite with Controlled Interfacial Reactions by Spark Plasma Sintering

In this study, Boron Nitride Nanotube (BNNT) reinforced Titanium matrix composites are synthesized by Spark Plasma Sintering. Two main challenges directly affecting the mechanical performance of BNNT-metal matrix composites are addressed:(i) Homogenous dispersion of high surface energy BNNTs, and (ii) Controlling interfacial reactions at the metal/nanotube interface. High-energy ultrasonication induced dispersion resulted in the functionalization of BNNTs by -OH radicals proving its suitability over surfactant assisted dispersion routes. The sintering of Ti (99% relative density) was achieved at 50% less processing temperature than those used in conventional sintering to minimize interfacial reactions when reinforced with BNNTs. The reduction of temperatures in addition to the reduction (by 91%) in processing times was shown to control reaction phases. Bulk compressive yield strengths of Ti-BNNT sintered at low (750oC) and high (950oC) temperatures were improved by 21% and 50% respectively, as compared to Ti alloy without reinforcement. Twin boundaries, pinning of dislocations by BNNTs, and crack bridging were strengthening mechanisms identified in the composites

Internal strain analysis of ceramics using scanning laser acoustic microscopy

Quantitative studies of material behavior characteristics are essential for predicting the functionality of a material under its operating conditions. A nonintrusive methodology for measuring the in situ strain of small dimeter (to 11 microns) ceramic fibers under uniaxial tensile loading and the local internal strains of ceramics and ceramic composites under flexural loading is introduced. The strain measurements and experimentally observed mechanical behavior are analyzed in terms of the microstructural development and fracture behavior of each test specimen evaluated. Measurement and analysis of Nicalon silicon carbide (SiC) fiber (15 microns diameter) indicate that the mean elastic modulus of the individual fiber is 185.3 GPa. Deviations observed in the experimentally determined elastic modulus values between specimens were attributed to microstructural variations which occur during processing. Corresponding variations in the fracture surface morphology were also observed. The observed local mechanical behavior of a lithium alumino-silicate (LAS) glass ceramic, a LAS/SiC monofilament composite, and a calcium alumino-silicate (CAS)/SiC fully reinforced composite exhibits nonlinearities and apparent hysteresis due to the subcritical mechanical loading. Local hysteresis in the LAS matrices coincided with the occurrence of multiple fracture initiation sites, localized microcracking, and secondary cracking. The observed microcracking phenomenon was attributed to stress relaxation of residual stresses developed during processing, and local interaction of the crack front with the microstructure. The relaxation strain and stress predicted on apparent mechanical hysteresis effects were defined and correlated with the magnitude of the measured fracture stress for each specimen studied. This quantitative correlation indicated a repeatable measure of the stress at which matrix microcracking occurred for stress relief of each material system. Stress relaxation occurred prior to the onset of steady state cracking conditions. The relaxation stress occurred at 18.5 percent of the fracture stress in LAS and 11.0 percent of the yield stress in CAS/SiC. The relaxation stress ratio was dependent upon the dominant fracture mode of the LAS/SiC specimens. Relaxation stress ratios greater than 0.30 were observed for specimens which fractured due to shear at the fiber matrix interface; specimens which fracture due to tensile cracking had relaxation stress ratios less than 0.30. The stress relaxation ratio appeared to be a specific characteristic of the glass ceramic material. The measured stress relaxation for LAS indicated a measure of the inherent residual stresses in the material due to processing and suggested localized toughening mechanisms for brittle material structures

Development of a digital manufacturing process chain for ceramic composites

Die Entwicklung von Verbundwerkstoffen mit keramischer Matrix, die zunehmend bei hohen Temperaturen und in korrosiven Umgebungen zum Einsatz kommen, ist im Vergleich zu anderen herkömmlichen Werkstoffen wie Metallen noch immer auf ein "Versuch-und-Irrtum"-Konzept beschränkt. Der Hauptgrund dafür ist der Mangel an experimentellen Daten aufgrund der hohen Herstellungskosten von CMCs, die im Allgemeinen eine Prozesskette aus mehreren komplexen Verfahrensschritten umfassen. Dies trägt zur Komplexität dieser Werkstoffklasse bei und macht es somit schwierig, eine Beziehung zwischen einem Bauteil mit gewünschten Eigenschaften und den Herstellungsparametern herzustellen. In der vorliegenden Arbeit werden die digitalen Aspekte aus zwei unterschiedlichen Blickwinkeln untersucht, um numerische Methoden zur Unterstützung der Werkstoffauslegung einzusetzen: 'Werkstoff' und 'Herstellungsprozess'. Im Mittelpunkt dieser Arbeit steht der "Werkstoff", bei dem die "Process-Structure-Property-Performance"-Beziehung (PSPP) hergestellt wird, um den gesamten Lebenszyklus eines CMC-Bauteils zu untersuchen. Angefangen bei den Zwischenprodukten, wie z. B. den Faser-Vorkörpern (Preform)vor dem Silizierverfahren, die die Basis der Verarbeitung bilden, bis hin zur mechanischen Belastungsgrenze des fertig bearbeiteten Bauteils unter Betriebsbedingungen. Jeder Aspekt der PSPP-Beziehung wird im Detail untersucht und ihre Umsetzung anhand eines numerischen Beispiels demonstriert. Kohäsive Zonenelemente auf der Mikroebene und homogene Schädigungsentwicklung auf der Makroebene wurden verwendet, um das nichtlineare Verhalten des Werkstoffs unter mechanischer Belastung zu definieren. Experimentelle Ergebnisse, die für verschiedene CMCs wie C/C-SiC, C/SiCN, SiC/SiCN und Al2O3/ Al2O3 erzielt wurden, dienten zur Validierung der Ergebnisse der Finite-Elemente-Modelle auf verschiedenen Skalen von Mikro bis Makro. Mit Hilfe von Datenanalysemethoden wie Bildsegmentierung und ‚Machine-Learning-Algorithmen‘ wurden aus genauen, aber rechenintensiven physikalischen Modellen zeiteffiziente datenbasierte Ersatzmodelle erstellt. Es wird ein detaillierter Überblick über die verfügbaren numerischen Methoden zur Modellierung des Fertigungsprozesses und der Prozessüberwachungstechniken gegeben. Auf der Grundlage der Daten und Informationen, die aus der Modellierung des Materials und der Herstellungsprozesse gewonnen wurden, wird ein Konzept für die optimierte Entwicklung eines CMC-Bauteils vorgeschlagen. Das Konzept kombiniert die generierten Daten mit quantifiziertem Fachwissen in den Bereichen der Materialwissenschaft, um eine Fertigungsprozesskette zu realisieren, die die Werkstoffauslegung für CMCs erleichtert. Mit der Umsetzung eines solchen Ansatzes können die Produktionskosten von CMCs durch eine wissensbasierte Auswahl der CMC-Bestandteile und Herstellungsparameter gesenkt werden. XIV. Dies wird die Tür für neue Anwendungen von CMCs öffnen, die es der Materialgemeinschaft ermöglichen wird, ihre Verwendung auf andere kosteneffiziente Hochtemperaturanwendungen auszuweite