Modelling and optimising micro-nozzle resin injection repair of impacted composites using CFD

Resin injection repair is identified to have a gap of knowledge and rigour in the modelling and execution of the process. We outline the strategy of our proposed predictive modelling strategy of ‘reconstruction-simulation-injection’ to simulate real cases to improve repair outcomes. We model the damage zone using Darcy’s law and determine permeability using two methods applied on the Kozeny-Carman equation. We then discuss how we evaluate porosity and detail two proposed methods on reconstructing the porosity field. We verify the model through simulation, and demonstrate verification using a novel comprehensive 2D porosity liquid-ideal gas phase flow model after deriving the analytical solution, which is a contribution of our work. Next, we apply the now-established model to reconstruct real damage cases using the two methods and compare them. We also calibrate the permeability parameter for the model by comparison to a simulation accuracy index, and also calibrate an ultrasonic scanning parameter to minimise reconstruction artefacts as well as the sensitivity of the reconstructed geometry characteristics to scan parameter variations. Then, we validate the model by simulating real repair cases and comparing them to the experimental outcomes, achieving simulation accuracy indices of about 70% or more. We demonstrate the application of the resin injection model by applying resin injection in a proof-of-concept simulation and use it for a case study, and examine the importance of hole configuration, vacuum usage as well as resin flow behaviour between inlet and outlet holes in the context of a given damage area geometry. It is important to maximise the total length of resin flow paths available, through carefully placing inlet and outlet holes, to allow resin to infiltrate the damage zone as much as possible. Vacuum increases the minimum achievable filling, and it is still invariably better to use vacuum with an optimal hole placement, instead of one or the other. In a second case study, we improve the predicted outcome by the model after intentionally changing the hole configuration to maximise resin infiltration, demonstrating that filling can be improved by placing holes intelligently (e.g. by using gathered information on the damage area, together with knowledge of how resin would flow). Using this, we conduct an optimisation study of the resin injection model by first setting up the optimisation strategy and carefully determining the methodology. The optimisation procedure is verified by using one and two degree-of-freedom optimisation cases, with known optima. Then, the optimisation strategy is applied to reconstructed repair cases to demonstrate and assess the efficacy of the optimisation procedure, with average reductions in unfilled volumes of approximately 28% compared to initial configurations.Open Acces

Characterization of vertical cracks using lock-in vibrothermography

214 p.Esta tesis se centra en la aplicación de la vibrotermografía lock-in para la detección y caracterización dedefectos verticales sumergidos. En esta técnica, la pieza se excita mediante ultrasonidos, que generancalor en los defectos por fricción o deformación plástica. Este calor se difunde por el material y susefectos se pueden detectar midiendo la temperatura superficial mediante una cámara infrarroja. Con el finde caracterizar defectos es necesario resolver el problema inverso, que consiste en recuperar la geometríade las fuentes de calor a partir de la distribución de temperatura superficial medida. Éste es un problemamal puesto, ya que su solución es fuertemente dependiente de pequeños errores en los datos y la inversiónes inestable. Se ha implementado un algoritmo de inversión robusto, basado en minimización pormínimos cuadrados estabilizados mediante términos de penalización basados en los funcionales deTikhonov, Total Variation y L1, capaz de reconstruir distribuciones de fuentes de calor partiendo de datosde vibrotermografía. El algoritmo se ha analizado con datos sintéticos y se ha optimizado con el fin deextender su aplicación a la caracterización del mayor rango de geometrías de fuentes de calor posible.Los resultados obtenidos se han verificado con datos experimentales obtenidos en ensayos devibrotermografía lock-in, utilizando muestras con fuentes de calor verticales calibradas. Finalmente, se hahecho uso del algoritmo de inversión para caracterizar grietas reales en una muestra soldada de Inconel718 y los resultados están en buena correlación cualitativa con los resultados del ensayo de líquidospenetrantes realizado posteriormente

Ultrasound Imaging

In this book, we present a dozen state of the art developments for ultrasound imaging, for example, hardware implementation, transducer, beamforming, signal processing, measurement of elasticity and diagnosis. The editors would like to thank all the chapter authors, who focused on the publication of this book

Twin Related Domains in Polycrystalline Nickel-Base Superalloys: 3D Structure and Fatigue

Fatigue is the life limiting property of polycrystalline nickel-base superalloys used in turbine disks in the hot section of turbine engines for aerospace and power generation applications. Fabricating components through a powder metallurgy route provides enhanced properties and removes many extrinsic defects associated with fatigue crack formation, driving cracks to initiate at intrinsic microstructrual extremes. Fatigue cracks in the powder metallurgy alloy René 88DT frequently initiate in large grains that are in the tail of the size distribution and contain favorably oriented annealing twin boundaries. Fully characterizing twin boundaries and twin related domains requires 3D microstructural volumes. Datasets of 3D microstructure for René 88DT were collected by TriBeam tomography across a range of resolutions and volumes to characterize microstructure and annealing twins. Algorithms developed to analyze these datasets allow identification of strain localizing sites from 2D cross sections and the frequency of microstructural features amenable to fatigue crack initiation is statistically assessed. Twin related domain structure is quantified via network analysis and leveraged to propose a criterion for identifying fatal fatigue crack sites

Characterization of vertical cracks using lock-in vibrothermography

214 p.Esta tesis se centra en la aplicación de la vibrotermografía lock-in para la detección y caracterización dedefectos verticales sumergidos. En esta técnica, la pieza se excita mediante ultrasonidos, que generancalor en los defectos por fricción o deformación plástica. Este calor se difunde por el material y susefectos se pueden detectar midiendo la temperatura superficial mediante una cámara infrarroja. Con el finde caracterizar defectos es necesario resolver el problema inverso, que consiste en recuperar la geometríade las fuentes de calor a partir de la distribución de temperatura superficial medida. Éste es un problemamal puesto, ya que su solución es fuertemente dependiente de pequeños errores en los datos y la inversiónes inestable. Se ha implementado un algoritmo de inversión robusto, basado en minimización pormínimos cuadrados estabilizados mediante términos de penalización basados en los funcionales deTikhonov, Total Variation y L1, capaz de reconstruir distribuciones de fuentes de calor partiendo de datosde vibrotermografía. El algoritmo se ha analizado con datos sintéticos y se ha optimizado con el fin deextender su aplicación a la caracterización del mayor rango de geometrías de fuentes de calor posible.Los resultados obtenidos se han verificado con datos experimentales obtenidos en ensayos devibrotermografía lock-in, utilizando muestras con fuentes de calor verticales calibradas. Finalmente, se hahecho uso del algoritmo de inversión para caracterizar grietas reales en una muestra soldada de Inconel718 y los resultados están en buena correlación cualitativa con los resultados del ensayo de líquidospenetrantes realizado posteriormente

Refinement of Ti-6Al-4V prior-β grain structure in the as-deposited condition via process control during wire-direct energy deposition

This study demonstrates that refinement of the prior-β grains generated during the wire-direct energy deposition of Ti‐6Al‐4V is achievable whilst maintaining a stable processing condition in the as-deposited condition, not reliant on penetration of the feedstock to the melt pool. Previous studies on prior-β grain refinement of Ti‐6Al‐4V have been reliant on either post-processing, alloy modification or agitation of the melt pool to achieve refinement. Through process control alone, it was identified that an increase in the deposition rate for a fixed energy input led to a reduction in the specific energy density of deposited material. Utilising pyrometry, it was determined that the reduction in the specific energy density led to a decrease in the thermal gradient, measured using a linear thermal gradient approximation, encouraging apparent homogenous nucleation within the melt pool. Whilst maintaining a stable ‘droplet’ transfer mode, the gradual reduction in specific energy density transformed the grain structure from the typical columnar morphology through a mixed morphology to an equiaxed grain morphology; confirmed via prior-β grain reconstructions and inverse pole figure analysis made possible by electron back scattered diffraction microscopy of the deposited samples. Microhardness measurements demonstrated larger variations in the refined prior-β grain specimens as compared to the columnar as a result of more complex α morphologies generated

in situ Nanomechanical Investigations of Bone

PhDMineralized collagen fibrils(MCFs)are the fundamental building blocks that contribute to the extraordinary mechanical behaviour of bone. Despite its importance in defining bone mechanics, especially the high resistance to fracture recorded in bone tissue, MCFs have yet to be mechanically tested and and, thus, MCF contributions to the global mechanical properties of bone is unclear. In this thesis, a complete strategy for performing direct mechanical testing on nanosized fibrous samples including MCFs from bone using a novel in situ atomic force microscope (AFM) – scanning electron microscope (SEM) combination was scanning electron microscope (SEM) combination was established. This technique was used to mechanically test MCFs from antler bone tissue for the first time and resultant stress behaviour was recorded to highlight the inhomogeneous response of fibrils, which is associated with fibrillar compositional heterogeneity. Mechanical properties of MCFs and bone tissue were found to be controlled by biomineralization process using additional tensile testing of MCFs and bulk samples from mouse limb bones at different ages. Extrafibrillar mineralization was found to have effects on the Young’s modulus of bone tissue rather than fibrils, indicating the importance of fibrillar interfaces in controlling overall mechanical behaviour of bone tissue. Interfaces between fibrils in bone were examined by carrying out single fibril pullout tests. A weak but reformable interface, dominated by ionic bonds between fibrils, was recorded and the sacrificial bond reforming activity at the interface was found to be be dependent on pullout strain rate. Finally, considerations of bone as a fibrous composite was used to evaluate nanomechanical testing data, with approximately 50 % of the bone fracture energy accounted for in failure of fibril interfaces