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

Automotive Inductive Position Sensor

Inductive angular position sensors (IAPS) are widely used for high accuracy and low cost angular position sensing in harsh automotive environments, such as suspension height sensor and throttle body position sensor. These sensors ensure high resolution and long lifetime due to their contactless sensing mode and their simple structure. Furthermore, they are suitable for wider application areas. For instance, they can be miniaturized to fit into a compact packaging space, or be adopted to measure the relative angle of multiple rotating targets for the purposes of torque sensing. In this work, a detailed SIMULINK model of an IAPS is first proposed in order to study and characterize the sensor performance. The model is validated by finite element analysis and circuit simulation, which provides a powerful design tool for sensor performance analysis. The sensor error introduced by geometry imperfection is thoroughly investigated for two-phase and three-phase configurations, and a corresponding correction method to improve the accuracy is proposed. A design optimization method based on the response surface methodology is also developed and used in the sensor development. Three types of sensors are developed to demonstrate the inductive sensor technology. The first type is the miniaturized inductive sensor. To compensate for the weak signal strength and the reduced quality (Q) factor due to the scaling down effect, a resonant rotor is developed for this type of sensor. This sensor is fabricated by using the electrodeposition technique. The prototype shows an 8mm diameter sensor can function well at 1.5mm air gap. The second type is a steering torque sensor, which is designed to detect the relative torsional angle of a rotating torsional shaft. It demonstrates the mutual coupling of multiple inductive sensors. By selecting a proper layout and compensation algorithm, the torque sensor can achieve 0.1 degree accuracy. The third type is a passive inductive sensor, which is designed to reduce power consumption and electromagnetic emissions. The realization and excellent performance of these three types of sensors have shown the robustness of the inductive sensor technology and its potential applications. The research conducted in this dissertation is expected to improve understanding of the performance analysis of IAPS and provide useful guidelines for the design and performance optimization of inductive sensors

Design of a permanent magnet axial flux high-speed generator

Electrical generating sets powered by gas turbines are required for many applications, in particular for emergency situations due to their critical attributes; high reliability, lightweight, small size, multi-fuel capabilities, low maintenance, low noise and low gas emissions. This research contends that a permanent magnet axial flux (PMAF) high-speed generator with a small gas turbine engine offers advantages over the radial flux permanent magnet generators. Higher power densities can be achieved with the axial flux configuration when compared to their counter parts of the radial flux machines of similar output power. The attributes of the PMAF machines were certainly appealing; lightweight, small size, high efficiency and ease of construction. In this research, a design approach for the PMAF high-speed generator which accounts for the mechanical and electrical aspects was provided. The machine's key components such as retainment ring was carefully designed and the materials utilised in their structures were appropriately selected to insure high mechanical integrity, ease of construction and low manufacturing cost. The generator's principle dimensions were determined from a theoretical model which was derived from the machine's main design parameters. This theoretical model was then correlated by some empirical coefficients determined through the manipulation of the experimentally validated finite element (FE) results. The analytical results have shown that with the appropriate design considerations, PMAF high-speed generators can be designed with high power densities in the range of 6-8 kW/kg and high efficiencies ideally in the range of 94 - 96 %. The mechanical integrity and the steady state electrical performance of the machine were analysed using three-dimensional (3D) FE models. More in this research, a parametric study was carried out on the most influential parameters of the machine to improve its electrical performance through minimise rotor and stator eddy current losses. In addition, the total harmonic distortion in the output waveform was minimised through the appropriate and careful design of the magnet shape and topology with the aid of 3D electromagnetic FE analysis. Furthermore, using FE it was possible to design, optimise and analyse the rotor back-iron disc through the selection of best material, shape and size for use in the PMAF high-speed generator. A prototype of the PMAF high-speed generator was constructed and tested preliminary at low speed for the purpose of the evaluation of the electrical performance of the machine. Experimental results have shown that the machine was capable to meet the design requirements. For the mechanical integrity of the machine, the rotors were safely tested on a cold run test rig at the speed of 47,000 rpm. This thesis describes also the trends and the technical details in the manufacturing, construction and experimental setup for the PMAF high-speed generator

Third International Symposium on Magnetic Suspension Technology

In order to examine the state of technology of all areas of magnetic suspension and to review recent developments in sensors, controls, superconducting magnet technology, and design/implementation practices, the Third International Symposium on Magnetic Suspension Technology was held at the Holiday Inn Capital Plaza in Tallahassee, Florida on 13-15 Dec. 1995. The symposium included 19 sessions in which a total of 55 papers were presented. The technical sessions covered the areas of bearings, superconductivity, vibration isolation, maglev, controls, space applications, general applications, bearing/actuator design, modeling, precision applications, electromagnetic launch and hypersonic maglev, applications of superconductivity, and sensors

CFRP Delamination Density Propagation Analysis by Magnetostriction Theory

While Carbon Fiber Reinforced Polymers (CFRPs) have exceptional mechanical properties concerning their overall weight, their failure profile in demanding high-stress environments raises reliability concerns in structural applications. Two crucial limiting factors in CFRP reliability are low-strain material degradation and low fracture toughness. Due to CFRP’s low strain degradation characteristics, a wide variety of interlaminar damage can be sustained without any appreciable change to the physical structure itself. This damage suffered by the energy transfer from high- stress levels appears in the form of microporosity, crazes, microcracks, and delamination in the matrix material before any severe laminate damage is observed. This research presents a novel Non- Destructive Evaluation (NDE) technique for assessing subsurface interlaminar interphacial health. A new self-sensing smart composite material is born by embedding microscopic magnetically activated sensors between CFRP ply. Magnetostrictive Carbon Fiber Reinforced Polymer (MagCFRP) is a self-sensing structural health composite material that is magnetically activated by an external magnetic field. This research merges the governing magnetoelasticity and general magnetization mechanics with analytical, experimental, and numerical results. For mode I and mode II fiber- matrix debonding, cracking, and shear delamination, there was an observed localized magnetic flux density gradient of more than 3 mT (2%) with a reversible flux of only 25% for low driving magnetic flux density (≈ 0.2 T) using the indirect magnetization stimulation method