Bridges Structural Health Monitoring and Deterioration Detection Synthesis of Knowledge and Technology

INE/AUTC 10.0

Residual stress effects and damage tolerance behaviour of integral lightweight structures manufactured by FSW and HSM

Estágio realizado na empresa Airbus Operations GmbH, orientado pelo Mr. Marco PacchioneTese de Programa Doutoral. Engenharia Mecânica. Universidade do Porto. Faculdade de Engenharia. 201

Dual-Parameter Opto-Mechanical Fiber Optic Sensors for Harsh Environment Sensing: Design, Packaging, Calibration, and Applications

This thesis concerns with the development of a dual-parameter sensor based on fiber Bragg grating (FBG) and a packaging design for high pressure sensing in harsh environment. This thesis starts by introducing a novel design of a partially coated FBG, using a metallic insert and a thermal curing epoxy. An analytical opto-mechanical model, based on couple mode theory, was developed and presented. The experimental and modelling result of the optical response of the partially coated FBG were compared and shown to be in excellent agreement. The experiments were executed on a custom-built fiber optic calibration station. The coated FBG sensor has a temperature sensitivity of 26.9 ± 0.3 pm/°C, which is 2.7 times higher than a bare fiber; and a force sensitivity of 0.104 nm/N, which is 13 times smaller than a bare fiber. The zero reference of the sensor has a drift of a maximum of 70 pm but the sensor is shown to settle within ±5 pm after 3 thermal cycles and 10 tensile loading cycles. A low profile packaging design is presented for a maximum pressure of 20.68 MPa (3000 psi) for harsh environment applications. A detailed study with FEM analysis revealed the optimal design for the package’s sleeve thickness is 0.5 mm. The temperature sensitivity is in close agreement with the unpackaged coated sensor with 10% difference. Compared to the modelling, the equivalent force sensitivity is 27% lower due to prototype dimensional uncertainties and modelling uncertainties with the material properties. The lack of pre-tension of the FBG sensor in the package also attributed to lower force sensitivity at pressure level lower than 4.13 MPa (600 psi).1 yea

A review on various optical fibre sensing methods for batteries

Batteries have rapidly evolved and are widely applied in both stationary and transport applications. The safe and reliable operation is of vital importance to all types of batteries, herein an effective battery sensing system with high performance and easy implementation is critically needed. This also requires the sensing system to monitor the states of batteries in real time. Among the available methods, optical fibre sensors have shown a significant advantage due to their advanced capabilities of which include the fast measurement of multiple parameters with high sensitivity, working without interfering the battery performance, being able to be composited in multiplexed configurations and being robust to various harsh environment conditions. This paper mainly discusses the current optical fibre sensing methods for batteries in terms of the working principles and critical reviews the sensing performance corresponding to different sensing parameters. Moreover, the challenges and outlooks for future research on battery sensing are derived

A structural health monitoring system for composite pressure vessels

Vehicles that run on compressed natural gas and hydrogen are currently being developed to reduce greenhouse gas emissions and smog. To meet the need for a safe, reliable fuel storage system, a low-cost, acoustic-ultrasonic system has been developed to detect damage in high-pressure storage cylinders made of Carbon Fiber Reinforced Polymers (CFRP). This structural health monitoring system could lead to lighter, lower cost cylinders, and improved safety in automotive applications that utilize hydrogen and natural gas.Several Non-Deconstructive Evaluation (NDE) techniques were investigated in the course of this work, and low-cost piezo-film sensors were selected to monitor the cylinder. These sensors were integrated into the carbon fiber structure, resulting in a sensor network that can be used for real-time structural health monitoring of composite cylinders. The system was operated by exciting the piezo-film sensors with an impulse and then the corresponding structural response (or signature) was measured and analyzed. This was compared to a previously measured response and evaluated for changes which can indicate failures in the tank. The analysis reduces the changes in the structural response to a single damage coefficient, which can then be used for malfunction indication and decision making in an automotive on-board microprocessor control system.The technology can be deployed at a reasonable cost, and has been designed to accurately detect damage with little or no maintenance required. Thirty cylinders were used in a test matrix to examine all possible failure mechanisms of the tanks, including: fatigue, cuts and gouges, impact and delaminations, stress rupture, heat damage, and combinations of these damage mechanisms. The damage detection system was capable of detecting damage long before a critical condition arose for all cases. However, further development and testing into larger cylinder designs and testing is still required to develop a final commercial product

Embedding optical sensors within additive manufactured high melting point metals for condition measurement within harsh environments

The use of optical fibre sensors, such as fibre Bragg gratings (FBG), provides opportunity for condition health monitoring of a structure or process. FBGs allow for in-situ measurement of temperature and strain. The measurement of these parameters is important for advanced and complex structures where these sensors can provide real-time information to support lifetime condition monitoring. In general, sensor reliability drops as the temperature, moisture content and environmental corrosiveness increases. These limitations can be overcome by embedding sensors in high melting point metals to extend their operation for use at elevated temperatures and within harsh environments. A fibre embedding process chain has been devised to facilitate embedding of optical fibres within additive layer manufactured (ALM) stainless steel (SS) components. The ALM process provides access to any point of the component during manufacture, which is beneficial for the embedding of sensors inside a functional component. Furthermore, parts with complex geometries and internal features, unattainable with other forms of manufacture, become feasible using ALM technologies, but pose additional challenges for accurate modelling and external monitoring. Embedding sensors directly into such structures is a possible solution to this challenge. Selective laser melting is a powder bed fusion ALM technique where a laser selectively melts metallic powder in accordance with the geometrical data of the build layer, defined by a 3D model. The small spot sizes achievable by selective laser melting (SLM) systems are well suited for fibre embedding as the localised melt pools limits interaction through conduction with the surrounding material. A system has been set up for use with SS-316 powder, that is capable of embedding fibres in test structures. The high nickel content within SS-316 allows for intermixing of the host material with the fibre protective nickel jacket thereby bonding the fibre to the surrounding material. The work of this thesis defines process parameters suitable for repeatable and reliable embedding of FBG sensors inside SS-316 coupons. 5µm thick Cr layers are deposited onto lengths of stripped optical fibres containing FBGs using the RF sputter deposition system (RF power 100W, deposition time 30mins, processing pressure 410 −4mBar). This is followed by a ≥300 µm Ni coating using the developed Ni plating system (current density 2-7 A/dm2 , voltage 30V max, plating time ≥16hrs). The SLM build parameters for building SS-316 coupons (100W Laser power, 300mm/s scanning velocity, 60μm hatch spacing, 200μs pulse duration, 1kHz modulation frequency and scan orientation rotated by 90° between layers) and the modified build parameters for the embedding process (90W laser power, 300mm/s scan velocity, 100μm hatch spacing, 200μs pulse duration, 1kHz modulation frequency and a scan orientation parallel to fibre profile) are defined with respect to optimisation of the available equipment for fibre embedding procedures

Fiber Optic Sensors for Energy Applications under Harsh Environmental Conditions

Real-time monitoring physical and chemical parameters in next generation energy-production system is of significant importance to improve the efficiency and reduce the emission for a wide range of applications. Traditional electrical point sensors have limited utilities for direct measurements at high temperature or in highly reactive and corrosive environment. Given the resilience at high temperatures, immunity to electromagnetic interference and intrinsic explosion proof in combustion gas, fiber optic sensors open up opportunity to perform various measurements in energy applications under harsh environments. In this thesis, both chemical and physical sensors were demonstrated to explore the potential of fiber optic sensors in energy industry. The first scheme is fiber optic chemical gas sensing enabled by nanostructured functional metal oxides. A scalable manufacturing approach was developed to produce nano-porous metal oxides with the refractive index tailored to match the optical fiber material. Combined with this functional semiconducting metal oxides, fiber optic chemical sensors with high selectivity and sensitivity was developed using both D-shaped fiber and single crystal sapphire fiber. The sensors performed accurate hydrogen measurement at a record-high temperature of 800 deg C. The second scheme covers a high temperature distributed sensing using Rayleigh backscatter based optical frequency domain reflectometry. Ultrafast laser direct writing method was used to enhance the in-fiber scattering signal and high-temperature stability. Due to the high signal-to-noise ratio and thermal stability of the inscribed nanogratings in the fiber, real-time monitoring of temperature distribution in the operational solid oxide fuel cell was achieved with 5-mm spatial resolution at 800 deg C. In the third scheme, a multi-point sensing system for thermal dynamics monitoring of lithium-ion battery assembly was demonstrated using multimode random air hole fibers infiltrated with quantum dots. The photoluminescence intensity dependence on the ambient temperatures were used to gauge the local operational temperature of lithium-ion batteries. Multi-point temperature sensing systems were developed by bundling quantum dots infiltrated random air hole fibers together. The temperature of the batteries can be real-time monitored using a low-cost UV diode laser as light source and a cellular phone CCD camera as detector

The Public Service Media and Public Service Internet Manifesto

This book presents the collectively authored Public Service Media and Public Service Internet Manifesto and accompanying materials.The Internet and the media landscape are broken. The dominant commercial Internet platforms endanger democracy. They have created a communications landscape overwhelmed by surveillance, advertising, fake news, hate speech, conspiracy theories, and algorithmic politics. Commercial Internet platforms have harmed citizens, users, everyday life, and society. Democracy and digital democracy require Public Service Media. A democracy-enhancing Internet requires Public Service Media becoming Public Service Internet platforms – an Internet of the public, by the public, and for the public; an Internet that advances instead of threatens democracy and the public sphere. The Public Service Internet is based on Internet platforms operated by a variety of Public Service Media, taking the public service remit into the digital age. The Public Service Internet provides opportunities for public debate, participation, and the advancement of social cohesion. Accompanying the Manifesto are materials that informed its creation: Christian Fuchs’ report of the results of the Public Service Media/Internet Survey, the written version of Graham Murdock’s online talk on public service media today, and a summary of an ecomitee.com discussion of the Manifesto’s foundations

Investigating the effect of ultrasonic consolidation on shape memory alloy fibres

This research was driven by the capability of the Ultrasonic Consolidation (UC) manufacturing process to create smart metal matrix composites for use within high value engineering sectors, such as aerospace. The UC process is a hybrid additive/subtractive manufacturing process that embeds fibres into metal matrices via the exploitation of a high plastic flow, low temperature phenomenon encountered at ultrasonic frequency mechanical vibrations. The research concerned an investigation of the use of the UC process for embedding Nickel-Titanium alloy (NiTi) shape memory alloy (SMA) fibres into Aluminium (Al) matrices which could potentially be used as vibration damping structures, stress state variable structures, as well as other future smart material applications. It was hypothesised that the fibre volume fraction within a UC matrix was limited due to a reduction in foil/foil bonding, caused by increased fibre numbers, as opposed to the total level of plastic flow of the matrix material being insufficient to accommodate the increased fibre numbers. This hypothesis was tested by increasing the NiTi SMA fibre volume fraction, within an Al 3003 (T0) metal matrix, beyond that of previous UC work. The metal matrix and the fibre matrix interface of these samples was then microscopically analysed and the overall UC sample integrity was tested via mechanical peel testing. It was found that a fibre volume fraction of ~9.8% volume (30 X Ø100 µm SMA fibres) was the maximum achievable using an Al 3003 (T0) 100 µm thick foil material and conventional UC fibre embedding. A revised hypothesis was postulated that the interlaminar structure created during UC was affected by the process parameters used. This interlaminar structure contained areas of un-bonded foil and the increase of UC process parameters would reduce this area of un-bonded foil. Areas of this interlaminar structure were also thought to have undergone grain refinement which would have created harder material areas within the structure. It was suggested that maximum plastic flow of the matrix had not been reached and thus the use of larger diameter NiTi SMA fibres were embedded to increase the effective SMA fibre volume fraction within Al 3003 (T0) UC samples. It was suggested that the embedding of SMA fibres via UC had an abrasive effect on the SMA fibres and the SMA fibres had an effect on the Al 3003 (T0) microstructure. It was further suggested that the activation of UC embedded SMA fibres would reduce the strength of the fibre/matrix interface and the matrix would impede the ability of the SMA fibres to contract causing a forceful interaction at the fibre to matrix interface, weakening the UC structure. The investigation to test the revised hypothesis was broken down into three sections of study. Study 1 was a methodology to determine the characteristics of the interlaminar surface created via UC and how this surface affected the nature of the consolidated sample. UC samples of Al 3003 (T0) were manufactured using a range of process parameters. The analysis involved optical microscopy to determine the UC weld density and the interlaminar surface; mechanical peel testing to quantify the interlaminar bond strength; white light interferometry to measure the interlaminar surface profile and microhardness measurements to determine the hardness of the interlaminar material. Study 2 was a methodology to allow the analysis of the microstructural and mechanical interactions at the fibre/matrix interface, post-UC. Al 3003 (T0) samples were manufactured via UC using a range of process parameters with various NiTi SMA fibre diameters embedded. The analysis involved using mechanical peel testing to determine the interlaminar bond strength; optical microscopy to determine the level of fibre encapsulation; scanning electron microscopy and focussed ion beam analysis to analyse the fibre and matrix grain structures and microscopic interactions. Study 3 was a methodology to investigate the fibre usage as would be expected from envisaged applications of an SMA containing metal matrix composite. Samples were manufactured using a range of UC process parameters with various SMA fibre diameters embedded and the embedded SMA fibres were subjected to different extension/contraction cycle numbers. The analysis involved using mechanical peel testing to determine the interlaminar bond strength; optical microscopy to determine the level of fibre encapsulation and the interlaminar effect of fibre activation; fibre pullout testing to measurement the strength of the fibre/matrix interaction and load rate testing of the activated SMA fibres to monitor performance. The interlaminar surface was found to affect the strength and density of interlaminar bonding during the UC process and the use of higher UC process parameters affected this interlaminar structure. Levels of un-bonded material were found within the interlaminar structure and these levels were found to decrease with increasing sonotrode amplitude and pressure with reducing speed. It was suggested that a specifically texture sonotrode could be developed to modify the interlaminar structure to the requirements of the intended sample application. The measurement of the interlaminar material hardness was unsuccessful and future work would likely require a different methodology to measuring this. The work identified a grain refining effect of the embedded SMA fibres on the Al 3003 (T0) matrix material, (grain sizes were reduced from ~15 µm to <1 µm within 20 µm of the SMA fibres), as well as localised damage caused by the UC process to the SMA fibres. The performance of the activated SMA fibres established that this damage did not prohibit the ability of the SMAs to function however the compressive nature of the Al 3003 (T0) matrix was identified as reducing the ability of the SMA fibres to contract. Additionally it was found that the activation of SMA fibres within an Al 3003 (T0) matrix resulted in a reduction of the fibre/matrix interface strength which allowed fibres to be pulled from the composite with greater ease (a loss of ~80% was encountered after a single activation and extension cycle). The use of larger SMA fibre diameters allowed for the fibre volume fraction to be increased however the activation of these SMA fibres had a delaminating effect on the Al 3003 (T0) structure due to the size of the radial expansion of the SMA fibre. The work furthered the understanding of the effect of UC on SMA fibres and highlighted the importance of the interlaminar surface in UC and that to increase the SMA fibre volume fraction to a useable level (25-50%) then an alternative fibre embedding method within UC is required. The fibre/matrix interface interactions during SMA activation have implications in the ability of UC SMA embedded smart metal matrix composites to function successfully due to weakening effects on fibre matrix interface strength and the ability to achieve SMA fibre activation within the metal matrix

Optical fibre sensors for monitoring prestressed concrete structures in nuclear power plants

This thesis was previously held under moratorium from 20th November and 20th November 2015.Lifetime extensions of nuclear fission reactors in the UK are required to satisfy growing demands for electrical power. Many of these reactors are nearing the end of their original design life, so the continued structural integrity, particularly of the reactors' prestressed concrete pressure vessels and containments is of prime concern. Currently, a lift-off inspection of a 1 % random sample of prestressing tendons is performed at 18 month to 5 year intervals to ensure adequate prestress is present in these structures, but the extended life times are making higher resolution, more frequent and in-depth monitoring techniques more desirable. In this thesis, a method of instrumenting prestressing strands with optical fibre Bragg grating strain sensors is outlined. An all-metal encapsulation and bonding technique is developed to ensure sensor reliability under the radioactive and high-stress environments of fission reactors. This 'smart strand' is complemented by a specially developed interrogation scheme capable of continuously and automatically monitoring static and dynamic nanoscale changes in Bragg grating strain. High-resolution interrogation was achieved by extending an interferrometric demodulation technique into the static measurement regime. By modulating the strain sensitivity using a fast optical switch, strain signals could be recovered independently of noise sources using various signal processing algorithms. The application of this technology could augment the continued monitoring of concrete vessel integrity, reducing both the risks and costs associated with performing lift-off measurements in the current and next generation of nuclear reactors.Lifetime extensions of nuclear fission reactors in the UK are required to satisfy growing demands for electrical power. Many of these reactors are nearing the end of their original design life, so the continued structural integrity, particularly of the reactors' prestressed concrete pressure vessels and containments is of prime concern. Currently, a lift-off inspection of a 1 % random sample of prestressing tendons is performed at 18 month to 5 year intervals to ensure adequate prestress is present in these structures, but the extended life times are making higher resolution, more frequent and in-depth monitoring techniques more desirable. In this thesis, a method of instrumenting prestressing strands with optical fibre Bragg grating strain sensors is outlined. An all-metal encapsulation and bonding technique is developed to ensure sensor reliability under the radioactive and high-stress environments of fission reactors. This 'smart strand' is complemented by a specially developed interrogation scheme capable of continuously and automatically monitoring static and dynamic nanoscale changes in Bragg grating strain. High-resolution interrogation was achieved by extending an interferrometric demodulation technique into the static measurement regime. By modulating the strain sensitivity using a fast optical switch, strain signals could be recovered independently of noise sources using various signal processing algorithms. The application of this technology could augment the continued monitoring of concrete vessel integrity, reducing both the risks and costs associated with performing lift-off measurements in the current and next generation of nuclear reactors