Developing Dynamic Digital Image Techniques with Continuous Parameters to Detect Structural Damage

Several earthquakes with strong magnitude occurred globally at various locations, especially the unforgettable tsunami disaster caused by the earthquake in Indonesia and Japan. If the characteristics of structures can be well understood to implement new technology, the damages caused by most natural disasters can be significantly alleviated. In this research, dynamic digital image correlation method for using continuous parameter is applied for developing a low-cost digital image correlation coefficient method with advanced digital cameras and high-speed computers. The experimental study using cantilever test object with defect control confirms that the vibration mode calculated using this proposed method can highly express the defect locations. This proposed method combined with the sensitivity of Inter-Story Drift Mode Shape, IDMS, can also reveal the damage degree of damage structure. These test and analysis results indicate that this proposed method is high enough for applying to achieve the object of real-time online monitoring of structure

Passive low frequency RFID for non-destructive evaluation and monitoring

Ph. D ThesisDespite of immense research over the years, defect monitoring in harsh environmental conditions still presents notable challenges for Non-Destructive Testing and Evaluation (NDT&E) and Structural Health Monitoring (SHM). One of the substantial challenges is the inaccessibility to the metal surface due to the large stand-off distance caused by the insulation layer. The hidden nature of corrosion and defect under thick insulation in harsh environmental conditions may result in it being not noticed and ultimately leading to failures. Generally electromagnetic NDT&E techniques which are used in pipeline industries require the removal of the insulation layer or high powered expensive equipment. Along with these, other limitations in the existing techniques create opportunities for novel systems to solve the challenges caused by Corrosion under Insulation (CUI). Extending from Pulsed Eddy Current (PEC), this research proposes the development and use of passive Low Frequency (LF) RFID hardware system for the detection and monitoring of corrosion and cracks on both ferrous and non-ferrous materials at varying high temperature conditions. The passive, low cost essence of RFID makes it an enchanting technique for long term condition monitoring. The contribution of the research work can be summarised as follows: (1) implementation of novel LF RFID sensor systems and the rig platform, experimental studies validating the detection capabilities of corrosion progression samples using transient feature analysis with respect to permeability and electrical conductivity changes along with enhanced sensitivity demonstration using ferrite sheet attached to the tag; (2) defect detection using swept frequency method to study the multiple frequency behaviour and further temperature suppression using feature fusion technique; (3) inhomogeneity study on ferrous materials at varying temperature and demonstration of the potential of the RFID system; (4) use of RFID tag with ceramic filled Poly-tetra-fluoro-ethyulene (PTFE) substrate for larger applicability of the sensing system in the industry; (5) lift-off independent defect monitoring using passive sweep frequency RFID sensors and feature extraction and fusion for robustness improvement. This research concludes that passive LF RFID system can be used to detect corrosion and crack on both ferrous and non-ferrous materials and then the system can be used to compensate for temperature variation making it useful for a wider range of applications. However, significant challenges such as permanent deployment of the tags for long term monitoring at higher temperatures and much higher standoff distance, still require improvement for real-world applicability.Engineering and Physical Sciences Research Council (EPSRC) CASE, National Nuclear Laboratory (NNL)

Observations of stress corrosion cracking behaviour in super duplex stainless steel

The new generation of highly alloyed super duplex stainless steels such as Zeron 100 are preferable materials for industrial applications demanding high strength, toughness and superior corrosion resistance, especially against stress corrosion cracking (SCC). SCC is an environmentally assisted failure mechanism that occurs due to exposure to an aggressive environment while under a tensile stress. The mechanism by which SCC of duplex stainless steel is expected to suffer depends on the combination of electrochemical and the mechanical interaction between austenite and ferrite in the duplex alloys. The main aims of this work are to study the suitability of digital image correlation (DIC) to monitor the initiation and propagation of SCC and to understand how the microstructure of duplex stainless steel influences the kinetics of crack initiation and growth. The combined analysis of DIC, SEM and EBSD was used to study the relative crack propagation and the effect of interphase boundaries on crack growth as well. Cracking was initiated beneath saturated MgCl2 droplets in an atmospheric environment at 80°C and relative humidity of 30-33%. As-received and 10% cold rolled samples (with two orientations transverse and longitudinal to the loading direction) were subjected to an applied strain of 0.03 under displacement controlled tests. Regular optical observations were recorded of the droplets and their surrounding area. DIC analyses used the differentiation of the displacement fields to obtain the apparent surface strains used to detect crack initiation and propagation, and to measure crack opening displacements. It was found that DIC was efficiently observed the strain developments and the displacements in observed surfaces outside of the droplets but it could not identify or quantify the initiation of the cracks inside the droplets because of the mobility of the salt film and the high amount of the corrosion products formed which obscure the vision under the droplets. In addition, results showed that early stage microcracks were initiated in α phase and α/γ interfaces and propagated preferentially in the ferrite phase. Also, SCC initiation and propagation was accelerated by cold rolling and the grains orientations were of major effects on the retardation of crack propagation which was more severe in the transverse rolling direction. Also, there was no relation established between the strain level and the density of pitting in either phase.EThOS - Electronic Theses Online ServiceSABICGBUnited Kingdo

Detection, Diagnosis and Prognosis: Contribution to the energy challenge: Proceedings of the Meeting of the Mechanical Failures Prevention Group

The contribution of failure detection, diagnosis and prognosis to the energy challenge is discussed. Areas of special emphasis included energy management, techniques for failure detection in energy related systems, improved prognostic techniques for energy related systems and opportunities for detection, diagnosis and prognosis in the energy field

Solid state phase transformations in Advanced Steels

In order to achieve progress in Advanced Steels development came more emphasis in solid state phase transformations are received. For achieving the desired mechanical and corrosion resistance properties in Duplex Stainless Steels (DSS), a precise knowledge of the precipitation kinetics of secondary phases, the morphology of the precipitates and effects of the alloying elements on different properties is needed. A complicated chemical composition and the production technology route make each grade of DSS a unique object for a study. Besides, when the market needs to reduce weight and increase product durability by utilizing Advance Strength Steels, a deeper understanding of their transformations is required. The aim of the present work was to study the main features of phase precipitation in diverse Duplex Stainless Steels grades, including Lean Duplex, Standard and Superduplex. Beside analyze the effects of metallurgical features on the properties of DSS and Advanced High Strength Dual Phase (DP) steels. One of the tasks was to study the effects plastic deformation after heat treatment in diverse duplex grades

Mechanical and electrochemical behavior of Fe3Al-xCr intermetallics

Different concentrations of Cr were added to the binary intermetallics, in order to enhance the ductility and pitting resistance of alloys. The results of nanoindentation in air show the influence of Cr on various mechanical properties like Young’s modulus, Gibbs free energy needed for homogeneous dislocation nucleation, and hardness. The increase of the Young’s modulus and Gibbs free energy after addition of Cr is due to the enhancement of the strength of interatomic bonds. Moreover, Cr decreases the flow stress and eases the cross slipping of dislocations. Furthermore, the results of nanoindentation under cathodic and anodic charging show the impact of hydrogen on the reduction of Young’s moduli of alloys; whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the dislocation line energy based on the defect acting agents concept. Based on our results, the mechanism of dislocation shielding should be considered for analyzing the fracture characteristics of in aqueous solutions, and in atmospheres containing hydrogen. Finally, the effect of Cr on electrochemical properties of passive layer, and susceptibility of alloys to pitting and crevice corrosion in solutions with different concentrations of ions, was studied using various methods like cyclic polarization, cyclic voltammetry, impedance spectroscopy and the Mott-Schottky.Um die Duktilität und den Widerstand gegen Lochkorrosion zu verbessern, wurde in einer intermetallischen - Legierung die Konzentrationen an Cr variiert. Durch Nanoindentations-Messungen an Luft konnte gezeigt werden, dass Cr die mechanischen Eigenschaften wie z.B. den E-Modul, die Gibbs-Energie für homogene Versetzungsbildung und die Härte beeinflusst. Der Anstieg des E-Moduls und der Gibbs-Energie durch die Zugabe von Cr kann auf die Verstärkung der interatomaren zurückgeführt werden. Außerdem verringert Cr die Fließspannung und erleichtert das Quergleiten von Versetzungen. Die Ergebnisse der Nanoindentation mit kathodischer und anodischer Beladung zeigten, dass Wasserstoff den E-Moduls der Legierung verringert; Bei geringem Cr-Gehalt kam es hingegen zu einem drastischen Abfall der „pop-in load“ bei kathodischer Beladung, was durch die Verringerung der Versetzungslinienenergie aufgrund des „defect acting agents“ Konzepts erklärt werden kann. Unsere Ergebnisse zeigen, dass der shielding-Effekt der Versetzungen für die Analyse des Bruchverhaltens von Legierungen in wässrigen Lösungen und wasserstoffhaltigen Umgebungen berücksichtigt werden sollte. Des Weiteren wurde die Wirkung von Cr auf passive Oxidschichten, elektrochemische Eigenschaften und die Neigung zu Loch- und Spaltkorrosion in Lösungen mit verschiedenen Ionen Konzentrationen mit Hilfe verschiedener Methoden u.a. Polarisation, zyklische Voltammetrie, Impedanz Spektroskopie und Mott-Schottky untersucht

Mechanical and electrochemical behavior of Fe3Al-xCr intermetallics

Different concentrations of Cr were added to the binary intermetallics, in order to enhance the ductility and pitting resistance of alloys. The results of nanoindentation in air show the influence of Cr on various mechanical properties like Young’s modulus, Gibbs free energy needed for homogeneous dislocation nucleation, and hardness. The increase of the Young’s modulus and Gibbs free energy after addition of Cr is due to the enhancement of the strength of interatomic bonds. Moreover, Cr decreases the flow stress and eases the cross slipping of dislocations. Furthermore, the results of nanoindentation under cathodic and anodic charging show the impact of hydrogen on the reduction of Young’s moduli of alloys; whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the dislocation line energy based on the defect acting agents concept. Based on our results, the mechanism of dislocation shielding should be considered for analyzing the fracture characteristics of in aqueous solutions, and in atmospheres containing hydrogen. Finally, the effect of Cr on electrochemical properties of passive layer, and susceptibility of alloys to pitting and crevice corrosion in solutions with different concentrations of ions, was studied using various methods like cyclic polarization, cyclic voltammetry, impedance spectroscopy and the Mott-Schottky.Um die Duktilität und den Widerstand gegen Lochkorrosion zu verbessern, wurde in einer intermetallischen - Legierung die Konzentrationen an Cr variiert. Durch Nanoindentations-Messungen an Luft konnte gezeigt werden, dass Cr die mechanischen Eigenschaften wie z.B. den E-Modul, die Gibbs-Energie für homogene Versetzungsbildung und die Härte beeinflusst. Der Anstieg des E-Moduls und der Gibbs-Energie durch die Zugabe von Cr kann auf die Verstärkung der interatomaren zurückgeführt werden. Außerdem verringert Cr die Fließspannung und erleichtert das Quergleiten von Versetzungen. Die Ergebnisse der Nanoindentation mit kathodischer und anodischer Beladung zeigten, dass Wasserstoff den E-Moduls der Legierung verringert; Bei geringem Cr-Gehalt kam es hingegen zu einem drastischen Abfall der „pop-in load“ bei kathodischer Beladung, was durch die Verringerung der Versetzungslinienenergie aufgrund des „defect acting agents“ Konzepts erklärt werden kann. Unsere Ergebnisse zeigen, dass der shielding-Effekt der Versetzungen für die Analyse des Bruchverhaltens von Legierungen in wässrigen Lösungen und wasserstoffhaltigen Umgebungen berücksichtigt werden sollte. Des Weiteren wurde die Wirkung von Cr auf passive Oxidschichten, elektrochemische Eigenschaften und die Neigung zu Loch- und Spaltkorrosion in Lösungen mit verschiedenen Ionen Konzentrationen mit Hilfe verschiedener Methoden u.a. Polarisation, zyklische Voltammetrie, Impedanz Spektroskopie und Mott-Schottky untersucht

Numerical analysis of fatigue crack growth in welded joints with multiple defects

In the case of welded steel structures (such as pressure equipment), welded joints are often critical location for stress concentrations, due to different mechanical properties and chemical composition compared to the parent material, and due to changes in geometry. In addition, the presence of imperfections (defects) in welded joints can contribute to the increase in local stress, resulting in crack initiation. Recently, standards that are related to acceptable dimensions of various types of defects in welded joints started taking fatigue loading into account as well. For the purpose of this research, a 3D numerical model was made, of a welded joint with different types of defects (linear misalignment and a crack in the weld metal), based on the previous work, which involved static loading of the same specimen. In this case, fatigue was taken into account, and the simulation was performed using ABAQUS software, as well as Morfeo, an add-on used for determining the fatigue behaviour of structures via XFEM (extended finite element method). The welded joint was made using steel P460NL1 as the parent material, and EPP2NiMo2 wire was used for the weld metal. An additional model was made, whose defects included a crack and an overhang. Fatigue crack growth analysis was performed for this model as well, and the results for stress intensity factors and stress/strain distribution were compared in order to obtain information about how different defects can affect the integrity of a welded joint