Relevant bibliographies by topics / Alternating current potential drop technique

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Alternating current potential drop technique'

Author: Grafiati
Published: 4 June 2021
Last updated: 18 February 2022

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Journal articles on the topic "Alternating current potential drop technique"

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Li, Wenyang, Fangji Gan, Shiping Zhao, Yongjie Zhou, and Xiaoming He. "Multidirectional Alternating Current Potential Drop Technique for Detecting Random Cracks." IEEE Access 6 (2018): 76640–45. http://dx.doi.org/10.1109/access.2018.2883757.

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Huang, Xuejun, Lun Yu, and Ronald Ballinger. "Alternating Current Potential Drop Technique to Detect Pit-to-Crack Transition." MRS Advances 1, no. 17 (2016): 1241–46. http://dx.doi.org/10.1557/adv.2016.262.

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ABSTRACTPitting and localized corrosion can occur under various conditions and accelerate the subsequent cracking and the failure of a component. Pit-to-crack transition is considered a critical transition process and has a significant impact on the total lifetime of a component. In this study, an alternating current potential drop (ACPD) system is built and applied the detection of the pit-to-crack transition. The results show that the ACPD system is capable and sensitive to crack initiation and that the sensitivity increased with increased frequency. Crack initiation sites from pits are characterized and discussed.
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Gan, Fangji, Yuting Li, Zhengjun Wan, and Junbi Liao. "Inner defect depth detection using a multifrequency alternating current potential drop technique." AIP Advances 6, no. 10 (October 2016): 105312. http://dx.doi.org/10.1063/1.4954294.

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Li, Yuting, Fangji Gan, Zhengjun Wan, Junbi Liao, and Wenqiang Li. "Novel Method for Sizing Metallic Bottom Crack Depth Using Multi-frequency Alternating Current Potential Drop Technique." Measurement Science Review 15, no. 5 (October 1, 2015): 268. http://dx.doi.org/10.1515/msr-2015-0037.

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Abstract Potential drop techniques are of two types: the direct current potential drop (DCPD) technique and alternating current potential drop (ACPD) technique, and both of them are used in nondestructive testing. ACPD, as a kind of valid method in sizing metal cracks, has been applied to evaluate metal structures. However, our review of most available approaches revealed that some improvements can be done in measuring depth of metal bottom crack by means of ACPD, such as accuracy and sensitivity of shallow crack. This paper studied a novel method which utilized the slope of voltage ratio-frequency curve to solve bottom crack depth by using a simple mathematic equation based on finite element analysis. It is found that voltage ratio varies linearly with frequency in the range of 5-15 Hz; this range is slightly higher than the equivalent frequency and lower than semi-permeable frequency. Simulation and experiment show that the novel method can measure the bottom crack depth accurately.
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Raja, Manoj K., S. Mahadevan, B. P. C. Rao, S. P. Behera, T. Jayakumar, and Baldev Raj. "Influence of crack length on crack depth measurement by an alternating current potential drop technique." Measurement Science and Technology 21, no. 10 (August 3, 2010): 105702. http://dx.doi.org/10.1088/0957-0233/21/10/105702.

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Li, Wenyang, Shiping Zhao, and Fangji Gan. "Characterisation of backwall crack depth using the pulsed potential drop method." Insight - Non-Destructive Testing and Condition Monitoring 62, no. 9 (September 1, 2020): 555–58. http://dx.doi.org/10.1784/insi.2020.62.9.555.

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The alternating current potential drop (ACPD) technique has been used for monitoring backwall cracks in electrical conductors. However, previous systems required too much labour when ACPD measurements were made over a large frequency range (1 Hz-10 kHz). In this paper, a pulsed potential drop (PPD) method is found to be superior, not only in efficiency and stability but also in accurate crack detection. The detected signal excited by the pulsed current appears to be more sensitive to depth variations and, therefore, can be used for estimating crack depth in PPD testing. Experiments have been performed on AISI 1045 plates with machined cracks; the results obtained from these tests show the feasibility of crack monitoring using the PPD method.
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Satyarnarayan, L., D. M. Pukazhendhi, Krishnan Balasubramaniam, C. V. Krishnamurthy, and D. S. Ramachandra Murthy. "Phased Array Ultrasonic Measurement of Fatigue Crack Growth Profiles in Stainless Steel Pipes." Journal of Pressure Vessel Technology 129, no. 4 (July 24, 2006): 737–43. http://dx.doi.org/10.1115/1.2767367.

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This paper reports experimental sizing of fatigue crack profiles that are initiated from artificially made circumferential starter notches in stainless steel pipes of 169mm outer diameter and 14.33mm thickness, which were subjected to cyclic bending loads in a four point bending load arrangement using two nondestractive evaluation (NDE) methods: (a) phased array ultrasonic technique and (b) alternating current potential drop technique. The crack growth estimated using the two NDE techniques were compared with the beach marks that were present in the fracture surface. A simulation study using the ray tracing method was carried out to model the ultrasonic wave propagation in the test specimen, and the results were compared with the experimental results.
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M Buss, Thomas, James P Rouse, Christopher J Hyde, and Seamus D Garvey. "Development of a technique for the real-time determination of crack geometries in laboratory samples." MATEC Web of Conferences 165 (2018): 09004. http://dx.doi.org/10.1051/matecconf/201816509004.

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Crack size determination using electrical potentials both in service and in the laboratory has been undertaken for many years. In the laboratory this has mainly concentrated on the measurement of crack depth, with either alternating current (AC) or direct current (DC) supplies. Some work to determine the varying depth along the width of cracks as an inspection tool of in service parts using mapping methods has been done. This has used both AC and DC utilising various models to understand the data recorded, in Alternating Current Potential Drop (ACPD) a range of frequencies have been used to give various skin depths. The resulting analyses have been grouped into two groups 'thin skin' and 'thick skin', in the thin skin case the skin depth is significantly smaller than the depth of the crack 1/10th of the crack depth whereas in the thick skin cases are for cases where skin depth is over this limit. Some work has been carried out to try and unify these two approaches. The work presented here looks to develop a method using variable frequency ACPD to resolve further information about cracks growing in laboratory specimens. A system has been developed to rapidly sweep a wide frequency band and record voltage drop across a crack or feature. A selection of steel samples with known geometries and features have been used to trial and benchmark the technique. These samples have a range of cross sections as well as machined features or a range of shapes and sizes to simulate a range of crack geometries. This work has been approximated using a 2D computational model. This has been done using a reduced thickness approach.
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Li, Yuting, Fangji Gan, Zhengjun Wan, and Junbi Liao. "An SVM approach with alternating current potential drop technique to classify pits and cracks on the bottom of a metal plate." AIP Advances 6, no. 9 (September 2016): 095202. http://dx.doi.org/10.1063/1.4962550.

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Koch, Alexander, Philipp Wittke, and Frank Walther. "Computed Tomography-Based Characterization of the Fatigue Behavior and Damage Development of Extruded Profiles Made from Recycled AW6060 Aluminum Chips." Materials 12, no. 15 (July 25, 2019): 2372. http://dx.doi.org/10.3390/ma12152372.

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The possibility of producing profiles directly by hot extrusion of aluminum chips, normally considered as scrap, is a promising alternative to the energy-intensive remelting process. It has to be taken into account that the mechanical properties depend on the quality of the weld seams between the chips, which arise during the extrusion process. To estimate the influence of the weld seams, quasistatic and cyclic investigations were performed on chip-based profiles and finally compared with cast-based extruded profiles. In order to gain comprehensive information about the fatigue progress, different measurement techniques like alternating current potential drop (ACPD)-technique, hysteresis measurements, and temperature measurements were used during the fatigue tests. The weld seams and voids were investigated using computed tomography and metallographic techniques. Results show that quasistatic properties of chip-based specimens are only reduced by about 5%, whereas the lifetime is reduced by about a decade. The development of the fatigue cracks, which propagate between the chip boundaries, was characterized by an intermittent testing strategy, where an initiation of two separate cracks was observed.
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Dissertations / Theses on the topic "Alternating current potential drop technique"

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Šubrt, Stanislav. "Návrh přístroje pro analýzu vzniku a šíření trhlin." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2014. http://www.nusl.cz/ntk/nusl-231511.

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The main goal of this thesis is to get an insight into a field of non-destructive testing using potential drop techniques that have nowadays become the standard not only in the fatigue and loading tests but also in the industry. These methods can serve to non-destructively and continuously measure material specimens, thickness, corrosion losses, deformations, spectroscopy and detection and analysis of crack geometry. They can help to identify materials and measure material changes over time. The second part of this thesis deals with designing the aperture for detection of cracks in steam and product piping using potential drop technique modified by Ing. Ladislav Korec, CSc. Last part deals with extensive testing, experimenting and evaluation of the aperture.
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Cevik, Gul. "Investigation Of The Effect Of Orientation And Heat Treatment On The Stress Corrosion Cracking Susceptibility Of 7050 Aluminum Alloy." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12605220/index.pdf.

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In the present work, the effect of variation in specimen orientation and heat treatment on the Stress Corrosion Cracking (SCC) susceptibility of 7050 aluminum alloy was investigated in 3,5% NaCl solution and under freely corroding conditions. For this purpose, Constant Extension Rate Tests (CERT) was performed on precracked Compact Tension (CT) specimens and the Direct Current Potential Drop technique was applied to measure the crack lengths. In addition to crack length versus time curves, the relationship between the crack growth rate and the stress intensity factor was determined. Fractographic analysis was utilized extensively to support the findings related with basic mechanisms of cracking. The alloy was found to be in the most susceptible state in the SL orientation, in which the crack propagation direction is parallel to the rolling direction. The resistance to SCC is higher in the TS but at maximum in LT orientation where the loading direction is parallel to the rolling direction. In the peak aging treatment, T651, alloy is susceptible to SCC in SL orientation. When the over aging treatment, T7651, is applied the resistance is increased and the two step over aging treatment, T73651, has resulted in an additional improvement in this orientation. On the other hand, the alloy showed higher resistance to SCC in TS and LT orientations in T651 condition compared to the T7651 and T73651 treatments. In these orientations, the alloy is less susceptible in T73651 condition than in T7651 treatment.
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Huang, Yongqiang. "Alternating current potential drop and eddy current methods for nondestructive evaluation of case depth /." 2004.

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Book chapters on the topic "Alternating current potential drop technique"

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Livingstone, F., and I. M. Kilpatrick. "On-Line Fatigue Crack Growth Monitoring in Externally Pressurised Vessels Using the Alternating Current Potential Drop (ACPD) Technique." In Review of Progress in Quantitative Nondestructive Evaluation, 1531–39. Boston, MA: Springer US, 1988. http://dx.doi.org/10.1007/978-1-4613-0979-6_79.

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Tenkamp, Jochen, Kevin Bleicher, Sven Klute, Karin Chrzan, Alexander Koch, and Frank Walther. "Advanced Characterization of the Cyclic Deformation and Damage Behavior of Al-Si-Mg Cast Alloys Using Hysteresis Analysis and Alternating Current Potential Drop Method." In Light Metals 2019, 167–75. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-05864-7_23.

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Chen, Xiang, Randy K. Nanstad, and Mikhail A. Sokolov. "J-R Curve Determination for Disk-Shaped Compact Specimens Based on the Normalization Method and the Direct Current Potential Drop Technique." In Small Specimen Test Techniques: 6th Volume, 70–87. 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959: ASTM International, 2014. http://dx.doi.org/10.1520/stp157620140012.

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Dias Tavares Costa, Alexandre, Anna Caroline Campos Aguiar, Angelina Moraes Silva, and Dhelio Batista Pereira. "Point-of-Care Strategies Applied to Malaria Diagnosis." In Current Topics and Emerging Issues in Malaria Elimination. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96721.

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Rapid and specific diagnosis of malaria remains one of the main strategies to fight the disease. The diagnosis is made primarily by the simple and low-cost thick drop technique, considered the gold standard test. However, the requirement for good quality microscopes and well-trained personnel often lead to inaccurate diagnosis, especially in cases of mixed infections or low parasitemia. Although PCR-based tests can help in these situations, this technique requires large and sensitive equipments, being unsuitable for point of care (POC) settings. A myriad of POC diagnostic tests have being developed in the last years, relying on molecular methods but also on novel strategies. New platforms, miniaturization techniques, and multiplexing possibilities promise great potential to improve disease diagnostics through fast and accurate detection of cases, even at remote places. Here, we will address the main POC strategies developed for the diagnosis of malaria, highlighting their strengths and weakness as POC applications.
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El-Azazy, Marwa. "Electrochemical Impedance Spectroscopy (EIS) in Food, Water, and Drug Analyses: Recent Advances and Applications." In Electrochemical Impedance Spectroscopy. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.92333.

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Electrochemical impedance spectroscopy (EIS) is a potent electrochemical technique with a variety of applications. EIS measurements involve the application of an alternating current (AC) voltage (or current) to the system under investigation, followed by measurement of the response in the form of AC current (or voltage) as a function of frequency. By and large, EIS is an exceptionally attractive in terms of applications. Being nondestructive with a feasibility of implementation to the system to be measured and the usefulness of data obtained in characterizing the studied systems, electrochemical impedance spectroscopy has realms of applications. As food and water safety and security is becoming a universal concern, the need for a technique that can detect water and food contaminants with relatively high sensitivity and selectivity is evolving. EIS has started to realize its potential with a wide-term use in water and food analyses.
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Gomes, Juliana Carneiro, Maíra Araújo de Santana, Clarisse Lins de Lima, Ricardo Emmanuel de Souza, and Wellington Pinheiro dos Santos. "Using Extreme Learning Machines and the Backprojection Algorithm as an Alternative to Reconstruct Electrical Impedance Tomography Images." In Biomedical Computing for Breast Cancer Detection and Diagnosis, 16–27. IGI Global, 2021. http://dx.doi.org/10.4018/978-1-7998-3456-4.ch002.

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Electrical Impedance Tomography (EIT) is an imaging technique based on the excitation of electrode pairs applied to the surface of the imaged region. The electrical potentials generated from alternating current excitation are measured and then applied to boundary-based reconstruction methods. When compared to other imaging techniques, EIT is considered a low-cost technique without ionizing radiation emission, safer for patients. However, the resolution is still low, depending on efficient reconstruction methods and low computational cost. EIT has the potential to be used as an alternative test for early detection of breast lesions in general. The most accurate reconstruction methods tend to be very costly as they use optimization methods as a support. Backprojection tends to be rapid but more inaccurate. In this work, the authors propose a hybrid method, based on extreme learning machines and backprojection for EIT reconstruction. The results were applied to numerical phantoms and were considered adequate, with potential to be improved using post processing techniques.
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Conference papers on the topic "Alternating current potential drop technique"

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Narayanan, Aditya, Catrin M. Davies, and Yasser K. Mahmoud. "Use of the Alternating Current Potential Drop (ACPD) Technique to Monitor Creep Behaviour of Austenitic Steels." In ASME 2013 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/pvp2013-97889.

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The Alternating Current Potential Drop (ACPD) strain sensor has been developed as a tool to monitor the condition of a material. It is comprised of a square array of sensors that measures the resistance in two orthogonal directions, using the changes in the material’s resistance over time as a measure of its deformation and evolution of damage within it due to creep. The method expresses the change in resistance as the ratio of axial to lateral resistance, suppressing temperature-related effects on material resistivity, which are mostly isotropic. Previous experiments have seen this method applied to samples of ferritic (2.25CrMoV) steel at 650°C [1]. Within this paper, the method has been extended to include work on the austenitic stainless steel 316H (17Cr11NiMo). Results of a series of interrupted creep tests are presented that show the resistance behaviour of the material at different points in its creep life. Metallographic studies have also been performed so as to establish how data gained using this technique is related to the condition of the material.
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Davies, Catrin M., Peter Nagy, Aditya Narayanan, and Peter Cawley. "Continuous Creep Damage Monitoring Using a Novel Potential Drop Technique." In ASME 2011 Pressure Vessels and Piping Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/pvp2011-57325.

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A new directional low-frequency Alternating Current Potential Drop (ACPD) technique has been developed for continuous in-situ monitoring of creep strain and damage in alloys. The sensor relies on a modified ACPD technique that measures simultaneously both values of resistance in the axial and lateral directions using a square electrode configuration. The technique monitors the variation in the ratio of the measured axial and lateral resistances, therefore can efficiently separate the mostly isotropic common part of the resistivity variation caused by reversible temperature variations from the mostly anisotropic differential part caused by direct geometrical and indirect material effects of creep. Initially, this ratio can be considered proportional to the axial creep strain, while at later stages, the resistance ratio accelerates due to the formation of directional discontinuities such as preferentially oriented grain boundary cavities and micro-cracking in the material. This ACPD technique has been applied to a series of accelerated creep tests on 2.25CrMoV Steel at 650 °C. The results are presented and the application of the method for online component monitoring is discussed.
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Le Delliou, Patrick. "Electric Potential Drop Method for Evaluating Crack Initiation and Crack Propagation: The Help of FE Simulation." In ASME 2019 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2019. http://dx.doi.org/10.1115/pvp2019-93144.

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Abstract The electric potential drop (EPD) method is a laboratory technique to monitor the initiation and the propagation of a crack, mainly in the field of fatigue research. It can also be used in fracture experiments, involving plasticity and large deformations. The size of a crack in a metallic member is predicted by applying a constant d.c. (direct current) or a.c. (alternating current) to the member and by measuring an increase in electric resistance due to the crack. Practically, several pairs of probes are attached to the specimen crossing over the crack and the voltage drop is measured periodically along the test. The main difficulty is to correlate the EPD changes to the crack extension. Thanks to the analogy between the thermal conduction problem and the electrical conduction problem, a classical thermo-mechanical finite element solver can be used to predict the EPD along a crack, given the electrical resistivity of the material, the current intensity and the geometry of the structure and of the crack. This technique works well for fatigue studies, where the structure remains elastic and whose shape is unchanged. However, in fracture experiments, the change in geometry and the possible effect of the plastic strain on electrical resistivity make the problem much more complex. The paper presents the principle of the EPD method, a work on the effect of the plastic strain on the electrical resistivity, FE computations for the elastic case (for fatigue pre-cracking) and for the plastic case (for ductile tearing experiments). Several practical applications will be presented on various metallic materials.
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Quddes, Mohammad R., Yuan Ji, and John R. Bowler. "Alternating current potential drop for measuring the case depth of hardened steel." In 41ST ANNUAL REVIEW OF PROGRESS IN QUANTITATIVE NONDESTRUCTIVE EVALUATION: Volume 34. AIP Publishing LLC, 2015. http://dx.doi.org/10.1063/1.4914646.

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Konstantinov, Dancho D., Philip J. Bowen, Richard Marsh, Peter J. Kay, Andrew P. Crayford, and Marco Derksen. "Developing Effervescent Atomisation for Alternative Fuels." In ASME Turbo Expo 2012: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/gt2012-69777.

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A wide range of atomiser types have been developed for industrial applications — such as rotary, pressure, air-assist and air-blast atomisers. Each type works on the principle of applying mechanical or kinetic energy to disintegrate a jet or sheet of liquid fuel, in preparation for combustion. The aim is to sufficiently increase the surface area to volume ratio of the fuel and presents it in a form suitable for a consistent combustion process. Traditional liquid fuels, such as fossil fuels, have been employed for some decades and combustion systems (and atomisers) have been optimised for their use. However, combustion engineers are being increasingly forced to consider the use of alternative, biologically-derived hydrocarbon fuels. Such fuels often have very different viscosities, densities and surface tensions or possess complex, non-linear properties when compared to conventional fuels. Effervescent atomisation is a promising two-phase atomisation technique offering potential improvements in fluid atomisation quality and reductions in fluid operating pressures. It appears particularly well suited to the atomisation of viscous fuels such as biofuels; this applicability to alternative fuels has led to a renewed interest in the method. After an extensive literature review of the current state of this technology [1] an adjustable geometry effervescent atomiser was designed, built and studied at the Cardiff School of Engineering. Water and air were used as the operating fluids. The sprays produced by the atomiser were characterised using a Phase Doppler Anemometry (PDA) system which allowed for simultaneous real-time droplet size and velocity data to be obtained. High quality data was achieved with data rates over 10 kHz and validation rates over 90% in 2-D LDA mode in the high density sprays. A PDA probe designed for dense spray applications was utilised. A number of important operating parameters identified during the literature review phase can be altered on the atomiser, and their effects on fuel spray quality investigated. The operating parameters investigated in this manner included air-to-liquid by mass ratio (ALR), pressure drop as well as a range of geometric parameters. This paper discusses and analyses the influence of ALR on the quality of atomisation and the associated two-phase flow field. Comparisons are made with previous studies and correlations, using earlier versions of the hardware or alternative techniques. Ongoing work will assess and optimise the performance of simulated biofuels mixtures.
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Sato, Yasumoto, and Tetsuo Shoji. "High sensitivity inspection of defects in welds by remotely induced current potential drop technique." In The ninth international symposium on nondestructive characterization of materials. AIP, 1999. http://dx.doi.org/10.1063/1.1301991.

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Takeo, Fumio, Masumi Saka, Seiichi Hamada, and Manabu Hayakawa. "DC Potential Drop Technique Selecting Probes Distances Properly for Sizing Deep Surface Cracks." In ASME 2005 International Mechanical Engineering Congress and Exposition. ASMEDC, 2005. http://dx.doi.org/10.1115/imece2005-79877.

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D-C potential drop (DCPD) technique is a powerful tool for quantitative NDE of cracks. The technique using four probes which are in close proximity to each other has been proposed for NDE of surface cracks; that is the closely coupled probes potential drop (CCPPD) technique. It has been shown that the sensitivity of CCPPD technique to evaluate a small crack is enhanced significantly in comparison with the usual method. On the other hand, since CCPPD technique has been developed to evaluate a small crack sensitively, it is not fit to evaluate deep cracks which are sometimes found in the structural components of power plants. The objective of this study was to enhance the sensitivity of evaluating deep surface cracks. By extending the distance between current input and output probes, the change in potential drop with the change in the depth of deeper crack becomes large. But the voltage of potential drop becomes small to measure, because the current density in the material becomes low. The voltage of the potential drop can be increased by increasing the applying current, but the current would also be limited by the equipment or contacting probes. Then the way to select the appropriate distances between probes from the viewpoints of the sensitivity and the required current has been shown.
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Hamada, Seiichi, Yasuki Ogawa, Hideo Iida, Tomoki Kuroiwa, Masahiko Kuroki, and Manabu Hayakawa. "Application of Potential Drop Technique to the Inspection of Welded Boiler Pressure Parts." In ASME/JSME 2004 Pressure Vessels and Piping Conference. ASMEDC, 2004. http://dx.doi.org/10.1115/pvp2004-2697.

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In this paper, a practical method using the electrical potential drop technique was discussed to evaluate the creep damage accumulated in the welded power piping such as main steam pipe and hot reheat pipe. Round robin experimental measurements conducted by the authors et al. as academic activities in the Japanese Society for Non-destructive Inspection showed that the potential drop technique is effective for the application to the inspection of welded boiler pressure parts. The authors have conducted additional experimental and numerical studies for verification focusing on the application of the pulsed direct current potential drop technique. The authors have proposed technical requirements on the potential drop technique for the application to the inspection of welded power piping to be implemented in JSME Codes for Thermal Power Generation Facilities (2003 Edition) as a non-mandatory appendix JA. And the practical on-line measurement in the high temperature and high pressure burst test using the repair-welded power piping has been conducted. In this burst test, Tokyo Electric Power Company has tried to monitor the creep damage accumulated in the seam-welded area using the commercialized tool based on pulsed direct current potential drop technique.
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Shukert, Douglas S. "Estimating the Depths of Cracks in SS Pipes by Varying the Frequency of an ACPD Sensor." In ASME 2005 Pressure Vessels and Piping Conference. ASMEDC, 2005. http://dx.doi.org/10.1115/pvp2005-71706.

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Alternating Current Potential Drop (ACPD) is one nondestructive evaluation method for detecting cracks within stainless steel pipes at industrial power plants. It is well known that the penetration depth of the excitation current from the ACPD sensor depends on the frequency of the applied alternating current. With respect to a “skin effect,” lower frequencies produce deeper penetration. This frequency versus depth relationship can be used to judge the depth of cracks that may exist within stainless steel pipes. By varying the frequency of the alternating current supplied to the excitation circuit of an ACPD sensor, crack depths can be estimated. If the penetration depth of the excitation current nearly reaches the depth of the crack tip, then the existence of the crack will cause an increase in the current and a corresponding decrease in the potential drop measured by the ACPD sensor. On the other hand, if the penetration depth of the excitation current reaches beyond the depth of the crack tip, then the crack impedes the electrical current and causes a corresponding increase in the potential drop measured by the ACPD sensor. The frequency at which the measured potential drop flip-flops from a decrease to an increase corresponds to the depth of the crack tip, which can be calculated by using the standard equation for skin depth according to excitation frequency.
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Singh, Yogesh P., Michael J. Presby, Kannan Manigandan, and Gregory N. Morscher. "Multi-Lead Direct Current Potential Drop (DCPD) for In-Situ Health Monitoring of Ceramic Matrix Composites." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-75803.

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The method of direct current potential drop (DCPD) can be utilized as an effective, and convenient approach for in-situ damage detection, and as a non-destructive evaluation technique. We present the results from use of a multiprobe DCPD technique for in-situ damage detection in loading of a SiC/SiC composite. It is shown that in three different modes of loading (monotonic, fatigue, and cyclic load-unload), the sensing capabilities of DCPD technique compares well to the techniques of modal acoustic emission (AE) and digital image correlation (DIC). It was also found that DCPD technique provides a far earlier warning of failure under fatigue loading than the other two methods. In addition, we show that strategically placed multiple voltage leads on the specimen surface provides a promising way of qualitatively determining the crack initiation site. Therefore, the use of multiple lead DCPD method, together with other techniques, provides a viable option for sensing damage in ceramic matrix composites (CMCs) with complex geometries, and for applications at higher temperatures.
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