23 results found
Leung MSH, Corcoran J, 2021, Evaluating the Probability of Detection Capability of Permanently Installed Sensors Using a Structural Integrity Informed Approach, Journal of Nondestructive Evaluation, Vol: 40, ISSN: 0195-9298
There is a growing interest in using permanently installed sensors to monitor for defects in engineering components; the ability to collect real-time measurements is valuable when evaluating the structural integrity of the monitored component. However, a challenge in evaluating the detection capabilities of a permanently installed sensor arises from its fixed location and finite field-of-view, combined with the uncertainty in damage location. A probabilistic framework for evaluating the detection capabilities of a permanently installed sensor is thus proposed. By combining the spatial maps of sensor sensitivity obtained from model-assisted methods and probability of defect location obtained from structural mechanics, the expectation and confidence in the probability of detection (POD) can be estimated. The framework is demonstrated with four sensor-component combinations, and the results show the ability of the framework to characterise the detection capability of permanently installed sensors and quantify its performance with metrics such as the a 90 | 95 value (the defect size where there is 95% confidence of obtaining at least 90% POD), which is valuable for structural integrity assessments as a metric for the largest defect that may be present and undetected. The framework is thus valuable for optimising and qualifying monitoring system designs in real-life engineering applications.
Hey Leung MS, Corcoran J, 2021, A probabilistic method for structural integrity assurance based on damage detection structural health monitoring data, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, ISSN: 1475-9217
ODowd NM, Madarshahian R, Leung MSH, et al., 2021, A probabilistic estimation approach for the failure forecast method using Bayesian inference, International Journal of Fatigue, Vol: 142, ISSN: 0142-1123
Positive-feedback mechanisms such as fatigue induce a self-accelerating behavior, captured by models displaying infinite limit-state asymptotics, collectively known as the failure forecast method (FFM). This paper presents a Bayesian model parameter estimation approach to the fully nonlinear FFM implementation and compares the results to the classic linear regression formulation, including a regression uncertainty model. This process is demonstrated in a cyclic loading fatigue crack propagation application, both on a synthetic data set and on a full fatigue experiment. A novel ”switch point” parameter is included in the Bayesian formulation to account for nonstationary changes in the growth parameter.
Zhang Y, Cegla F, Corcoran J, 2020, Ultrasonic monitoring of pipe wall interior surface temperature, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, ISSN: 1475-9217
Corcoran J, Leinov E, Jeketo A, et al., 2020, A guided wave inspection technique for wedge features, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol: 67, Pages: 997-1008, ISSN: 0885-3010
Numerous engineering components feature prismatic wedge-like structures that require Non-destructive Evaluation (NDE) in order to ensure functionality or safety. This paper focuses on the inspection of the wedge-like seal fins of a jet engine drum, though the capabilities presented will be generic. It is proposed that anti-symmetric flexural edge modes, feature guided waves localised to the wedge tips, may be used for defect detection. Although analytical solutions exist that characterise the ultrasonic behaviour of ideal wedges, in practise real wedges will be irregular (containing for example truncated tips, are built onto an associated structure or have non straight edges) and therefore generic methodologies are required to characterise wave behaviour in non-ideal wedges. This paper uses a semi-analytical finite element (SAFE) methodology to characterise guided waves in wedge-like features with irregular cross-sections to assess their suitability for NDE inspection and compare them to edge modes in ideal wedges. The science and methodologies required in this paper are necessary to select an appropriate operating frequency for the particular application at hand. Additionally, this paper addresses the practical challenge of excitation and detection of flexural edge modes by presenting a piezoelectric based dry-coupled transducer system suitable for pulse-echo operation. The paper therefore presents the scientific basis required for industrial exploitation, together with the practical tools that facilitate use. The study concludes with the experimental demonstration of the edge wave based inspection of a seal fin, achieving a signal-to-noise ratio of 28 dB from a 0.75 mm radial tip defect.
Corcoran J, Davies CM, Cawley P, et al., 2020, A quasi-DC potential drop measurement system for materials testing, IEEE Transactions on Instrumentation and Measurement, Vol: 69, Pages: 1313-1326, ISSN: 0018-9456
Potential drop measurements are well established for use in materials testing and are commonly used for crack growth and strain monitoring. Traditionally, the experimenter has a choice between employing direct current (DC) or alternating current (AC), both of which have strengths and limitations. DC measurements are afflicted by competing spurious DC signals and therefore require large measurement currents (10’s or 100’s of amps) to improve the signal to noise ratio, which in turn leads to significant resistive Joule heating. AC measurements have superior noise performance due to utilisation of phase-sensitive detection and a lower spectral noise density, but are subject to the skin-effect and are therefore not well suited to high-accuracy scientific studies of ferromagnetic materials. In this work a quasi-DC monitoring system is presented which uses very low frequency (0.3-30 Hz) current which combines the positive attributes of both DC and AC while mitigating the negatives. Bespoke equipment has been developed that is capable of low-noise measurements in the demanding quasi-DC regime. A creep crack growth test and fatigue test are used to compare noise performance and measurement power against alternative DCPD equipment. The combination of the quasi-DC methodology and the specially designed electronics yields exceptionally low-noise measurements using typically 100-400 mA; at 400mA the quasi-DC system achieves a 13-fold improvement in signal to noise ratio compared to a 25A DC system. The reduction in measurement current from 25A to 400mA represents a ~3900 fold reduction in measurement power, effectively eliminating resistive heating and enabling much simpler experimental arrangements.
Corcoran J, Nagy P, 2019, Passive thermoelectric power monitoring for material characterisation, Structural Health Monitoring, Vol: 18, Pages: 1915-1927, ISSN: 1475-9217
Monitoring deterioration of material properties is important for assessing the structural integrity of engineering components, as it may indicate susceptibility to damage. This article focusses on the example of thermoelectric power measurements, which are known to be indicative of thermal and irradiation embrittlement and may therefore act as a proxy metric for material integrity. A passive thermoelectric power–monitoring technique is proposed which is suitable for permanent installation on engineering components. In passive measurements, the active perturbation (in this case, the heating required to create a temperature gradient) is replaced by incidental perturbation from the environment. The reduction in the ‘signal’ amplitude associated with relying on incidental perturbations may be compensated by increasing the number of individual measurements, facilitated by the greatly reduced power demand of the passive modality. Experimental studies using a stainless steel tube as a test component demonstrate thermoelectric power accuracy of <0.03 μV/°C is achievable with temperature gradients of the order of 2°C; in many cases of practical importance, this is sufficient to track the anticipated changes in thermoelectric power associated with thermal degradation.
Leung M, Corcoran J, Cawley P, et al., 2019, Evaluating the use of Rate-based Monitoring for Improved Fatigue Remnant Life Predictions, International Journal of Fatigue, Vol: 120, Pages: 162-174, ISSN: 0142-1123
The ability to perform accurate remnant life predictions is crucial to ensure the integrity of engineering components that experience fatigue loading during operation. This is conventionally achieved with periodic inspections, where results from non-destructive evaluation and estimation of the operating conditions are obtained to perform remnant life predictions using empirical crack growth laws. However, remnant life predictions made with this approach are very sensitive to their input parameters; uncertainty in each parameter would aggregate and result in great uncertainty in the final prediction. With the increasing viability of permanently-installed systems, it is proposed that the rate of damage growth can be used to more accurately and confidently gauge the integrity of an engineering component and perform remnant life predictions using the Failure Forecast Method. A statistical analysis of an example fatigue crack growth test was performed to compare the uncertainties of the remnant life predictions made using the conventional inspection approach and the proposed rate-based monitoring approach. It is shown that the Failure Forecast Method produces significantly more accurate and confident predictions compared to the inspection approach. The use of the Failure Forecast Method under non-constant amplitude loading conditions was also investigated. An equivalent cycles method is introduced to accommodate step changes in operating conditions. The effect of load interactions was also studied through a fatigue test with isolated overloads and a random variable amplitude loading test. Overall, the study has shown that the frequent data obtained from permanently installed monitoring systems provides new opportunities in remnant life estimates and potentially opens the way to increasing the intervals between outages and safely reducing conservatism in life predictions.
Leung M, Corcoran J, Nagy PB, 2019, The influence of the dynamic magnetoelastic effect on potential drop measurements, NDT & E International, Vol: 102, Pages: 153-160, ISSN: 0963-8695
Alternating Current Potential Drop (ACPD) measurements are routinely used for monitoring crack length in laboratory based fatigue tests, and so measurements will be taken on components which are exposed to cyclic dynamic stresses. It has been empirically observed that cyclic stresses cause a strong increase (above 10% is shown in this paper) in measured resistance that is both AC inspection frequency and loading frequency dependent. The excess resistance will result in erroneous measurements; this paper investigates the cause and provides recommendations to limit the influence. Applied stresses influence ACPD measurements through the magnetoelastic effect; elastic strain induces magnetization in ferromagnetic materials, which in turn influences the magnetic permeability and therefore skin depth. Further, it has recently been realised that cyclic magnetization results in a frequency dependent concentration of the magnetic flux at the surface of the component, and consequently a non-uniform spatial distribution of magnetic permeability. In this study it is found that the interaction between the non-uniform spatial distribution of both the current density and magnetic permeability results in significant non-linear modulation of the measurement signal. A combination of finite element simulations and experimental results are used to explore this phenomenon.
Corcoran J, Nagy PB, 2018, Magnetic stress monitoring using a directional potential drop technique, Journal of Nondestructive Evaluation, Vol: 37, ISSN: 0195-9298
An alternating current potential drop technique is presented that exploits anisotropic magnetostriction to monitor changes inapplied stress in steel. The background to the technique is provided together with an ad hoc approximation that describes thesensitivity of the sensor to the underlying properties. A uniaxial loading experiment has been conducted on duplex and mildsteel specimens showing that changes in stress are measureable. Saturation and hysteresis afflict the measurement, which, inaddition to sensitivity to temperature and magnetisation, may undermine inversion. With the capabilities and limitations ofthe proposed technique introduced, guidance on possible suitable applications are given, concluding that use for monitoringthe number and relative size of fatigue stress cycles may be a suitable and attractive opportunity.
Corcoran J, Davies C, 2018, Monitoring power-law creep using the failure forecast method, International Journal of Mechanical Sciences, Vol: 140, Pages: 179-188, ISSN: 0020-7403
Creep is considered to be the life limiting damage mechanism in many load bearing high temperature components. A range of different parameters determine the creep life of a component, many of which are unlikely to be known to sufficient accuracy to enable satisfactory estimation of remnant life. Instead,the integrity of a component shouldbe established through direct measurement of the response of the component to the operating conditions. Creep deformation is shown to be a positive feedback mechanism; anincreasein strain leadsto an increasing strain rate. It has recently been shown that as a consequence of positive feedback the Failure Forecast Method, a generalised framework for predicting time to criticality based on rates of change of damage, may beapplied for remnant life calculations. A range of strain rate based assessments have been proposed in the literature but it is proposed that the Failure Forecast Method unifies many of these techniques and provides additional insight into creep behaviour by virtue of the underlying positive feedback. The methodology has been demonstrated using experiment datasets that are pertinent to creep in high temperature pressure vessels and piping; it is shown that failure times are accurately predicted shortly after the minimum creep strain rate.
Todd MD, Leung M, Corcoran J, et al., 2018, Fatigue prognosis using the uncertainty-quantified failure forecast method, Pages: 129-137
Several material failure modes such as fatigue have been noted to occur, after initiation phases, as a consequence of a positive-feedback mechanism. Positive feedback systems continually "accelerate" their underlying physics until failure, and as such, are unstable processes that result in the tendency of the rate of change in the observable data (or more generally, damage-sensitive features) to approach infinity. Models have been proposed based on this asymptotic property of positive feedback mechanisms for predicting the time to criticality, generally now known as the "failure forecast method". The typical implementation of this approach is to compute the inverse time rate-of-change in the features and linearly regress that data vs. time; inevitable uncertainties in the data, measurement process, or environmental contamination noise will corrupt the regression, leading to distributions in the parameters used to make the failure forecast. This study will look at a parametric implementation of the failure forecast method using a probability density function computed from the regression process and evaluating its predictive performance on fatigue data, considering regression window, sampling time, noise level, and predictor. A comparison is also drawn between the Failure Forecast Method and a conventional periodic inspection realization.
Todd MD, Leung M, Corcoran J, 2018, A probability density function for uncertainty quantification in the failure forecast method
It has been observed that many material failure modes follow empirically similar trends across many types of materials and load states. This commonality, rooted in the underlying hypothesis in a positive feedback mechanism, has led to several generic models that exhibit this mechanism, generally now known as the “failure forecast method”. This method essentially links the rate of change in structural health monitoring (SHM) data (features), which indicate something about current structural state or performance, to a prediction of when such data are representative of failure (characterized by an infinite data rate of change). Given inevitable noise in data, this paper will derive an uncertainty model in a practical implementation of the classic failure forecast method, where the inverse rate of change of the feature is linearly related to the time of expected failure. A probability density function (PDF) is proposed for the estimation of that failure time from updated linear regressions of data obtained during a simulated fatigue experiment. The mean, median, and mode of the data will be compared as predictors of the time of failure, and the effects of regression selection parameters (e.g., regression time frame, regression block overlap, etc.) will be explored.
Corcoran J, Raja S, Nagy PB, 2017, Improved thermoelectric power measurements using a four-point technique, NDT and E International, Vol: 94, Pages: 92-100, ISSN: 0963-8695
The Seebeck coefficient of a material is dependent on its composition and microstructure and is consequently sensitive to service related material degradation; of particular interest is the sensitivity to thermal and irradiation embrittlement which may be exploited for the material characterisation of in service components. Conventionally, thermoelectric measurements are taken using a two-point contact technique which introduces a temperature differential in the test component through a heated ‘hot tip’ electrode; it is argued that measurements using this methodology are sensitive to the thermal contact resistance between the component and the electrodes. An alternative three- or four-point technique is proposed where heat is introduced to the component remotely which leads to much less sensitivity to contact condition. An experiment is presented that compares the two techniques and demonstrates the improved performance of the four-point technique. Aside from the improved accuracy, the modified technique also facilitates a ‘passive’ implementation that could be used from continuous monitoring of components in service.
Corcoran J, 2017, Rate based structural health monitoring using permanently installed sensors, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 473, ISSN: 1364-5021
Permanently installed sensors are becoming increasingly ubiquitous, facilitating very frequent in situ measurements and consequently improved monitoring of ‘trends’ in the observed system behaviour. It is proposed that this newly available data may be used to provide prior warning and forecasting of critical events, particularly system failure. Numerous damage mechanisms are examples of positive feedback; they are ‘self-accelerating’ with an increasing rate of damage towards failure. The positive feedback leads to a common time-response behaviour which may be described by an empirical relation allowing prediction of the time to criticality. This study focuses on Structural Health Monitoring of engineering components; failure times are projected well in advance of failure for fatigue, creep crack growth and volumetric creep damage experiments. The proposed methodology provides a widely applicable framework for using newly available near-continuous data from permanently installed sensors to predict time until failure in a range of application areas including engineering, geophysics and medicine.
Corcoran J, Nagy PB, Cawley P, 2017, Monitoring creep damage at a weld using a potential drop technique, INTERNATIONAL JOURNAL OF PRESSURE VESSELS AND PIPING, Vol: 153, Pages: 15-25, ISSN: 0308-0161
Corcoran J, Nagy PB, 2016, Compensation of the skin effect in low-frequency potential drop measurements, Journal of Nondestructive Evaluation, Vol: 35, ISSN: 1573-4862
Potential drop measurements are routinely used in the non-destructive evaluation of component integrity. Potential drop measurements use either direct current (DC) or alternating current (AC), the latter will have superior noise performance due to the ability to perform phase sensitive detection and the reduction of flicker noise. AC measurements are however subject to the skin effect where the current is electromagnetically constricted to the surface of the component. Unfortunately, the skin effect is a function of magnetic permeability, which in ferromagnetic materials is sensitive to a number of parameters including stress and temperature, and consequently in-situ impedance measurements are likely to be unstable. It has been proposed that quasi-DC measurements, which benefit from superior noise performance, but also tend to the skin-effect independent DC measurement, be adopted for in-situ creep measurements for power station components. Unfortunately, the quasi-DC measurement will only tend to the DC distribution and therefore some remnant sensitivity to the skin effect will remain. This paper will present a correction for situations where the remnant sensitivity to the skin effect is not adequately suppressed by using sufficiently low frequency; the application of particular interest being the in-situ monitoring of the creep strain of power station components. The correction uses the measured phase angle to approximate the influence of the skin effect and allow recovery of the DC-asymptotic value of the resistance. The basis of the correction, that potential drop measurements are minimum phase is presented and illustrated on two cases; the creep strain sensor of practical interest and a conducting rod as another common case to illustrate generality. The correction is demonstrated experimentally on a component where the skin effect is manipulated by application of a range of elastic stresses.
Corcoran J, Hooper P, Davies C, et al., 2016, Creep strain measurement using a potential drop technique, International Journal of Mechanical Sciences, Vol: 110, Pages: 190-200, ISSN: 0020-7403
This paper will demonstrate the use of a potential drop sensor to monitor strain. In particular, the suitability of the technique to high temperature or harsh environment applications presents an opportunity for monitoring strain in components operating under creep conditions. Monitoring creep damage in power station components is a long standing technological challenge to the non-destructive evaluation community. It is well established in the literature that strain rate serves as an excellent indicator of the progress of creep damage and can be used for remnant life calculations. To facilitate the use of such strain rate based evaluation methods, a permanently installed, strain sensitive, potential drop technique has been developed. The technique has very simple and robust hardware lending itself to use at high temperatures or in harsh environments. Strain inversions are presented and demonstrated experimentally; a room temperature, plastic deformation experiment is used for validation and additionally an accelerated creep test demonstrates operation at high temperature (600 °C+). Excellent agreement is shown between potential drop inverted strain and control measurements.
Corcoran J, Nagy PB, Cawley P, 2015, Potential Drop Monitoring of Creep Damage at a Weld, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics (AIP), ISSN: 1551-7616
Creep failure at welds will often be the life limiting factor for pressurised power station components, offering a site for local damage accumulation. Monitoring the creep state of welds will be of great value to power station management and potential drop monitoring may provide a useful tool. This paper provides a preliminary study of potential drop monitoring of creep damage at a weldment, suggesting a measurement arrangement for a previously documented quasi-DC technique that is well suited to the application. The industrial context of the problem of creep damage at a weldment is explored, together with a numerical simulation of the effect of cracking, finally, a cross-weld accelerated creep test demonstrating the promise of the technique is presented.
Corcoran J, Davies CM, Nagy PB, et al., 2015, Potential Drop Strain Measurement for Creep Monitoring, 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 917-925, ISSN: 0094-243X
Corcoran J, Davies C, Nagy P, et al., 2014, POTENTIAL DROP STRAIN SENSOR FOR CREEP MONITORING, ASME 2014 Pressure Vessels and Piping Conference (PVP-2014), Publisher: AMER SOC MECHANICAL ENGINEERS
Corcoran J, Cawley P, Nagy PB, 2014, A Potential Drop Strain Sensor for In-Situ Power Station Creep Monitoring, 10th International Conference on Barkhausen and Micro-Magnetics (ICBM), Publisher: AMER INST PHYSICS, Pages: 1482-1487, ISSN: 0094-243X
Corcoran J, Cawley P, Nagy PB, 2013, A potential drop strain sensor for in-situ power station creep monitoring, Pages: 172-179
Creep is a high temperature damage mechanism of interest to the power industry and at present lacks a satisfactory inspection technique. Existing material inspection techniques are extremely laborious while strain measurements rely on often infrequent off-load measurements. A quasi-DC directional potential drop technique has been suggested that is able to suppress the effects of permeability and is primarily sensitive to changes in resistivity and also the geometry that will develop through strain. The change in creep related resistivity is shown by an equivalent effective resistivity approach to be small at <1% change when compared to the >100% change in transfer resistance that occurs due to strain as observed in laboratory tests. A biaxial inversion is then presented and demonstrated on in-lab samples showing good performance. The result is a sensor that performs as a very robust high temperature strain gauge. © (2013) by the British Institute of Non-Destructive Testing. All rights reserved.
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