E. A. Patterson

University of Liverpool, Liverpool, England, United Kingdom

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Publications (237)217 Total impact

  • Eann A. Patterson · Richard J. Taylor · Mark Bankhead
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    ABSTRACT: A conceptual framework is proposed for a digital environment extending from the prototype design of nuclear plants through operations and decommissioning to storage and waste disposal. The environment consists of a series of interconnected multi-scale, multi-physics computational models linked to the real-world by data acquired during validation of prototypes, in-service monitoring and inspections of plant, post-shut-down inspections of plant and in-situ monitoring of stored waste. The technology gaps for the implementation of the integrated nuclear digital environment (INDE) are identified and discussed together with the advantages to be gained from its implementation. Implementation of INDE will be dependent on future advances in High Performance Computing systems approaching the exascale and parallel advances in the development of algorithms for processing large amounts of data. The data itself will be acquired through innovations in measurement, analysis and uncertainty and will be applied through projects relating to lifetime extension, decommissioning and resurgent national science programmes. It is postulated that the existence of this type of framework might be inevitable given both nuclear-specific and non-nuclear drivers and may be essential for the nuclear industry to deliver current and future challenges from the clean-up of legacy waste sites to time and budget, future generation nuclear reactors and small-scale mass-production of modular nuclear power plants. It is proposed that implementation of INDE will lead to shorten development times, reduced costs and increased credibility, operability, reliability and safety.
    No preview · Article · Mar 2016 · Progress in Nuclear Energy
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    ABSTRACT: A Kriging regression model is developed as a post-processing technique for the treatment of measurement uncertainty in classical subset-based Digital Image Correlation (DIC). Regression is achieved by regularising the sample-point correlation matrix using a local, subset-based, assessment of the measurement error with assumed statistical normality and based on the Sum of Squared Differences (SSD) criterion. This leads to a Kriging-regression model in the form of a Gaussian process representing uncertainty on the Kriging estimate of the measured displacement field. The method is demonstrated using numerical and experimental examples. Kriging estimates of displacement fields are shown to be in excellent agreement with 'true' values for the numerical cases and in the experimental example uncertainty quantification is carried out using the Gaussian random process that forms part of the Kriging model. The root mean square error (RMSE) on the estimated displacements is produced and standard deviations on local strain estimates are determined.
    No preview · Article · Mar 2016 · Optics and Lasers in Engineering
  • Wenran Gong · Jinlong Chen · Eann A. Patterson
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    ABSTRACT: Buckling behaviour and delamination growth have been investigated in Carbon Fibre-Reinforced Plastic (CFRP) laminates with artificial and impact-induced delaminations when subject to four-point bending. The energy of the impact was such that the induced damage, observed using ultrasound, did not extend across the entire width of the laminates and was barely visible on the impacted face. Stereoscopic digital image correlation was used to measure the evolution of the deformation of the laminate during bending to structural failure; and the resulting full-field displacement maps and observations of failure modes from Scanning Electron Microscopy (SEM) were used to conclude that appropriately shaped and located artificial delaminations could be employed to represent damage-induced delaminations. This enabled the development of a non-linear Finite Element Analysis (FEA) incorporating a fibre/matrix constitutive model, a modified fibre/matrix failure criterion and a delamination growth criterion to examine the interaction between the buckling behaviour and delamination growth. The predictions of the surface displacements in bending were validated, with the aid of image decomposition, using the measured data fields for a crossply laminate. The model reliably predicted the load-displacement curve and the propagation of damage in laminates with a low level impact damage, which did not extend across the width of laminates, unlike in prior reported models.
    No preview · Article · Dec 2015
  • Erwin Hack · George Lampeas · Eann A Patterson
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    ABSTRACT: The terminology of validation of computational models and the framework within which it should be performed has been well-defined in a series of standards documents developed in the United States. However, there is no universally accepted protocol for performing validation, although a number of approaches have been proposed. The objective of the reported study was to assess the effectiveness and usefulness of a recently published approach that provides an efficient method for comparing data fields from the simulations and experiments, and which incorporates the uncertainty arising in the experimental data in the assessment of the model validity. An international comparison exercise was designed based on the standard for Inter-Laboratory Studies. Fifteen organisations participated in the Inter-Laboratory Study and the results demonstrated the efficacy of the validation protocol and provided feedback on a number of issues, including the definition of regions of interest, the need for a measure of the quality of the simulation results and importance of designing experiments specifically for validation exercises. The refined validation protocol has been incorporated into CEN Workshop Agreement CWA 16799:2014.
    No preview · Article · Dec 2015 · The Journal of Strain Analysis for Engineering Design
  • J.M. Vasco-Olmo · F.A. Díaz · E.A. Patterson
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    ABSTRACT: The effect of single cycle overloads, ranging in size from 10% to 50%, on fatigue crack growth behaviour in compact tension specimens subject to constant amplitude loading with an R-ratio of 0.6 has been investigated using electronic speckle pattern interferometry. The resultant displacement fields have been used to evaluate crack opening and closing loads and effective stress intensity factors using the Christopher-James-Patterson model that takes explicit account of the effect of crack tip and wake plasticity on the singularity-dominated elastic fields surrounding the crack. The results show that the crack opening loads and effective stress intensity factors at the overload event are proportional to the magnitude of the overload and that period of post-overload retardation of crack growth is also proportional to the magnitude of the overload. These findings demonstrate the usefulness of the CJP model and should help enhance understanding of plasticity-induce closure phenomena.
    No preview · Article · Oct 2015 · International Journal of Fatigue
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    R. B. Berke · C. M. Sebastian · R. Chona · E. A. Patterson · J. Lambros
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    ABSTRACT: The mechanical behavior of solids in combined high-temperature and vibratory environments, such as those experienced during hypersonic flight, are historically not well explored. In this work on Hastelloy-X plates, elevated temperatures were achieved by induction heating and periodic vibratory loading was applied using a shaker. Surface displacements and strains were measured using stereo digital image correlation (DIC) in the blue spectrum to alleviate issues associated with thermal radiation. Through the use of image decomposition techniques the resultant high-quality experimental data were used to validate numerical simulations of combined thermoacoustic loading. The simulations were based on the deformed shape and the corresponding temperature distributions measured experimentally as well as taking into account the thermal dependence of Hastelloy-X mechanical properties.
    Preview · Article · Sep 2015 · Experimental Mechanics
  • E Hack · X Lin · E A Patterson · C M Sebastian
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    ABSTRACT: A simple reference material for establishing the minimum measurement uncertainty of optical systems for measuring 3D surface displacement fields in deforming objects is described and its use demonstrated by employing 3D digital image correlation as an exemplar technique. The reference material consists of a stepped bar, whose dimensions can be scaled to suit the application, and that can be clamped rigidly at its thick end to create an idealized cantilever. The cantilever was excited at resonance to generate out-of-plane displacements and, in a separate experiment, loaded statically in-plane to provide in-plane displacement fields. The displacements were measured using 3D digital image correlation and compared to the predicted displacement fields derived from tip deflections obtained using a calibrated transducer that provided traceability to the national standard for length. The minimum measurement uncertainties were evaluated by comparing the measured and predicted displacement fields, taking account of the uncertainties in the input parameters for the predictions. It was found that the minimum measurement uncertainties were less than 3% for the Cartesian components of displacement present during static in-plane bending and less than 3 µm for out-of-plane displacements during dynamic loading. It was concluded that this reference material was more straightforward to use, more versatile and yielded comparable results relative to an earlier design.
    No preview · Article · Jul 2015 · Measurement Science and Technology
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    G. Laboviciute · C.J. Christopher · M.N. James · E.A. Patterson
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    ABSTRACT: The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model has been successful in achieving a sensible rationalisation of crack growth rate data for the specimens considered in this work, although some observations are not easily explained. Nonetheless, considering the complexity of characterising crack growth rates for cracks with an initial orientation of 30°, 45° or 60° to the horizontal and which subsequently change angle during growth, the results found so far indicate that there is value in further pursuing the CJP approach. The paper introduces future research directions for the CJP model.
    Full-text · Article · Jun 2015 · Frattura ed Integrità Strutturale
  • Wenran Gong · Jinlong Chen · Eann A. Patterson
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    ABSTRACT: Delamination is one of the most common forms of damage suffered by laminated composites and often occurs as a consequence of manufacturing defects or an impact. This paper reports an investigation of the buckling behaviour and resultant damage modes in delaminated composites subjected to four-point bending. The stereoscopic Digital Image Correlation (DIC) method was used to measure full-field deformations and to evaluate maps of surface principal strains in Carbon Fibre-Reinforced Plastic (CFRP) laminates with artificial delaminations. The effect of delamination size and shape on buckling behaviour was investigated using circular and elliptical delaminations in thin beams under four-point bending. For circular delaminations, initially the delamination grew along the transverse direction and then changed to the longitudinal direction. For elliptical delaminations, the delamination grew only along the longitudinal direction. Furthermore, the orientation of the delamination had a small influence (10–15%) on the critical delamination-buckling load, which decreased with increasing ratio of minor to major axis length of the delamination.
    No preview · Article · May 2015 · Composite Structures
  • G. Labeas · Vasilis P Pasialis · X.Lin · E.A. Patterson
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    ABSTRACT: Engineering simulation has a significant role in the process of design and analysis of most engineered products at all scales and is used to provide elegant, light-weight, optimized designs. A major step in achieving high confidence in computational models with good predictive capabilities is model validation. It is normal practice to validate simulation models by comparing their numerical results to experimental data. However, current validation practices tend to focus on identifying hot-spots in the data and checking that the experimental and modeling results have a satisfactory agreement in these critical zones. Often the comparison is restricted to a single or a few points where the maximum stress/strain is predicted by the model. The objective of the present paper is to demonstrate a step-by-step approach for performing model validation by combining full-field optical measurement methodologies with computational simulation techniques. Two important issues of the validation procedure are discussed, i.e. effective techniques to perform data compression using the principles of orthogonal decomposition, as well as methodologies to quantify the quality of simulations and make decisions about model validity. An I-beam with open holes under three-point bending loading is selected as an exemplar of the methodology. Orthogonal decomposition by Zernike shape descriptors is performed to compress large amounts of numerical and experimental data in selected regions of interest (ROI) by reducing its dimensionality while preserving information; and different comparison techniques including traditional error norms, a linear comparison methodology and a concordance coefficient correlation are used in order to make decisions about the validity of the simulation.
    No preview · Article · Mar 2015 · Simulation Modelling Practice and Theory
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    Full-text · Dataset · Sep 2014
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    Full-text · Article · May 2014 · Fatigue & Fracture of Engineering Materials & Structures
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    ABSTRACT: An approach for the measurement of surface displacement fields in three dimensions is presented based on the combination of two-dimensional digital image correlation with fringe projection. Only a single RGB image is required at each deformation state, thereby allowing real-time data acquisition, which is achieved using red speckle and projected blue fringes that are captured in the single image and separated using a Bayer filter. The approach allows both a perpendicular alignment relative to a flat reference surface and self-calibration, i.e., no calibration object is employed. The minimum measurement uncertainty of such a system is found to be 0.0083 +/- 0.00239 and 0.0238 +/- 0.0068 mm, respectively, for the in-plane and out-of-plane displacements. The potential of the approach is demonstrated for an elastic membrane undergoing large (5 to 20 mm) applied out-of-plane displacements, and the results show no significant difference (< 1%) in the measured in-plane displacement fields compared with a commercially available system for stereoscopic digital image correlation. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
    No preview · Article · Apr 2014 · Optical Engineering
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    ABSTRACT: The combination of fringe projection (FP) and two-dimensional digital image correlation (2D-DIC) has been proposed in previous work [1] as an alternative method to obtain displacement maps in the three spatial directions. However, if a telecentric lens is not employed in the experimental setup, the in-plane displacements obtained with 2D-DIC are influenced by the out-of-plane displacements occurring during deformation. Nevertheless, this error can be corrected if the out-of-plane displacements are known, for instance from measurements using the FP technique. In this paper a novel methodology based on the combination of FP and 2D-DIC is employed to perform the correction of the in-plane displacements, and is applied to several experimental examples. Results are compared and validated with those obtained using a commercial 3D-DIC system showing an average displacement error of 4% for X-displacements and 6.5% for Y-displacements.
    No preview · Article · Jan 2014 · Optics and Lasers in Engineering
  • M.N. James · Y. Lu · C.J. Christopher · E.A. Patterson
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    ABSTRACT: A significant amount of research has been directed towards characterising and predicting sub-critical crack growth mechanisms in polycarbonate (PC) materials. In particular the initiation of crazes, damage evolution and growth of fatigue cracks has attracted significant attention. It is only relatively recently that there has been clarification of the underlying physics of craze initiation and growth, and of the craze influence on crack paths. In the interpretation of mechanisms of deformation, the polymer community has perhaps not embraced the use of fractographic crack path information as fully as the metals community. This paper considers the ability of advanced imaging techniques including confocal laser scanning microscopy (CLSM), and field emission scanning electron microscopy (FESEM) to provide evidence of crack path morphology for existing models of plastic deformation and crazing in amorphous polycarbonate. It also presents the outline of a new model of crack tip stresses which takes account of craze-induced shielding mechanisms and appears able to characterise fatigue crack growth in PC.
    No preview · Article · Aug 2013 · Engineering Fracture Mechanics
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    ABSTRACT: A composite bonnet liner subject to a high-velocity (70 m/s), low-energy (<300 J) impact by a 50-mm-diameter projectile has been investigated using computational simulation and by experiment. High-speed digital image correlation was employed to generate maps of displacement fields over the 1-m2 bonnet at 0.2 ms increments for 0.1 s, that is, 500 datasets, and the results have been compared to those predicted by finite element analysis. Image decomposition was utilised to reduce the dimensionality of both datasets by representing them using adaptive geometric moment descriptors; these descriptors were used to perform quantitative comparisons of the datasets and to test the validity of the model based on all the available data. The model was found to be a good representation of the physical experiment during the first half of the impact event but a less good representation in the remainder of the test, probably because damping effects were not adequately incorporated into the simulation. The methodologies for data comparison and evaluation of model validity proposed and demonstrated in this study represent a significant advance in procedures for ensuring model fidelity and for creating model credibility in the simulation of dynamic engineering events.
    No preview · Article · Apr 2013 · The Journal of Strain Analysis for Engineering Design
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    David Backman · Eann A. Patterson
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    ABSTRACT: Fatigue tests carried out on three configurations (unexpanded, cold expanded and riveted) of fiber metal laminate material clearly demonstrated the beneficial effect of riveting compared to cold expansion in zero load transfer joints, for an approximately equivalent level of interference. Digital image correlation was used to measure the in-plane surface strain on cold expanded and riveted coupons during fatigue loading, and for the first time, digital image correlation was combined with pressure sensitive films to measure the strains resulting from the application of the rivet, including those under the rivet head. A comparison of the resultant strain field showed that the application of a rivet significantly reduces the stress concentration at the central hole and is effective in extending fatigue life. Some rivet heads were removed by milling, and the results from subsequent fatigue tests were used together with closed-form calculations to explain the findings of this study. It was concluded that the beneficial effect of riveting was less as a result of interference hole filling on the part of the rivet shank, but more a combination of the effect of interference and compression through the joint thickness.
    Preview · Article · Mar 2013 · The Journal of Strain Analysis for Engineering Design
  • Eann A. Patterson · Mara Feligiotti · Erwin Hack
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    ABSTRACT: Experimental strain analysis, structural health monitoring and non-destructive testing and evaluation are regarded as separate disciplines that, in general, are deployed independently at different phases in the life cycle of an engineering component, i.e. in the design process, in service and after an event or service period, respectively. It is proposed that the integrated use of these three disciplines is advantageous and beneficial in terms of reduced capital and operational costs for critical and safety-relevant components, as well as, in validating simulations, in both quantifying and reducing risk of unexpected failure, and in estimating remanent life. We propose the foundation of this integration to be data-rich strain fields measured and compared quantitatively, with each other and with data from simulations, at temporal intervals during the life of a component.
    No preview · Article · Jan 2013 · The Journal of Strain Analysis for Engineering Design
  • Eann Patterson · David Backman · Gary Cloud

    No preview · Article · Jan 2013
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    ABSTRACT: Reflection photoelasticity has been used to study the location of the onset of yielding in bolted T-stub joint models subjected to strength testing (as defined by Eurocode 3). Force-displacement behavior and local strains are also characterized. Experimental results are compared with predictions from Finite Element Analyses and previous investigations. Results shown demonstrate that reflection photoelasticity could be a useful tool for the better understanding of the complex behavior of T-stubs. Overall, results obtained from experimental work and theoretical analysis reveal that the behavior of the T-stub is more complex than claimed by Eurocode due to contact forces, bolt interaction and plastic behavior.
    No preview · Chapter · Jan 2013

Publication Stats

3k Citations
217.00 Total Impact Points

Institutions

  • 2011-2016
    • University of Liverpool
      Liverpool, England, United Kingdom
  • 2005-2014
    • Michigan State University
      • • Department of Mechanical Engineering
      • • Department of Chemical Engineering and Materials Science
      • • Composite Vehicle Research Center
      East Lansing, Michigan, United States
  • 2000-2011
    • University of Plymouth
      • Faculty of Science and Technology
      Plymouth, England, United Kingdom
  • 2008
    • The University of Manchester
      • School of Materials
      Manchester, ENG, United Kingdom
  • 1990-2008
    • The University of Sheffield
      • Department of Mechanical Engineering
      Sheffield, England, United Kingdom
  • 1994
    • University of Cambridge
      Cambridge, England, United Kingdom