E. A. Patterson

University of Liverpool, Liverpool, England, United Kingdom

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Publications (215)208.43 Total impact

  • 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.
    Measurement Science and Technology 07/2015; 26(7). DOI:10.1088/0957-0233/26/7/075004 · 1.43 Impact Factor
  • 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.
    Composite Structures 05/2015; 123. DOI:10.1016/j.compstruct.2014.12.008 · 3.32 Impact Factor
  • 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.
    Simulation Modelling Practice and Theory 03/2015; 52(C):92-107. DOI:10.1016/j.simpat.2014.12.006 · 1.38 Impact Factor
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    Fatigue & Fracture of Engineering Materials & Structures 05/2014; 38(2). DOI:10.1111/ffe.12213 · 1.56 Impact Factor
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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)
    Optical Engineering 04/2014; 53(4):044106. DOI:10.1117/1.OE.53.4.044106 · 0.95 Impact Factor
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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.
    Optics and Lasers in Engineering 01/2014; 52(1):66-74. DOI:10.1016/j.optlaseng.2013.07.025 · 2.24 Impact Factor
  • 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.
    Engineering Fracture Mechanics 08/2013; 108:89-97. DOI:10.1016/j.engfracmech.2013.02.003 · 1.77 Impact Factor
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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.
    The Journal of Strain Analysis for Engineering Design 04/2013; 49(4):212-223. DOI:10.1177/0309324713498074 · 0.91 Impact Factor
  • M. N. James · C. J. Christopher · Yanwei Lu · E.A. Patterson
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    ABSTRACT: This paper presents the background and development of a novel ‘plastic inclusion’ approach for dealing with the local plasticity which occurs at the tip of a growing fatigue crack. Localised plasticity arises from crack growth mechanisms and essentially blunts the crack, creates a reversed cyclic plastic zone, and induces shear along the crack flanks, along with the possible generation of wake contact stresses which act on the applied elastic stress field at the boundary of the elastic–plastic enclave surrounding the crack. The paper outlines the development of a meso-scale model of the elastic stress field around a growing crack that explicitly incorporates these interaction effects. The outcome is a modified crack tip stress intensity factor that includes some aspects of the magnitude of plastic wake-induced crack tip shielding and which the authors propose has the potential to help resolve some long-standing controversies associated with plasticity-induced closure. A full-field approach is developed for stress using photoelasticity and also for displacement using digital image correlation.
    International Journal of Fatigue 01/2013; 46:4–15. DOI:10.1016/j.ijfatigue.2012.04.015 · 2.28 Impact Factor
  • International Journal of Fatigue 01/2013; 46:1. DOI:10.1016/j.ijfatigue.2012.08.001 · 2.28 Impact Factor
  • Christopher Sebastian · Erwin Hack · Eann Patterson
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    ABSTRACT: The need to provide strong evidence of the validity of predictions from computational solid mechanics models used in engineering design decisions is discussed. A new procedure is proposed, based on image decomposition, for reducing the dimensionality of strain field data from models and experiments and then comparing the resultant feature vectors via a simple linear correlation in which validation is deemed to be achieved when the coordinate pairs from the two feature vectors lie within a scatter band defined by the minimum measurement uncertainty. The procedure is illustrated by some simple examples that allow the advantages and drawbacks of the approach to be highlighted. It is anticipated that the procedure could become part of a corporate plan or regulatory process for verification and validation of computational solid mechanics models.
    The Journal of Strain Analysis for Engineering Design 01/2013; 48(1):36-47. DOI:10.1177/0309324712453409 · 0.91 Impact Factor
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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.
    Imaging Methods for Novel Materials and Challenging Applications, Volume 3, 01/2013: pages 359-367;
  • 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.
    The Journal of Strain Analysis for Engineering Design 01/2013; 48(1):48-58. DOI:10.1177/0309324712444681 · 0.91 Impact Factor
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    Eann A. Patterson · Amol S. Patki
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    ABSTRACT: One approach to damage assessment in composite structures is to examine the strain field induced by service loads and compare the fields measured during maintenance with those observed in pristine or virgin components. Levels of damage that cause appreciable changes in the strain field observed in service are significant since it is very likely that they will cause premature failure and the measured strain field provides the input data for predicting the reduced life. While visual observation and comparison of strain fields is possible, it does not offer a very viable approach to large-scale inspections. The automation of the process is not straightforward because data collected in-service during maintenance inspections may not be located in the same spatial coordinate system, at the same scale or orientation as the benchmark data acquired from a virgin component. In addition, each data set may consist of the order of million pieces of information rendering quantitative comparisons cumbersome and potentially expensive. Image decomposition allows such images to be represented by less than a hundred coefficients through exploiting the redundancy present in most images. In this research, two-dimensional fields of strain, i.e. maps of strain, have been treated as images; thereby, enabling the use of geometric moments that are invariant to rotation, scale and translation as a means of representing strain data. The image descriptors for a specific strain field can be grouped in a feature vector so that the feature vectors for strain fields in damaged and virgin component can be compared using the Euclidean distance between the vectors in multi-dimensional space. The Euclidean distance between feature vectors represent strain fields in undamaged and damage laminates has been found to correlate well with the level of damage measured using ultrasound and extremely well with the energy of impact used to induce the damage.
    12/2012; 4:126-132. DOI:10.1016/j.piutam.2012.05.014
  • C. Sebastian · E.A. Patterson
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    ABSTRACT: The use and results of the procedure published by Standardisation Project for Optical Techniques of Strain measurement (SPOTS) for a successful calibration of a digital image correlation (DIC) system are described. The details of the calibration specimen used are discussed together with procedure and criteria that must be met to achieve an acceptable calibration. The DIC system was evaluated over a strain range of 289 to 2110 µstrain, with a resulting calibration uncertainty ranging from 14 to 28.7 µstrain. The optical strain measurements were obtained from images taken directly from the bare metal surface, which had been prepared with grit paper, as opposed to generating a speckle pattern by painting the surface.
    Experimental Techniques 12/2012; 39(1). DOI:10.1111/ext.12005 · 0.55 Impact Factor
  • A. S. Patki · E. A. Patterson
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    ABSTRACT: Shape analysis techniques such as geometric moment descriptors, Fourier descriptors, wavelet descriptors etc. have been used commercially in the fields of biometrics for finger print matching, iris matching and facial recognition for almost over a decade. These techniques are capable of decomposing high resolution images with 105 to 106 pixels into only a few hundred unique shape descriptors which are a true representation of the features in the corresponding images thus tremendously reducing the computational data and time required for image analysis and comparison. This paper explores the possibility of employing shape analysis techniques to facilitate the comparison of full-field data obtained from techniques such as digital image correlation, thermoelasticity and photoelasticity for the purpose of validation of computational models and damage assessment. A new shape descriptor is introduced which combines Fourier decomposition with Zernike moments. The Fourier-Zernike descriptor is shown to be capable of decomposing full-field strain distributions containing engineering features and discontinuities arising from damage by combining the desirable properties of its parent shape descriptors while eliminating their individual limitations.
    Experimental Mechanics 10/2012; 52(8). DOI:10.1007/s11340-011-9570-4 · 1.55 Impact Factor
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    Y. Yang · M. Crimp · R. A. Tomlinson · E. A. Patterson
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    ABSTRACT: A novel approach is introduced to map the mesoscale plastic strain distribution resulting from heterogeneous plastic deformatio in complex loading and component geometries, by applying the discrete Fourier transform (DFT) to backscattered electron (BSE images of polycrystalline patches. These DFTs are then calibrated against the full width at half the maximum of the centra peak of the DFTs collected from the same material tested under in situ scanning electron microscopy uniaxial tensile conditions, which indicates a close relationship with the global tensile strain. In this work, the technique is demonstrated by measuring the residual strain distribution and plastic zone size around a fatigu crack tip in a commercially pure titanium compact tension specimen, by collecting BSE images in a 15×15 array of 115 μm squar images around the fatigue crack tip. The measurement results show good agreement with the plastic zone size and shape measure using thermoelastic stress analysis.
    Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences 08/2012; 468(2144):2399-2415. DOI:10.1098/rspa.2011.0682 · 2.19 Impact Factor
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    Y. Yang · M. A. Crimp · R. A. Tomlinson · E. A. Patterson
    Microscopy and Microanalysis 07/2012; 18(S2):692-693. DOI:10.1017/S1431927612005314 · 1.88 Impact Factor
  • Mahmoodul Haq · Conway A · Patterson EA · Sebastian C.
    2012 SEM XII, International Congress and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA USA; 06/2012

Publication Stats

2k Citations
208.43 Total Impact Points


  • 2013–2015
    • 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
  • 2010–2011
    • University of Plymouth
      • Faculty of Science and Technology
      Plymouth, England, United Kingdom
  • 1985–2008
    • The University of Sheffield
      • Department of Mechanical Engineering
      Sheffield, England, United Kingdom
  • 1994
    • University of Cambridge
      Cambridge, England, United Kingdom