E. A. Patterson

University of Liverpool, Liverpool, England, United Kingdom

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Publications (201)175.83 Total impact

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    Fatigue & Fracture of Engineering Materials & Structures 05/2014; 38(2). DOI:10.1111/ffe.12213 · 1.06 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; 52:66-74. DOI:10.1016/j.optlaseng.2013.07.025 · 1.70 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 · 1.66 Impact Factor
  • The Journal of Strain Analysis for Engineering Design 04/2013; 49(4):212-223. DOI:10.1177/0309324713498074 · 1.01 Impact Factor
  • D. Backman, E. A. Patterson
    The Journal of Strain Analysis for Engineering Design 03/2013; 49(3):141-153. DOI:10.1177/0309324713493082 · 1.01 Impact Factor
  • 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 · 1.01 Impact Factor
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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 · 1.69 Impact Factor
  • International Journal of Fatigue 01/2013; 46:1. DOI:10.1016/j.ijfatigue.2012.08.001 · 1.69 Impact Factor
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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 · 1.01 Impact Factor
  • 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; DOI:10.1111/ext.12005 · 0.58 Impact Factor
  • 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 · 2.00 Impact Factor
  • Y. Yang, M. A. Crimp, R. A. Tomlinson, E. A. Patterson
    Microscopy and Microanalysis 07/2012; 18(S2):692-693. DOI:10.1017/S1431927612005314 · 1.76 Impact Factor
  • 2012 SEM XII, International Congress and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA USA; 06/2012
  • 2012 SEM XII, International Congress and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA USA; 06/2012
  • Mahmoodul Haq, Conway A, Patterson EA
    2012 SEM XII, International Congress and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA USA; 06/2012
  • Mahmoodul Haq, Patterson EA, Drzal LT
    2012 SEM XII, International Congress and Exposition on Experimental and Applied Mechanics, Costa Mesa, CA USA; 05/2012
  • Amol S. Patki, Eann A. Patterson
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    ABSTRACT: This study explores the use of a generic shape descriptor for quantitative comparisons between the full-field strain data acquired from virgin and damaged composite panels using digital image correlation. These descriptors are capable of decomposing images with 103 to 106 pixels into a feature vector with less than a few hundred elements. Strain distributions in four composite specimens with incremental impact damage and a virgin specimen, all subject to a tensile load, were decomposed using the newly developed Fourier–Zernike descriptors. Pearson’s correlation coefficient, cosine similarity and Euclidean distance were employed to compare quantitatively the feature vectors evaluated for the strain distributions in the four damaged specimens with the strain distribution in the virgin specimen. The deviation of the Pearson correlation coefficient from unity was found to be an effective damage indicator, which could be evaluated automatically and without the need for subjective assessment of the damage.
    The Journal of Strain Analysis for Engineering Design 05/2012; 47(4):244-253. DOI:10.1177/0309324712440554 · 1.01 Impact Factor
  • M. N. James, C. J. Christopher, Y. Lu, E.A. Patterson
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    ABSTRACT: This paper expounds a revised characterisation of the elastic stresses ahead of a crack tip in polycarbonate which takes account of the elastic–plastic boundary stresses induced by the presence of the crazed region that surrounds a crack. The advanced experimental techniques used in this work have provided insights into fractography, identification of the crazed region and location of the crack tip position (using confocal laser scanning microscopy and scanning electron microscopy). In addition, the four-parameter model of crack tip stresses has led to modified definitions for crack tip stress intensity factors which explicitly account for craze-induced shielding effects on the fatigue crack growth rate in polycarbonate. The model is generic and offers the potential for increased understanding of fatigue crack growth in polycarbonate.
    Polymer 03/2012; 53(7):1558–1570. DOI:10.1016/j.polymer.2012.01.032 · 3.77 Impact Factor
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    ABSTRACT: For holography and speckle interferometry the calibration of the sensitivity is a must, because illumination and observation directions vary across the field of view. A numerical estimate or a static calibration using rigid body motions is standard, and reference materials exist for static strain calibration. Recently, reference materials for the dynamic calibration of optical instruments of displacement and strain measurement were designed and prototypes were manufactured in the European FP7 project ADVISE. We review the properties of the reference material and the concept of traceability for the field of displacement values by using a calibrated single point transducer. The mode shape is assessed using out-of-plane DSPI, Finite Element Analysis as well as analytic solutions of the plate vibration. We present measurements using stroboscopic DSPI on the reference material under acoustic excitation and compare the measured mode shapes to the ones predicted by FE analysis. We apply different comparison methodologies based on point-by-point deviations and on decomposition of the mode shapes into a set of orthogonal basis functions. The latter method is well suited to assess stability and reproducibility of a mode shape. Finally, the deviations are used to estimate the reference material uncertainty which is an essential parameter for determining the calibration uncertainty. Uncertainty contributions of the DSPI set-up are taken into account. To conclude, the application area and limitations of the reference material are discussed.
    Proceedings of SPIE - The International Society for Optical Engineering 01/2012; DOI:10.1117/12.977950 · 0.20 Impact Factor

Publication Stats

2k Citations
175.83 Total Impact Points

Institutions

  • 2013–2014
    • 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
  • 2010–2013
    • University of Plymouth
      • School of Marine Science and Engineering
      Plymouth, England, United Kingdom
  • 1990–2008
    • The University of Sheffield
      • Department of Mechanical Engineering
      Sheffield, England, United Kingdom
  • 2006
    • Warsaw University of Technology
      • Institute of Micromechanics and Photonics
      Warszawa, Masovian Voivodeship, Poland