Keynote lectures

Stéphane Avril, France


Title: Identification of regional, nonlinear and anisotropic material properties in soft tissue biomechanics using 2D and 3D full-field measurements


Abstract : Histopathological changes that occur in diseased soft tissues manifest at the macroscopic level as altered mechanical functionality and structural integrity. Correlations between local tissue composition and mechanical properties can thus provide increased insight into conditions that render a soft tissue susceptible to failure or disease. Toward this end, we have used the virtual fields method to determine locally varying values of constitutive parameters from a set of full-field data acquired during tension-inflation tests of arteries using a combination of panoramic digital image correlation (p-DIC) and of optical coherence tomography - digital volume correlation (OCT-DVC). The approach has permitted to reveal for the first time the local material heterogeneities of aortic aneurysms and to relate them to the biological dysfunctions that render blood vessels susceptible to potential rupture.


Bio: Stéphane Avril is Full Professor at Institut Mines Telecom with affiliations at Mines Saint-Etienne and University of Lyon in France. He runs a group of 20+ in soft tissue biomechanics, with a special focus on constitutive modeling and identification using imaging techniques. He is also director of the CIS center for biomedical and healthcare engineering (65+ people) and deputy director of SAINBIOSE (INSERM endorsed laboratory with 100+ researchers). Stéphane received his PhD in mechanical and civil engineering in 2002 at Mines Saint-Etienne (France). After positions at Arts et Métiers ParisTech (France) and Loughborough University (UK) where he developed the Virtual Fields Methods, Stéphane returned to his alma mater in 2008 and extended his broad experience of inverse problems to soft tissue biomechanics, especially regarding aortic aneurisms in close collaboration with vascular surgeons. Stéphane was a visiting Professor at the University of Michigan Ann Arbor (USA) in 2008 and has been a visiting professor at Yale University since 2014. In 2015, Stéphane was awarded an ERC (European Research Council) consolidator grant of 2m€ for the Biolochanics project on: Localization in biomechanics and mechanobiology of aneurysms: Towards personalized medicine.


Bing Pan, China




Title : Towards High-Accuracy Digital Image/Volume Correlation Measurements : A Perspective From Imaging


Abstract : In the experimental mechanics community, digital image/volume correlation (DIC/DVC) techniques have been widely accepted as the most popular, practical and versatile tool for full-field surface/internal displacement and deformation measurements. Basically, the implementation of DIC/DVC measurements involves two consecutive stages: namely image acquisition and image processing. At present, the state-of-the-art DIC/DVC algorithms using inverse compositional Gauss-Newton (IC-GN) algorithm and B-spline interpolation scheme allow subpixel/subvoxel registration with an accuracy higher than 0.005 pixels/voxels for computer simulated speckle pattern. However, for real experimental images recorded by common imaging systems, the accruacy of DIC/DVC measurements can be seriously degraded. Since measurement accuracy is always the most important objective in various experimental mechanics applications, the errors associated with image acquisition must be understood, quantified and minimized.

In this talk, we will first point out that all the common imaging systems (e.g. a single camera for 2D-DIC, synchronized two cameras for stereo-DIC, or a x-ray CT scanner for DVC) are neither perfect nor stable, because of the existence of lens distortion and the continual slight changes in imaging geometry associated with the self-heating effect or ambient temperature variations. Then, we systematically investigate the measurement errors in 2D-DIC, stereo-DIC and DVC from the perspective of the stability of image acquisition devices. Our experimental results show that the maximum temperature-induced artificial strains can reach an magnitude of 200, 150, and 400 microstrains for the specific imaging devices used by the authors. Finally, we discuss several approaches that can be used to mitigate or correct these errors. In particular, we focus on an easy-to-implement but effective reference specimen compensation method, and validate its efficacy and practicality by real experiments.


Bio : Dr. Bing Pan is a full professor in School of Aerospace Science & Engineering at Beihang University (BUAA), China. He received his Ph.D degree in Mechanical Engineering from Tsinghua University in 2008. After working with Professor Anand Asundi in Nanyang Technological University (Singapore) as a postdoctor, he joined Institute of Solid Mechanics, BUAA in 2009. His current research interests mainly focus on advanced optical techniques and their applications in experimental mechanics, especially the digital image correlation, digital volume correlation techniques for surface or internal deformation measurement of solid materials and structures, as well as new experimental techniques for characterizing thermo-mechanical behavior of hypersonic materials and structures. He has published more than 80 peer-reviewed articles in international journals, and six of these papers were selected as ESI highly cited papers. All his publications have been cited more than 2600 times according to Web of Science and more than 4800 times according to Google Scholar. Dr. Pan was selected for Youth Changjiang Scholars (MOE) in 2016, and won the National Natural Science Funds for Excellent Young Scholar in 2013.


Eric Whitenton, USA



Title:  Imaging of material deformation processes – Examples of thermal-, visible-, combined- and hyper-spectrum image streams blended with scalar data streams.


Abstract:  Thermal imaging is used to study material deformation processes such as machining. However, determining uncertainty for measured temperatures must take many factors into consideration. Combining traditional, single wavelength thermal imaging with other measured image and scalar data can significantly improve temperature measurements.

For example, when using mid wave infrared cameras, the relatively long wavelength of light cause high magnification images to appear somewhat blurry. For situations where the material is rapidly moving, it is sometimes difficult to know exactly what is being imaged. Without knowing the speed of imaged objects, effects such as motion blur are difficult to account for. Combining thermal spectrum images with visible spectrum images can resolve these issues due to the shorter wavelength of visible light, coupled with the fact that visible cameras can often use shorter integration times than thermal cameras. Another example is when emissivity is unknown or rapidly changing. The additional information provided by imaging multiple wavelengths can help by providing estimates of emissivity. Also, image and scalar data streams may be blended. Examples include when embedded thermocouple data is compared to imaged temperatures.

This talk will discuss using single and multiple data stream approaches in several research activities at the National Institute of Standards and Technology. These include situations such as metal cutting, a rapidly heated Split-Hobkinson bar, determining fiber orientation angle effects in machining of unidirectional CFRP laminated composites, metal powder-bed additive manufacturing, and others.

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Bio:  In 1980, Mr Eric Whitenton started at the National Institute of Standards and Technology (NIST) in the American Dental Association facility. He subsequently moved to the Tribology Group, and then the Precision Machining Research Facility Group. He is currently a guest researcher in the Production Systems Group.  For the past 15 years, he has been using visible and thermal spectrum imaging to better understand high-speed deformation processes, primarily of metals. Previous activities include macro scale, high speed, dual spectrum imaging where thermal and visible spectrum images are simultaneously acquired through a shared lens, as well as uncertainty estimation for traditional thermal spectrum imaging. Current activities include using hyperspectral thermal imaging to measure temperatures, and using joint time-frequency analysis of inexpensive infrared spectrum sensors for improved understanding of metal powder‑bed additive machining.

Publication related awards include: In 2015, best paper award in the Dynamic Behavior of Materials Division of the Society for Experimental Mechanics for the 2014 paper “Dynamic Flow Stress Measurements for Machining Applications.” In 2014, outstanding paper award from the North American Manufacturing Research Institution of SME for “Fiber orientation angle effects in machining of unidirectional CFRP laminated composites.” In 2009, the NAMRI/SME Outstanding Paper Award at the 37th Annual North American Research Conference held at Clemson University for the paper titled "High-Speed Microvideography Observations of the Periodic Catastrophic Shear Event in Cutting AISI 1045 Steel."

Project related awards include: In 2008, a NIST Bronze Metal Award for outstanding achievements and scientific contributions that have advanced the state-of-the-art of measurement science for fundamental phenomena that occur during manufacturing processes. In 2004, a NIST Allen V. Astin Measurement Science Award for work on the Rapidly Heated Kolsky Bar in recognition of “outstanding achievements and scientific contributions in the measurement of stress-strain relationships of materials under high heating-rate, high strain-rate conditions.” In 2001, a US Department of Commerce Gold Metal Award for Distinguished Service for technical leadership in designing, fabricating, assembling, and testing of new encasements for the Nation's Charters of Freedom documents (Declaration of Independence, Constitution, and Bill of Rights).




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