Laboratoire de Mécanique des Solides, Institut Polytechnique de Paris
In-situ full-field measurements of strain and temperature at small scales: a perspective in sensor characterization and design
Full-field measurements of either strain or temperature are now ubiquitous in solid mechanics and have reached small-scale and high-speed capabilities. Such advances have provided significant insight into deformation mechanisms as well as data for identification. This presentation will discuss the application of these measurement techniques for probing motion mechanisms in nano-architectured sensors as well as multiphysics couplings and damage in micro-electronic devices. Full-field measurements of strains, performed via digital image correlation on carbon nanotube networks (CNNs) under tensile strain in a scanning electron microscope, can indeed provide valuable insight into the local motion mechanisms arising within CNNs. High-resolution temperature measurements in graphene devices can also prove themselves useful for investigating how damage propagates when devices are submitted to high current density. Finally, it will be shown how this data can be exploited to develop more accurate physical models and to design more efficient devices.
Department of Mechanical Engineering, University College London
Fibre Tracking in Soft Tissue using Synchrotron Tomography and Digital Volume Correlation
X-ray microtomography and digital volume correlation (DVC) have increasingly been used in biomechanics for full-field strain measurement. Whilst improvements in in situ x-ray microtomography of calcified tissues have driven nanometric precision DVC results, resolution of soft tissues has been limited due to their low absorption contrast. It has only recently been possible to resolve native soft tissue microstructure using in-line phase contrast synchrotron tomography (sCT) and apply DVC for micro-scale strain maps in large tissue regions, but the results can be difficult to interpret. For example, the intervertebral disc has concentric curved layers of alternating-orientated collagen fibres which dominate multiscale structural dynamics. A new approach in which a pre-processing step specifies points along traced fibres to be tracked by DVC, allows quantification of individual fibre kinematics on a comprehensive scale of ~200k points, every 8 µm along ~10k fibres within an individual sample region. Biomechanically relevant measurements such as fibre reorientation, change in curvature and fibre strain with applied load can then be calculated. Use of these fibre-tracking-DVC results for future research goals, including improving finite element models of tissues, will be discussed.
Department Production Control
Fraunhofer Institute for Physical Measurement Techniques IPM
Combining GPU-based full-field and strain-controlled 2D-DIC for simplified crack growth experiments
Today, mechanical extensometers are used in crack-growth experiments to control integral strain during crack growth whereas digital image correlation (DIC) is well established for measuring crack depth or crack-flank displacements. Often, sensors have to be unmounted during the experiment because both observe the same surface on the specimen. A 2D digital image correlation (DIC) system based on a graphics processing unit (GPU) enables real-time evaluation of both, integral strain for strain-control and full-field DIC on images selected automatically in real-time. This combination enables the use of one single sensor for strain-controlled crack growth and crack characterization. The full-field displacement is compared to a finite-element model (FEM) using the crack contour measured by the DIC system. Results from uni- and biaxial crack growth experiments show that DIC is able to increase information although the setup and the experimental procedure are simplified.
Eindhoven University of Technology (TU/e)
Advancement of Integrated Digital Image Correlation, Integrated Digital Height Correlation, and Mechanical Shape Correlation
In the field of full-field model parameter identification, Integrated Digital Image Correlation (IDIC) was introduced a decade ago as a one-step method to directly correlate digital images by optimizing the parameters of a FEM model of the specimen, making it more accurate than the two-step method of element model updating (FEMU), particularly in challenging test cases (small displacements, complex kinematics, specimen misalignment, image noise). Recently, the IDIC family was extended with correlation of Height profiles instead of Images, named IDHC, while Mechanical Shape Correlation (MSC) was introduced for correlation of the specimen contour for cases where the specimen rotates out of view. In this presentation, I will present the pitfalls, challenges and eventual successful application of IDIC, IDHC, and MSC for (i) mixed-mode interface identification in microelectronics, (ii) correction of SEM imaging artifacts, (iii) absolute cross-grain stress and orientation correlation using EBSD, (iv) time-dependent anelasticity characterization in MEMS microbeams, and (iv) parameter identification of micron-sized freestanding stretchable electronic interconnects.
Professor of Solid Mechanics
Faculty of Engineering and Physical Sciences
School of Mechanical Engineering
University of Southampton
Next generation of camera-based high strain rate material tests: the “IB” series
This presentation will provide an overview of a series of new high strain rate tests based on ultra-high speed imaging and the Virtual Fields Method. Three tests form part of the so-called “IB” series: the Image-Based Inertial Impact (IBII) test, the Image-Based Ultrasonic Shaking (IBUS) test and the Image-Based Inertial Release (IBIR) test. The principle of each test will be presented and some applications will be shown to illustrate their capabilities.
California Institute of Technology (Caltech)
Recent advances in capturing the behavior of dynamic shear cracks using ultrahigh-speed digital image correlation
In recent years, the digital image correlation (DIC) method has been used in a range of high- and ultrahigh-speed applications to characterize the dynamic behavior of materials. Yet it was not possible to quantify the full-field behavior of dynamic shear cracks due to several metrological challenges, including camera technologies and correlation techniques. In this presentation, we discuss our recent advances to characterize dynamic frictional ruptures using DIC coupled with ultrahigh-speed photography. Our measurements map the displacements, velocities, strains, and strain rates at a level of detail that, until recently, was only possible to achieve with numerical simulations. They also allow us to track the local changes in dynamic friction, and study friction evolution with relevant quantities, such as slip and slip rate. Dynamic friction controls how ruptures develop and understanding its evolution is of paramount importance for a wide range of applications, including earthquake mechanics.