A numerical photogrammetry technique for measuring microscale kinematics and fabric in Schneebeli materials

Studia Geotechnica Et Mechanica

Villard

2015

The mechanical performance of underground flexible structures such as buried pipes or culverts made of plastics depend not only on the properties of the structure, but also on the material surrounding it. Flexible drains can deflect by 30% with the joints staying tight, or even invert. Large deformations of the structure are difficult to model in the framework of Finite Element Method, but straightforward in Discrete Element Methods. Moreover, Discrete Element approach is able to provide information about the grain-grain and grain-structure interactions at the microscale. This paper presents numerical and experimental investigations of flexible buried pipe behaviour with focus placed on load transfer above the buried structure. Numerical modeling was able to reproduce the experimental results. Load repartition was observed, being affected by a number of factors such as particle shape, pipe friction and pipe stiffness.

Section: Experimental Programmentioning

confidence: 99%

Particle Shape Effect on Macroscopic Behaviour of Underground Structures: Numerical and Experimental Study

Szarf

Studia Geotechnica Et Mechanica

Villard

2015

“…The macroscopic behavior in terms of stress and strain is deduced from forces and displacements measured at the boundary. In addition, Digital Image Correlation of successive pictures of the deforming specimen allows to obtain the kinematics of each individual rod, see [3].…”

Section: Experimental and Numerical Proceduresmentioning

confidence: 99%

Mechanical behavior of mixtures of circular and rectangular 2D particles

Charalampidou¹,

AIP Conference Proceedings

Viggiani

et al. 2009

This paper presents the results of experimental compression tests on a 2D granular material composed of a mixture of circular and rectangular rods. Numerical simulations of the tests, using a Discrete Element Method (Molecular Dynamics), successfully reproduce the experimental results. The results of the comparison between experimental and numerical results highlights the important role of the contact laws (especially the rolling resistance). A statistical study of the rotations of rectangular particles during compression (experimental and numerical) is carried out. The results of such study are finally compared to the predictions of continuum mechanics.

“…Thus, a new numerical photogrammetry technique to obtain semi-automated measurements of kinematics was used [4]. The use of digital cameras made the shots easier (no need of the photography silver film processing step), however the image analysis procedure proposed by [4] was not able to reduce the process time: between each couple of successive pictures, even if most particles move almost like continuum mechanics dictates, many of them have unpredictable displacements and it was necessary to manually "help" the process to find the right position and rotation of grains. Moreover, the accuracy was very coarse (in the order of the pixel, which correspond to 10 −2 of particle's mean diameter with the 16 Mpixels digital camera used at this time).…”

Section: Introductionmentioning

confidence: 99%

“…Moreover, the accuracy was very coarse (in the order of the pixel, which correspond to 10 −2 of particle's mean diameter with the 16 Mpixels digital camera used at this time). It was therefore decided to develop a new way to assess full 2D kinematic from digital photographs of granular samples made of Schneebeli rods with the following specifications: fully automated measurement of grain kinematic (translations and rotations) able to handle more than 1000 digital photographs and above all, a displacement accuracy strongly increased compared to that obtained by [4].…”

Section: Introductionmentioning

confidence: 99%

TRACKER: A particle image tracking (PIT) technique dedicated to nonsmooth motions involved in granular packings

AIP Conference Proceedings

Richefeu

2013

Abstract. We present a new approach to assess the 2D motion of rigid bodies in granular materials. Although it was adapted from Digital Image Correlation (DIC) technique, the heart of the presented technique relies on specific treatments related to the discrete nature of grain-displacement fields. The code called TRACKER has been developed to process the digital images and measure the in-plane displacement and rotation of each individual grain from one image to another. A remarkable feature is the use of a specific strategy that allows tracking all particles, without losing any of them (which is a typical problem when tracking assemblies of discrete particles over many images). This is achieved by a two-step procedure, where, in case of problematic tracking of a grain, the size of the search zone is increased in an adaptive manner, i.e., taking into account the results of tracking in the neighborhood of the particle. The accuracy of the measured displacements and rotations was tested on both perfect synthetic images and digital photographs of a sheared assembly of grains. The accurate assessment of the grain kinematics opens very interesting perspectives, especially in the study of displacement fluctuations in granular media.