Edward Ando

Projector-based augmented stacking framework for irregularly shaped objects

Edward Ando, Katrin Beyer, Julien Gamerro, Andrea Settimi, Qianqing Wang, Yves Weinand

Augmented reality in additive fabrication is predominantly applied to the manufacturing of structures from regularly shaped materials. Our work however embraces natural heterogeneity, by focusing on the assembly of irregularly shaped elements such as mineral scraps. We introduce a computer-aided framework with a 3D stacking engine and an augmented reality interface capable of guiding users through the balanced positioning of discrete and highly nonuniform objects according to an on-the-fly computed model and without prior trimming of the building unit. The pipeline is tested by the construction of two dry-stone structures (i.e., lacking any adhesives), and its accuracy is validated with a comparative study between the point cloud of the as-built digitized artifacts and the generated execution model, which shows an average 2.9 ± 1.8 cm error between the stones of the two models. We finally show how the proposed framework could be improved both in terms of software and hardware. In the interests of reproducibility, all the methods are shared as open source with the community.

2023

augmented-stacking

Edward Ando, Katrin Beyer, Julien Gamerro, Andrea Settimi, Qianqing Wang, Yves Weinand

Augmented Stacking is an augmented system designed to guide inexperienced users through the stacking of complex and irregular geometries. This digital fabrication system was applied to the assembly of one layer of a half-timber dry-stone wall. Augmented Stacking is composed of two components: the stacking algorithm (which calculates the pose for each stone or irregular object fed to the system) and the augmented pipeline to display the information.

2022

Experimental quantification of 3D deformations in sensitive clay during stress-probing

Edward Ando

Unique four-dimensional (4D) deformation data are collected during drained triaxial tests on intact specimens of a natural sensitive clay. This requires the development of a miniature triaxial cell for advanced stress path testing, specifically designed for X-ray computed tomography. Salient features include the omission of a membrane, and a mounting procedure that minimises disturbance by the experimenter. Three distinct drained stress ratios are studied for pseudo-isotropic, K-0, and highly deviatoric loading paths. The results indicate that the K-0 path shows the most uniform deformation mechanism, where the measured ratio of deviatoric and volumetric strain increments reach the stress ratio applied at boundary value level for large magnitudes of total strain. The pseudo-isotropic test also reaches a strain ratio close to eta at large total strain levels; however, the deformation field is less uniform. Furthermore, the highly deviatoric stress path shows the most heterogeneous deformation fields commensurate with the applied stress ratio, although the ratio of deviatoric and volumetric strain increments falls above the eta applied. The mean value of the three-dimensional spatial fields of strain corresponds well with the changes observed at boundary level, supporting prior research on drained stress-probing on clays for which there are no 4D deformation data available.

ICE PUBLISHING2022

Freezing-induced stiffness and strength anisotropy in freezing clayey soil: Theory, numerical modeling, and experimental validation

Edward Ando, Gioacchino Viggiani

This paper presents a combined experimental-modeling effort to interpret the coupled thermo-hydro-mechanical behaviors of the freezing soil, where an unconfined, fully saturated clay is frozen due to a temperature gradient. By leveraging the rich experimental data from the microCT images and the measurements taken during the freezing process, we examine not only how the growth of ice induces volumetric changes of the soil in the fully saturated specimen but also how the presence and propagation of the freezing fringe front may evolve the anisotropy of the effective media of the soil-ice mixture that cannot be otherwise captured phenomenologically in the isotropic saturation-dependent critical state models for plasticity. The resultant model is not only helpful for providing a qualitative description of how freezing affects the volumetric responses of the clayey material, but also provide a mean to generate more precise predictions for the heaving due to the freezing of the ground.

WILEY2022

Influence of depositional fabric on mechanical properties of naturally deposited sands

Edward Ando, Gioacchino Viggiani

Fabric characteristics and shear deformation behaviour were analysed in four intact small-scale samples, including two disturbed and two undisturbed samples of naturally deposited sand from a shoal in the San Francisco Bay. Triaxial compression tests were performed on each sample while incrementally imaging with X-ray micro-computed tomography (XRCT). The grains in each intact sample exhibited a nearly unidirectional orientation with their long axes oriented within a narrow range of horizontal directions, in stark contrast to the randomly oriented grains of a reconstituted sample. The disturbed intact samples exhibited lower peak strengths and lower yet positive rates of dilation as compared with undisturbed samples. Higher rates of dilation corresponded with larger quantifiable decreases in the average number of grain-to-grain contacts and contact areas per grain within the shear band. The XRCT images of the shear bands were quantified by way of large incremental deviatoric strains and large incremental grain rotations. The grain orientations within the fully developed shear band of each sample reached a consistent orientation independent of their initial fabric. These results are a promising step toward a systematic study of granular deposits from different depositional environments needed for the development of more advanced models of their mechanical behaviour.

ICE PUBLISHING2022

Micromechanically inspired investigation of cemented granular materials: part I-from X-ray micro tomography to measurable model variables

Edward Ando, Gioacchino Viggiani

Cemented granular materials are abundant in nature and are often artificially produced. Their macroscopic behaviour is driven by small-scale material processes, which are generally classified as: grain breakage, cement damage and fragment rearrangement. This paper presents an experimental analysis of the latter two processes as observed through in-situ X-ray tomography and quantified by a suite of novel image processing approaches. This allows for example all particles and the bonds between them to be identified and their evolution to be individually quantified on a statistically representative volume, in 3D, throughout a loading test. We reveal the high spatial correlation between cement damage and strain rate and their effect on the isotropy of the bonds. Being the second of a two-part contribution, the overarching aim of this paper is to propose a general framework for the micro-inspired study of cemented granular materials. This is developed here, in Part I, in terms of multi-scale experimental quantification at sample and grain-level, while in Part II in terms of a two-way interaction with micro-inspired constitutive modelling.

SPRINGER HEIDELBERG2022

The effect of high relative humidity on a network of water-sensitive particles (couscous) as revealed by in situ X-ray tomography

Edward Ando, Gioacchino Viggiani

Water significantly influences the mechanical behaviour of all granular materials but none as much as hygroscopic amorphous particles. With sufficiently high water content, particles can swell, agglomerate and their mechanical properties can be reduced, having direct effects on the macroscopic response of the material. In the food and pharmaceutical industry this can cause loss of product functionality. Despite their relevance, very little is known about the microscopic processes that induce these phenomena. Previous studies focused on single particle behaviour, the strength of agglomerated particles and the material flowability, leaving unexplored the link connecting the particle behaviour and the bulk response. This experimental study aims to investigate this aspect with quantitative measurements at both particle and macroscopic scales. A sample of fine couscous is exposed to a high relative humidity (RH) air flow, while being subjected to oedometric conditions, in order to reproduce the storage-silo conditions. In the meantime, X-ray tomographies are acquired continuously and the resulting images are analysed. The designed spatial resolution allows each particle of the sample to be identified and tracked, allowing volumetric evolution to be compared to the properties of the whole sample. The analysis reveals a dilation-compaction macroscopic behaviour, a result of the competition between the particle swelling and the higher deformability as the water content increases. The number, orientations and inter-particle contacts are computed. Their area is related to the applied boundary conditions, and is found to be consistent with the particle swelling and dependent on the applied stress direction.

ROYAL SOC CHEMISTRY2022

Single-projection reconstruction technique for positioning monodisperse spheres in 3D with a divergent x-ray beam

Edward Ando

The measurement of the position of single-sized spheres in 3D from a single, divergent, radiographic projection is addressed in the present study with the development of a novel method. Generally speaking, the location of the shadow cast by a single sphere on a detector defines a source-detector ray; the position of the particle along this ray is identified by the strong prior knowledge of its radius and the size of the shadow. For a dense assembly of equal-sized particles whose projections overlap, a novel Fourier transform based technique is introduced to give a first 3D determination of the particle centres. The uncertainty of this measurement is calculated from synthetic data with a known noise distribution. A further refinement of this measurement is performed based on the minimisation of the projection residual. The combined approach is validated both on synthetic data, and on real radiographs of a glass bead packing. The effect of noise on the measurement uncertainty is evaluated. The technique is made available to the community in the open source python package radioSphere.

2021