The strength of granular material, specifically sand is of pivotal importance for understanding p... more The strength of granular material, specifically sand is of pivotal importance for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated three measures of strength (peak, confined flow, and unconfined flow friction angle) in Earth, Martian, Lunar, and near-zero gravity. The angles were captured in a passive Earth pressure experiment conducted on a reduced gravity flight. The results showed no dependence of the peak friction angle on gravity, a weak dependence of the confined flow friction angle on gravity, and no dependence of the unconfined flow friction angle on gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular material at different levels of gravity.
Experimental analysis of running gear–soil interaction traditionally focuses on the measurement o... more Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granu... more Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granular microstructures at ever-greater resolutions. The non-destructive technique has enabled deep insight into the morphology and behavior of granular materials, in situ and as a function of macroscopic states, e.g., loads. However, a significant bottleneck in this paradigm is that it ultimately yields qualitative ‘pictures’ of microstructure. Hence, a major challenge is to extract quantitative descriptors of grain-scale processes, e.g., morphological description of particles, kinematics, and spatial interactions. Existing methods, including watershed and burn algorithms, are plagued with limitations related to image resolution and with the inability to sharply identify grain-to-grain contact regions, which is crucial for studying force transmission and strength in granular materials. In this work, we propose a method to overcome these drawbacks. Specifically, a novel way to extract grain ...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit:
It has been said that porous materials are like music: the gaps are as important as the filled-in... more It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of
A recently published constitutive model for drying of a partially saturated porous material is ex... more A recently published constitutive model for drying of a partially saturated porous material is extended to take into account finite air (gas) pressure as well as finite external load, variables that are absent during simple drying under atmospheric conditions. We further use the result to derive a general form of effective stress in a partially saturated material. The proposed framework
Experimental analysis of running gear–soil interaction traditionally focuses on the measurement o... more Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
Proquest Dissertations and Theses Thesis Northwestern University 2010 Publication Number Aai3402499 Isbn 9781109746235 Source Dissertation Abstracts International Volume 71 05 Section B Page 3221 144 P, 2010
It has been said that porous materials are like music: the gaps are as important as the filled-in... more It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of
A recently published constitutive model for drying of a partially saturated porous material is ex... more A recently published constitutive model for drying of a partially saturated porous material is extended to take into account finite air (gas) pressure as well as finite external load, variables that are absent during simple drying under atmospheric conditions. We further use the result to derive a general form of effective stress in a partially saturated material. The proposed framework
ABSTRACT Experimental analysis of running gear–soil interaction traditionally focuses on the meas... more ABSTRACT Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
ABSTRACT Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access... more ABSTRACT Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granular microstructures at ever-greater resolutions. The non-destructive technique has enabled deep insight into the morphology and behavior of granular materials, in situ and as a function of macroscopic states, e.g., loads. However, a significant bottleneck in this paradigm is that it ultimately yields qualitative ‘pictures’ of microstructure. Hence, a major challenge is to extract quantitative descriptors of grain-scale processes, e.g., morphological description of particles, kinematics, and spatial interactions. Existing methods, including watershed and burn algorithms, are plagued with limitations related to image resolution and with the inability to sharply identify grain-to-grain contact regions, which is crucial for studying force transmission and strength in granular materials. In this work, we propose a method to overcome these drawbacks. Specifically, a novel way to extract grain topology in particulate materials via level sets is introduced. It is shown that the proposed method can sharply resolve the topology of grain surfaces near to and far from grain-to-grain contact regions with sub-voxel resolution, and is capable of grain extraction directly in three dimensions. The proposed method still relies on traditional techniques for input, but ultimately leads to much improved grain characterization. We validate the approach using three dimensional CT images of highly rounded (Caicos ooid) and highly angular (Hostun sand) natural materials, with excellent results.
The strength of granular material, specifically sand is of pivotal importance for understanding p... more The strength of granular material, specifically sand is of pivotal importance for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated three measures of strength (peak, confined flow, and unconfined flow friction angle) in Earth, Martian, Lunar, and near-zero gravity. The angles were captured in a passive Earth pressure experiment conducted on a reduced gravity flight. The results showed no dependence of the peak friction angle on gravity, a weak dependence of the confined flow friction angle on gravity, and no dependence of the unconfined flow friction angle on gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular material at different levels of gravity.
Experimental analysis of running gear–soil interaction traditionally focuses on the measurement o... more Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granu... more Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granular microstructures at ever-greater resolutions. The non-destructive technique has enabled deep insight into the morphology and behavior of granular materials, in situ and as a function of macroscopic states, e.g., loads. However, a significant bottleneck in this paradigm is that it ultimately yields qualitative ‘pictures’ of microstructure. Hence, a major challenge is to extract quantitative descriptors of grain-scale processes, e.g., morphological description of particles, kinematics, and spatial interactions. Existing methods, including watershed and burn algorithms, are plagued with limitations related to image resolution and with the inability to sharply identify grain-to-grain contact regions, which is crucial for studying force transmission and strength in granular materials. In this work, we propose a method to overcome these drawbacks. Specifically, a novel way to extract grain ...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the a... more This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit:
It has been said that porous materials are like music: the gaps are as important as the filled-in... more It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of
A recently published constitutive model for drying of a partially saturated porous material is ex... more A recently published constitutive model for drying of a partially saturated porous material is extended to take into account finite air (gas) pressure as well as finite external load, variables that are absent during simple drying under atmospheric conditions. We further use the result to derive a general form of effective stress in a partially saturated material. The proposed framework
Experimental analysis of running gear–soil interaction traditionally focuses on the measurement o... more Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
Proquest Dissertations and Theses Thesis Northwestern University 2010 Publication Number Aai3402499 Isbn 9781109746235 Source Dissertation Abstracts International Volume 71 05 Section B Page 3221 144 P, 2010
It has been said that porous materials are like music: the gaps are as important as the filled-in... more It has been said that porous materials are like music: the gaps are as important as the filled-in bits. In other words, in addition to the solid structure, pore characteristics such as size and morphology play a crucial role in defining the overall physical properties of the porous materials. This work goes a step further and examines the behaviors of
A recently published constitutive model for drying of a partially saturated porous material is ex... more A recently published constitutive model for drying of a partially saturated porous material is extended to take into account finite air (gas) pressure as well as finite external load, variables that are absent during simple drying under atmospheric conditions. We further use the result to derive a general form of effective stress in a partially saturated material. The proposed framework
ABSTRACT Experimental analysis of running gear–soil interaction traditionally focuses on the meas... more ABSTRACT Experimental analysis of running gear–soil interaction traditionally focuses on the measurement of forces and torques developed by the running gear. This type of measurement provides useful information about running gear performance but it does not allow for explicit investigation of soil failure behavior. This paper describes a methodology based on particle image velocimetry for analyzing soil motion from a sequence of images. A procedure for systematically identifying experimental and processing settings is presented. Soil motion is analyzed for a rigid wheel traveling on a Mars regolith simulant while operating against a glass wall, thereby imposing plain strain boundary conditions. An off-the-shelf high speed camera is used to collect images of the soil flow. Experimental results show that it is possible to accurately compute soil deformation characteristics without the need of markers. Measured soil velocity fields are used to calculate strain fields.
ABSTRACT Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access... more ABSTRACT Imaging, epitomized by computed tomography, continues to provide unprecedented 3D access to granular microstructures at ever-greater resolutions. The non-destructive technique has enabled deep insight into the morphology and behavior of granular materials, in situ and as a function of macroscopic states, e.g., loads. However, a significant bottleneck in this paradigm is that it ultimately yields qualitative ‘pictures’ of microstructure. Hence, a major challenge is to extract quantitative descriptors of grain-scale processes, e.g., morphological description of particles, kinematics, and spatial interactions. Existing methods, including watershed and burn algorithms, are plagued with limitations related to image resolution and with the inability to sharply identify grain-to-grain contact regions, which is crucial for studying force transmission and strength in granular materials. In this work, we propose a method to overcome these drawbacks. Specifically, a novel way to extract grain topology in particulate materials via level sets is introduced. It is shown that the proposed method can sharply resolve the topology of grain surfaces near to and far from grain-to-grain contact regions with sub-voxel resolution, and is capable of grain extraction directly in three dimensions. The proposed method still relies on traditional techniques for input, but ultimately leads to much improved grain characterization. We validate the approach using three dimensional CT images of highly rounded (Caicos ooid) and highly angular (Hostun sand) natural materials, with excellent results.
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