More Like this

1. LEAP-2017 Simulation Exercise: Calibration of Constitutive Models and Simulation of the Element Tests

   https://doi.org/10.1007/978-3-030-22818-7_9  

   Manzari, M.T. (November 2019, Proceedings of LEAP-UCD-2017 workshop)

   This paper presents a summary of the element test simulations (calibration simulations) submitted by 11 numerical simulation (prediction) teams that participated in the LEAP-2017 prediction exercise. A significant number of monotonic and cyclic triaxial (Vasko, An investigation into the behavior of Ottawa sand through monotonic and cyclic shear tests. Masters Thesis, The George Washington University, 2015; Vasko et al., LEAP-GWU-2015 Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019) and direct simple shear tests (Bastidas, Ottawa F-65 Sand Characterization. PhD Dissertation, University of California, Davis, 2016) are available for Ottawa F-65 sand. The focus of this element test simulation exercise is to assess the performance of the constitutive models used by participating team in simulating the results of undrained stress-controlled cyclic triaxial tests on Ottawa F-65 sand for three different void ratios (El Ghoraiby et al., LEAP 2017: Soil characterization and element tests for Ottawa F65 sand. The George Washington University, Washington, DC, 2017; El Ghoraiby et al., LEAP-2017 GWU Laboratory Tests. DesignSafe-CI, Dataset, 2018; El Ghoraiby et al., Physical and mechanical properties of Ottawa F65 Sand. In B. Kutter et al. (Eds.), Model tests and numerical simulations of liquefaction and lateral spreading: LEAP-UCD-2017. New York: Springer, 2019). The simulated stress paths, stress-strain responses, and liquefaction strength curves show that majority of the models used in this exercise are able to provide a reasonably good match to liquefaction strength curves for the highest void ratio (0.585) but the differences between the simulations and experiments become larger for the lower void ratios (0.542 and 0.515). 

   more » « less
2. Stress-strain behavior of Ottawa sand in cyclic direct simple shear and modeling of cyclic strength using Artificial Neural Networks

   https://doi.org/10.1016/j.soildyn.2022.107585  

   Lbibb, Sarra; Manzari, Majid T. (January 2023, Soil Dynamics and Earthquake Engineering)

   The stress-strain behavior of Ottawa F65 sand is investigated through an extensive series of constant volume stress-controlled cyclic direct simple shear (CDSS) tests performed at different densities, overburden pressures, and static shear stresses prior to cyclic shearing to quantify their effects on the cyclic strength of Ottawa F65 sand. Results of the CDSS tests are used in the constitutive model calibration exercise for the Liquefaction Experiments and Analysis Project (LEAP-2022). The collected database of CDSS tests is used to develop an Artificial Neural Network (ANN) model capable of predicting Ottawa F65 liquefaction strength for a specified set of relative density, overburden pressure, static shear stress ratio, and cyclic shear stress ratio. After training, validation and testing, the ANN model is further assessed using blind prediction of the liquefaction strength in new CDSS tests for a relative density and overburden stress that are not available in the training dataset. CDSS tests under similar conditions were then carried out in the laboratory for validation of the ANN model. The comparisons of the predictions with the experimental results have demonstrated the ANN model predictive capability for liquefaction strength and its sensitivity to changes in relative density, overburden stress and cyclic stress ratio. 

   more » « less
3. Effect of Process Parameters on Void Distribution, Volume Fraction, and Sphericity within the Bead Microstructure of Large-Area Additive Manufacturing Polymer Composites

   https://doi.org/10.3390/polym14235107  

   Sayah, Neshat; Smith, Douglas E. (December 2022, Polymers)

   Short carbon fiber-reinforced composite materials produced by large-area additive manufacturing (LAAM) are attractive due to their lightweight, favorable mechanical properties, multifunctional applications, and low manufacturing costs. However, the physical and mechanical properties of short carbon-fiber-reinforced composites 3D printed via LAAM systems remain below expectations due in part to the void formation within the bead microstructure. This study aimed to assess void characteristics including volume fraction and sphericity within the microstructure of 13 wt% short carbon fiber acrylonitrile butadiene styrene (SCF/ABS). Our study evaluated SCF/ABS as a pellet, a single freely extruded strand, a regularly deposited single bead, and a single bead manufactured with a roller during the printing process using a high-resolution 3D micro-computed tomography (µCT) system. Micro voids were shown to exist within the microstructure of the SCF/ABS pellet and tended to become more prevalent in a single freely extruded strand which showed the highest void volume fraction among all the samples studied. Results also showed that deposition on the print bed reduced the void volume fraction and applying a roller during the printing process caused a further reduction in the void volume fraction. This study also reports the void’s shape within the microstructure in terms of sphericity which indicated that SCF/ABS single freely extruded strands had the highest mean void sphericity (voids tend to be more spherical). Moreover, this study evaluated the effect of printing process parameters, including nozzle temperature, extrusion speed and nozzle height above the printing table on the void volume fraction and sphericity within the microstructure of regularly deposited single beads. 

   more » « less
4. Modelling the strength and stiffness behavior of coarse-grained soils using 3D printed soil analogs

   Alejandro Martinez and Sharif Ahmed (September 2022, 10th International Conference on Physical Modelling in Geotechnics)

   Inherent particle properties such as size, shape, gradation, surface roughness and mineralogy govern the mechanical behavior of coarse-grained soils. Obtaining a detailed understanding of soil behavior requires parametrization of the individual effects of these properties; however, isolating these effects is a challenge in experimental studies. The advances in 3D printing technology provide the ability to generate artificial sand- and gravel-sized particles with independent control over their size, shape, and gradation. This paper summarizes the strength and stiffness behavior of specimens composed of 3D printed (3DP) particles. Specifically, results of triaxial compression and bender element tests on 3DP sands are provided and compared to corresponding results on the natural sands. The 3DP sands show characteristic behaviors of natural sands, such as dependence on effective stress and stress-dilatancy. However, the 3DP soils are more compressible due to the smaller stiffness of the constituent polymeric material. The results show a decrease in critical state friction angle (φ′cs) and an increase in shear wave velocity (Vs) as the particle roundness and sphericity are increased, in agreement with published trends for natural soils. The agreement in trends highlights the potential for investigations using 3DP soils to extend the understanding of soil behavior. 

   more » « less
5. Cyclic Direct Simple Shear tests - Effect of relative density

   https://doi.org/10.17603/ds2-z7zb-bq89  

   Lbibb, Sarra; Manzari, Majid (October 2022, Designsafe-CI)

   The stress-strain behavior and liquefaction strength of Ottawa F65 sand was investigated through an extensive series of cyclic direct simple shear (CDSS) tests. The study quantified the effects of relative density on the cyclic strength of Ottawa F65 sand. The database of CDSS tests was used to develop an Artificial Neural Networks model to predict Ottawa F65 cyclic strength. 

   more » « less