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Various construction activities (such as piling) often generate high-intensity ground vibrations that adversely affect the surrounding environment. A common way of assessing vibration impact is to conduct on-site ground vibration monitoring at several selected locations. However, as vibration sources are often not pinpointed in the construction process, this approach cannot predict the vibration intensities at locations other than those monitored points. Therefore, the localization of vibration sources (e.g., vibratory sheet pile driving location) is crucial to quantify the corresponding vibration intensities in a broad area. This paper investigates a time-based source localization method based on wave propagation characteristics derived via three-dimensional finite element modeling of vibratory sheet pile driving in an infinite half-space soil domain. Satisfactory accuracy in the localization of the vibratory driving sources was achieved in all investigated numerical examples. Field validation tests were also conducted on a construction site with ongoing vibratory sheet pile driving work. A site-specific empirical formula was adopted to model the attenuation of measured vibration intensities with the increasing distance from the localized vibration source. As such, the combined utilization of the estimated vibration source location and the adopted empirical formula can achieve vibration intensity assessment in a broad surrounding area rather than being confined to a few monitored points. [ABSTRACT FROM AUTHOR]

Various construction activities (such as piling) often generate high-intensity ground vibrations that adversely affect the surrounding environment. A common way of assessing vibration impact is to conduct on-site ground vibration monitoring at several selected locations. However, as vibration sources are often not pinpointed in the construction process, this approach cannot predict the vibration intensities at locations other than those monitored points. Therefore, the localization of vibration sources (e.g., vibratory sheet pile driving location) is crucial to quantify the corresponding vibration intensities in a broad area. This paper investigates a time-based source localization method based on wave propagation characteristics derived via three-dimensional finite element modeling of vibratory sheet pile driving in an infinite half-space soil domain. Satisfactory accuracy in the localization of the vibratory driving sources was achieved in all investigated numerical examples. Field validation tests were also conducted on a construction site with ongoing vibratory sheet pile driving work. A site-specific empirical formula was adopted to model the attenuation of measured vibration intensities with the increasing distance from the localized vibration source. As such, the combined utilization of the estimated vibration source location and the adopted empirical formula can achieve vibration intensity assessment in a broad surrounding area rather than being confined to a few monitored points.

This article presents numerical and experimental study on the postfire behavior of concentrically loaded slurry-infiltrated fibrous concrete (SIFCON) columns after being exposed to flame from four sides for 2 hours while evaluating the effect of some testing parameters including column section type (solid or hollow), hollow section ratios of 25 and 50%, and the shape of the column section (square or circular). The first part is an experimental work to ensure that the model developed is adequate while the second part is a three-dimensional (3-D) finite element modeling of the SIFCON columns with the program ABAQUS using a sequentially coupled thermal displacement analysis. The test results indicated that SIFCON columns lost approximately 47 to 55% of their bearing capacity after fire exposure at 900°C and with 2 hours fire duration. Increasing the hollow ratio of the cross section is shown to decrease the postfire behavior of SIFCON columns. Moreover, the SIFCON columns with circular cross section exhibit higher values of ultimate load-carrying capacity than the square SIFCON columns with the equivalent cross-sectional area prior to and later after fire exposure. [ABSTRACT FROM AUTHOR]

Bone aging involves structural and molecular modifications, especially at the level of type I tropocollagen. This macromolecule shows two main age-related alterations, which are the decrease of both molecular diameter (due to the loss of hydration) and number of hydrogen bonds. In this work, it is proposed to investigate the influence of these two parameters (molecular diameter and number of hydrogen bonds) on the mechanical behavior of tropocollagen using finite element method. To this end, a novel three-dimensional finite element model of collagen molecule accounting for hydrogen bonds was developed. Then, a numerical design of experiments for the diameter of tropocollagen and variations in the number of hydrogen bonds has been established. The mechanical properties ("load-strain" curve and apparent Young's modulus) of the collagen molecule were obtained by employing the proposed model to uniaxial tensile tests. The parametric study demonstrates that the mechanical properties of tropocollagen are slightly affected by the rate of hydration but considerably affected by variation of the number of hydrogen bonds. Finally, a fitted analytical function was deduced from the above results showing effects of the two parameters (hydration rate and hydrogen bonds) on the apparent Young's modulus of tropocollagen. This study could be useful to understand the influence of structural age modifications of tropocollagen on the macroscopic mechanical properties of bone. [ABSTRACT FROM AUTHOR]

Highlights • A novel variant of the Newton-Raphson method within a time integration scheme tailored for nonlinear 3D mesoscale mechanical model of CNT nanocomposite. • An optimized numerical solution scheme suitable for damping material optimizations via Differential Evolution, usually requiring thousands of cyclic analyses. • Efficiency, while retaining numerical accuracy, obtained by a unique iteration (elastic stiness) matrix. • Both serial and parallel computations numerically tested to assess performance. • Performance further improved by a caching mechanism coupled with parallel execution of numerical simulations. Abstract The accuracy and efficiency of a numerical strategy for sequential nonlinear cyclic analyses of carbon nanotube nanocomposites are investigated. The computational approach resorts to a nonlinear 3D finite element implementation that seeks to solve the cyclic hysteretic response of the nanocomposite. A variant of the Newton-Raphson method within a time integration scheme is proposed whereby the elastic tangent matrix is chosen as iteration matrix without paying the price of its iterative update. This is especially rewarding in the context of the employed mechanical model which exhibits hysteresis manifested through a discontinuous change in the stiffness at the reversal points where the loading direction is reversed. Key implementation aspects – such as the integration of the nonlinear 3D equations of motion, the numerical accuracy/efficiency as a function of the time step or the mesh size – are discussed. In particular, efficiency is regarded as performing fast computations especially when the number of cyclic analyses becomes large. By making use of laptop CPU cores, a good speed of computations is achieved not only through parallelization but also employing a caching procedure for the iteration matrix. [ABSTRACT FROM AUTHOR]

This contribution deals with a computational investigation highlighting the effects of cutting speed and depth of cut on chip morphology and surface finish for down-cut milling case. The global aim concerns the comprehension of multiphysical phenomena accompanying chip formation in rough, semifinish, and finish cutting operations, exploiting a three-dimensional finite element model. Numerical work has been performed in two phases. In the first phase, a three-dimensional model for rough cut operation has been validated with the experimental results, including chip morphology and cutting force evolution for an aerospace grade aluminum alloy A2024-T351. In the second phase, the model has been extended to semifinish and finish three-dimensional cutting operations. The numerical findings show that as depth of cut decreases (toward finish cutting), spatial displacement of workpiece nodes along the depth of cut increases. This represents an increase/extension in the percentage of volume undergoing shear deformation, resulting in higher dissipation of inelastic energy, hence contributing to size effect in finish cutting operation. The results also depict that material strain rate hardening enhances the material strength at higher cutting speeds. These material strengthening phenomena help to generate a smooth continuous chip morphology and better surface texture in high-speed finishing operations. The study highlights the significance of three-dimensional numerical modeling to better understand the chip formation process in semifinish and finish machining operations, regardless of the immense effort in computational time. [ABSTRACT FROM AUTHOR]

Abstract: A study is made of longitudinal “channel” cracking in tooth enamel from axial compressive loading. The cracks simulate those generated in the molar and premolar teeth of humans and animals by natural tooth function. Contact loading tests are made on extracted human molars with hard and soft indenting plates to determine the evolution of such cracks with increasing load. Fracture is largely stable, with initial slow growth followed by acceleration as the cracks approach completion around an enamel side wall. A simple power law relation expresses the critical load for full fracture in terms of characteristic tooth dimensions—base radius and enamel thickness—as well as enamel toughness. Extended three-dimensional finite element modeling with provision for growth of embedded cracks is used to validate this relation. The cracks leave “fingerprints” that offer valuable clues to dietary habits, and provide a basis for a priori prediction of bite forces for different animals from measured tooth dimensions. [Copyright &y& Elsevier]

Bone aging involves structural and molecular modifications, especially at the level of type I tropocollagen. This macromolecule shows two main age-related alterations, which are the decrease of both molecular diameter (due to the loss of hydration) and number of hydrogen bonds. In this work, it is proposed to investigate the influence of these two parameters (molecular diameter and number of hydrogen bonds) on the mechanical behavior of tropocollagen using finite element method. To this end, a novel three-dimensional finite element model of collagen molecule accounting for hydrogen bonds was developed. Then, a numerical design of experiments for the diameter of tropocollagen and variations in the number of hydrogen bonds has been established. The mechanical properties ("load-strain" curve and apparent Young's modulus) of the collagen molecule were obtained by employing the proposed model to uniaxial tensile tests. The parametric study demonstrates that the mechanical properties of tropocollagen are slightly affected by the rate of hydration but considerably affected by variation of the number of hydrogen bonds. Finally, a fitted analytical function was deduced from the above results showing effects of the two parameters (hydration rate and hydrogen bonds) on the apparent Young's modulus of tropocollagen. This study could be useful to understand the influence of structural age modifications of tropocollagen on the macroscopic mechanical properties of bone.