Micromechanical modeling of fiber reinforced pervious concrete composites

Pervious concrete is widely used in today’s construction industry, e.g.. parking lots, airport runways, etc. However, the durability and strength of the porous concrete remains a challenge, as the binding material proportion is low and the use of fine aggregates is nearly 0. Increasing the compressive load, the failure appears first in the weak concrete zone induced by the random distribution of voids. The process continues until the failure of the whole specimen occurs. In this study, the influence of random distribution of voids and void percentage on the strength and permeability of earlier concrete specimen is studied. A finite element model is generated by using MATLAB & ANSYS with a subroutine written in ANSYS Parametric Design Language. Load-deflection plots are generated and the obtained results including stiffness, strength and permeability are compared with the results from the experiments conducted following ASTM standards. A numerical fiber reinforced concrete specimen is also generated and the stiffness of the specimen was calculated and compared with the Kerner model. All the results numerically obtained are around or \u3e90% accuracy of the experiment derived values, which validates the suggested micromechanical model of earlier concrete composite is a viable approach for predicting behavior of earlier concrete composites and could guide its future design for any specific functions

Impact Mechanics and High-Energy Absorbing Materials: Review

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models. and computational methods (finite-element, finite-difference, and mesh-free methods. used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys. are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures

Possibility of Bridge Inspection through Drive-By Vehicles

Based on virtual simulations of vehicle–bridge interactions, the possibility of detecting stiffness reduction damages in bridges through vehicle responses was tested in two dimensional (2D) and three dimensional (3D) settings. Short-Time Fourier Transformation (STFT) was used to process vehicles’ acceleration data obtained through the 2D and 3D virtual simulations. The energy band variation of the vehicle acceleration time history was found strongly related to damage parameters. More importantly, the vehicle’s initial entering conditions are critical in obtaining correct vehicle responses through the vehicle bridge interaction models. The offset distance needed before executing the vehicle–bridge interaction (VBI) modeling was obtained through different road profile roughness levels. Through the above breakthroughs in VBI modeling, the presented study provides a new and integrated method for drive-by bridge inspection

Exploration of Carbon Dioxide Curing of Low Reactive Alkali-Activated Fly Ash

In this paper, the effect of carbon curing procedure on low reactive fly ash alkali-activated pastes was investigated. Specimens were cured with pure carbon dioxide (CO2) gas for different curing times under 4 bar pressure. Chemical and physical characteristics of the geopolymer pastes were obtained from mass monitoring, titration test, XRD, FTIR and TGA-DTG analyses. Regarding the test results, after three days of CO2 curing, the highest CO2uptake was obtained at 4.8 wt% of fly ash precursor, with carbon sequestration efficiency at 22.6%. The ratio of carbon dioxide absorbed as efflorescence to the total absorbed CO2 was measured. The results show that at early age, almost 50% of carbonated products appeared as efflorescence; however, by increasing the curing time, and after 3 days of curing, about 80% of carbon dioxide was stored in the matrix. It was found that, in all cases, carbonation curing was detrimental to the geopolymerization process due to a high amount of efflorescence and led to a reduction in the compressive strength. At 24 h and 3 days, the specimens showed a lower reduction in compressive strength in comparison to CO2 samples cured at 3 h, 6 h and 12 h. Regarding the XRD results, calcite was detected in the 24 h and 3 days specimens, which contributes to lower pore sizes due to a higher molar volume and production of silica gel that might participate in the polymerization processes and results in densified microstructures

Higher-order impact modeling of sandwich structures with flexible core

In this study, a higher-order impact model is presented to simulate the response of a soft-core sandwich beam subjected to a foreign object impact. A free vibration problem of sandwich beams is first solved, and the results are validated by comparing with numerical finite element modeling results of ABAQUS and the solution by Frostig and Baruch [Frostig, Y., Baruch, M., 1994. Free vibration of sandwich beams with a transversely flexible core: a high order approach. Journal of Sound and Vibration 176(2), 195–208]. Then a foreign object impact process is incorporated in the higher-order model, and the contact force and deflection history as well as the propagation of transverse normal, shear, and axial stresses during the impact are analyzed and discussed. The validity of the model in the impact response predictions is demonstrated by comparing with finite element solutions of LS-DYNA. The calculated stresses caused by a foreign object impact are then used to assess failure locations, failure time, and failure modes in sandwich beams, which are shown to compare well with the available experimental results. The effects of impact mass, initial velocity, core stiffness, and core height on the impact stresses generated in the beams are discussed. The influences of impact mass and initial velocity on the contact force history are close to those by the linearized impact solution, but the proposed higher-order impact model captures the non-linear impact process and different generated stresses. Compared to the fully backed sandwich case, the core height shows a great influence over the impact process of a simply supported sandwich system, in which the global behavior of the sandwich is dominant; while the core stiffness shows minor effect over the impact process. The higher-order impact model of sandwich beams developed in the study provides accurate predictions of the generated stresses and impact process and can be used effectively in design analysis of anti-impact structures made of sandwich materials

An Advanced Edge-Detection Method for Noncontact Structural Displacement Monitoring

A non-contact vision sensor system for monitoring structural displacements with advanced Zernike subpixel edge detection technique is suggested in this paper. Edge detection can detect features of objects effectively without using templates. Subpixel techniques provide more accurate and cost-effective results when compared to integer pixel methods. Built on these two techniques, a new version sensor method was developed to detect the vibrations of structures in this study. Satisfactory agreements were found between the displacements measured by the vision sensor system and those recorded by the Multipurpose Testing System (MTS). A field test was then carried out on a street sign using the proposed vision system. Satisfactory results were obtained using the new version of the sensor system at many points simultaneously without any manually marked targets. Moreover, the system was able to provide natural frequencies and mode shapes of the target instantaneously, which could be used to accurately locate damage