• Advances in nano research
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• v.14 no.4
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• pp.363-373
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• 2023

A novel type of steel fiber with a rounded-end shape is presented to improve the bonding behavior of fibers with Carbon Nanotubes (CNT)-reinforced Ultra-High Performance Concrete (UHPC) matrix. For this purpose, by performing a parametric study and using the nonlinear finite element method, the impact of geometric characteristics of the fiber end on its bonding behavior with UHPC has been studied. The cohesive zone model investigates the interface between the fibers and the cement matrix. The mechanical properties of the cohesive zone model are determined by calibrating the finite element results and the experimental fiber pull-out test. Also, the results are evaluated with the straight steel fibers outcomes. Using the novel presented fibers, the bond strength has significantly improved compared to the straight steel fibers. The new proposed fibers increase bond strength by 1.1 times for the same diameter of fibers. By creating fillet at the contact area between the rounded end and the fiber, bond strength is significantly improved, the maximum fiber capacity is reachable, and the pull-out occurs in the form of fracture and tearing of the fibers, which is the most desirable bonding mode for fibers. This also improves the energy absorbed by the fibers and is 4.4 times more than the corresponding straight fibers.

• Composites Research
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• v.36 no.5
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• pp.303-309
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• 2023

In this paper, a Progressive Damage and Failure Analysis (PDFA) modeling method was developed using ABAQUS/EXPLICIT to predict in-plane damage and delamination for Open-Hole Compression (OHC) testing. The proposed PDFA model was constructed based on Hashin criteria and cohesive behavior. The strength and stiffness of OHC specimens with three types of stacking sequences [(45/-45/0₂)₃]_s , [(45/0/-45/90)₃]_s and [45/-45/0/45/-45/90/(45/-45)₂]_s were compared to comprehensively evaluate the validity of the Finite Element(FE) model of PDFA. The strength and stiffness of the OHC specimens were predicted relatively well, with less than a percentage error 10.0 %. For the numerical simulation case for each layup, the damage initiation/evolution of OHC specimens were evaluated for delamination and tension/compression matrix damage before and after failure.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4D
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• pp.387-393
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• 2010

This paper studies static crack growth of asphalt pavement using the extended finite element method (XFEM). To consider nonlinear characteristics of asphalt concrete, a viscoelastic constitutive equation using the Maxwell chain is used. And a linear cohesive crack model is used to regularize the crack. Instead of constructing the viscoelastic constitutive law from the Prony approximation of compliance and retardation time measured experimentally, we use a smooth log-power function which optimally fits experimental data and is infinitely differentiable. The partial moduli of the Maxwell chain from the log-power function make analysis easy because they change more smoothly in a more stable way than the ordinary method such as the least square method. Using the developed method, we can simulates the static crack growth test results satisfactorily.

• Steel and Composite Structures
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• v.43 no.5
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• pp.565-579
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• 2022

This study investigated the yielding capacity and performance of seismic dampers constructed with steel ring plates using numerical and analytical approaches. This study aims to provide an analytical relationship for estimating the yielding capacity and initial stiffness of steel ring dampers. Using plastic analysis and considering the mechanism of plastic hinge formation, a relation has been obtained for estimating the yielding capacity of steel ring dampers. Extensive parametric studies have been carried out using a nonlinear finite element method to examine the accuracy of the obtained analytical relationships. The parametric studies include investigating the influence of the length, thickness, and diameter of the ring of steel ring dampers. To this end, comprehensive verification studies are performed by comparing the numerical predictions with several reported experimental results to demonstrate the numerical method's reliability and accuracy. Comparison is made between the hysteresis curves, and failure modes predicted numerically or obtained/observed experimentally. Good agreement is observed between the numerical simulations and the analytical predictions for the yielding force and initial stiffness. The difference between the numerical models' ultimate tensile and compressive capacities was observed that average of about 22%, which stems from the performance of the ring-dampers in the tensile and compression zones. The results show that the steel ring-dampers are exhibited high energy dissipation capacity and ductility. The ductility parameters for steel ring-damper between values were 7.5 to 4.1.

• Structural Engineering and Mechanics
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• v.33 no.4
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• pp.529-537
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• 2009

A key parameter in the design of a laterally loaded pile is the determination of its performance level. Performance level of a pile is usually expressed as the maximum head deflection and bending moment. In general, uncertainties in the performance of a pile originates from many factors such as inherent variability of soil properties, inadequate soil exploration programs, errors taking place in the determination of soil parameters, limited calculation models as well as uncertainties in loads. This makes it difficult for practicing engineers to decide for the reliability of laterally loaded piles both in cohesive and cohesionless soils. In this paper, limit state functions and consequent performance functions are obtained for single concrete piles to predict the maximum bending moment, a widely accepted design criterion along with the permissible pile head displacement. Analyses were made utilizing three dimensional finite element method and soil-structure-interaction (SSI) effects were accounted for.

• Composites Research
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• v.34 no.6
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• pp.337-344
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• 2021

In this study, the progressive failure behavior of the composite fan blade dovetail element under tensile loading is numerically investigated through finite element(FE) simulation. The accuracy of prediction by FE simulation is verified through tensile testing. The dovetail element is one of the joints for coupling the fan blade with the disk in a turbofan engine. The dovetail element is usually made of a metal material such as titanium, but the application of composite material is being studied for weight reduction reasons. However, manufacturing defects such as drop-off ply and resin pocket inevitably occur in realizing complex shapes of the fan blade made by composite materials. To investigate the effect of these manufacturing defects on the composite fan blade dovetail element, we performed numerical simulation with FE model to compare the prediction of the FE model and the tensile test results. At this time, the cohesive zone model is used to simulate the delamination behavior. Finally, we found that FE simulation results agree with test results when considering thermal residual stress and through-thickness compression enhancement effect.

• Land and Housing Review
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• v.11 no.2
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• pp.95-104
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• 2020

This study aims to explore a purely mechanistic pavement analysis approach where viscoelasticity and fracture of asphalt mixtures are considered to accurately predict deformation and damage behavior of flexible pavements. To do so, the viscoelastic and fracture properties of designated pavement materials are obtained through experiments and a fully mechanistic damage analysis is carried out using a finite element method (FEM). While modeling crack development can be done in various ways, this study uses the cohesive zone approach, which is a well-known fracture mechanics approach to efficiently model crack initiation and propagation. Different pavement configurations and traffic loads are considered based on three main functional classes of roads suggested by FHWA i.e., arterial, collector and local. For each road type, three different material combinations for asphalt concrete (AC) and base layers are considered to study damage behavior of pavement. A concept of the approach is presented and a case study where three different material combinations for AC and base layers are considered is exemplified to investigate progressive damage behavior of pavements when mixture properties and layer configurations were altered. Overall, it can be concluded that mechanistic pavement modeling attempted in this study could differentiate the performance of pavement sections due to varying design inputs. The promising results, although limited yet to be considered a fully practical method, infer that a few mixture tests can be integrated with the finite element modeling of the mixture tests and subsequent structural modeling of pavements to better design mixtures and pavements in a purely mechanistic manner.

• Journal of Korean Society of Disaster and Security
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• v.12 no.2
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• pp.57-63
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• 2019

The road sinks in the sewer line or subway section are affected by the ground characteristics. Therefore, it is necessary to accurately identify the relationship between the soil properties and the ground motion in the area where cavities occurred in order to establish a countermeasure against the road sink. In this paper, simulation was performed by using EDEM program, which is one of the Discrete Element Method programs, for sandy soil and clayey soil, which are most common in alluvial deposits, with different locations and sizes of cavities in the underground. As a result, it was found that the sink size occurred more in the sandy soil than in the cohesive soil. Deeper and larger cavity is more likely to occur the road sink In the sand soil model while road sink in the clay model is easy to occur when the cavity is more shallower.

• Journal of Drive and Control
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• v.20 no.4
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• pp.71-79
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• 2023

In the field of agricultural machinery, various on-field tests are conducted to measure design load for optimal design of agricultural equipment. However, field test procedures are costly and time-consuming, and there are many constraints on field soil conditions due to weather, so research on utilizing simulation to overcome these shortcomings is needed. Therefore, this study aimed to model agricultural soils using discrete element method (DEM) software. To simulate draft force, predictions are made according to travel speed and compared to field test results to validate the prediction accuracy. The measured soil properties are used for DEM modeling. In this study, the soil property measurement procedure was designed to measure the physical and mechanical properties. DEM soil model calibration was performed using a virtual vane shear test instead of the repose angle test. The DEM simulation results showed that the prediction accuracy of the draft force was within 4.8% (2.16~6.71%) when compared to the draft force measured by the field test. In addition, it was confirmed that the result was up to 72.51% more accurate than those obtained through theoretical methods for predicting draft force. This study provides useful information for the DEM soil modeling process that considers the working speed from the perspective of agricultural machinery research and it is expected to be utilized in agricultural machinery design research.

• Journal of Drive and Control
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• v.21 no.3
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• pp.46-55
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• 2024

In the agricultural machinery field, load analysis is mostly done through field tests. However, field tests are time-consuming and costly. There are also limitations in test conditions due to weather conditions. To overcome these environmental limitations, research on load analysis through simulation in a virtual environment is actively being conducted. This study aimed to select the most appropriate soil particle size for modeling by analyzing the effect of soil particle size on the prediction of draft force of the implement using simulation and soil particle modeling in a virtual environment with the discrete element method (DEM) software. The accuracy was verified by simulating the draft force for the same moving speed by soil particle size. For soil particle modeling, DEM soil modeling was performed by designing soil property measurement procedure. Soil particle correction was performed with a virtual vane shear test. Average DEM simulation results showed an error of 27.39% (19.43~40.66%) compared to actual measured data. The possibility of improvement was confirmed through additional research. Results of this study provide useful information for selecting soil particle size in soil modeling using DEM from the perspective of agricultural machinery research.