• 한국철도학회:학술대회논문집
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• 한국철도학회 1998년도 추계학술대회 논문집
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• pp.497-504
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• 1998

The manufacturing processes of the head hardened rails and the principles of the heat treatment for carbon steels are introduced in this paper, To get the good wear resistance of the rail, many kinds of microstructure had been developed for the rail head hardening. One of these is the tempered martensitic structure, which is very hard but brittle because of Quenching-Tempering Process. Another is the fine pearlitic structure by Slack Quenching. Now Banitic structure steels are emerging as a potential new material to replace eutectoid pearlitic steels for rail. The main reason of this change is due to the limitaion of pearlitic microstructure with regard to mechanical properties and wear resistances of railway rails.

• Computers and Concrete
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• 제23권3호
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• pp.217-233
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• 2019

This paper describes the numerical modelling of an interior slab-column connection to investigate the punching shear resistance of reinforced concrete (RC) slabs under fire conditions. Parameters of the study were the fire direction, flexural reinforcement ratio, load levels, shear reinforcement and compressive strength of concrete. Moreover, the efficiency of the insulating material, gypsum, in reducing the heat transferred to the slab was assessed. Validation studies were conducted comparing the simulation results to experiments from the literature and common codes of practice. Temperature dependencies of both concrete and reinforcing steel bars were considered in thermo-mechanical analyses. Results showed that there is a slight difference in temperature endurance of various models with respect to concrete with different compressive strengths. It was also concluded that compared to a slab without gypsum, 10-mm and 20-mm thick gypsum reduce the maximum heat transferred to the slab by 45.8% and 70%, respectively. Finally, it was observed that increasing the flexural reinforcement ratio changes the failure mode from flexural punching to brittle punching in most cases.

• Coupled systems mechanics
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• 제7권6호
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• pp.669-690
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• 2018

This paper deals with numerical modeling of dynamic failure phenomena in rate-sensitive brittle and/or ductile materials. To this end, a two-dimensional continuum viscodamage-embedded discontinuity model, which is based on our previous work (see Do et al. 2017), is developed. More specifically, the pre-peak nonlinear and rate-sensitive hardening response of the material behavior, representing the fracture-process zone creation, is described by a rate-dependent continuum damage model. Meanwhile, an embedded displacement discontinuity model is used to formulate the post-peak response, involving the macro-crack creation accompanied by exponential softening. The numerical implementation in the context of the finite element method exploiting the second-order mid-point scheme is discussed in detail. In order to show the performance of the model several numerical examples are included.

• Computers and Concrete
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• 제23권1호
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• pp.25-36
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• 2019

In this paper, an algorithm is presented to simulate numerically the reinforced concrete (RC) columns having any geometric form of section, loaded eccentrically along one or two axes. To apply the algorithm, the columns are discretized into two macro-elements (MEs) globally and the critical sections of columns are discretized into fixed rectangular finite elements locally. A proposed triple simultaneous dichotomy convergence method is applied to find the equilibrium state in the critical section of the column considering the three strains at three corners of the critical section as the main characteristic variables. Based on the proposed algorithm a computer program has been developed for simulation of the nonlinear behavior of the eccentrically-loaded columns. A good agreement has been witnessed between the results obtained applying the proposed algorithm and the experimental test results. The simulated results indicate that the ultimate strength and stiffness of the RC columns increase with the increase in axial force value, but large axial loads reduce the ductility of the column, make it brittle, impose great loss of material, and cause early failure.

• 대한금속재료학회지
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• 제47권11호
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• pp.759-772
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• 2009

Amorphous alloys, in addition to being promising materials for a variety of practical applications, provide an excellent test bed for evaluating our understanding of the underlying physics on deformation in amorphous solids. Like many amorphous materials, amorphous alloys can exhibit either homogeneous or inhomogeneous deformation depending on the stress level. The mode of deformation has a strong influence on whether the material behavior is classified as ductile or brittle. It was observed that the characteristics of these deformations are largely dependent on the atomic-scale structures of the alloys and determine the amount of the plastic deformation prior to failure. In this study, the structural features that control the homogeneous deformation of amorphous alloys are outlined on the basis on experiments and molecular dynamics simulations.

• 열처리공학회지
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• 제35권5호
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• pp.239-245
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• 2022

The purpose of this study is to evaluate the degree of microstructural change of materials using ultrasonic nonlinear parameters. For microstructure change, isothermal heat-treated ferritic 2.25Cr steel and low-cycle fatigue-damage copper alloy were prepared. The variation in ultrasonic nonlinearity was analyzed and evaluated through changes in hardness, ductile-brittle transition temperature, electron microscopy, and X-ray diffraction tests. Ultrasonic nonlinearity of 2.25Cr steel increased rapidly during the first 1,000 hours of deterioration and then gradually increased thereafter. The variation in non-linear parameters was shown to be coarsening of carbides and an increase in the volume fraction of stable M6C carbides during heat treatment. Due to the low-cycle fatigue deformation of oxygen-free copper, the dislocation that causes lattice deformation developed in the material, distorting the propagating ultrasonic waves, and causing an increase in the ultrasonic nonlinear parameters.

• Coupled systems mechanics
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• 제10권6호
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• pp.475-490
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• 2021

With glass becoming a structural material there is a whole new approach for loading and ensuring the safety of construction. Due to its brittle nature, it is necessary to predict all possible problems so that structural integrity would not be endangered. In this paper, different approaches to modelling the glass elements are presented with references to the advantages, disadvantages, and application of each of them. The intention is clear, there is a need to improve and simplify the design guidelines. Given the increasing use of glass in construction it is not practical to produce experimental tests each time when the verification is needed. Today, architecture is bringing us different types of structures and every project presents a new challenge for engineers. A practical and simple approach is crucial for progress and efficiency. In this paper, different approaches to modelling glass are presented with an emphasis on soft body impact.

• Advances in concrete construction
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• 제13권1호
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• pp.1-10
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• 2022

Concrete is a brittle material and weak in tension. Traditionally, web reinforcement in the form of vertical stirrups is used in reinforced concrete (RC) beams to take care of principal stresses that may cause failure when they are subjected to shear stresses. In recent decades, the potential of various types of fibers for improving post-cracking behavior of RC beams and replacing stirrups completely or partially have been studied. It has been shown that the use of steel fibers randomly dispersed and oriented in concrete has a significant potential for enhancing mechanical properties of RC beams. However, the studies on deep steel fiber reinforced concrete (SFRC) beams are limited when compared to those focusing on slender beams. An experimental program consisting of three RC and nine SFRC deep beams without stirrups were conducted in this study. Besides, various models developed for predicting the ultimate shear strength and diagonal cracking strength of SFRC deep beams without stirrups were applied to experimental data obtained from the literature and this study.

• Structural Engineering and Mechanics
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• 제88권2호
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• pp.189-200
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• 2023

Silicate glass is usually a brittle and plate-like material, and it is difficult to measure the elastic modulus by the traditional method. This paper develops a test method for the glass elastic modulus based on the fundamental frequency of the cantilever beam with an elastic support and a free end. The method installs the beam-type specimen on a semi-rigid support to form an elastic support-free end beam. The analytic solution of the stiffness coefficients of the elastic support is developed by the fundamental frequency of the two specimens with known elastic modulus. Then, the glass elastic modulus is measured by the fundamental frequency of the specimens. The method significantly improves the measurement accuracy and is suitable for the elastic modulus with the beam-type specimen whether the glass is homogeneous or not. Several tests on the elastic modulus measurement are conducted to demonstrate the reliability and validity of the test method.

• 한국지진공학회논문집
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• 제10권5호
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• pp.85-97
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• 2006

성능보장설계는 교각이 완전한 소성회전성능을 발휘할 때까지 다른 구조요소들과 교각 자체가 취성파괴 되지 않도록 설계하여 교량 전체 시스템의 연성파괴를 보장하기 위한 것으로서, 현행 도로교설계기준에는 명시적으로 규정되어 있지 않으나 대부분의 외국 교량내진설계기준에 채택되어 있다. 성능보장설계에서는 철근콘크리트 교각의 휨 초과강도를 구하고 이를 변환한 전단력을 교각, 기초, 말뚝에 작용하는 횡하중 설계전단력으로 결정하여 교각의 전단설계, 기초설계, 말뚝설계를 수행하도록 규정한다. 이 때 교각의 최대 소성모멘트를 결정하는 방법은 설계기준별로 각기 다른데, 이는 각 국의 재료 시공환경이 다르기 때문이다. 본 연구에서는 국내에서 사용하는 철근의 인장강도 측정치 3,407개와 콘크리트 압축강도 측정치 5,405개의 분석을 통하여 재료 초과강도계수를 제안하였고, 이를 적용하여 휨 초과강도를 결정하는 방법을 제시하였으며, 1,500개의 교각단면에 대한 모멘트-곡률 해석을 수행한 후 통계분석을 통하여 우리나라 실정에 적합한 초과강도계수를 제안하였다.