• 한국안전학회지
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• 제27권3호
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• pp.15-19
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• 2012

The fatigue behavior of AM60 magnesium alloy produced by equal channel angular pressing(ECAP) process was investigated through fatigue lifetime and fatigue crack propagation rate tests. The grain structure of the material was refined from 19.2 ${\mu}m$ to 2.3 ${\mu}m$ after 6 passes of ECAP at 493 K. The yield strength(YS) and ultimate tensile strength (UTS) increase after two passes but decrease with further pressing, although the grain size becomes finer with increasing pass number. The softening effect due to texture anisotropy overwhelmed the strengthening effect due to grain refinement after 2 passes. A large enhancement in fatigue strength was achieved after two ECAP passes. The current finding suggests that two passed material is better than the multi-passed material in view of the static strength and fatigue performance.

• Steel and Composite Structures
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• 제42권1호
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• pp.49-57
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• 2022

This paper presents a study on the behavior of a bolted T-stub to square tube connection using Thread-fixed One-side Bolts (TOBs) through tests and numerical simulations. It outlines a research work of four connections with focus on the failure modes and strengths of the connection under tensile load. It was observed that the thread anchor failure caused by shear failure of hole threads controlled the final failure of the connection in the tests. Meanwhile, the out-of-plane deformation of tube wall resulted in the contact separation between hole threads and bolt threads, which in turn reduced the shear strength of hole threads. Finite element models (FEMs) allowing for the configuration details of the TOBs fixed connection are then developed and compared with the test results. Subsequently, the failure mechanism of hole threads and stress distribution of each component are analyzed based on FEM results. It was concluded that the ultimate strength of connection was not only concerned with the shear strength of hole threads, but also was influenced by the plastic out-of-plane deformation of tube wall. These studies lay a foundation for the establishment of suitable design methods of this type of connection.

• Computers and Concrete
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• 제32권1호
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• pp.1-13
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• 2023

This paper discusses a framework for predicting the flexural strength of prestressed and non-prestressed FRP reinforced T-shaped concrete beams using soft computing techniques. An analysis of 83 tests performed on T-beams of varying widths has been conducted for this purpose with different widths of compressive face, beam depth, compressive strength of concrete, area of prestressed and non-prestressed FRP bars, elasticity modulus of prestressed and non-prestressed FRP bars, and the ultimate tensile strength of prestressed and non-prestressed FRP bars. By analyzing the data using two soft computing techniques, named artificial neural networks (ANN) and gene expression programming (GEP), the fundamental parameters affecting the flexural performance of prestressed and non-prestressed FRP reinforced T-shaped beams were identified. The results showed that although the proposed ANN model outperformed the GEP model with higher values of R and lower error values, the closed-form equation of the GEP model can provide a simple way to predict the effect of input parameters on flexural strength as the output. The sensitivity analysis results revealed the most influential input parameters in ANN and GEP models are respectively the beam depth and elasticity modulus of FRP bars.

• 대한건축학회논문집:구조계
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• 제35권4호
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• pp.157-165
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• 2019

Recently, lean duplex stainless steel, STS329FLD with less nickel (reduced to 0.5~1.5%) has been developed as a substitute of austenitic stainless steel (8%~10.5% nickel in STS304) and included in Korean standards (KS). This paper investigates the block shear behavior of cold-formed duplex stainless steel (STS329FLD, nominal plate thickness of 1.5mm) fillet-welded connection with base metal fracture. Main variables are weld lengths in the longitudinal and the transverse directions of applied force ranged from 20mm to 50mm. As a result, specimens failed by typical block shear facture (the combination of gross section tensile fracture and shear fracture or shear yielding) and ultimate strength of the specimens got higher with the increase of weld length. Block shear fracture strengths predicted by current design specifications (KBC2016/AISC2016 and EC3) and existing proposed equations for welded connections by Topkaya, Oosterhof & Driver and Lee et al. were compared with test strengths. KBC2016/AISC2016 and EC3 design specifications underestimated block shear strength of STS329FLD welded connections by on average 24%, 29%, respectively and Oosterhof & Driver, Topkaya and Lee et al's equations overestimated the ultimate strength of the welded connection by the range of 3% to 44%.

• 한국재료학회지
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• 제10권11호
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• pp.770-777
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• 2000

기계적 합금화 공정으로 제조한 $1{\mu\textrm{m}}$ 이하 크기의 $Cu_6Sn_5$를 63Sn-37Pb 솔더합금에 첨가하여, $Cu_6Sn_5$ 첨가분율에 따른 미세구조와 기계적 성질을 Cu를 첨가한 솔더합금과 비교하였다. $Cu_6Sn_5$를 첨가한 솔더합금에 비해 Cu를 첨가한 솔더합금에서 첨가분율에 따른 $Cu_6Sn_5$ 함량의 증가와 크기 성장의 정도가 더욱 현저하게 발생하였다. Cu를 첨가한 솔더합금에 비해 $Cu_6Sn_5$를 첨가한 솔더합금에서 항복강도의 향상 정도는 저하하였으나, 더 높은 최대인장강도를 얻을 수 있었다. 1~9 vol%의 $Cu_6Sn_5$를 첨가함에 따란 63Sn-37Pb 솔더합금의 항복강도가 23 MPa에서 36MPa 정도로 증가하였으며, 1~9vol%의 Cu 첨가시에는 항복강도가 40 MPa로 향상되었다. 각기 5 vol%의 $Cu_6Sn_5$와 Cu를 첨가함에 따라 63Sn-37Pb 솔더합금의 인장강도가 34.7 MPa에서 45.3MPa and to 43.1 MPa로 향상되었다.

• 한국산학기술학회논문지
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• 제17권2호
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• pp.220-226
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• 2016

MS(Multi-Strand) 케이블은 여러 개의 강연선으로 이루어져있어, 케이블 시공시 각 강연선을 차례대로 개별적으로 긴장한다. 그리고 마지막 강연선이 정착되었을 때, 모든 강연선에 동일한 장력이 도입되어야하며, 이것이 MS 균등긴장의 핵심기술이다. 본 연구에서는 엑스트라도즈(Extradosed)교 및 사장교의 사재케이블(Stay Cable)에 적용되는 2,200MPa 초고강도 강연선들을 균등하게 긴장, 제어할 수 있는 MS 케이블 균등긴장시스템을 개발하였다. 개발한 균등긴장시스템은 전기저항식 로드셀, 유압잭, 유압펌프 그리고 통합제어기로 구성되며, Master 강연선과 Slave 강연선의 장력변화를 실시간으로 예측하며 제어하는 알고리즘을 탑재하였다. 개발시스템의 기능과 성능을 검증하기 위해 균등긴장 실험을 수행한 후, 광양 태인2교(ED교)의 사재케이블 가설긴장에 성공적으로 적용하였다.

• 한국주조공학회지
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• 제35권6호
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• pp.155-162
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• 2015

The effect of Sr addition on mechanical and bio-corrosion properties of as-cast Mg-3wt.%Zn-0.5wt.%Ca-xwt.%Sr (x = 0.3, 0.6, 0.9) alloys were examined for application as biodegradable implant material. The microstructure, mechanical properties and corrosion resistance of the as-cast Mg-Zn-Ca-Sr alloys were characterized by using optical microscopy, scanning electron microscopy, tensile testing and electrochemical measurement in Hank's solution. The as-cast alloys contained ${\alpha}$-Mg and eutectic $Ca_2Mg_6Zn_3$ phases, while the alloys contained ${\alpha}$-Mg, $Ca_2Mg_6Zn_3$ and Mg-Zn-Ca-Sr intermetallic compound when the Sr addition was more than 0.3 wt.%. The yield strength, ultimate tensile strength and elongation increased with the increasing of Sr content up to 0.6 wt.% but decreased in the 0.9 wt.% Sr-added alloy, whereas the corrosion resistance of 0.3 wt.% Sr-added alloy was superior to other alloys. It was thought that profuse Mg-Zn-Ca-Sr intermetallic compound deteriorated both the mechanical properties and corrosion resistance of the as-cast alloy.

• Nuclear Engineering and Technology
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• 제48권2호
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• pp.518-524
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• 2016

The thermal aging effects on mechanical properties and microstructures in China low-activation martensitic steel have been tested by aging at $550^{\circ}C$ for 2,000 hours, 4,000 hours, and 10,000 hours. The microstructure was analyzed by scanning and transmission electron microscopy. The results showed that the grain size and martensitic lath increased by about $4{\mu}m$ and $0.3{\mu}m$, respectively, after thermal exposure at $550^{\circ}C$ for 10,000 hours. MX type particles such as TaC precipitated on the matrix and Laves-phase was found on the martensitic lath boundary and grain boundary on aged specimens. The mechanical properties were investigated with tensile and Charpy impact tests. Tensile properties were not seriously affected by aging. Neither yield strength nor ultimate tensile strength changed significantly. However, the ductile-brittle transition temperature of China low-activation martensitic steel increased by $46^{\circ}C$ after aging for 10,000 hours due to precipitation and grain coarsening.

• Smart Structures and Systems
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• 제29권2호
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• pp.267-278
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• 2022

Pre-stressed concrete circular spun piles are widely used in various infrastructure projects around the world and offer an economical deep foundation system with consistent and superior quality compared to cast in-situ and other concrete piles. Conventional methods for measuring the lateral response of piles have been limited to conventional instrumentation, such as electrical based gauges and pressure transducers. The problem with existing technology is that the sensors are not able to assist in recording the lateral stiffness changes of the pile which varies along the length depending on the distribution of the flexural moments and appearance of tensile cracks. This paper describes a full-scale bending test of a 1-m diameter spun pile of 30 m long and instrumented using advanced fibre optic distributed sensor, known as Brillouin Optical Time Domain Analysis (BOTDA). Optical fibre sensors were embedded inside the concrete during the manufacturing stage and attached on the concrete surface in order to measure the pile's full-length flexural behaviour under the prescribed serviceability and ultimate limit state. The relationship between moments-deflections and bending moments-curvatures are examined with respect to the lateral forces. Tensile cracks were measured and compared with the peak strains observed from BOTDA data which corroborated very well. By analysing the moment-curvature response of the pile, the structure can be represented by two bending stiffness parameters, namely the pre-yield (EI) and post-yield (EI_cr), where the cracks reduce the stiffness property by 89%. The pile deflection profile can be attained from optical fibre data through closed-form solutions, which generally matched with the displacements recorded by Linear Voltage Displacement Transducers (LVDTs).

• 한국강구조학회 논문집
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• 제26권3호
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• pp.219-229
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• 2014

원형 강관으로 보강된 GFRP 재질의 원통형 쉘구조에 대한 극한 휨 실험 및 범용 유한요소해석 프로그램인 ABAQUS를 사용한 전산해석을 수행하였다. 개인하수처리 시설의 설계 기준에서 제시된 직사각형 단면형상의 GFRP 재질의 보강링이 적용된 설계기준을 바탕으로 원형 강관 보강링에 대한 단면 재료 특성이 반영된 식을 검토하여 설계하였다. 보강링의 단면, GFRP 본체의 직경과 두께에 의한 극한 거동 특성을 분석하기 위하여 총 4개의 시험체를 설계 제작하여 집중하중 정적재하 시험을 수행하였다. 실험결과 강관 보강링이 사용된 GFRP 쉘구조는 휨파괴가 발생할 때까지 충분한 연성도를 가지고 있으며, 강관 보강링의 휨강성 증가에 따른 전체 구조물의 강도증진이 효과적임을 확인하였다.