• Advances in materials Research
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• 제5권3호
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• pp.193-203
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• 2016

Compared to metal-to-metal tribology, polymer tribology presents further complexity as it is more prone to be influenced by operating conditions. Over the past two decades, progress in the field of wear of polymers has led to the establishment of more refined wear mechanisms. The current paper establishes the link between different load parameters and the wear rate of polymers, based on experimental investigations. A pin-on-plate reciprocating tribometer was used to examine the wear behaviour of polyamide sliding against a steel counterface, under constant and fluctuating loads, in dry conditions. In addition, the influence of controlled imperfections in the polymer surface upon its wear rate were examined, under cyclic and steady loading, in order to better understand surface fatigue wear of polymers. The imposed imperfections consisted of vertical artificial deep crack (slit) perpendicular or parallel to the direction of sliding. The study concludes with the followings findings; in general, wear of polymers shows a significant tendency to the type of applied load. Under cyclic loads, polymers show an increase in wear rate compared to those tested under static loads. Such increase was found to increase with the increase in cyclic load frequency. It is also demonstrated that surface cracks results in higher wear rates, particularly under cyclic loads.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.97-97
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• 2017

This study investigated the corrosion protection by electrodeposited copper layer on AZ31 Mg alloy with and without additional silver layer by immersion test, salt spray test, OCP transient and potentiodynamic polarization experiment. The single electrodeposited Cu layer on AZ31 Mg alloy showed a nodular structure with many imperfections of crevices between the nodules, which resulted in the fast initiation of pitting corrosion within first few hours of immersion. Double-layer coating of Cu and outer Ag layer slightly increased the initiation time for pitting corrosion. Triple-layer coatings of Cu/Ag/Cu exhibited the most efficient corrosion protection of AZ31 Mg alloy, compared to the single- and double-layer coatings. Surface morphology of the outer Cu layer in the triple-layer was changed from the nodular structure to fine particle structure with no crevices due to the presence of an additional Ag layer. Thus, the improved corrosion resistance of AZ31 Mg alloy by electrodeposited Cu/Ag or Cu/Ag/Cu layers is readily ascribed to the decreased number of imperfections in the electrodeposited layers due to the additional silver layer. It is concluded that the additional silver layer provides many nucleation sites for the second Cu plating, resulting in the formation of finer and denser structure than the first Cu electrodeposit.

• Steel and Composite Structures
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• 제34권4호
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• pp.561-580
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• 2020

Buckling restrained braces (BRBs) were developed as an enhanced alternative to conventional braces by restraining their global buckling, thus allowing development of a stable quasi-symmetric hysteretic response. A wider adoption of buckling restrained braced frames is precluded due to proprietary character of most BRBs and the code requirement for experimental qualification. To overcome these problems, BRBs with capacities corresponding to typical steel multi-storey buildings in Romania were developed and experimentally tested in view of prequalification. In the second part of this paper, a complex nonlinear numerical model for the tested BRBs was developed in the finite element environment Abaqus. The calibration of the numerical model was performed at both component (material models: steel, concrete, unbonding material) and member levels (loading, geometrical imperfections). Geometrically and materially nonlinear analyses including imperfections were performed on buckling restrained braces models under cyclic loading. The calibrated models were further used to perform a parametric study aiming at assessing the influence of the strength of the buckling restraining mechanism, concrete class of the infill material, mechanical properties of steel used for the core, self-weight loading, and frame effect on the cyclic response of buckling restrained braces.

• 한국표면공학회지
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• 제53권2호
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• pp.80-86
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• 2020

This paper is concerned with type of imperfections present within the anodic oxide films on AA2024 and surface hardness of the anodic film measured after ink-impregnation. The anodic oxide films were formed for 25 min at 40 mA/㎠ and 15±0.5℃ and 300 rpm of magnet stirring rate in 20% sulfuric acid solution. The ink-impregnation allows clear observations of not only the imperfections within the anodic oxide films but also an indentation mark on the oxide film surface made by a pyramidal-diamond penetrator for the hardness measurement. There were observed four different regions in the anodic oxide films on AA2024 and the surface hardness of the anodic oxide films appeared to be crucially dependent on the type of defects, showing 60~100 H_v on the oxide surface region I with large size black defect, 100~140 H_v on the oxide surface region II with large size grey defect, 140~170 H_v on the oxide surface region III with mall size black and/or grey defects and 170~190 H_v on the oxide surface region IV without defects. The pyramidal indentation marks were observed to be distorted in the regions with a large size black and grey defects, while no distortion of the indentation mark was observed in the regions with small size defects and without visible defects.

• Composites Research
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• 제17권2호
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• pp.34-39
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• 2004

본 연구에서는 폐쇄형 발포금속의 인장 특성을 이해하기 위하여 수정된 단위모델을 제시하였다. 또한 발포금속의 밀도는 가우스 분포에 의거하여 확률적으로 분포한다고 가정하고 본 연구에서 제시된 수정 단위 모델을 조합하여 유한요소 모델을 제안하였다. 이 모델은 실제 인장 시험과 유사한 변형거동을 보이는 것을 확인하였고, 적절한 밀도 분포와 내부 기공을 고려하게 되면, 해석에서 구해진 최대 인장 강도가 근사적으로 실험결과와 일치하는 것을 볼 수 있었다. 또한, 발포 알루미늄의 최대 인장 강도는 밀도 분포의 표준편차보다는 내부 기공 부피분율에 더 민감하게 변하는 것으로 밝혀졌다.

• Ocean Systems Engineering
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• 제6권1호
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• pp.99-115
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• 2016

In meeting the technical needs for deepwater conditions and overcoming the shortfalls of single-layer pipes for deepwater applications, pipe-in-pipe (PIP) systems have been developed. While, for PIP pipelines directly laid on the seabed or with partial embedment, one of the primary service risks is lateral buckling. The critical axial force is a key factor governing the global lateral buckling response that has been paid much more attention. It is influenced by global imperfections, submerged weight, stiffness, pipe-soil interaction characteristics, et al. In this study, Finite Element Models for imperfect PIP systems are established on the basis of 3D beam element and tube-to-tube element in Abaqus. A parameter study was conducted to investigate the effects of these parameters on the critical axial force and post-buckling forms. These parameters include structural parameters such as imperfections, clearance, and bulkhead spacing, pipe/soil interaction parameter, for instance, axial and lateral friction properties between pipeline and seabed, and load parameter submerged weight. Python as a programming language is been used to realize parametric modeling in Abaqus. Some conclusions are obtained which can provide a guide for the design of PIP pipelines.

• Smart Structures and Systems
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• 제6권7호
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• pp.793-810
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• 2010

This paper addresses the control issue of vibratory MEMS-based gyroscopes. This study considers a gyroscope that can be modeled by an inner mass attached to an outer mass by four springs and four dampers. The outer mass itself is attached to the rotating frame by an equal number of springs and dampers. In order to measure the angular rate of the rotating frame, a driving force is applied to the inner mass and the Coriolis force is sensed along the y-direction associated with the outer mass. Due to micro-fabrication imperfections, including anisoelasticity and damping effects, both gyroscopes do not allow accurate measurements, and therefore, it becomes necessary to devise feedback controllers to reduce the effects of such imperfections. Given an ideal gyroscope that meets certain performance specifications, a feedback control strategy is synthesized to reduce the error dynamics between the actual and ideal gyroscopes. For a dual-mass gyroscope, it is demonstrated that the error dynamics are remarkably decreased with the application of four actuators applied to both masses in the x and y directions. It is also shown that it is possible to reduce the error dynamics with only two actuators applied to the outer mass only. Simulation results are presented to prove the efficiency of the proposed control design.

• 한국산학기술학회논문지
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• 제10권8호
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• pp.2032-2037
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• 2009

본 논문은 공용중인 교량구조물의 내하력 평가시 획일적이고 실제 거동특성을 적극적으로 활용하지 않아 발생할 수 있는 내하력 평가의 오류에 대하여 연구하였다. 내하력의 평가시 지점의 경계조건과 같은 현재의 거동특성을 반영하기 위하여 초기 결함을 갖는 부재에 대한 좌굴방정식에 처짐을 적용시켜 산정된 축방향력과 처짐에 의해 구해진 모멘트를 고려하여 교량의 내하력을 평가하였다. 기존의 내하력 평가시에 다소 획일적으로 적용되어지는 응력보정 계수를 좌굴방정식을 통하여 각 주형에 대하여 선 반영함으로서 내하력 평가의 오류를 다소 제거하고자 하였다.

• Steel and Composite Structures
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• 제32권1호
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• pp.141-156
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• 2019

This paper presents the flexural behaviour of stainless steel beam-to-tubular column joints with extended endplates subjected to static loading. Moment-rotation relationships were investigated numerically by using Abaqus software with geometric and material nonlinearity considered. The prediction of damages among components was achieved through ductile damage models, and the influence of initial geometric imperfections and residual stresses was evaluated in large fabricated stainless steel joints involving hollow columns and concrete-filled columns. Parametric analysis was subsequently conducted to assess critical factors that could affect the flexural performance significantly in terms of the initial stiffness and moment resistance. A comparison between codes of practice and numerical results was thereafter made, and design recommendations were proposed for further applications. Results suggest that the finite element model can predict the structural behaviour reasonably well with the component damage consistent with test outcomes. Initial geometric imperfections and residual stresses are shown to have little effect on the moment-rotation responses. A series of parameters that can influence the joint behaviour remarkably include the strain-hardening exponents, stainless steel strength, diameter of bolts, thickness of endplates, position of bolts, section of beams and columns. AS/NZS 2327 is more reliable to predict the joint performance regarding the initial stiffness and moment capacity compared to EN 1993-1-8.

• Corrosion Science and Technology
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• 제23권3호
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• pp.179-194
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• 2024

A layer-by-layer coating was produced using electrophoretic deposition for a HA/Al₂O₃ coating layer and a bioglass coating layer on Co-Cr-Mo alloy with a roughness of 0.5 ㎛ (400 emery paper SiC). The corrosion behaviour was analyzed by assessing the coating layers' exceptional corrosion resistance, which outperformed the substrate. Cr ion release test using AAS was carried out, indicating that factional graded coating inhibited ion release from the uncoated substrate to coated sample. The porosity was expressed as a percentage, representing the extent of imperfections on the surface of all coatings. These imperfections fell within an acceptable range of 1% to 3%. The roughness of the coated surface was measured using atomic force microscopy, which revealed an excellent roughness value of 3.32 nm. Tape test technique for adhesion revealed that the removal area of the substrate coating layer varied by 11.92%. X-ray diffraction analysis confirmed the presence of all coating material peaks and verified phases of the deposited coating layers. These findings provided evidence that the coating composition remains unaffected by the electrophoretic deposition process. The bioactivity was assessed by immersion in a simulated bodily fluid, which revealed the formation of HCA during a period of 5 days.