• Advances in nano research
• /
• 제6권1호
• /
• pp.57-80
• /
• 2018

In this study, the thermal loading effect on free vibration characteristics of carbon nanotubes (CNTs) with multiple cracks is studied. Various boundary conditions for nanotube are taken in to account. In order to take the small scale effect, the nonlocal elasticity of Eringen is employed in the framework of Euler-Bernoulli beam theory. This theory states that the stress at a reference point is a function of strains at all points in the continuum. A cracked nanotube is assumed to be consisted of two segments that are connected by a rotational spring which is located in the position of the cracked section. Hamilton's principle is used to achieve the governing equations. Influences of the nonlocal parameter, crack severity, temperature change and the number of cracks on the system frequencies are investigated. Also, it is found that at room or lower temperature the natural frequency for CNT decreases as the value of temperature change increases, while at temperature higher than room temperature the natural frequency of CNT increases as the value of temperature change increases. Various boundary conditions have been applied to the nanotube.

• Advances in nano research
• /
• 제4권2호
• /
• pp.65-84
• /
• 2016

This paper investigates the buckling behavior of shear deformable piezoelectric (FGP) nanoscale beams made of functionally graded (FG) materials embedded in Winkler-Pasternak elastic medium and subjected to an electro-magnetic field. Magneto-electro-elastic (MEE) properties of piezoelectric nanobeam are supposed to be graded continuously in the thickness direction based on power-law model. To consider the small size effects, Eringen's nonlocal elasticity theory is adopted. Employing Hamilton's principle, the nonlocal governing equations of the embedded piezoelectric nanobeams are obtained. A Navier-type analytical solution is applied to anticipate the accurate buckling response of the FGP nanobeams subjected to electro-magnetic fields. To demonstrate the influences of various parameters such as, magnetic potential, external electric voltage, power-law index, nonlocal parameter, elastic foundation and slenderness ratio on the critical buckling loads of the size-dependent MEE-FG nanobeams, several numerical results are provided. Due to the shortage of same results in the literature, it is expected that the results of the present study will be instrumental for design of size-dependent MEE-FG nanobeams.

• Steel and Composite Structures
• /
• 제41권6호
• /
• pp.787-803
• /
• 2021

The size-dependent nonlinear thermomechanical vibration analysis of pre- and post-buckled tapered two-directional functionally graded (2D-FG) microbeams is presented in this study. In the context of the modified couple stress theory, the formulations are derived based on the parabolic shear deformation beam theory and von Karman nonlinear strains. Different thermomechanical material properties are assumed to be temperature-dependent and smoothly vary in both length and thickness directions using the power law and the physical neutral axis concept is employed. The nonlinear governing equations are derived using the Hamilton principle and the resulting variable coefficient equations of motion are solved using the differential quadrature method (DQM) and iterative Newton's method for clamped-clamped and simply supported boundary conditions. Comparison studies are presented to validate the derived model and solution procedure. The impacts of induced thermal moments, temperature power index, two gradient indices, nonuniform cross-section, and microstructure length scale parameter on the frequency-temperature configurations are explored for both clamped and simply supported microbeams.

• Computers and Concrete
• /
• 제34권4호
• /
• pp.447-476
• /
• 2024

The current research proposes an innovative finite element model established within the context of higher-order beam theory to examine the bending and buckling behaviors of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams resting on Winkler-Pasternak elastic foundations. This two-node beam element includes four degrees of freedom per node and achieves inter-element continuity with both C¹ and C⁰ continuities for kinematic variables. The isoparametric coordinate system is implemented to generate the elementary stiffness and geometric matrices as a way to enhance the existing model formulation. The weak variational equilibrium equations are derived from the principle of virtual work. The mechanical properties of FG-CNTRC beams are considered to vary gradually and smoothly over the beam thickness. The current investigation highlights the influence of porosity dispersions through the beam cross-section, which is frequently omitted in previous studies. For this reason, this analysis offers an enhanced comprehension of the mechanical behavior of FG-CNTRC beams under various boundary conditions. Through the comparison of the current results with those published previously, the proposed finite element model demonstrates a high rate of efficiency and accuracy. The estimated results not only refine the precision in the mechanical analysis of FG-CNTRC beams but also offer a comprehensive conceptual model for analyzing the performance of porous composite structures. Moreover, the current results are crucial in various sectors that depend on structural integrity in specific environments.

• 한국지진공학회논문집
• /
• 제7권3호
• /
• pp.69-77
• /
• 2003

본 연구는 8개의 RBS(reduced beam section) 내진 철골모멘트접합부의 실물대 실험결과를 요약한 것이다. 실험의 주요변수는 보 웨브 접합법 및 패널존 강도를 택하였다. 균형 패널존 시험체는 접합부의 내진성능을 감소시키지 않으면서, 보와 패널존이 함께 균형적으로 지진에너지를 소산시키도록 설계하여 값비싼 패널존 보강판(doubler plates)의 수요를 줄이고자 시도한 것이다. 보 웨브를 용접한 시험제는 모두 특별 연성모멘트골조에서 요구되는 접합부 회전능력을 충분히 발휘하였다. 반면 보 웨브를 볼트 접합한 시험체는 조기에 스캘럽을 가로지르는 취성파단이 발생하는 열등한 성능을 보였다. 보 그루브 용접부 자체의 취성파괴가 본 연구에서와 같이 양질의 용접에 의해 방지되면, 스켈럽 부근의 취성파단이 다음에 해결해야 할 문제로 대두되는 경향을 보인다. 보 웨브를 볼팅한 경우에 접합부 취성파단의 빈도가 월등히 높은 이유를 실험 및 해석결과를 토대로 제시하였다. 측정된 변형도 데이터에 의할 때, 접합부의 전단력 전달메카니즘은 흔히 가정하는 고전 휨이론에 의한 예측과 전혀 다르다. 이는 전통적 보 웨브 설계법을 재검토할 필요가 있음을 시사하는 것이다. 아울러, 접합부에서 요구되는 바람직한 거동기준을 제시하고 이를 근거로 균형 패널존의 강도범위에 대한 예비적 추정치를 제시하였다.

• Coupled systems mechanics
• /
• 제13권4호
• /
• pp.337-357
• /
• 2024

This paper studies, the analysis of nonlinear thermal vibration of fluid-infiltrated FG nanobeam with voids. The effect of nonlinear thermal in a FG ceramic-metal nanobeam is determined using Murnaghan's model. Here the influence of fluids in the pores is investigated using the Skempton coefficient. Hamilton's principle is used to find the equation of motion of functionally graded nanobeam with the effect of refined higher-order state space strain gradient theory (SSSGT). Numerical solutions of the FG nanobeam are employed using Navier's solution. These solutions are validated against the impact of various parameters, including imperfection ratio, fluid viscosity, fluid velocity, amplitude, and piezoelectric strain, on the behavior of the fluid-infiltrated porous FG nanobeam.

• 한국전산구조공학회논문집
• /
• 제29권3호
• /
• pp.229-235
• /
• 2016

본 논문에서는 기존에 개발된 생브낭의 원리를 이용한 응력개선방법에 부가적인 면외 워핑함수를 도입하여 후처리함으로써 기계 및 열응력을 개선할 수 있는 방법을 소개하였다. 열응력 예측이 중요한 문제로 다루어지고 있으며, 이에 따라 수많은 보이론들이 개발되어왔다. 일반적으로 고차이론들이 열응력 예측에 유용하다고 알려져 있지만, 자유도가 많아 계산과정이 복잡하다는 단점이 존재한다. 이러한 단점들을 보완하기 위해, 본 연구에서는 계산이 비교적 간단한 고전 보이론의 변위장에 면외 워핑함수를 부가적으로 도입하고 합응력 등가를 통해 후처리함으로써 보 구조물의 열응력을 정확하게 예측할 수 있는 방법을 제시하였다. 그리고 다양한 경계조건을 가지는 수치예제들을 통해 탄성해와 비교함으로써 그 정확도를 검증하고, 면외 워핑함수가 응력개선에 미치는 영향에 대해 분석하였다.

• 한국화재소방학회논문지
• /
• 제28권2호
• /
• pp.76-81
• /
• 2014

화재와 같은 고온 시 구조부재의 붕괴를 방지함으로써 재실자와 소방관계자 그리고 재산을 보호할 수 있는 방법은 구조부재의 내화성능을 확보하는 것이며, 이는 시방적 내화설계방법인 내화시험을 통하여 확보되어 왔다. 그러나 내화시험에 수반되는 시험체 제작과 운반 그리고 막대한 시험 비용의 반복적 사용 등은 새로운 공법과 재료 개발의 문제점으로 대두되었다. 따라서 본 연구에서는 일반 등급(SS 400) 강재의 고온 시 항복강도, 탄성계수와 열전달 및 열응력 해석을 적용하여 H형강 보부재의 표면온도 상승 및 고온 시 내력 변화를 평가하였다. 또한 H형강 보부재의 길이 변화에 따른 고온 시의 보부재의 내력평가를 수행하여 각각의 길이변화에 따른 내력 변화의 차이를 평가하였다.

• Earthquakes and Structures
• /
• 제26권1호
• /
• pp.31-48
• /
• 2024

In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

• Advances in nano research
• /
• 제16권5호
• /
• pp.509-519
• /
• 2024

In this study, the static analysis of carbon nanotube-reinforced composites (CNTRC) beams resting on a Winkler-Pasternak elastic foundation is presented. The developed theories account for higher-order variation of transverse shear strain through the depth of the beam and satisfy the stress-free boundary conditions on the top and bottom surfaces of the beam. To study the effect of carbon nanotubes distribution in functionally graded (FG-CNT), we introduce in the equation of CNT volume fraction a new exponent equation. The SWCNTs are assumed to be aligned and distributed in the polymeric matrix with different patterns of reinforcement. The rule of mixture is used to describe the material properties of the CNTRC beams. The governing equations were derived by employing Hamilton's principle. The models presented in this work are numerically provided to verify the accuracy of the present theory. The analytical solutions are presented, and the obtained results are compared with the existing solutions to verify the validity of the developed theories. Many parameters are investigated, such as the Pasternak shear modulus parameter, the Winkler modulus parameter, the volume fraction, and the order of the exponent in the volume fraction equation. New results obtained from bending and stresses are presented and discussed in detail. From the obtained results, it became clear the influence of the exponential CNTs distribution and Winkler-Pasternak model improved the mechanical properties of the CNTRC beams.