• Wind and Structures
• /
• 제32권1호
• /
• pp.31-46
• /
• 2021

The current research deals with, stability/instability and cylindrical composite nano-scaled shell's resonance frequency filled by graphene nanoplatelets (GPLs) under various thermal conditions (linear and nonlinear thermal loadings). The piece-wise GPL-reinforced composites' material properties change through the orientation of cylindrical nano-sized shell's thickness as the temperature changes. Moreover, in order to model all layers' efficient material properties, nanomechanical model of Halpin-Tsai has been applied. A functionally modified couple stress model (FMCS) has been employed to simulate GPLRC nano-sized shell's size dependency. It is firstly investigated that reaching the relative frequency's percentage to 30% would lead to thermal buckling. The current study's originality is in considering the multifarious influences of GPLRC and thermal loading along with FMCS on GPLRC nano-scaled shell's resonance frequencies, relative frequency, dynamic deflection, and thermal buckling. Furthermore, Hamilton's principle is applied to achieve boundary conditions (BCs) and governing motion equations, while the mentioned equations are solved using an analytical approach. The outcomes reveal that a range of distributions in temperature and other mechanical and configurational characteristics have an essential contribution in GPLRC cylindrical nano-scaled shell's relative frequency change, resonance frequency, stability/instability, and dynamic deflection. The current study's outcomes are practical assumptions for materials science designing, nano-mechanical, and micromechanical systems such as micro-sized sensors and actuators.

• Steel and Composite Structures
• /
• 제19권4호
• /
• pp.1011-1033
• /
• 2015

In this article, large amplitude bending behaviour of laminated composite flat panel under combined effect of moisture, temperature and mechanical loading is investigated. The laminated composite panel model has been developed mathematically by introducing the geometrical nonlinearity in Green-Lagrange sense in the framework of higher-order shear deformation theory. The present study includes the degraded composite material properties at elevated temperature and moisture concentration. In order to achieve any general case, all the nonlinear higher order terms have been included in the present formulation and the material property variations are introduced through the micromechanical model. The nonlinear governing equation is obtained using the variational principle and discretised using finite element steps. The convergence behaviour of the present numerical model has been checked. The present proposed model has been validated by comparing the responses with those available published results. Some new numerical examples have been solved to show the effect of various parameters on the bending behaviour of laminated composite flat panel under hygro-thermo-mechanical loading.

• Structural Engineering and Mechanics
• /
• 제38권6호
• /
• pp.803-823
• /
• 2011

In this paper, the three dimensional Parallel Realistic Failure Process Analysis ($RFPA^{3D}$-Parallel) code based on micromechanical model is employed to investigate the bonding behavior in FRP sheet bonded to concrete in single shear test. In the model, the heterogeneity of brittle disordered material at a meso-scale was taken into consideration in order to realistically demonstrate the mechanical characteristics of FRP-to-concrete. Modified Mohr-coulomb strength criterion with tension cut-off, where a stressed element can damage in shear or in tension, was adopted and a stiffness degradation approach was used to simulate the initiation, propagation and growth of microcracks in the model. In addition, a Master-Slave parallel operation control technique was adopted to implement the parallel computation of a large numerical model. Parallel computational results of debonding of FRP-concrete visually reproduce the spatial and temporal debonding failure progression of microcracks in FRP sheet bonded to concrete, which agrees well with the existing testing results in laboratory. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.

• 소성∙가공
• /
• 제12권1호
• /
• pp.60-65
• /
• 2003

HIP diffusion bonding of Ni-based superalloys, cast Mar-M247 (MM247) and Udimet 720 (U720) powder, was experimentally and numerically studied. Subsolvus HIP treatment was optimized by investigating the variations of high temperature tensile properties of HIP-bonded specimens with powder size, HIP'ing time, etc. While the tensile strength at high temperatures showed no detectable changes, the tensile elongation and reduction in area were slightly increased as the powder size decreased from -140 mesh to -270 mesh. While as-HIP'ed U720 showed a high tensile strength comparable to that of lorded U720 alloy, the HIP diffusion-bonded specimen showed a strength lower than the forged U720 alloy and the cast MM247 alloy The increase of HIP'ing tune from 2 hours to 3 hours resulted in a rapid risc of tensile strength and elongation due to the disappearence of microvoids in the cast MM247. FEM simulation for HIP process was conducted by applying the McMeeking micromechanical model, which uses power-law creep model as constitutive equations. ABAQUS user subroutine CREEP with an implemented microscopic model was used for the simulation. Numerical simulation was shown to be essential for the near-net shape manufacturing as well as the HIP process optimization.

• Computers and Concrete
• /
• 제19권5호
• /
• pp.501-507
• /
• 2017

The predictive utility of a damage model depends heavily on its particular choice of a damage variable, which serves as a macroscopic approximation in describing the underlying micromechanical processes of microdefects. In the case of spatially perfectly randomly distributed microcracks or microvoids in all directions, isotropic damage model is an appropriate choice, and scalar damage variables were widely used for isotropic or one-dimensional phenomenological damage models. The simplicity of a scalar damage representation is indeed very attractive. However, a scalar damage model is of somewhat limited use in practice. In order to entirely characterize the isotropic damage behaviors of damaged materials in multidimensional space, a system theory of isotropic double scalar damage variables, including the expressions of specific damage energy release rate, the coupled constitutive equations corresponding to damage, the conditions of admissibility for two scalar damage effective tensors within the framework of the thermodynamics of irreversible processes, was provided and analyzed in this study. Compared with the former studies, the theoretical formulations of double scalar damage variables in this study are given in the form of matrix, which has many features such as simpleness, directness, convenience and programmable characteristics. It is worth mentioning that the above-mentioned theoretical formulations are only logically reasonable. Owing to the limitations of time, conditions, funds, etc. they should be subject to multifaceted experiments before their innovative significance can be fully verified. The current level of research can be regarded as an exploratory attempt in this field.

• 한국지반공학회논문집
• /
• 제23권3호
• /
• pp.77-88
• /
• 2007

본 연구에서는 사질토의 탄성 및 탄소성 거동을 모사하기 위한 미시역학 기반의 구성 모델을 개발하였다. 개발 모델은 접촉 방향의 공간 분포를 통계적으로 처리한 조직 이방성, 응력비에 따른 조직 이방성의 변화, 간극비 변화에 따른 접촉점 수의 변화, 그리고 미시적 탄성-탄소성 접촉 강성을 고려하였다. 금속 재료에 대한 시험결과를 이용하여 미시적 탄소성 접촉 강성 모델을 수직 접촉력과 입자의 항복 접촉력에 대한 거듭제곱 함수의 형태로 유도하였다. 모델 변수를 정량적으로 평가하기 위해 직교 이방 탄성 계수의 근사식을 유도하였다.

• Structural Engineering and Mechanics
• /
• 제86권4호
• /
• pp.519-533
• /
• 2023

This work focuses on the dynamic analysis of thermal barrier coated straight and curved turbine blades modelled as functionally graded sandwich panel under thermal environment. The pre- twisted straight/curved blade model is considered to be fixed to the hub and, the complete assembly of the hub and blade are assumed to be rotating. The functionally graded sandwich composite blade is comprised of functionally graded face-sheet material and metal alloy core. The constituents' material properties are assumed to be temperature-dependent, however, the overall properties are evaluated using Voigt's micromechanical scheme in conjunction with the modified power-law functions. The blade model kinematics is based on the equivalent single-layer shear deformation theory. The equations of motion are derived using the extended Hamilton's principle by including the effect of centrifugal forces, and further solved via 2D- isoparametric finite element approximations. The mesh refinement and validation tests are performed to illustrate the stability and accurateness of the present model. In addition, frequency characteristics of the pre-twisted rotating sandwich blades are computed under thermal environment at various sets of parametric conditions such as twist angles, thickness ratios, aspect ratios, layer thickness ratios, volume fractions, rotational velocity and blade curvatures which can be further useful for designing the blade type structures under turbine operating conditions.

• Coupled systems mechanics
• /
• 제6권2호
• /
• pp.207-227
• /
• 2017

In this paper Timoshenko beam theory is employed to investigate the vibration characteristics of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) Beams with a stiff core in thermal environment. The material characteristic of carbon nanotubes (CNT) are supposed to change in the thickness direction in a functionally graded form. They can also be calculated through a micromechanical model where the CNT efficiency parameter is determined by matching the elastic modulus of CNTRCs calculated from the rule of mixture with those gained from the molecular dynamics simulations. The differential transform method (DTM) which is established upon the Taylor series expansion is one of the effective mathematical techniques employed to the differential governing equations of sandwich beams. Effects of carbon nanotube volume fraction, slenderness ratio, core-to-face sheet thickness ratio, different thermal environment and various boundary conditions on the free vibration characteristics of FG-CNTRC sandwich beams are studied. It is observed that vibration response of FG-CNTRC sandwich beams is prominently influenced by these parameters.

• 한국공작기계학회:학술대회논문집
• /
• 한국공작기계학회 1996년도 추계학술대회 논문
• /
• pp.173-179
• /
• 1996

A computer simulation has been performed for the application to the elastoplastic stress analysis in a discontinuous composite solid. To obtain the internal field quantities of composite the micromechanics analysis and finite element analysis (FEA) were implemented. As the procedure the reasonably optimized FE mesh generations the appropriate imposition of boundary condition and the relevant postprocessing such as elastoplastic thermomechanical analysis were taken into account. For the numerical illustration an aligned axisymmetric single fiber model has been employed to assess field quantities. It was found that the proposed simulation methodology for stress analysis is applicable to the complicated inhomogeneous solid for the investigation of micromechanical behavior.

• 한국공작기계학회논문집
• /
• 제16권5호
• /
• pp.115-121
• /
• 2007

Phase contrast imaging in atomic force microscopy showed a promise as an effective tool for better understanding of micromechanical properties of surfaces at nano scale. A qualitative estimation model for phase contrast images obtained with a tapping mode AFM was developed. This investigation demonstrated the high efficiency of combined analysis of topography and phase contrast images for characterizing nanosurfaces. Phase contrast images allowed estimation of relative stiffness(elastic modulus) of the sample surface. The phase contrast images revealed a significant inhomogeneity of the nano scale worn surfaces. Phase contrast images are also capable of revealing the formation of tribofilms.