• 제목/요약/키워드: Deformation gradient

검색결과 269건 처리시간 0.028초

Vibration analysis of FG nanobeams based on third-order shear deformation theory under various boundary conditions

  • Jandaghian, Ali Akbar;Rahmani, Omid
    • Steel and Composite Structures
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    • 제25권1호
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    • pp.67-78
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    • 2017
  • In this study, free vibration of functionally graded (FG) micro/nanobeams based on nonlocal third-order shear deformation theory and under different boundary conditions is investigated by applying the differential quadrature method. Third-order shear deformation theory can consider the both small-scale effects and quadratic variation of shear strain and hence shear stress along the FG nanobeam thickness. The governing equations are obtained by using the Hamilton's principle, based on third-order shear deformation beam theory. The differential quadrature (DQ) method is used to discretize the model and attain the natural frequencies and mode shapes. The properties of FG micro/nanobeam are assumed to be chanfged along the thickness direction based on the simple power law distribution. The effects of various parameters such as the nonlocal parameter, gradient index, boundary conditions and mode number on the vibration characteristics of FG micro/nanobeams are discussed in detail.

Application the mechanism-based strain gradient plasticity theory to model the hot deformation behavior of functionally graded steels

  • Salavati, Hadi;Alizadeh, Yoness;Berto, Filippo
    • Structural Engineering and Mechanics
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    • 제51권4호
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    • pp.627-641
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    • 2014
  • Functionally graded steels (FGSs) are a family of functionally graded materials (FGMs) consisting of ferrite (${\alpha}$), austenite (${\gamma}$), bainite (${\beta}$) and martensite (M) phases placed on each other in different configurations and produced via electroslag remelting (ESR). In this research, the flow stress of dual layer austenitic-martensitic functionally graded steels under hot deformation loading has been modeled considering the constitutive equations which describe the continuous effect of temperature and strain rate on the flow stress. The mechanism-based strain gradient plasticity theory is used here to determine the position of each layer considering the relationship between the hardness of the layer and the composite dislocation density profile. Then, the released energy of each layer under a specified loading condition (temperature and strain rate) is related to the dislocation density utilizing the mechanism-based strain gradient plasticity theory. The flow stress of the considered FGS is obtained by using the appropriate coefficients in the constitutive equations of each layer. Finally, the theoretical model is compared with the experimental results measured in the temperature range $1000-1200^{\circ}C$ and strain rate 0.01-1 s-1 and a sound agreement is found.

XGB 및 LGBM을 활용한 Ti-6Al-4V 적층재의 변형 거동 예측 (Predicting Deformation Behavior of Additively Manufactured Ti-6Al-4V Based on XGB and LGBM)

  • 천세호;유진영;김정기;오정석;남태현;이태경
    • 소성∙가공
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    • 제31권4호
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    • pp.173-178
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    • 2022
  • The present study employed two different machine-learning approaches, the extreme gradient boosting (XGB) and light gradient boosting machine (LGBM), to predict a compressive deformation behavior of additively manufactured Ti-6Al-4V. Such approaches have rarely been verified in the field of metallurgy in contrast to artificial neural network and its variants. XGB and LGBM provided a good prediction for elongation to failure under an extrapolated condition of processing parameters. The predicting accuracy of these methods was better than that of response surface method. Furthermore, XGB and LGBM with optimum hyperparameters well predicted a deformation behavior of Ti-6Al-4V additively manufactured under the extrapolated condition. Although the predicting capability of two methods was comparable, LGBM was superior to XGB in light of six-fold higher rate of machine learning. It is also noted this work has verified the LGBM approach in solving the metallurgical problem for the first time.

주조 공정 시 열변형 예측과 제어를 통한 금형의 최적 설계에 관한 연구 (The Optimum Design of Casting Process through Prediction and control of Thermal Deformation)

  • 최봉학;곽시영;김정태;최정길;이동일
    • 한국주조공학회지
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    • 제25권5호
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    • pp.209-215
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    • 2005
  • The design of the Metal mold casting should consider several variables such as the material properties and shape of the mold. In particular, the thermal stress generated by the thermal expansion and contraction depending on the thermal gradient of the mold causes partial plastic deformation on the mold, which causes damage or fracture of the cast. Consequently, the thermal deformation along with thermal stress leads to thermal deformation of the cast itself. In this study, the temperature analysis of the cast and mold is simulated by FDM to control the thermal deformation and stress as a result of the thermal gradient of mold. Using the results from FDM simulation, the thermal deformation and stress are analyzed by FEM and, the optimal mold design with minimum thermal deformation of the cast is suggested.

Free vibration analysis of a three-layered microbeam based on strain gradient theory and three-unknown shear and normal deformation theory

  • Arefi, Mohammad;Zenkour, Ashraf M.
    • Steel and Composite Structures
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    • 제26권4호
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    • pp.421-437
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    • 2018
  • Free vibration analysis of a three-layered microbeam including an elastic micro-core and two piezo-magnetic face-sheets resting on Pasternak's foundation are studied in this paper. Strain gradient theory is used for size-dependent modeling of microbeam. In addition, three-unknown shear and normal deformations theory is employed for description of displacement field. Hamilton's principle is used for derivation of the governing equations of motion in electro-magneto-mechanical loads. Three micro-length-scale parameters based on strain gradient theory are employed for prediction of vibrational characteristics of structure in micro-scale. The results show that increase of three micro-length-scale parameters leads to significant increase of three natural frequencies especially for increase of second micro-length-scale parameter. This result is according to this fact that stiffness of a micro-scale structure is increased with increase of micro-length-scale parameters.

광열변위의 위상곡선을 이용한 금속재료의 열확산계수 측정 (Thermal Diffusivity Measurement for Metal Using Phase Curve of Photothermal Displacement)

  • 이은호;이광재;유재석
    • 대한기계학회논문집B
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    • 제25권1호
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    • pp.47-53
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    • 2001
  • As the technology has developed and new materials have been produced, it is important to measure the thermal diffusivity of material and to predict the heat transfer in the solid subject to thermal processes. This measurement can be done in a non-contact way using photothermal displacenent spectroscopy. In this study, photothermal displacement method was used to measure the thermal diffusivity quantitatively. The specimens used in this study were the pure materials. The Ar-ion laser was used as an energy source and the periodical deformation induced by this pump laser was detected by the He-Ne laser. The magnitude and the phase angle of deformation gradient were measured. The thermal diffusivity was obtained by analyzing the phase angle of deformation gradient. As the result, comparing with the literature value, the thermal diffusivities of materials measured were showed about 2% error.

온도 구배에 의한 날개 외피의 열변형 특성 연구 (Investigation of thermal deformation of wing skin induced by temperature gradient)

  • 김정범;김홍일;김재영
    • 한국항공우주학회지
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    • 제43권10호
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    • pp.896-901
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    • 2015
  • 온도 구배에 의한 날개 외피의 열변형 특성을 연구하기 위하여 비행체 날개의 포켓 형상을 본 딴 프레임 외피 구조 시편을 제작하였다. 날개에 발생하는 온도 구배 현상을 효과적으로 모사하기 위하여 프레임 외피 시편의 프레임에 수냉 시스템을 개발, 적용하였다. 공력 특성에 영향을 미치는 날개 외피의 면외 열변형을 정량적으로 평가하기 위하여 디지털 영상 상관 기법(Digital Image Correlation technique, DIC)을 사용하고, 면외 변위 측정 불확도 평가를 통해 측정 정확도를 분석하였다. SUS304 소재로 만들어진 프레임 외피 구조 시편의 시험을 수행하여 온도에 따른 외피의 면외 변형 특성을 성공적으로 획득하였다.

A high-order gradient model for wave propagation analysis of porous FG nanoplates

  • Shahsavari, Davood;Karami, Behrouz;Li, Li
    • Steel and Composite Structures
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    • 제29권1호
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    • pp.53-66
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    • 2018
  • A high-order nonlocal strain gradient model is developed for wave propagation analysis of porous FG nanoplates resting on a gradient hybrid foundation in thermal environment, for the first time. Material properties are assumed to be temperature-dependent and graded in the nanoplate thickness direction. To consider the thermal effects, uniform, linear, nonlinear, exponential, and sinusoidal temperature distributions are considered for temperature-dependent FG material properties. On the basis of the refined-higher order shear deformation plate theory (R-HSDT) in conjunction with the bi-Helmholtz nonlocal strain gradient theory (B-H NSGT), Hamilton's principle is used to derive the equations of wave motion. Then the dispersion relation between frequency and wave number is solved analytically. The influences of various parameters (such as temperature rise, volume fraction index, porosity volume fraction, lower and higher order nonlocal parameters, material characteristic parameter, foundations components, and wave number) on the wave propagation behaviors of porous FG nanoplates are investigated in detail.

Effects of size-dependence on static and free vibration of FGP nanobeams using finite element method based on nonlocal strain gradient theory

  • Pham, Quoc-Hoa;Nguyen, Phu-Cuong
    • Steel and Composite Structures
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    • 제45권3호
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    • pp.331-348
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    • 2022
  • The main goal of this article is to develop the finite element formulation based on the nonlocal strain gradient and the refined higher-order deformation theory employing a new function f(z) to investigate the static bending and free vibration of functionally graded porous (FGP) nanobeams. The proposed model considers the simultaneous effects of two parameters: nonlocal and strain gradient coefficients. The nanobeam is made by FGP material that exists in un-even and logarithmic-uneven distribution. The governing equation of the nanobeam is established based on Hamilton's principle. The authors use a 2-node beam element, each node with 8 degrees of freedom (DOFs) approximated by the C1 and C2 continuous Hermit functions to obtain the elemental stiffness matrix and mass matrix. The accuracy of the proposed model is tested by comparison with the results of reputable published works. From here, the influences of the parameters: nonlocal elasticity, strain gradient, porosity, and boundary conditions are studied.