Browsing by Author "Tsai, Jia-Lin"

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2-D analytical model for characterizing flexural damping responses of composite laminates
(2009-07-01)
Tsai, Jia-Lin
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Chang, Nai-Ren
;
機械工程學系
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Department of Mechanical Engineering
The flexural damping behaviors of composite laminates were characterized analytically in this study. A 2-D analytical model was developed based on the extension of Ni-Adams model [Ni RG, Adams RD. The damping and dynamic moduli of symmetric laminated composite beams-theoretical and experimental results. J Compos Mater 1984:18(2):104-21] accounting for the energy dissipation contributed by the laminar stresses of sigma(xy) and sigma(yy), The specific damping capacity (SDC) of the composite was determined in accordance with the energy dissipation concept, which was defined as the ratio of the dissipated energy to the stored energy for per circle of vibration. The 2-D analytical model was validated by comparing the SDC of [0/-60/60](s) and [0/90/45/-45](s) laminates with the experimental data and the finite element (FEM) results. In addition, the effects of interlaminar stress on the flexural damping responses of laminated plates were also characterized in the 3-D FEM analysis. Results indicated that the interlaminar stress effect may not be so significant that the current 2-D model is adequate for the evaluation of the damping responses of the composite laminates. Furthermore, the present predictions, as compared to the Ni-Adams [Ni RG, Adams RD. The damping and dynamic moduli of symmetric laminated composite beams-theoretical and experimental results. J Compos Mater 1984; 18(2):104-21] and Adams-Maheri [Adams RD, Maheri MR. Dynamic flexural properties of anisotropic fibrous composite beams. Compos Sci Technol 1994;50(4):497-514] models, generally demonstrate good agreements with the experimental data and the FEM results. (C) 2008 Elsevier Ltd. All rights reserved.
Characterization of Young's modulus and thermal conductivity of graphene/epoxy nanocomposites
(2019-03-01)
Wang, Tai-Yuan
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Tseng, Po-Ying
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Tsai, Jia-Lin
;
交大名義發表
;
機械工程學系
Atomistic simulation together with micromechanical analysis was employed to characterize the Young's modulus and thermal conductivity of graphene/epoxy nanocomposites. Nanocomposites containing pristine graphene, carboxyl (COOH)-functionalized graphene, and COOH- and amine (NH2)-functionalized graphene were considered in the simulations. The effect of atomistic interaction between the graphene and the surrounding epoxy was accounted for in the molecular dynamics simulations and then used to derive the effective properties of graphene. Subsequently, the Young's modulus and thermal conductivity of nanocomposites containing randomly oriented graphene were modeled using the Mori-Tanaka micromechanical model. The results indicated that the COOH- and NH2-functionalized graphene nanocomposite had superior mechanical and thermal properties to the other two material systems. Moreover, the model predictions were in favorable agreement with the experimental data.
Characterizing elastic properties of carbon nanotubes/polyimide nanocomposites using multi-scale simulation
(2010-01-01)
Tsai, Jia-Lin
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Tzeng, Shi-Hua
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Chiu, Yu-Tsung
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機械工程學系
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Department of Mechanical Engineering
This research is aimed at characterizing the elastic properties of carbon nanotubes (CNTs) reinforced polyimide nanocomposites using a multi-scale simulation approach. The hollow cylindrical molecular structures of CNTs were modeled as a transverse isotropic solid, the equivalent elastic properties of which were determined from the molecular mechanics calculations in conjunction with the energy equivalent concept. Subsequently, the molecular structures of the CNTs/polyimide nanocomposites were established through h molecular dynamics (MD) simulation, from which the non-bonded gap as well as the non-bonded energy between the CNTs and the Surrounding polyimide were evaluated It was postulated that the normalized non-bonded energy (non-bonded energy divided by surface area of the CNTs) is correlated with the extent of the interfacial interaction. Afterwards. an effective interphase was introduced between the CNTs and polyimide polymer to characterize the degree of non-bonded interaction. The dimension of the interphase was assumed equal to the non-bonded gap, and the corresponding elastic stiffness was calculated from the normalized non-bonded energy. The elastic properties of the CNT nanocomposites were predicted by a three-phase micromechanical model in which the equivalent solid cylinder of CNTs, polyimide matrix. and the effective interphase were included. Results indicated that the longitudinal moduli of the nanocomposites obtained based on the three-phase model were in good agreement with those calculated from MD simulation. Moreover, they fit well with the conventional rule of mixture predictions. On the other hand, in the transverse direction, the three-phase model is superior to the conventional micromechanical model since it is capable of predicting the dependence of transverse modulus on the radii of nanotubes. (C) 2009 Elsevier Ltd. All rights reserved.
Characterizing failure behaviors of debonded composite sandwich structures under compressive loading
(2015-09-01)
Nieh, Yi-Hsin
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Lai, Yen-Kun
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This research investigated the failure behaviors of the composite sandwich structures with face sheet and core debond subjected to compressive loading. Experiments and numerical simulations were conducted to determine the effects of the face sheet thickness and debond length on the compressive strength and failure mechanisms of the composite sandwich structures. Experimental results revealed that sandwich structures with either thicker face sheets or a shorter debond length exhibited a higher buckling load and greater failure strength. Moreover, when the debond length was short, failure was primarily caused by global buckling; conversely, when the debond length was long, failure was caused by local buckling and crack extension from the debond edge. To characterize the failure mechanism, a nonlinear finite element simulation of sandwich specimens containing imperfections was conducted. The simulation revealed that, when the dominant failure mode was global buckling, failure occurred at the intermediate portion of the foam core and strength could be characterized using the maximum principal strain criterion. However, when the failure mode was local buckling, failure was initiated at the debond tip, and strength could be predicted using the damage zone method.
Characterizing load transfer efficiency in double-walled carbon nanotubes using multiscale finite element modeling
(2013-01-01)
Lu, Ting-Chu
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Tsai, Jia-Lin
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機械工程學系
;
Department of Mechanical Engineering
Load transfer efficiency from matrix to carbon nanotubes (CNTs) plays an important role in the mechanical response of CNTs nanocomposites as it may affect the effectiveness of the nano-reinforcements. For double-walled carbon nanotubes (DWCNTs), the outer graphene layer as well as the inner layer may be responsible for the load bearing capacity. In this study, the load transfer efficiency within DWCNTs was investigated using a multiscale simulation scheme. The multiscale simulation consists of two steps. First, the atomistic behaviors between the adjacent graphite layers in DWCNTs were characterized using molecular dynamic (MD) simulation, from which a cylindrical equivalent continuum solid of DWCNTs with embedded spring elements was proposed to describe the interactions of neighboring graphene layers. Two kinds of interatomistic properties in DWCNTs, i.e., van der Walls (vdW) interactions and artificial build-up covalent bonds, were considered in the equivalent solid. Subsequently, the equivalent solid was implemented as reinforcement in the micromechanical model of CNTs nanocomposites for evaluating the load transfer efficiency. Results indicated that the DWCNTs with covalent bonds exhibit superior load transfer efficiency than those with only vdW interactions. In addition, when the DWCNTs get long, the load transfer efficiency of DWCNTs increases accordingly. (C) 2012 Elsevier Ltd. All rights reserved.
Characterizing mechanical behaviors of a flexible AMOLED during the debonding process
(2016-10)
Fu, Yun
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Tsai, Chen-Chu
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
The stress distribution of a flexible active-matrix organic light-emitting diode (AMOLED) display during the debonding process was investigated using finite element analysis. During the fabrication of an AMOLED display, an AMOLED with a polyimide (PI) substrate is detached from a glass carrier; this is a critical process and generally results in failure of the AMOLED. To enhance the yielding rate of AMOLEDs, their stress states generated during the debonding process must be reduced. The interfacial fracture behavior between the PI substrate and glass carrier was characterized on the basis of bimaterial fracture mechanics, and the fracture toughness associated with mode mixity determined through peeling tests was considered a criterion for detaching the AMOLED from the glass carrier. The stress distribution of the AMOLED at the inception of debonding crack extension was evaluated according to fracture toughness. In addition, the parameters possibly influencing the stress states of the AMOLED in the debonding process are discussed.
Characterizing mechanical properties of graphite using molecular dynamics simulation
(2010-01-01)
Tsai, Jia-Lin
;
Tu, Jie-Feng
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機械工程學系
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Department of Mechanical Engineering
The mechanical properties of graphite in the forms of single graphene layer and graphite flakes (containing several graphene layers) were investigated using molecular dynamics (MD) simulation. The in-plane properties, Young's modulus, Poisson's ratio, and shear modulus, were measured, respectively, by applying axial tensile stress and in-plane shear stress on the simulation box through the modified NPT ensemble. In order to validate the results, the conventional NVT ensemble with the applied uniform strain filed in the simulation box was adopted in the MD simulation. Results indicated that the modified NPT ensemble is capable of characterizing the material properties of atomistic structures with accuracy. In addition, it was found the graphene layers exhibit higher moduli than the graphite flakes: thus, it was suggested that the graphite flakes have to be expanded and exfoliated into numbers of single graphene layers in order to provide better reinforcement effect in nanocomposites. (C) 2009 Elsevier Ltd. All rights reserved.
Characterizing mechanical properties of particulate nanocomposites using micromechanical approach
(2008-11-01)
Tsai, Jia-Lin
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Tzeng, Shi-Hua
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機械工程學系
;
Department of Mechanical Engineering
This research aims to propose a continuous micromechanical model for characterizing the mechanical properties of the nanocomposites containing silica nanoparticles embedded in polyimide matrix. The molecular structures of the nanocomposites were established through molecular dynamic ( MD) simulation, from which the non-bonded gap as well as the non-bonded energy between the nano-sized inclusion and the surrounding matrix were evaluated. It was postulated that the normalized non-bonded energy (non-bonded energy divided by surface area of the inclusion) is correlated with the degree of interfacial interaction. Subsequently, an effective interphase micromechanical model including inclusion, matrix and effective interphase was developed, in which the dimension of the effective interphase was assumed equal to the non-bonded gap and the corresponding elastic stiffness was calculated from the normalized non-bonded energy. Comparison of the results calculated from the micromechanical model and the MD simulation indicates that the effective interphase model is capable of describing Young's modulus of particulate nanocomposites with accuracy. In addition, it was revealed that when the particulate size decreases, the corresponding modulus of the nanocomposites increases.
Characterizing nonlinear rate-dependent behaviors of graphite/epoxy composites using a micromechanical approach
(2007-05-01)
Tsai, Jia-Lin
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Chen, Kuei-Han
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機械工程學系
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Department of Mechanical Engineering
This research aims to characterize the nonlinear rate-dependent behaviors of graphite/epoxy composites using micromechanical analysis. In this analysis, graphite fibers are considered as elastic solids, while the surrounding epoxy matrix exhibiting rate sensitivities are described using the three-parameter viscoplasticity model. By using Aboudi's generalized method of cells (GMC), the incremental form of the constitutive relations of the composites are expressed in terms of the constituent properties as well as the geometry parameters of the representative volume element. After a numerical iteration, the corresponding stress and strain relations of composites at different strain rates are generated. In order to verify the model predictions, off-axis graphite/epoxy composite specimens are tested at strain rates from 10(-4) to 550/s. For strain rates less than 1/s, the experiments are conducted using a hydraulic MTS machine, while high-strain-rate tests were carried out using a split Hopkinson pressure bar. Experimental results indicate that the stress and strain curves are quite sensitive to the strain rate; moreover, when the strain rates increase, the material stiffens. A comparison of model predictions with experimental results indicates that the rate-dependent behaviors of composites can be characterized effectively with the GMC model in conjunction with the viscoplastic properties of epoxy.
CHARACTERIZING TENSILE STRENGTH OF NOTCHED CROSS-PLY AND QUASI-ISOTROPIC COMPOSITE LAMINATES
(2009)
Tsai, Jia-Lin
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Chen, Chung-Wen
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機械工程學系
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Department of Mechanical Engineering
This study aims to investigate fracture behaviors of notched cross-ply and quasiisotropic laminates with different stacking configurations. The fracture criterion developed by Vaidya and Sun (1997), based on the postulation that the failure was dominated by the 0 degree ply, was adopted to characterize the failure stresses of the notched laminates. The failure mechanisms of the samples were determined through X-ray examinations. It was found that for [0/90](2s), [90/0](2s), [0/+/- 45/90](2s), and [90/+/- 45/0](2s) laminates, the strengths were quite close to the model predictions. This occurred because there were no severe damage zones observed near the crack tip; therefore, the failure stresses of the notched laminates were dominated by the stress states of 0 degree ply, which can be properly characterized using the fracture mechanics in conjunction with the laminated plate theory. However, for [0(2)/90(2)](2s) and [90(2)/0(2)](s) laminates, there were severe damage zones observed near the crack tip such that the predicted failures stresses were lower than the experimental data. In contrast, for the [90(2)/+/- 45(2)/0(2)](s) and [02/+/- 45(2)/90(2)](s), because of the edge delamination taking place within the plies, the failure stresses were considerably lower than the predictions.
Characterizing the fracture parameters of a graphene sheet using atomistic simulation and continuum mechanics
(2010-02-01)
Tsai, Jia-Lin
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Tzeng, Shi-Hua
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Tzou, Yu-Jen
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機械工程學系
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Department of Mechanical Engineering
The fracture behavior of a graphene sheet, containing a center crack (length of 2a) was characterized based on the atomistic simulation and the concept of continuum mechanics. Two failure modes, i.e., opening mode (Mode I) and sliding mode (Mode II), were considered by applying remote tensile and shear loading, respectively, on the graphene sheet. In the atomistic simulation, the equilibrium configurations of the cracked graphene subjected to applied loadings, before and after the crack extension of 2 Delta a, were determined through molecular dynamics (MD) simulation, from which the variation of the potential energy and the strain energy release rate of the discrete graphene sheet because of crack extension was calculated accordingly. It is noted that because of the discrete attribute, there is no stress singularity near the crack tip, and thus, the concept of stress intensity factor that is generally employed in the continuum mechanics may not be suitable for modeling the crack behavior in the atomistic structures. For the sake of comparison, the continuum finite element model with the same geometric parameters and material properties as the atomistic graphene sheet was constructed, and the corresponding strain energy release rate was calculated from the crack closure method. Results indicated that the strain energy release rates obtained from the continuum model exhibit good agreement with those derived from discrete atomistic model. Therefore, it is suggested that the strain energy release rate is an appropriate parameter, which can be employed in the atomistic model and the continuum model for describing the fracture of covalently bonded graphene sheet. (C) 2009 Elsevier Ltd. All rights reserved.
Characterizing the interfacial shear strength of graphite/epoxy composites containing functionalized graphene
(2016-08-01)
Lee, Ming-Wei
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Wang, Tai-Yuan
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This study investigated the interfacial shear strength (IFSS) of graphite/epoxy composites containing functionalized graphene. Epoxy resin together with pristine graphene and functionalized graphene were employed as a matrix in the fiber composites, with graphene loadings in the epoxy matrix of 0.1, 0.3, and 0.5 wt%. The functional groups grafted on the functionalized graphene were characterized through Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The IFSS of the fiber composites were evaluated through microdroplet testing, and the corresponding failure mechanism was examined using scanning electrical microscopy. The experimental results indicated that the IFSS increased with the graphene loadings in the matrix. Furthermore, both functionalized graphene and pristine graphene provided a similar IFSS in the fiber composites. Observation of the failure interface showed that the failure mechanism of the IFSS was dominated by interfacial failure between the fiber and matrix in conjunction with adhesive failure in the matrix. Introducing graphene in the matrix can enhance IFSS by improving the adhesive strength in the interface as well as complicating the crack extension in the matrix. (C) 2016 Elsevier Ltd. All rights reserved.
Characterizing the Stress Intensity Factor of Graphene Sheet with Central Crack
(2015-05-01)
Tsai, Jia-Lin
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Sie, Meng-Jhe
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機械工程學系
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Department of Mechanical Engineering
This paper aims to characterize the stress intensity factor (SIF) of atomistic graphene sheet with central crack subjected to uniaxial loading. The equilibrium configuration of the defective graphene sheet with missing covalent bonds was generated through molecular dynamics (MD) simulation. Subsequently, the local stress distribution near the crack tip of atomistic structure was evaluated using the Hardy stress formulation as well as the non-local elasticity theory. Based on the local stress distributions, the SIF of the atomistic graphene sheet was determined through the projection process. In comparison, the graphene sheet was also treated as a continuum solid, and the stress distribution near the crack tip as well as the SIF were evaluated from the finite element method (FEM). In an attempt to understand the crack size effect, the crack length was assumed to vary from 3 lattice distance to around 80 lattice distance. Results revealed that the SIF calculated based on the nonlocal elasticity theory in conjunction with the projection process is quite sensitive to the selection of the projection point. However, for the Hardy stress distribution, when the projection position is 1 lattice distance away from the crack tip, the SIF is quite consistent and the result is compatible to that obtained from the FEM analysis. Moreover, the agreement is better as the crack size is increasing. Therefore, the SIF calculated based on the Hardy stress formulation together with the projection approach could be a physical quantity correlating the defective atomistic graphene sheet with its continuum counterpart.
Characterizing thermal and mechanical properties of graphene/epoxy nanocomposites
(2014-01-01)
Shiu, Sung-Chiun
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This study aims to investigate the thermal and mechanical properties of graphene/epoxy nanocomposites using molecular dynamics (MD) simulation. Three different formats of graphene: graphene flakes, intercalated graphene and intercalated graphene oxide, were incorporated respectively in an epoxy matrix to form the graphene/epoxy nanocomposites. The mechanical properties of the graphene/epoxy nanocomposites, including Young's modulus (E), glass transition temperature (T-g) and coefficient of thermal expansion (CTE), in terms of three different formats of graphene, were characterized in this study. In addition to the mechanical properties, the influences of graphene on the density distribution of epoxy polymers in the nanocomposites were also examined. The results showed that the local density in the vicinity of the graphene is relatively high, and then progressively decreases to the bulk value in regions further away from the interface. On the other hand, for the mechanical and thermal properties, the nanocomposites with intercalated graphene exhibit a higher Young's modulus, a higher glass transition temperature and a lower thermal expansion coefficient than do those with graphene flakes. This is because the intercalated graphene can lead to a high amount of high density polymer in the nanocomposites, and thus enhance the overall properties of the nanocomposites. In addition, the interacted graphene oxide provides the best reinforcement of the three systems of nanocomposites. Based on the calculation of interaction energy, it appears that the oxide modification of the graphene surface can effectively lead to the high interaction energy, such that the graphene oxide can demonstrate a relatively high reinforcing efficiency. (C) 2013 Elsevier Ltd. All rights reserved.
Characterizing thermal and mechanical properties of graphene/epoxy nanocomposites
(2013-01-01)
Shiu, Sung-Chiun
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This study aims to investigate the thermal and mechanical properties of graphene/epoxy nanocomposites using molecular dynamics (MD) simulation. Three different formats of graphene: graphene flakes, intercalated graphene and intercalated graphene oxide, were incorporated respectively in an epoxy matrix to form the graphene/epoxy nanocomposites. The mechanical properties of the graphene/epoxy nanocomposites, including Young's modulus (E), glass transition temperature (T-g) and coefficient of thermal expansion (CTE), in terms of three different formats of graphene, were characterized in this study. In addition to the mechanical properties, the influences of graphene on the density distribution of epoxy polymers in the nanocomposites were also examined. The results showed that the local density in the vicinity of the graphene is relatively high, and then progressively decreases to the bulk value in regions further away from the interface. On the other hand, for the mechanical and thermal properties, the nanocomposites with intercalated graphene exhibit a higher Young's modulus, a higher glass transition temperature and a lower thermal expansion coefficient than do those with graphene flakes. This is because the intercalated graphene can lead to a high amount of high density polymer in the nanocomposites, and thus enhance the overall properties of the nanocomposites. In addition, the interacted graphene oxide provides the best reinforcement of the three systems of nanocomposites. Based on the calculation of interaction energy, it appears that the oxide modification of the graphene surface can effectively lead to the high interaction energy, such that the graphene oxide can demonstrate a relatively high reinforcing efficiency. (C) 2013 Elsevier Ltd. All rights reserved.
Characterizing vibration damping response of composite laminates containing silica nanoparticles and rubber particles
(2015-03-01)
Huang, Chien-Yang
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Tsai, Jia-Lin
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機械工程學系
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Department of Mechanical Engineering
This research aims to characterize the damping properties of fiber/epoxy composites containing different degrees of silica nanoparticles and rubber particles. Conventionally, adding rubber particles into fiber/epoxy composites would lead to dramatic reduction of stiffness although the vibration damping could be improved accordingly. In order to enhance the damping properties of the fiber composites without sacrificing the stiffness, silica nanoparticles together with rubber particles were introduced into the epoxy resin through the sonication process. The epoxy resin was then treated as matrix and impregnated into the fiber layer by means of the vacuum hand lay-up process to form the composite laminates. The vibration damping as well as the flexural stiffness of the fiber composite was measured using the forced vibration technique together with the half-power method. In addition, the vibration damping of the composite laminates, consisting of silica nanoparticles and rubber particles, was characterized using the micromechanical analysis. The repeated unit cell with the fibers displaying randomly in the matrix was employed to represent the microstructures of the unidirectional composites. The loss factor as well as the moduli obtained from the micromechanical analysis were regarded as the effective properties homogenizing within the fiber composites. In conjunction with the modal shapes, the vibration damping of the composite laminates with stacking sequence of [0](10), [90](10), [+/- 45](2s), and [90/0](2s) was calculated using the finite element analysis. Experimental results indicated that with the incorporation of the silica nanoparticles together with the rubber particles, the reduction of flexural stiffness of fiber composites, especially for the [90](10) laminates, was diminished while the damping properties of laminates were improved. Moreover, it was found that the effect of the particles in the [0](10) laminates is relatively minimal. The vibration damping responses of composites laminates obtained using the micromechanical analysis together with the modal analysis exhibit an agreement with the experimental data.
Effect of fiber array on damping behaviors of fiber composites
(2008-10-01)
Tsai, Jia-Lin
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Chi, Yang-Kai
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機械工程學系
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Department of Mechanical Engineering
This study aims to investigate the fiber array effect on modal damping behaviors of fiber composites. Three different fiber arrays, i.e., square edge packing (SEP), square diagonal packing (SDP), and hexagonal packing (HP), were considered to represent the microstructures of the unidirectional composites. Repeating unit cells (RUCs) suitable for describing the characteristics of the microstructure were adopted in the generalized method of cell (GMC) micromechanical analysis. The energy dissipation concept was then employed to calculate the specific damping capacities of composites in the material principal directions. The specific damping capacities obtained from micromechanical analysis were regarded as the equivalent damping properties homogenizing in the composites. In conjunction with the modal shapes of the composite structures determined from the finite element analysis, the specific damping capacity was extended to characterize the corresponding modal damping of the composite rods and plates. Both free-free and clamped-free boundary conditions were taken into account in the composite structures. Results indicated that the structures constructed from the composites with SDP fibers exhibit better damping behaviors than the other two cases. (c) 2008 Elsevier Ltd. All rights reserved.
Enhancing Fracture Toughness of Glass/Epoxy Composites by Using Rubber Particles Together with Silica Nanoparticles
(2009-12-01)
Tsai, Jia-Lin
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Huang, Bao-Hung
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Cheng, Yi-Lieh
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機械工程學系
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Department of Mechanical Engineering
The research aims to investigate the interlaminar fracture toughness of glass fiber/epoxy composites, which consist of the silica nanoparticles and the rubber particles. Two kinds of rubber particles, one is the reactive liquid rubber (CTBN) and the other is the core-shell rubber (CSR), were employed to modify the fracture toughness of epoxy resin. In general, the disadvantage of adding rubber particles into polymeric resin is the dramatic reduction of stiffness although the toughness could be modified accordingly. In order to enhance the fracture toughness of the fiber composites without sacrificing their stiffness, the silica nanoparticles in conjunction with the rubber particles were introduced into the epoxy matrix to form a hybrid nanocomposite. Experimental results obtained from tensile tests on bulk epoxy confirm the presumption that the reduction of the epoxy stiffness because of the presence of rubber particles can be effectively compensated by the silica nanoparticles. Furthermore, the fracture tests conducted on the double cantilever beam specimens revealed that the inclusion of silica nanoparticles together with the CSR particle can appreciably increase the fracture toughness of the glass/epoxy composites up to 82%. On the other hand, when the epoxy matrices were modified with CTBN rubber particles and silica nanoparticles, the improvement of the interlaminar fracture toughness was around 48%. It is noted that the role of the silica nanoparticles on the fracture toughness of fiber composites with rubber-modified epoxy matrix is different. For the CSR-modified epoxy matrix, the contribution of silica nanoparticle on the fracture toughness is destructive. In contrast, for the CTBN-modified epoxy matrix, the silica nanoparticles can synchronously improve the fracture toughness of composites.
Investigate Mechanical Behavior of Gold Nanowire with Defect
(2014)
Tsai, Jia-Lin
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Hong, Cheng-Fong
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機械工程學系
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Department of Mechanical Engineering
This study aims to investigate the mechanical properties of gold nanowires using molecular dynamics (MD) simulation. The effects of the cross section size and the defects on the stress strain curves of the nanowires are examined. Moreover, the inception as well as the processing of dislocationin the nanowire is accounted by means of the centro-symmetry parameter and meanwhile, the energy variation during the dislocation is calculated. Results indicated for the pristine gold nanowire, as the cross section size increases, Young\'s modulus increases, but the yielding stress decreases accordingly. Once the ultimate linear point is attained, the dislocation takes place abruptly from the nanowire surfaceand extended along the {111} planes. On the other hand, for the nanowire with defect, it was found that the dislocation is initiated from the defect which can significantlyreduce the yielding stress of the nanowires.
Investigating Mechanical Behaviors of Silica Nanoparticle Reinforced Composites
(2010-02-01)
Tsai, Jia-Lin
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Hsiao, Hung
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Cheng, Yi-Lieh
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機械工程學系
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Department of Mechanical Engineering
The research is aimed to investigate the mechanical behaviors of epoxy-based nanocomposites reinforced with spherical nanoparticles. Five different contents of silica nanoparticles -5, 10, 15, 20, and 40 wt% - were introduced in the samples. Through a sol-gel technique, the silica particles with a diameter of 25 nm were exfoliated uniformly in the epoxy matrix. Experimental results obtained from tensile tests indicate that the modulus of nanocomposites increases with the increment of particulate inclusions, and the enhancing behavior is coincided with the model predictions obtained from the Mori-Tanaka micromechanical model. In addition, the fracture tests conducted on single-edge-notch bending specimens reveal that the inclusion of nanoparticles can effectively increase the fracture toughness of the nanocomposites. Furthermore, the extent of the enhancement is more appreciable in the brittle matrix system rather than in the ductile matrix system. Subsequently, by inserting the silica epoxy mixture into the unidirectional glass fiber through a vacuum hand lay-up process, the glass fiber/silica/epoxy composite samples were fabricated. Results depicted that the in-plane shear strength increases until the increment of particle loadings are up to 10 wt%. In addition, results obtained from the compression tests revealed that the glass/epoxy specimens with 20 wt% silica loading exhibit superior compressive strengths than those that do not contain any silica particles.