Browsing by Author "Tsou, Nien-Ti"

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A Hybrid Model for Predicting Bone Healing around Dental Implants
(2020-06-01)
Kung, Pei-Ching
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Chien, Shih-Shun
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Tsou, Nien-Ti
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材料科學與工程學系
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Department of Materials Science and Engineering
Background: The effect of the short-term bone healing process is typically neglected in numerical models of bone remodeling for dental implants. In this study, a hybrid two-step algorithm was proposed to enable a more accurate prediction for the performance of dental implants. Methods: A mechano-regulation algorithm was firstly used to simulate the tissue differentiation around a dental implant during the short-term bone healing. Then, the result was used as the initial state of the bone remodeling model to simulate the long-term healing of the bones. The algorithm was implemented by a 3D finite element model. Results: The current hybrid model reproduced several features which were discovered in the experiments, such as stress shielding effect, high strength bone connective tissue bands, and marginal bone loss. A reasonable location of bone resorptions and the stability of the dental implant is predicted, compared with those predicted by the conventional bone remodeling model. Conclusions: The hybrid model developed here predicted bone healing processes around dental implants more accurately. It can be used to study bone healing before implantation surgery and assist in the customization of dental implants.
Classification and analysis of trigonal martensite laminate twins in shape memory alloys
(2015-05-01)
Tsou, Nien-Ti
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Chen, Chih-Hsuan
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Chen, Chuin-Shan
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Wu, Shyi-Kaan
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材料科學與工程學系
In the trigonal martensite shape memory alloys (SMAs), typically only the well-known classic herringbone pattern satisfies the nonlinear compatibility theory. However, many other interesting trigonal patterns are still possible. Thus, geometrically linear compatibility theory is first used to obtain the full set of rank-2 laminate twin patterns which can possibly form in the trigonal SMAs. There are only seven families of twin pattern, including many new structures, such as checkerboard, toothbrush and non-classic herringbone patterns. These microstructures are confirmed in the trigonal R-phase Ti50.3Ni48.2Fe1.5 SMA. The interfaces separating the seven families and their parent phase (austenite) are also determined and observed. The results show that minor geometrical incompatibility of microstructures can be tolerated in the trigonal R-phase SMAs. Next, a numerical method based on non-linear compatibility theory is developed to evaluate the parameter for measuring the defect of disclination in these patterns. The greater the value of the parameter is, the less likely the pattern could be observed in the experiments. The likelihood of occurrence of all seven families in the typical trigonal SMAs is revealed in the current work. Moreover, 3-dimensional unit cell alignment of the patterns is illustrated. The loading conditions to avoid the disclination are also discussed. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Control of Dopant Distribution in Yttrium-Doped Bioactive Glass for Selective Internal Radiotherapy Applications Using Spray Pyrolysis
(2019-03-25)
Tesfay, Abadi Hadush
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Chou, Yu-Jen
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Tan, Cheng-Yan
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Bakare, Fetene Fufa
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Tsou, Nien-Ti
In this study, we demonstrate the fabrication of Y-doped bioactive glass (BG), which is proposed as a potential material for selective internal radiotherapy applications. Owing to its superior bioactivity and biodegradability, it overcomes the problem of yttrium aluminosilicate spheres that remain in the host body for a long duration after treatment. The preparation of Y-doped BG powders were carried out using a spray pyrolysis method. By using two different yttrium sources, we examine the change of the local distribution of yttrium concentration. In addition, characterizations of phase information, particle morphologies, surface areas, and bioactivity were also performed. The results show that both Y-doped BG powders are bioactive and the local Y distribution can be controlled.
Giant Resistivity Change of Transparent ZnO/Muscovite Heteroepitaxy
(2020-05-13)
Yen, Min
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Lai, Yu-Hong
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Zhang, Chun-Li
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Cheng, Hou-Yung
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Hsieh, Yi-Ting
The piezoresistive effect has shown a remarkable potential for mechanical sensor applications and been sought for its excellent performance. A great attention was paid to the giant piezoresistive effect and sensitivity delivered by silicon-based nanostructures. However, low thermal stability and complicated fabrication process hinder their practical applications. To overcome these issues and enhance the functionalities, we envision the substantial piezopotential in a zinc oxide (ZnO)/muscovite (mica) heteroepitaxy system based on theoretical consideration and realize it in practice. High piezoresistive effect with giant change of resistivity (-80 to 240%) and large gauge factor (>1000) are demonstrated through mechanical bending. The detailed features of heteroepitaxy, electrical transport, and strain are probed to understand the mechanism of such a giant resistivity change. In addition, a bending model is established to reveal the distribution of strain. Finally, we demonstrate a flex sensor featuring high sensitivity, optical transparency, and two-segment sensing with a great potential toward practical applications. Such an oxide heteroepitaxy exhibits excellent piezoresistive properties and mechanical flexibility. In the near future, the importance of flex sensors will emerge because of the precise control in the automation industries, and our results lead to a new design in the field of flex sensors.
Hardening steels by the generation of transient phase using additive manufacturing
(2019-06-01)
Huang, E-Wen
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Lee, Soo Yeol
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Jain, Jayant
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Tong, Yang
;
An, Ke
In the present work, the tensile properties of 15-5 PH steel fabricated by selective laser melting (SLM) were examined with respect to the transient austenite phase. Compared with the 8%-transient-phase sample, the 18%-transient-phase one shows higher ultimate tensile strength and relatively low yield strength, as well as hardening behavior. We conducted in-situ neutron-diffraction study to examine the microstructure evolution for mechanistic understanding. After applying the external load, most non-equilibrium, retained austenite in the 8% transient-phase sample transforms before the yield strength, whereas in the 18%-transient-phase sample only 50% of the austenite transforms. Accompanying with the phase transformation, a decrease in the dislocation density and the dislocation strain energy-assisted phase transformation of the ferrite phase are found in the 8%-transient-phase sample even before yielding, which, however, is not the case in the 18%-transient-phase sample. The study demonstrates the SLM enables tuning the amount of transient-phase ratio and coherency between phases to realize a mechanical property control for additive manufactured steel.
Microstructural analysis and molecular dynamics modeling of shape memory alloys
(2017-04-15)
Yang, Chia-Wei
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Tsou, Nien-Ti
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材料科學與工程學系
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Department of Materials Science and Engineering
Molecular dynamics (MD) is an effective tool for studying the microstructures in shape memory alloys at the atomic level. However, microstructural analysis of the results generated by MD is typically done by examining lattice constants or monoclinic angles, and only a limited set of the crystal variants can be identified. In the current work, a numerical method that can identify the crystal variants and multiple phases is proposed. By observing the pattern of the components in the transformation matrix of the lattice in the crystal, the corresponding variant of the lattice can be determined. The method is then applied to study the martensitic transformation induced by temperature and ultrahigh shear strain, and the resulting microstructures are verified by literature. Moreover, the microstructural evolution and the volume fraction variation of the crystal variants under ultrahigh shear strain are examined. The observed multiple stages of phase transitions imply that the current method is able to identify the austenitic, orthorhombic, trigonal (R phase), monoclinic, and body-centered orthorhombic crystal systems simultaneously. The proposed method also reveals that the nanometer-sized R phase is a transition zone that maintains the compatibility between the two phases in the different crystal systems. The proposed method is rapid, accurate, and sufficiently versatile to be applicable to other crystal systems and related materials. (C) 2017 Elsevier B.V. All rights reserved.
Multi-scale mapping for collagen-regulated mineralization in bone remodeling of additive manufacturing porous implants
(2019-05-15)
Tsai, Pei-I.
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Lam, Tu-Ngoc
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Wu, Meng-Huang
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Tseng, Kuan-Ying
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Chang, Yuan-Wei
Long term success of metallic fusion cages depends on mechanobiological processes through the bone incorporation and rich osseointegration. An optimal configuration of porous titanium-aluminum-vanadium (Ti-6Al-4V) implant fabricated via the additive manufacturing was evaluated in complimentary structure examinations to investigate the growth of autologous osseous at multi-length scales. X-ray microcomputed tomography (micro-CT) and transmission X-ray microscopy (TXM) using newly-built analysis method indicate the porous Ti-6Al-4V is much better for bone ingrowth compared to commercially non-porous titanium (Ti) and porous tantalum (Ta) implants at the ultramicrostructural level. The evolution of bone formation and remodeling acquired by nano X-ray Laue diffraction mapping exhibits the isotropic orientation and low crystallinity of all newly formed bone whereas mature bone in Ti-6Al-4V discloses the preferential alignment and higher crystallinity volumes of constituent hydroxyapatite (HA) crystallites. The high degree in mineral crystallinity of the fully mature bone suggests additive manufactured Ti-6Al-4V pores enhance the collagen-regulated mineralization.
Numerical Method for the Design of Healing Chamber in Additive-Manufactured Dental Implants
(2017)
Lee, Hsiao-Chien
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Tsai, Pei-I
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Huang, Chih-Chieh
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Chen, San-Yuan
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Chao, Chuen-Guang
The inclusion of a healing chamber in dental implants has been shown to promote biological healing. In this paper, a novel numerical approach to the design of the healing chamber for additive-manufactured dental implants is proposed. This study developed an algorithm for the modeling of bone growth and employed finite element method in ANSYS to facilitate the design of healing chambers with a highly complex configuration. The model was then applied to the design of dental implants for insertion into the posterior maxillary bones. Two types of ITI (R) solid cylindrical screwed implant with extra rectangular-shaped healing chamber as an initial design are adopted, with which to evaluate the proposed system. This resulted in several configurations for the healing chamber, which were then evaluated based on the corresponding volume fraction of healthy surrounding bone. The best of these implants resulted in a healing chamber surrounded by around 9.2% more healthy bone than that obtained from the original design. The optimal design increased the contact area between the bone and implant by around 52.9%, which is expected to have a significant effect on osseointegration. The proposed approach is highly efficient which typically completes the optimization of each implant within 3-5 days on an ordinary personal computer. It is also sufficiently general to permit extension to various loading conditions.
Numerical Method for the Design of Healing Chamber in Additive-Manufactured Dental Implants
(2017-01-01)
Lee, Hsiao-Chien
;
Tsai, Pei-I
;
Huang, Chih-Chieh
;
Chen, San-Yuan
;
Chao, Chuen-Guang
The inclusion of a healing chamber in dental implants has been shown to promote biological healing. In this paper, a novel numerical approach to the design of the healing chamber for additive-manufactured dental implants is proposed. This study developed an algorithm for the modeling of bone growth and employed finite element method in ANSYS to facilitate the design of healing chambers with a highly complex configuration. The model was then applied to the design of dental implants for insertion into the posterior maxillary bones. Two types of ITI (R) solid cylindrical screwed implant with extra rectangular-shaped healing chamber as an initial design are adopted, with which to evaluate the proposed system. This resulted in several configurations for the healing chamber, which were then evaluated based on the corresponding volume fraction of healthy surrounding bone. The best of these implants resulted in a healing chamber surrounded by around 9.2% more healthy bone than that obtained from the original design. The optimal design increased the contact area between the bone and implant by around 52.9%, which is expected to have a significant effect on osseointegration. The proposed approach is highly efficient which typically completes the optimization of each implant within 3-5 days on an ordinary personal computer. It is also sufficiently general to permit extension to various loading conditions.
Preface: Nano/Micro Structures in Application of Computational Mechanics
(2019-01-01)
Lee, Chang-Chun
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Tsou, Nien-Ti
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Kim, Taek-Soo
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材料科學與工程學系
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Department of Materials Science and Engineering
Preparation and in Vitro Bioactivity of Micron-sized Bioactive Glass Particles Using Spray Drying Method
(2019-01-01)
Chou, Yu-Jen
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Hsiao, Chih-Wei
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Tsou, Nien-Ti
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Wu, Meng-Huang
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Shih, Shao-Ju
In recent years, bioactive glasses (BGs) have attracted enormous attention with their superior bioactivity, non-toxicity and degradability. Owing to their properties, they have been applied in various biological applications. In the present work, we demonstrated that micron-sized BGs can be prepared with a spray drying method. This technique offers the advantages of low contamination and the ability of mass production, in contrast to the two major synthetic methods, conventional glass-melting and sol-gel, previously used for preparation of BGs. Characterizations of phase composition, morphology and specific surface area of spray dried BG powders were carried out and bioactivity was examined in vitro with respect to the ability to form a hydroxyapatite layer on the surface of the particles after they were immersed in simulated body fluid.
Relationships among the structural topology, bond strength, and mechanical properties of single-walled aluminosilicate nanotubes
(2015-01-01)
Liou, Kai-Hsin
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Tsou, Nien-Ti
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Kang, Dun-Yen
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材料科學與工程學系
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Department of Materials Science and Engineering
Carbon nanotubes (CNTs) are regarded as small but strong due to their nanoscale microstructure and high mechanical strength (Young\'s modulus exceeds 1000 GPa). A longstanding question has been whether there exist other nanotube materials with mechanical properties as good as those of CNTs. In this study, we investigated the mechanical properties of single-walled aluminosilicate nanotubes (AlSiNTs) using a multiscale computational method and then conducted a comparison with single-walled carbon nanotubes (SWCNTs). By comparing the potential energy estimated from molecular and macroscopic material mechanics, we were able to model the chemical bonds as beam elements for the nanoscale continuum modeling. This method allowed for simulated mechanical tests (tensile, bending, and torsion) with minimum computational resources for deducing their Young\'s modulus and shear modulus. The proposed approach also enabled the creation of hypothetical nanotubes to elucidate the relative contributions of bond strength and nanotube structural topology to overall nanotube mechanical strength. Our results indicated that it is the structural topology rather than bond strength that dominates the mechanical properties of the nanotubes. Finally, we investigated the relationship between the structural topology and the mechanical properties by analyzing the von Mises stress distribution in the nanotubes. The proposed methodology proved effective in rationalizing differences in the mechanical properties of AlSiNTs and SWCNTs. Furthermore, this approach could be applied to the exploration of new high-strength nanotube materials.
The Analysis of Superelasticity and Microstructural Evolution in NiTi Single Crystals by Molecular Dynamics
(2019-01-01)
Lu, Hung-Yuan
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Chen, Chih-Hsuan
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Tsou, Nien-Ti
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材料科學與工程學系
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Department of Materials Science and Engineering
Superelasticity in shape memory alloys is an important feature for actuators and medical devices. However, the function of the devices is typically limited by mechanical bandwidth and fatigue, which are dominated by the microstructures. Thus, in order to correlate the mechanical response and the microstructures, the microstructural evolution in NiTi single crystals under the compression, tensile, and shearing tests is simulated by molecular dynamics (MD) in the current study. Then, the martensite variant identification method, which identifies the crystal variants/phases of each lattice based on the transformation matrix, is used to post-process the MD results. The results with the detailed information of variants and phases reveal many features that have good agreement with those reported in the literature, such as X-interfaces and the transitional orthorhombic phase between the austenite and monoclinic phases. A new twin structure consisting of diamond and wedge-shaped patterns is also discovered. The macroscopic behavior, such as stress-strain curves and the total energy profile, is linked with the distribution of dislocation and twin patterns. The results suggest that the loading cases of shear and compression allow a low critical strain for the onset of martensitic transformation and a better superelasticity behavior. Therefore, the two loading cases are suitable to apply to the NiTi actuators. The current work is expected to provide insight into the mechanical responses and design guideline for NiTi shape memory alloy actuators.
The Analysis of Thermal-Induced Phase Transformation and Microstructural Evolution in Ni-Ti Based Shape Memory Alloys By Molecular Dynamics
(2019-01-01)
Chen, Hsin-Yu
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Tsou, Nien-Ti
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材料科學與工程學系
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Department of Materials Science and Engineering
Shape memory alloys has been widely applied on actuators and medical devices. The transformation temperature and microstructural evolution play two crucial factors and dominate the behavior of shape memory alloys. In order to understand the influence of the composition of the Ni-Ti alloys on the two factors, molecular dynamics was adopted to simulate the temperature-induced phase transformation. The results were post-processed by the martensite variant identification method. The method allows to reveal the detailed microstructural evolution of variants/phases in each case of the composition of Ni-Ti. Many features were found and having good agreement with those reported in the literature, such as the well-known Rank-2 herringbone structures; the X-interface; Ni-rich alloys have lower transformation temperature than Ti-rich alloys. In addition, some new features were also discovered. For example, the Ti-rich alloys enabled an easier martensitic transformation; the nucleated martensite pattern determined the microstructural evolution path, which also changed the atomic volume and temperature curves. The results generated in the current study are expected to provide the design guidelines for the applications of shape memory alloys.
The design and analysis for low-frequency piezoelectric cymbal transducers
(2017-01-01)
Goh, Pin Hong
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Li, Ming-Jun
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Tsou, Nien-Ti
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機械工程學系
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材料科學與工程學系
Piezoelectric cymbal transducers (PCT) have been widely used in energy harvesting. Previous researches recommend PCTs with symmetric geometry to avoid the disadvantages, such as failure of the epoxy layers due to the high frequency loads. In the current study, the applicability of the asymmetric cymbal transducer for low frequency is evaluated by finite element method. Three types of transducers are compared, including Type I, which is the conventional transducer, Type II with the apexes of the top and bottom cymbals shifted in the same directions, and Type III with the apexes shifted in the opposite direction. The results show that the optimized Type II and III transducers improve power output by 7.1% and 15.9%, respectively, compared with Type I. Moreover, a numerical method is proposed to decompose the strain states of the piezoelectric disc into the superposition of sets of the strain state basis of the radial resonance modal shapes. The results reveal the relationship between the resonant modal shapes and the increase of the power output. A new design of PCT is proposed. The current work provides design guideline for the application to energy harvesting systems which is particularly suitable for traffic-induced vibrations.
The evolution of compatible microstructures in shape memory alloys
(2014-01-01)
Tsou, Nien-Ti
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材料科學與工程學系
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Department of Materials Science and Engineering
Shape memory alloys (SMAs) have been extensively used in sensors and actuators. Their behavior is dominated by the microstructures. Observations show that martensite twins usually form laminated patterns with interfaces that satisfy the compatibility equation to minimize the total energy. However, due to high nonlinearity of the material, the relationship between the overall response and microstructure has not yet been revealed. In this study, we identify the set of possible twin structures and the paths along which the microstructure evolves continuously between austenite and martensite phases under loads. The variational principle is used to capture the dissipative nature of interface motion in microstructures when phase transformation occurs. The model is applied to study superelasticity effect in Cu-Al-Ni single crystals. Many subtle features are explained. (C) 2014 Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.