• Journal of Periodontal and Implant Science
• /
• 제49권1호
• /
• pp.25-38
• /
• 2019

Purpose: This study evaluated differences in bone healing and remodeling among 3 implants with different surfaces: sandblasting and large-grit acid etching (SLA; IS-III $Active^{(R)}$), SLA with hydroxyapatite nanocoating (IS-III $Bioactive^{(R)}$), and SLA stored in sodium chloride solution ($SLActive^{(R)}$). Methods: The mandibular second, third, and fourth premolars of 9 dogs were extracted. After 4 weeks, 9 dogs with edentulous alveolar ridges underwent surgical placement of 3 implants bilaterally and were allowed to heal for 2, 4, or 12 weeks. Histologic and histomorphometric analyses were performed on 54 stained slides based on the following parameters: vertical marginal bone loss at the buccal and lingual aspects of the implant (b-MBL and l-MBL, respectively), mineralized bone-to-implant contact (mBIC), osteoid-to-implant contact (OIC), total bone-to-implant contact (tBIC), mineralized bone area fraction occupied (mBAFO), osteoid area fraction occupied (OAFO), and total bone area fraction occupied (tBAFO) in the threads of the region of interest. Two-way analysis of variance (3 types of implant $surface{\times}3$ healing time periods) and additional analyses for simple effects were performed. Results: Statistically significant differences were observed across the implant surfaces for OIC, mBIC, tBIC, OAFO, and tBAFO. Statistically significant differences were observed over time for l-MBL, mBIC, tBIC, mBAFO, and tBAFO. In addition, an interaction effect between the implant surface and the healing time period was observed for mBIC, tBIC, and mBAFO. Conclusions: Our results suggest that implant surface wettability facilitates bone healing dynamics, which could be attributed to the improvement of early osseointegration. In addition, osteoblasts might become more activated with the use of HA-coated surface implants than with hydrophobic surface implants in the remodeling phase.

• 대한기계학회논문집A
• /
• 제26권1호
• /
• pp.196-202
• /
• 2002

In this work, we propose a new type of HDD suspension featuring shape memory alloy (SMA) actuator in order to prevent the contact between the slider and disk. The principal design parameters are obtained from the modal analysis using finite element analysis, and then the dynamic model is established to formulate the control scheme for Non-Contact Start/stop mode drive. Subsequently, a robust H$\_$$\infty$/ control algorithm is designed by integrating experimentally-Obtained SMA actuator dynamics to the proposed HDD suspension system. The controller is empirically realized and control results for the load/unload profiles are presented in time domain. In addition, the contact signal between the slider and disk is measured by the electrical resistance method.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2014년도 추계학술대회 논문집
• /
• pp.975-977
• /
• 2014

Recently, As portability of storage device has been increased, it is important to analyze the precise anti-shock analysis. For non-operational shock analysis, the accuracy of non-operational shock simulation has been improved. However, because operational shock analysis includes nonlinear process, it is hard to get clear result from operational shock simulation. In this paper, by using Lagrange multiplier method, the FE model including ramp-disk contact of nonlinear process will be analyzed. Through this, we find ramp-disk contact affect the dynamic of slider. Additionally, for the more accurate analysis, we should include ramp-disk contact process at the FE model.

• 대한기계학회논문집A
• /
• 제38권7호
• /
• pp.751-756
• /
• 2014

우리 주변에는 수많은 알갱이들이 서로 상호작용하면서 운동하는 모습을 주로 볼 수 있다. 본 연구에서는 수많은 알갱이들의 접촉에 따른 동적 거동을 분석하였다. 접촉에 의한 각 요소의 거동을 해석하기 위해 이산 요소법(Discrete element method)을 사용하였다. 접촉 관계에 있어서 접촉 판별을 위해 Neighboring-Cell 알고리즘을 사용하였고, 접촉력 계산에 Hertzian contact model과 Tangential sliding friction contact 모델을 사용하였다. 수많은 알갱이의 접촉해석을 위해 GPU 기반의 병렬 프로그램을 구성하였다. 해석을 검증하기 위해서 댐 붕괴 실험을 수행하였다. 거동 종료시점에 입자들의 쌓인 형상을 시뮬레이션 결과와 비교하여 해석 프로그램의 신뢰성을 검증하였다.

• Tribology and Lubricants
• /
• 제38권5호
• /
• pp.199-204
• /
• 2022

This paper presents a numerical investigation of the influence of water molecule thickness on frictional behavior at the nanoscale using molecular dynamics simulation. Three different models, comprising water thin films of various thicknesses, were built, and indentation and sliding simulations were performed using the models. Various normal loads were applied by indenting the Si tip on the water film for the sliding simulation to evaluate the interplay between the water thin film thickness and the normal load. The results of the simulations showed that the friction force generally increased with respect to the normal load and thickness of the water thin film. The friction coefficient varied with respect to the normal load and the water film thickness. The friction coefficient was the smallest under a moderate normal force and increased with decreasing or increasing normal loads. As the water film became thicker, the contact area between the tip and water film became larger. Under well-lubricated conditions, the friction force was proportional to the contact area regardless of the water film thickness. As the normal force increased above a critical condition, the water molecules beneath the Si tip spread out; thus, the film could not provide lubrication. Consequently, the substrate was permanently deformed by direct contact with the Si tip, while the friction force and friction coefficient significantly increased. The results suggest that a thin water film can effectively reduce friction under relatively low normal load and contact pressure conditions. In addition, the contact area between the contacting surfaces dominates the friction force.

• Interaction and multiscale mechanics
• /
• 제6권3호
• /
• pp.301-316
• /
• 2013

The influence of indenter geometry on nanoindentation was studied using a static molecular dynamics simulation. Dislocation nucleation, dislocation locks, and dislocation movements during nanoindentation into Al (001) were studied. Spherical, rectangular, and Berkovich indenters were modeled to study the material behaviors and dislocation activities induced by their different shapes. We found that the elastic responses for the three cases agreed well with those predicted from elastic contact theory. Complicated stress fields were generated by the rectangular and Berkovich indenters, leading to a few uncommon nucleation and dislocation processes. The calculated mean critical resolved shear stresses for the Berkovich and rectangular indenters were lower than the theoretical strength. In the Berkovich indenter case, an amorphous region was observed directly below the indenter tip. In the rectangular indenter case, we observed that some dislocation loops nucleated on the plane. Furthermore, a prismatic loop originating from inside the material glided upward to create a mesa on the indenting surface. We observed an unusual softening phenomenon in the rectangular indenter case and proposed that heterogeneously nucleating dislocations are responsible for this.

• Tribology and Lubricants
• /
• 제26권1호
• /
• pp.37-43
• /
• 2010

Precise prediction of rotordynamic coefficients for annular type seal of turbomachinery is necessary for enhancing their vibrational stability and various prediction methods have been developed. As the seal passage is designed complicatedly, the analysis based on Bulk-flow concept which has been mainly used in predicting seal dynamics is limited. In order to improve the seal rotordynamic prediction, full Navier-Stokes Equations with turbulent model derived in the seal flow passage have to be solved. In this study, 3D CFD(Computational Fluid Dynamics) analysis has been performed for predicting rotordynamic coefficients of non-contact type annular plain seal using FLUENT. Comparing with the results of Bulk-flow model analysis, the result of 3D CFD analysis shows good agreement.

• 한국정밀공학회지
• /
• 제17권6호
• /
• pp.135-142
• /
• 2000

In this paper, 3-dimensional numerical model of an escalator is developed to study the vibration characteristics. This proposed model is able to consider the elastic deformation of the frame during transient dynamic analysis. Deformation modes which are used to calculate the elastic deformation are selected from the FE model analysis. Because low frequency vibration is very important to the ride quality of fore/aft direction, low frequency deformation modes of the frame below 20Hz are considered. To show validity of this dynamics model, longitudinal acceleration of a step is compared with test data in frequency domain. Then robust design technique is applied to determine important design factors and improve ride quality with small number of experiments.

• Journal of Mechanical Science and Technology
• /
• 제15권6호
• /
• pp.735-742
• /
• 2001

This paper reports on the dynamics and friction characteristics of piston skirt with consideration of mixed lubrication. Piston skirt is an important part of the engine that transforms fuel into mechanical energy. The durability and low friction characteristics are important recent issues in piston skirt design. In this paper, the piston skirt motion is analyzed with consideration of mixed lubrication and piston skirt tilting motion. The entire trajectory of piston motion is obtained by using transient numerical method. Also various parameter studies are performed for piston skirt design and the development of lower frictional engine.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1993년도 춘계학술대회 논문집
• /
• pp.160-165
• /
• 1993

The cutting mechanism of ultrasonic vibration machining is characterized as two phases, that is an impact at the cutting edge and a reduction of cutting force due to non-contact interval between tool and workpiece. In this paper, in order to identfy cutting dynamics of a system with ultrasonically vibrated cutting tool, an ARMA modelling is performed on experimental cutting force signals which have a dominant effect on cutting dynamics. The aim of this study is, through Dynamic Data System methodology, to find the inherent characteristics of an ultrasonic vibration cutting process by considering natural frequencyand damping coefficient. Surface roughness and stability of cutting process under ultrasonic vibration are also considered