• Restorative Dentistry and Endodontics
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• v.33 no.4
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• pp.323-331
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• 2008

Flexibility and fracture properties determine the performance of NiTi rotary instruments. The purpose of this study was to evaluate how geometrical differences between three NiTi instruments affect the deformation and stress distributions under bending and torsional conditions using finite element analysis. Three NiTi files (ProFile .06 / #30, F3 of ProTaper and ProTaper Universal) were scanned using a Micro-CT. The obtained structural geometries were meshed with linear, eight-noded hexahedral elements. The mechanical behavior (deformation and von Mises equivalent stress) of the three endodontic instruments were analyzed under four bending and rotational conditions using ABAQUS finite element analysis software. The nonlinear mechanical behavior of the NiTi was taken into account. The U-shaped cross sectional geometry of ProFile showed the highest flexibility of the three file models. The ProTaper, which has a convex triangular cross-section, was the most stiff file model. For the same deflection, the ProTaper required more force to reach the same deflection as the other models, and needed more torque than other models for the same amount of rotation. The highest von Mises stress value was found at the groove area in the cross-section of the ProTaper Universal. Under torsion, all files showed highest stresses at their groove area. The ProFile showed highest von Mises stress value under the same torsional moment while the ProTaper Universal showed the highest value under same rotational angle.

• Restorative Dentistry and Endodontics
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• v.34 no.5
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• pp.442-449
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• 2009

The aim of this study was to examine that thick dentin bonding agent application or low modulus composite restoration could reduce stresses on dentin bonding agent layer. A mandibular first premolar with abfraction lesion was modeled by finite element method. The lesion was restored by different composite resins with variable dentin bonding agent thickness ($50{\mu}m$, $100{\mu}m$, $150{\mu}m$). 170N of occlusal loading was applied buccally or lingually. Von Mises stress on dentin bonding agent layer were measured. When thickness of dentin bonding agent was increased von Mises stresses at dentin bonding agent were decreased in both composites. Lower elastic modulus composite restoration showed decreased von Mises stresses. On root dentin margin more stresses were generated than enamel margin. For occlusal stress relief at dentin boning agent layer to applicate thick dentin bonding agent or to choose low elastic modulus composite is recommended.

• The korean journal of orthodontics
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• v.41 no.6
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• pp.384-398
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• 2011

Objective: The purpose of this study was to analyze the stress distribution and the displacement pattern of mandibular anterior teeth under various intrusive force vectors according to the position of orthodontic miniscrews and hooks, using three-dimensional finite element analysis. Methods: A three-dimensional finite element model was constructed to simulate mandibular teeth, periodontal ligament, and alveolar bone. The displacement of individual tooth on three-dimensional planes and the von Mises stress distribution were compared when various intrusion force vectors were applied. Results: Intrusive forces applied to 4 mandibular anterior teeth largely resulted in remarkable labial tipping of the segment according to the miniscrew position. All 6 mandibular anterior teeth were labially tipped and the stress concentrated on the labiogingival area by intrusive force from miniscrews placed mesial to the canine. The distointrusive force vector led to pure intrusion and the stress was evenly distributed in the whole periodontal ligament when the hook was placed between the central and lateral incisors and the miniscrew was placed distal to the canine. Conclusions: Within the limits of this study, it can be concluded that predictable pure intrusion of the 6 anterior teeth segment may be accomplished using miniscrews placed distal to the canine and hooks located between the central and lateral incisors.

• Journal of the Korean Data and Information Science Society
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• v.20 no.2
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• pp.261-272
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• 2009

Kolmogorov-Smirnov (K-S) statistic has been widely used for testing homogeneity of two distributions in the credit rating models. Joseph (2005) used K-S statistic to obtain validation criteria which is most well-known. There are other homogeneity test statistics such as the Cramer-von Mises, Anderson-Darling, and Watson statistics. In this paper, these statistics are introduced and applied to obtain criterion of these statistics by extending Joseph (2005)'s work. Another set of alternative criterion is suggested according to various sample sizes, type a error rates, and the ratios of bads and goods by using the simulated data under the similar situation as real credit rating data. We compare and explore among Joseph's criteria and two sets of the proposed criterion and discuss their applications.

• Journal of the Korean Data and Information Science Society
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• v.7 no.1
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• pp.37-46
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• 1996

In this paper, we introduce the goodness of fit test procedure for lifetime distribution using step stress accelerated lifetime data. Using the nonpapametric estimate of acceleration factor, we prove the strong consistence of empirical distribution function under null hypothesis. The critical vailues of Kolmogorov-Smirnov, Anderson-Darling, Cramer-von Mises statistics are computed when the lifetime distibution is assumed to be exponential and Weibull. The power of test statistics are compared through Monte-Cairo simulation study.

• Journal of the Korean Institute of Gas
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• v.20 no.2
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• pp.43-48
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• 2016

This paper presents the finite element analysis results for bearing loads and stress distributions of safety helmets with an extruded structure. Five different analysis models with given same displacement load of 9.4mm have been analyzed for bearing loads and maximum von Mises stress. In these models, model 4 and model 5 are recommended as a maximum bearing load and low maximum stress for given displacement load of 9.4mm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.515-516
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• 2006

The goal of total disc replacement is to restore pain-free mobility to a diseased functional spinal unit, by replacing the degenerated disc with a mobile bearing prosthesis. SB Charite III is named commercial product as the Artificial Intervertebral Disc (AID). SB Charite III consists of sliding core and endplate made by Ultra-high Molecular Weight Polyethylene (UHMWPE) and cobalt chrome alloy, respectively. To evaluate the effect of von-Mises stress in AID, and three-dimensional finite element model of AID analysis was preformed for four different loading types of sliding core. Consequently, endplate was compared with a compressive preload at 400N and flexion moment at $3{\sim}9Nm4. Therefore, this research has obtained result that von-Mises stress of sliding core in AID disc by radius curvature.

• Proceedings of the Korean Reliability Society Conference
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• 2000.04a
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• pp.213-222
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• 2000

In present study, a stochastic model is developed for the low cycle fatigue life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. In the proposed model, fatigue phenomenon is considered as a Markov process, and damage vector and reliability are defined on every plane. Any low cycle fatigue damage evaluating method can be included in the proposed model. The model enables calculation of statistical reliability and crack initiation direction under variable multiaxial loading, which are generally not available. In present study, a critical plane method proposed by Kandil et al., maximum tensile strain range, and von Mises equivalent strain range are used to calculate fatigue damage. When the critical plane method is chosen, the effect of multiple critical planes is also included in the proposed model. Maximum tensile strain and von Mises strain methods are used for the demonstration of the generality of the proposed model. The material properties and the stochastic model parameters are obtained from uniaxial tests only. The stochastic model made of the parameters obtained from the uniaxial tests is applied to the life prediction and reliability assessment of 316L stainless steel under variable multiaxial loading. The predicted results show good accordance with experimental results.

• Proceeding of EDISON Challenge
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• 2016.03a
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• pp.240-245
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• 2016

In this paper, stress contour plots depending on length, load, and diameter of the implant are presented. Depending on the condition and amount of cortical bone, process of implanting can be difficult and stress becomes important. Therefore deciding the right length and diameter of implant is critical. When analyzing stress in the implant, Von-mises yield criterion is often used; however, due to hardship of acquiring the actual material property of surrounding bones, simplified model of a implant was adapted in finite element analysis program of EDISON. The result acquired from EDISON program was then compared with results of different research papers.

• Journal of the Korean Society for Precision Engineering
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• v.18 no.1
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• pp.201-212
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• 2001

If defects are located far apart, fatigue cracks are independently initiated from them and gradually approach other cracks so that the fatigue life becomes influenced by the crack growth behavior of those interacting cracks. In this study, the effect of the stress interaction between defects on the fatigue crack propagation behavior is investigated experimentally and these results are verified by finite element method. In addition, fatigue crack propagation behaviors under micro hole interaction field are studied.