• Tribology and Lubricants
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• v.37 no.4
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• pp.136-143
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• 2021

This paper presents the loosening behavior that occurs after the application of an external load to internal and external connection types of dental implants using the finite element method. We use fastening force between an abutment and a fixture to clamp the dental implant system; however, loosening and breakage may occur owing to cyclic external loads. In this study, we considered the initial fastening condition in the pre-load analysis and then investigated the change in stress and contact surface status when applying external loads. After the application of the initial fastening load, we verified that the internal connection-type model exhibited a relatively lower stress distribution than that of the external connection-type one. Moreover, we found that the former model showed a lower stress concentration after the application of the external load. In addition, after the application of this load, we found that the higher the shear load acting on the implant system, the higher the possibility of loosening. The study results showed the change in stress distribution and contact surface according to the connection type of the dental implants and the phenomenon of loosening by cyclic loads. We expect that the results of this study will be useful for the study of reliability and design of dental implant systems.

• The Journal of the Korean dental association
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• v.53 no.5
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• pp.307-317
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• 2015

Although the long-term success of osseointegrated endosseous implants for the support of fixed dental prostheses has been reported, the increasingly widespread use of implant-supported prostheses has led to problems associated with their structural integrity. The most common biomechanical complications observed in dental implant treatment are fracture and screw loosening. The nature of loosening or fracture of dental implant components is complex, since it involves fatigue, fitness, and varied chewing patterns and loads. To assess the service life of the components of the prosthetic system, a knowledge of the loads transmitted through the system is necessary. Design of the final restoration and occlusion in relation to the geometry of a prosthetic restoration has a great influence on the mechanical loading of the implant. It is proposed that control of force in oral cavity may play a larger role in failures than previously believed. Based on theoretic consideration and clinical experiences with dental implant, this article gives simple guidelines for controlling these loads.

• Proceedings of the KSME Conference
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• 2004.11a
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• pp.486-491
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• 2004

A comparative study on the implant screw loosening under the initial clamping force and cyclic loads was conducted. The experiments were performed to evaluate the screw loosening behavior of the internal and external implant systems. It was found that the screw loosening torques of implant systems were significantly affected by the way how the abutment and fixture were connected due to the difference in the load transfer mechanism between abutment and fixture.

• Tunnel and Underground Space
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• v.12 no.2
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• pp.107-114
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• 2002

It is the common practice to over design the reinforcement for the secondary tunnel lining due to the lack of rational insight into the ground loosening loads. and due to the conservative application of the empirical design methods. The main loads of the secondary lining are the ground Loosening loads and the ground water pressure, and the ground load is critical in the reinforcement design of the secondary lining in the case of drained tunnel. If the external load is absent around a tunnel, the reasons of the load far secondary tunnel lining are the deterioration of the primary supports such as shotcrete, steel rib, and rockbolts. Accordingly, the analysis method considering the ground-primary supports-secondary lining interaction should be required tar the rational design of the secondary tunnel lining. In this paper, the interaction was conceptually described by the simple mass-spring model and the load transfer from the ground and primary supports to the secondary lining is showed by the ground-primary supports-secondary lining reaction curves fur the theoretical solution of a circular tunnel. And also, the application of this proposed model to numerical analysis is verified in order to check the potential far the tunnel with the complex analysis conditions.

• Smart Structures and Systems
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• v.16 no.2
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• pp.281-294
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• 2015

Bolted joint connection is the most commonly used connection element in structures and devices. The loosening due to external dynamic loads cannot be observed and measured easily and may cause catastrophic loss especially in an extreme requirement and/or environment. In this paper, an innovative Real-time Cross-Correlation Method (RCCM) for monitoring of the bolted joint loosening was proposed. We apply time reversal process on stress wave propagation to obtain correlation signal. The correlation signal's peak amplitude represents the cross-correlation between the loosening state and the baseline working state; therefore, it can detect the state of loosening. Since the bolt states are uncorrelated with noise, the peak amplitude will not be affected by noise and disturbance while it increases SNR level and increases the measured signals' reliability. The correlation process is carried out online through physical wave propagation without any other post offline complicated analyses and calculations. We implemented the proposed RCCM on a single bolt/nut joint experimental device to quantitatively detect the loosening states successfully. After that we implemented the proposed method on a real large structure (reaction wall) with multiple bolted joint connections. Loosening indexes were built for both experiments to indicate the loosening states. Finally, we demonstrated the proposed method's great anti-noise and/or disturbance ability. In the instrumentation, we simply mounted Lead Zirconium Titanate (PZT) patches on the device/structure surface without any modifications of the bolted connection. The low-cost PZTs used as actuators and sensors for active sensing are easily extended to a sensing network for large scale bolted joint network monitoring.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.543-560
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• 2018

With the increased development in downtown underground space facilities that vertically cross under a railway at a shallow depth, the demand for non-open cut method is increasing. However, most construction sites still adopt the pipe roof method, where medium and large diameter steel pipes are pressed in to form a roof, enabling excavation of the inside space. Among the many factors that influence the loosening region and loads that occur while pressing in steel pipes, the size of the pipe has the largest impact, and this factor may correspond to the magnitude of load applied to the underground structure inside the steel pipe roof. The super equilibrium method (SEM) has been developed to minimize ground disturbance and loosening load, and uses small diameter pipes of approximately 114 mm instead of conventional medium and large diameter pipes. This small diameter steel pipe is called an SEM pile. After SEM piles are pressed in and the grouting reinforcement is constructed, a crossing structure is pressed in by using a hydraulic jack without ground subsidence or heaving. The SEM pile, which plays the role of timbering, is a fore-poling pile of approximately 5 m length that prevents ground collapse and supports surface load during excavation of toe part. The loosening region should be adequately calculated to estimate the spacing and construction length of the piles and stiffness of members. In this paper, we conducted a comparative analysis of calculations of loosening load that occurs during the press-in of SEM pile to obtain an optimal design of SEM. We analyzed the influence of factors in main theoretical and empirical formulas applied for calculating loosening regions, and carried out FEM analysis to see an appropriate loosening load to the SEM pile. In order to estimate the soil loosening caused by actual SEM-pile indentation and excavation, a steel pipe indentation reduction model test was conducted. Soil subsidence and soil loosening were investigated quantitatively according to soil/steel pipe (H/D).

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.109-114
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• 2003

It is the common practice to reinforce excessively the secondary tunnel lining due to the lack of rational insights into the ground loosening loads. The main load of the secondary lining for drained-type tunnels is the ground loosening. The main cause of the load for secondary tunnel lining is the deterioration of the primary support members such as shotcrete, steel ribs, and rockbolts. Accordingly, the development of the analysis model to consider the ground-primary supports-secondary lining interaction is very important for the rational design of the secondary tunnel lining. In this paper, the interaction is conceptually described by the simple mass-spring model and the load transfer from the primary supports to the ground and the secondary lining is showed by the characteristic curves including the secondary lining reaction curve for the theoretical solution of a circular tunnel. And also, the application of this model to numerical analysis is verified in order to review the potential tool for practical tunnel problems with the complex conditions like non-circular shaped tunnels, multi-layered ground, sequential excavation and so on.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.65-80
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• 2014

This study conducted Trapdoor tests with actual tunnel shape, investigated the mechanical behavior of ground and loosening load on tunnels, and evaluated the mechanism of progressive failure by numerical simulation. The loosening load sharply decreased initially, but it generally increased and reached the stabilized level exhibiting the arching effect, and loose sand showed relatively higher values than those of dense sand. The shear band started from the tunnel shoulder with $63^{\circ}$ (loose sand) to $69^{\circ}$ (dense sand), and gently curved inward to the ground surface. The widths of shear band formation above the tunnel showed a range from 1.8b to 1.9b (b=Tunnel width), which are similar to those values calculated from existing formular. The vertical height of this shear band for deep tunnel was turned out to be a bit lower than that from existing studies (3.0*Tunnel Height).

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.3
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• pp.261-268
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• 2003

Terzaghi's tunnel theory has been accepted to calculate tunnel loads conservatively in practical design until now. In this study, Terzaghi's tunnel theory was expanded to the inclined-layer ground with inclination of ground and stratification. Finally a new tunnel load equation was induced utilizing the original Terzaghi's tunnel theory and Terzaghi's tunnel theory was reviewed as well.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.2
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• pp.92-98
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• 2012

Purpose: The aim of this study was to evaluate the effects of different abutment materials on abutment screw loosening and settling-down effect in conical connection type implant system. Materials and methods: Three types of abutment, cementation, gold UCLA, and metal UCLA abutment were used. Two UCLA groups were fabricated in a similar pattern to cementation abutment. Type III gold alloy and Nickel-Chromium alloy was used for casting gold UCLA abutment and metal UCLA abutment, respectively. Fixture and abutment were tightened to 30 Ncm by using digital torque controller and re-tightening was conducted with same force after 10 minutes. Digital torque gauge was used to measure loosening torque and fixture/abutment length was measured by digital micrometer. Dynamic loads between 25 N and 250 N were applied with $0^{\circ}$ angle to the abutment axis. After loading, fixture/abutment length was re-measured and amount of settlement was calculated. Loosening torque value was also measured for comparison Results: All three groups showed significant differences of length when comparing before and after loading, but there was no significant difference of settling amount in all groups. Loosening torque values were significantly decreased when comparing before and after loading in all groups($P$<.05). However, there was no significant difference in loss of loosening torque values when compared to groups. Conclusion: In internal conical connection type implants, dynamic load affected on settlement and loosening torque of implant, but there was no differences between abutments materials. Likewise gold UCLA abutment, metal UCLA abutment might be able to withstand functional load.