• Tribology and Lubricants
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• 제35권1호
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• pp.65-70
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• 2019

Self-loosening of bolts owing to external forces occurs in several machines that are clamped by bolts and nuts. This study focuses on the self-loosening of the aiming bolt of the head lamp in a vehicle. It is important to prevent the aiming bolt from self-loosening as it has a decisive effect on the angle of the head lamp. A nut clamped with a bolt, known as a retainer, is made of plastic and has a partial screw thread. In addition, a transverse load has a considerable impact on the self-loosening of a bolt. We concentrate on the self-loosening of a bolt by a transverse load. The aim of this study is to define the limits of the external force that loosen the bolt. Based on the above conditions, we derive a theoretical equation and develop a numerical analysis program that can calculate the limiting forces for self-loosening. To verify the developed program, we design a test device that can measure the self-loosening by applying sliding forces to the aiming bolt. Using this method, we can draw the following conclusions. First, the developed testing device is suitable to prove the theory for calculating the self-loosening force. Second, the equation confirms the relationship of bolt self-loosening between resistance torque and shear force. Finally, the equation obtains the minimum value of the resistance torque required to decrease the change in the angle of the head lamp, thereby improving the possibility of increasing the stability of the head lamp.

• Structural Engineering and Mechanics
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• 제55권3호
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• pp.639-654
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• 2015

Bolted joints are essential elements of mechanical structures and metal constructions. Although their static behaviour is fairly well known, their dynamic behaviour due to shocks and vibrations has been less studied, because of the large size of the finite element models needed for a detailed simulation. This work presents four different simplified models suitable for studying the dynamic behaviour of an elementary bolted joint. Three of them include contact elements to allow sliding of the screw head and the nut on the assembled parts, and the last one allows rotation between screw and nut. A penalty approach based on the Coulomb friction model is used to model contact. The results show that these models effectively represent the dynamic behaviour, with different accuracy depending on the model details. The last model simulates the self loosening of a bolt subjected to transversal vibrations.

• 한국안전학회지
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• 제18권2호
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• pp.1-5
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• 2003

By using an approach developed to determine the torque-tension relationship for bolted joints, frictional properties of several typical bolted joints were studied experimentally. The specific property by bolted joints certify that the most significant influence of materials and bearing surface condition. Experiments on thread friction shows that prevailing torque nuts with distorted threads provide benefit for preventing self-loosening of the nut. Repeated tightening-loosening generally increases frictions in a bolted joint. It was noted that the data scatter of the experimental results of frictions in a belted joint may overshadow the influence of size. speed, and contact positions. The results from the experimental investigation will help to better design bolted joints.

• Smart Structures and Systems
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• 제17권1호
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• pp.135-147
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• 2016

This paper describes a smart structural system, which uses smart materials for real-time monitoring and active control of bolted-joints in steel structures. The goal of this research is to reduce the possibility of failure and the cost of maintenance of steel structures such as bridges, electricity pylons, steel lattice towers and so on. The concept of the smart structural system combines impedance based health monitoring techniques with a shape memory alloy (SMA) washer to restore the tension of the loosened bolt. The impedance-based structural health monitoring (SHM) techniques were used to detect loosened bolts in bolted-joints. By comparing electrical impedance signatures measured from a potentially damage structure with baseline data obtained from the pristine structure, the bolt loosening damage could be detected. An outlier analysis, using generalized extreme value (GEV) distribution, providing optimal decision boundaries, has been carried out for more systematic damage detection. Once the loosening damage was detected in the bolted joint, the external heater, which was bonded to the SMA washer, actuated the washer. Then, the heated SMA washer expanded axially and adjusted the bolt tension to restore the lost torque. Additionally, temperature variation due to the heater was compensated by applying the effective frequency shift (EFS) algorithm to improve the performance of the diagnostic results. An experimental study was conducted by integrating the piezoelectric material based structural health monitoring and the SMA-based active control function on a bolted joint, after which the performance of the smart 'self-monitoring and self-healing bolted joint system' was demonstrated.

• 한국강구조학회 논문집
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• 제23권5호
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• pp.629-636
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• 2011

본 연구는 압전 센서를 이용한 구조물의 실시간 모니터링과 강구조물 볼트접합부의 동적 컨트롤이 가능한 자가치유 시스템에 관한 것이다. 볼트접합부의 볼트 풀림 손상 탐색을 위해서 압전 물질의 전기역학적 커플링 성질을 이용하는 임피던스 기반의 구조물건전성평가 기법을 이용하였다. 계측된 임피던스 값을 기준치 값과 비교함으로써 볼트 풀림 손상 진단이 가능하다. 볼트 풀림 손상은 손상지수를 이용하여 정량적으로 평가되어지고, 손상이 진단되면 형상기억합금 와셔에 감겨있는 외부히터가 와셔에 열을 가하게 된다. 열이 가해진 형상기억합금 와셔는 축방향으로 팽창하고, 볼트접합부는 볼트풀림으로 인해 잃어버린 토크력을 회복하게 된다. 압전 센서를 이용한 임피던스 기반의 구조물건전성 평가기법과 형상기억합금 기반의 볼트접합부 동적 컨트롤 기능과 이를 이용한 자가치유 볼트접합부 시스템의 적용가능성과 성능을 실험을 통해 평가하였다.

• 대한치과보철학회지
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• 제43권3호
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• pp.379-392
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• 2005

Statement of problem. One of the common problems of dental implant prosthesis is the loosening of the screw that connects each component, and this problem is more common in single implant-supported prostheses with external connection, and in molars. Purpose. The purposes of this study were: (1) to compare the initial abutment screw detorque values of the six different implant-abutment interface designs, (2) to compare the detorque values of the six different implant-abutment interface designs after cyclic loading, (3) to compare the detorque values of regular and wide diameter implants and (4) to compare the initial detorque values with the detorque values after cyclic loading. Material and methods. Six different implant-abutment connection systems were used. The cement retained abutment and titanium screw of each system were assembled and tightened to 32Ncm with digital torque gauge. After 10 minutes, initial detorque values were measured. The custom titanium crown were cemented temporarily and a cyclic sine curve load(20 to 320N, 14Hz) was applied. The detorque values were measured after cyclic loading of one million times by loading machine. One-way ANOVA test, scheffe’s test and Mann-Whitney U test were used. Results. The results were as follows : 1. The initial detorque values of six different implant-abutment connections were not significantly different(p>0.05). 2. The detorque values after one million dynamic cyclic loading were significantly different (p<0.05). 3. The SS-II regular and wide implant both recorded the higher detorque values than other groups after cyclic loading(p<0.05). 4. Of the wide implants, the initial detorque values of Avana Self Tapping Implant, MIS and Tapered Screw Vent, and the detorque values of MIS implant after cyclic loading were higher than their regular counterparts(p<0.05). 5. After cyclic loading, SS-II regular and wide implants showed higher detorque values than before(p<0.05).

• 성인간호학회지
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• 제27권6호
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• pp.695-706
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• 2015

Purpose: This study was aimed to explore and describe the disease experience of Korean women with eating disorders within psychological and sociocultural context. Methods: The participants were 12 young adult women suffering with eating disorders or have recovered from the diseases. Data were collected via in-depth interviews and analyzed according to the grounded theory methodology by Strauss and Corbin. Results: The core category of the disease experience was 'becoming the master of life through desperate efforts'. The disease experience was categorized into five different phases including 'falling under the influence of others', 'collapsing the self: life swallowed by loosening weight', 'facing the wrecked self', 'struggling between the self and others', 'truly facing the self'. The intervening conditions were various supporting systems such as 'support from family', 'economic support' and 'support from trustworthy health professionals'. Conclusion: The findings of this study indicate that it is necessary to develop nursing interventions to support women with eating disorders and alleviate their suffering from eating disorders. Also specialized educational programs are warranted to prevent the eating disorders, and to reduce social stigma of eating disorders.

• 지식경영연구
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• 제20권1호
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• pp.133-153
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• 2019

Due to the uncertainty of dynamic business environment, modern organizations have been giving attention to dynamic capabilities beyond traditional notion of core competence. Among them, absorptive capacity and boundary-spanning activity are considered the most important. The former refers to activities regarding acquisition, assimilation, transformation and exploitation of internal and external knowledge. The latter is composed of boundary-loosening and boundary-tightening activities to detect internal or external information and then to preserve, protect, or acquire resources. Thus, both have achieved wide recognition as a potential source of change and innovation. This study investigated the cross-level relation between boundary-spanning leadership at team level and absorptive capacity at individual level. We also explored self-efficacy and extra-role behavior that can affect employees' absorptive capacity. To test multi-level analysis, the survey data were collected from 862 members in 137 teams of different firms. Results revealed that boundary-spanning leadership had the positive cross-level impact on absorptive capacity in the team context. Moreover, absorptive capacity was positively associated with self-efficacy and extra-role behavior at individual level. Based on these findings, we provided theoretical and practical implications to address rapidly changing environments and discussed limitations of this paper for further research.

• 한국정밀공학회지
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• 제32권7호
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• pp.591-595
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• 2015

The roller rig tester for safety performance evaluation of wheel derailment is a test facility which can give the test load condition to the test wheel, similar to the actual dynamic condition in actual running condition. This study describes the evaluation result on the durability of the resilient wheel equipped with the ring damper and the damping material, and installed in the half part of a full scaled bogie in combination with the primary spring when it rotates under the dynamic condition. The evaluation result on durability of resilient wheel after load test of 2 million cycles shows that the safety of wheel is not affected by the applied load in visual inspection and nondestructive test, however, in the bolt used for fastening the ring damper to the wheel the loosening was found. Accordingly the use of self-locking nut and washer is recommended.

• 농촌지도와개발
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• 제7권1호
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• pp.101-119
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• 2000

Agricultural Extension Services in Korea have accomplished a significant role in self- sufficiency of rice, a national staple food, through green revolution in 1970's; supplying green vegetables even during the winter season through white revolution in 1980's; and establishing technical agriculture by organizing rural leaders and 4-H members. In 1990s changes were made in international situations under the Uruguay Round multilateral trade negotiations and inauguration of the World Trade Organization. This was followed by localization of the extension staffs and the functions of extension services in Korea changed dramatically from national government to local governments. Thus, a weakened national function resulted in loosening of the linkages of research and extension in central government and local extension offices. Difficulties were reported in diffusion of new agricultural technology and efficient management of extension personnel. Developmental tasks for better extension services for the 21st century in Korea would include recovering national functions of agricultural extension, and developing a new paradigm for extension service. This should include the following measures; 1) Cooperative extension service should be adapted to involve national as well as local governments and non-government organization. 2) The target groups for extension services should be expanded to include farmers, noel residents as well as urban consumers. 3) The role of the extension service should cover agricultural technological diffusion of innovations as well as managerial skills and leadership development for rural organizations. 4) Extension services should be introduced to small farmers as well as consultation services for advanced farms. Diversified approaches should be employed for mama effective services. 5) Pre-service as well as in-service education should be offered to secure better extension educators equipped with knowledge, understanding and abilities on agricultural technology, information, agricultural philosophy, instructional methods and communication skills.