• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.21 no.11
• /
• pp.1896-1911
• /
• 1997

Effects of fiber-matrix interphases on the micro-and macro-mechanical behaviors of unidirectionally fiber-reinforced composites subjected to transverse shear loading at remote distance have been studied. The interphases between fibers and matrix have been modeled by the spring-layer which accounts for continuity of tractions, but allows radial and circumferential displacement jumps across the interphase that are linearly related to the normal and tangential tractions. Numerical calculations for basic cells of the composites have been carried out using the boundary element method. For an undamaged composite the micro-level stresses at the matrix side of the interphase and effective shear stiffness have been computed as functions of fiber volume ratio $V_f$ and interphase stiffness k. Results are presented for various interphase stiffnesses from the perfect bonding to the case of total debonding. For a square array composite the results show that for a high interphase stiffness k>10, an increase of $V_f$ increases the effective transverse shear modulus G over bar of the composite. For a relatively low interphase stiffness k<1, it is shwon that an increase of $V_f$ slightly decreases the effective transverse shear modulus. For the perfect bonding case, G over bar for a hexagonal array composite is slightly larger than that for a square array composite. Also for a damaged composite partially debonded at the interphase, local stress fields and effective shear modulus are calculated and a decrease in G over bar has been observed.

• Structural Engineering and Mechanics
• /
• v.74 no.4
• /
• pp.567-576
• /
• 2020

Considerable controversy surrounds the choice of the best abutment type for implant prosthetics. The two most common structures are hex and non-hex abutments. The non-hex abutment typically furnishes a larger contact area between itself and the implant than that provided by a hex structure. However, when a hex abutment is loaded, the position of its contact area may be deeper than that of a non-hex abutment. Hence, the purpose of this study is to determine the different biomechanical behaviors of an internal bone-level implant based on the abutment type-hex or non-hex-and clinical crown length under static and cyclic loadings using finite element analysis (FEA). The hex structure was found to increase the implant and abutment stability more than the nonhex structure among several criteria. The use of the hex structure resulted in a smaller volume of bone tissues being at risk of hypertrophy and fatigue failure. It also reduced micromovement (separation) between the implant components, which is significantly related to the pumping effect and possible inflammation. Both static and fatigue analyses, used to examine short- and long-term stability, demonstrated the advantages of the hex abutment over the non-hex type for the stability of the implant components. Moreover, although its impact was not as significant as that of the abutment type, a large crown-implant ratio (CIR) increased bone strain and stress in the implant components, particularly under oblique loading.

• Journal of the Korean Geotechnical Society
• /
• v.30 no.4
• /
• pp.21-34
• /
• 2014

This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.

• Korean Journal of Child Studies
• /
• v.37 no.3
• /
• pp.147-166
• /
• 2016

Objective: The purpose of this study was to gain an understanding of parenthood of mothers of early school-age children, with emphasis on cognitive, behavioral, and emotional aspects of parenthood. Methods: Nineteen mothers whose children were 1st and 2nd grade elementary school children participated in this study. Data were collected through individual in-depth interviews. During the interview, mothers were asked to speak freely about their experiences as parents of early-school age children, including parenting beliefs, parenting behaviors, and emotional experiences related to parenting. These interviews were transcribed verbatim and analyzed in a thematic way using MAXQDA. Results: Using qualitative methods, five major themes were emerged: (1) Recognizing the role of parents as a supporter of growth; (2) recognizing parenthood of the present generation that imposes expanded roles to mothers; (3) co-parenting of early school-age children and marital relationship; (4) co-existence of different parenting styles based on specific mother-child interaction situations; (5) experiencing a wide spectrum of emotions including anxiety, guilt, and depression, as well as happiness. Conclusion: This study revealed the unique cognitive, behavioral, and emotional aspects of parenthood experienced by mothers with early school-age children. Results of this study can fill a gap in our understanding of parenthood of mothers when their children entered into the new developmental stage of middle childhood. The results could also be used as a basis for developing parent education and family relationship programs.

• Korean Journal of Health Education and Promotion
• /
• v.28 no.5
• /
• pp.145-160
• /
• 2011

Objectives: This study attempted to apply the Intervention mapping and Transtheoretical models to develop a program to promote moderate alcohol drinking in university students. Methods: Surveyed data from 1,137 university students were analyzed to identify personal and environmental determinants for alcohol drinking. Based on these determinants, program objectives were established. Crossing the objectives with related important determinants resulted in matrices of learning objectives for which educational strategies were developed. Subsequently, an intervention program were designed to achieve those objectives. Results: Identified personal determinants included awareness, attitudes, self-efficacy and behavioral skills. Environmental determinants were binge drinking behaviors of family members and peers, and social pressure for drinking. Program, impact and learning objectives were developed to change the identified determinants. Program activities included provision of information on positive and negative consequences of binge drinking, opportunities for assessing one's drinking pattern, increasing outcome expectancies of and skill building for monitoring drinking, resisting peer pressure and managing stress. To facilitate adoption and maintenance of the program, an intervention diffusion plan was suggested. An evaluation plan was developed by utilizing RE-AIM framework. Conclusions: In order to expand evidence bases for effective theory-based programs, the developed program should be tested in diverse university settings.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.3
• /
• pp.429-436
• /
• 2013

This study considers how the fatigue behavior and probabilistic properties of SAE1055 steel are related to its hardness level. SAE1055 steel was heat-treated using induction hardening. Five types of specimens were prepared (A: base material, B: through hardened material with HV390, C: through hardened material with HV510, D: through hardened material with HV700, and E: surface hardened material with HV700). Fatigue tests were performed under a stress ratio of R = -1 using a 4-point rotary bending fatigue tester. The fatigue behaviors were greatly influenced by the hardness, but the fatigue limit did not increase over a hardness of HV510. In addition, the effect of the hardness level on the failure mechanism was evaluated using a scanning electron microscope. The probabilistic properties of the fatigue life were investigated using a probabilistic S-N approach, and the effect of the hardness level on these properties was evaluated using a residue analysis.

• Journal of Computational Design and Engineering
• /
• v.1 no.1
• /
• pp.27-36
• /
• 2014

Similar to the essential components of many mechanical systems, the geometrical properties of the teeth of spiral bevel gears greatly influence the kinematic and dynamic behaviors of mechanical systems. Logarithmic spiral bevel gears show a unique advantage in transmission due to their constant spiral angle property. However, a mathematical model suitable for accurate digital modeling, differential geometrical characteristics, and related contact analysis methods for tooth surfaces have not been deeply investigated, since such gears are not convenient in traditional cutting manufacturing in the gear industry. Accurate mathematical modeling of the tooth surface geometry for logarithmic spiral bevel gears is developed in this study, based on the basic gearing kinematics and spherical involute geometry along with the tangent planes geometry; actually, the tooth surface is a parametric surface defined on a parallelogrammic domain. Equivalence proof of the tooth surface geometry is then given in order to greatly simplify the mathematical model. As major factors affecting the lubrication, surface fatigue, contact stress, wear, and manufacturability of gear teeth, the differential geometrical characteristics of the tooth surface are summarized using classical fundamental forms. By using the geometrical properties mentioned, manufacturability (and its limitation in logarithmic spiral bevel gears) is analyzed using precision forging and multiaxis freeform milling, rather than classical cradle-type machine tool based milling or hobbing. Geometry and manufacturability analysis results show that logarithmic spiral gears have many application advantages, but many urgent issues such as contact tooth analysis for precision plastic forming and multiaxis freeform milling also need to be solved in a further study.

• Journal of the Society of Disaster Information
• /
• v.5 no.1
• /
• pp.48-62
• /
• 2009

Bodyguards always perform their duty with psychological burdens in their mind, not only because security situations are developed in various forms dependent on the surrounding environments or circumstances, but because bodyguards only take follow-up actions while the criminal decides time, place, and style of every attack. Thus, in the security situation, it is not uncommon for bodyguards to experience muscle rigidity, uncontrollable emotional elevation, difficulty in concentration, negative perception, frustration and enervation, which are caused by continuous physical/mental burdens, stimulations by various interpersonal behaviors or minute environmental stimulants. In conclusion, the result of performing security duties is related in the first place with the degree of the bodyguard's potential, in the second place with the degree of training and efficiency. And the result can also be changed by the way they control their negative psychological state of the moment when they carry out the skills they acquired. Maximizing the performance of the bodyguards by helping them overcome these psychological factors may be facilitated by detecting their psychological factors, understanding the causes, and training them in applying appropriate measures for overcoming these factors. When these measures are applied, the positive perception is indispensable that duties of protecting clients can be carried out successfully. No single measure can be declared to be more effective than the other because the effect of each measure is expressed differently by the individual characteristics of the bodyguards. However, it is important to select and apply the measures most appropriate to the bodyguard. Besides, they should devote themselves to the training with persistence because efficient implement of the measures for overcoming psychological factors takes a lot of time.

• Journal of the Society of Naval Architects of Korea
• /
• v.53 no.2
• /
• pp.85-91
• /
• 2016

The most important factor in the structural design of ships and offshore structures operating in arctic region is ice load, which results from ice-structure interaction during the ice collision process. The mechanical properties of ice related to strength and failure, however, show very complicated aspect varying with temperature, volume fraction of brine, grain size, strain rate and etc. So it is nearly impossible to establish a perfect material model of ice satisfying all the mechanical characteristics completely. Therefore, in general, ice collision analysis was carried out by relatively simple material models considering only specific aspects of mechanical characteristics of ice and it would be the most significant cause of inevitable errors in the analysis. Especially, it is well-known that the most distinctive mechanical property of ice is high dependency on strain rate. Ice shows brittle attribute in higher strain rate while it becomes ductile in lower strain rate range. In this study, the simulation method of ice collision to ship hull using the nonlinear dynamic FE analysis was dealt with. To consider the strain rate effects of ice during ice-structural interaction, strain rate dependent constitutive model in which yield stress and hardening behaviors vary with strain rate was adopted. To reduce the huge amount of computing time, the modeling range of ice and ship structure were restricted to the confined region of interest. Under the various scenario of ice-ship hull collision, the structural behavior of hull panels and failure modes of ice were examined by nonlinear FE analysis technique.

• Journal of Convergence for Information Technology
• /
• v.11 no.11
• /
• pp.1-9
• /
• 2021

This study aimed to find out the factors influencing the fall of middle-aged women aged 40 to 64 and to use it as basic data for the development of a fall prevention program. The study was based on raw data from the 2019 Korea Community Health Survey. To establish the impact of fall experience of middle-aged women, descriptive statistics, chi-square test, and multiple logistic regression were used. Of the 43,917 people surveyed, 11.9% of middle-aged women said that they had experienced a fall. Falls were more common among women with increasing age or without a spouse. Those who experienced a lot of depression and perceived stress and were diagnosed with diabetes also had a higher fall experience. In the case of drinking, women who drank more than non-drinkers were more likely to fall. The results of this study can lead to a better understanding middle-aged women who have experienced falls, and they can be used as basic data for the development of related health programs.