• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.5
• /
• pp.890-895
• /
• 2002

Cold expansion method is retarded of crack initiation due to the compressive residual stress developed on the hole surface. Previous research has just been study about residual stress distribution in the hole surrounding. But, The purpose of this study was to improve the understanding of the residual stress effect in hole surrounding as crack growth from another hole. In this paper, it is shown that residual stress is redistributed due to the application of cold expansion process for CT specimen using finite element method. It is further shown that tensile stress increases in proportion to cold expansion ratio in the vicinity of crack. It is thought that stress intensity factor increases with cold expansion ratio.

• 한국방재학회:학술대회논문집
• /
• 2007.02a
• /
• pp.307-311
• /
• 2007

In the case of the railway bridges, uplift forces were occurred at the edge of the segments when vehicular loads were applied. These forces made the compressive and tensile forces occur in the fastening system. Therefore, the structural analysis was performed to investigate the safety of fastening system which was modeled as one directional spring element. In this case, the stiffness of the spring element was obtained from experimental study which was conducted by compressive load. For that reason, to perform rational and exact structural analysis, the translational stiffness of the fastening system obtained from the experimental study applied the tensile load and the rotational stiffness should be considered because it was occurred the tensile force as well as the compressive force in fastening system. In this study, an elastic and inelastic experimental study was performed for six specimens. The translational stiffness along the vertical axis of rail and the rotational stiffness along the strong axis of rail were investigated. Also structural behavior of the fastening system was analyzed.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.26 no.4
• /
• pp.67-80
• /
• 1989

This Paper is concerned with the fracture behavoir of Unidirectional Laminate(UD) and the characteristic length of Multidirectional Laminate(MD) around hole under the Uniform Tensial Strain. Two fracture mechanical concepts of the Waddoups-Eisenman-Kaminski(WEK) model based on the Linear Elastic Fracture Mechanics(LEFM) and the Whitney-Nuismer Model based on Point and Average Stress Criteria were applied. The characteristic length of a laminate with a hole is then obtained using the coefficient of stress reduction and the experimental results, and it can be utilized in predicting the stress level at which the specimen will fracture. The results of the fracture characteristics and the strength of the specimens having a hole in the center can be used as the important experimental data in the research branch of the mechanical fastening of laminated structures. The Ultrasonic scanning and the Acoustic Emission(AE) method were utilized in order to find out the initial defects and the fracture behavior, respectively.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.18 no.5
• /
• pp.68-75
• /
• 2010

The one of the major problems in the development of PEMFC was regarding to the assurance of sealing on stack. The failure on the sealing creates the problems of fuel leakage, mixing, internal combustion, damage on parts and can be a direct reason for the degrading the efficiency of fuel cell. This paper studies on the analytical approach for improving the contacting pressure distribution on the gasket at the evaluation on the sealing of fuel cell stack. So, the assembly analysis on multi layered fuel cell stack was performed. The research on the simplification of finite element model was performed for three dimensional analysis at the multi layered state. The improved contact pressure distribution was obtained through the case studies on gasket for better sealing. In addition, the number of the cell was determined for the effective analysis and the structural characteristics were evaluated based on this research.

• Journal of the Korean Society for Precision Engineering
• /
• v.20 no.1
• /
• pp.172-178
• /
• 2003

Two types of bolted lap joints, one with a viscoelastic layer and the other without the viscoelastic layer were chosen to analyze the dynamic characteristics of the joints with the mechanical properties of the bolts in the joints are considered as computational variables. The finite element method was used along with the modal testing to verify the PEM model. The results in the bolted lap joints reveal that the higher the Young's modulus for the bolts we use the higher the natural frequencies we obtain fur the joints. However, the natural frequency differences in the first and second mode are not substantial but become noticeable in the higher modes. Lower natural frequencies were obtained for the bolted lap joints with the viscoelastic layer when compared with those of the bolted lap joints without the viscoelastic layer. And the differences in the natural frequencies for the two types of joints are relatively small in the first and second mode whereas in the higher mode the differences become significant. The loss factors were observed to be significant especially in the second mode for the bolted lap joints with the viscoelastic layer.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.3
• /
• pp.333-340
• /
• 2011

We evaluated the stress-reduction effect for different shapes of a composite adherend with or without a spew fillet. Six different single-lap joint specimens were modeled and assessed using nonlinear finite element analysis. Moreover, we investigated the effect of the stiffness ratio of the adherend and adhesive. The single-lap joint with normal tapering had the highest stress values, and the single-lap joint with reverse tapering and a spew fillet had the lowest stress values. The composite adherends with higher stiffness had lower stress values, and the adhesives with lower stiffness had lower stress values.

• Journal of Korean Society of Steel Construction
• /
• v.11 no.1 s.38
• /
• pp.23-31
• /
• 1999

The concept models are used for the analysis of joints because they are simple to use and accurate. The modeling parameters of concept models are estimated using the results of experiments performed on the joints. The concept joint models accurately describe the behavior of joints under the loads which are used in the experiments for the estimation of parameters. However, they may not be accurate under the loads which are not used in the experiments. The accuracy can be dependent on the loads which are used in the evaluation of accuracy. In this study, antioptimization is presented to find the worst possible loads, under which the accuracy of concept joint models can be evaluated. The procedure was applied to the accuracy evaluation of concept joint models in an isolated 3-D joint and 2-D joints of a vehicle structure.

• Composites Research
• /
• v.25 no.6
• /
• pp.186-190
• /
• 2012

With the wide application of fiber-reinforced composite material in aero-structures and mechanical parts, composite joint have become a very important research area because they are often the weakest sites in composite structures. In this paper, the failure strengths of the bolted joint and pin joint which have variable hole clearance were evaluated and compared. From the tests, the first failure loads of the bolted joint and pin joint with $880{\mu}m$ hole clearance have decreased by 24.2 % and 51.3 % compared to those of joints with $0{\mu}m$ hole clearance, respectively. Also, the failure index of the joints were calculated by the finite element method and compared with experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.5 s.248
• /
• pp.528-532
• /
• 2006

In the aerospace industry, Cold expansion has been used the most important method that is retarded of crack initiation from fastener hole surface. Cold expansion method(CEM) is that a oversized tapered mandrel goes through the hole in order to develop a compressive residual stress as the passing of the mandrel around the hole. Therefore, because of characteristic of mandrel inserting, Residual Stress Distributions (RSD) are differently generated form Entry, Mid and Exit position of the plate. Also, it is respected that RSD are changed as distances between holes. In this paper, It is performed a FE analysis of RSD by CEM and it is respectively shown RSD in the Entry, Mid and Exit position. It is compared residual stress results form the cold expansion in these two cases: the concurrent CEM and the sequential CEM. From this research, it has been found that compressive residual stress of Entry position is lower than other positions. Also, the concurrent CE of adjacent holes leads to much higher compressive residual stress than the sequential CE. In addition, in the sequential CE case, a compressive RSD of 1 step's hole around is lower than compressive RSD of 2 step's hole around.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.29 no.9 s.240
• /
• pp.1175-1182
• /
• 2005

General systems have many substructures assembled at joints. The bolted joint is generally used in assembling the mechanical parts. However, there are no effective modeling methods to analyze the dynamic characteristics of bolt jointed structure using the finite element (FE) analysis, especially in case of large area contact. Moreover, the design methods for the appropriate bolt locations and the number of bolts considering the dynamic characteristics are not guided properly. In this study, a proper modeling method is developed to simulate the dynamic characteristics of a structure with the large interfaced area using the cone frusta method and spring elements. The natural frequencies are also controlled by adjusting the bolt-joint location and the number of bolts considering relative distances in mode shapes at the interface of bolt-jointed plates. The Modeling method and the optimized design method are verified based on the experimental and the FE analysis results.