• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.25 no.3
• /
• pp.74-80
• /
• 2017

As for A rotary wing aircraft, the configuration change about split yaw swaged rod was executed to improve hit treat capability for dealing with a long rod. The purpose of this study was to analyze if or not the quality of the split yaw swaged rod was obtained, and so the flight safety was ensured or not. Buckling analysis, Coupling Thread Strength Analysis, Thermal Stress analysis and Rod Natural Frequency Analysis were executed for structural analysis. The results of the analysis were presented that the split rod had the sufficient margin of safety and so there were no anomalies in the limit load and no failures in the ultimate load. And there were no resonances in result of natural frequency analysis. In conclusion, this study showed that the split yaw swaged rod had structural safety, so flight safety of rotary wing aircraft was secured and there was no problem in aircraft operation. It is certain that the technology of splitting the yaw swage rod will contribute to the operational Safety of the rotary wing aircraft in the future.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.6
• /
• pp.1-10
• /
• 2013

Probabilistic nonlinear first ply failure loads of flat composite panels and nonlinear buckling loads of curved composite panels with cutouts are estimated to provide the more reliable main load carrying structure in the renewable energy industry and offshore structures. The response surface method approximates limit state surface to a second order polynomial form of random variables with the results of deterministic finite element analyses at given sampling design points. Furthermore, the iterative linear interpolation scheme is used to obtain a more accurate approximation of the limit state surface near the most probable failure point (MPFP). The advanced first order second moment method and the Monte Carlo method are performed on an approximated limit state surface to evaluate the probability of failure. Finally, the sensitivity of the reliability index with respect to transformed random variables is investigated to figure out the main random variables that have an effect on failures.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2004.05a
• /
• pp.214-220
• /
• 2004

The automotive industry has recently shown a growing interest in tube hydroforming. Even though many structural parts in automotives have been produced from the cylindrical tubes, many failures - wrinkling, buckling, folding back, bursting and so on - are frequently experienced during the tube hydroforming process under improper forming conditions. In this paper, analytical studies are performed to determine the forming limits for the tube hydroforming process and demonstrate how the loading path influences the forming limit. The theoretical results for the forming limits of the wrinkling and bursting are then compared with the experimental results for an aluminum tube.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.5
• /
• pp.665-673
• /
• 2008

The composite structures of steel and reinforced concrete, which have been widely used in large-scale concrete structures, werestudied to investigate the cause of unexpected cracks and to verify the composite actions between the two materials. Vertical stiffeners between flanges, studs and dowel bars, stirrups, and concrete strength were chosen as experimental variables in afour-point loading test. The results showed that the vertical stiffener prevented not only the local web buckling, but also bond failures between steel and concrete. It increased the flexural resistance (fracture loads) due to the composite action of two materials, compared withthose of any experimental variable. However, the composite behavior of steel reinforced concrete beam was not affected seriously by additional studs, dowel bars, stirrups, and concrete strength.

• Transactions of Materials Processing
• /
• v.17 no.1
• /
• pp.52-58
• /
• 2008

Tube hydroforming process is generally consisted with pre-bending, preforming and hydroforming processes. Among forming defects which may occur in tube hydroforming such as buckling, wrinkling and bursting, the wrinkling and bursting by local instability under excessive tensile stress mode were mainly caused by thinning phenomenon in the manufacturing process. Thus the accurate prediction and suitable evaluation of the thinning phenomenon play an important role in designing and producing the successfully hydroformed parts without any failures. In this work, the formability on hydroformed part for automobile, i.e. engine cradle, was evaluated using finite element analysis. The initial tube radius, loading path with axial feeding force and internal pressure, and preformed configuration after preforming process were considered as the dominant process parameters in total tube hydroforming process. The effects on these process parameters could be confirmed through the numerical experiments with respect to several kinds of finite element simulation conditions. The degree of enhancement on formability with each process parameters such as initial tube radius, loading path and preform configuration were also compared. Therefore, it is noted that the evaluation approach of the formability on hydroformed parts for lots of industrial fields proposed in this study will provide one of feasible methods to satisfy the increasing practical demands for the improvement of the formability in tube hydroforming processes.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.34 no.3
• /
• pp.37-43
• /
• 2006

Six types of hat stiffened composite panels were manufactured with different bonding methods and stiffener section shapes and compression testing of these panels were performed. The panels showed similar behaviors in bucking and postbuckling region before a skin-stiffener separation failure occurred. Although all the separation failures occurred at the same locations of stiffener flanges close by skin buckling crests, the separation loads, separation failure growth behaviors and final collapse loads were different with respect to bonding methods and stiffener section shapes. As the separation failure initiated early and propagated larger area, collapse loads and structural efficiency of the panels decreased.

• Wind and Structures
• /
• v.25 no.1
• /
• pp.79-100
• /
• 2017

The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65 m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

• Journal of Korean Society of Steel Construction
• /
• v.20 no.2
• /
• pp.279-288
• /
• 2008

In this study, the slip behavior of high-tension bolted joints subjected to compression force is investigated through 3D finite element analysis and experiments. The relation with sliding load, bolt deformation, and failure load are studied with the metal thickness affecting the bolted joint. The post-sliding behavior considering bolt stiffness is presented and compared with the results by finite element and experiments. The finite element model is constructed by solid elements in ABAQUS, in consideration of all the friction effects between metal plates and bolts. The stress-strain relations in the literature are used, and the sliding displacements and axial stresses around the bolt connection are investigated. The flexural buckling of species happened when the plate thickness is less than the bolt diameter. However, the shear failures of bolt occurred in the opposite case.

• Journal of Korean Society of Steel Construction
• /
• v.21 no.3
• /
• pp.257-266
• /
• 2009

The results of the analysis of the structural behavior of diagrid nodes that were subjected to cyclic loads such as wind and earthquakes was not fully understood due to difficulties in considering the welding type. In this study, diagrid nodes were tested to determine their behavior when they are subjected to seismic or wind loads. Five specimens were designed and fabricated. The corresponding test parameters were the welding type for each point and the length of the overlap of the side stiffener and the brace web. Tensile force was applied to one diagrid brace member, and compression force was applied to the other diagrid brace member. Cyclic loading was applied until the failure. The test showed that failures are due to axial stress from axial force and the additional bending moment of the two combined axial forces that have different directions. Tensile failure was observed from the tensile force, and local buckling was observed from the compressive force at the flange of the brace member. In addition, the welding type and the length overlap affected the initial stiffness, the yielding stress, and the energy absorption of the diagrid node.

• Composites Research
• /
• v.16 no.6
• /
• pp.16-22
• /
• 2003

This paper studied the AE(acoustic emission) characteristics of the laminated composite structures. The composite stiffened panels under the compressive loading emitted various AE signals when they buckled or changed the buckling modes. In addition, the failure initiated and propagation generated a lot of complex signals. From the continuous signal generation. we identified when the failures initiated and whether they propagated or not. The single lap joint of laminated plates under tensional load also generated AE signals when bonding region failed. The first failure occurrence and its propagation are monitored by generated AE signals. The characteristics of AE signals used in this analysis are cumulative hits, hit distribution, peak frequency of generated AE waveform and amplitude of signals. The analysis of AE signals shows that continuous increment of cumulative hits can be regarded as damage propagation and three dominant peak frequencies can correspond to typical failure modes in the laminated composites.