• Journal of the Society of Naval Architects of Korea
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• v.52 no.3
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• pp.248-254
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• 2015

The strength and fatigue life of Satin and Twill-woven CF/epoxy composite(CFRP) have been investigated. Damage mechanism fatigue method has been used to assess fatigue damage accumulation. It is based on measured residual stiffness and residual strength of carbon-fiber reinforced plastic(CFRP) laminates under cyclic loading. Fatigue damage evolution in composite laminates and predict fatigue life of the laminates were simulated by finite element analysis(FEA) method. The stress analysis was carried out in MSC patran/Nastran. A modified Hashin's failure criterion di rmfjapplied to predict the failure of the experimental data of fatigue life but a Ye-delamination criterion was ignored because of 2D modeling. Almost linear stiffness and strength degradation were observed during most of the fatigue process. These stress distribution data were adopted in the simulation to simulate fatigue behavior and estimate life of the laminates. From the results, the predicted fatigue life is more conservatively estimated than the experimental results.

• Steel and Composite Structures
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• v.17 no.5
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• pp.573-599
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• 2014

A new type of connection for steel-concrete composite bridges was developed by the Steel Structures Laboratory of Ecole Poytechinque $F{\acute{e}}d{\acute{e}}rale$ de Lausanne. Resistance to longitudinal shear is based on the development of shear stresses in the confined interfaces which form the connection. Confinement is provided by the reinforced concrete slab which encloses the connection and restrains the uplift (lateral separation) of the interfaces by developing normal stresses. The experimental investigation of the interfaces, under static and cyclic loading, enabled the development of the laws describing the structural behaviour of each interface. Those laws were presented by the authors in previous papers. The current paper focuses on the continuity of the research. It presents the experimental investigation on the new connection by means of push-out tests on specimens submitted to static and cyclic shear loading. Investigation revealed that the damage in the connection, due to cyclic loading, is expressed by the accumulation of a residual slip. A safe fatigue failure criterion is proposed for the connection which enabled the verification of the connection for the fatigue limit state with respect to the limit of fatigue. A numerical model is developed which takes into account the laws describing the interface behaviour and the analytical expressions for the confinement effect, the latter obtained by performing finite element analysis. This numerical model predicts the shear resistance of the connection and enables to assess its fatigue limit which is necessary for the fatigue design proposed.

• Steel and Composite Structures
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• v.24 no.4
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• pp.467-479
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• 2017

The stud is one of the most frequently used shear connectors which are important to the steel-concrete composite action. The static and fatigue behavior of stud in the steel fiber reinforced concrete (SFRC) were particularly concerned in this study through the push-out tests and analysis. It was for the purpose of investigating and explaining a tendency proposed by the current existing researches that the SFRC may ameliorate the shear connector's mechanical performance, and thus contributing to the corresponding design practice. There were 20 test specimens in the tests and 8 models in the analysis. According to the test and analysis results, the SFRC had an obvious effect of restraining the concrete damage and improving the stud static performance when the compressive strength of the host concrete was relatively low. As to the fatigue aspect, the steel fibers in concrete also tended to improve the stud fatigue life, and the favorable tensile performance of SFRC may be the main reason. But such effect was found to vary with the fatigue load range. Moreover, the static and fatigue test results were compared with several design codes. Particularly, the fatigue life estimation of Eurocode 4 appeared to be less conservative than that of AASHTO, and to have higher safety redundancy than that of JSCE hybrid structure guideline.

• Composites Research
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• v.17 no.4
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• pp.68-73
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• 2004

An analytical study was conducted to characterize the fatigue crack growth behavior of pre-cracked aluminum plates repaired with asymmetric bonded composite patch. For single-sided repairs, due to the asymmetry and the presence of out-of$.$plane bending, crack front shape would become skewed curvilinear started from a uniform through-crack profile, as observed from Previous studies. Therefore, for the accurate investigation of fatigue behavior, it is necessary to predict the actual crack front evolution and take it into consideration in the analysis. In this study, the fatigue analysis of single-sided repairs considering crack front shape development was conducted by implementing three-dimensional successive finite element method coupled with linear elastic fracture mechanics (LEFM) concept, which enables the growing crack front to be directly traced and modeled in a step by step way. Through conducting present analysis technique, crack path of the patched plate as well as the fatigue life was evaluated with sufficient accuracy. The analytical predictions of both the crack front shape evolution and the fatigue life were in good agreement with the experimental observations.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.651-657
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• 2010

A composite piston with a crown made of steel and a skirt made of NCI is used in a marine diesel engine, which has a maximum firing pressure of over 180 bar and a high thermal load. In the fatigue design of the composite piston, the fatigue is influenced by factors such as the load type, surface roughness, and temperature; further, the distribution ratio of the firing force from the crown to the skirt is important for optimizing the design of the crown and skirt. In this study, the stress gradient method was used to consider the effect of the load type. The temperature field on the piston was predicted by cocktail-shaking cooling analysis, and influence of high temperature on fatigue strength was investigated. The load transfer ratio and contact pressure were optimized by design of the surface shape and accurate tolerance analysis. Finally, the cooling performance and durability design of the composite piston were verified by performing a long-term prototype test.

• Steel and Composite Structures
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• v.18 no.5
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• pp.1279-1290
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• 2015

The main role of studs, which act as connectors of the steel-concrete composite structures, is to ensure that the steel and the concrete work together as a whole. The studs in steel-concrete composite structures bear the shearing force in the majority of cases, but in certain locations, such as the mid-span of a simply supported composite beam, the studs bear axial uplift force. The previous studies mainly focused on the shearing performance of the stud by some experimental and theoretical effort. However, rare studies involved the uplift performance of studs. In this paper, the single stud uplift test on 10 composite specimens was performed. Meanwhile, based on the test, numerical analysis was introduced to simulate the concrete damage process due to the stud uplifted from concrete. The static ultimate bearing capacity, under which the stud connector was pulled out from the damaged reinforced concrete, is much larger than the cyclic ultimate bearing capacity, under which the weld joint between stud and steel plate fractured. According to the fatigue test results of 7 specimens, the fatigue S-N curve of the construction detail after minus 2 times standard deviation is $logN=24.011-9.171\;log{\Delta}{\sigma}$, the fatigue strength corresponding to $2{\times}10^6$ cycles is 85.33 MPa.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.121-124
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• 2004

The purpose of this study is to define the optimized layer pattern of composite wind turbine blade by using a commercial FEM program and to perform the fatigue test of T-Bolt. FEM analysis is done by using a PATRAN and ABAQUS to get a information about stress distribution ,critical deformation shape and get a critical load factor in local buckling analysis. As a result of the linear and nonlinear structural analysis, layer pattern of blade was optimized. T-Bolt is a connecting part of wind turbine blade and rotor hub, therefore T-bolt is cirtical part of wind turbine blade. T-bolt fatigue test is conducted to get a information of life cycle of T-bolt. The test is done by using a hydraulic actuator system

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1281-1289
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• 2011

This paper deals with several statistical distribution functions for the analysis of fatigue life data of composite laminates for small wind-turbine blades. A series of tensile tests was performed on triaxial glass/epoxy laminates for loading directions of $0^{\circ}$, $45^{\circ}$, and $90^{\circ}$. Then, fatigue tests were carried out to determine the fatigue life at the aforementioned loading directions and the fatigue stresses at four levels. Two-parameter Weibull, three-parameter Weibull, normal, and log-normal distributions were used to fit the fatigue life data of the triaxial composite laminates. The three-parameter Weibull distribution most accurately described the fatigue life data measured experimentally for all the cases considered. Furthermore, the variation of fatigue life was simultaneously affected by the loading direction and fatigue stress level.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3176-3183
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• 2010

A multi-scale fatigue life prediction methodology of composite pressure vessels subjected to multi-axial loading has been proposed in this paper. The multi-scale approach starts from the constituents, fiber, matrix and interface, leading to predict behavior of ply, laminates and eventually the composite structures. The multi-scale fatigue life prediction methodology is composed of two steps: macro stress analysis and micro mechanics of failure based on fatigue analysis. In the macro stress analysis, multi-axial fatigue loading acting at laminate is determined from finite element analysis of composite pressure vessel, and ply stresses are computed using a classical laminate theory. The micro stresses are calculated in each constituent from ply stresses using a micromechanical model. Three methods are employed in predicting fatigue life of each constituent, i.e. a maximum stress method for fiber, an equivalent stress method for multi-axially loaded matrix, and a critical plane method for the interface. A modified Goodman diagram is used to take into account the generic mean stresses. Damages from each loading cycle are accumulated using Miner's rule. Monte Carlo simulation has been performed to predict the overall fatigue life of a composite pressure vessel considering statistical distribution of material properties of each constituent, fiber volume fraction and manufacturing winding angle.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.310-315
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• 2003

This paper described that rotating test and fatigue test of a small-scale hingeless hub system with composite rectangular blades. Generally Rotating stability and fatigue test technique is one of Key-technology on test and evaluation for helicopter rotor system Rotating test of hingeless rotor system was achieved by means of rotor vibration characteristic and aeroelastic stability test GSRTS, equipped with hydraulic actuator and 6-component rotating balance was used to test hingeless rotor system especially for an observation of blade motion including flawing, lagging and feathering. Rotating test was done in hover and forward flight condition. Small-scaled blade fatigue test condition was determined by blade load analysis with the reference table of composite materials(S-N curve). Fatigue test bench was developed for the estimation of blade fatigue life, and tested its characteristic.