• Carbon letters
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• v.6 no.3
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• pp.173-180
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• 2005

In this study, AR (aromatic resin) pitch was employed as the matrix-precursor for carbon/carbon composite because it exhibits much higher coke yield than coal tar pitch. As a result, a fabrication process of carbon/carbon composites can be shortened. It has been known that the pitches may cause swolling problem during the carbonization process. In order to restrain the swelling occurrence, a small quantity of carbon black was added to the AR pitch. Due to addition of carbon black the swelling was decreased largely and the perform can be infiltrated with the AR pitch. The densification efficiency of the performs was compared with various matrix-precursors. The coke yield of matrixprecursors, the morphology and the degree of graphitization of carbon matrix were analyzed.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.113-121
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• 1997

Human reliability attempts to make precise quantitative analyses and predictions of the performance of human-machine(or product) systems. In order to yield more precise human error analysis, precise human error probabilities(HEPs) must be used in the analysis. However, because human behavior is influenced by factors that are called performance shaping factors(PSFs), the effects of PSFs must be considered to obtain precise HEPs, These are called basic HEPs or situation-specific HEPs. This paper presents a theoretical method for obtaining basic HEPs (i.e. , considering PSFs) in quantitative human error analysis. In this method, the weight which characterizes the degree of importance of several PSFs is obtained by the analytic hierarchy process. The quality scores of PSFs in the task situation are obtained by percentile concept. These scores are used in conjunction with the relative Importance weights of PSFs to compute the composite quality percentile score of PSFs in the task situation. Then, a new mapping method of the composite quality percentile score of PSFs into a situation-specific basic HEP is proposed with a numerical example.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.04a
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• pp.87-90
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• 2003

In this paper, the electromechanical displacements of curved actuators such as THUNDER are calculated by finite element method to design the optimal configuration of curved actuators. To predict the pre-stress in the device due to the mismatch in coefficients of thermal expansion, the adhesive as well as metal and PZT ceramic is also numerically modeled by using hexahedral solid elements. Because the modeling of these thin layers causes the numbers of degree of freedom to increase, large-scale structural analyses are performed in a cluster system in this study. The curved shape and pre-stress in the actuator are obtained by the cured curvature analysis. The displacement under the piezoelectric force by an applied voltage is also calculated to compare the performance of curved actuator. The thickness of metal and adhesive, the number of metal layer are chosen as design factors.

• Steel and Composite Structures
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• v.23 no.2
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• pp.239-250
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• 2017

In the concept of two-parameter fatigue failure criterion, the material fatigue failure is determined by the damage degree and the current stress level. Based on this viewpoint, a residual strength degradation model for stud shear connectors under fatigue loads is proposed in this study. First, existing residual strength degradation models and test data are summarized. Next, three series of 11 push-out specimen tests according to the standard push-out test method in Eurocode-4 are performed: the static strength test, the fatigue endurance test and the residual strength test. By introducing the "two-parameter fatigue failure criterion," a residual strength calculation model after cyclic loading is derived, considering the nonlinear fatigue damage and the current stress condition. The parameters are achieved by fitting the data from this study and some literature data. Finally, through verification using several literature reports, the results show that the model can better describe the strength degradation law of stud connectors.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05c
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• pp.233-236
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• 2002

This paper describes the properties of between the residual voltage for ${\gamma}$-irradiated in electric power cable using in nuclear power generating station. As these properties related with ${\gamma}$-irradiation dose, it is suggested that these properties can be utilized as a index of irradiation degradation. From theory and experiment We found the residual voltage is not influenced by cable length. We found that residual voltage of basic composite and practical composite have not a difference an occasion be the same cable length. As the ratio of degradation increases, the residual voltage in the initial time range increases and the peak moves to the shorter time. Therefore, We can know the degree of radiation degradation from the position of the peak.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.04a
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• pp.103-108
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• 1999

A synthesized model of pultrusion process considering thermally induced deformatiion was established. The model was composed of liquid resin flow model thermo-chemical analysis and linear elastic analysis. in order to verify the above-mentioned models several experiments were performed. A laboratory scale pultrusion line was established and glass/polyester composites were fabricated. the experimental results were compared with the calculated ones. The model successfully could estimate degree of cure pulling force and amount of process-induced deformation.

• Steel and Composite Structures
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• v.19 no.6
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• pp.1369-1379
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• 2015

In this study, a progressive damage modeling is developed to predict functional failure pressure of GRP pipes subjected to internal hydrostatic pressure. The modeling procedure predicts both first-ply failure pressure and functional failure pressure associated with the weepage phenomenon. The modeling procedure is validated using experimental observations. The random parameters attributed to the filament winding production process are identified. Consequently, stochastic simulation is conducted to investigate the influence of induced inconsistencies on the functional failure pressures of GRP pipes. The obtained results are compared to realize the degree to which random parameters affect the performance of the pipe in operation.

• Structural Engineering and Mechanics
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• v.43 no.2
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• pp.253-271
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• 2012

To analyze the bending and transverse shear effects of laminated composite plates, a thirteen nodes triangular element will be presented. The suggested formulations consider a parabolic variation of the transverse shear strains through the thickness. As a result, there is no need to use shear correction coefficients in computing the shear stresses. The proposed element can model both thin and thick plates without any problems, such as shear locking and spurious modes. Moreover, the effectiveness of $w_{,n}$, as an independent degree of freedom, is concluded by the present study. To perform the accuracy tests, several examples will be solved. Numerical results for the orthotropic materials with different boundary conditions, shapes, number of layers, thickness ratios and fiber orientations will be presented. The suggested element calculates the deflections and stresses more accurate than those available in the literature.

• Proceedings of the KIEE Conference
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• 1994.07b
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• pp.1499-1501
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• 1994

This paper studies on the outdoor field test facilities which are established for weather-resist and mechanical-resist property teat of composite insulator. We have established measuring and data acquisition system for various test conditions -leakage current, temperature, humidity, wind direction, wind velocity and rainfall. The merry-go-round test and salt fog test have been studied in order to evaluate non tracking property of rubber material. Especially we have checked the relationship between hydrophobicity and outdoor exposure degree by contact angle measurement.

• Journal of Industrial Technology
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• v.18
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• pp.97-105
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• 1998

The most of the design engineers for construction has academic background of bachelors degree. Theories for advanced composite structures are too difficult for such engineers and some simple but accurate enough methods are necessary. The senior author has reported that some laminate orientations have decreasing values of $D_{16}$, $B_{16}$, $D_{26}$ and $B_{26}$ stiffnesses as the ply number increases. Such plates behave as special orthotropic plates and simple formulas developed by the author can be used. Most of the bridge and building slabs on girders have large aspect ratios. For such cases further simplification is possible by neglecting the effect of the longitudinal moment terms($M_x$) on the relevant partial differential equations of equilibrium. In this paper, the result of the study on the subject problem is presented.