• Journal of the Korean Society for Nondestructive Testing
• /
• v.36 no.3
• /
• pp.175-180
• /
• 2016

Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2006.03a
• /
• pp.180-190
• /
• 2006

Effects of panel zone (PZ) strength on cyclic seismic performance of the RBS connections was studied based on the validated finite element analysis. High-profile cyclic correlation of finite element model with the full-scale test results based on the material and geometric nonlinear post-buckling analysis was among the most significant consideration in this study. Numerical response results as affected by the panel zone strength reproduced the experimentally observed results quite reasonably. The finite element modeling capability of this study can be used to supplement or to replace in part the costly full-scale connection testing.

• Nuclear Engineering and Technology
• /
• v.55 no.5
• /
• pp.1665-1670
• /
• 2023

It is shown that in the IBR-2M reactor by the end of the reactor cycle, changes in dynamics are observed associated with a strong weakening of the fast power feedback (PF), as a result of which the reactor becomes oscillatorily unstable. After each week of zero-power operation the negative changes in reactor dynamics disappear and the stability of the reactor is restored. Thus, the reactor undergoes cyclic changes in the oscillatory instability. The correlation between of a fast PF and a slow PF is experimentally observed, which makes it possible to almost completely eliminate the cyclic component of instability by changing the control mode of rods of the control system.

• The Research Journal of the Costume Culture
• /
• v.4 no.3
• /
• pp.383-394
• /
• 1996

Even it's not easy to in the cycle of the change without the qualification of the data, but we can try to figure out a cycle of change in fashion as Kroeber used content analysis. As content analysis with quantitative data increases the objectivity, especially in the case of highly complex materials like s appearance, multi-directional research method; quantitative and qualitative methods are combined in this study. In this research, first the change in hair length(HL), hair width(HW), hair height(HH) was examined to find out possible cyclic aspects of change in each elements and the significant relationships among the hair style was probed and the cyclic aspects between hair style elements and skirt style elements were compared. The data was analyzed by using Time series analysis and Pearson correlation coefficients. The statistical analysis of the hair style of 20th century showed that the hair style's elements changed independently and indicated the cyclic aspects in hair style as Kroeber's fashion cycle. To consider of this result, the hair style changed in a cyclic pattern, its pattern were different from skirt style's. And as hair style's change was affected by change, the hair styles change appeared during wars and disappeared during a social stabilization; this result supports social change theory.

• Computers and Concrete
• /
• v.10 no.4
• /
• pp.419-434
• /
• 2012

This paper presents a finite element (FE) model for predicting the nonlinear response and behavior of a reinforced concrete T-beam deficient in shear under cyclic loading. Cracking loads, failure loads, response hysteresis envelopes and crack patterns were used as bench mark for comparison between experimental and FE results. A parametric study was carried out to predict the optimum combination of the open and close crack shear transfer coefficients (${\beta}_t$ and ${\beta}_c$) of the constitutive material model for concrete. It is concluded that when both shear transfer coefficients are equal to 0.2 the FE results gave the best correlation with the experimental results. The results were also verified on a rectangular shear deficient beam (R-beam) tested under cyclic loading and it is concluded that the variation of section geometry has no effect on the optimum choice of the values of shear transfer coefficients of 0.2. In addition, a parametric study based on the variation of concrete compressive strength, was carried out on the T-beam and it is observed that the variation of concrete compressive strength has little effect on the deflection. Further conclusions and observations were also drawn.

• Coupled systems mechanics
• /
• v.10 no.6
• /
• pp.545-560
• /
• 2021

An in situ experiment imaged via X-ray computed tomography was performed on a continuous glass fiber mat reinforced epoxy resin composite. The investigated dogbone specimen was subjected to uniaxial cyclic tension. The reconstructed scans (i.e., gray level volumes) were registered via Digital Volume Correlation. The calculated maximum principal strain fields and correlation residual maps exhibited strain localization areas within the material bulk, thus indicating damage inception and growth toward the specimen surface. Strained bands and areas of elevated correlation residuals were mainly concentrated in the narrowest gauge section of the investigated specimen, as well as on the specimen ligament edges. Gray level residuals were laid over the corresponding mesostructure to highlight and characterize damage development within the material bulk.

• Journal of the Korean Geosynthetics Society
• /
• v.10 no.3
• /
• pp.33-41
• /
• 2011

In this study, it conducted a compaction quality control test in 29 domestic construction sites and investigated the relationship between classical method (Cyclic Plate bearing test) and LFWD test with subgrade materials which consist in sandy soil and gravelly soil. According to the test results, the most of soil types were mostly satisfied with specification criterion and gravelly soils were easily satisfied with values over 3 times greater than specification criterion. In term of the correlation relation of soil modulus with the two compaction quality control test methods, it is shown that the sandy soil types were a good correlation, while gravelly soil types with a high stiffness materials were indicated less correlation. After the compensation for stress condition, a linear regression for elastic modulus were higher correlation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2004.05a
• /
• pp.708-711
• /
• 2004

A typical structure was selected for a prototype and four 1:2.5 scaled models, representing the subassemblage including the interior column and the deep beam, were constructed. The transverse reinforcement was designed according to ACI procedure and the procedure proposed by Sheikh. In this study, the correlation between the experimental and analytical responses of the subassemblages subjected to the cyclic lateral displacement were evaluated through investigation of lateral load-lateral deformation, local deformation characteristics by using a nonlinear FEM analysis program RCAHEST.

• Proceedings of the IEEK Conference
• /
• 1999.06a
• /
• pp.81-85
• /
• 1999

DWMT VDSL system needs A/D converter clock, bit clock, symbol clock, frame clock, etc. DMT ADSL system utilizes a correlation method which makes use of cyclic prefix or preamble pattern for clock recovery. But the correlation method is difficult to apply to the DWMT system because modulated symbols are overlapped in the time domain. This paper proposes a novel clock recovery method which can be used for the DWMT system due to its inherent independence of the modulation method. This new method is verified by SPICE simulations.

• Journal of Korean Society for Atmospheric Environment
• /
• v.9 no.3
• /
• pp.183-190
• /
• 1993

For the efficient control of photochemical smog materials, the researches on the change patterns of photochemical smog precursors are indispensable. In this study, a time-series analysis was performed for the auto-monitoring data of Kwanghwamun and Jamsil stations in 1990, and the change patterns of photochemical smog materials were studied. Especially, auto-correlation coefficients were analyzed to investigate the cyclic characteristics of pollutants in question and cross-correlation coefficients to investigate the correlations between pollutants adjusted for time lag and between $O_3$ and meteorological factors. Results of researches are as follows: First, in the case of NO and $NO_2$ intimately related to human activities, 12-hour cycle was prevalent. But $O_3$ showed 24-hour cycle. Second, NO showed a relatively high correlation with $O_3$ and usually developed into $O_3$ 5 to 7 hours later. Third, temperature, insolation intensity, and wind speed showed a positive correlation with $O_3$ while relative humidity a negative correlation.