• Title/Summary/Keyword: Cross effects

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Transverse cracking based numerical analysis and its effects on cross-ply laminates strength under thermo-mechanical degradation

  • Abdelatif, Berriah;Abdelkader, Megueni;Abdelkader, Lousdad
    • Structural Engineering and Mechanics
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    • v.60 no.6
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    • pp.1063-1077
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    • 2016
  • Components manufactured from composite materials are frequently subjected to superimposed mechanical and thermal loadings during their operating service. Both types of loadings may cause fracture and failure of composite structures. When composite cross-ply laminates of type [$0_m/90_n]_s$ are subjected to uni-axial tensile loading, different types of damage are set-up and developed such as matrix cracking: transverse and longitudinal cracks, delamination between disoriented layers and broken fibers. The development of these modes of damage can be detrimental for the stiffness of the laminates. From the experimental point of view, transverse cracking is known as the first mode of damage. In this regard, the objective of the present paper is to investigate the effect of transverse cracking in cross-ply laminate under thermo-mechanical degradation. A Finite Element (FE) simulation of damage evolution in composite crossply laminates of type [$0_m/90_n]_s$ subjected to uni-axial tensile loading is carried out. The effect of transverse cracking on the cross-ply laminate strength under thermo-mechanical degradation is investigated numerically. The results obtained by prediction of the numerical model developed in this investigation demonstrate the influence of the transverse cracking on the bearing capacity and resistance to damage as well as its effects on the variation of the mechanical properties such as Young's modulus, Poisson's ratio and coefficient of thermal expansion. The results obtained are in good agreement with those predicted by the Shear-lag analytical model as well as with the obtained experimental results available in the literature.

Effects of Pretreatment for Controlling Internal Water Transport Direction on Moisture Content Profile and Drying Defects in Large-Cross-Section Red Pine Round Timber during Kiln Drying

  • Bat-Uchral BATJARGAL;Taekyeong LEE;Myungsik CHO;Chang-Jin LEE;Hwanmyeong YEO
    • Journal of the Korean Wood Science and Technology
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    • v.51 no.6
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    • pp.493-508
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    • 2023
  • Round timber materials of 600 mm length, cut from large-cross-section round timber of red pine (Pinus densiflora S. et Z.) of 450 mm width and 4.2 m length, were prepared as the target of kiln drying in this study. After treating the target materials through end sealing (ES), end sealing - kerfing (ES-K), lateral sealing - end sealing - boring (LS-ES-B), or lateral sealing - partial end sealing (LS-PES), the effects of the treatment on the incidence of drying defects were determined. The target materials with exposed lateral surface and sealed cross surface were steamed at the initial temperature of 65℃ above the official pest control temperature of 56℃, followed by kiln drying toward the final temperature of 75℃. The target materials with sealed lateral surfaces, on the other hand, were dried at the initial temperature of 90℃ at almost the maximum temperature of conventional kiln drying, as there is no risk of early check formation caused by surface moisture evaporation. The final temperature was set at approximately 100℃. The drying time, taken for the target materials with initial moisture content of 70%-80% to reach the target moisture content of 19%, varied across treatment conditions. The measured drying time was 1,146 hours (approximately 48 days) for the timber with sealed cross surface and 745 hours (approximately 31 days) for the timber with sealed lateral surface, until the moisture content reached the target level. The formation of surface checks could not be prevented in the control and ES groups, but a definite preventive effect was obtained for the LS-ES-B and LS-PES groups.

Effect of Cross Beams on Live Load Distribution in Rolled H-beam Bridges (압연형강(H형강) 거더교의 가로보가 활하중 횡분배에 미치는 영향)

  • Yoon, Dong Yong;Eun, Sung Woon
    • Journal of Korean Society of Steel Construction
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    • v.18 no.5
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    • pp.535-542
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    • 2006
  • In this study, the effects of cross beams on the lateral distribution of live loads in composite rolled H-beam girder bridges, were investigated through three-dimensional finite element analysis. The parameters considered in this study were the inertial moment ratio between the main girder and the cross beam, the presence of the cross beam, and the number of cross beams. The live load lateral distribution factors were investigated through finite element analysis and the customary grid method. The results show that there was no difference between the bridge models with and without a cross beam. The cross beam of the beam and frame types also showed almost the same live load lateral distribution factors. However, the finite element analysis showed that the concrete slab deck plays a major role in the lateral distribution of a live load, and consequently, the effect of the cross beam is not so insignificant that it can be neglected.

The Effects of Annealing on Resistant Starch Contents of Cross-linked Maize Starches (Annealing 처리가 가교결합 옥수수전분의 저항전분 수율에 미치는 영향)

  • Mun, Sae-Hun;Shin, Mal-Shick
    • Korean Journal of Food Science and Technology
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    • v.34 no.3
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    • pp.431-436
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    • 2002
  • To develop a method for increasing RS level in maize starch, cross-linked resistant starches treated with annealing were prepared. Maize starch and amylomaize VII were used in the study and annealed at $40{\sim}60^{\circ}C$ before cross-linking modification. To compare effect of annealing below gelatinization temperature, starches were heat treated at 70 and $100^{\circ}C$. RS contents were assayed by pancreatin-gravimetric (P/G) method. When maize starch and amylomaize VII were cross-linked at $45^{\circ}C$ and pH 11.0 by slurrying the starch on a solution of STMP(sodium trimetaphosphate), STPP(sodium tripolyphosphate), and sodium sulfate, RS content was 14.7% and 45.3%, respectively. Annealing below gelatinization temperature before cross-linking increased RS contents of prepared cross-linked starches but did not affect the swelling power. Heat treatment above gelatinization temperature increased the swelling power of cross-linked starch prepared from maize starch. The characteristics by X-ray diffractometry and scanning electron microscopy of cross-linked resistant starch were not changed by annealing.

Experimental Study of Three-Dimensional Turbulent Flow in a $90^{\circ}C$ Rectanglar Cross Sectional Strongly Curved Duct (직사각형 단면을 갖는 $90^{\circ}C$ 급곡관 내의 3차원 난류유동에 관한 실험적 연구)

  • 맹주성;류명석;양시영;장용준
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.15 no.1
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    • pp.262-273
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    • 1991
  • In the present study, the steady, incompressible, isothermal, developing flow in a 90.deg. rectangular cross sectional strongly curved duct with aspect ratio 1:1.5 and Reynolds number of 9.4*10$^{4}$ has been investigated. Measurements of components of mean velocities, pressures, and corresponding components of the Reynolds stress tensor are obtained with a hot-wire anemometer and pitot tube. In general, flow in a curved duct is characterized by the secondary vortices which are driven mainly by centrifugal force-radial pressure gradient imbalance, and the stress field stabilizing effects near the convex wall and destablizing effects close to the concave wall. It was found that the secondary mean velocities attain values up to 39% of the bulk velocity and are largely responsible for the convections of Reynolds stress in the cross stream plane. Therefor upstream of the bend the Reynolds stress are low. Corresponding to the small boundary layer thickness. At successive planes, large values of Reynolds stress were observed near the concave surface and the side wall.

Kinetics and Mechanism of the Anilinolysis of Bis(aryl) Chlorophosphates in Acetonitrile

  • Barai, Hasi Rani;Lee, Hai-Whang
    • Bulletin of the Korean Chemical Society
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    • v.32 no.6
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    • pp.1939-1944
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    • 2011
  • The nucleophilic substitution reactions of bis(Y-aryl) chlorophosphates (1) with substituted anilines and deuterated anilines are investigated kinetically in acetonitrile at 35.0 $^{\circ}C$. The kinetic results of 1 are compared with those of Y-aryl phenyl chlorophosphates (2). The substrate 1 has one more identical substituent Y compared to substrate 2. The cross-interaction between Y and Y, due to additional substituent Y, is significant enough to result in the change of the sign of cross-interaction constant (CIC) from negative ${\rho}_{XY}$ = -1.31 (2) to positive ${\rho}_{XY}$ = +1.91 (1), indicating the change of reaction mechanism from a concerted $S_N2$ (2) to a stepwise mechanism with a rate-limiting leaving group departure from the intermediate (1). The deuterium kinetic isotope effects (DKIEs) involving deuterated anilines ($XC_6H_4ND_2$) show secondary inverse, $k_H/k_D$ = 0.61-0.87. The DKIEs invariably increase as substituent X changes from electron-donating to electron-withdrawing, while invariably decrease as substituent Y changes from electron-donating to electron-withdrawing. A stepwise mechanism with a rate-limiting bond breaking involving a predominant backside attack is proposed on the basis of positive sign of ${\rho}_{XY}$ and secondary inverse DKIEs.

Effect of Formaldehyde on the Water Resistance of MDF Cement Composites

  • Nho, Jun-Seok;Park, Choon-Keun;Park, Sang-Heul
    • The Korean Journal of Ceramics
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    • v.5 no.3
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    • pp.278-283
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    • 1999
  • Formaldehyde has widely been used for the cross-linking of polyvinyl alcohol polyvinyl alcohol polymer. The effects of formaldehyde on the water resistance of MDF cement composites were investigated as a function of types of catalyst, base or acid, and the amount of formaldehyde. The acetalization, reaction of OH group of PVA with aldehyde, was ended incompletely under base atmosphere. However, by addition of citric acid, the cross-linking of PVA polymer could be acheved through acetalization of PVA and formaldehyde. The effects of these different patterne according to the types of catalyst on the water resistance of MDF cement were studied by the preparation of PVA films and MDF composites. Thanks to the cross-linking reaction of PVA polymer chains by formaldehyde, the modified PVA films and MDF composites showed a good water-resistant propety. The modified MDF cement composite to which 3 wt% formaldehyde and 1 wt% cirtic acid were added showed 80% of initial flexural strength and good interfacial state between cement grain and polymer matrix. However, 4 wt% formaldehyde deteriorted the processing conditions, microstructures and eventually the flexural strength, causing sharp increase in the viscosity of sample dough during the mixing process. To study the relatins of flexural strength and interface of cement grain and polymer matrix, SEM and MIP measurement were performed.

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A Short-Term Longitudinal Study on the Reciprocal Relations between Mothers' Depression and Their Preschoolers' Emotional Problems (어머니의 우울과 학령전기 유아의 정서 문제 간의 상호적 관계에 대한 단기 종단연구)

  • Chang, Young Eun;Han, Hyo Jeong
    • Human Ecology Research
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    • v.54 no.5
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    • pp.551-564
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    • 2016
  • This study examined the causal relationship between a mothers' depression and the emotional problems of their preschool-aged children as indicated by anxiety, depression and emotional reactivity. We analyzed data from 1,528 mothers and their children from the Panel Study of Korean Children (PSKC) collected when the children were 4 years old and 5 years old. Autoregressive cross-lagged modeling was conducted using AMOS ver. 23.0 to investigate the longitudinal reciprocal effects between mothers' depression and children's emotional problems. The results indicated that both mothers' depression and children's emotional problems were relatively stable between the ages of 4 to 5. There were significant cross-lagged effects from the mothers' depression to children's emotional problems and from children's emotional problems to mothers' depression. Mothers reported higher levels of depression when the children were 4 years old and the children showed more anxiety, depression and emotional reactivity when they were 5 years old. Emotional problems when the children were 4 predicted greater depression among mothers 1 year later. We also examined the group difference (between boys and girls) in the study model. Gender differences were not statistically supported. The results suggested that early assessment and intervention for mothers' depression and children's emotional problems are essential for a healthy mother-child relationship and later child outcomes.