• Composites Research
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• v.24 no.1
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• pp.10-16
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• 2011

Many tests are required to predict the fatigue life of composite laminates made of various materials and having different layup sequences. Aiming at reducing the number of tests, a methodology was presented in this paper to predict fatigue life of composite laminates based on fatigue life prediction of constituents, i.e. the fiber, matrix and interface, using micromechanics of failure. For matrix, the equivalent stress model which is generally used for isotropic materials was employed to take care of multi-axial fatigue loading. For fiber, a maximum stress model considering only stress along fiber direction was used. The critical plane model was introduced for the interface of the fiber and matrix, but fatigue life prediction was ignored for the interface since the interface fatigue strength was presumed high enough. The modified Goodman equation was utilized to take into account the mean stress effect. To check the validity of the theory, the fatigue life of three different GFRP laminates, UDT[$90^{\circ}2$], BX[${\pm}45^{\circ}$]S and TX[$0^{\circ}/{\pm}45^{\circ}$]S was examined experimentally. The comparison between predictions and test measurements showed good agreement.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Korean Journal of Metals and Materials
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• v.56 no.12
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• pp.915-920
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• 2018

With the development of modern microelectronics technologies, the power density of electronic devices is rapidly increasing, due to the miniaturization or integration of device elements which operate at high frequency, high power conditions. Resulting thermal problems are known to cause power leakage, device failure and deteriorated performance. To relieve heat accumulation at the interface between chips and heat sinks, thermal interface materials (TIMs) must provide efficient heat transport in the through-plane direction. We report on the enhanced thermal conduction of $Al_2O_3-based$ polymer composites, fabricated by the surface wetting and texturing of thermally conductive hexagonal boron nitride(h-BN) nanoplatelets with large anisotropy in morphology and physical properties. The thermally conductive polymer composites were prepared with hybrid fillers of $Al_2O_3$ macro beads and surface modified h-BN nanoplatelets. Hexagonal boron nitride (h-BN) has high thermal conductivity and is one of the most suitable materials for thermally conductive polymer composites, which protect electronic devices by efficient heat dissipation. In this study, we synthesized hexagonal boron nitride nanoparticles by the pyrolysis of cost effective precursors, boric acid and melamine. Through pyrolysis at $900^{\circ}C$ and subsequent annealing at $1500^{\circ}C$, hexagonal boron nitride nanoparticles with diameters of ca. 50nm were synthesized. We demonstrate that the addition of a small amount of calcium fluoride ($CaF_2$) during the preparation of the melamine borate adduct significantly enhanced the crystallinity of the h-BN and assisted the growth of nanoplatelets up to 100nm in diameters. The addition of a small amount of h-BN enhanced the thermal conductivity of the $Al_2O_3-based$ polymer composites, from 1.45W/mK to 2.33 W/mK.

• Geomechanics and Engineering
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• v.5 no.5
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• pp.463-483
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• 2013

Considering the influences of fluid penetration, casing, excavation processes of wellbore and perforation tunnels, the seepage-deformation finite element model of oil and gas well coupled with perforating technique is established using the tensile strength failure criterion, in which the user-defined subroutine is developed to investigate the dynamic evolvement of the reservoir porosity and permeability. The results show that the increases of perforation angle and decreases of perforation density lead to a higher fracture initiation pressure, while the changes of the perforation diameter and length have no evident influences on the fracture initiation pressure. As for initiation location for the fracture in wellbore, it is on the wellbore face while considering the presence of the casing. By contrast, the fractures firstly initiate on the root of the tunnels without considering casing. Besides, the initial fracture position is also related with the perforation angle. The fracture initiation position is located in the point far away from the wellbore face, when the perforation angle is around $30^{\circ}$; however, when the perforation angle is increased to $45^{\circ}$, a plane fracture is initiated from the wellbore face in the maximum horizontal stress direction; no fractures was found around perforation tunnels, when the angel is close to $90^{\circ}$. The results have been successfully applied in an oilfield, with the error of only 1.1% comparing the fracture initiation pressure simulated with the one from on-site experiment.

• Archives of Plastic Surgery
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• v.41 no.4
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• pp.407-413
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• 2014

Background Implant malposition can produce unsatisfactory aesthetic results after breast augmentation. The goal of this article is to identify aspects of the preoperative surgical planning and intraoperative flap fixation that can prevent implant malposition. Methods This study examined 36 patients who underwent primary dual plane breast augmentation through an inframammary incision between September 1, 2012 and January 31, 2013. Before the surgery, preoperative evaluation and design using the Randquist formula were performed. Each patient was evaluated retrospectively for nipple position relative to the breast implant and breast contour, using standardized preoperative and postoperative photographs. The average follow-up period was 10 months. Results Seven of 72 breasts were identified as having implant malposition. These malpositions were divided into two groups. In relation to the new breast mound, six breasts had an inferiorly positioned and one breast had a superiorly positioned nipple-areolar complex. Two of these seven breasts were accompanied with an unsatisfactory breast contour. Conclusions We identified two main causes of implant malposition after inframammary augmentation mammaplasty. One cause was an incorrect preoperatively designed nipple to inframammary fold (N-IMF) distance. The breast skin and parenchyma quality, such as an extremely tight envelope, should be considered. If an extremely tight envelope is found, the preoperatively designed new N-IMF distance should be increased. The other main cause of malposition is failure of the fascial suture from Scarpa's fascia to the perichondrium through an inframammary incision. As well, when this fixation is performed, it should be performed directly downward to the perichondrium, rather than slanted in a cranial or caudal direction.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.81-88
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• 1999

In order to properly evaluate the shear strength of reinforced concrete circular columns due to the transverse shear reinforcement, the average of fractions of forces generated along the circular transverse hoops across the shear failure plane in the loading direction is calculated. For this, the center-to-center diameter of circular transverse hoops. spacing and the crack angle measured to the column longitudinal axis are considered. Using these variables, an equation representing the effective section area of circular transverse shear steel is proposed. The study result shows that the constant parameter. used for the calculation of the effective section area of circular hoops over the last 10 years, should not universally be applied any more. The use of the constant parameter may not seriously do harm to the evaluation of shear strength for circular columns with non-seismically designed transverse hoop reinforcement, since it gives slightly conservative results. However. for well-confined circular columns with close spacing or circular steel jacketing. it gives about 20% overestimation of the shear capacity contributed by the transverse hoop steel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.182-192
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• 2023

In this study, the efficacy of Engineered Cementitious Composite(ECC) jacket for masonry fences subjected to lateral dynamic load was experimentally verified through a shaking table test, comparing it with the performance of an unreinforced masonry(URM) fence. Firstly, dominant frequencies, modal damping ratios and deformed shapes were identified through an impact hammer test. URM and ECC-strengthened fences with heights of 940mm and 970mm had natural frequencies of 6.4 and 35.3Hz, and first modal damping ratios of 7.0 and 5.3%, respectively. Secondly, a shaking table test was conducted in the out-of-plane direction, applying a historical earthquake, El Centro(1940) scaled from 25 to 300%. For the URM fence, flexural cracking occurred at the interface of brick and mortar joint(i.e., bed joint) at the ground motion scaled to 50%, and out-of-plane overturning failure followed during the subsequent test conducted at the ground motion scaled to 30%. On the other hand, the ECC-jacketed fence showed a robust performance without any crack or damage until the ground motion scaled to 300%. Finally, the base shear forces exerted upon the URM and ECC-jacketed fences by the ground motions scaled to 25~300% were evaluated and compared with the ones calculated according to the design code. In contrast to the collapse risk of the URM fence at the ground motion of 1,000-year return period, the ECC-jacketed fence was estimated to remain safe up to the 4,800-year return period ground motion.

• Composites Research
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• v.33 no.5
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• pp.296-301
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• 2020

Laminated composite materials have excellent in-plane properties, but are vulnerable in thickness directions, making it easy to delamination when bending and torsion loads are applied. Thickness directional reinforcement methods of composite materials that delay delamination include Z-pinning, Stitching, Tufting, etc., and typically Z-pinning and Stitching method are commonly used. The Z-pinning is reinforcement method by inserting metal or carbon pin in the thickness direction of prepreg, and the conventional stitching process is a method of reinforcing the mechanical properties in the thickness direction by intersecting the upper and lower fibers on the preform. In this paper, I-fiber stitching method, which complement and improve weakness of Z-pinning and Stitching method, was proposed, and the static strength of composite single-lap joints using I-fiber stitching process were evaluated. The single-lap joints were fabricated by a co-curing method using an autoclave vacuum bag process. The thickness of the composite adherend was fixed, and 5 types of specimens were manufactured with varying the stitching pattern (5×5, 7×7) and angle (0°, 45°). From the test, the failure load of the specimen reinforced by the I-fiber stitching process was increased by up to 143% compared to that of specimen without reinforcement.

• Korean Journal of Applied Biomechanics
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• v.12 no.2
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• pp.279-293
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• 2002

In the study the subjects who 10 university golfers act, and the kinetic factors were analyzed by the ground reaction system. the conclusion are as follows. 1) In the golf putting swing, the ground reaction factors of sagital plane in aspect are showen that the left and right foot sufficient difference, in the level of p <.05. 2) In the golf putting swing, the ground reaction factors of frontal plane in aspect is showen that the left foot has no significant difference in AD BS in the level of p < .05. In success, IP, FS. It can show significant difference. In addition, the right foot is shown the success, There is significant difference. 3) In the golf putting swing, the ground reaction factors of the vertical plane in aspect are shown that the left foot has no significant difference in BS, FS in the level p < .05. In success, AD, IP. It can show significant difference. In addition, the right foot is shown the success, There is significant difference. 4) In the golf putting swing, the ground reaction factors of torque in aspect are shown that the left foot had no significant difference in BS in the level p < .05. In success, AD, IP, FS. It can show significant difference. In addition, the right foot has no significant difference in IP in the level p < .05. AD, BS, FS. There is significant difference. The summarized conclusions are as follows. The first that the power of sagital plane needs the motion which can get the good power change in the stabilized pose. The second is that the small motion can make good putting in stabilized pose. The third is that the body weight move to the direction of the ball. The fourth is that the putting which looks perfect oscillation is good motion.