• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.51-59
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• 2004

An experimental procedure to identify failure modes of impact damage using sensor signals and to analyze their general features is examined. A series of low-velocity impact tests from low energy to damage-induced high energy were performed on the instrumented drop weight impact tester to monitor the stress wave signals due to failure modes such as matrix cracking, delamination, and fiber breakage. The wavelet transform(WT) and Short Time Fourier Transform(STFT) are used to decompose the piezoelectric sensor signals in this study. The extent of the damage in each case was examined by means of a conventional ultrasonic C-scan. The PVDF sensor signals are shown to carry important information regarding the nature of the impact process that can be extracted from the careful signal processing and analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.5
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• pp.381-387
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• 2017

Fiber-reinforced composites not only have a direction of thermal expansion coefficient, but also inevitably suffer thermal stress effects due to the difference between the manufacturing process temperature and the actual use temperature. The damage caused by thermal stress is more prominent in the case of thick composite laminates, which are increasingly applied in the aerospace industry, and have a great influence on the mechanical function and fracture strength of the laminates. In this study, the dimensional reduction and thermal stress recovery theory of composite beam structure having high slenderness ratio is introduced and show the efficiency and accuracy of the thermal stress comparison results between the 3-D finite element model and the dimension reduction beam model. Efficient recovery analysis study will be introduced by reconstructing the thermal stress of the composite beam section applied to the thermal environment by constructing the dimensional reduction modeling and recovery relations.

• Composites Research
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• v.32 no.5
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• pp.258-264
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• 2019

In this paper, a progressive failure analysis method was developed using the Hashin failure criterion and crack band model. Using the failure criterion, the failure initiation was evaluated. If the failure initiation is occurred, the damage variables at each failure modes (fiber tension & compression, matrix tension & compression) was calculated according to linear softening degradation behavior and the variables are used to derive the damaged stiffness matrix. The damaged stiffness matrix is reflected to damaged material and the progressive failure analysis is continued until the damage variables to be 1 that complete failure of material. A series of processes were performed using FE commercial code ABAQUS with user defined material subroutine (UMAT). To evaluate the proposed progressive failure model, the experimental results of open hole composite laminate tests was compared with numerical result. Using digital image correlation system, the strain behavior also was compared. The proposed numerical results were coincided well with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.960-968
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• 2002

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, Al laminate was etched using FPL methods. The static indentation test were conducted by using UTM under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber breakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. The Angle ply FML has a critical cross-angle which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

• Journal of the Korea Concrete Institute
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• v.26 no.1
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• pp.47-55
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• 2014

As increasing number of large-size earthquake around Korean peninsula, many interests have been focused to the earthquake strengthening of existing structures. The brittle fracture of Non-seismic designed columns lead to full collapse of the building. In the past, cross-sectional extension method, a steel plate reinforcing method and fiver-reinforced method are applied to Seismic Rehabilitation Technique mainly. However, the reinforcement methods have drawbacks that induce physical damage to structures, large space, long duration time. So, in this study, performance evaluation of previously developed FRP seismic reinforcement which do not induce physical damage and short duration time was enforced. The specimens were constructed with 80% downscale. FRP seismic reinforcement are manufactured of glass fiber or aluminum plate with holes and glass fiber. From the experiment results, seismic performance of specimens which reinforced with FRP seismic reinforcement were increased.

• Journal of the Society of Disaster Information
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• v.13 no.1
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• pp.81-88
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• 2017

In this paper, the behaviour of composite steel-CFRP members is studied experimentally and using FE-analysis. The use of advance composite materials in construction for repair and rehabilitation has become a frequent used method in the last decade. FRP composites have many advantages over the traditional technique of steel bonding for a number of reasons: 1. Composites add little or no additional weight to a building, eliminating the need for costly foundation strengthening. 2. FRP composites are very thin (1.2mm to 1.4mm). So there is no loss of floor space and negligible effect over the architectural aspect. 3. FRP composites do not corrode, this makes it long lasting. However, the method is yet to become a mainstream application due to a number of economical and design related issues. Brittle debonding failure, aging effect on bonding, broad based awareness and proper design guidelines are the main concern for future research works. This paper is focused on the ultimate load carrying capacity of the CFRP-strengthened beams and their effect on the deflection and failures modes by varying the amount of CFRP content.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.34 no.4
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• pp.303-309
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• 2008

Deficiency of collagen regeneration, denaturalization of elastic fibers, and promotion of reactive oxygen species formation are important factors for deterioration of skin function. They induce wrinckle formation and decrease skin elasticity. Vitamin C and its derivatives have been used as cosmetic ingredients for anti-aging effects but their chemical instability has been a major problem. In an attempt to develop a novel anti-aging agent with a improved stability and bioactivity, the anti-wrinkle effect of 3-O-cetyl-L-ascorbic acid (VCCE), a new vitamin C derivative, was investigated in this study. VCCE increased procollagen type-1 synthesis in a dose-dependent manner (149% at 0.002%) in cultured fiboroblasts. Its potent anti-wrinkle effect was confirmed in vivo by analyzing human skin replica by a visiometer and the PRIMOS system. It did not cause any irritation in human patch test. Taken together, our findings suggest that the VCCE has potential benefits applicable to cosmetics for anti-wrinkle effects.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.17 no.3
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• pp.261-269
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• 2004

The existing concrete beams can be retrofitted or reinforced by attaching carbon fiber or glass fiber sheet beneath the beams. Although diverse design methods and application techniques of the retrofitting are studied and developed, the testing method of examining retrofitted beams have not been put into practice yet. In this study, a bond delamination has been modeled and studied to provide a basis for the development of actual testing equipments. For this purpose, Gaussian and sinusoidal waves with 3GHz and 5GHz center frequency are used as an incident wave and 1mm and 3mm bond delamination under the reinforcement are modeled. In the modeling, Finite Difference-Time Domain algorithm is used to investigate the behavior of electromagnetic waves in concrete. The results have shown that 5GHz waves are suitable for the detection of delamination.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.2
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• pp.104-113
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• 2020

The study aims to improve the previous theory-based algorithm on the lightweight design of laminate structures of a composite ship based on the mechanical properties of fiber, resin, and laminates obtained from experiments. From a case study on using a hydrometer to measure the specific gravity of e-glass fiber woven roving fabric/polyester resin used as the raw material for the hull of a 52 ft composite ship, the equation for calculating the weight of laminate was redefined, and the relationship between decreasing mechanical properties and increasing glass content was determined from the results of material testing according to ASTM D5083 and ASTM D790. After applying these experimental data to the existing algorithm and improving it, a possible laminate design that maximizes the specific strength of the composite material was confirmed. In a case study that applied the existing algorithm based on rules, the optimal lightweight design of composite structures was achieved when the weight fraction of e-glass fiber was increased by 57.5% compared with that in the original design, but the improved algorithm allowed for an increase of only 17.5%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.10
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• pp.6959-6968
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• 2015

This study aims to update the supply-demand model of wood products(FOSMO-2013) and to forecast mid and long run supply and demand for each products. The subjects of the study include sawnwood, plywood, particle board, fiberboard(MDF), and pulp. The updated partial equilibrium model is composed of supply function, import demand function, demand function, price relation function. The long run outlooks of world prices of wood and wood products are imported from the results of Buongiorno(2012). This study also adopt Buongiorno's scenarios, which includes three scenarios of IPCC(A1B, A2, B2) and the other one with assumption of increasing fuelwood consumption of A1B scenario. The result says that the domestic productions of wood products are expecting to decrease while the imports of them increase even there are some differences among the products as well as scenarios.