• Proceedings of the KSR Conference
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• 2001.10a
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• pp.211-216
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• 2001

It is well known that composite laminates are easily damaged by low velocity impact. Low velocity impact damage characteristics and residual compressive strength of composite laminates used in light rail transit are investigated. The damage of composite laminates subjected to impact loading are occurred matrix cracking, delamination, and fiber breakage. The damage of matrix cracking and delamination are reduced suddenly the compressive strength after impact. The objectives of this study is to evaluate impact characteristics and the relationship between impact force and inside damage of composite laminates by low velocity impact loading. UT C-scan is used to determine impact damage areas by impact loading.

• Structural Engineering and Mechanics
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• v.48 no.1
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• pp.41-56
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• 2013

Initiation and growth of delamination is a great concern of designers of composite structures. Interface elements with de-cohesive constitutive law in the content of continuum damage mechanics can be used to predict initiation and growth of delamination in single and mixed mode conditions. In this paper, an interface element based on the cohesive zone method has been developed to simulate delaminatoin growth of post-buckled laminate under fatigue loading. The model was programmed as the user element and user material by the "User Programmable Features" in ANSYS finite element software. The interface element is a three-dimensional 20 node brick with small thickness. Because of mixed-mode condition of stress field at the delamination-front of post-buckled laminates, a mixed-mode bilinear constitutive law has been used as user material in this model. The constitutive law of interface element has been verified by modelling of a single element. A composite laminate with initial delamination under quasi-static compressive Loading available from literature has been remodeled with the present approach. Moreover, it will be shown that, the closer the delamination to the free surface of laminate, the slower the delamination growth under compressive fatigue loading. The effects of laminate configuration on delamination growth are also investigated.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1402-1405
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• 2003

The main object of this study was evaluated by the delamination damage for fiber stacking angle. Therefore, this work need to compare the shape of delamination for a different fiber stacking angie. So this study uses a method of fatigue test which was created [0]$_2$,[+45]$_2$[90]$_2$. The extension of the delamination zone formed between aluminium alloy and glass fiber-adhesive layer were measured by an ultrasonic C-scan image. As a result, the shapes of delamination zone don't depend upon the crack propagation. We could know that the delamination zone grew interaction between stress flow of fiber layer and crack driving force. Hence, the existing study were applied to the stress transfer, fiber bridging effect, delaminantion growth rate should need to the develop useful factor because of change of fiber stacking angle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.2
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• pp.387-398
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• 2002

The impact response and damage of CLAS panel was investigated experimentally. The facesheet material used was RO4003 woven-glass hydrocarbon/ceramic and the core material was Nomex honeycomb with a cell size of 3.2mm and a density of 96 kg/㎥. The shield plane used was RO4003 and 2024-T3 aluminum. Static indentation and impact test was conducted to characterize the type and extent of the damage observed in two CLAS panels, and the performance of antenna used in a wireless LAN system. Correlation of peak contact force, residual indentation and the delamination area shows impact damage of the panel with an aluminum shield plane is larger than that of the panel with RO4003 shield plane, although the former is more penetration resistant. The damage was observed by naked eye, ultrasonic inspection and cross sectioning. The shape and size of delamination was estimated by ultrasonic inspection, and the area of delamination linearly increases as impact energy increases. The performance of impact damaged antenna was estimated by measuring return loss and radiation pattern. It was revealed that the performance of antenna was related to the impact damage and there was a threshold that the performance of antenna fell as impact energy level changed. The threshold was between the impact energies of 1.5J and 1.75J.

• Journal of Conservation Science
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• v.38 no.4
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• pp.314-326
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• 2022

Investigation of conservation status, optical survey, infrared thermography, and ultrasonic examination were performed on Avalokitesvara Bodhisattva mural and Buddhist Monk Bodhidharma mural to determine the conservation status and physical properties. As a result of investigation of conservation status, the types of damage are largely divided into the wall and finishing layer damage, painting layer degradation, damage due to restoration materials, stains and contamination, and biological damage. As a result of the optical survey, drawing, stains, and repainted site were confirmed. Result of the infrared thermography, the delamination of the finishing layer was confirmed, and some locations and shapes of the wooden lath inside the wall were identified. The result of the 3D scanning, the deviation, and the separation of the wall was confirmed. As a result of ultrasonic examination, it was confirmed that the physical properties of the mural were identified and the ultrasonic speed was relatively low due to physical damage such as delamination and exfoliation of the finishing layer and cracking. Ultrasonic speed values were also high in some wall cracks or delamination, and it was confirmed by the infrared thermography results that the wooden lath inside the wall was located in those parts. It was possible to understand that the wooden lath inside the walls affects the ultrasonic speed during the ultrasonic examination. Therefore, management through periodic inspection of the relevant elements is necessary, and a countermeasure for damage that may occur in the future should be prepared along with intensive monitoring of the major damage identified in this diagnosis result.

• Journal of the Korean Society for Precision Engineering
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• v.15 no.1
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• pp.43-50
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• 1998

The purpose of the paper is to protect the damage of plastic IC package with searching the cause of the fracture due to the delamination and crack when the encapsulant of plastic IC package is on viscoelastic behavior with the effect of creep on high temperature, The model for analysis is the plastic SOJ package with dimpled diepad in the IR soldering process of surface mounting technology. The risk of delamination with calculating the distribution of viscoelastic thermal stress in the package without the crack in the surface mounting process is checked. The package model with the perfect delamination between chip and diepad is chosen to estimate the resistance against fracture in thermal loading with calculating C (t)-integrals according to the change of the design. The optimum design to depress the delamination and crack is presented.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.214-215
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• 2013

The tapping test has simplicity of procedure for detection of the damage in aircraft structure. However, the result of tapping test depends on the subjective experience of inspector. In this paper, more objective tapping test has proposed. The impact force histories and tapping sounds are used as reference data to evaluate the delamination. The WT(wavelet transform) is used to decompose the test data. From the results, we could know that high frequency components of force and sound are reduced due to delamination in composite laminate. On these results, the tapping force and sound caused by tapping could be used for the reference data to evaluate the delamination in composite structure.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.8 no.2
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• pp.80-85
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• 1999

The purpose of this work is to investigate fatigue damage of quasi-isotropic laminates under tensile loading in different directions. Low cycle fatigue tests of [0/-60/+60]a laminates and [+30/-30/90]s lamina tes were carried out. Material systems used are AS4/Epoxy and AS4/PEEK. The fatigue damage of [+30/-30/90]s is very different from that of [0/-60/+60]s. The position of delamination generated at AS4/Epoxy and AS$/PEEK laminates were differentiated by the matrix difference that is, we suppose, the value of both GIcr(critical energy release rate of mode-I) and GIIIcr(critical energy release rate of mode-III) difference.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.350-355
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• 2013

Electrical resistance change measurements were performed, to detect fatigue damage of a quasi-isotropic CFRP and cross-ply CFRP laminates. A four-probe method was used to measure the exact electrical resistance change. A three-probe method was used to measure the electrical contact resistance change, during long cyclic loading. The specimen side surface was observed using a video-microscope to detect damage. The measured electrical resistance changes were compared with the observed damage. The results of this study show that the electrical resistance increase of the quasi-isotropic laminate was caused by a delamination crack between ${\pm}45^{\circ}$ plies. Matrix cracking caused a small electrical resistance increase of the cross-ply laminate, but the decreased electrical resistance caused by the shear-plastic deformation impedes matrix-cracking detection.

• Journal of the Korean Society of Safety
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• v.18 no.2
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• pp.34-39
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• 2003

In this paper, when CF/PEEK laminates for high efficiency space structure are subjected to FOD(Foreign Object Damage), the effects of temperature change on the impact damages(interlaminar separation and transverse crack) of CF/PEEK laminates and the relationship between residual lift and impact damages are experimentally investigated. Composite laminates used in this experiment are CF/PEEK orthotropic laminated plates, which have two-interlaces [$0^{\circ}_4/90^{\circ}_8/0^{\circ}_4$]. A steel ball launched by the air gun collides against CF/PEEK laminates to generate impact damages. And then CF/PEEK specimens with impact damages are observed by a scanning acoustic microscope under room and high temperatures. In this experimental results, various relations are experimentally observed including the delamination area vs. temperature change, the bending strength vs. impact energy and the residual bending strength vs. impact damage of CF/PEEK laminates.