• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10b
• /
• pp.839-844
• /
• 1998

The purpose of this study is to analyze the interface debonding failure on RC beams strengthened with carbon fiber sheet(CFS). The behavior of damaged RC beams strengthened with CFS is analytically investigated using both linear elastic fracture mechanics (LEFM) approach and the finite element method. This study includes the investigation of the separation mode by interface fracture of the strengthening materials due to the interfacial shear and normal stresses.

• Korean Journal of Materials Research
• /
• v.8 no.9
• /
• pp.807-812
• /
• 1998

Interfacial reaction and mechanical properties between Sn-Bi-X ternary alloys(X : 2Cu. 2Sb 5In) and Cu-substrate were studied. Cu/solder joints were subjected to aging treatments for up to 60days to see interfacial reaction at $100^{\circ}C$ and then were examined changes of microstructure and interfacial compound by optical microscopy, SEM and EDS. Cu/solder joints were aged to 30days and then loaded to failure at cross head speed of 0.3mm $\textrm{min}^{-1}$ to measure strength and elongation. According to the result of EDS, it is supposed that the soldered interfacial zone was composed of $\textrm{Cu}_{3}\textrm{Sn}$ and $\textrm{Cu}_{6}\textrm{Sn}_{5}$. According to the tensile test of Cu/solder joint, joint strength was decreased by aging treatment. Fractographs of Cu/Sn-Bi solder detailed the effect of aging on fracture behavior. When intermetallic was thin, the fracture occurred through the solder. But as the interfacial intermetallic is thickened, the fracture propagated along the intermetallic/solder interface.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2002.05a
• /
• pp.255-258
• /
• 2002

Dental chewing masticator, which is an essential device for evaluating the wear of dental resin and the interfacial failure between the filling resin and enamel of tooth used in conservative dentistry, was developed. This dental chewing masticator mimics the chewing motion and loading by adapting DC motor and rotary cam system. Chewing loading of 49N was imposed by computer-displacement control, loadcell, LM guide, and spring system. Extracted tooth was fixed into a holding jig, and this jig was mounted with rubber pad on the $15^{\circ}$inclined surface to consider the lateral movement of periodontal ligament. A water bath was installed for providing the environment of inside mouth and for circulating the $5^{\circ}C-55^{\circ}C$ water to evaluate the effect of hydrothermal cycling on the damage of resin filled teeth during long-term chewing activity.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2003.04a
• /
• pp.139-142
• /
• 2003

As composite materials are gaining wide acceptance in aircraft structure, repair of damaged composite is becoming an important issue. The issues in composite repair include high cost, material interchangeability, water ingression, and structural integrity. To address these problems, researchers have studied on the composite repair in various aspects. In this paper, an Internet-based advisory service (called Repair Advisory Service, RAS) for composite repair is proposed to increase efficiency for repair process. In the RAS system the web browser is used as its user interface, which provides easy access to the service. The RAS server provides web-based tools for failure prediction, Structural Repair Manual (SRM), automated prepreg cutting process, material properties, inventory and knowledge base. The computer codes implemented for repair design estimate the tensile failure and shear failure of repaired structures. The prediction of failure is based on the maximum strain criterion for tensile failure while elastic-perfect plastic shear failure model is applied for interfacial failure. The OEM's SRM is provided in the PDF format for viewing and searching by web browsers instead of looking up paper version SRM. The knowledge base in this site offers a room to share and distribute ideas, memos, publications, or suggestions from the repair engineers. The fabrication tool of RAS reads repair geometry from engineers then generates a CNC toolpath to cut prepreg patches. The RAS service is open to public and available at http://nano.gsnu.ac.kr/. Broad feedback from field technicians and engineers is welcome to improve the usefulness of RAS.

• Journal of Adhesion and Interface
• /
• v.5 no.1
• /
• pp.21-28
• /
• 2004

In this work, glass fiber/nylon 6 and woven glass fiber/nylon 6 composites have been fabricated using glass fiber reinforcements sized with 3-chloropropyltrimethoxysilane(CTMS) having a chloropropyl organo-functional group in the molecular chain end. The interfacial shear strength of glass fiber/nylon 6 composite was measured using a single fiber microbonding test and the interlaminar shear strength and the storage modulus of woven glass fabric/nylon 6 composites were measured using a short-warn shear test and a dynamic mechanical analysis, respectively, informing the effect of the concentration of CTMS on the properties. With increasing CTMS concentration, the interfacial properties of the composites were improved. The results on the interfacial shear strength, interlaminar shear strength, interlaminar failure pattern, and storage modulus with varying the CTMS concentration agree with each other.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.12 no.6
• /
• pp.109-118
• /
• 2008

Carbon fiber reinforced polymer(CFRP) can be bonded to the soffit of a concrete beam as a means of repairing and strengthening the beam. In such beams, materials, concrete and carbon fiber sheets, are different in coefficient of thermal expansion. Consequently, interfacial shear stresses can be increased and debonding failure may occur at the plate ends due to temperature rising. This paper presents a method of approximate closed-form solutions for the interfacial shear stresses and conducts a beam test to compare the numerical results. In case of temperature rising over $30^{\circ}C$, interfacial stress of 0.91MPa is occurred at the end of sheet. Therefore, using carbon fiber sheet for strengthening the concrete beam, it is necessary to consider the thermal effects and to evaluate the long time behavior of the concrete beam by temperature change.

• Composites Research
• /
• v.22 no.5
• /
• pp.30-36
• /
• 2009

The failure strengths and modes in carbon fiber reinforced polymeric composites, with two serial bolt-fastened composite joints, were investigated to evaluate the typical joint configurations of composite components. The parametric studies were performed experimentally at room temperature dry and elevated temperature wet, $82.2^{\circ}C$ on several different laminate configurations. Based on the experimental data presented, two basic load-displacements curves are observed. Each failure mode has the characteristic curve. It is showed that the bearing failure mode occurs in elevated temperature wet condition. It is analysed that the strength of bearing failure mode is not highly depending on the effective modulus of specimen. The failure strength at elevated temperature wet is decreased by the cause of interfacial deterioration between fiber and matrix with moisture absorption.

• Korean Journal of Materials Research
• /
• v.12 no.10
• /
• pp.820-824
• /
• 2002

It is of importance to know that the bonding strength and interfacial stress of SOI wafer pairs to meet with mechanical and thermal stresses during process. We fabricated Si/2000$\AA$-SiO$_2$ ∥ 2000$\AA$-SiO$_2$/Si SOI wafer pairs with electric furnace annealing, rapid thermal annealing (RTA), and fast linear annealing (FLA), respectively, by varying the annealing temperatures at a given annealing process. Bonding strength and interfacial stress were measured by a razor blade crack opening method and a laser curvature characterization method, respectively. All the annealing process induced the tensile thermal stresses. Electrical furnace annealing achieved the maximum bonding strength at $1000^{\circ}C$-2 hr anneal, while it produced constant thermal tensile stress by $1000^{\circ}C$. RTA showed very small bonding strength due to premating failure during annealing. FLA showed enough bonding strength at $500^{\circ}C$, however large thermal tensile stress were induced. We confirmed that premated wafer pairs should have appropriate compressive interfacial stress to compensate the thermal tensile stress during a given annealing process.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.24 no.4
• /
• pp.151-157
• /
• 2014

The degradation mechanisms of thermal barrier coatings (TBCs) were investigated in different thermal fatigue condition in terms of microstructural analyses. The isothermal and cyclic oxidation tests were conducted to atmospheric plasma sprayed-TBCs on NIMONIC 263 substrates. The delamination occurred by the oxide layer formation at the interface, the Ni/Cr-based oxide was formed after Al-based oxide layer grew up to ${\sim}10{\mu}m$ in the isothermal condition. In the cyclic oxidation with dwell time, the failure occurred earlier (500 hr) than in the isothermal oxidation (900 hr) at same temperature. The thickness of Al-based oxide layer of the delaminated specimen in the cyclic condition was ${\sim}4{\mu}m$ and the interfacial cracks were observed. The acoustic emission method revealed that the cracks generated during the cooling step. It was considered that the specimens were prevented from the formation of the Al-based oxide by cooling treatment, and the degradation mode in the cyclic test was dominantly interfacial cracking by the difference of thermal expansion coefficients of the coating layers.

• Journal of the Korea Concrete Institute
• /
• v.26 no.1
• /
• pp.79-86
• /
• 2014

In this paper, a stress transfer mechanism between near surface-mounted (NSM) fiber reinforced polymer (FRP) plate and concrete was investigated and a reliable analytical procedure for it was presented by using bilinear bond-slip model simulating the bond behavior of NSM FRP plate. As a result, critical values in the bi-linear model such as maximum shear strength, slip at that time and failure slip at the initiation of softening de-bonding were suggested for being used in the differential equation considering he interfacial characteristic between NSM FRP and concrete. Also, it was found that the bond-slip behavior could be suitably redicted by using the proposed procedure even in the case of various bond lengths from the comparison with bond test result.