• Composites Research
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• v.24 no.4
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• pp.11-16
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• 2011

Retention of interfacial shear strength (IFSS) of polymer composites at cryogenic temperature application is very important. In this work, single carbon tiber reinforced epoxy compositc was used to evaluate IFSS and apparent modulus under room and cryogenic temperatures. The property change of carbon and selected epoxy for particularly cryogenic temperature application were tested in tension and compression. Tensile strength and elongation of carbon fiber decreased at cryogenic temperature, whereas tensile modulus was almost same. On the other hand, epoxy matrix showed the increased tensile strength but decreased elongation. It can be due to maximum thermal contraction existing free volume in cryogenic temperature. IFSS increased up to $-10^{\circ}C$ and then decreased steadily. However, IFSS at cryogenic temperature was still similar to that at room temperature. This result is very useful to cryogenic application since selected epoxy toughness and interfacial adhesion can keep at such low temperature.

• Journal of Adhesion and Interface
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• v.3 no.2
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• pp.17-29
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• 2002

Interfacial properties and microfailure degradation mechanisms of the bioabsorbable composites for implant materials were investigated using micromechanical technique and measurement of surface wettability. As hydrolysis time increased, the tensile strength, the modulus and the elongation of poly(ester-amide) (PEA) and bioactive glass fibers decreased, whereas those of chitosan fiber almost did not change. Interfacial shear strength (IFSS) between bioactive glass fiber and poly-L-lactide (PLLA) was much higher than PEA or chitosan fiber/PLLA systems using dual matrix composite (DMC) specimen. The decreasing rate of IFSS was the fastest in bioactive glass fiber/PLLA composites whereas that of chitosan fiber/PLLA composites was the slowest. Work of adhesion, $W_a$ between bioactive glass fiber and PLLA was the highest, and the wettability results were consistent with the IFSS. Interfacial properties and microfailure degradation mechanisms can be important factors to control bioabsorbable composite performance.

• Composites Research
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• v.24 no.6
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• pp.12-17
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• 2011

Interfacial durability and electrical properties of CNT or ITO coated PVDF nanocomposites were investigated for self-sensor and micro actuator applications. Electrical resistivity of nanocomposites for the durability on interfacial adhesion was measured using four points method via fatigue test under cyclic loading. CNT/PVDF nanocomposite exhibited lower electrical resistivity and good self-sensing performance due to inherent electrical property. Durability on the interfacial adhesion was good for both CNT and ITO/PVDF nanocomposites. With static contact angle measurement, surface energy, work of adhesion, and spreading coefficient between either CNT or ITO and PVDF were obtained to verify the correlation with interfacial adhesion durability. The optimum actuation performance of CNT or ITO coated PVDF specimen was measured by the displacement change using laser displacement sensor with changing frequency and voltage. The displacement of actuated nanocomposites decreased with increasing frequency, whereas the displacement increased with voltage increment. Due to nanostructure and inherent electrical properties, CNT/PVDF nanocomposite exhibited better performance as self-sensor and micro actuator than ITO/PVDF case.

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

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.417-420
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• 2002

마이크로 캡슐에 관한 연구는 벽 혹은 내부 물질의 성질, 캡슐화의 방법, 내부 구성물질의 내구성과 안정성 그리고, 확산, 투과, 부식, 용해등에 의한 유출현상등을 중심으로 진행되어 왔으며$^{1.2}$ , 1980년대 후반부터 섬유의 열적 성능을 개선하고자 캡슐화된 상전이 물질을 이용한 연구들이 시작 되었다[3-4]. 본 연구에서는 온도 조절 기능을 가지고 온도 감응형 섬유로의 적용을 위하여 상전이 물질(phase change materials: PCMs)을 함유하는 마이크로 캡슐을 제조하여 그 특성을 분석하고자 하였다. (중략)

• Journal of the Korean Ceramic Society
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• v.35 no.3
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• pp.303-309
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• 1998

The fabrication of Al2O3/Al composite by pressureless infiltration was investigated by the change of Mg and Si content in Al alloy infiltration process and infiltration atmosphere. The effect of alloying elements infiltration atmosphere and interfacial reactants between Al alloy matrix and Al2O3 particles were in-vestigated in terms of bendingstrength and harness test,. The fabrication of Al2O3/Al composite by the vestigated in terms of bending strength and hardness test. The fabrication of Al2O3/Al composite by the pressureless infiltration was done in nitrogen atmosphere with Mg in Al alloy. It was successfully fabricated at $700^{\circ}C$ according to Mg contents in Al alloy and infiltration condition. Because Mg in the Al alloy and ni-trogen atmosphere of infiltratio condition produced Mg-N compound(Mg3N2) it decreased the wetting an-gle between molten Al alloy and Al2O3 particles by coating on surface of Al2O3 particles. The fracture strength of Al2O3/Al-Mg composite was 800MPa and Al2O3/Al-Si-Mg composite was 400MPa. Si in Al alloy decreased the interfacial strength between Al alloy matrix and Al2O3 particles.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.143-146
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• 2002

Unsized AS-4 carbon fibers were etched by RF plasma and then coated via plasma polymerization in order to enhance adhesion to vinyl ester resin. The gases utilized for the plasma etching were Ar, $N_2 and O_2$, while the monomers used for the plasma polymerization coating were acetylene, butadiene and acrylonitrile. The conditions for the plasma etching and the plasma polymerization were optimized by measuring interfacial adhesion with vinyl ester resin via micro-droplet tests. Among the treatment conditions, the combination of Ar plasma etching and acetylene plasma polymerization provided greatly improved interfacial shear strength (IFSS) of 69MPa compared to 43MPa with as-received carbon fiber. Based on the SEM analysis of failure surface and load-displacement curve, it was assume that the failure might be occurred at the carbon fiber and plasma polymer coating. The plasma etched and plasma polymer coated carbon fibers were subjected to analysis with SEM, XPS, FT-IR or Alpha-Step, and dynamic contact angles and tensile strengths were also evaluated. Plasma polymer coatings did not change tensile strength and surface roughness of fibers, but decreased water contact angle except butadiene plasma polymer coating, possibly owing to the functional groups introduced, as evidenced by FT-IR and XPS.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.12
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• pp.2227-2238
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• 2000

The interfacial features of suspension system made of $CaCO_3$ particles have been investigated for the purpose of designing its effective treatment process. For the examination of variation of electrokinetic potential as a function of pH. the value of potential was observed to shift in the negative direction, which was thought to be due to the adsorption of hydroxide ion on the particle surface. Adsorption of surfactant on suspended particles resulted in the change of surface charge and shift in electrokinetic potential, which was dependent upon the sign of head charge and concentration of surfactant. Addition of inorganic salts affected stability of suspension greatly and sedimentation rate of suspension was influenced by the electric valence and amount of ions produced by dissolution of inorganic coagulants. DLVO theory made it possible to construct a energy profile diagram and a close correlation was found between experimental result and theoretically derived consequences. Non-specific adsorption of indifferent electrolyte resulted in the compression of electrical double layer and specific adsorption induced the shift of IEP and PZC in the opposite direction.

• Journal of Welding and Joining
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• v.29 no.1
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• pp.99-106
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• 2011

Joint strength between a solder ball and a pad on a substrate is one of the major factors which have effects on electronic device reliability. The effort to improve solder joint strength via surface cleaning, heat treatment and solder composition change have been in progress. This paper will discuss the method of solder ball joint strength improvement using LF hydrogen radical cleaning treatment and focus on the effects of surface treatment condition on the solder ball shear strength and interfacial reactions. In the joint without radical cleaning, voids were observed at the interface. However, the specimens cleaned by hydrogen-radical didn't have voids at the interface regardless of cleaning time. The shear strength between the solder ball and the pad was increased over 120%(about 800gf) when compared to that without the radical treatment (680gf) under the same reflow condition. Especially, at the specimen treated for 5minutes, ball shear strength was considerably increased over 150%(1150gf). Through the observation of fracture surface and cross-section microstructure, the increase of joint strength resulted from the change of fracture mode, that is, from the solder ball fracture to IMC/Ni(P) interfacial fracture. The other cases like radical treated specimen for 1, 3, 7, 9min. showed IMC/solder interfacial fracture rather than fracture in the solder ball.

• Journal of Korean Vacuum Science & Technology
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• v.2 no.2
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• pp.63-77
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• 1998

The oxidation of NiAl(110) was investigated in the temperature regime between 300K and 1300 K using LEED (low energy electron diffraction), TPD (temperature programmed desorption) and HREELS (high resolution electron energy loss spectroscopy). The adsorption of N2O and O2 up to reconstructions. Stepwise annealing of the oxygen-saturated sample from 600 K to 1300K in UHV (ultra-high vacuum,) results in firstly the onset of randomly oriented then finally fairly well-ordered. 5 ${\AA}$ Al2O3 film with quasi-hexagonal periodicity. Ordered thicker oxide films of 18-30 ${\AA}$ seem to be grown on this interfacial oxide layer by direct oxidation of sample at elevated temperature between 1150 and 1300 K because of the LEED pattern consisting of new broad hexagonal spots and the previous 5 ${\AA}$ spots. Although the periodicity of surface oxygen arrays shows no significant change from an hexagonal close-packing, the O-O distance changes from ∼3.0 ${\AA}$ film to ∼2.9 ${\AA}$ for thicker oxides. with the appearance of Auger parameter, for the 5${\AA}$ film can be described better as an interfacial oxide layer. The observation of three symmetric phonon peaks can be also a supporting evidence for this phase assignment since thicker oxide films on the Same Ni2Al3(110) show somewhat different phonon structure much closer to that of the ${\gamma}$-Al2O3. The adsorption/desorption of methanol further proves the preparation of less-defective and/or oxygen-terminated Al2O3 films showing ordered phase transitions with the change of oxide thickness between 5 ${\AA}$ to 30 ${\AA}$.