• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.05a
• /
• pp.109-113
• /
• 2002

Interfacial and electrical properties for the carbon fiber reinforced epoxy-amine terminated (AT) PEI composites were performed using microdroplet test and electrical resistance measurements. As AT PEI content increased, the fracture toughness of epoxy-AT PEI matrix increased, and IFSS was improved due to the improved toughness and energy absorption mechanisms of AT PEI. The microdroplet in the carbon fiber/neat epoxy composite showed brittle microfailure mode. At 15 wt% AT PEI content, ductile microfailure mode appeared because of improved fracture toughness. After curing, the changes of electrical resistance (ΔR) with increasing AT PEI content increased gradually because of thermal shrinkage. The matrix fracture toughness was correlated to IFSS, TEC and electrical resistance. In cyclic strain test, the maximum stress and their slope of the neat epoxy case were higher than those of 15 wt% AT PEI. The results obtained from electrical resistance measurements under curing process and reversible stress and strain were consistent well with matrix toughness properties.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.11a
• /
• pp.17-21
• /
• 2000

Logarithmic electrical resistivity of the untreated or thin diameter carbon fiber composite increased suddenly to the infinity when the fiber fracture occurred by tensile electro-micromechanical test, whereas that of the ED or thick fiber composite increased relatively broadly up to the infinity. Electrical resistance of single-carbon fiber composite increased suddenly due to electrical disconnection by the fiber fracture in tensile electro-micromechanical test, whereas that of SFC increased stepwise due to the occurrence of the partial electrical contact with increasing the buckling or overlapping in compressive test. Electrical resistivity measurement can be very useful technique to evaluate interfacial properties and to monitor curing behavior of single-carbon fiber/epoxy composite under tensile/compressive loading.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.10a
• /
• pp.261-264
• /
• 2002

Interfacial evaluation, damage sensing and cure monitoring of single carbon fiber/thermosetting composite with different curing processes was investigated using electro-micromechanical test. After curing, residual stress was monitored by measurement of electrical resistance (ER) and then it was compared to correlate with various curing processes. In thermal curing, curing shrinkage appeared significantly by matrix shrinkage and residual stress due to the difference in thermal expansion coefficient (TEC). The change in electrical resistance (ΔR) on thermal curing was higher than that on ultraviolet (UV) curing. For thermal curing, apparent modulus was the highest and reaching time until same strain was faster. So far thermal curing shows strong durability on the IFSS after boiling test.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2001.05a
• /
• pp.258-262
• /
• 2001

The contact resistivity was correlated with IFSS and microfailure modes in conductive fiber/cement composites electro-pullout and AE. As IFSS increased, the number of AE signals increased and the contact resistivity increased latter to the infinity. In dual matrix composite (DMC) test and AE, the number of signals with high amplitude and energy in g]ass fiber composite is significantly larger than that of no-fiber composite. Many vertical and diagonal cracks were observed in glass fiber and no-fiber composite under tensile test, respectively. Electro-micromechanical technique and AE can be used efficiently for sensitive nondestructive (NDT) evaluation and to detect microfailure mechanisms in various conductive fibers reinforced brittle and nontransparent cement composites.

• Composites Research
• /
• v.22 no.5
• /
• pp.8-14
• /
• 2009

Interfacial evaluation of glass fiber reinforced carbon nanotube (CNT)-epoxy nanocomposite was investigated by micromechanical technique in combination with wettability test. The contact resistance of the CNT-epoxy nanocomposite was measured using a gradient specimen, containing electrical contacts with gradually-increasing spacing. The contact resistance of CNT-epoxy nanocomposites was evaluated by using the two-point method rather than the four-point method. Due to the presence of hydrophobic domains on the heterogeneous surface, the static contact angle of CNT-epoxy nanocomposite was about $120^{\circ}$, which was rather lower than that for super-hydrophobicity. For surface treated-glass fibers, the tensile strength decreased dramatically, whereas the tensile modulus exhibited little change despite the presence of flaws on the etched fiber surface. The interfacial shear strength (IFSS) between the etched glass fiber and the CNT-epoxy nanocomposites increased due to the enhanced surface energy and roughness. As the thermodynamic work of adhesion, $W_a$ increased, both the mechanical IFSS and the apparent modulus increased, which indicated the consistency with each other.

• Composites Research
• /
• v.34 no.5
• /
• pp.305-310
• /
• 2021

Mechanical properties of fiber reinforced composites were affected to fiber volume fractions (FVF) and interfacial property by sizing agent conditions. An optimum interface can relieve stress concentration by transferring the mechanical stress from the matrix resin to the reinforcements effectively, and thus can result in the performance of the composites. The interfacial properties and wettability between the epoxy resin and glass fiber (GF) were evaluated for different sizing agent conditions and FVFs. The surface energies of epoxy resin and different sizing agent treated GFs were calculated using dynamic and static contact angle measurements. The work of adhesion, W_a was calculated by using surface energies of epoxy matrix and GFs. The wettability was evaluated via the GF tow capillary test. The interfacial shear strength (IFSS) was evaluated by microdroplet pull-out test. Finally, the optimized GFRP manufacturing conditions could be obtained by using wettability and interfacial property.

• Composites Research
• /
• v.12 no.4
• /
• pp.55-61
• /
• 1999

Interfacial shear strength (IFSS) of poly(arylene ether phosphine oxide) (PEPO) coated carbon fibers was evaluated via microdroplet test and compared with results obtained from carbon fibers coated with poly(arylene ether sulfone) (PES), Udel$^{\circledR}$ P-1700 and Ultem$^{\circledR}$ 1000. Interfacial adhesion between thermoplastics and uncoated carbon fibers was also measured in order to understand the adheion mechanism. PEPO coated carbon fibers showed the highest IFSS, followed by PES, Udel and Ultem coated fibers. A similar trend was observed for thermoplastic/uncoated fibers. SEM analysis indicated that only PEPO coated fiber exhibited cohesie failure in the vinylester resin, while others showed failure at or near the interface of polymer coating and vinylester resin. The enhanced interfacial adhesion by PEPO coating could be attributed to the strong interaction of P = 0 moiety to the fiber as well as to the vinylester resin.

• Journal of Adhesion and Interface
• /
• v.10 no.4
• /
• pp.162-168
• /
• 2009

As a preliminary study of optimum composite properties under cryogenic temperature, the comparison of interfacial properties of carbon or glass fibers reinforced epoxy composites was evaluated at ambient and intermediate low temperature, i.e., 25 and $-10^{\circ}C$ by using micromechanical techniques. Under tensile and compressive loading conditions, their mechanical modulus at low temperature was higher than that atambient temperature. Interfacial shear strength (IFSS) at ambient and low temperatures was compared to each other, depending on epoxy matrix toughness and apparent modulus at the interface. The IFSS was much higher at low temperature than that at room temperature because of the increased epoxy matrix modulus. Statistical distributions of tensile strengths of glass and carbon fibers were evaluated for different temperature ranges, which is dependent upon fiber's inherent flaws and rigidity.

• Composites Research
• /
• v.16 no.2
• /
• pp.68-73
• /
• 2003

Interfacial properties and electrical sensing fer fiber fracture in carbon and SiC fibers/epoxy composites were investigated by the electrical resistance measurement and fragmentation test. As fiber-embedded angle increased, the interfacial shear strength (IFSS) of two-type fiber composites decreased, and the elapsed time takes long until the infinity in electrical resistivity. The initial slope of electrical resistivity increased rapidly to the infinity at higher angle, whereas electrical resistivity increased gradually at small angle. Furthermore, both fiber composites with small embedded angle showed a fully-developed stress whitening pattern, whereas both composites with higher embedded angle exhibited a less developed stress whitening pattern. As embedded angle decreased, the gap between the fragments increased and the debonded length was wider for both fiber composites. Electro-micromechanical technique could be a feasible nondestructive evaluation to measure interfacial sensing properties depending on the fiber-embedded angle in conductive fiber reinforced composites.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2005.04a
• /
• pp.42-45
• /
• 2005

Interfacial evaluation of various combinations of both Flax and Hemp fibers/polypropylene were performed by using micromechanical test and nondestructive acoustic emission (AE). It can be because interfacial adhesion between the natural fiber surface and matrix plays an important role in controlling the overall mechanical properties of polymer composite materials by transferring the stress from the matrix to the fiber. It is necessary to characterize the interphase and the level of adhesion to understand the performance of the composites properly. Microfailure mechanism of single Flax fiber bundles were investigated using the combination of single fiber tensile test and nondestructive acoustic emission. Microfailure modes of the different natural fiber/polypropylene systems were observed using optical microscope and determined indirectly by AE and their FFT analysis.