Chang-Kwon Moon

Effect of molecular weight and fiber diameter on the interfacial behavior in glass fiber/PP composites

In this study, the effects of fiber diameter, molecular weight of the matrix polymer, and interfiber spacing in glass fiber-reinforced polypropylene composites were investigated on the interfacial microstructure. The influences of the surface state of the fiber and the heat-treatment condition on the interfacial morphology and the spherulitic formation process in the matrix were also investigated. Consequently, it was found that both the fiber diameter and molecular weight of the polymer significantly influence the thickness of the transcrystalline layer. Also, as the interfiber spacing becomes smaller, the spherulites in the matrix polymer are not seen to be formed between the transcrystalline layers developed on the glass-fiber surface. In addition, the radius of the largest spherulites in the matrix polymer was found to be about the same as the thickness of transcrystalline region and to largely depend on the holding time at the crystallization temperature and cooling condition (or rate).

Durability of GFRP composite exposed to various environmental conditions

This paper presents a short-term durability test program for E-glass/vinylester composite exposed to various environmental conditions. The main objective of this study is to investigate the degradation of GFRP composite and its influence on the tensi le strength. A total of 530 strand-type E-glass/vinylester specimens were fabricated and exposed to six different environmental conditions for up to 150 days. To examine the degradation of conditioned specimens, the weight gain was measured and scanning electronic microscope images were taken at fractured section. Also, the tensile strength of the specimens was tested. From the test results, it is clear that the tensile strength of the conditioned specimens was significantly reduced due to the degradation of GFRP under the environmental conditions considered.

Multiple fiber technique for the single fiber fragmentation test

The single fiber fragmentation test has been modified by embedding multiple fibers into matrix resin. During testing, we examined the interfacial shear strengths between the fibers and the matrix. In addition, the time-dependent nature of the fragmentation process was considered. In the fragmentation test, we examined the failure process of two fibers placed far from each other, and we found that the failure profile of the two fibers were similar to the failure profiles from tests done on single fibers. When we examined three fibers, we found that the measured interfacial shear strength values were much greater than the shear strength values from either the single or two fiber tests. However, when we used three fibers, we found it difficult to control the interfiber spacing. Consequently, whenever the interfiber spacing was too small, breaks in one fiber caused breaks in the adjacent fiber. In conclusion, using multiple fibers in a fragmentation test has many merits, such as saving time in testing, ease of comparing the effects of fiber surface treatment, and testing different fibers in the same matrix exposed to the same processing conditions.

Study on Mechanical and Thermal Properties of Tio2/Epoxy Resin Nanocomposites

The purpose of this study was to improve the properties of epoxy resin using titanium oxide nanoparticles. The effects of particle weight fraction, dispersion agent, and curing agents with different molecular weights on the thermal and mechanical properties of titanium-oxide-reinforced epoxy resin were investigated. In addition, the effect of the particle dispersion condition on the mechanical properties of nanocomposites was studied. As a result, it was found that the glass transition temperature of film-shaped nanocomposites decreased with an increase in the nanoparticle content. Because nanoparticles interrupted the cross linkage between the epoxy resin and the amine curing agent, the cross-link density of the epoxy became lower and led to a decrease in Tg in the nanocomposites. The tensile strength and modulus in film-shaped nanocomposites also increased with the particles content. But in the case of dog-bone-shaped nanocomposites, the values were not similar to the trend for the film-shaped nanocomposites. This was probably a result of the different nanoparticles dispersions in the epoxy resins resulting from the respective-thicknesses of the film and dog-bone-shaped samples.

Nanoparticle Effect on Durability of Carbon fiber/ Epoxy Composites in Saline Water Environment

This study was conducted to investigate the durability of carbon fiber/epoxy composites (CFRP) in a saline water environment. The carbon fiber/epoxy composites were modified to use nanoparticles such as carbon nanotubes and titanum oxide. These hybrid composites were exposed to a saline water environment for a certain period. The weight gain according to the immersion time, a quasi-static tensile test, and micro-graphic characterization were used to investigate the samples exposed to the saline water environment. The weight gains increased with increasing immersion time. The weight gains of the hybrid composites were lower than that for pure CFRP throughout the entire immersion time. The tensile strengths decreased with increasing immersion time. The tensile strengths of the hybrid composites were higher than that of the pure CFRP throughout the entire immersion time. The pure CFRP was observed to be more degraded than the hybrid composites in the saline water environment. Therefore, it was concluded that the addition of nanoparticles to CFRP could lead to improved durability in a saline water environment.

Corrosion Resistance of Galvanized Steel by Treating Modified Si Organic/Inorganic Hybrid Coating Solution

Galvanized steel has gone through a chemical process to keep it from corroding. The steel gets coated in layers of zinc because rust will not attack this protective metal. For countless outdoor, marine, or industrial applications, galvanized steel is an essential fabrication component. The reduction of the corrosion rate of zinc is an important topic. In the past, a very popular way to reduce the corrosion rate of zinc was to use chemical conversion layers based on . However, a significant problem that has arisen is that the use of chromium salts is now restricted because of environmental protection legislation. Therefore, it is very important to develop new zinc surface treatments that are environmentally friendly to improve the corrosion resistance of zinc and adhesion with a final organic protective layer. In this study, a Urethane solution (only Urethane 20 wt.%; S-700) and an organic/inorganic solution with Si (Si polysilicate 10 wt.% + Urethane 10 wt.%; LRO-317) are used. Based on the salt spray test of 72 h, S-700 and LRO-317 had a superior effect for the corrosion resistance on EGI and HDGI, respectively.

Nanoparticle Size Effect on Mechanical Properties of Carbon Fiber-reinforced Polymer Composites

TiO2 nanoparticles can be used to improve the performance of carbon fiber-reinforced epoxy resin composites. In this study, the effect of the size of TiO2 nanoparticles on the mechanical properties of carbon fiber-reinforced epoxy resin composites was investigated. The size of the TiO2 nanoparticles was easily controlled using heat treatment. The size of the TiO2 nanoparticles for this study were20nm, 100nm, and 200nm. Three types of carbon fibers with different diameters we re also used in this study. The carbon fiber-reinforced epoxy resin composites with 20-nm TiO2 powder showed the highest tensile strength compared to the other types of CFRP, regardless of the fiber maker or fiber diameter. The size of the TiO2 powder and the diameter of the carbon fiber strongly affected t he interfacial properties of all kinds of CFRP in this study.

Characteristics of Elastic Wave Generated by Wear and Friction of SiC f /SiC Composites

The wear characteristics of SiCf/SiC composites were evaluated according to the alignment direction of the fibers, and the elastic wave-generated friction was detected and analyzed in wearing. The friction coefficient and wear loss were similar in the longitudinal and the transverse direction of the fibers. However, these values were lower in the vertical direction of the fibers because of the brittle nature of the fiber. The friction coefficient and the wear loss were directly proportional to each other. The dominant frequencies were 58.6 kHz for monolithic SiC and 117.2 and 136.7 kHz for SiCf/SiC composites, respectively.

Evaluation of dispersion degree of nanoparticles in TiO₂/epoxy resin nanocomposites

The purpose of this study was to evaluate the dispersion degree of particles using a nanoindentation test for titanium oxide nanoparticles/epoxy resin nanocomposites. Thus, the effects of the particle size and weight fraction, dispersion agent, and position of the sample on the modulus and degree of particle dispersion in the nanocomposites were investigated. As a result, the dispersion degree of large particles was found to be better than that of smaller particles in composites. It could be found that the aggregation or agglomeration of small particles with large surface energy occurred more easily in nanocomposites because of the large specific surface area. The moduli of the upper side of the film-shaped sample obtained from a nanoindentation test were low scattering, while the values for the bottom side were high scattering. Thus, the dispersion situation of the nanoparticles on the upper side of film-shaped samples could be considered to be better than that for the bottom side. This could be concluded due to the non-uniform nanoparticle dispersion in the same sample. The modulus obtained from nanoindentation test increased slightly with the content of nanoparticles and increased with the indented depth for the same sample. The latter is presumably due to the increase in the accumulated particles facing the indenter with the indented depth. The nanoindentation test was found to be a useful method to evaluate the dispersion status of nanoparticles in nanocomposites.

Cyclic Crack Healing Effect of Al 2 O 3 Ceramics

In this study, the crack healing effects of Al 2O3 ceramics based on the heat treatment conditions were investigated. The influence of the additive amounts of SiC nanoparticles and the cycling process of indentation-heat treatment on the crack healing effect of Al2O3 ceramics were also examined. Three-point bending tests were carried out and the morphological changes in the fracture surface were observed by using FE-SEM. As a result, heat-treated samples in a vacuum or air atmosphere showed improved bending strengths compared to un-heat treated samples. This means that cracked specimens can be healed by heat treatment in a vacuum or air atmosphere. The crack healing effect of Al 2O3 ceramics that were heat treated in an air atmosphere was much higher than that of those heat treated in a vacuum. After heat treatment, the Al2O3 ceramics with 30 wt% SiC nano- particles showed a higher bending strength than those with 15 w t% SiC. The cyclic indentation and heat treatment did not remarkably affect the crack healing effect. The SEM images showed that the median crack, indenter mark on the surface, and pores in the fracture surface of a specimen almost disappeared after being heat treated in an air atmosphere.