A study on flexural properties of carbon-basalt/epoxy hybrid composites

The objective of this research is to investigate the performances of the carbon-basalt/epoxy hybrid composites under flexural loading. In this work, the hybrid composites were manufactured by the vacuum assisted resin transfer molding (VARTM) process. The variations of flexural strength and modulus of the hybrid composite according to the number of basalt fabric were investigated, and we obtained the expression to calculate their mechanical properties. In the study of flexural properties for the hybrid composites with different stacking sequence of the reinforcements, we knew that their properties strongly depend on the reinforcing position of carbon and basalt fabric.     

Effect of temperature on the magnetic abrasive finishing process of Mg alloy bars

Experiments were conducted to evaluate the effect of temperature during magnetic abrasive finishing of Mg alloy bars. A magnetic abrasive finishing process is an unconventional finishing technique that has been used to achieve high-quality surfaces with dimensional accuracy. In this study, a Mg alloy bar, which is widely used in automobiles, aircraft, IT, and the defense industry, was chosen as a cylindrical workpiece. The workpiece was then finished with a magnetic abrasive finishing process at three different temperatures, i.e., a cryogenic temperature, room temperature, and high temperature. In the cryogenic temperature condition, liquid nitrogen and argon gas were used as the cryogenic cooling gases in the finishing process; the results from this treatment were compared with those obtained at room temperature and high temperature conditions. At the room temperature condition, the finishing process of the cylindrical workpiece was performed at 24 °C. To carry out the high temperature condition, a hot air dryer was used to maintain a finishing temperature of 112 °C. The experimental results show that the room and cryogenic temperatures could yield excellent performance in terms of the surface roughness. However, in terms of the removal weight and change in diameter, the high temperature condition was found to be superior. In the present research, the improvements of the surface roughness (Ra) at room temperature (24 °C) and cryogenic temperature (-120 °C) conditions were 84.21 % and 55 %, respectively.

     

Robust and Flexible Polyurethane Composite Nanofibers Incorporating Multi‐Walled Carbon Nanotubes Produced by Solution Blow Spinning

Using a technique called solution blow spinning, polyurethane–carbon nanotube‐based composite nanofibers are fabricated. These composite nanofibers exhibit uniform diameter, even with increasing polyurethane density, with the use of a dual‐solvent mixture during spinning. It is possible to produce the fibers at a high production rate even after the addition of a large amount of carbon nanotubes with a uniform size distribution of 300–400 nm. In addition, for composites with 3 wt% carbon nanotubes, the tensile strength, elongation, and elastic strain energy increase to 102, 166, and 167%, respectively, compared to pure PU nanofibers. The thermal stability improves as well. The prepared composite nanofibers could potentially be used as an inter‐reinforcing agent in carbon‐fiber‐reinforced plastics and as a buffer, and in the biomedical field.

     

Effect of postpeak tension-softening behavior on the fracture properties of 2-D carbon fiber reinforced carbon composite

The fracture properties of commercial carbon fiber reinforced carbon (C/C) composites (CCM190C, CCM191C) that have different interfacial shear strength were investigated. Postpeak tension-softening phenomena were observed through the fracture mechanics test for these composites. The failure manner in the fracture process zone was primarily fiber pull-out for CCM190C and fiber breakage for CCM191C, respectively. It was confirmed that the scale of pseudo strain hardening for CCM190C with low interfacial shear strength was larger than that of CCM191C. The bridging energy at the postpeak part and the total energy consumed to produce a unit area of fracture surface were calculated based on the J-based technique. The bridging energy at the postpeak part accounted for 12.3% of the total energy consumed to produce a unit area of fracture surface for CCM190C. From this result, it can be deduced that the effect of the postpeak bridging energy on the fracture toughness is large for CCM190C. In contrast, the contribution of the postpeak bridging energy for the total energy per fracture surface was very small for CCM191C. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Yonjig Kim received B. S. and M. S. degrees in Mechanical Design Engineering and Mechanical Engineering at Chonbuk National University in 1983 and 1985, respectively. He enlisted in the army as a soldier and leaved the army in 1988, and then got a ph. D. degree in Mechanical Engineering at Chonbuk National University in 1993. Dr. Kim is currently working as a professor in his alma mater, Chonbuk National University. His major area of study is materials and fracture mechanics and he is interested mainly in fracture of fiber reinforced polymer composites.