Woo-Kyun Jung

Measurement and Compensation of Spring-back of a Hybrid Composite Beam

Fiber-reinforced composite materials have been advanced in various applications for their excellent mechanical and electromagnetic properties. On their manufacturing processes, however, thermo-curing inherently produces the undesired thermal deformation, so-called spring-back, mainly caused by temperature drop from the process temperature to room temperature. In order to fabricate designed part geometry, the spring-back must be understood especially in hybrid composites consisting of distinct groups of different materials. In this research, the spring-back of a hybrid composite beam is measured by a series of experiments, and is predicted by the classical lamination theory (CLT) and finite element analysis (ANSYS). To confirm the predicted spring-back, {glass fiber/epoxy} + {carbon fiber/epoxy} asymmetric hybrid composites are fabricated under various conditions such as cure cycle, laminate thickness, stacking sequence, and curing sequence. The results from CLT and FEA agree well with the experimental data, but the spring-back cannot be removed completely. To fabricate flat hybrid composite beams, a web-based spring-back compensation service is developed. The CLT-based code allows the user to predict spring-back and to fabricate a mold that compensates spring-back.

Effect of nanoparticles and ion implantation on the electromagnetic shielding of glass-epoxy composites

The research on electromagnetic (EM) shielding has been advanced for various applications. Recently, researchers have been interested in nano-sized particles to modify electromagnetic properties of a base material. In this research, glass fiber–epoxy–nanoparticle composites (GFR nanocomposites) are fabricated using four types of nanoparticles, and their properties in electromagnetic shielding are compared. Carbon black (CB), multiwalled carbon nanotube (MWCNT), silver nanoflake (SNF), and silver nanopowder (SNP) are used as the added particles. For the visual observation of the nanocomposites, scanning electron microscope (SEM) and transmission electron microscope (TEM) are used. The characteristics of EM shielding of the composites are measured using HP8719ES Sparameter Vector Network Analyzer System for the frequency range between 8 and 12GHz. Composites using MWCNT and CB show outstanding shielding effect of 17 and 43 dB, respectively, but silver nanoparticles do not show significant EM shielding. In addition, change of EM shielding characteristics by the ion implantation process is observed. After ion implantation, the EM shielding of the composites containing silver is increased in the frequency range.

Fabrication of micro parts using nano composite deposition system

Purpose – The purpose of this research, is to develop a nano composite deposition system (NCDS) to fabricate three dimensional functional nano composite parts.Design/methodology/approach – The NCDS is a hybrid system in which material removal process by mechanical micro machining and/or the deposition process is combined.Findings – Hybrid RP technology showed higher precision than those made by casting or deposition process. Tensile strength of the hydroxyapatite‐acrylic composite was about four times higher than that of resin‐only specimen while MWCNT composite did not show much improvement.Originality/value – The paper illustrates new approaches for rapid prototyping techniques with various materials and high precision.