Polymer microlens manufacturing using thermal reflow was simulated and optimized by a numerical approach. Microlenses are used in various industrial fields, such as optical, semiconductor, and observation experiment equipment. Therefore, polymer microlens fabrication using an economical thermal reflow process is important for mass production and cost reduction. The feasibility of a thermal reflow process for microlens fabrication was analyzed in this paper by numerical methods. First, we refer to the previous studies and papers for the theoretical shape of the microlens. Second, for numerical simulation of the process above Tg (Glass Transition Temperature), we studied the multiphase flow simulation using a VOF method and adopted a Cross-WLF model to consider the rheological characteristics of PMMA. Finally, several parametric studies were carried out to compare the simulation profile and the theoretical lens shape in order to optimize the thermal reflow process. The numerical approach presented in this paper would enable a more efficient analysis and provide better understanding of reflow behavior to obtain the optimal process.

The cryogenic ball milling was performed on carbon nanotubes (CNTs) at an extremely low temperature to increase the dispersion of CNTs. The effects of milling speed and time on the deagglomeration and structural changes of CNTs were studied. FESEM was used to analyze the dispersion and the change of particle size before and after milling process. Transmission electron microscopic (TEM) analysis was also investigated the effect of cryogenic ball milling on the morphological characteristics of CNTs. The structural changes by the cryogenic ball milling process were further confirmed by x-ray diffraction (XRD) and Raman spectroscopic analysis. The results showed that the agglomeration of CNTs was significantly reduced and amorphous structure was observed at high milling speed. However, the milling time has no great effect on the dispersion property and structural change of CNTs compared with milling speed.

Polyethylene is a typical hydrophobic material and it is difficult to bond the polyethylene material with metal material. Thus, it is important to modify the surface of polyethylene material to improve the bonding strength between the polyethylene and the metal materials. In this study, the surface modification of polyethylene material was investigated to improve the interfacial strength between the polyethylene and the steel materials. Polyethylene material was surface-modified in a plasma cleaner using an oxygen gas. Two cases of composites (surface-modified polyethylene/steel composite and regular (as-received) polyethylene/steel composite) were fabricated using a secondary bonding method. Shear and bending tests have been performed using the two cases of composites. The results showed that the contact angle did not change much as the modification time increased. However, the contact angle decreased from -76° to ~41° with the modification. The results also showed that the shear strength and the bending strength were improved about 3030 % and 7 %, respectively when the polyethylene was plasma-modified using an oxygen gas.

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by a strain rate. In this work, we investigated the effect of strain rate on the compressive elastic modulus, fracture stress, and fracture strain of carbon/epoxy composites under hydrostatic pressure environment. The material used in the compressive test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 270 MPa. Compressive tests were performed applying three strain rates of 0.05 %/sec, 0.25 %/sec, and 0.55 %/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate. The results also showed that the fracture strain decreased with increasing strain rate.