Evaluation of physical properties of thin film and measurement of unsteady thermal stress

Winding defect such as the roll wrinkles or slips to lose the value of the product. Winding defect is caused by the internal stress condition in the roll and the temperature change of the roll after winding. Therefore, it is essential to analyze the internal stress theoretically. However, the tendency of internal stress to occur as the film thickness becomes thin is not known. The internal stress of the roll was measured at each temperature. Further changes in internal stress were also measured by changing the ambient temperature around the roll.The winding device used in this research is a structure reproducing the unwinding and the rewinding in the roll-to-roll production system. A film-like pressure sensor was used to measure the radial internal stress of the roll. After winding up the film, the internal stress in the radial direction inside the roll was measured when the temperature around the roll was heated for 12 hours. Measurement frequency was measured for internal stress every hour.In the PET film with a film thickness of 40 μm, the internal stress in the radial direction inside the roll was measured when the roll surrounding temperature was heated for 12 hours. For the middle and outer layers, the internal stress gradually increased with the lapse of time. It is considered that this increased the pressure by thermal expansion from the outer peripheral side of the roll. However, the value of the stress in the inner layer decreased greatly. This is thought to be caused by uneven heating due to the heat source, winding wrinkles occurred in the vicinity of the sensor sandwiched between the rolls, and stress relaxation occurred

Surface Modification Inspired by Malayopython Reticulatus for Friction Control

This research is to study the frictional characteristics of a real Malayopython Reticulatus snake ventral scales and to evaluate its feasibility as an inspiration for surface modification designs. Two types of experiments were carried out at different sliding directions and surfaces to analyze the frictional characteristics of snake ventral scales. From this study, snakeskin demonstrates frictional anisotropy and it is prominent under wet condition. Based on these findings, surface designs inspired by snakeskin is suitable for parts or components that are subjected to directional friction especially in wet conditions

Measurements of Film Thickness and Pressure Distribution for Optimized Thrust Air Bearing

In this paper, we describe the film thickness and pressure measurement of the optimized thrust air bearing. In our recent study, a new optimization technique of the bearing groove geometry of the hydrodynamic thrust air bearings was proposed and a new groove geometry having a bending curve in outer vicinity of the bearing surface was obtained. Furthermore, in this study, the drastic improvement of the bearing dynamic stiffness was verified by the dynamic characteristic experiment using the original high-speed bearing test rig. However the relative error of the film thickness between the theory and experiment is large compared with that of dynamic stiffness. Consequently, it has been considered that the improvement of the measurement accuracy for film thickness is one of the most important problems. On the other hand, the generation of the negative pressure on the optimized bearing surface has not been confirmed experimentally, and it is also important to verify the negative pressure generation by measurement. Therefore, in this study, we examined the improvement of the measurement accuracy of the film thickness and the pressure measurement of the optimized bearing. As a result, the accuracy of air film thickness is drastically improved applying a newly proposed compensation method and the negative pressure on the optimized bearing can be found experimentally

Streamlined vessels for speedboats: Macro modifications of shark skin design applications

Functional properties of shark denticles have caught the attention of engineers and scientist today due to the hydrodynamic effects of its skin surface roughness. The skin of a fast swimming shark reveals riblet structures that help to reduce skin friction drag, shear stresses, making its movement to be more efficient and faster. Inspired by the structure of the shark skin denticles, our team has conducted a study on alternative on improving the hydrodynamic design of marine vessels by applying the simplified version of shark skin skin denticles on the surface hull of the vessels. Models used for this study are constructed and computational fluid dynamic (CFD) simulations are then carried out to predict the effectiveness of the hydrodynamic effects of the biomimetic shark skins on those models. Interestingly, the numerical calculated results obtained shows that the presence of biomimetic shark skin implemented on the vessels give improvements in the maximum speed as well as reducing the drag force experience by the vessels. The pattern of the wave generated post cruising area behind the vessels can also be observed to reduce the wakes and eddies. Theoretically, reduction of drag force provides a more efficient vessel with a better cruising speed. To further improve on this study, the authors are now actively arranging an experimental procedure in order to verify the numerical results obtained by CFD. The experimental test will be carried out using an 8 metre flow channel provided by University Malaysia Sarawak, Malaysia. © 2018 Author(s)

Analysis of Fractures and Microstructures on Different Injection Speeds in High-Pressure Die-Casting Magnesium Alloy

In this study, to clarify the unknown physical properties of the Mg-Al-Th-RE alloy, the relationship between the injection conditions and the internal porosities, and the mechanical properties exerted by the solidification microstructure was investigated. The obtained cast samples were investigated using X-ray CT internal measurements, tensile tests, Vickers hardness tests, and solidification microstructure observations. The tensile strength and the elongation at the injection speed of 5.0 m/s were higher than at 2.0 m/s. The number of porosities affected the tensile strength and the elongation even at the same fracture position. In addition, it was confirmed that segregation affected the destruction smaller the porosity size and the greater the variability of porosity. As the injection speed increased, the amount of heat transferred between the molten metal and the wall surface also increased, resulting in quick freezing and solidification. The tensile strength increased at the injection speed of 5.0 m/s because the interface between the scattered primary crystals and eutectic systems was narrow. On the other hand, at the injection speed of 2.0 m/s, the tensile strength decreased because the molten metal was delayed in solidification and dendrite growth became remarkable

Numerical and Experimental Analysis on Runner and Gate Positioning for Magnesium Alloy Die-casted Test Piece

High Pressure Die Casting (HPDC) is a manufacturing process producing complex and precise products by injecting molten material into mold cavity at top speed and pressure. The quality of product is highly related with mold cavity design. Casting defects due to inappropriate mold design will affect mechanical properties, surface quality and product life cycle. Optimization of runner system is essential to manufacture complex and precision product design with minimal defects. The combination of runner and gating system is investigated in this paper. This paper investigated the effect of runner and gating optimization in reducing the gas porosity inside casting by evaluating the fluid and thermal distribution behavior in experimental and Computational Fluid Dynamic (CFD). The gas porosity generated in the molten magnesium alloy is due to the turbulent flow and the inconsistency of the fluid flow to push the gas bubble away from the main casting. This paper includes an X-ray of a sample product that shows correlation between gas porosity and CFD results. Results show that localize porosity gathered at the bottom of the main casting. Based on localized porosity position, runner and gating system is modified and numerical simulation is carried out for analysis. An inspection instrument step-type test piece is taken as an investigation sample to illustrate the technique of design modifications and improvements. Process parameters considered in this paper are injection speed, injection pressure, melt temperature and mold temperature. This paper proposed new runner designs that can generate balanced velocity and temperature distribution inside mold cavity, improving the solidification process aimed for reducing casting defects

Friction measurement of modified PDMS surfaces inspired by Malayopython Reticulatus

The lack of limbs on snakes enables its ventral scales to be in almost constant contact with the substrate. Their skin is presumably adapted to generate high and low friction to slither. This frictional characteristics in snakes were hypothesized to be contributed by the be tooth-shaped or denticle-like microstructures found on the snake ventral scales. The frictional properties of the microstructures found on snake ventral scales was studied and its feasibility as an inspiration for surface modifications was observed. This study was carried out to analyze the frictional anisotropy exhibit by the snake ventral scale microstructures and also how it changes the frictional properties of the PDMS surface when the microstructures are replicated on to it. The PDMS embedded-elastomeric stamping method was used in this experiment to replicate the snake ventral scales onto the PDMS. Based on the data collected the microstructures on the snake ventral scales does exhibit frictional anisotropy. The PDMS with replicated snakeskin microstructures displays higher COF compared to PDMS with smooth surface. When sliding on most types of surfaces, the COF of real snakeskin and replicated snakeskin is higher if the surface is semi wet. Whereas for smooth PDMS the COF is lower when the surfaces are semi wet. Generally, from both experiments, when the replicated snakeskin is sliding on the surface in the lateral direction, it is observed that the COF is the lowest followed by the caudal then the rostral direction