Yu-Si Lee

Effect of coating material and lubricant on forming force and surface defects in wire drawing process

A pilot wire drawing machine as well as wire end-pointing roller was developed. Using these machines, a wire drawing test for four different coating materials and two different lubricants was performed as the reduction ratio increased from 10% to 30%. Materials used for a substrate in this study are plain carbon steel (AISI1045) and ultra low carbon bainite steel. To compute the friction coefficient between the coating layer of wire and the surface of die for a specific lubricant, a series of finite element analyses were carried out. SEM observations were also conducted to investigate the surface defects of wire deformed. Results show that the behavior of drawing force varies with the lubricant-type at the initial stage of drawing. The powder-typed lubricant with a large particle causes the retardation of full lubrication on the entire contact surface and the local delamination of coating layer on the wire surface. As the flow stress of a substrate increases, the delamination becomes severe.

Experimental and finite element analysis for fracture of coating layer of galvannealed steel sheet

Abstract Mechanical properties of galvannealed (GA) steel sheet used for automotive exposed panel and predicted failure phenomenon of its coating layer were evaluated using finite element method. V-bending test was performed to understand better the fracture of coating layer of GA steel sheet during plastic deformation. Yield strength of the coating layer was calculated by using a relative difference between hardness of coating layer measured from the nano-indentation test and that of substrate. To measure shearing strength at the interface between substrate and coating layer, shearing test with two specimens attached by an adhesive was carried out. Using the mechanical properties measured, a series of finite element analyses coupled with a failure model was performed. Results reveal that the fracture of coating layer occurs in an irregular manner at the region where compressive deformation is dominant. Meanwhile, a series of vertical cracks perpendicular to material surface are observed at the tensile stressed-region. It is found that 0.26-0.28 of local equivalent plastic strain exists at the coating and substrate at the beginning of failure. The fracture of coating layer depends on ductility of the coating layer considerably as well.

Exposure assessment of caffeine in children’s snacks in Korea

This study was conducted to develop an appropriate management strategy for the safe consumption of children’s snacks. In this study, a caffeine content analysis was performed on children’s snacks which were distributed at stores located near to schools. A total of 213 samples (63 chocolates, 40 ice cakes, 19 canned instant coffees, and 91 beverages) were analyzed for caffeine content. The caffeine content of chocolates, ice cakes, canned instant coffees, and beverages was 94.30, 35.03, 391.78, and 68.32 mg/kg, respectively. The results of the exposure assessment for caffeine were expressed as estimated daily intake (EDI) compared to the acceptable daily intake (ADI). The EDI/ADI ratio of the high risk group (95th percentile) for caffeine intake was 7.63–27.13 %. The results of this study indicate that the EDI of caffeine from snacks sold at stores located near to schools is much lower than the ADI in general. Consequently, children’s snacks are thought to be safe for consumption.

Potential risk and sodium content of children’s ready-to-eat foods distributed at major amusement parks in Korea

This study was conducted to help better understand the current sodium intake of Korean children and to establish children’s good eating habits through investigation of the sodium content of ready-to-eat foods collected from nine major amusement parks in Korea. The sodium content of a total of 322 products was analysed by using ICP and then the potential risk based on the recommended daily intake of sodium as described in the Korean dietary reference intakes was determined. The results showed that sodium content was the lowest in muffins (245 mg/100 g) and the highest in seasoned dried filefish (1825 mg/100 g). The average amounts of sodium per serving of seasoned dried filefish, tteokbokki and fish paste were 1150, 1248 and 1097 mg, respectively. The values were above 50% of the daily intake of sodium recommended by the Korean dietary reference intake. The ready-to-eat foods were also classified into high, medium and low sodium content on the basis of standards recommended by the Korean Food and Drug Administration. Most snacks were classified as high sodium foods because they exceeded “300 mg (84.5% of the total daily allowance)”. Furthermore, the meal substitution foods such as kimbab, tteokbokki, mandus, sandwiches and hamburgers exceeded “600 mg (90.3% of the total daily allowance)” and were also classified as high sodium foods. In addition, ready-to-eat foods in amusement parks are similar to foods eaten on streets and foods around school zones, which contain high sodium content; thus, the intake frequency might be high, which would induce high risk to children health. Koreans already consume a high amount of sodium daily via their usual diets. So, the sodium content in snacks and substitution foods needs to be reduced. Consequently, this study noted that parents and guardians should carefully consider their children’s consumption of ready-to-eat foods from Korean amusement parks.

Study on roll force and dynamic recrystallization of high-strength interstitial-free steels in hot rolling

Abstract This paper presents a constitutive model for two interstitial-free (IF) steels that can be used for calculating the roll force during hot rolling. The constitutive models assume that the deformation behaviour of material can be described with reference to strain, strain rate, and temperature together with the volume fraction of dynamically recrystallized grains. The two IF steels are Nb-Ti-added IF steel containing 0.001 wt% B and 0.1 wt% P, and IF steel with no B and P. To verify the proposed constitutive model, a laboratory-scale hot-plate rolling experiment, together with three-dimensional finite element analysis coupled with the proposed model, has been performed. The capability of the proposed model was demonstrated through comparing predicted roll forces with measured values. A series of finite element simulations has then been carried out to study the variation in the distribution of the dynamically recrystallized volume fraction in the deformed workpiece by changing the rolling temperature and reduction ratio. Good agreement was obtained between the predicted roll forces and experimental measurements for two IF steels. The roll force of IF steel with P and B components was 11.6 per cent larger than that of IF steel without them since dynamic recrystallization was delayed owing to the alloying elements. It has been found that, as the reduction ratio increases, the effect of those alloys on the volume fraction of dynamic recrystallization becomes more dominant and leads to considerable differences between the roll force of the steels.