• Transactions of Materials Processing
• /
• v.31 no.4
• /
• pp.173-178
• /
• 2022

The present study employed two different machine-learning approaches, the extreme gradient boosting (XGB) and light gradient boosting machine (LGBM), to predict a compressive deformation behavior of additively manufactured Ti-6Al-4V. Such approaches have rarely been verified in the field of metallurgy in contrast to artificial neural network and its variants. XGB and LGBM provided a good prediction for elongation to failure under an extrapolated condition of processing parameters. The predicting accuracy of these methods was better than that of response surface method. Furthermore, XGB and LGBM with optimum hyperparameters well predicted a deformation behavior of Ti-6Al-4V additively manufactured under the extrapolated condition. Although the predicting capability of two methods was comparable, LGBM was superior to XGB in light of six-fold higher rate of machine learning. It is also noted this work has verified the LGBM approach in solving the metallurgical problem for the first time.

• Design & Manufacturing
• /
• v.17 no.1
• /
• pp.1-5
• /
• 2023

In multi-material injection molding, since two or more materials with different process conditions are used, it is essential to maximize process efficiency by operating the cooling or heating system to a minimum. In this study, Liquid silicone rubber (LSR) that can be cured at a low temperature suitable for the multi-material injection molding was selected and the cure behavior according to the process conditions was analyzed through differential scanning calorimetry (DSC). Dynamic measurement results of DSC with different heating rate were obtained, and through this, the total heat of reaction when the LSR was completely cured was calculated. Isothermal measurement results of DSC were derived for 60 minutes at each temperature from 80 ℃ to 110 ℃ at 10 ℃ intervals, and the final degree of cure at each temperature was calculated based on the total heat of reaction identified from the Dynamic DSC measurement results. As the result, it was found that when the temperature is lowered, the curing start time and the time required for the curing reaction increase, but at a temperature of 90 ℃ or higher, LSR can secure a degree of cure of 80% or more. However, at 80 ℃., it was found that not only had a relatively low degree of curing of about 60%, but also significantly increased the curing start time. In addition, in the case of 110 ℃, the parameters were derived from experimental result using the Kamal kinetic model.

• Journal of the Korean Wood Science and Technology
• /
• v.51 no.5
• /
• pp.381-391
• /
• 2023

Densification is a technique used to improve biomass quality in wood pellet manufacturing and torrefaction treatment. In this study, the effects of torrefaction on the quality of Calliandra wood pellets were investigated, and pellets of Calliandra wood (Calliandra calothyrsus) and bark were evaluated. The study was conducted using a completely randomized design with two treatment factors, namely torrefaction temperature (250℃ and 300℃) and torrefaction duration (30, 45, and 60 min). The results showed that the interaction between temperature and torrefaction duration significantly affected the compressive strength, proximate value, and calorific value of the torrefied Calliandra wood pellets. An increase in the temperature and torrefaction duration decreased the compressive strength, moisture content, volatile matter content, and ash content of the torrefied Calliandra wood pellets. Conversely, the calorific value of Calliandra wood pellets increased with increasing temperature and torrefaction duration. The best-quality Calliandra wood pellets were produced at a torrefaction temperature and duration of 300℃ and 60 min, respectively. In terms of important quality parameters, ash content of 0.90% and calorific value of 6,303.80 cal/g were observed, which complied with the quality standards of Indonesian National Standard 8675:2018 and Deutsche Industrie Norm 51731.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.17 no.4
• /
• pp.1182-1199
• /
• 2023

Fractional repetition (FR) codes can achieve exact uncoded repair for multiple failed nodes, with lower computational complexity and bandwidth overhead, and effectively improve repair performance in distributed storage systems (DSS). The actual distributed storage system is dynamic, that is, the parameters such as node storage overhead and number of storage nodes will change randomly and dynamically. Considering that traditional FR codes cannot be flexibly applied to dynamic distributed storage systems, a new construction scheme of adaptive-and-resolvable FR codes based on hypergraph coloring is proposed in this paper. Specifically, the linear uniform regular hypergraph can be constructed based on the heuristic algorithm of hypergraph coloring proposed in this paper. Then edges and vertices in hypergraph correspond to nodes and coded packets of FR codes respectively, further, FR codes is constructed. According to hypergraph coloring, the FR codes can achieve rapid repair for multiple failed nodes. Further, FR codes based on hypergraph coloring can be generalized to heterogeneous distributed storage systems. Compared with Reed-Solomon (RS) codes, simple regenerating codes (SRC) and locally repairable codes (LRC), adaptive-and-resolvable FR codes have significant advantages over repair locality, repair bandwidth overhead, computational complexity and time overhead during repairing failed nodes.

• Structural Engineering and Mechanics
• /
• v.86 no.5
• /
• pp.687-704
• /
• 2023

This study aims to examine the structural response of glass fibre-reinforced polymer (Glass-FRP) reinforced geopolymer electronic waste aggregate concrete (GEWC) compression elements under axial compression for sustainable development. The research includes the fabrication of nine GEWC circular compression elements with different reinforcement ratios and a 3-D nonlinear finite element model using ABAQUS. The study involves a detailed parametric analysis to examine the impact of various parameters on the behavior of GEWC compression elements. The results indicate that reducing the vertical distance of glass-FRP ties improves the ductility of GEWC compression elements, and those with eight longitudinal rebars have higher axial load-carrying capacities. The finite element predictions were in good agreement with the testing results, and the put forwarded empirical model shows higher accuracy than previous models by involving the confinement effect of lateral glass-FRP ties on the axial strength of GEWC compression elements. This research work contributes to minimizing the carbon footprint of cement manufacturing and electronic waste materials for sustainable development.

• Design & Manufacturing
• /
• v.17 no.2
• /
• pp.15-21
• /
• 2023

In this study, a diamond turning machine and a laser-assisted machining module were utilized for the complex combined cutting of aspheric shapes and fine patterns on the surface of high-hardness brittle material, silicon. The analysis of material's form accuracy and corrective machining was conducted based on key factors such as laser output, rotational speed, feed rate, and cutting depth to achieve form accuracy below 1 ㎛ and surface roughness below 0.1 ㎛. The cutting condition and corrective machining methods were investigated to achieve the desired form accuracy and surface roughness. The rotational speed of the spindle and the linear feed rate of the diamond turning machine were varied in five stages for the cutting condition test. Surface roughness and form accuracy were measured using both a contact surface profilometer and a non-contact surface profilometer. The experimental results revealed a tendency of improved surface roughness with increased rotational speed of the workpiece, and the best surface roughness and form accuracy were observed at a feed rate of 5 mm/min. Furthermore, based on the cutting condition experiments, corrective machining was performed. The experimental results demonstrated an improvement in form accuracy from 0.94 ㎛ to 0.31 ㎛ and a significant reduction in the average value of the surface roughness curve from 0.234 ㎛ to 0.061 ㎛. This research serves as a foundation for future studies focusing on the machinability in relation to laser output parameters.

• Advances in aircraft and spacecraft science
• /
• v.9 no.4
• /
• pp.301-318
• /
• 2022

This paper presents the free vibration analysis of 3D printed sandwich beams by using high-order theories based on the Carrera Unified Formulation (CUF). In particular, the component-wise (CW) approach is adopted to achieve a high fidelity model of the printed part. The present model has been used to build an accurate database for collecting first natural frequency of the beams, then predicting Young's modulus based on an inverse problem formulation. The database is built from a set of randomly generated material properties of various values of modulus of elasticity. The inverse problem then allows finding the elastic modulus of the input parameters starting from the information on the required set of the output achieved experimentally. The natural frequencies evaluated during the experimental test acquired using a Digital Image Correlation method have been compared with the results obtained by the means of CUF-CW model. The results obtained from the free-vibration analysis of the FDM beams, performed by higher-order one-dimensional models contained in CUF, are compared with ABAQUS results both first five natural frequency and degree of freedoms. The results have shown that the proposed 1D approach can provide 3D accuracy, in terms of free vibration analysis of FDM printed sandwich beams with a significant reduction in the computational costs.

• Design & Manufacturing
• /
• v.18 no.2
• /
• pp.29-34
• /
• 2024

This study intends to reduce forming load by adding die rotation to flange-upsetting process. Materials arc formed by the compression and rotational torque which are accrued from rotation of the lower die accompanied by axial compression of the punch. For the theoretic analysis of flange-upsetting process using rotation die, slab method was used. Furthermore, for the verification of the theoretic analysis results, FEM simulation using DEFORM 3D a commercial software was done, and through the model material experiment using Prasticine, the results were compared and reviewed. Flange-upsetting process using rotation die shows reduced forming load compared with process without die rotation and demonstrates uniform distribution of strain. And as for the effect of the reduction of forming load, the less the aspect ratio(h₀/d₀) and the greater friction coefficient, the greater effect is. With increase in die rotation velocity, the effect of forming load reduction also increases little by little, but its effect on forming load reduction is very negligible compared with other forming parameters. Theoretic analysis results and simulation results coincided pretty well. The flange-upsetting process using die rotation are evaluated as useful process that can produce reduction of forming load and uniform strain.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.11 no.3
• /
• pp.190-197
• /
• 2001

Noise-induced hearing loss(NIHL) was the highest rate (43.5%~58.5% from 1996 to 1998) of positive findings through specific medical program in Korea. There were much more NIHL at workers of automobile manufacturing factories than other manufacturing factories. The specific aim of the present study was to determine the noise exposure of automobile press lines, according to their job titles, press line types(auto, semiauto), dosimeter parameters setting. There were a total 11 press lines sampled at a automobile manufacturing company. Among those press lines, 10 press lines were autolines with acoustic enclosure, one semiauto press line was no aucostic enclosure Noise exposure data were sampled for an work shift using noise dosimeter, which recorded both time-weighted average(TWA) and 1-min average. The mean OSHA TWA(Korea TWA with threshold 90) was $80.7dB(A){\pm}4.7dB(A)$ for leader, $82.8dB(A{\pm}4.5dB(A)$ for pallette man, $76.7dB(A){\pm}4.3dB(A)$ for press operators, $76.6dB(A){\pm}5.6dB(A)$ for crane operators, $77.1dB(A){\pm}2.8dB(A)$ for forklift drivers, whereas the mean NIOSH TWA was $88.9dB(A){\pm}1.7dB(A)$ for leader, $89.6dB(A){\pm}2.1dB(A)$ for pallette man, $86.7dB(A){\pm}1.8dB(A)$ for press operators, $88.5dB(A){\pm}2.0dB(A)$ for crane operators, $87.7dB(A){\pm}1.0dB(A)$ for forklift drivers. While L10 for NIOSH TWA samples was 84.8 dB(A) ~ 87.3 dB(A), L10 for OSHA TWA samples was 69.5 dB(A) ~ 77.4 dB(A). L10 means that the TWA for 90% of the samples exceeded L10. Among OSHA TWA(Korea TWA with threshold 90) samples for pallette man, 7.7 % exceeded 90 dB(A), the OSHA permissible exposure level, but OSHA TWA samples for the other job titles didn't. Among NIOSH TWA samples, the samples over 85 dB(A), the NIOSH recommended exposure limit, was 100% (leaders), 83.3 %(operators), 97.4%(palletteman), 100%(forklift drivers), 91.7 %(crane operator). The results of One-way random effects analysis of variance models shows that the difference between job titles was significant by OSHA TWA(p<0.05), but not significant by NIOSH TWA(p>0.05). NIOSH TWA samples were significantly higher than OSHA TWA samples(P<0.05). Regression analysis was used to obtain relationships between OSHA TWA samples and NIOSH TWA samples. In this case the coefficient of determination = 0.90, which shows the high degree association between two methods. Regression equation, NIOSH TWA = 0.552 * OSHA TWA + 42.13 dB(A), shows that if OSHA TWA is known, NIOSH TWA can be predicted by the equation. The mean TWA difference between threshold 80 dBA and 90 dBA was significant(p<0.01). While the TWA noise exposures were 7.7% above the Korea(OSHA) PEL, they were more than 83.3% over NIOSH REL. Automobile workers were exposed to noise level that could be potentially damaging to their hearing. It found that there is approximately 25% excess risk of hearing loss even if a worker is protected to the PEL in according to NIOSH study.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.6 no.2
• /
• pp.187-205
• /
• 2014

The global price of oil, which is both finite and limited in quantity, has been rising steadily because of the increasing requirements for energy in both developing and developed countries. Furthermore, regulations have been strengthened across all industries to address global warming. Many studies of hull resistance, propulsion and operation of ships have been performed to reduce fuel consumption and emissions. This study examined the design parameters of the propeller boss cap fin (PBCF) and hub cap for 6,000TEU container ships to improve the propulsion efficiency. The design parameters of PBCF have been selected based on the geometrical shape. Computational fluid dynamics (CFD) analysis with a propeller open water (POW) test was performed to check the validity of CFD analysis. The design of experiment (DOE) case was selected as a full factorial design, and the experiment was analyzed by POW and CFD analysis. Analysis of variance (ANOVA) was performed to determine the correlation among design parameters. Four design alternatives of PBCF were selected from the DOE. The shape of a propeller hub cap was selected as a divergent shape, and the divergent angle was determined by the DOE. Four design alternatives of PBCF were attached to the divergent hub cap, and the POW was estimated by CFD. As a result, the divergent hub cap with PBCF has a negative effect on the POW, which is induced by an increase in torque coefficient. A POW test and cavitation test were performed with a divergent hub cap with PBCF to verify the CFD result. The POW test result showed that the open water efficiency was increased approximately 2% with a divergent hub cap compared to a normal cap. The POW test result was similar to the CFD result, and the divergent hub cap with the PBCF models showed lower open water efficiency. This was attributed to an increase in the torque coefficient just like the CFD results. A cavitation test was performed using the 2 models selected. The test result showed that the hub vortex is increased downstream of the propeller.