As the global manufacturing industry moves toward carbon neutrality, improving energy efficiency of machine tools has become essential. Although machine tools contribute significantly to industrial energy consumption, systematic methods for evaluating their energy consumption remain insufficient. To address this issue, this study developed an energy consumption evaluation system based on ISO 14955, the international standard for machine tool energy efficiency. The proposed system enabled a detailed analysis of energy usage patterns in different operating states, identifying key areas for energy reduction. The developed system could measure energy consumption of individual machine tool components in various operating states using power meters and automatically generates reports. This allows users to identify which components and operating states consume the most energy. We tested and validated this system on three different machine tools and analyzed strategies for reducing energy consumption. The developed evaluation system can help machine tool manufacturers integrate it into their equipment, develop energy-efficient technologies, and contribute to sustainable manufacturing.

Recently, X-ray images through chest radiography (CXR) can distinguish gas, fat, soft tissue, bone, and metal based on their densities. It is the most basic chest imaging technique. With advancement of technology, CXR is becoming safer by lowering the radiation dose. It has become the first examination performed on patients with thoracic abnormality syndrome for early diagnosis of various chest diseases worldwide, accounting for up to 26% of all diagnostic radiology examinations. Despite its various advantages, CXR can distinguish only a few densities. Various thoracic anatomical structures can overlap in a single 2D image and various pathologies can show the same density, making accurate interpretation at various densities difficult. Errors in CXR interpretation have been present since the mid-20th century, with 10-20% of tuberculosis cases being interpreted differently by various radiologists and 19% of lung cancer cases being misinterpreted. To address these issues in interpreting chest CXR and to increase its usability in emergency situations and various environments, the quality of CXR images needs to be improved. In order to improve the quality of these images, this study aimed to establish a portable multi-energy X-ray field technique using MCNP with dual energies of 40 and 70 keV.

In this study, we investigated characteristics and mechanical properties of SKD61 repaired using the direct energy deposition (DED) process. Mechanical properties of the repaired product can vary depending on the base material and powder used in the DED process. To prepare for DED repairing for a damaged part, we conducted experiments using two different powders (H13 and P21). Experimental results showed that both powders were deposited without defects in the surface or interface between the deposited zone and the substrate. Hardness measurements indicated that the repaired region of the Repaired-H13 sample exhibited higher hardness than the base material, while the Repaired-P21 sample showed a sharp increase in hardness in the heat-affected zone (HAZ). Additionally, tensile test results revealed that the Repaired-H13 sample had lower tensile strength and elongation than the base material, whereas the Repaired-P21 sample demonstrated higher tensile strength and yield strength with a higher elongation than the Repaired-H13 sample. In case of Repaired-H13, it was confirmed that interfacial crack occurred due to a high hardness difference between the repaired part and the substrate.

We demonstrate a practical and efficient hybrid triboelectric-piezoelectric energy harvesting structure that consists of a nanopatterned and/or metal-deposited polymer film and a piezoelectric elastomeric sponge. When a polymer (here, polycarbonate (PC)) and an elastomer (here, polydimethylsiloxane (PDMS)) make contact with and detach from each other, triboelectric energy can be harvested. In this case, the PC surface can be nanopatterned by continuous dynamic nanoinscribing and/or coated by a metal (here, Cu) layer for enhanced performance. When a piezoelectric material (here, lead zirconate titanate (PZT)) and sugar powder are mixed with PDMS, and the sugar is later dissolved, a porous piezoelectric elastomeric sponge (PES) can be fabricated. When a PC film and a PES make contact with and detach from each other, both triboelectric and piezoelectric energies can be simultaneously harvested. We systematically study the effect of PES and Cu thicknesses and dynamic nanoinscribed nanopattern on the energy harvesting performance of the hybrid triboelectric–piezoelectric nanogenerator (HTPENG). The performance of the HTPENG can be improved by using the PES of optimal thickness, and by applying the nanopattern and Cu layer. The HTPENG can be utilized in many systems where wireless self-powering is desired, such as wearable devices, flexible sensors, and skin electronics.

Additive manufacturing (AM) technology, also known as 3D printing, is a highly promising technology that can drive innovation in various industrial areas, including the nuclear industry. Although the nuclear industry is traditionally conservative when it comes to adopting new technologies, it is crucial that AM technology is eventually applied for a variety of reasons. To overcome the barriers that currently hinder the adoption of AM in the nuclear industry, it is essential to ensure the reliability of AM products. One key factor is ensuring that AM products have mechanical properties equivalent to those of traditionally manufactured products. This paper presents the results of mechanical property tests conducted on additive manufactured specimens of stainless steel 316 L after heat treatment. We performed tensile tests, hardness tests, and microstructure analysis on specimens produced using two types of metal AM technologies: powder bed fusion (PBF) and directed energy deposition (DED). The results of the tests indicate that certain weaknesses, such as anisotropy and brittleness, in AM products can be improved through three types of heat treatments. In particular, AM products produced using the PBF method and subjected to heat treatments show potential for application in the nuclear industry in terms of materials.

Estimating energy expenditure is essential in monitoring the intensity of physical activity and health status. Energy expenditure can be estimated based on wearable sensors such as inertial measurement unit (IMU). While a variety of methods have been developed to estimate energy expenditure during day-to-day activities, their performances have not been thoroughly evaluated under walking conditions according to various speeds and inclines. This study investigated IMU-based neural network models for energy expenditure estimation under various walking conditions and comparatively analyzed their performances in terms of sensor attachment locations and training/testing datasets. In this study, two neural network models were selected based on a previous study (Slade et al., 2019): (M1) a multilayer perceptron using sensor signals during each gait cycle, and (M2) a recurrent neural network using sensor signal sequences of a fixed window size. The results revealed the following: (i) the performance of the foot attachment model was the best among the five sensor attachment locations (0.89 W/kg for M1 and 1.14 W/kg for M2); and (ii) although the performance of M1 was superior to that of M2, M1 requires accurate gait detection for data segmentation by each stride, which hinders the usefulness of M2.

In highly mobile workplaces, wearable walking assistant robots can reduce muscle fatigue in the lower extremities of workers and increase energy efficiency. In this study, walking efficiency according to the development of an ultralight wearable hip-assist robot for industrial workers was verified. Five healthy adult males participated in this study. Their muscle fatigue and energy consumption were compared with and without the robot while walking on a flat treadmill and stairs. When walking on the treadmill while wearing the robot, muscle fatigue in the rectus femoris and gastrocnemius decreased by 90.2% and 37.7%, respectively. Oxygen uptake and energy expenditure per minute also decreased by 8.9% and 13.1%, respectively. When climbing stairs while wearing the robot, fatigue of the tibialis anterior, semitendinosus, and gastrocnemius muscles decreased by 18.2%, 33.3%, and 63.6%, respectively. Oxygen uptake and energy expenditure per minute also decreased by 3.6% and 3.7%, respectively. Although wearing a hip-assist robot could reduce muscle fatigue and use metabolic energy more efficiently, it is necessary to further increase the energy efficiency while climbing stairs. This study is intended to provide basic data to improve the performance of robots.

With global warming leading to abnormal weather phenomena and increasing carbon emissions, countries are implementing carbon emission reduction policies. Europe’s Carbon Border Adjustment Mechanism (CBAM) aims to promote environmentally responsible practices while maintaining industrial competitiveness. To avoid potential tariffs in the European market, Korea must vigorously pursue carbon emission reduction. Emphasizing renewable energy adoption is crucial for achieving eco-friendly and sustainable energy production. This study conducted an economic feasibility assessment for constructing small hydroelectric power plants using discharged energy from Goseong Green Power Plant. By evaluating economic viability, decision-makers could assess potential benefits and costs to support effective planning and implementation. Findings of this study could encourage investments in renewable energy projects, fostering a greener and more sustainable energy landscape for the future.

In this paper, we develop a cylindrical triboelectric nanogenerator (TENG) for omnidirectional wind energy harvesting, by designing a slanted slit structure along the outer surface of the cylinder. The TENG consists of an inner cylinder based on Al film and a 3D printed outer structure. Wind blowing through the slits of the outer structure causes the inner cylinder to rotate in the slanted direction, and the contact-separation between the Al cylinder and polytetrafluoroethylene attached to the inner surface of the outer structure generates an output voltage. The performance of the harvester with different inner cylinder diameters under various wind speeds is experimentally studied. The results indicate that the TENG with a smaller Al cylinder is suitable for a self-powered wind speed sensor while that with a larger cylinder is optimal for efficient energy harvesting. In addition, the TENG is capable of harvesting wind energy in all directions. Its potential utility to be used as a supplementary power source for small electronic devices is verified through various experiments. Based on its compact size, simple design, and ease of manufacturing, the proposed TENG can be used as a low-cost, portable harvester.

In this study, based on directed energy deposition (DED) technology, one of the additive manufacturing technologies, a porous material fabricated by mixing various aluminum alloys and foaming agent was manufactured. First, the foaming agent formed pores inside the deposited materials and differences in foaming characteristics were observed depending on the type of aluminum. Also, the foaming characteristics according to the laser power, which is a representative process variable, were analyzed. As a result, a closed-cell porous material with a maximum porosity at a laser power of 1,100 W was manufactured. Results of the compression test showed that the porous material made by the pores generated therein collapses to absorb energy, and the internal pores disappear to become high density. Therefore, Young’s modulus and yield stress were reduced by the pores inside the sample of pure aluminum and Al6063. However, it was found that the specific energy absorption, which is an advantage of the foamed materials, increased compared to non-porous materials. The findings of this study confirmed that it was possible to manufacture DED-applied foam materials using aluminum powder and a foaming agent.

A hybrid cladding technology was developed by combining direct energy deposition (DED) and ultrasonic nanocrystal surface modification (UNSM). This is an effective process to control the mechanical properties inside the metal-clad layer, but the scope to improve the internal properties is low. Therefore, in this study, the UNSM process was applied while heating at 300 and 600℃ to increase the effectiveness of this hybrid additive process. To validate the characteristics of this method, a study on the cross-sectional properties upon application of heating was conducted. Hybrid cladding at 300 degrees produced improvements- over a 40% larger area than the results at room temperature. At 600 degrees, the hybrid cladding improved mechanical properties over a larger area by nearly 2 times. In this study, the characteristics of the roomtemperature and the high-temperature hybrid cladding process were analyzed. The proposed method shows a high improvement effect and is a promising method to improve the internal mechanical properties of the cladded layer.

The design of a substrate greatly affects the residual stress distribution and the deformation behavior of the repaired region by a directed energy deposition (DED) process. The objective of the present study was to investigate effects of edge length and slope of the substrate on residual stress and deformation characteristics in the vicinity of the repaired region for the repair of the straight damaged region using a DED process. Two-dimensional finite element analysis (FEA) was carried out using SYSWELD. Materials of the substrate and deposited powders were AISI 1045. The maximum residual stress during the deposition decreased when the edge length of the substrate increased, but increased when the slope of the substrate increased. The residual stress after a cooling state increased when the edge length and the slope increased. The displacement of the specimen increased when the slope of the substrate augmented. Finally, the methodology to select a proper edge length and slope of the substrate are discussed in this study.

Hybrid additive manufacturing (AM) refers to a combination of two metal AM techniques: material deposition by powder bed fusion (PBF) and additional building by directed energy deposition (DED). This study focused on different characteristics in accordance with relative deposition directions of PBF and DED during hybrid AM production. Characteristics of the sample fabricated by hybrid AM (i.e., hybrid sample) were compared with those of the sample fabricated by PBF or DED. Ferrite was dominant in the microstructure of PBF deposits with very fine retained austenite observed locally. In contrast, lath martensite and retained austenite were formed uniformly in the microstructure of DED deposits. Different microstructures in the two processes were attributed to differences of cooling rate. In DED deposits, microhardness was significantly decreased owing to a high retained austenite fraction. However, in the hybrid sample, microhardness was rapidly increased in the HAZ owing to aging heat treatment for long-term deposition. Principal wear mechanisms of PBF and DED samples were oxidative wear and plastic deformation, respectively.

This research developed a CAM S/W, which generates an adaptive 5-axis tool path, to optimize the quality of Direct Energy Deposition (DED) 3D printing. After reconstructing part shapes and generating printing paths in each shape, the path simulation including automatic collision detection was implemented. Productivity and printing quality were improved through equipment improvement and process optimization. In addition, high-quality parts with desirable physical and mechanical properties were produced by generating an adaptive 5-axis path specialized in the printing process that reflects various physical phenomena and monitoring results. Finally, the performance of CAM S/W was verified through the production of prototypes for industrial components.