Geopolymer, also known as alkali aluminum silicate, is used as a substitute for Portland cement, and it is also used as a binder because of its good adhesive properties and heat resistance. Since Davidovits developed Geopolymer matrix composites (GMCs) based on the binder properties of geopolymer, they have been utilized as flame exhaust ducts and aircraft fire protection materials. Geopolymer structures are formed through hydrolysis and dehydration reactions, and their physical properties can be influenced by reaction conditions such as concentration, reaction time, and temperature. The aim of this study is to examine the effects of silica size and aging time on the mechanical properties of composites. Commercial water glass and kaolin were used to synthesize geopolymers, and two types of silica powder were added to increase the silicon content. Using carbon fiber mats, a fiber-reinforced composite material was fabricated using the hand lay-up method. Spectroscopy was used to confirm polymerization, aging effects, and heat treatment, and composite materials were used to measure flexural strength. As a result, it was confirmed that the longer time aging and use of nano-sized silica particles were helpful in improving the mechanical properties of the geopolymer matrix composite.

Among the Additive Manufacturing (AM) technologies, the Binder-Jetting printing technology is a method of spraying an adhesive on the surface of powder and laminate layer by layer. Recently, this technique has become a major issue in the production of large casting products such as ship-building, custom vehicles and so on. In this study, we performed research to make actual mold castings and increase mechanical property by using special sand and water-based binders. For use as a mold, it has a strength of more than 3MPa and permeability. Various experiments were carried out to obtain suitable them. The major process parameters were binder jetting volume, binder types, layer thickness and heat treatment condition. As a result of this study, the binder drop quantity was measured to be about 60 pico-liter, layer thickness was 100μm and the heat treatment condition was measured about 1,000℃ and compressive strength were measured to be more than 5MPa. The optimum condition of this experiment was established through actual casting of aluminum. The equipment used in this study was a Freeforms T400 model (SFS Co., Ltd.), and the printing area of 420 * 300 * 250mm and resolution of 600dpi can be realized.

In this paper, the mechanical properties of glass fiber reinforced plastic (GFRP) rebar, which has been applied as an concrete reinforcement, and produced carbon fiber reinforced plastic (CFRP) grid were compared to develop a concrete reinforcement material with excellent mechanical properties. In addition, the mechanical properties of CFRP prepared with each molding process were evaluated. Three molding processes were evaluated: prepreg oven bagging, reaction injection molding (RIM), and pultrusion. The tensile strength of the CFRP grid prepared through pultrusion was 2.85GPa, the elastic modulus was 169.81GPa, and the strain was 1.68%, which was 2.85 times better in tensile strength, and 2.83 times better in elastic modulus compared mechanical properties of GFRP rebar. The strain was confirmed to be equivalent to GFRP rebar.

In this paper, the mechanical properties according to the rCF weight percent(10, 20, 30, 40, 50wt%) of the rCFRP specimen were evaluated and analyzed. First, to prepare rCFRP specimens, pellets were prepared according to the type of weight percent, and rCFRP tensile specimens according to ASTM D638 were prepared using an injection molding machine. Tensile tests were performed on each of 10 specimens according to weight percent conditions, and tensile strength and modulus of elasticity were calculated. For a detailed analysis of the correlation between the internal structure of the specimen and the mechanical properties, the weight percent to the constituent materials of the rCFRP specimen was calculated using mCT and used for the analysis of mechanical properties. For a more detailed analysis, a detailed analysis of the mechanical properties of rCFRP was performed through the fracture surface analysis of the specimen using FE-SEM.

The CoCrFeMnNi high-entropy alloy (HEA), which is the most widely known HEA with a single facecentered cubic structure, has attracted significant academic attention over the past decade owing to its outstanding multifunctional performance. Recent studies have suggested that CoCrFeMnNi-type HEAs exhibit excellent printability for selective laser melting (SLM) under a wide range of process conditions. Moreover, it has been suggested that SLM can not only provide great topological freedom of design but also exhibit excellent mechanical properties by overcoming the strength–ductility trade-off via producing a hierarchical heterogeneous microstructure. In this regard, the SLM-processed CoCrFeMnNi HEA has been extensively studied to comprehensively understand the mechanisms of microstructural evolution and resulting changes in mechanical properties. In this review, recent studies on CoCrFeMnNi-type HEAs produced using SLM are discussed with respect to process-induced microstructural evolution and the relationship between hierarchical heterogeneous microstructure and mechanical properties.

Conversion to modern hydrogen energy is required, and research on liquefied hydrogen cargo containment systems is needed for large-capacity transport and storage. In this study, changes in the mechanical properties of the adhesive required for storage and transport in liquid hydrogen were confirmed. The lap shear test was performed by realizing cryogenic conditions in a small chamber using liquid nitrogen and liquid helium. There was an increase of 11.0% in the -180℃ condition compared to room temperature, and an increase of 1.8% in the -230℃ condition compared to the -180℃ condition was confirmed. In the case of shear strain, it is known that it decreases as the temperature goes down. As a result of the experiment, it was confirmed that the value at room temperature and the value at -180℃ reduced the shear strain by 5.0%, and -230˚ compared to the -180℃ condition. An increase of 1.5% was confirmed in the C condition. In the case of the specimen tested at -230℃, the deformation in the gripper part was larger than in other tests, and it is judged that the maximum shear strength and shear strain were affected. In addition, in this study, there is a limitation in the experiment at -230°C rather than 253°C, which is the boiling point of hydrogen

In modern times, where problems due to environmental pollution are continuously occurring, hydrogen is in the spotlight as the energy of the future. Hydrogen is an eco-friendly energy resource that does not even generate CO2, and is actively supporting research to utilize hydrogen energy at the national level. This study is a study on the cryogenic mechanical properties of the elements constituting the cargo hold during the transportation of liquid hydrogen. Among the various components, the evaluation of mechanical properties of the cryogenic adhesive under liquid helium conditions was confirmed. The related contents are summarized as follows. As a result of performing SSRT by curing the adhesive, it was confirmed that tensile strength and maximum strain were increased at cryogenic temperature (-230°C) compared to room temperature (25°C). It was confirmed that the adhesive-hardened specimen showed a brittle fracture mode at both room temperature and cryogenic temperature during tensile. Improvements in this study, such as pores occurring during adhesive curing, the use of standard specimens, and experiments at -253°C, the boiling point of hydrogen, exist, and are planned to be carried out in subsequent studies.

Hydrogen is one of the main candidates in replacing fossil fuels in the forthcoming years. However, hydrogen technologies must deal with safety aspects due to the specific sub�stance properties. This study aims to provide an overview on the loss of mechanical properties of cryogenic materials, which may lead to serious consequences, such as fires and explosions. The hydrogen embrittlement of cryogenic steels was investigated through slow strain rate tensile tests (SSRTs) and thermal desorption analyses of electrochemically H-charged specimens. As a prior study to confirm mechanical properties under liquid hydrogen conditions, the amount of diffusive hydrogen that causes hydrogen embrittlement was confirmed after charging hydrogen using an electrochemical method for 4 types of steel materials applied as cryogenic materials did. When exposed to the same hydrogen charging conditions, the amount of hydrogen diffused into the 9% nickel steel is the highest compared to the austenitic steel type. It is considered that this is because the diffusion and integration of hydrogen into the interior is easy. It is necessary to analyze the relationship between hydrogen loading and mechanical properties, and this will be carried out in a follow-up study.

Because of the International Maritime Organization(IMO)'s regulation to regulate emissions of ships, a change is taking place to replace ship fuels from Heavy Fule Oil(HFO) to Liquefied Natural Gas(LNG). In the case of LNG, it is a material obtained by liquefying Natural Gas(NG), and it is -163 degrees below zero, and the volume is reduced to 1/600 level. The material of the tank that can store LNG must be a material that can safely store LNG in a cryogenic environment, and the materials of the tank that can store LNG are limited in the International Code of the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk(IGC Code). Among the materials listed in the IGC Code, 9% nickel steel is used as a material for LNG fuel propulsion tanks that are recently ordered because of relatively high mechanical properties under cryogenic environments. In this study, the mechanical properties of butt welds were measured following the weld reliability evaluation of Flux Cored Arc Welding(FCAW) butt welds made of 9% nickel steel by PARTI. The measured mechanical properties are tensile strength, bending strength, hardness, and cryogenic impact test required by the classification for Welding Procedure Specification(WPS) approval.

Additive manufacturing technology, 3D printing, has been applied to various industrial fields. This production method is a production method with less material, cost and time savings, and less restrictions in shape, and is also making a leap forward in the field of eco-friendly product production. In particular, FDM (fused depositon modeling) method of extrusion lamination manufacturing is widely applied in products and medical fields. And as an alternative to mold manufacturing, it is widely used in manufacturing plastic products and parts. Therefore, this paper quantitatively and qualitatively analyzes the mechanical properties according to the processing factors of the specimen through the processing of the ABS tensile specimen printed by the FDM type 3D printer and derives the optimum value.

As the International Maritime Organization (IMO)'s environmental regulations on ship emissions become strict, the demand for ships powered by Liquefied Natural Gas (LNG) is rapidly increasing worldwide. Compared to other materials, high manganese steel has the advantages of superior impact toughness at cryogenic temperatures, a small coefficient of thermal expansion, and low cost of base materials and welding rods. However, there is a limitation in that the mechanical properties of the filler material are lower than the base material having excellent mechanical properties. In this study, after performing a high manganese steel laser butt welding experiment, the welding performance was evaluated through mechanical property (yield strength, tensile strength, hardness, cryogenic impact strength) tests of the weld. As a result, it was observed that the yield strength and tensile strength of the high manganese steel laser welding part was 97.5% and 93.5% of the base metal respectively. Also the hardness of welding part was 84.2% of the base metal. The cryogenic impact strength of the welding part and the base metal were over the 27J, the level of welding part is 76.1% of the base metal.

This study is related to the development of lightweight automotive materials that were carried out to develop eco-friendly vehicles worldwide. High-strength aluminum alloy is used as one of the significant lightweight materials in the field of transportation machinery, and it is used as a lightweight material in various areas, including automobiles. The A356 alloy used in this study is an excellent aluminum alloy material that has widely used as a high strength aluminum alloy material in various forming methods. In this study, to examine the characteristics of the two alloys in which Mn and Sr elements were added to the A356 alloy and the A356 alloy, both alloys were manufactured by metal mold casting, which is a gravity casting method. The obtained specimens were heat-treated under the same conditions. In this study have investigated of the microstructure analysis, thermal analysis, crystal phase analysis, and mechanical property evaluation were performed to confirm how the added Mn and Sr elements influenced the microstructure, precipitate formation, and mechanical properties.

This study has related to lightweight automobiles due to global warming with the reduction of fossil fuel reserves are rapidly progressing around the automobile industry. This study has revealed the relationship for the mechanical properties via the analyzed microstructure, precipitated phase variation of the wheel hub of a commercial vehicle manufactured using molten forging technology using A356 and A357 alloys, which are high-strength Al-Si-Mg base cast aluminum alloys. Differential scanning calorimetry has performed to analyze the precipitation amount of each alloy that influences the mechanical properties of aluminum alloy. The XRD analysis has measured for the microstructure's crystal phase on A356 and A357 alloys. In this paper has evaluated to compare the properties of the A356 alloy and the A357 alloy for the mechanical properties. The A356 alloy has confirmed that a microstructure is finer than A357 alloy, and a quantity of precipitated material is more than A357 alloy. Therefore, this study confirmed that the A356 alloy has better mechanical properties than the A357 alloy.

In the development of advanced ceramic tools, material improvements and design freedom are critical in improving tool performance. However, in the die press molding method, many factors limit tool design and make it difficult to develop innovative advanced tools. Ceramic 3D printing facilitates the production of prototype samples for advanced tool development and the creation of complex tooling products. Furthermore, it is possible to respond to mass production requirements by reflecting the needs of the tool industry, which can be characterized by small quantities of various products. However, many problems remain in ensuring the reliability of ceramic tools for industrial use. In this study, alumina inserts, a representative ceramic tool, was manufactured using the digital light process (DLP), a 3D printing method. Alumina inserts prepared by 3D printing are pressurelessly sintered under the same conditions as coupon-type specimens prepared by press molding. After sintering, a hot isostatic pressing (HIP) treatment is performed to investigate the effects of relative density and microstructure changes on hardness and fracture toughness. Alumina inserts prepared by 3D printing show lower relative densities than coupon specimens prepared by powder molding but indicate similar hardness and higher fracture toughness values.

Aluminum High Vacuum Die-casting process has become more prevalent in automotive manufacturing industry which require high productive rate, weldable process and heat treatment process. However, high pressure die castings usually contain gas porosity due mainly to the entrapment of air or gas in the die during the high speed injection of the molten metal into the die cavity. Vacuum block system with disk spring was developed and vacuum chanel was optimized with numerical flow analysis. The porosity of die castings was analyzed by X-ray CT, and the effect of porosity on the mechanical properties was analyzed by hardness and tensile test. Tensile strength was improved 49.5% for 50mbar high vacuum die-casting process compare then 300mbar. And then, Surface property was analyzed with plunger velocity and fast shot set point.