건설 자재와 건설 폐기물의 환경적 영향에 대한 사회적 관심이 높아지고 있다. 고강도 콘크리트의 필요성이 점차 커짐에 따라, 본 연구에서는 서로 연관된 환경 문제에 대한 두 가지 잠재적 해결책을 검토하였다. 첫째는 재활용 콘크리트 골재의 사용량 증가 가능성이고, 둘째는 고로 슬래그를 시멘트로 활용(재활용)할 가능성이다. 일반적으로 재활용 골재를 사용하면 고강도 콘크리트의 강도 가 저하되는 것으로 알려져 왔다. 따라서, 본 연구에서는 재활용 골재 콘크리트의 배합비와 함량 변화를 분석하여 고층 건축에 재활용 골재가 실용적인지, 그리고 어떤 방식으로 활용되는지를 규명하고자 하였다.

This study examines the effect of delayed quenching (DQ) temperature on the microstructure and mechanical properties of API X70 linepipe steels. Three types of steels were fabricated by varying the DQ conditions: Base (without DQ), LDQ (low-temperature delayed quenching at 700 °C), and HDQ (high-temperature delayed quenching at 740 °C). The microstructures were characterized using optical microscopy, scanning electron microscope (SEM), and electron back-scattered diffraction (EBSD), and their mechanical properties were evaluated through tensile and Charpy impact tests. The Base specimen exhibited the finest effective grain size and the highest bainite fraction, resulting in superior yield strength and impact toughness. In contrast, the LDQ specimen showed increased pearlite content and coarser grains, leading to the highest tensile strength due to work hardening, but reduced impact properties due to crack initiation at the pearlite regions. The HDQ specimen, with the highest ferrite fraction, showed the best ductility and acceptable strength, as well as improved lowtemperature toughness owing to increased resistance to cleavage propagation. EBSD analysis confirmed that finer grains and higher fractions of high-angle grain boundaries play a crucial role in enhancing impact energy and lowering the ductile-to-brittle transition temperature (DBTT). These findings highlight the importance of optimizing DQ parameters to achieve a balanced combination of strength–toughness in high-strength linepipe steels.

In this study, we analyzed the structural and mechanical properties of aluminum foams fabricated using aluminum powders of varying sizes and mixtures. The effects of sintering and pore structure at each size on the integrity and mechanical properties of the foams were investigated. Structural characteristics were examined using scanning electron microscopy and micro–computed tomography, while mechanical properties were evaluated through compression testing. The experimental results demonstrated that smaller powder sizes improved foam integrity, reduced porosity and pore size, and resulted in thinner cell walls. In combination, these effects increased compressive strength as the powder size decreased. The findings of this study contribute to the understanding and improvement of the mechanical properties of aluminum foams and highlight their potential for use in a wide range of applications.

In this paper, the uniaxial tensile mechanical characteristics after synchronous biaxial pre-tension analysis are investigated on a ETFE film crown model. After the biaxial pre-stretching is completed, the rectangular specimens are cut along the MD and TD directions of the biaxially pre-stretched ETFE film to conduct the uniaxial stretching test. The uniaxial tensile mechanical properties of the ETFE film after biaxial pre-stretching are investigated, the specific uniaxial tensile mechanical property parameters of the biaxially pre-stretched film are determined, and the influence of biaxial pre-stretching on the uniaxial tensile mechanical properties of the ETFE film is analyzed.

To further increase the mechanical properties of polyacrylonitrile-based carbon fibers, a multiple stretching technique was applied. Carbon fibers were multiple stretched at 2200 °C and characterizations such as SEM, Raman, XRD, and TEM were used to investigate the evolution of microstructure of carbon fibers. It was found that the grooves on the surface of carbon fibers along the fiber axis direction became more obvious and the cross-section of fibers were twisted from nearly circular to elliptical after multiple stretching. Growth and slippage of graphite microcrystals along the fiber axis direction resulted decrease in disordered structure and defects in the carbon fibers and increase in the degree of graphitization. The multiple stretching effectively enhanced the length-to-width ratio of microcrystals. An increase of 75 GPa in tensile modulus and a retention rate of 0.95 in tensile strength were realized for carbon fibers multiple stretched at 2200 °C.

In this paper, poly(glycolic acid–co-DL–lactic acid) (PGDLLA)/poly(ɛ-caprolactone) (PCL) incompatible nanocomposites were combined with multiscale modeling (MSM) in a ratio of 80/20. Since the behavior and mechanical properties of blends depend significantly on the interphase region, the compatibilizer poly(l,l-lactic acid–co-ɛ-caprolactone) (P(lLA-co-ɛ-CL)) was used to improve compatibility and graphene oxide (GO) was used to increase the interphase strength of PGDLLA matrix/PCL. This work was done by mixing solvent to achieve the optimum disperse of GO in the matrix. The investigation of interfacial phenomenon by the theoretical interfacial models is important. Under the assumption of constant modulus and elastic deformation in the zero interface region, the predictions in this region are more unreliable when the calculations of experimental mechanical properties are analyzed in detail. In this study, PGDLLA/P(lLA-co-ɛ-CL)/PCL compounds were compared with the MSM approach to predict the plastic deformation in the stress–strain behavior. In contrast to the hypothesis that a simple look at the interphase area in nanocomposites, a finite element code is proposed to evaluate the efficiency of the interphase area. Both experimental results and FEM analysis showed that Young’s modulus increases by incorporating GO into GO/PGDLLA/P(lLA-co-ɛ-CL)/PCL nanocomposites; the amount of increase for incorporating 1 phr GO is about 61%.

본 연구는 아민화 셀룰로오스 나노섬유(CNF)를 시멘트 복합체에 적용하여 기계적 및 미세구조적 성능 향상을 도모하고자 하였다. CNF는 (3-aminopropyl) triethoxysilane (APTES)를 활용해 화학적으로 개질하였으며, 이는 시멘트 수화 생성물과의 계면 결합력 및 분산성을 향상시키기 위한 목적이다. 표면 개질의 성공 여부는 주사전자현미경(SEM)과 X-선 회절 분석(XRD)을 통해 확인 하였다. 다양한 함량의 개질 및 비개질 CNF를 혼입한 모르타르를 제작하여 압축강도 및 휨강도를 평가하였다. 그 결과, 아민화 CNF는 0.2% 혼입 시 압축강도 향상 효과가 가장 두드러졌으며, 휨강도는 0.3%에서 가장 우수한 성능을 나타내었다. 미세구조 분석을 통해, 아민화 CNF가 시멘트 수화물과의 상호작용을 통해 내부 조직을 치밀하게 형성하고 공극률을 저감시키는 것으로 확인되었다. 본 연구는 화학적으로 개질된 CNF가 지속가능하고 고성능인 시멘트 복합재료 개발에 있어 유효한 기능성 첨가제로 활용될 수 있음을 시사한다.

전 세계 이산화탄소 배출량이 지속적으로 증가하면서, 환경 개선 및 탄소 격리를 위한 다양한 연구들이 진행되고 있 다. 건설 산업에서도 탄소를 줄이기 위한 연구로 바이오차를 건설 자재에 사용하여, 탄소 격리를 위한 방법으로 진행되고 있다. 바이오차는 바이오매스를 열분해하여 생성한 숯으로, 높은 탄소 함량과 다공성 구조가 특징이며, 탄소 격리를 위한 물질로 떠오 르고 있다. 본 연구에서는 시멘트 사용량을 줄이고 바이오차를 혼입한 콘크리트를 건설 자재로써 가능성을 확인하고자 하였다. 이를 위해 시멘트의 일부를 바이오차로 치환하여 혼입한 콘크리트의 역학적 특성(슬럼프, 공기량, 압축강도)과 질량 기반 특성 (흡수율, 밀도, 공극률)을 평가하였다. 바이오차의 시멘트 치환율은 0%, 5%, 10%로 설정하였다. 바이오차의 수분 흡수 및 보유 력에 따라 바이오차의 시멘트 치환율이 증가할수록 슬럼프는 감소하였다. 바이오차의 다공성 구조를 SEM 실험으로 확인하였으 며, 이에 따라 콘크리트에서의 공극 형성으로 바이오차의 시멘트 치환율이 증가할수록 공기량과 흡수율이 증가하였다. 바이오차 의 시멘트 치환율 5%에서 압축강도와 비강도가 가장 높은 값으로 나타났으며, 탄소 격리를 위한 방법으로 건설 자재 활용의 가능성을 확인하였다.

Sodium sulfate, as a commonly used early strengthening agent, has been widely used in different areas. Because of its sulfonic acid group, sodium sulfate is also used as a cement capillary crystal waterproof material. However, temperature has a significant effect on concrete mixed with sodium sulfate. The effect of sodium sulfate on the early hydration rate at different temperatures was studied by conducting a time and hydration thermal analysis. The effects of sodium sulfate on the mechanical properties of concrete at different temperatures were studied through compressive strength experiments. Impermeability at different temperatures was studied by testing resistance to chloride ion penetration and resistance to water penetration. The effect of resistance to sulfate attack was also experimentally. The hydration products were analyzed by electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The experimental results showed that at low temperature, sodium sulfate can accelerate the early hydration reaction rate, and the effect becomes weaker with increasing temperature. At low temperature, the addition of sodium sulfate can effectively improve the degree of hydration, and enhance the permeability resistance and ion erosion resistance of the matrix.

In this paper, the changes of the uniaxial tensile mechanical properties of the ETFE film after the uniaxial pre-stretching stress exceeds the first yield stress and the second yield stress was investigated. The ETFE film is first pre-stretched uniaxially along the MD direction or TD direction. After the pre-stretching loading stress exceeds the first yield stress and the second yield stress to cause the ETFE film to undergo plastic deformation, rectangular uniaxial tensile specimens are cut from the pre-stretched film along the MD direction and the TD direction for subsequent uniaxial tensile tests, thereby determining the uniaxial tensile mechanical property parameters of the ETFE film after uniaxial pre-stretching, including yield stress, tensile strength and elongation at break, and discussing the changes in its uniaxial tensile mechanical properties.

Three-dimensional printed polycaprolactone/β-tricalcium phosphate (PCL/β-TCP) scaffolds reinforced with carbon nanotubes (CNTs) were fabricated and characterized for bone tissue engineering applications. The incorporation of CNTs significantly enhanced the mechanical properties, with the aligned PCL/β-TCP/CNT scaffold (1 wt% CNTs) exhibiting a 125% and 123% increase in compressive modulus (180.3 ± 10.1 MPa) and strength (7.8 ± 0.6 MPa), respectively, compared to the PCL/β-TCP scaffold. The β-glycerol phosphate (BGP)-modified PCL/β-TCP/CNT scaffold showed similar mechanical properties to the aligned scaffold. All scaffolds maintained high porosity (> 70%) and a wide pore size distribution (50–500 μm). The scaffolds demonstrated excellent biocompatibility, with hemolysis rates below 5% and high cell viability. The aligned PCL/β-TCP/ CNT scaffold promoted the highest rat adipose-derived stem cell proliferation, while the BGP-modified scaffold enhanced human dental pulp stem cell proliferation and mineralization.

This study employed a cross-rolling process to fabricate oxide dispersion strengthened (ODS) steel plates and investigated their microstructures and mechanical properties. The 9Cr-1W ODS ferritic steel was fabricated using mechanical alloying and hot isostatic pressing. The hot cross-rolling process produced thick ODS ferritic steel plates with a well-extended rectangular shape. The working direction greatly affected the grain structure and crystal texture of the ODS ferritic steel. Cross-rolled plates showed fine micro-grains with random crystal orientation, while unidirectionally rolled plates exhibited a strong orientation with larger, elongated grains. Transmission electron microscopy revealed a uniform distribution of nano-oxide particles in both rolling methods, with no major differences. Tensile tests of the ODS ferritic steel plates showed that the unidirectional rolled plates had anisotropic elongation, while cross-rolled plates exhibited isotropic behavior with uniform elongation. Cross-rolling produced finer, more uniform grains, reducing anisotropy and improving mechanical properties, making it ideal for manufacturing wide ODS steel components.

This study investigated the effect of the hatch spacing parameter on the microstructure and mechanical properties of SA508 Gr.3 steel manufactured by laser powder bed fusion (L-PBF) for a nuclear pressure vessel. Materials were prepared with varying hatch spacing (0.04 mm [H4] and 0.06 mm [H6]). The H4 exhibited finer and more uniformly distributed grains, while the H6 showed less porosity and a lower defect fraction. The yield strength of the H4 material was higher than that of the H6 material, but there was a smaller difference between the materials in tensile strength. The measured elongation was 5.65% for the H4 material and 10.41% for the H6 material, showing a significantly higher value for H6. An explanation for this is that although the H4 material had a microstructure of small and uniform grains, it contained larger and more numerous pore defects than the H6 material, facilitating stress concentration and the initiation of microcracks.

As global greenhouse gas reduction regulations are strengthened and the demand for eco-friendly energy increases, renewable energies, including offshore wind power, are growing rapidly. Unlike onshore wind power generation, offshore wind power is located in the ocean. As a result, the offshore wind power substructure is exposed to low temperatures, corrosion, and continuous fatigue loads. Therefore, selecting appropriate materials and welding techniques is crucial for durability. In this study, FCAW welding was performed on S355ML steel (EN10025) for offshore wind power applications. After the welding process, the mechanical properties of the welded joint were evaluated through tensile, low-temperature impact, and hardness tests to assess the welding condition. The study revealed that the tensile and yield strength of the welded joint were superior to those of the base material. Additionally, the impact strength at low temperatures was confirmed to exceed the standard.

본 연구는 꼬막 패각 잔골재와 PP 폐어망 섬유를 혼입한 자원순환 콘크리트의 역학적 성능과 계면 변화 영역에서의 미세구조 특성 을 분석하였다. 패각 잔골재와 폐어망 섬유를 적절한 방법으로 전처리하고 자원화를 고려하여 3D 프린팅 콘크리트 배합을 선정해 콘 크리트 시편을 제작하였다. 제작된 시편은 KS L ISO 679 규정에 따라 압축강도와 휨강도를 측정하였고, BSE 모드를 이용한 SEM 이 미지 촬영을 통해 미세구조를 분석하였다. SEM 이미지는 히스토그램 및 형상 기반 상 분리 방법, 그리고 계면 변화 영역의 픽셀값 차 이를 활용하여 이미지를 분리하고 미세구조를 분석하였다. 역학적 성능을 확인하기 위해 PP 섬유를 0.0%, 0.5%, 1.0vol.% 혼입한 시 편의 압축강도와 휨강도를 측정한 결과, PP 섬유 0.5vol.% 혼입 시 섬유 브릿징 효과로 인해 가장 높은 압축 및 휨강도가 나타났다. SEM 이미지 분석 결과, 일반 잔골재와 바인더 계면보다 패각 잔골재와 바인더 계면에서 더 큰 직경의 공극이 관찰되었으며, PP 섬유 와 바인더 계면에서는 상대적으로 작은 공극이 형성됨을 확인하였다. 이를 바탕으로 미세구조 분석 결과와 역학적 성능 간의 상관관 계를 규명하였다.

A cold roll-bonding (CRB) process is applied to fabricate an AA1050/AA5052 layered sheet. In the process, commercial AA1050 and AA5052 sheets of 1 mm thickness, 40 mm width and 300 mm length are stacked onto each other, and then reduced to a thickness of 0.5 mm through a 2-pass cold rolling process without lubricant. The roll-bonded AA1050/AA5052 layered sheet is then annealed for 1 h at various temperatures from 200 to 400 °C. The specimens annealed at temperatures below 250 °C showed a typical deformation structure in which the grains were elongated along the rolling direction. However, the specimens annealed at temperatures higher than 300 °C exhibited recrystallization structures in both the AA1050 and AA5052 regions. All the roll-bonded and subsequently annealed specimens showed an inhomogeneous distribution of hardness in the thickness direction, in which the hardness in the AA5052 regions was higher than that in the AA1050 regions. As the annealing temperature increased, the tensile and yield strengths decreased and the elongation increased gradually. The mechanical properties were compared to those of commercial AA1050 and AA5052 materials and CRBed AA5052-2L materials from a previous study.

Battery electrodes, essential for energy storage, possess pores that heavily influence their mechanical properties based on the level of porosity and the nature of the pores. The irregularities in pore shape, size, and distribution complicate the accurate determination of these properties. While stress-strain measurements can shed light on a material’s mechanical behavior and predict compression limits, the complex structure of the pores poses significant challenges for accurate measurements. In this research, we introduce a simulation-driven approach to derive stress-strain data that considers porosity. By calculating relative density and the rate of volume change under compression based on porosity, and applying pressure, we conducted a parametric study to identify the elastic modulus (E) in relation to the rate of volume change. This information was utilized within a material modeling equation, generating stress-strain (S-S) curves that were further analyzed to replicate the compression behavior of the electrode material. The outcomes of this study are expected to improve the prediction accuracy of mechanical properties for porous electrode materials, potentially enhancing battery performance and refining manufacturing processes.

Magnesium alloys, among various non-ferrous metals, are utilized in diverse fields from the automotive industry to aerospace due to their light weight and excellent specific strength. In the previous Part I study, fiber laser BOP experiments were conducted to derive basic welding characteristics and appropriate bu竹 welding conditions. Subsequently, in the Part II experiment, butt welding was performed, and through tensile tests, hardness tests, and cross-sectional observations, it was found that at laser power of 2.0 kW and welding speed of 50 mm/s, 93% of the base metafs tensile strength and 63.4% of its elongation could be achieved. In this Part III experiment, the microstructures of the base metal and the center of the weld were observed in butt-welded specimens. Through this, laser power and welding speed, on the mechanical behavior and microstructure of magnesium alloys were analyzed