탄소섬유보강근을 철근 대체재로 사용하기 위해서 단기 역학적 특성뿐 아니라 장기간 역학적특성에 대한 연구가 필히 수행 되어야 하고 현재도 진행 중이다. 이에 따라 본 연구에서는 CFRP bar의 지속하중에 대한 저항성을 평가하기 위해 ASTM 기준에 따라 약 1,000시간 동안 탄소섬유보강근 인장강도의 40%를 재하하는 크리프 시험을 진행 후 잔류 인장강도 확인을 위한 추가 인장시험을 진행하였다. 크리프 시험 결과, 탄소섬유보강근의 변형률은 지속하중 하에서 1,000시간 경과 후 하중재하 초기 변형률보다 약 4.9% 상 승하였고 크리프 파괴는 발생하지 않았다. 잔류 인장강도는 일반 인장강도의 95% 수준으로 측정되었고 잔류 탄성계수는 일반 탄성계 수의 85 % 수준이었다. 따라서 본 연구에서 진행한 인장강도의 40 %가 1,000시간 동안 재하되었을 때 탄소섬유보강근은 안전한 것으 로 확인되었다.

FRP 복합재료 중 CFRP(탄소 섬유 강화 플라스틱)는 현재 RC 구조물의 내부 및 외부 보강재로서 그리드 형태로 활용되고 있다. 그러나 CFRP 그리드에 대한 성능평가 기준은 매우 미흡하여 FRP 보강근 기준을 사용하고 있다. 따라서 본 연구에서는 그리드 가닥 수와 경계조건과 변수를 고려하여 CFRP 그리드의 인장 성능을 평가하기 위한 실험이 수행되었다. 가닥 수는 1, 2, 3가닥에 대한 인장시험이 수행되었으며, 경계조건의 경우 모르타르, 에폭시, 에폭시 + 모르타르로 변수를 지정하였다. 인장시험을 통하여 최적 가닥 수 및 최적 경계조건으로 개발한 시편을 토대로 고온 노출 시간에 따라 CFRP 그리드의 인장 성능 평가가 수행되었다. 온도는 130°C 로 유지되었으며, 5개의 시편을 각각 70분(Case 2), 100분(Case 3), 120분(Case 4), 150분(Case 5) 고온에 노출하여 비 고온 노출 시편 과 비교하였다. 실험 결과, 비 고온 노출 시편과 비교하여 Case 5에서는 인장강도와 탄성계수가 각각 최대 51.32% 및 44.4% 감소한 것으로 나타났다.

Al-Mg-Si alloys are light weight and have excellent corrosion resistance, and are attracting attention as a liner material for high-pressure hydrogen containers in hydrogen fuel cell vehicles. Because it has excellent plastic hardening properties, it is also applied to car body panel materials, but it is moderate in strength, so research to improve the strength by adding Si-rich or Cu is in progress. So far, the authors have conducted research on the intergranular fracture of alloys with excessive Si addition from the macroscopic mechanical point of view, such as specimen shape. To evaluate their impact tensile properties, the split-Hopkinson bar impact test was performed using thin plate specimens of coarse and fine grain alloys of Al-Mg-X (X = Cr,Si) alloy. The effect of the shape of the specimen on the characteristics was studied through finite element method (FEM) analysis. As a result, it was found that the intergranular fracture of the alloy with excessive Si depended on the specimen width (W)/grain size (d), which can be expressed by the specimen size and grain size. As W/d decreases, the intergranular fracture transforms into a transgranular fracture. As the strain rate increases, the fracture elongation decreases, and the fracture surface of the intergranular fracture becomes more brittle. It was confirmed that intergranular fracture occurred in the high strain rate region even in materials with small grain sizes.

In this study, the relationship between the color of the pigment added to the plastic resin and the size of the fractured part of the specimen was confirmed when processing ABS plastic tensile specimens using a sealed 3D printer. Through the test, it was confirmed that the fracture dimension existed in the range of 13.104 to 13.138 ㎜ and there was no significant difference in dimension according to the color of the additive, and the null hypothesis was adopted. In addition, it was confirmed that a significant difference occurred in the order of red, black, white, and green colors.

강재를 대처할 수 있는 다양한 복합재료 중 CFRP (Carbon Fiber Reinforced Polymer)를 사용하여 인장 물성 실험을 실시한다. KS F ISO 10406 (콘크리트용 섬유강화 폴리며(FRP 보강재 - 시험방법) 에서 FRP의 측정길이는 지름 (D)의 40 배를 기준으로 제시되어진다. 그러나 25 mm 이상의 시험체는 양단 보강부를 포함하게 된다면 대략 2 m 이상으로 제작되어지게 되고 시험이 상당히 번거롭게 됨으 로써 시험법 개선을 위해서 측정 길이별로 설정하여 성능평가 후 비교분석 한다.

콘크리트 구조의 인장 보강재로 주로 사용되는 철근은 높은 인장강도와 연성이 우수한 변형 특성에 도 불구하고 부식이 발생할 수 있다는 단점을 갖고 있다. 이러한 문제점을 개선하기 위하여 부식이 발 생하지 않는 다양한 재료 중 FRP(Fiber Reinforced Polymer)를 철근과 유사한 형태의 Rod로 제작하 여 철근을 대체하는 보강재로 사용하기 위한 연구가 진행되고 있다. 그중에서도 인장강도가 우수한 탄 소 및 유리섬유를 일방향으로 성형하고 Rod 표면을 굴곡 처리한 CFRP 및 GFRP 보강근을 중심으로 콘크리트 구조에 적용하기 위한 연구가 활발하게 진행되고 있다. 이 연구에서는 FRP Rod를 보강근으 로 하는 콘크리트 부재의 부착특성과 균열폭, 처짐과 같은 사용성 평가에 중요한 역할을 하는 인장강 화효과를 포함한 균열거동 특성을 파악하기 위하여 단변의 피복두께와 FRP 보강근 지름의 비를 1.0에 서 3.5 까지 0.5배씩 증가하는 직사각형 단면을 갖는 길이 1,000mm의 인장부재를 제작하여 만능재료 시험기(Universal Testing Machine)를 이용한 직접인장실험을 수행한 후, 피복두께와 FRP 보강근의 지름 비에 따른 균열거동(Cracking Behavior) 및 인장강화효과(Tension Stiffening Effect)를 분석하고 현행 설계기준의 규정과 비교하였다. 작용하중에 따라 발생하는 균열에 대해서 횡방향균열(Transverse Crack)과 쪼갬균열(Splitting Crack)로 각각 구분하고, DAQ(Data Acquisition) 시스템을 이용하여 콘 크리트 인장부재에 매입된 CFRP 및 GFRP 보강근의 변형량 및 작용하중을 측정하였으며, 그 결과로 부터 하중-변형률 관계로 대표되는 인장강화효과를 분석하였다. 균열거동 및 인장강화효과를 분석한 결과, CFRP 또는 GFRP Rod를 보강근으로 하는 콘크리트 인장부재는 FRP 보강근과 콘크리트의 부 착강도를 감소시키는 쪼갬균열이 발생하지 않도록 피복두께를 보강근 지름의 2.5배 이상 확보하였을 때, 각 보강근별로 극한강도 fu의 60-70%에 해당하는 하중이 작용하는 단계에서 인장강화효과는 우 수한 것으로 나타났으며, 철근을 보강근으로 하는 현행 설계기준의 규정으로 예측한 결과보다 우수한 인장강화효과를 얻을 수 있음을 확인하였다.

FRP 복합재 중 CFRP(Carbon Fiber Reinforcement Plastic)는 현재 Rebar, Plate, Grid 등 다양한 형태로 RC 구조물에 내‧외부 보강재로써 사용되고 있다. 이 중 CFRP Grid의 경우 국내에서 상용화가 되지 않아 다른 형태의 보강재보다 성능 분석 및 평가 기준이 미흡한 실정이다. 이에 따라 본 연구에 서는 Grid의 Strand, 경계조건, ASTM 고정장치의 유무 등 다양한 실험을 통하여 CFRP 그리드의 인 장 성능평가를 진행하였다. 선행 연구에서는 CFRP Grid의 인장시험 고정단의 경계조건에 따른 영향 성 분석을 위해 ASTM D7205 및 ASTM D6637에 따라 Tap-Tap (Type 1), Tap-Mortor (Type 2) 로 구성하여 인장시험을 수행하였으며, 시편의 파단 형상 및 시험 결과값이 가장 안정적인 Type 2를 CFRP Grid의 고정단 경계조건으로 설정하였다. 이러한 선행 연구를 바탕으로 고온 노출에 따른 CFRP 그리드의 인장 성능시험 평가를 진행하였으며, 인장시험은 만능재료시험기 및 고성능 카메라를 활용하여 최대 응력과 탄성계수를 도출하였다. 온도는 FRP의 전이온도인 150℃ 이내의 130℃에서 각 Case 별 5개의 시편을 70분(Case 2), 100분(Case 3), 120분(Case 4), 150분(Case 5) 노출한 후, 고온 에 노출하지 않은 시편(Case 1)과 비교하였다. 실험 결과, Case 5와 Case 1을 비교하여 인장강도와 탄성계수는 각각 최대 51.32%, 44.4% 감소하였다. 결론적으로 고온 환경에서 지속적으로 노출될 경 우, CFRP Grid의 성능이 최대 절반 수준으로 감소 되며 RC 부재 내‧외부에 보강 시에 고온 조건을 면밀히 검토하여 성능 감소를 최소화할 필요가 있다고 판단된다.

The challenge of incorporating photothermal conversion function into chitosan (CS) hybrid fibers lies in balancing functionality and mechanical properties. In this study, we successfully prepared a chitosan/graphene oxide/gelatin (CS/GA/GO) hybrid fiber using the wet spinning process, achieving improved mechanical properties and efficient photothermal conversion capabilities. When compared with pure CS fiber with a breaking strength of 1.07 cN/dtex, the breaking strength of the CS/ GA composite fiber increased by 46.73%, while the CS/GA/GO hybrid fiber showed an even greater increase of 85.98%. In addition, the introduction of gelatin (GA) led to secondary scattering of near-infrared light, enhancing the photothermal conversion efficiency. As a result, the CS/GA/GO hybrid fiber exhibited a faster temperature rise rate and higher maximum temperatures (94.3 °C, 103.0 °C, and 111.3 °C) as compared to the CS/GO hybrid fiber. The successful incorporation of GA not only improved the mechanical properties but also enhanced the photothermal performance of the hybrid fiber.

The emergence of ferrous-medium entropy alloys (FeMEAs) with excellent tensile properties represents a potential direction for designing alloys based on metastable engineering. In this study, an FeMEA is successfully fabricated using laser powder bed fusion (LPBF), a metal additive manufacturing technology. Tensile tests are conducted on the LPBF-processed FeMEA at room temperature and cryogenic temperatures (77 K). At 77 K, the LPBF-processed FeMEA exhibits high yield strength and excellent ultimate tensile strength through active deformation-induced martensitic transformation. Furthermore, due to the low stability of the face-centered cubic (FCC) phase of the LPBFprocessed FeMEA based on nano-scale solute heterogeneity, stress-induced martensitic transformation occurs, accompanied by the appearance of a yield point phenomenon during cryogenic tensile deformation. This study elucidates the origin of the yield point phenomenon and deformation behavior of the FeMEA at 77 K.

In recent automobile development, vehicle weight reduction has become a very important goal. Seat weight reduction is a large portion of vehicle weight reduction. In this study, a specimen tensile tests were conducted on the Almag material, which is an alloy of aluminum and magnesium, and also conducted on SAFH440, SAFH 590, SAFC780, and SAFH980, which are mild steel materials used in the seat frame. The tensile specimen tests were carried out in two speed; 2mm/s and 4mm/s, and the obtained stress to strain curve was converted to the analysis material card of true stress to true strain curve to be used in the seat structural analysis. The constructed analysis material card was used in the specimen tensile finite element analysis, and the analysis result was able to obtain the stress to strain curve similar to the test result.

A thorough knowledge and understanding of the structure–property relationship between thermal conductivity and C-fiber morphology is important to estimate the behavior of carbon fiber components, especially under thermal loading. In this paper, the thermal conductivities of different carbon fibers with varying tensile modulus were analyzed perpendicular and parallel to the fiber direction. Besides the measurement of carbon fiber reinforced polymers, we also measured the thermal conductivity of single carbon fibers directly. The measurements clearly proved that the thermal conductivity increased with the tensile modulus both in fiber and perpendicular direction. The increase is most pronounced in fiber direction. We ascribed the increase in tensile modules and thermal conductivity to increasing anisotropy resulting from the orientation of graphitic domains and microvoids.

The membrane structure should maintain the membrane materials in tension for structural stability guaranty. The anchoring part in the membrane structure is an important part. It has the function to introduce tension into membrane materials and function to transmit stress which membrane materials receives to boundary structure such as steel frames. In this paper, it grasps anchoring system of the anchoring part in the membrane structure concerning the fracturing characteristic condition of membrane structure, and the influence which is caused to yield it designates the stress state when breaking the membrane structure which includes the anchoring part and that stress transition mechanism is elucidated as purpose. This paper follows to previous paper, does 1 axial tensile test concerning the bolting part specimen, grasp of fracturing progress of the bolting part and the edge rope and hardness of the rubber, does the appraisal in addition with the difference of bolt tightening torque. As a result, the influence which the bolt anchoring exerts on the fracturing characteristics of the membrane material in the membrane structure anchoring part is examined.

The occurrence of shear failure in a rock mass, resulting from the sliding of joint surfaces, is primarily influenced by the surface roughness and contact area of these joints. Furthermore, since joints serve as crucial conduits for the movement of water, oil, gas, and thermal energy, the aperture and geometric complexity of these joints have a significant impact on the hydraulic properties of the rock mass. This renders them critical factors in related industries. Therefore, to gain insights into the mechanical and hydraulic behavior of a rock mass, it is essential to identify the key morphological characteristics of the joints mentioned above. In this study, we quantified the morphological characteristics of tensile fractures in granitic rocks using X-ray CT imaging. To accomplish this, we prepared a cylindrical sample of Hwang-Deung granite and conducted splitting tests to artificially create tensile fractures that closely resemble rough joint surfaces. Subsequently, we obtained 2D sliced X-ray CT images of the fractured sample with a pixel resolution of approximately 0.06 mm. By analyzing the differences in CT numbers of the rock components (e.g., fractures, voids, and rock matrix), we isolated and reconstructed the geometric information of the tensile fracture in three dimensions. Finally, we derived morphological characteristics, including surface roughness, contact area, aperture, and fracture volume, from the reconstructed fracture.

Ring Tensile Test (RTT) is mainly performed for comparing tensile strength and total strain between nuclear fuel cladding specimens under various initial conditions. Through RTT, the loaddisplacement (F-D) curve obtained from the uniaxial tensile test can also be obtained. However, the Young’s modulus estimated from the gradient of the straight portion is much lower than general value of materials. The reasons include tensile machine compliance, slack in the fixtures, or elastic deformation of the fixtures and the tooling. Another reason is that the bending of the test part in the ring is stretched with two pieces of tools. Although the absolute value of the Young’s modulus is smaller than the actual value, it is applicable to calculate the ratio of the Young’s moduli of different materials, that is, the relative value. The Young’s modulus, or slope of the linear section, varies slightly depending on which location data is used and how much data is included. In order to obtain a more accurate ratio of Young’s moduli between materials using the RTT results, a post-processing method for the ring tensile test results that can prevent such human errors is proposed as follows. First, the slope of the linear section is obtained using the displacement and load when the load increase is the largest and the displacement and load of the position that is 95% of the maximum load increase. To replace the section where the ring-shaped specimen is stretched at the beginning of the F-D curve, a straight line equal to the slope of the linear section is drawn to the displacement axis from the position of maximum load increase and moved to the origin to obtain the final F-D curve for a RTT. Lastly, the yield stress uses the stress at the point where the 0.2% offset straight line and the F-D curve meet as suggested in the ASTM E8/E8M-11 “Standard test methods for tensile testing of metallic materials”. RTT results post-processing method was coded using FORTRAN language so that it could be performed automatically. In addition, sensitivity analysis of the included data range on the Young’s modulus was performed by using the included data range as 90%, 85%, and 80% of the maximum load increase.

The hydride reorientation (HR) of used nuclear fuel cladding after operation affects the integrity during intermediate and disposal storage, as well as the handling processes associated with transportation and storage. In particular, during dry storage, which is an intermediate storage method, the radial hydrogen redistributes into circumferential hydrogen, increasing the embrittlement of used nuclear fuel cladding. This hydride reorientation is influenced by various key factors such as circumferential stress (hoop stress) due to internal rod pressure, maximum temperature reached, cooling rate during storage, and the concentration of precipitated hydrogen during irradiation. To simulate long-term dry storage of used nuclear fuel, hydrogenated Zircaloy-4 cladding (CWSRA) specimens were used in hydride reorientation tests under various hoop stress conditions (70, 80, 90, and 110 MPa) for extended cooling periods (3 months, 6 months, and 12 months). After the hydride reorientation tests, the cladding’s offset strain (%) was evaluated through a ring compression test, a mechanical property test encompassing both ductility and brittleness. In this study, the offset deformation of the hydride reorientation specimens was compared and evaluated through ring tensile tests. In this study, the offset deformation values were compared and evaluated through ring tensile tests of the hydride reorientation test specimens. Hydrogen in zirconium cladding reduces ductility from a physical perspective and induces rapid plastic deformation. Generally, even in hydrogenated unirradiated cladding, it maintains a tensile strength of around 800 MPa at room temperature. However, high hydrogen content accelerates plastic deformation. In contrast, samples with radial hydrogen distribution exhibit fracture behavior in the elastic region below 500 MPa. This is attributed to the directional of radial hydrogen distribution. Specimens with a hydrogen concentration of 200 ppm fracture faster than those with hydrogen concentrations exceeding 400 ppm. This is believed to be due to the ease of reorientation of radial hydrogen in cladding with relatively low hydrogen content. Although the consistency of the test results is not ideal, ongoing research is needed to identify trends in hydride reorientation from a cladding perspective.

미세구조 특성의 불확실성은 재료 특성에 많은 영향을 준다. 시멘트 기반 재료의 공극 분포 특성은 재료의 역학적 특성에 큰 영향을 미치며, 재료에 랜덤하게 분포되어 있는 많은 공극은 재료의 물성 예측을 어렵게 한다. 공극의 특성 분석과 재료 응답 간의 상관관계 규명에 대한 기존 연구는 통계적 관계 분석에 국한되어 있으며, 그 상관관계가 아직 명확히 규명되어 있지 않다. 본 연구에서는 합성곱 신경망(CNN, convolutional neural network)을 활용한 이미지 기반 데이터 접근법을 통해 시멘트 기반 재료의 역학적 응답을 예측하 고, 공극분포와 재료 응답의 상관관계를 분석하였다. 머신러닝을 위한 데이터는 고해상도 마이크로-CT 이미지와 시멘트 기반 재료의 물성(인장강도)로 구성하였다. 재료의 메시 구조 특성을 분석하였으며, 재료의 응답은 상장균열모델(phase-field fracture model)에 기 반을 둔 2D 직접 인장(direct tension) 유한요소해석 시뮬레이션을 활용하여 평가하였다. 입력 이미지 영역의 기여도를 분석하여 시편 에서 재료 응답 예측에 가장 큰 영향을 미치는 영역을 CNN을 통하여 식별하였다. CNN 과정 중 활성 영역과 공극분포를 비교 분석하 여 공극분포특성과 재료 응답의 상관관계를 분석하여 제시하였다.

The use of hanging scaffolding for exterior wall painting and cleaning in building construction and maintenance carries the inherent risk of fall accidents. While periodic rope replacement is crucial for preventing accidents resulting from rope breakage, current regulations lack specificity in determining appropriate disposal period for fiber ropes. This study analyzed the tensile strength of the most commonly used PP fiber ropes with different diameters (16 mm, 20 mm) in the domestic construction industry. Additionally, the effect of outdoor exposure was examined by measuring the tensile strength of new ropes and ropes exposing to outdoor conditions for 30 days and 90 days. The results showed that the new ropes and those exposed to outdoor for 30 days met the KS (Korean Standards) criteria for tensile strength. However, a significant decrease in tensile strength was observed in ropes exposed to outdoor for 90 days compared to both the new ropes and those exposed for 30 days. Furthermore, the ropes exposed for 90 days did not meet the KS criteria. These findings indicate the degradation of PP fiber ropes due to UV (Ultra Violet) radiation, highlighting the importance of considering this factor when determining the replacement period for fiber ropes used in scaffolding work.