Rapid development of carbon nanotubes (CNTs) reinforced to polymer composites has been recently noticed in many aspects. In this work, the latest developments on fatigue and fracture enhancement of polymer composites with CNTs reinforcement with diverse methods are thoroughly compiled and systematically reviewed. The existing available researches clearly demonstrate that fatigue fracture resistance of polymer composites can be improved accordingly with the addition of CNTs. However, this work identifies an interesting research gap for the first time in this field. Based on the systematic reviewing approach, it is noticed that all previously performed experiments in this field were mostly focused upon studying one factor only at a time. In addition, it is also addressed that there were no previous studies reported a relationship or effect of one factor upon others during examining the fatigue fracture of carbon nanotubes. Moreover, there was no adequate discussion demonstrating the interaction of parameters or the influence of one parameter upon another when both were examined simultaneously. It is also realized that the scope of the conducted fatigue fracture studies of carbon nanotubes were mainly focused on microscale fatigue analysis but not the macroscale one, which can consider the effect of environment and service condition. In addition, the inadequacy of fatigue life predicting models via analytical and numerical methods for CNT-reinforced polymer composites have also been highlighted. Besides, barriers and challenges for future directions on the application of CNT-reinforced polymer composite materials are also discussed here in details.

The purpose of this study is to develop the analysis procedures for the evaluation of the structural integrity of the spent fuel in normal condition of transport at sea. Spent nuclear fuel must be transported from the wet storage facility in the nuclear power plant to the intermediate storage facility, and the structural integrity must be maintained in vibration and shock loads during the transportation. In general, the transport of spent nuclear fuel is performed in three kinds of modes: road, rail, and sea. During transport, the spent nuclear fuel is subjected to repeated vibration and shock loads by road surfaces, railroad tracks, and waves of the sea. It should be evaluated whether the structural integrity of the spent fuel is maintained under these load conditions. All nuclear power plants in Korea are located in coastal sites, and the interim storage facility for spent nuclear fuel is highly likely to be decided as a coastal site as well. Therefore, the main mode of the spent nuclear fuel transport is expected to be maritime transport by ships. In this study, the analysis procedure was developed to evaluate the safety of spent fuel at maritime transport by ships, and the procedure for evaluating the integrity of spent fuel under normal conditions of maritime transport were proposed. CFD analysis using SeaFEM was performed for the vibration analysis of the ship by waves, and the structural vibration analysis of the transport system was simulated using the developed in-house codes. The fatigue durability of the cladding was also evaluated using the developed fatigue analysis program and the fatigue analysis used the strain data obtained from the structural analysis. It was concluded that the value of the fatigue damage on the spent fuel cladding during normal conditions of maritime transportation is close to “0” and the structural integrity of the spent fuel is maintained in the same condition.

Thick-walled pressure vessel has been autofrettaged in order to improve the fatigue life of the pressure vessel. The compressive tangential residual stress near the bore of the pressure vessel due the autofrettage process is benefical to the fatigue crack initiation and propagation of the pressure vessel. However, a reverse yielding due to the Bauschinger effect during the unloading process in autofrettage causes the reduction of the compressive residual stress near the bore. In order to evaluate the fatigue crack propagation life of the autofrettaged thick-walled pressure vessel, the Bauschinger effects were considered. Stress intensity factors of the crack at the inside surface of the pressure vessel due to operating pressure loading of 707 MPa and autofrettage loading with different levels of overstrain were calculated by using finite element methods, and used for evaluating fatigue crack propagation lives. Fatigue lives of the pressure vessel with the Bauschinger effects resulted in 45% to 67% reductions in fatigue life compared to those of the pressure vessel with ideal residual stress distributions depending on the autofrettage level.

The steel structure of the Molten steel carrier is eroded due to environmental conditions such as high temperature and corrosion, and corrosion and erosion reduce the thickness of the structure and cause erosion around gas outlets. Since this increases the stress of the structure, it is necessary to study the safety of the structure. In this study, fatigue properties were estimated using the expert system that can estimate fatigue properties based on mechanical properties such as tensile strength or hardness, and the fatigue strength of the structure was evaluated using the estimated fatigue properties. As a result, the evaluated fatigue life was greater than 106 cycles, indicating that it has sufficient fatigue strength.

The objectives of this paper are to evaluate the factors affecting the fatigue crack propagation(FCP) behavior in AZ31 magnesium alloy. FCP experiments have been performed on the specimens of AZ31 magnesium alloy under various conditions such as a loading frequency, a specimen thickness, a maximum fatigue load, and a load ratio and the obtained results were analyzed to find the influence factors on the FCP behavior in magnesium alloy. It is necessary to consider the influence factors for the design and the maintenance of lightweight structures. The correlation between the crack growth rate exponent and the crack growth rate coefficient, which are FCP behavior parameters, was also analyzed and the regression model was presented.

상⋅하수도 관로 시설은 대표적인 국가기반 시설물로서 국민생활에 있어서 매우 중요한 라이프 라인이다. 지진으로 인한 관로시설의 손상은 급수의 차단을 유발하여 심각한 피해를 초래할 가능성이 매우 크다. 그러므로 상⋅하수도 관로 시설은 지진으로부터 반듯이 안전하게 보호되어야 할 필요가 있다. 지진 및 지반침하로 인한 설계변위를 초과하는 상대변위는 구조물과 연결되는 배관의 이음부에서 손상을 발생시킨다. 벨로우즈형 신축이음관은 온도차에 의한 배관의 팽창 및 변형을 흡수하고 기계진동에 의한 배관의 손상을 막기 위한 장치이다. 본 연구에서는 매설된 상⋅하수도 관로를 보호하고자 지진변위와 지반침하 대응을 목적으로 벨로우즈를 적용하였다. 적층형 하이드로포밍 메탈 벨로우즈는 기존의 벨로우즈와 달리 지진과 같은 저주 기피로하중에 대한 내구성이 우수하다. 따라서 3ply 벨로우즈형 신축이음관을 대상으로 반복가력 굽힘시험을 수행하고 지진안전성과 내침하성능을 평가하였다. 그 결과, 3ply 벨로우즈형 신축이음관은 8.8°이상의 횡방향 변형각에 대응할 수 있는 것으로 나타났다.

This study analyzed the effects of consumer confusion on shopping fatigue and negative purchasing behaviors in an internet shopping environment. Further, the effects of shopping fatigue on negative purchasing behaviors were analyzed. The survey was conducted among consumers in their 20s and 40s in the Seoul metropolitan area who had experience of purchasing fashion products through internet shopping. A total of 392 questionnaire were analysis, with frequency, reliability, factor, correlation, and regression analysis completed using the SPSS statistics program. The results of the study showed that consumer confusion and shopping fatigue in internet shopping environment affected negative purchasing behaviors. First, consumer confusion comprised overload confusion, similarity confusion, and ambiguity confusion. It was found that overload confusion and similarity confusion significantly affected shopping fatigue. Second, shopping fatigue significantly affected negative purchasing behaviors, and an increased level of shopping fatigue result in, increased purchase delay and non-purchase behavior. Third, consumer confusion (overload confusion, similarity confusion, ambiguity confusion) significantly affected purchase delay behavior, while similarity confusion and ambiguity confusion significantly affected non-purchasing behavior. These results will provide useful data for e-CRM and marketing directions of internet companies and will contribute to rational decision-making of internet consumers and improve the quality of consumer life.

Diesel engine is used many industrial fields such as ship, power plant and big-sized vehicles and so on. Roto cap is one of the parts of system of intake and exhaust valve. Roto cap consists of body, disc spring, spring & steel ball, retainer and stop ring. Disc spring is known as taking cyclic load and cyclic load leads to fatigue damage. This study aims to investigate the stability of disc spring due to fatigue damage. As the results, the fatigue life of disc spring according to cylic load could be predicted using fatigue analysis. Consequently, disc spring showed the stability of about 1.7~2 times for criterion load of 1370N.

본 연구에서는 해양플랫폼의 탑사이드 구조에서 주로 채택하고 있는 파이프 연결 구조의 피로 수명 증가를 위한 방안을 찾기 위하여, 유한요소해석을 수행하였다. 상용해석프로그램인 MSC Patran/Nastran을 적용하였으며, 대표적인 중앙부 구조 형상을 해석 모델로 선정하였다. 하중에 따른 응력집중 현상을 구현하기 위하여, 8 절점 솔리드 요소를 이용한 모델링을 구현하였다. 주요하중은 횡방향 하중 2가지와 대각선 파이프에 인장 하중을 고려하였다. 주요 위치에서의 Hot spot 응력을 확인하기 위하여, 0.01 mm dummy 쉘 요소를 적용하였으며, 0.5 t와 1.5 t 위치에서의 주응력을 계산한 후 외삽법에 따라 용접부에 발생하는 응력을 추정하였다. 일부 구간에서는 만족해야 하는 피로 수명 이하로 평가되어, 보강이 필요하였다. 보강은 기존 설계된 파이프의 두께나 지름을 변경하지 않고, 피로 수명이 부족한 부위에 응력집중계수를 낮출 수 있도록 브래킷을 추가하였다. 인장 하중에 대해서는 bracket toe에서 응력은 23 % 증가하였고, 기존에 문제가 된 파이프의 내측, 외측에서의 응력은 약 8 % 감소하였다. 휨 하중에 대해서는 bracket toe에서 응력은 3 % 증가하였고, 기존에 문제가 된 파이프의 내측, 외측에서의 응력은 약 48 % 감소하였다. 신규 브래킷 보강으로 인하여, bracket toe의 응력증가 가 발생하였지만, S-N 커브 자체가 파이프 조인트에 비해 좋으므로 큰 문제가 되지는 않는다. 본 연구에서 적용한 국부 보강을 통한 피로 수명 개선 방법은 기존 설계안의 변경을 최소화하면서 피로 수명 증가를 효율적으로 할 수 있다는 점에서 관련 산업에서 유용하게 활용될 수 있을 것으로 기대된다.

The main purpose of this study was to examine the correlation between the consumption of red ginseng-based ‘SSR’ for 30 days and the reduction in human fatigue, blood component changes, and immune cell activity in 35 human subjects. ‘SSR’ is composed of zinc oxide, folic acid, and D-α-tocopherol with red ginseng as the main component. According to the protocol criteria of the study, 35 subjects who understood the purpose of the study and signed an informed consent form were selected. The fatigue survey was conducted through a questionnaire, and after taking ‘SSR', a decreased tendency of physical, mental, and neurosensory fatigue was observed. In hematological analysis, no significant changes were observed in the levels of WBC, RBC, and hemoglobin; however, AST (SGOT) and ALT (SGPT) levels were statistically significantly decreased. In immunological analysis, it was observed that the proliferative effect of T cells (CD3+CD4+) was greater than that of NK cells (CD16+CD56+). The collected data were subjected to t-test analysis using the SPSS 25.0 statistical program. The result from this study proposes that ‘SSR’ can be used as a functional food material as it reduces human fatigue and enhances immune function.

In this study, using the plasma spray method, tensile and compression fatigue tests are performed in saline solution to examine the effect of Ti undercoat on corrosion fatigue behavior of alumina-coated specimens. The alumina-coated material using Ti in the undercoat shows better corrosion fatigue strength than the base material in the entire stress amplitude range. Fatigue cracking of UT specimens occurs in the recess formed by grit-blasting treatment and progresses toward the base metal. Subsequently, the undercoat is destroyed at a stage where the deformation of the undercoat cannot follow the crack opening displacement. The residual stress of the UT specimen has a tensile residual stress up to about 100 μm below the surface of the base material; however, when the depth exceeds 100 μm, the residual stress becomes a compressive residual stress. In addition, the inside of the spray coating film is compressive residual stress, which contributes to improving the fatigue strength characteristics. A hardened layer due to grit-blasting treatment is formed near the surface of the UT specimen, contributing to the improvement of the fatigue strength characteristics. Since the natural potential of Ti spray coating film is slightly higher than that of the base material, it exhibits excellent corrosion resistance; however, when physiological saline intrudes, a galvanic battery is formed and the base material corrodes preferentially.

복합재료의 구조물 활용에 있어 동적하중에 의한 재료성능에 대한 영향성은 빈번하게 발생할 수 있다. 이들 동적하중들 중 피로하중은 실제적으로 복합재료 구조 또는 부재의 손상이나 파괴를 야기하는 주요 원인이 된다. 본 연구의 일차적인 목표는 이들 복합재료의 휨 피로 성능을 조사할 수 있는 장비 개발이며 두 번째 목표로는 이들 장비를 활용, 바잘트 복합재료에 대한 휨-피로성능에 대한 초기 연구를 수행하는 것이다. 이를 위하여 진공압출공법을 활용, 평균 두께 4.0mm의 바잘트 섬유보강 플레이트를 제작하였다. 총 5개의 휨-피로 시편들이 제작되었으며 각 시편들은 반복응력 비 Smin/Smax = 1의 크기로 각 시편에 작용하였다. 이때 초기 응력레벨은 122.24MPa로 고려되었으며 재료의 파괴 한계상태를 국외자료를 토대로 초기 강 성 대비 20% 강성 감소로 고려하였다. 최종적으로 본 연구를 통하여 총 3단계 구간들에서 강성값의 감소 변화를 확인할 수 있었다. 첫 번째 구간에서는 대체적으로 높은 강성 감소가 시험체에서 발생하였으며 이후 두 번째 구간에서도 지속적인 강성값 감소가 확인되었다. 최종적으로 3단계 구간에서 복합재료 내 섬유 파단과 더불어 복합재료 전체에 대한 한계파괴상태에 도달하였다.

In this study, the fatigue properties of press die steel, such as SKD11, and three high-durability die steel for the cold forming of ultra-high-strength steel sheets are evaluated. Specimens for fatigue, tensile, and hardness tests are manufactured through the heat treatment recommended by steelmakers and ultra-high precision processing. The general mechanical properties and fatigue properties are derived from hardness, tensile, and fatigue tests for four die steel. The tensile and fatigue properties of die steel derived through the tests are compared and analyzed. In particular, the correlation between the fatigue limit and the general mechanical properties such as tensile strength and elongation is analyzed, which allows relational expressions to be obtained through regression analysis. Finally, the study confirms that applying high-durability die steel is necessary for improving the die life in the manufacturing of press dies for ultra-high-strength steel sheets.

Background: Backpacks are one of the most widely used accessories in modern society. However, previous studies have shown that carrying a backpack can cause various musculoskeletal problems. Objectives: To investigate the effects of a body-adhesive backpack on craniovertebral angle, sagittal shoulder angle and the muscle fatigue in the upper extremity. Design: Randomized cross-over design. Methods: For this study, 36 healthy university students participated in this study. The experiment was conducted three times using common backpack, and body-adhesive backpack condition. The angles of the cervical spine and shoulder joints of the subjects were calculated without the backpack. Electrodes were placed at upper trapezius, lower trapezius, rectus abdominis and erector spinae to check for muscle fatigue. Subjects carried a backpack and walked on a treadmill for 15 minutes at 4 km/h. The muscle fatigue signal was also measured while walking. After walking, the craniovertebral and sagittal shoulder angles were measured again while subjects carried backpack. Results: As a result of this study, body-adhesive backpack condition showed significant decrease and significant increase in craniovertebral angle and sagittal shoulder angle than common backpack (P<.05). Body-adhesive backpack condition showed significant decrease in upper trapezius, lower trapezius, erector spinae, and rectus abdominis when compared to a common backpack (P<.05). Conclusion: This study suggests that a body-adhesive backpack is more beneficial in correcting body posture than a common backpack.

In this study, the structural and fatigue analyses were carried out according to the shape of the self-made car frame. As a result of structural analysis, all models are shown to have the weak strength and large deformation, as the equivalent stress increases at the forward part of the impact force. It can be seen that model 3 is deformed less than other models 1 or 2. And model 3 with the truss structure prevents the great deformation from the collision. In case of irregular fatigue loads, the fatigue life of the ‘Sample history’ increased by about 59.3 times compared to the ‘SAE bracket history’ under extreme fatigue load conditions, indicating that the fatigue load condition of the ‘Sample history’ were stable. The fatigue life and deformation of model 3 among all models are significantly different to models 1 and 2. If the research results are applied to the design of self-made cars, it will be useful for improving the durability and preventing the damage. The results of this study can be effectively utilized to investigate the values of stresses and deformations, and fatigue lives without the experiments of fracture and fatigue according to the shape of the car frame.