• Title/Summary/Keyword: Fatigue design curve

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Damage Tolerant Design for the Tilt Rotor UAV (틸트 로터형 무인항공기의 손상허용 설계)

  • Park, Young Chul;Im, Jong Bin;Park, Jung Sun
    • Journal of Aerospace System Engineering
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    • v.1 no.2
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    • pp.27-36
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    • 2007
  • The Damage Tolerant Design is developed to help alleviate structural failure and cracking problems in aerospace structures. Recently, the Damage Tolerant Design is required and recommended for most of aircraft design. In this paper, the damage tolerant design is applied to tilt rotor UAV. First of all, the fatigue load spectrum for the tilt rotor UAV is developed and fatigue analysis is performed for the flaperon joint which has FCL (fatigue critical location). Tilt rotor UAV has two modes: helicopter mode when UAV is taking off and landing; fixed wing mode when the tilt rotor UAV is cruising. To make fatigue load spectrum, FELIX is used for helicopter mode. TWIST is used for fixed wing mode. Fatigue analysis of flaperon joint is performed using fatigue load spectrum. E-N curve approach is used for picking crack initiation point. The LEFM(Linear Elastic Fracture Method) is considered for analyzing crack growth or propagation. Finally, including the crack initiation and propagation, the fatigue life is evaluated. Therefore the Damage Tolerant Design can be done.

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Design of Composite Multilayer Surface Antenna Structure and Its Bending Fatigue Characteristics

  • Moon, Tae-Chul;Hwang, Woon-Bong
    • Advanced Composite Materials
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    • v.17 no.3
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    • pp.215-224
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    • 2008
  • The present study aims to design a multilayer microstrip antenna with composite sandwich construction and investigate fatigue behavior of this multilayer SAS (surface antenna structure) that was asymmetric sandwich structure for the next generation of structural surface technology. This term, SAS, indicates that the structural surface becomes an antenna. Constituent materials were selected considering electrical properties, dielectric constant and tangent loss as well as mechanical properties. For the antenna performance, antenna elements inserted into structural layers were designed for satellite communication at a resonant frequency of 12.2 GHz. From electrical measurements, it was shown that antenna performances were in good agreement with design requirements. In cyclic 4-point bending, flexure behavior was investigated by static and fatigue test. Fatigue life curve of the SAS was obtained. The experimental results of bending fatigue were compared with single load level fatigue life prediction equations and in good agreement. The SAS concept is can be extended to give a useful guide for manufacturers of structural body panels as well as antenna designers.

Reliability based optimization of spring fatigue design problems accounting for scatter of fatigue test data (피로시험 데이터의 산포를 고려한 스프링의 신뢰성 최적설계)

  • An, Da-Wn;Won, Jun-Ho;Choi, Joo-Ho
    • Proceedings of the KSME Conference
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    • 2008.11a
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    • pp.1314-1319
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    • 2008
  • Fatigue reliability problems are nowadays actively considered in the design of mechanical components. Recently, Dimension Reduction Method using Kriging approximation (KDRM) was proposed by the authors to efficiently calculate statistical moments of the response function. This method, which is more tractable for its sensitivity-free nature and providing the response PDF in a few number of analyses, is adopted in this study for the reliability analysis. Before applying this method to the practical fatigue problems, accuracies are studied in terms of parameters of the KDRM through a number of numerical examples, from which best set of parameters are suggested. In the fatigue reliability problems, good number of experimental data are necessary to get the statistical distribution of the S-N parameters. The information, however, are not always available due to the limited expense and time. In this case, a family of curves with prediction interval, called P-S-N curve, is constructed from regression analysis. Using the KDRM, once a set of responses are available at the sample points at the mean, all the reliability analyses for each P-S-N curve can be efficiently studied without additional response evaluations. The method is applied to a spring design problem as an illustration of practical applications, in which reliability-based design optimization (RBDO) is conducted by employing stochastic response surface method which includes probabilistic constraints in itself. Resulting information is of great practical value and will be very helpful for making trade-off decision during the fatigue design.

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Static and fatigue behavior of through-bolt shear connectors with prefabricated HFRC slabs

  • He, Yuliang;Zhuang, Jie;Hu, Lipu;Li, Fuyou;Yang, Ying;Xiang, Yi-qiang
    • Structural Engineering and Mechanics
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    • v.83 no.1
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    • pp.109-121
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    • 2022
  • Twelve push-out test specimens were conducted with various parameters to study the static and fatigue performance of a new through-bolt shear connector transferring the shear forces of interface between prefabricated hybrid fiber reinforced concrete (HFRC) slabs and steel girders. It was found that the fibers could improve the fatigue life, capacity and initial stiffness of through-bolt shear connector. While the bolt-hole clearance reduced, the initial stiffness, capacity and slippage of through-bolt shear connector increased. After the steel-concrete interface properties were improved, the initial stiffness increased, and the capacity and slippage reduced. Base on the test results, the equation of the load-slip curve and capacity of through-bolt shear connector with prefabricated HFRC slab were obtained by the regression of test results, and the allowable range of shear force under fatigue load was recommended, which could provide the reference in the design of through-bolt shear connector with prefabricated HFRC slabs.

Fatigue Strength Assessment of TLP Tendon Porch Using API 2W Gr.50 Steel

  • Im, Sung-Woo;Seo, Young-Seok;Lee, Joo-Sung
    • Journal of Ship and Ocean Technology
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    • v.11 no.1
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    • pp.25-35
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    • 2007
  • This paper is concerned with the fatigue strength assessment of tendon porch found which is categorized as the special structural member in TLP. Large-scale tendon porch specimens have been designed and fabricated with API 2W Gr.50 steel recently produced by POSCO. Fatigue test has been carried out for three tendon porch specimens under various load level. Fatigue strength has been evaluated based on the nominal stress range and the results are compared with the fatigue design curve of DnV RP-C203. From the present experimental study, it has been found that the porch specimens satisfy the fatigue design rule although test was carried out under the positive stress ratio. It can be, therefore, said that the API 2W steel produced by POSCO possess sufficient fatigue strength.

Fatigue life Evaluation of Rib Weldment for Generator Shaft (회전기 shaft의 rib 용접부 피로수명 평가)

  • Yun Jung-Geun;Kim Hyeon-Su;Hwang Ju-Hwan
    • Proceedings of the KWS Conference
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    • 2006.05a
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    • pp.83-85
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    • 2006
  • The purpose of this study is to evaluate the fatigue life at the rib weldment of generator shaft. In order to do it, the stress distributions at the weldment under design loading condition were evaluated using FEA and analytical approach. The fatigue strengths of the as welded and toe machined rib specimen were estimated using 3-points bending fatigue test. Based on the fatigue test results, the S-N curve far the rib weldment of the generator shaft with post treatment was established.

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Development of Optimum Design Technique for Bus Window Pillar Member (버스 윈도우 필라 부재의 형상 최적 설계기술 개발)

  • 김명한;김대성;임석현;서명원;배동호
    • Transactions of the Korean Society of Automotive Engineers
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    • v.7 no.6
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    • pp.156-164
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    • 1999
  • The body structure of a bus is generally assembled by using various spot welded box sectional members. The shape of window pillar joint is ordinarily built up by T-type member. It has been shown that T-type member has problems like high stress concentrations, low fatigue strength and low structural rigidity. In this study, to solve these problems a new approach to optimize the design of the bus window pillar joint was tried by FEM analysis and experiments. To describe the shape of the gusset connecting the vertical and horizontal members of the T-type window pillar joint B-spline curve was adopted and this curve was optimized . It was found that the new model developed could effectively improve fatigue durability an structural rigidity.

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Investigation into Conservatism of Various Fatigue Life Evaluation Procedures Using Round-Notched CT Specimens (원형 노치 CT 시편을 이용한 다양한 피로수명평가 절차의 보수성 평가)

  • Kang, Ju-Yeon;Chang, Dong-Joo;Kim, Jun-Young;Kim, Sang-Eun;Lee, Jong-Min;Huh, Nam-Su;Kim, Jong-Sung;Kim, Jin-Weon;Kim, Yun-Jae;Kim, Dae-Soo
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.15 no.2
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    • pp.19-30
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    • 2019
  • In this study, to evaluate conservatism of various fatigue life evaluation procedures, fatigue tests were conducted using compact tension (CT) specimens with a round notch, made of A516 Gr.70 carbon steel and A240 TP304 stainless steel, under load-controlled cyclic condition. Experimental fatigue failure cycles were measured and compared with predicted fatigue lives using two different life evaluation methods; (1) Design-By-Analysis (DBA) procedure given in ASME B&PV Code, Sec. III, Div. 1, Subsec. NB-3200 and (2) structural stress-based approach provided in ASME B&PV Code, Sec. VIII, Div. 2, Part 5. To predict fatigue failure cycles, three-dimensional elastic finite element analysis was conducted. Fatigue lives were predicted by both design fatigue curve given in ASME B&PV Code, Sec. III, Div. 1, Appendices and best-fit fatigue curve suggested in NUREG/CR-6815 for the DBA procedure. Finally, fatigue lives evaluated by various methods were compared with test results, and then conservatism between each evaluation procedure was discussed.

Development of Ergonomic Backrest for Office Chairs

  • Kim, Chang Yong;Song, Gyung Yong;Jang, Yeon Sik;Ko, Hyo Eun;Kim, Hee Dong;Park, Gemus;Hwang, Jung Bo;Jung, Hwa Shik
    • Journal of the Ergonomics Society of Korea
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    • v.34 no.2
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    • pp.151-165
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    • 2015
  • Objective: This study aims to develop and scientifically investigate the efficacy of the Spine S-curve Reactive Backrest that responds to the spine curvature of the user when seated, and maintains and enhances the natural S-curve of the lower back, thereby helping to relieve fatigue, correct posture and prevent spine deformities. Background: The focus of current development, design guidelines and/or standards for office chairs is mainly placed on the chair's dimensions, incline angle, adjusting features and lumbar support. Research and development was called for developing a chair backrest that maintains and improves the S-curve of the full spine. Method: The Spine S-curve Reactive Backrest was ergonomically designed to maintain correct posture and enhance user comfort. When leaned on, the backrest responds to the user's spine line and the whole lower back sits closely against the backrest, thereby aligning the user's lower back and backrest as one to maintain and improve the natural S-curve formation of the spine. In order to evaluate the efficacy of the newly designed chair (new design) and the comparison target (chair), five male college students of standard body type with normal spine curvature were selected as test subjects, and a motion analyzer and electromyography were utilized to measure S-curve and erector spinae muscle activity when seated. Results: The spine S-curve was better maintained and improved when sitting in the new design than in the comparison chair. Particularly notable was the greater displacement gap of the thoracic spine than the cervical spine, and also that of the lumbar more than the thoracic spine, with the increase of the backrest tilting angle. Furthermore, the electromyogram results showed the new design caused a lower fatigue level of the erector spinae muscles compared to the comparison chair, and also earned a higher preference in the subjective opinion results. Conclusion: The newly designed chair in this study responds to the user's spine curvature and maintains and enhances the lower back's natural S-curve, and thereby relieves fatigue, promotes better posture, and helps to prevent spine deformities better than existing office chairs. There is a need to widely introduce and supply this new design. Application: The new design is applicable to office and student chairs, and is expected to improve concentration and work efficiency.