Papers by Keyword: Super-Long Life

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Authors: Yong Xiang Zhao, Bing Yang, Ming Fei Feng
Abstract: The structures of railway vehicles are required to service in super-long life regime. Determination of the probabilistic S-N curves including the regime should be a basic work to realize the real fatigue life prediction and reliability assessment. Based on the test results of Chinese railway LZ50 axle carbon steel, a statistical extrapolating method is proposed to determine the curves by applying the conventional test data in mid-long life regime. Some phenomena, i.e. the response of “fatigue limit”, a great of heat affecting using the high frequency ultrasonic fatigue test system, and the non-conservative test results using the conventional frequency tiny multi-specimen test system (machine C), are firstly mentioned in the existent super-long life researches. The too much conservative offers are also noted by the determinations of existent codes. To address the variable amplitude loads in production, the present method extrapolates continuously the curves from the mid- to super-long life regimes under the statistical controls of conventional fatigue limits. The practice for the present material indicates that the curves can well reflect the scattered data not only in mid-long life regime but also in super-long life regime. The non-conservative test results using machine C are also safely included by the curves.
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Authors: Z.X. Song, Dong Po Wang, G.A. Wei, C.H. Yang
Abstract: Fatigue test was carried out on E36 steel no reinforcement welding joint under the same constant amplitude load with ultrasound fatigue tester independent designed by Tianjin University. Test results showed that the specimen would enter infinite life area after 1 x 109 cycle times; All broken specimens fractured in the welding seam. We observed fracture surface using SEM and found all the crack initiation from defects. This paper further analysed the influence of nature, size, position, and distribution of defects on fatigue life.
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Authors: Yong Xiang Zhao
Abstract: For an engineering structure with an actual fatigue life over that corresponding to a so-called fatigue limit, appropriate reliability assessment and fatigue life prediction are essential for developing the structure and sustaining its high quality in service. Basic clues are explored. A competition fatigue initial mechanism is shown to provide a requirement of material primary quality management. Affordable deduced material and structural probabilistic S-N curves are presented by fitting into material mid-and-long life S-N data and fatigue limits and, then, comparing to structural fatigue limits. Random cyclic stress-strain relations are depicted for constructing random stressing history of structures. Reliability assessment and fatigue life prediction are established to synthetically consider the interference of applied stresses deduced from the random cyclic stress-strain relations and capacity strengths derived from the structural S-N relations with an expected life. Affordable and appropriate method has been then developed to realize the reliability assessment and fatigue life prediction including the super long life regime. Availability of the present method has been indicated through a reliability analysis to the velocity related reliabilities and fatigue lives of a railway axle.
17
Authors: Ling Ling Jin, Cai Yan Deng, Dong Po Wang, Rui Ying Tian
Abstract: Fatigue property of 45 steel was studied in this paper with the method of ultrasonic fatigue testing, and SEM was used to analyze microscopic characteristics of the fatigue fracture. Fatigue test results show that: S-N curves descend continuously after 108 cycles, there is no fatigue limit as the traditional fatigue conception describes. Therefore, it is very dangerous to design welded structure working in the ultra-high cycle interval with the fatigue strength corresponding to 5×106 cycles. In the super-long life range, the fatigue property of welded joints is worse than the base metal. SEM analysis shows that: fatigue crack mainly initiates from the defects in the surface or sub-surface.
1911
Authors: Q.Y. Wang, Hong Yan Zhang, S.R. Sriraman, S.L. Liu
Abstract: Magnesium alloys, on account of their lightweight, find useful applications in the automotive sector. During service, they experience very high number of fatigue cycles. Therefore, the understanding of their long life fatigue behavior becomes extremely important. This is possible by using ultrasonic fatigue testing, which is the only feasible way of doing it. In this study, the two such alloys viz. AE42 and AM60 has been investigated for their long life fatigue characteristics under fully reversed loading conditions, using a piezoelectric fatigue testing machine operating at a frequency of 20 kHz. The S-N data does not reach a horizontal asymptote at 107 cycles in either of the alloys. However, the alloy AM60 seems to show a fatigue limit at about at 109 cycles. The fractures examined by scanning electron microscopy (SEM) were found to be brittle in character. In very high cycle fatigue conditions, the crack was found to initiate from the specimen subsurface.
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