Papers by Keyword: Fatigue Behaviour

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Authors: J.R. Moon
Abstract: It is now fairly well established that to achieve low values of the Paris exponent for the growth of fatigue cracks in PM steels, high values of fracture toughness are required. Fracture toughness is related to other measures of toughness, such as impact tests and the mechanical work that the material can absorb before fracturing. All of these are functions of the basic ductility of the material. A coherent picture of all these inter-relationships is presented.
Authors: Ki Weon Kang, Byeong Choon Goo, J.H. Kim, Heung Seob Kim, Jung Kyu Kim
Abstract: This paper deals with the fatigue behavior and its statistical properties of SM490A steel at various temperatures, which is utilized in the railway vehicle. For these goals, the tensile ad fatigue tests were performed by using a servo-hydraulic fatigue testing machine at three temperatures: +20°C, -10°C and -40°C. The static strength and fatigue limits of SM490A steel were increased with decreasing of test temperature. The probabilistic properties of fatigue behavior are investigated by means of probabilistic stress-life (P-S-N) curve and they are well in conformance with the experimental results regardless of temperature. Also, based on P-S-N curves, the variation of fatigue life is investigated and as the temperature decreases, the variation of fatigue life increases moderately.
Authors: Zoltan Major, Mikel Isasi, Thomas Schwarz
Abstract: Thermoplastic elastomers are a relatively new group of engineering materials and are increasingly used in various technical applications (i.e., seals, gaskets, damping elements, and membranes) where the fatigue resistance plays an important role. The fracture behavior of elastomers is often characterized using the tearing energy concept, T. However, hardly any data are available for these types of materials. Hence, an unfilled and a filled thermoplastic polyurethane (TPU) type were investigated under cyclic loading conditions. The pure shear specimen configuration was used in the experimental part of this study. Crack growth kinetics curves were determined and the cycle number and the tests frequency dependence of these curves investigated. While a stable crack growth process was observed at 2 Hz the crack growth became unstable above specific test amplitude at 10 Hz.
Authors: Xiao Cong He
Abstract: Friction stir welding (FSW) is a rapidly emerging joining technology due to significant advancements in tooling and process development. Latest literature relating to finite element analysis (FEA) of mechanical behaviour of FSW joints is reviewed in this paper. The recent development in FEA of mechanical behaviour of FSW joints is described with particular reference to two major factors that influence the performance of FSW joints: static behaviour and fatigue behaviour. The main FE methods used in FSW performance are discussed and illustrated with brief case studies from the literature.
Authors: Claudia Kühn, Eberhard Kerscher
Abstract: Component surfaces can be modified by micro-structuring processes like micro-milling or laser structuring for functionality reasons. This modification induces small notches, whose dimensions are in the same order as the grain size. This could have an influence on the mechanical properties. This paper presents the results of tension-compression fatigue tests with structured and – for comparison – with unstructured micro-tensile specimens of cp-titanium grade 2. Longitudinal metallographic microsections illustrate the grain size of the microstructure and the geometry of the notches. The results of the fatigue tests show the influence of the notches on lifetime and endurance limit. With a Scanning Electron Microscope (SEM) the fracture surfaces, the crack initiation sites, and the crack propagation areas of all samples were analyzed. With these analyses we want to determine which notch structure dimensions relative to the grain size are tolerable.
Authors: Nicolae Constantin, Viorel Anghel, Mircea Găvan, Ştefan Sorohan
Abstract: The research work behind this paper focused a rather extensive assessment of hybrid composites made of pure aluminium sheets, alternating with GFRP and CFRP layers. Static, fatigue and low velocity impact tests were performed, combined with NDI on damaged samples, using Lockin thermography, on specimens obtained from the two hybrid laminates and from genuine GFRP and CFRP laminates, all having five layers. The static and fatigue tests were made on parallel specimens, un-notched and having a central 5 mm drilled hole, with various failure modes. The low velocity impact tests were followed by CAI tests, meant to evaluate residual mechanical performance and damage tolerance. Lockin thermography was used for prior assessment of damage.
Authors: G.Y. Wang, Peter K. Liaw, Yokoyama Yoshihiko, A. Peker, M. Freels, D.E. Fielden, A. Inoue
Abstract: Recent research works on bulk-metallic glasses (BMGs) have opened a window to create a new generation of structural materials for applications. Although the mechanical behavior of BMGs is being studied widely, the fatigue characteristics are poorly understood. The uniaxial tension-tension high-cycle fatigue (HCF) studies were performed on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr50Cu40Al10, Zr50Cu30Al10Ni10, Zr50Cu37Al10Pd3, and Zr41.2Cu12.5Ni10Ti13.8Be22.5, in atomic percent. The HCF experiments were conducted using an electrohydraulic machine at a frequency of 10 Hz with a R ratio of 0.1, where R = σmin./σmax., where σmin. and σmax. are the applied minimum and maximum stresses, respectively. The fatigue-endurance limit of Zr50Cu37Al10Pd3 was significantly greater than those of Zr50Cu40Al10, Zr50Cu30Al10Ni10, and Zr41.2Ti13.8Cu12.5Ni10Be22.5. In order to compare the fatigue property with the crystalline alloys, the same HCF experiments were also performed on Ti-6-4, drill tool steel, and Al 7075. The fatigue lifetime of Zr-based BMGs is generally comparable to those of Ti-6-4 and drill-tool-steel crystalline alloys and is greater than that of Al 7075 alloy. The fracture morphology of BMGs indicates that fatigue-crack-propagation region included the distinct rough striations and the fine striations. The possible mechanism for the striation formation was proposed.
Authors: Xing Lin Guo, Jun Ling Fan, Yan Guang Zhao
Abstract: Fatigue tests were carried out at different stress levels on cruciform welded joints made from mastensitic stainless steel. The purpose of the present paper was to verify the validity of the thermographic method and to extend its capability on welded structural evaluation, considering the real operating situations. Due to limitations of the traditional fatigue test, the infrared thermographic technique was developed to predict and assess the fatigue limit and the entire S-N (Stress-Life) curve of cruciform welded joints. Through the comparison, the predictions of the fatigue behavior by the thermographic method (TM) manifested good agreement with the traditional method. The present research paper concludes that the TM as a promising method enables us to rapidly obtain reliable fatigue characteristics of welded structural components.
Authors: Hui Min Zhou, Qing Fen Li, Yu Feng Zheng, Li Li
Abstract: Nickel-titanium alloy are extensively used in engineering and biomedical fields for their excellent properties of shape-memory, super-elasticity and biocompatibility. Their fatigue performance has been attracted increasingly attention, because they are often used under cyclic conditions. In this paper, the ultrasonic fatigue behavior of nickel-titanium endodontic files under unconstrained condition has been studied using the self-designed ultrasonic fatigue testing equipment. The vibration and harmonious response properties of nickel-titanium endodontic files are also analyzed using finite element method. Experimental results show that the average ultrasonic fatigue life of nickel-titanium endodontic files under unconstrained conditions is more than 108. Fracture of the files always occurred at the position about 2 -3 mm near the file tip. Results of finite element analysis show that the maximum stress of the nickel-titanium endodontic files located at the position about 2 -3 mm near the file tip, where is prone to generate fatigue cracks. The results of finite element analysis are consistent with the experimental results. The scanning electronic microscope (SEM) results show that the ultrasonic fatigue cracks always initiated at the surfaces of the files, where the secondary phases or impurities existed and induced fatigue cracks under repeated stress.
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