The Experts below are selected from a list of 120411 Experts worldwide ranked by ideXlab platform
Michael L Schmidt - One of the best experts on this subject based on the ideXlab platform.
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influence of microstructure and Load Ratio on cyclic fatigue and final fracture behavior of two high strength steels
Materials & Design, 2014Co-Authors: K Manigandan, T S Srivatsan, Thomas J Quick, Shivakumar Sastry, Michael L SchmidtAbstract:Abstract The results of a recent study aimed at understanding the conjoint influence of Load Ratio and microstructure on the high cycle fatigue properties and resultant fracture behavior of two high strength alloy steels is presented and discussed. Both the chosen alloy steels, i.e., AerMet® 100 and PremoMet™ 290 have much better strength and ductility properties to offer in comparison with the other competing high strength steels having near similar chemical composition. Test specimens were precision machined from the as-provided stock of each steel. The machined specimens were deformed in both uniaxial tension and cyclic fatigue under conditions of stress control. The test specimens of each alloy steel were cyclically deformed over a range of maximum stress at two different Load Ratios and the number of cycles to failure recorded. The specific influence of Load Ratio on cyclic fatigue life is presented and discussed keeping in mind the maximum stress used during cyclic deformation. The fatigue fracture surfaces were examined in a scanning electron microscope to establish the macroscopic mode and to concurrently characterize the intrinsic features on the fracture surface. The conjoint influence of nature of Loading, maximum stress and microstructure on cyclic fatigue life is discussed.
P B Hirsch - One of the best experts on this subject based on the ideXlab platform.
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modelling the threshold conditions for propagation of stage i fatigue cracks
Acta Materialia, 1998Co-Authors: Angus J Wilkinson, S G Roberts, P B HirschAbstract:Abstract Under near threshold conditions fatigue cracks often propagate along crystallographic slip planes with a marked mode II contribution to the Loading, particularly when the crack is short. We present here a model for this stage I fatigue crack in which a mode II crack generates dislocations either through activation of a source ahead of the crack or through direct emission from the tip, and the motion and interaction of these dislocations are then simulated dynamically throughout the Load–unLoad cycle. The crack is assumed to grow when cyclic displacement occurs at the crack tip, so that the condition that at least one emitted dislocation per cycle must return to the crack tip, allows the threshold cyclic stress intensity (Δ K th ) to be calculated. In accord with experimental data we find that Δ K th increases with decreasing Load Ratio. At high Load Ratio the fatigue threshold is best defined by the need for the cyclic stress intensity to exceed some critical value, while at low Load Ratio, the requirement is that the maximum stress intensity exceeds a second critical value.
Adel B Elshabasy - One of the best experts on this subject based on the ideXlab platform.
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effects of Load Ratio r and test temperature on fatigue crack growth of fully pearlitic eutectoid steel fatigue crack growth of pearlitic steel
International Journal of Fatigue, 2004Co-Authors: Adel B ElshabasyAbstract:Abstract The effects of changes in Load Ratio, R , and test temperature on the fatigue crack growth behaviour of fully pearlitic eutectoid steel have been investigated. Separate fatigue crack growth experiments were performed at Load Ratios of 0.1, 0.4, and 0.7 at −125 °C and compared to the behaviour at room temperature. An increase in Load Ratio at −125 °C decreased the fatigue threshold and significantly increased the Paris Law slope. Similar effects of changes in R , but less in magnitude, were observed in tests conducted at 25 °C. Fracture surfaces were examined using SEM. The significantly increased Paris Law slope exhibited in separate tests conducted at −125 °C and/or higher Load Ratio was coincident with an increase in the amount of cleavage fracture present on the fracture surface.
Hanspeter Ganser - One of the best experts on this subject based on the ideXlab platform.
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fatigue crack growth threshold as a design criterion statistical scatter and Load Ratio in the kitagawa takahashi diagram
Microelectronics Systems Education, 2016Co-Authors: Stefan Kolitsch, Jurgen Maierhofer, Hanspeter Ganser, Reinhard PippanAbstract:Cracks in components reduce the endurable stress so that the endurance limit obtained from common smooth fatigue specimens cannot be used anymore as a design criterion. In such cases, the Kitagawa-Takahashi diagram can be used to predict the admissible stress range for infinite life, at a given crack length and stress range. This diagram is constructed for a single Load Ratio R. However, in typical mechanical engineering applications, the Load Ratio R varies widely due to the applied Load spectra and residual stresses. In the present work an extended Kitagawa-Takahashi diagram accounting for crack length, crack extension and Load Ratio is constructed. To describe the threshold behaviour of short cracks, a master resistance curve valid for a wide range of steels is developed using a statistical approach.
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modified nasgro equation for physically short cracks
International Journal of Fatigue, 2014Co-Authors: Jurgen Maierhofer, Reinhard Pippan, Hanspeter GanserAbstract:Abstract A typical fatigue crack growth curve consists of the threshold region, the Paris region (linear in a logarithmically scaled diagram) and the transition region from the Paris region to unstable crack growth. For cracks exceeding a certain material-dependent length, this curve depends only on the Load Ratio R and is well described by commonly accepted crack growth models such as the Forman/Mettu (NASGRO) equation. However, cracks below this length typically grow significantly faster due to the absence of crack-closure effects, leading to an additional dependence of the crack growth curve on the crack extension Δ a . In this paper, a simple analytical model for describing the crack growth behavior for any crack length and Load Ratio R is presented. For the QT steel 25CrMo4, the model is applied to describe the crack growth behavior for different crack length and Load Ratios between −3 and 0.5.
S E Stanzltschegg - One of the best experts on this subject based on the ideXlab platform.
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near threshold fatigue crack growth at positive Load Ratio in aluminium alloys at low and ultrasonic frequency influences of strain rate slip behaviour and air humidity
International Journal of Fatigue, 2004Co-Authors: B Holper, H Mayer, A K Vasudevan, S E StanzltscheggAbstract:Abstract Fatigue crack growth near threshold has been studied in 2024-T3 and in over-aged 7075 (7075-OA) using servo-hydraulic equipment (cycling frequency 20 Hz) and ultrasonic equipment (20 kHz). Experiments have been performed at Load Ratio R =0.05 and R =0.5 in ambient air and in vacuum. Below 10 −9 m/cycle, fatigue crack growth in vacuum is not influenced by the cycling frequency and no strain rate effects are found. Air humidity accelerates near threshold fatigue crack growth, and threshold stress intensities at 10 −10 m/cycle in ambient air are approximately 50–60% of those measured in vacuum. Similar threshold stress intensities at 20 Hz and 20 kHz, however, higher crack growth rates at the lower frequency at stress intensities above threshold were found in ambient air, where the frequency influence was most pronounced for fully reversed Loading. Near threshold 2024-T3 shows planar slip behaviour and crystallographic (stage I-like) fatigue crack growth in vacuum, whereas stage II fatigue crack growth is found in ambient air. 7075-OA shows homogeneous slip properties and stage II fatigue crack growth in both environments. No apparent influences of Load Ratio and cycling frequency on fracture surfaces produced at very low growth rates are visible.
