Papers by Keyword: Fatigue

Abstract: Fatigue has a serious influence on people’s production and life. In this paper, which using the discrete Fourier transform algorithm to segment and extract person's facial image, so we can have a effective monitoring of people’s fatigue state base on the facial characteristic. With the help of the parameters characteristic of the Fourier transform, we can extract the key facial information from the image and achieve accurate position of the eyes. Simulation results show that the use of discrete Fourier transform to the exact position of the human eye, having a greatly improve on the operation speed of the eyes position system, and improving its accuracy and robustness.

Abstract: Directly-generated compressive residual stress has become a widely used surface modification technique. Intentional residual stress in solid materials can be produced by different surface compression methods. It is well known how residual stress field is influenced by the parameters of inducing technology, but during the operation of a surface compressed machine element the problem of compressive residual stress relaxation can occur. Only few articles address this phenomenon. The literature on residual stress decrease caused by fatigue load is scarce and the kinetics of this mechanism is not yet investigated. The present work reports on the examination of the effect of the fatigue load on compressive residual stress strengthened specimens. Investigations have been conducted at three stress levels. Residual stress data have been measured before fatigue load and measurements have been repeated after defined fatigue cycles.

Abstract: In order to improve fatigue life of wheel steel, secondary-refining process was done with Al-deoxidation and slag of high basicity, high Al2O3 content and low oxidizing property. By morphology observation and composition analysis with FESEM, it is found that during LF-VD process, by slag-steel-inclusion interaction, Al2O3 inclusions could transform to MgO-Al2O3 spinel, and later on to CaO-MgO-Al2O3 inclusions, which are inclined to be eliminated by floatation, lowering T[O] content to 0.0007%, enhancing fatigue life of wheel steel. By In-Situ observation with CONFOCAL laser scanning microscope, it is found that MnS precipitates during solidification process, which would core oxide inclusion to form MnS-oxide complex inclusion, contributing to fatigue life improvement of wheel steel. By INSTRON fatigue testing machine, it is found that by successful inclusion control, tested samples achieve ultra-high cycle of 108 above, realizing experimental purpose of improving fatigue life of wheel steel, boosting domestic production process of CRH high speed wheel steel.

Abstract: This paper present the geometrical parameters were conducted to study how they impact the fatigue of the girders with corrugated web by a comprehensive finite element method. Different parameters, such as the oblique angle of the web, the radius of curvature between the web folds, the thickness and width of flange, the height of the beam were investigated. The research object were : promote the application of this structure, especially for corrugated steel web composite bridges on the fatigue design theory and method provide the standard. The numerical results show that geometrical parameters of girders with corrugated webs have great effect on the stress concentration of weld toes. In addition, weld depth and angle have greater impact on the fatigue of the beams with corrugated webs.

Abstract: The fatigue limit of a plain specimen of a tool steel JIS SK85 was investigated. The initial crack length in the fatigue process is related to the size of a single crystal in the case of low carbon steel. However, that is independent of the crystal size in the case of pure aluminum, a lamellar pearlitic steel, etc. In this study, the relationship between the initial crack length and the fatigue limit was investigated. The original microstructure of this material includes a spherical microstructure. However, after heat treatment under some conditions, that microstructure changed to a lamellar microstructure. The fatigue limit of heat-treated SK85 could be evaluated by an equation in which the parameters are the hardness and initial crack length. Finally, this result was discussed based on the observations of crack growth behavior and fracture surface.

Abstract: Nylon 6 clay hybrid (NCH) composite consists of nano-sized Montmorillonite and nylon 6 matrix. The testing materials were nylon 6, NCH-2 (2 wt% clay reinforced composite) and NCH-5 (5 wt% clay reinforced composite). Fatigue tests at the glass transition temperatures (35 °C and 50 °C) were performed with a stress ratio of 0.1 and frequency of 0.1Hz. NCH-2 had the highest fatigue strength at room temperature, but NCH-5 had the highest fatigue strengths at 35 °C and 50 °C. It was found that the fracture origin changed from surfaces to interior of specimens with an increase in temperature in NCH-2 and NCH-5.

Abstract: The residual strength of dental porcelain discs were test after cycling fatigue compressive load in this study. Moreover, the effects of stress intensity and cycle frequency to the damage of porcelain were explored. The porcelain specimens were bonded to the epoxy resin blocks, with 12.5mm height. The cycling fatigue contact loads were subjected on the porcelain surfaces of the bi-layer composites with silicon nitride spheres of radius 2.5mm. The crosshead speed was 6mm/min. The top load value was varied from 10N-20N in every load cycles. The cycling number was from 50-300. After cycling test, the residual strength of all porcelain samples was measured by bi-axial bending test. Fractured pieces of the specimens were collected and examined with optical microscope and SEM. On the fracture surfaces of porcelain discs after bi-axial bending test, Hertz cone cracks were presented due to cycling fatigue load. The result showed that the residual strength of dental porcelain had negative correlation with the fatigue load values and cycles. When the fatigue load cycles were lower than 100, the residual strength of porcelain presented no significant different under 10 or 20N fatigue load. In contrary, when the fatigue load cycles were over 100, the residual strength of porcelain was much lower under 20N fatigue load than 10N fatigue load. Based on the limited results of this study, the conclusion could be drawn that the residual strength of porcelain under fatigue compressive stress was main determined by load cycles in the range of small load values. The porcelain could be destroyed after very few cycles if the load is up to a critical value.

Abstract: Performance of cracked fibre metal laminate (Glare) under fatigue load differs from that of cracked plain aerospace aluminum alloy. Load transfer towards stronger fibres in Glare shields crack tips in aluminum layers that retards fatigue crack growth rates. The paper experimentally investigates the fatigue behaviour of Glare at variable stress ratio’s in an ambient environment for comparison with that of plain aerospace aluminum alloy.

Abstract: In the present study, surface mechanical grinding treatment method was developed to induce a gradient nanograined structures in commercial pure iron bar. The gradient structures and hardness were characterized by optical microscope and micro-indentation. Fatigue behaviors of samples in gradient nanograined structures and in as-annealed state were examined at room temperature, and the fatigue fracture behavior was characterized with scanning electron microscope. The result showed that the thickness of deformation layer was about 300 μm, and the fatigue strength of the treated case was 252 MPa based on fatigue life of 10⁷ cycles, but the fatigue strength of the as-annealed sample was 186 MPa. Fatigue cracks source of samples in gradient nanograined structures gradually transformed into the internal of gradient structures layer, but cracks sources of as annealed samples were observed to be initiated at surface.

Abstract: Martensitic high carbon high strength SAE 52100 bearing steel is one of the main alloys used for rolling contact applications where high wear resistance are required. Due to its high fatigue strength, SAE 52100 is recently being used not only for the production of bearings but also shafts. In this work, quenched SAE 52100 steel fatigue strength under rotating bending was investigated. Especially, we focus on “fisheye around inclusion” where the fatigue crack starts. Quantitative evaluation of its optical micrograph has not been enough carried out. In order to develop easy evaluation method for the fisheye area, we apply homology technique to the optical observation.