Development of Computational Multiaxial Fatigue Modelling For Notched Components

Fatigue failures of driveline and suspensions components for ground vehicles under multiaxial loading conditions are common, since most those components are subjected to complex multiaxial loadings in service. In addition to the multiaxial loadings, many of those components contain notches and geometrical irregularities where the fatigue failure often occurs due to stress concentrations. Therefore, the origins of the multiaxiality can be related to various combinations of external loadings and notch geometries. A computational fatigue analysis methodology has been proposed here for performing multiaxial fatigue life prediction for notched components using analytical and numerical methods. The proposed multiaxial fatigue analysis methodology consists of an elastic-plastic stress/strain model and a multiaxial fatigue damage parameter. The multiaxial stress-strain notch analysis method originally proposed by Buczynski and Glinka is adapted to develop the elastic-plastic stress/strain model to compute local stress-strain responses using linear elastic FE results of notched components. An original multiaxial fatigue damage parameter based on the maximum fatigue damage plane is proposed to predict the fatigue life for notched components under multiaxial loadings. Results of the proposed multiaxial fatigue analysis methodology are compared to sets of experimental data published in the literature to verify the prediction capability of the elastic-plastic stress/strain model and the multiaxial fatigue damage parameter. Based on the comparison between calculated results and experimental data, it is found that the multiaxial elastic-plastic stress/strain model correlates well with experimental strain data for SAE 1070 steel notched shafts subjected to several non-proportional load paths. The proposed multiaxial fatigue damage parameter, when applied to the uniaxial loading to account for the mean stress effect on fatigue life, is found to correlate very well with four sets of experimental uniaxial mean stress fatigue data. In the case of multiaxial loadings, the proposed multiaxial fatigue damage parameter provides very good correlation with experimental fatigue data of thin-walled tube specimens of 1045 steel and Inconel 718. In addition, the proposed fatigue damage parameter is found to correlate reasonably well with experimental fatigue data of SAE 1045 steel notched shafts subjected to proportional and non-proportional loadings. The proposed multiaxial fatigue analysis methodology enables rapid durability evaluation for notched components design. The effect of changes in material, geometry and loads on the fatigue life can then be assessed in a short time frame. The proposed multiaxial fatigue analysis methodology provides more efficient and appropriate analysis methods preferable to very expensive experimental durability tests and more complex and time consuming life prediction methods using non-linear FE stress-strain analysis

Numerical Simulation of Residual Stresses in Welding and Ultrasonic Impact Treatment Process

Welding technology is considered as a reliable and efficient joining method, which has been widely used in almost all the industry departments. Detrimental factors induced by welding such as micro-cracks/flaws, tensile residual stresses, high stress concentration may degrade the mechanical and fatigue properties of weld joints. Ultrasonic impact treatment (UIT) is considered one of the most efficient post-weld treatment which could improve the fatigue performance of weld joints. In this study, the effect of the UIT on residual stress distribution of 304L weld joints was particularly investigated. FE analysis simulation and the XRD experiment were performed to predict and measure residual stresses of both as-welded and the UIT-treated joints. Compared results show that simulated stresses are in good agreement with the experimental results along various paths, confirming the validity of welding model. The UIT introduces a compressive residual stress layer with depth between 2 and 3 mm near the impacting surface of weld joint

Load path sensitivity and fatigue life estimation of 30CrNiMo8HH

The final publication is available at Elsevier via http://dx.doi.org/10.1016/j.ijfatigue.2011.10.009 © 2012. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/A set of strain-controlled biaxial proportional and non-proportional tests were conducted on solid and tubular specimens of 30CrNiMo8HH steel. The effect of the phase angle on fatigue life was studied. This effect becomes noticeable when applying a 90 degrees out-of-phase loading, reducing the fatigue life by a factor up to 5. It has been shown that the material has no additional hardening due to out-of-phase loading. To account for this severe path dependency, a material dependent non-proportionality modification factor is proposed. This path dependent sensitivity factor is applied to six different fatigue parameters including maximum equivalent total strain, maximum equivalent stress, Smith-Watson-Topper, Fatemi-Socie, plastic strain energy density and total strain energy density to correlate the fatigue results. The predicted fatigue lives are compared with the experiments. The cyclic plasticity models of Mroz and Chaboche were successfully employed to model the cyclic behavior of 30CrNiM08HH steel. It has been shown that estimations based on the proposed non-proportionality modification factor agree well with the experimental results.Natural Sciences and Engineering Research Council (NSERC) of Canad

AMELIORATING EFFECT OF HAWTHORN (CRATAEGUS OXYACANTHA) AND PHYSICAL EXERCISE ON ACUTE PENICILLIN INDUCED SEIZURES IN GERBILS

The aim of the present study was to assess the effect of Hawthorn (Crataegus oxyacantha) and physical activity. We studied its effect on penicilline induced epilepticus (Pie) in gerbils. Pie was induced by administration of penicilline G (500 IU, ip). The gerbils were divided randomly in four groups (6 animals per each group) and studied as described below: 1) Control group 2) Exercise group (30 min/each day for 8 weeks) (Eg) 3) Extract group, 50mg/kg/day/animal in 1 ml saline, 3 h prior to exercise (Exe) 4) Exercise+Extract + (Exe+Ex). The severity of Pie was observed and recorded. The means of latencies (Mean±SE) were 236±45, 369±36, 386±58 and 433±37 ms in groups of control, Exe, Ex, and Exe+Ex respectively. The mean spike latency significantly (P=0,033 F=3,560) decreased in Exe, Ex and Exe+Ex when compared control. Although spike frequency significantly (

Learning Mathematics with Interactive Whiteboards and Computer-Based Graphing Utility

The purpose of this study was to explore the effect of a technology-supported learning environment utilizing an interactive whiteboard (IWB) and NuCalc graphing software compared to a traditional direct instruction-based environment on student achievement in graphs of quadratic functions and attitudes towards mathematics and technology. Sixty-five high school graduates attending cram schools (called dershane in Turkish) to study for the university entrance examination participated in the study. The significant interaction effect between time of testing and groups indicated that student performance across time of testing was dependent upon the presence or absence of the treatment. Comparisons suggest that although both experimental and control group students' performances increased from pre-test to post-test and then decreased from post-test to retention test, the rate of decrease was about the same and the rate of increase was different, with students showing a greater rate of increase in the experimental group. The results also revealed that the treatment had positively affected students' attitudes towards technology and mathematics. Moreover, students' reasoning and interpretation skills regarding graphs of quadratic functions were better in the experimental group as compared to those in the control group

An Investigation on Forage Yield Capacity of Kermes Oak (Quercus coccifera L.) and Grazing Planning of Mediterranean Maquis Scrublands for Traditional Goat Farming

This study investigated grazing capacities of maquis scrubland and preparation principles of grazing management in forest resources. Kermes oak (Quercus coccifera L.), which is widespread as a main shrub species in maquis vegetation in Turkey, and pure hair goats (Capra hircus L.) feeding on shoots and leaves of this shrub were selected for study. The study was conducted in two stages. Green leaf and shoot samples were taken from kermes oaks in the first stage and the amount of green herbage yield (g*m−1) and dry matter yield (kg*ha−1) that may be obtained per unit area from these samples was identified. The considered amount of dry matter consumed by pure hair goats daily and the number of goats being fed within 1 year on land of 1 ha according to different land coverage rates of kermes oaks (goat head*ha*yr) were calculated. In the second stage, grazing capacities of sample areas where kermes oak spread were identified and compared with the grazing plan prepared by the forestry administration for this area. Forage yield variance according to land coverage rates of maquis scrublands should be considered when determining optimum animal numbers for grazing per area for sustainable goat farming