A Study On Low Cycle Fatigue Life Assessment of Notched Specimens Made of 316LN Austenitic Stainless Steel

The local strains obtained from the best known analytical approximations namely; Neuber's rule, Equivalent Strain Energy Density method, and linear rule, were compared to those resulting from finite- element analysis. It was found that apart from Neuber's rule with elastic stress concentration factor Kt, all the mentioned methods underestimate the local strains for all notch root radius, strain amplitudes level, at room temperature, and 550°C. Neuber's rule with Kt slightly overestimates the maximum strains for 1.25mm notch-root radius at high-temperature. Based on the analytically and numerically obtained notch root strains, the fatigue lives were estimated using the Coffin-Manson-Basquin equation. Besides, a numerical assessment of fatigue lives was estimated based on Brown-Miller and maximum shear strain equations. It was found that all these methods considerably underestimate the fatigue lives for all notch root radius, strain amplitude level, and under both temperature conditions. A new method was suggested, for which only the applied strain amplitude is needed to calculate the fatigue life of notched components. It was revealed that the suggested-method provides a good fatigue life prediction at a high-temperature loading state.

Experiment and Simulation Research on the Fatigue Wear of Aircraft Tire Tread Rubber

The road surface and the tread pattern structures directly affect the wear performance of aircraft tire, especially for lateral sliding conditions. In this paper, wear tests of tread block with different draft angles and root radiuses, different interfaces, and different slip angles were carried out, and combined with the simulation, the effects of tread groove structure and slip angle on the wear mechanism were analyzed. Results indicated that the influences of draft angle were greater than the root radius; the wear geometry of the tread block decreased when the draft angle increased in the range of 0° to 15°, but for the root radius, the wear geometry of each sample was similar to a strip shape. A considerable material loss occurred at the front edge when the slip angle increased, and the slip angle was larger in the range of 0° to 45°. Combined with the simulation and wear test, fatigue wear and abrasive wear of the slide surface are dominant factors when considering the effects of tread groove structure and slip angle, and both front edges of the tread blocks roll up repeatedly; the coefficient decreases with the increase in load when the cement concrete pavement interface is dry, but for a wet interface, the coefficient decreases softly.

Effect of Notch on Strain Rate Concentration Factor of 304 Stainless Steel Bar

In this study, the notch effect of different types of 304 stainless steel rod notch is studied because of the problem of difficulty in measuring the notch root strain of 304 rod stainless steel, and the parameters of the annular notch root are analyzed. The notch angle, notch depth, and notch root radius are the main parameters of the stress field affecting the annular notch, and the mathematical expression of the strain rate concentration factor is derived. In order to verify the accuracy of the theory, the mechanical model of 304 stainless steel bar is established by finite element and numerical simulation calculation. The results show that the theoretical and finite elements have a high degree of agreement. When the notch angle increases, both theoretical and finite elements show a downward trend. When the notch depth of 304 stainless steel bar increases, both theoretical and numerical simulations show an increasing trend. The notch root radius of 304 stainless steel bar increases with decreasing numerical simulation.

Effects of root radius and pitch difference on fatigue strength and anti-loosening performance for high strength bolt–nut connections

The fatigue strength improvement and anti-loosening performance are studied experimentally and analytically for JIS M16 bolt–nut connections. Three different root radii are considered coupled with three different pitch differences. The enlarging the bolt root radius improves the fatigue limit of the bolt by more than 30% because both stress amplitude and mean stress can be reduced. Furthermore, suitable pitch difference improves the fatigue limit by more than 25%. This is because under no pitch difference the crack initiation always occurs at No.1 or No.2 threads close to the bolt head causing the final failure; however, under a suitable pitch difference the crack initiation occurs at No.6 or No.7 threads far away from the bolt head. Good anti-loosening performance can be expected for the bolt–nut connections having enlarged root radius because the prevailing torque [Formula: see text] = 19 Nm and the residual prevailing torque [Formula: see text] are not smaller compared to other special bolt–nut connections.

Effects of shot peening and artificial surface defects on fatigue properties of 50CrV4 steel

Shot peening processes are commonly used for improving the fatigue properties of steels. Shot peening introduces a compressive residual stress field in the near surface of steel, which can reduce or stop the growth of fatigue cracks and improve fatigue properties. This study experimentally investigated the effect of shot peening on the fatigue properties of 50CrV4 steel alloys with different artificial surface defects. Drilling tools were used to introduce different artificial defects with root radii of 0.585 mm and 0.895 mm on the surface of unpeened samples. The shot peening was applied to the drilled and undrilled samples. Scanning electron microscopy (SEM) observations, micro-hardness and X-ray diffraction residual stress measurements were conducted to analyse the characteristics of the shot-peened and unpeened samples. The results show that the shot peening leads to the transformation of the retained austenite to martensite in the near-surface microstructure. The hardness rates of the surface and near surface both increase by 8% after the shot peening. The peened samples exhibit compressive residual stresses with a high degree of isotropy in the near surface. The fatigue properties of samples were experimentally evaluated by conducting 3-point bending tests. The results indicate that the shot peening improves the fatigue life of drilled and undrilled samples. For the defects with the root radius of 0.895 mm, the shot peening leads to a 500% improvement in the fatigue life compared to unpeened samples regardless of defect depth. For the defects with the root radius of 0.585 mm, the improvement in fatigue life is 40% for the defect depth of 0.2 mm compared to unpeened samples. The improvement increases to 60% and 200% by increasing the defect depths to 0.4 mm and 0.6 mm. The fatigue properties are linked to the changes in the features of defects mainly caused by the deformation hardening and compressive residual stress after shot peening.

Tensile Notch Sensitivity of Additively Manufactured IN 625 Superalloy

The notch sensitivity of additively manufactured IN 625 superalloy produces by laser powder bed fusion (LPBF) has been investigated by tensile testing of cylindrical test pieces. Smooth and V-notched test pieces with four different radii were tested both in as-built state and after a stress relief heat treatment for 1 h at 900 °C. Regardless of the notch root radius, the investigated alloy exhibits notch strength ratios higher than unity in both as-built and in stress-relieved states, showing that the additive manufactured IN 625 alloy is not prone to brittleness induced by the presence of V-notches. Higher values of notch strength ratios were recorded for the as-built material as a result of the higher internal stress level induced by the manufacturing process. Due to the higher triaxiality of stresses induced by notches, for both as-built and stress-relieved states, the proof strength of the notched test pieces is even higher than the tensile strength of the smooth test pieces tested in the same conditions. SEM fractographic analysis revealed a mixed mode of ductile and brittle fracture morphology of the V-notched specimens regardless the notch root radius. A more dominant ductile mode of fracture was encountered for stress-relieved test pieces than in the case of the as-built state. However, future research is needed to better understand the influence of notches on additive manufactured IN 625 alloy behaviour under more complex stresses.

Evaluation of Nutrient Supply, Kinetics, and Prediction of Iron (Fe) Uptake in Iron-deficient Soil using a Mechanistic Model

A pot culture experiment in the factorial completely randomized design (FRCD) was formulated with the three levels of iron (Fe) @ 0, 20 and 40 mg kg-1 in the iron-deficient Typic Ustochrept sandy loam soil at Anand Agricultural University, Gujarat, India to evaluate and predict the iron uptake, nutrient efficiency and its depletion of in the rhizosphere of efficient and in-efficient chick pea cultivars using mechanistic model NST 3.0. The current investigation was carried out with the four chickpea cultivars namely, Fe-efficient (GG-1 and GAG-735) and Fe-inefficient (ICCC-4 and GJG-305). Plant observations were recorded during three different growth stages viz., 20 DAG, 40 DAG and maturity, respectively. The shoot weight and shoot length of Fe-inefficient varieties (ICCC-4 and GJG-305) well responded to the application of Fe as compared to Fe-efficient varieties (GG-1 and GAG-735) with 20 mg Fe Kg-1 application through FeSO4. Lower dose of 20 mg Fe kg-1 was found equally effective in increasing root length and root radius. Root radius (ro) and initial soil solution concentration of Fe (CLi) were found most sensitive parameters influencing Fe uptake, which was followed by maximum net influx (Imax). In no Fe treatment, increasing r0, CLi by a factor of 2.0 times individually caused increase in Fe uptake by 1.60, 1.45 times, 1.36, 1.53 times, 1.16, 1.15 times and 1.05, 1.25 times, respectively in GG-1, GAG-735, ICCC-4 and GJG-305 varieties of chickpea. While, increasing Imax and Km separately by a factor of 2.0 Fe uptake altered in proportions by 1.03, 0.57 times, 0.93, 0.57 times, 0.73, 0.54 times and 0.69 and 0.48 times, respectively in GG-1, GAG-735, ICCC-4 and GJG-305 varieties of chickpea. The ICCC-4 instead of GG-1 and GAG-735 could be rational choice to grow on Fe deficient soil to get with dense Fe content. On the other hand, Fe-Inefficient varieties had 2 times of higher mean Fe-influx at 40 mg Fe kg-1 application than Fe-Efficient varieties.