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• The UPM and PI iterative methods can accurately reconstruct the residual stress field induced by rolling processing. • The extended finite element method and the weight function method are applied to solve the stress intensity factor. • The necessity of deep rolling treatment for axles is verified. • The influence of interference and initial crack position on the remaining life of axle is explored. • The damage tolerance analysis of the axle was carried out. Deep rolling surface strengthening is an effective way to introduce compressive residual stress (CRS) along the railway axle, which can improve the fatigue resistance of the material. The CRS field was rebuilt adopting the proportional-integral (PI) iteration method and the unit pressure method (UPM) to study the fatigue cracking behavior of deep-rolled EA4T railway axles. The remaining life prediction model and the stress intensity factor (SIF) solution method were then validated using simulations and testing with small-sized specimens. The remaining life of the EA4T railway axle was then calculated by applying a realistic vertical load spectrum. The results showed that CRS prevented crack propagation, enhanced the critical propagation size of railway axle cracks, and prolonged the remaining life of the axle. Additionally, the remaining life of the axle may not support the following maintenance period if a crack with an extendable size emerges at the unloading groove of the railway axle. This work provides a theoretical basis for the optimization of the non-destructive testing (NDT) interval of deep-rolled EA4T railway axles. [ABSTRACT FROM AUTHOR]

• Fatigue life prediction method of 25CrMo4 steel is investigated using fracture mechanics and machine learning methods. • Residual stress relaxation process is incorporated into fatigue crack growth in combination with NASGRO equation and equivalent initial flaw size (EIFS) methodology. • Different machine learning methods areemployed to investigate theireffectiveness in fatigue life prediction. In this work, fracture mechanics and machine learning methods are separately employed to predict the high cycle fatigue (HCF) life of micro-shot peened 25CrMo4 alloy steel containing artificial notches. The influences of notch size, stress level, and surface condition on fatigue life are incorporated into the prediction model. The results shows that the fatigue life of shot-peened specimens is enhanced by the compressive residual stress (CRS) compared with that of the un-peened specimens. The prediction result using fracture mechanics method is within the error band of ±2, while that using machine learning method almost lies in the error band of ±1.5. The stress level and notch size are the most critical factors affecting the HCF fatigue life. The applicability and limitation of the two methods are finally discussed. [ABSTRACT FROM AUTHOR]

The effects of micro-shot peening (MSP) and artificial surface defects were investigated in relation to the defect tolerance of Al-Si-0.6Mg alloy in the framework of fracture mechanics. The results indicated that coral-shaped casting defects inside the alloy could be effectively quantified using the X-ray synchrotron radiation technique. An affected layer with a surface roughness (Ra) of 1.25 and residual stress of − 125 MPa was introduced on the MSP specimen compared to the un-peened (UP) specimen. The fatigue strengths of the UP and MSP specimens containing the artificial defects decreased as the defect size increased under rotating bending fatigue tests, except in the case of defects with the equivalent size of 395 and 490 µm, respectively. MSP could shift the crack initiation site toward the subsurface, while all the cracks of the specimens with the artificial defects originated from the surface and maintained an aspect ratio of 0.66 during the crack growth process. The relationship between the defect sizes and the fatigue strengths could be reasonably assessed by the modified Kitagawa-Takahashi (K-T) diagrams. The critical defect size of the MSP specimens was increased from 450 to 542 µm compared with that of the UP specimens, owing to the beneficial effect of the compressive residual stress. The defect tolerance of the Al-Si-0.6Mg alloy was improved by the MSP process. • Effects of micro-shot peening (MSP) on the fatigue properties of Al-Si-0.6Mg alloy are explored. • Casting defect inside the alloy was identified using synchrotron radiation X-ray computed microtomography (SR-μCT) technique. • The influence of MSP on the fatigue tolerance was characterized by Kitagawa-Takahashi (K-T) diagrams. • The critical defect size harmless to fatigue strength was evaluated using fracture mechanics. [ABSTRACT FROM AUTHOR]

• Effects of the corrosive environment on the fatigue strength of EA4T axle steel are explored. • The evolution of corrosion process during fatigue loading is fully investigated. • Crack aspect ratio in the corrosive environment is obtained by using synchrotron radiation X-ray computed microtomography (SR-μCT). • Fatigue life prediction model is developed based on the pit growth, short crack growth, and long crack growth stages. High-speed railway axle is the critical safety component of modern ground vehicles, which experiences extremely complex environments. In this paper, the effect of corrosion on the fatigue behavior of EA4T axle steel was investigated in an artificial rainwater environment. Combining scanning electron microscopy (SEM) and synchrotron radiation X-ray micro computed microtomography (SR-μCT) with theoretical analysis, damage measurement enabled a full evolution characterization of the corrosion process for exploring the corrosion mechanism and its influence on the fatigue life. It is found that the corrosive environment significantly reduced fatigue strength and facilitated multiple crack initiation, while showed relatively little effect on the long fatigue crack growth. The fitness of the 3-P Weibull distribution was slightly higher than that of the Gumbel distribution in terms of crack population. The life prediction model incorporating the pit growth, short crack, and long crack stages showed a good agreement within the 95% and 5% probabilistic S-N curve. [ABSTRACT FROM AUTHOR]

• The extended finite element method is used in the fracture mechanics simulation of EA4T axle steel specimen and full-scale axle. • Numerical model is built considering residual stress and wheelset press-fitting. • The effectiveness of the extended finite element method (XFEM) was verified by comparing the simulation and experimental results. • The measured load spectrum was applied, and the NASGRO equation was used to calculate the residual life of the axle. High-speed railway axles may be damaged during service or maintenance. Therefore, to ensure axle service safety, the residual life of damaged axles is necessary for an accurate assessment. In this study, a small-sized specimen was analyzed and the effectiveness of the extended finite element method (XFEM) was verified by comparing the simulation and test results. Subsequently, the residual life of the EA4T axle with an initial crack was evaluated using the XFEM, which is based on fracture mechanics, and the actual axle service load spectrum. The results show that the critical failure sizes for the residual life of the power axle and non-power axle were 7 and 4 mm, respectively, for a crack located in the middle of the axle body; in contrast, for a crack located in the arc transition of the wheel seat, the critical failure dimensions were 9 and 5 mm, respectively. Based on the NASGRO equation and considering the damage tolerance safety factor, the residual lives of the power axle for the two crack locations were estimated to be 1.3953 × 106 and 9.636 × 105 km, respectively, while those of the non-power axle were 2.095 × 106 and 1.2583 × 106 km, respectively. The results of this study can provide a reference for the axle non-destructive testing (NDT) period. [ABSTRACT FROM AUTHOR]

• The overset mesh technology is used to simulate the train running in the tube. • The flow topology considering the ground effect has been visualized numerically. • The influence of the nose length on the wave systems is reported. • Two distinct mechanisms for the formation of flow separation are identified. • The relationship between the aerodynamic loads and flow structures is described. The flow structure and aerodynamic loads in evacuated tube transportation with three nose lengths (5, 10 and 15 m) at 1500 km/h are investigated by overset mesh technology. The governing equations of the IDDES model for 3-D, unsteady compressible flow are employed. The numerical algorithm is validated via moving model and wind tunnel experimental data. The flow topology considering the ground effect is revealed and compared. The wake is highly complex, characterized mainly by wave systems and trailing vortices. Additionally, the influence of the nose length on the generation of wave systems is discussed in detail. The largest shock intensity is identified at 5 m case, followed by 15 m case, and the smallest case at 10 m. Differences in wave systems also caused the two distinct mechanisms for the formation of flow separation and the evolution pattern of the wake vortex to be identified for three nose configurations. By comparison, the nose length increase is helpful to reduce the length of the disturbed region of the leading shock wave, the aerodynamic loads on the train surface and aerodynamic drag. A qualitative description is also presented of the relationship between the fluctuations of aerodynamic loads and flow structures. [ABSTRACT FROM AUTHOR]

Global climate change has significantly increased the frequency and intensity of high temperature and drought stresses. Additionally, the high temperature and drought are often concurred, which make the situation of maize production tougher. However, the influence of the combined stresses of high temperature and drought on summer maize production remains uncertain. The study aimed to investigate the effects of high temperature, drought, and their combined stress at different growth stages on photosynthetic and senescence characteristics of summer maize. Denghai 605 (DH605) was used as the experimental material. High temperature (T), drought (D), and their combined stress (T-D) for 6 days were set at the 3rd leaf stage, 12th leaf stage, and tasseling stage, respectively. The natural temperature and normal water management were used as the control (CK). The results showed that high temperature, drought, and their combined stress at different growth stages decreased the activities of antioxidant enzymes and soluble protein content in leaves, leading to increases in MDA content and damage to cell membranes, which accelerated the senescence of the plant. Accordingly, the activities of RuBPcase and PEPCase were decreased, indicating the abilities of plants to harvest and utilize light energy declined due to high temperature, drought, and combined stresses at different growth stages. As a result, the Pn and thus, the dry matter accumulation rate were decreased by these stresses. In addition, the translocation of dry matter to ears was impeded by stresses, especially by the high temperature at the VT stage. While, high temperatures concurred with drought aggravated the adverse effects on summer maize, compared with single stresses. Significantly, high temperature, drought, and their combined stresses at the VT stage decreased the yield mostly, followed by stresses at the V12 stage, and then by stresses at the V3 stage. Compared with CK, the yield of VT-T-D, V12-T-D, and V3-T-D were decreased by 61.6 %, 13.7 %, and 10.4 %, respectively. As global climate change is unstoppable, the superimposed changes of various meteorological factors make the growth conditions for crop production extreme. Studies to explore the combined effects of two or even more meteorological factors on crop growth are becoming more and more important. This study fulfilled the current knowledge gap of the combined stresses on maize production, however, the underlying mechanisms should be dug out in the future. • High temperature, drought and their combined stress at different growth stages accelerated the senescence of the plant. • Drought concurred with high temperature aggravated the adverse effects on summer maize, compared with single stresses. • Drought concurred with high temperature certainly aggravated the increases of VPD, straining the relationship of CO 2 intakes and water losses. [ABSTRACT FROM AUTHOR]