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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]

• Prior shot peening improves the CF limit of AO coated aluminum alloy by 50 %. • AO specimens exhibit different CF failure modes under low and high applied stress. • Substrate residual stress and microstructure affect the CF crack propagating path. • Substrate residual stress relaxes in distinct mode under low and high applied stress. Plain (anodic oxidation) and composite (prior shot peening + anodic oxidation) coatings were prepared to investigate their effects on the corrosion-fatigue (CF) property of 6082-T6 aluminium alloy in a 3.5 wt% NaCl aqueous solution. The results indicate that plain coated specimens exhibited similar CF properties to as-machined specimens at low applied stresses. However, under high applied stresses, the plain coating led to a preferential fracture and was unable to effectively prevent corrosion medium. Hence, the CF property of plain coated specimens was found to be inferior to as-machined specimens at high applied stresses. The synergetic effect of substrate residual stress and microstructure beneath the coating-substrate interface reduced the crack propagating rate in the initial stage by deflecting the crack at the grain boundary. Therefore, the CF property of composite coated specimens improved as a whole when compared with as-machined and plain coated specimens. Besides, under low applied stresses, the near-interface substrate residual stress of composite coated specimens occurred the relaxation due to the substrate crack propagation, while under high applied stresses, this was due to the synergetic effect of materials' local cyclic yield and plastic flow, as well as the substrate crack propagation. [ABSTRACT FROM AUTHOR]

Abstract In this study, the precipitate strengthened Cu-Ni-Si alloy was micro-shot peened by ceramic balls with a diameter of 40 μm. The fatigue tests using the peened specimens were conducted in air and in salt atmosphere respectively. The results show that a fine and hardening layer is formed on the surface of peened specimen and the compressive residual stress is introduced. There is no fatigue limit for specimens in both test conditions. The S-N curve of specimens in salt atmosphere shows a continuous decrease with the increasing number of loading cycles, while that in air shows a step-wise shape. Compared with the un-peened specimens, the fatigue strengths of specimens at 107 cycles are increased by 47% and 67% in air and in salt atmosphere respectively. The peened specimens in air condition failed from subsurface zone in high cycle fatigue region, while all the other specimens failed from surface. The micro-shot peening can improve the surface property and delay the crack initiation and propagation, so as to enhance the fatigue strength greatly. Highlights • The fatigue failure changes from surface to subsurface by micro-shot peening. • Micro-shot peening can delay both the crack initiation and early propagation. • The micro-shot peening can further improve the fatigue strength in salt atmosphere. [ABSTRACT FROM AUTHOR]

• The surface properties of EA4T axle steel treated by ultrasonic surface rolling process (USRP) are investigated. • Effect of USRP on the electrochemical corrosion resistance and corrosion fatigue performance is elucidated. • Residual stress relaxation mechanism of USRP-treated EA4T axle steel in air and corrosion is revealed. • Influence of residual stress relaxation on the corrosion fatigue resistance is clarified. The fatigue properties and residual stress relaxation behavior of EA4T axle steel treated by ultrasonic surface rolling process (USRP) are investigated in air and corrosive environments. The result reveals that the surface roughness (Ra) is decreased from 1.42 to 0.17 μm after the USRP. A surface layer with ultrafine grains, work hardening, and compressive residual stress (CRS) is achieved by the USRP. Compared with the as-machined specimens, the USRP specimens exhibit slightly lower electrochemical corrosion resistance but superior fatigue performance in air and corrosive environments. The dislocation density is significantly decreased in the corrosive environment during fatigue loads, accompanied by a rapid relaxation of surface CRS. The influence of USRP on the corrosion fatigue performance is elucidated. The residual stress relaxation mechanism and its influence on fatigue resistance are also analyzed. [ABSTRACT FROM AUTHOR]

Low, medium and high-intensity (0.19, 0.26 and 0.34 mmA) shot peening treatments and 0.34 mmA high-intensity shot peening combined with slight and severe polishing treatments were used as the pre-treatments to improve the fatigue property of micro-arc oxidation (MAO) coated 6082-T6 aluminum alloy, respectively. In consideration of the significance of substrate residual stress beneath the coating-substrate interface on MAO coated specimens' fatigue property, the substrate residual stress of various coated specimens was analyzed by the X-ray's powerful penetrability. Results indicate that the substrate residual stress state of MAO coated specimens is changed from tensile (+93 MPa) to compressive (−65 to −93 MPa) by the above pre-treatments, which is beneficial for inhibiting the crack initiation at the substrate or resisting the crack's further propagation from the coating into the substrate. Whereas, similar to the compressive residual stress induced by shot peening, the compressive substrate residual stress for prior shot peening + MAO composite coated specimens will also relax during the fatigue tests. In addition, the gradient compressive residual stress beneath the interface induced by prior shot peening reduce the crack propagating rate, thus improving the fatigue property of coated specimens; after the 0.26 mmA shot peening pre-treatment, the fatigue strength at 2 × 107 cycles of MAO coated specimens increases by 59.1 %. Finally, the effects of surface and interface roughness, substrate residual stress and in-depth compressive residual stress on the fatigue life of MAO coated specimens are further discussed. • Pre-treatments improve MAO coated Al alloys' fatigue life by 2.41 to 4.35 times. • Grain refinement of substrate increases MAO coatings' pore size and thickness. • Compressive substrate residual stress inhibits crack propagation beneath interface. • Compressive substrate residual stress relaxes by 8 % to 41 % at 104 fatigue cycles. [ABSTRACT FROM AUTHOR]

In this study, EA4T axle steel specimens were subjected to three shot peening treatments: conventional shot peening (CSP), micro-shot peening (MSP) and their combination, i.e. dual shot peening (DSP). The residual stress, surface roughness, morphology, microhardness, were used to characterize the affected surface layer. The results indicated that MSP achieved maximum surface compressive residual stress (SCRS), minimum surface roughness, high surface microhardness. Moreover, compared to CSP, DSP improved the SCRS and microhardness while reducing surface roughness. However, scanning electron microscopy (SEM) observations indicated the presence of intensive defects of the DSP-treated specimens, which hindered the fatigue strength of the specimens. Fatigue tests were conducted to evaluate the effect of different treatments on fatigue life, the median S - N curve demonstrated that the fatigue limit at 107 cycles was improved by 24, 32, and 27% for the CSP, MSP, and DSP specimens, respectively. Furthermore, SEM observation was conducted to analyze the fracture mechanisms, the results indicated that the failure of all specimens originated at the surface and the fracture mechanisms were not changed by the shot peening treatments. The SCRS during the cyclic loading have also been analyzed. Moreover, the factors influencing fatigue limit improvement were discussed. [ABSTRACT FROM AUTHOR]

• Effect of artificial notches is studied in terms of fatigue crack non-propagation behaviors. • Non-propagation crack rate firstly increases and then decreases with the increased notch depth. • Gradient residual stress and microstructure are responsible for the crack non-propagation. • Crack traces of post-mortem specimen in the hardened layer and the matrix are compared. Abnormal damages in railway axles can lead to a significant hazard to running safety and reliability. To this end, a surface treatment was selected to effectively inhibit fatigue crack initiation and growth. In this study, a single-edge notch bending fatigue test campaign with artificial notches was conducted to elucidate the fatigue crack non-propagation behavior in railway S38C axles subjected to an induction hardening process. The fatigue cracking behavior in the gradient structure was revealed by optical microscopy, electron backscatter diffraction, and fractography. The microhardness distribution was measured using a Vickers tester. The obtained results show that the microhardness of the strengthening layer is nearly triple that of the matrix. Owing to the gradient microstructures and hardness, as well as compressive residual stress, the fatigue long crack propagates faster once it passes through the hardened zone (approximately 2.0 mm in the radial depth). Thereafter, local retarding (including deflection, branching, and blunting) of the long crack occurs because of the relatively coarse ferrite and pearlite in the transition region and matrix. Totally, this fatigue cracking resistance is reasonably believed to be due to the gradient microstructure and residual stress. These findings help to tailor a suitable detection strategy for maximum defects or cracks in railway axles. [ABSTRACT FROM AUTHOR]

• Surface rolling deformed severity-dependent fatigue mechanism of titanium alloy was revealed. • The microstructural evolutions of the samples with different surface rolling deformation severities during fatigue loading were revealed. • The residual stress evolutions during fatigue loading for the different surface rolling deformed samples were clarified. • A surface strengthening strategy was given to enhance the stress-controlled fatigue property of titanium alloy. This work investigates the effect of initial surface plastic deformation on the fatigue behavior of Ti-6Al-4V alloy based on the microstructure and residual stress evolution under fatigue loading. The high strain hardening ability, full play of compressive residual stress, and excellent surface integrity of samples with low plastic deformation severity resulted in relatively higher fatigue strength. Microstructural analysis revealed that the ultrasonic surface rolling process (USRP) applied to samples with low plastic deformation severity accommodated plastic strain by refining the grains, whereas the grains coarsened in the USRP samples with high plastic deformation severity for accommodating the plastic strain. [ABSTRACT FROM AUTHOR]