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• Point-wise stress criterion was coupled to the energy release rate criterion. • The proposed criterion gives identical predictions with Carpinteri's criterion. • Carpinteri's criterion gives a lower prediction than Leguillon's criterion due to the higher stress employed. • Carpinteri's criterion is more accurate than Leguillon's criterion. In the framework of finite fracture mechanics, two coupled criteria were proposed by Leguillon and Carpinteri, respectively. Leguillon's criterion uses the point-wise stress criterion, whereas Carpinteri's criterion uses the averaged stress criterion. Both criteria employ the same incremental energy release rate criterion which can be considered as an averaged energy criterion. Mathematically, the averaged energy criterion can be transformed into an equivalent point-wise criterion. In this paper, a new coupled criterion based on the point-wise stress and energy criteria was proposed. The proposed criterion is equivalent to Carpinteri's criterion when predicting notch fatigue limits. All the three forms of coupled criteria were checked and compared by a large number of experimental results including V-shaped and central hole specimens. When performing the coupled criteria, power functions derived from finite element analysis were used to express the energy release rate and notch stress distributions. The effect of notch size on the crack extension lengths were investigated. [ABSTRACT FROM AUTHOR]

• High strength bolts used for braking discs failed prematurely. • Physical and chemical analysis results show no material defects. • The high stress induced by transverse loading is the reason to the bolt failure. • Remedies have been proposed to avoid further failures. This paper presents a fatigue failure analysis of high strength bolts used for braking disc of Chinese high speed railway vehicle. First of all, a set of physical and chemical analysis were conducted. The results show material properties meet all the requirements. Furthermore, combined with the field test results of vibrations of the braking disc, a finite element analysis including the whole braking disc structure and bolts were performed to determine the relative movement between the disc and hub. Then, a refined sub-model of the bolt and nut was performed to get the accurate stress states of the thread root region. Finally, a fatigue damage parameter was employed to compare the damage induced by vibration with the endurance limit of the bolt. It is found the main reason leading to premature bolt failure is the high level of vertical vibrations of the braking disc due to the worn wheels. This high level of vertical vibrations induce transverse fatigue loadings onto the bolt which is beyond the fatigue limit. [ABSTRACT FROM AUTHOR]

• Fine particle peening was used to improve fatigue properties of high strength bolts under transverse loading. • Surface roughness, compressive residual stress and micro-hardness was measured. • A finite element analysis combined with equivalent stress method was performed. In order to avoid the fatigue failure of high strength bolt under cyclic transverse loading, fine particle peening (FPP) treatment was conducted to the bolt using steel beads. The surface roughness, residual stress and surface hardness of the treated bolts were examined. Fatigue tests were performed for bolts with or without FPP treatment under transverse loading. The test results show that FPP treatment effectively improves the fatigue resistance of high strength bolt through reducing the surface roughness, increasing the surface hardness and introducing high compressive residual stress in the surface layer. For the FPP treated bolts, failure location changes from the bolt head fillet to thread root as loading displacement decreases to 0.3 mm. A finite element analysis was performed to analyze the failure behavior before and after FPP treatment. [ABSTRACT FROM AUTHOR]