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The fatigue crack growth behavior in single‐crystal titanium with a prismatic crack was simulated using molecular dynamics (MD) considering the effects of applied temperature, strain ratio, and strain rate. The results indicate that the material exhibits transient cyclic hardening behavior and dominant cyclic softening behavior. The peak tensile stress decreases with increasing temperature or decreasing strain rate. The deformation mechanism for crack growth involves prismatic dislocation emission and the formation of vacancy defects at different loading conditions. Deformation twinning occurs at the highest temperature, and a secondary crack emerges at the highest strain rate. The Mises stress concentration at the twin boundary and the coalescence between the initial and secondary cracks may accelerate crack propagation. The ΔJ shows good linear relationships with fatigue crack growth rate (FCGR), indicating that ΔJ possesses the potential to assess fatigue crack growth behavior at the atomic scale for ductile metallic materials. Highlights: Peak tensile stress is increased by increasing temperature or decreasing strain rate.Prismatic dislocation emission and vacancy defects are the primary failure mechanisms.Twinning and crack coalescence accelerate fatigue crack propagation.The energy‐related ΔJ shows good linear relationships with fatigue crack growth rate. [ABSTRACT FROM AUTHOR]

The current work reveals the influence of loading parameters on the crack growth behavior of a Zr/Ti/steel composite plate with a crack normal to the interface by using an experiment and the finite element method. The Chaboche model was first used to study cyclic plastic evolution in composite materials. The results reveal that an increase in Fmax, Fm, and Fa can promote da/dN; meanwhile, an increase in R will reduce da/dN. The plastic strain accumulation results indicate that Fm mainly contributes to the tensile strain and compressive stress after the first cycle. Additionally, Fa increases the stress range and compression stress and greatly improves the plastic strain accumulation degree in subsequent loading cycles. The Fmax can significantly increase the stress amplitude and plastic strain accumulation level. When R increases, the plastic strain accumulation increases a little, but the stress amplitude and compression stress decrease greatly. Furthermore, it is also found that the elastic–plastic mismatch also affects the plastic evolution, that is, strengthening or weakening the effect of the loading parameters. [ABSTRACT FROM AUTHOR]

• Biaxial ratcheting and creep behavior mutually promote each other. • Biaxial fatigue crack propagation is controlled by the maximum principal strain. • Activities of non-prismatic slip and twinning increases with the loading ratio. • A modified model with higher prediction is proposed for biaxial dwell fatigue. This study investigates the biaxial dwell fatigue behavior of commercial pure titanium (CP-Ti) under different load ratios and dwell times. The evolution of mean strain, ratcheting strain, and creep strain was systematically analyzed. The findings reveal that with the decrease of load ratio or the increase of dwell time, both ratcheting and creep strain exhibit an upward trend. The interaction between ratcheting strain and creep strain promotes crack initiation and propagation. The statistical analysis of crack paths by the digital image correlation (DIC) method indicates that crack initiation occurs between 0.7 N f and 0.8 N f , and fatigue failure is governed by the maximum principal strain. Moreover, the electron backscatter diffraction (EBSD) analysis results indicate that as the load ratio increases, the activity of prismatic slip systems decreases, while the activities of other slip systems and twinning modes increases. To enhance predictive accuracy, a modified SWT model by incorporating time-dependent creep damage and anisotropy is proposed for life prediction under biaxial dwell fatigue conditions. [ABSTRACT FROM AUTHOR]

In this paper, the effects of maximum load, load ratio, and average load on fatigue crack propagation of Zr702/TA2/Q345R composite plate with a crack normal to the interface are studied by experiment and finite element method. When crack propagates to the interface from the compliant material side, the crack growth rate decreases to the minimum at first. After crack penetrates through the interface, the fatigue crack growth rate accelerates continuously. When crack propagates to the interface from the stiff material side, the fatigue crack growth rate generally increases with the crack length. Regardless of the direction of crack growth, the increase of load ratio will weaken the difference of crack growth rate near the interface caused by material property mismatch. Finite element results show that elastic modulus mismatch significantly changes the variation of the stress intensity factor amplitude. All results demonstrate that crack growth rate is dependent on the competition of the stress intensity factor amplitude, the fatigue crack growth rate in the corresponding material, and the interface strength. [ABSTRACT FROM AUTHOR]

• Influence of micronotch size on fatigue life is quantified by a new model. • Average crack arrest cycle decreases with the equivalent micronotch size. • Post-arrest behavior is characterized by crack coalescence and the alternation of slip system. • A high crack propagation rate is correlated with the dominate slip system of prismatic . • Micronotch size has little effect on the long crack propagation rate. The influence of the micronotch size on the small fatigue-crack behavior of CP-Ti was investigated in this study. With an increase in the equivalent micronotch size, the fatigue life and average crack-arrest cycle decreased. Microstructural analysis revealed that crack arrest results from high-angle grain boundaries, and the post-arrest behavior is mainly characterized by the connection of main and secondary cracks, or the alternation of the slip system. A high crack propagation rate is correlated with prismatic < a > slip. The activation of other slip modes may decrease the crack propagation rate. The micronotch size affected the distribution of the crack growth regions but had little influence on the long crack propagation rate. [ABSTRACT FROM AUTHOR]

Abstract: The uniaxial fatigue and ratcheting behavior of commercial pure titanium (CP‐Ti) was investigated by asymmetric cyclic stress‐controlled experiments at room temperature. The effects of mean stress, stress amplitude, stress ratio, and peak stress on ratcheting behavior and fatigue life were discussed. It was found that increasing mean stress, stress amplitude, and peak stress or decreasing stress ratio reduced fatigue life and promoted ratcheting behavior. The applicability of different fatigue life models was analyzed, and a new stress ratio‐related failure model was proposed based on the exponential increase of fatigue life with stress ratio. Among all the models investigated in this study, the exponential stress ratio‐related model has more advantage in fatigue life predictions for CP‐Ti under ratcheting‐fatigue interaction. [ABSTRACT FROM AUTHOR]

• Three-dimensional models of the fractured surface are scanned by OM system. • CP-Ti's critical plane is more in line with maximum principal strain rather than maximum shear strain plane. • A new KBM-U model incorporating the effect of multiaxial strain ratio is proposed. • The established KBM-P model provides a superior life prediction of CP-Ti compared to other mentioned models. • The cleavage characteristics disappear at higher strain ratios with some shear dimples appearing. Multiaxial low cycle fatigue (MLCF) tests were performed on commercial pure titanium (CP-Ti) at different multiaxial strain ratios (λ = 0.865, 1.73, 3.46, 5.19). A higher λ accelerated the initial cyclic hardening for the axial stress. For torsional stress responses, all specimens showed initial cyclic hardening characteristics. Optical microscopy (OM) observations of the fracture surfaces showed that the critical plane of CP-Ti is better aligned with the maximum principal strain plane rather than the maximum shear strain plane. The fatigue-life curves obtained from the tests were constructed using the Zamrik, ESN, SWT, FS, and KBM models. According to the modified critical plane, a KBM-P model based on the maximum principal strain plane is proposed. A unified life prediction KBM-U model incorporating the effect of λ is further proposed. Scanning electron microscopy (SEM) observations of fatigue fractures showed that fatigue cracks initiated from the outer surface of the specimen at all λ. Many small cleavage surfaces of different sizes and heights were observed in the crack propagation zone. At higher λ, these cleavage characteristics were accompanied by shear dimples. [ABSTRACT FROM AUTHOR]

In this paper, the effects of load ratio, elastic mismatch and plastic mismatch on the fatigue crack growth behavior of zirconium-titanium-steel composite plate are discussed in detail. Firstly, considering the crack closure effect caused by load ratio, different effective driving force models of crack tip are studied. The results show that Daniel's two parameter driving force model has the best normalization effect. Then, based on the material inhomogeneity theory, the equation of actual stress intensity factor at crack tip is obtained, and the crack growth rate equation considering elastic mismatch is obtained. Furthermore, the influence of plastic mismatch is studied. Finally, by dividing the influence area of the elastic-plastic mismatch and combining the respective crack growth criteria, the crack growth rate equation considering the load ratio and elastic-plastic mismatch is obtained. • The effects of property mismatch of composites are discussed in detail. • The influence areas of different property mismatches are divided in detail. • The crack propagation law of Zr/Ti/steel composite plate is obtained. [ABSTRACT FROM AUTHOR]

In this paper, the through-wall crack of Zr702/TA2/Q345R composite plate is studied by experiment and finite element method. The influence of loading parameters on crack growth rate, stress intensity factor, monotonic plastic zone and interaction effect between component materials are investigated. The elastic mismatch and yield strength between Q345R, TA2 and Zr702 leads to different crack driving force at the crack tip. Although the crack driving force is higher in component material with higher elastic module and yield strength, the crack growth rate of component materials in Zr702/TA2/Q345R composite plate is closely related to the ability of corresponding single material to resist crack propagation and the interaction effect between component materials. In addition, the fatigue crack propagation characteristic and damage mechanism are analyzed, and the effect of complex microstructures near Zr702/TA2 and TA2/Q345R interface on crack propagation behavior is clarified. Besides, it is found that the interface with higher properties mismatch preferentially delaminates. [ABSTRACT FROM AUTHOR]

Highlights • A process of inhibiting and promoting crack growth is performed. • The dimples and striations cover up the facet creep fracture characteristic. • The fatigue-creep interaction diagram based on the analyses is depicted. Abstract In this paper, the effect of the cold creep on fatigue crack growth rate are investigated by experiment considering wide ranges of load amplitudes and load ratios with or without certain degrees of dwell time. To further illustrate the cold creep influence, a series of finite element results are carried out. Finally fracture morphology analyses are also made to explain related crack growth behavior. Results show that fatigue crack growth rate either increases or decreases with certain degrees of hold load and dwell time imposed, depending on the values of the load amplitude and load ratio. This finding is the same as that in the fatigue life. Discussion shows that the effect of creep on fatigue crack growth can be attributed to the competition of the creep stress relaxation and creep strain. A process of inhibiting and promoting crack growth is performed. The fatigue-creep interaction diagram based on the analyses is depicted, by which the interaction between cold creep and fatigue can be well understood. Finally further studies and discussion are carried out by fracture morphology analyses from the dislocation pile-ups, which is in accordance with the finite element results from local creep behavior. This research will provide support to the clear understanding of the cold creep effects on the fatigue crack growth behavior. [ABSTRACT FROM AUTHOR]