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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]

The influence of pre-strain on the fatigue crack growth behavior of Zr702/TA2/Q345R composite plate is studied by experiments and the finite element method. The crack perpendicular to the interface and the through-wall crack are considered at the same time. For the crack perpendicular to the interface, the monotonic plastic zone and cyclic plastic zone at the crack tip are used to study the influence of pre-strain on the plastic zone. Furthermore, the influence of pre-strain on the evolution of the plastic damage at the crack tip is analyzed in detail by studying the variation in the initial plastic energy and equivalent plastic strain. For the through-wall crack, the effect of pre-strain on the propagation behavior of cracks on both sides and the whole crack is studied systematically. The results show that the strengthening of the cracks on the Zr702 side is significantly higher than that on the Q345R side, so the inhibitory effect of pre-strain on the whole crack of the through-wall specimen is mainly due to the increase in the resistance to crack growth on the Zr702 side. [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]

• Effects of crack plane orientation and crack propagation direction on crack tip plasticity are discussed. • Atomic stress distribution around the crack tip are analyzed to explain the difference of toughness in different models. • Simulation results are compared with theoretical predictions based on the linear elastic fracture mechanics. This work presents atomic simulations of crack tip behavior in HCP titanium single crystal with center crack under mode I loading condition. The simulation results show that the crack tip plasticity in most of the studied crack orientations is attributed to the activation of basal or prismatic 〈 a 〉 slips, which is in accordance with the slip characteristics analysis. Comparing the increment of crack tip advance with the applied strain under different conditions, it is found that brittle mode has the highest crack propagation rate, following by twinning dominated crack tip behavior and the latter is dislocation slip dominated crack tip behavior. The above toughness difference is further explained from the perspective of the atomic stress distribution in front of the crack tip. Finally, the simulation results are compared with theoretical predictions based on the linear elastic fracture mechanics. Besides, the observed crack kinking phenomenon is attributed to the preference of cleavage along the plane with lower critical stress intensity factor. In general, the simulation results indicate that titanium is an intrinsically ductile metal as plastic deformation can be observed in the vicinity of the crack tip for most of the studied crack orientations, though some slip modes that have relatively Schmid factors are suppressed by the applied boundary condition. [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]

In this work, finite element (FE) method is used to determine plastic limit load solutions for pipe bends with circumferential through-wall crack under torsion moment. Both extrados and intrados crack are considered regarding of crack location. Based on FE results estimated solutions are proposed for application, and are also compared with corresponding solutions in previous literatures showing that existing solutions are unfit for prediction of torsion load. The weakening factor W decreases with crack length increasing, and the decreasing rate exhibits three typical stages which performs a similar trend to that with bending moment. Finally a detailed analysis for the mechanical behavior of pipe bends has been conducted which provides some evidence to explain the weaken effect caused by the presence of crack. In torsion mode results show that the non-uniform distributed shear stress is performing symmetric to the profile plane and may have a crucial influence on the weakening factor, while in bending mode the distribution in axial stress and circumferential stress is symmetric to the profile plane and has a decisive influence. Therefore crack is pulled open by in-plane bending load while torn open by torsion load. Some evidence also can be obtained from the Mises stress distribution, where similar variation rule will provide another argument to support such description. [ABSTRACT FROM AUTHOR]

• An unique double-stress peak-type nature of the deviatoric stress–strain curve of the single-cracked limestone was found. • The effect of crack inclination angle β on the equivalent crack stress intensity factor K e and mixing factor M e was obtained. • A single-cracked limestone initiation model for hydro-mechanical coupling is proposed to predict the relationship between the initiation stress σ c i and the crack inclination angle β and water pressure P. This paper creates single cracked specimens by the prefabricated crack in the middle of a standard cylindrical specimen of limestone. The MTS815 rock mechanics test system was used to perform conventional triaxial compression tests on single cracked limestone specimens under different confining pressures and water pressures. The theory of linear elastic fracture mechanics is used, the fracture mode of single-cracked limestone is analyzed and the rock compression-shear fracture criterion under hydro-mechanical coupling is deduced and verified experimentally. The results show that the deviatoric stress–strain curve of single-cracked limestone has a unique double stress peak behavior of high front and low back (crack inclination angle β = 15°) and low front and high back (crack inclination angle β = 45°). The crack initiation stress and peak strength of single crack limestone show a significant decreasing trend with increasing water pressure and increasing with increasing confining pressure. The highest values of crack initiation stress and peak strength for specimens with crack inclination angle β = 75°, secondary for specimens with β = 15° and smallest for specimens with β = 45° under the same confining pressure and water pressure. Based on the fracture mechanics theories, the stress intensity factor of open crack and open crack closed by force increases with the increase of water pressure. The effective stress intensity factor and mixing factor increase with the increase of the crack inclination angle. In addition, the advantage angle β m is detected to be related to the friction coefficient of the crack surface, and the range of values of the advantage angle of the open crack subjected to pressure to closure is obtained to vary between 45° and 67.5°. Additionally, the advantage angle for the open crack is 45°, which indicates that the specimen crack inclination angle with β = 45° is the easiest to initiate cracking, and the conclusion is in concordance with the test results. [ABSTRACT FROM AUTHOR]