ObjectiveAiming at the problem of predicting the crack propagation path and crack tip deflection angle of pitch bearings, on the premise of ensuring calculation accuracy, a prediction method based on the equivalent finite element model and multivariate polynomial regression model was proposed, which has a high calculation efficiency.MethodsFirstly, the influence laws of different parameters such as crack aspect ratio, crack radial angle, crack position angle, and bolt preload on the stress intensity factor of the crack front were analyzed, and a finite element model describing the operating conditions and geometric characteristics of the pitch bearing was established. Secondly, based on fracture mechanics theory, the Paris formula, and the maximum shear stress criterion, the mechanism of the effect of crack surface characteristics on the crack tip deflection angle was analyzed. Finally, a prediction model for the crack tip deflection angle under the influence of multiple factors was established using a multivariate polynomial regression model.ResultsThe results show that the crack initiation region is mainly located in the radial area of the bolt holes on the outer ring, with the cracks being dominated by the opening mode. The initial radial angle of the crack has the most significant influence on the crack tip deflection angle, and the crack propagation rate increases with the increase of the crack depth-length ratio. The prediction model for the crack tip deflection angle established based on the multivariate polynomial regression model exhibits good prediction performance. The research results can be effectively applied to the prediction of crack propagation paths of pitch bearings by wind farm operation and maintenance personnel, providing a reference for the crack assessment and life prediction of pitch bearings.
ObjectiveBowl-shaped metal rubber is a kind of porous metallic material with high elasticity and large damping, which is widely used in vibration and noise reduction fields. Due to its complex structural characteristics, fatigue damage evolution cannot be accurately characterized by traditional test and empirical formulas. Therefore, a remaining useful life prediction model based on temporal convolutional network was constructed.MethodsFirstly, 20 statistical features in time and frequency domains were extracted. Three indicators including monotonicity, robustness and temporal correlation were adopted for comprehensive evaluation and feature screening, and nine key features that best characterize the fatigue damage of bowl-shaped metal rubber were obtained. Secondly, the mapping relation between feature variables and the remaining useful life of bowl-shaped metal rubber was established by deep learning method. Finally, verification was carried out for the remaining useful life prediction results using test set data.ResultsThe results show that the proposed model can effectively capture the temporal correlation of fatigue data and realize highaccuracy prediction for the remaining useful life of bowl-shaped metal rubber. Satisfactory prediction performance is achieved when the input feature dimension is set to 8. The proposed model provides a new idea for intelligent life prediction and evaluation of metal rubber type damping materials.
ObjectiveFatigue fracture frequently occurs in titanium alloy components with laser deposition surface repair during service. Investigations on crack propagation behavior and life prediction were performed to provide reference for damage tolerance design and safety performance evaluation of structural components.MethodsFirstly, TA15 titanium alloy CT specimens with three repair thicknesses of 2 mm, 3 mm and 4 mm were fabricated, and fatigue crack propagation tests were conducted to obtain the crack propagation rates under different repair thicknesses. Secondly, a three-dimensional finite element model was established using Abaqus software. Material parameters of the substrate zone, heat-affected zone and repair zone were set respectively, and load constraints application and meshing were completed to provide a calculation basis for subsequent simulation. Thirdly, the finite element model was imported into FRANC3D software. The initial crack was defined, and the stress intensity factor was solved via the ΔK gradient iterative algorithm to realize three-dimensional crack propagation simulation. Finally, crack propagation parameters were fitted based on the Paris formula, and the accuracy of the joint simulation method was verified through comparison.ResultsThe results show that The crack growth rate of specimens with repair thicknesses of 2, 3 and 4 mm decreases gradually. The maximum relative error between the fatigue life predicted by FRANC3D software and test results is 5.25%, and the relative error of stress intensity factor calculation results is less than 4. 002%. The basketweave microstructure in the repair zone can increase the energy consumption of crack propagation. With the increase of repair thickness, the crack propagation resistance of the specimen is gradually improved.
ObjectiveTo investigate the thermo-mechanical response state and thermal fatigue crack propagation behavior of train brake disc under different braking conditions.MethodsThe three-dimensional cyclic symmetric brake disc finite element model and virtual crack closure technique were used to carry out the thermo-mechanical analysis and crack propagation analysis under emergency braking, common braking and ramp braking conditions.ResultsThe temperature and circumferential stress of the brake disc take the maximum point of the friction surface as the origin, and are diffused in a shell shape within the disc body. The circumferential stress on the inner side of the brake disc is greater than that on the outer side, and the deflection degree of the circumferential stress distribution in emergency braking and common braking is greater than that in ramp braking. Furthermore, the magnitude of circumferential stress is not only related to the amplitude of temperature, but also significantly affected by the rate of temperature change. During the braking stage, the circumferential compressive stress of the brake disc first increases and then decreases, and the thermal fatigue crack remains closed under the action of the compressive stress. During the cooling stage, the circumferential stress of the brake disc changes to the tensile state. The thermal fatigue crack gradually opens under the action of tensile stress, and the crack propagation rate increases with the increase of cooling time. Under the emergency braking condition, the crack propagation rate is the largest, and the propagation rate gap on the crack front is the smallest. Under common braking and ramp braking conditions, the crack mainly extends radially towards the outer side of the brake disc.
ObjectiveOilfield production data in recent years show that failure accidents of threaded connections in fracturing strings have increased year by year, which seriously restricts the development of multi-stage fracturing and large-scale fracturing technologies. To address this issue, stress analysis and failure evaluation of threaded connections for fracturing strings were carried out.MethodsFirstly, the connection thread of 2-7/8 heavy-wall fracturing tubing was selected as the research object, and a three-dimensional finite element model of fracturing tubing threads considering the thread lead angle was established. Secondly, the make-up torque was applied using the rotation angle method. When the make-up turns were controlled in the range of 1.5-1.75, the make-up torque specification can be satisfied, and thread galling failure can be avoided. Accordingly, the make-up turn number was set to 1.5. External loads including internal and external pressure, axial force, and torque generated by rotary jetting of the sand blaster were applied to the thread for static and dynamic numerical simulations.ResultsThe results indicate that the contact pressure and equivalent stress between thread teeth increase with rising internal pressure. The maximum equivalent stress of the upper coupling thread teeth reaches 870 MPa, exceeding the yield strength of 758 MPa, so galling failure occurs on the upper coupling thread teeth. Thread disengagement failure takes place when the loosening torque reaches 3 800 N·m, and secondary make-up occurs when the tightening torque increases to 3 800 N·m. Under vibratory internal pressure, the equivalent stress of thread teeth rises with the increase in the mean value, amplitude and frequency of vibratory internal pressure, inducing galling failure. Under vibratory axial load, thread disengagement and galling failures occur when the vibration amplitude exceeds 1 600 kN. At this time, excessively low frequency leads to thread disengagement failure of tubing threads. When the frequency is higher than 6 Hz, thread disengagement failure can be avoided, but the equivalent stress of thread teeth increases and galling failure occurs. The research findings provide references for the safety evaluation of downhole fracturing tubing threads.
