Search Results (11)

This paper aims to develop a model for calculating the ball load of the thin-walled flexible bearing (FB) in a harmonic drive under various external torque conditions. The effect of the flexspline (FS) on the FB ball load is considered, and the equivalent ring is improved to calculate the ball load of the FB. Then, the accuracy of the proposed model in calculating the ball load is verified using a finite element analysis model. Finally, a fitting formula is obtained to rapidly evaluate the FB ball load via the geometrical parameters of the FB and the FS under various external torques. The results show that the FB ball load is mainly affected by the FB maximum radial deformation under low external torque. When subjected to heavy external torque, the maximum ball load is mainly affected by the FS’s geometric parameters. Full article

Addressing the issues of easy deformation and difficult-to-control machining accuracy of thin-walled bearing rings during precision grinding due to clamping forces, existing research mainly employs methods such as elastic clamping, hydraulic control, pneumatic control, and vacuum adsorption to tackle the clamping problem. However, these methods still suffer from problems such as uneven clamping force, insufficient adaptability, and limited machining accuracy. In this paper, a novel fixture suitable for precision grinding of thin-walled bearing rings is designed. By analyzing the working principle of the fixture and considering the processing characteristics of thin-walled bearing rings, the fixture structure is designed and optimized to enhance its clamping stability and machining accuracy. Modal analysis and stress-displacement analysis are conducted to verify the stability and performance of the new fixture during the machining process. The research results show that the fixture can effectively reduce the deformation of thin-walled bearing rings, improve machining quality and efficiency, and provide a feasible solution for high-precision grinding of thin-walled bearing rings. Full article

Thin-walled conical cylinders with three ring ribs (TWCCTRR) are the critical bearing-load components of aerospace equipment, and now the high-performance fabrication of TWCCTRR is confronting great challenges. Constraint ring rolling (CRR) is a new plastic-forming technique that shows great potential in forming high-performance TWCCTRR. However, unreasonable material flow (UMF) is prone to occur in the CRR of TWCCTRR, which weakens its performance. Therefore, the problem of UMF in the CRR of TWCCTRR is investigated in this work. Through finite element (FE) simulation, it is found that UMF occurs at the bottom of the middle rib in single-pass CRR of TWCCTRR because the rib at the middle part is the earliest among the three ribs to be completely filled. Therefore, the double-pass CRR process is proposed for forming TWCCTRR without UMF, which makes the three ribs fully fill simultaneously to avoid UMF. Based on the FE simulation, in contrast to the single-pass CRR, the deformation homogeneity of TWCCTRR obviously improved, and meanwhile, the maximum radial forming force is approximately reduced by 15% in double-pass CRR due to the variation in material flow mode. Investigation results offer theoretical guidance for the CRR of high-performance TWCCTRR. Full article

Thin-walled bearings are widely used owing to the advantages of their light structure, high hardness, and strong load-carrying capacity. However, thin-walled bearings are often prone to deformation during the machining process, which can seriously affect the performance of the bearings. In addition, the machining deformation and quality of bearings are difficult to balance. To address the above issues, this paper investigates the effects of the machining parameters on the machining deformation, surface quality, and machining efficiency of a thin-walled bearing during the roughing stage. The dynamic balance between deformation inhibition and high quality in rough grinding was studied, and the optimal parameters for thin-walled bearing outer ring grinding were obtained. The deformation mechanism of thin-walled bearings caused by grinding was revealed through simulation and experimental analysis. The results show that the machining deformation and quality reach a balance when the workpiece speed is 55 r/min, the grinding wheel rotational speed is 2000 r/min, and the feed rate is 0.1 mm/min. Deformation increases with the increase in workpiece speed and grinding wheel speed. At the same time, the surface roughness increases with the increase in the workpiece speed, but the increase in the wheel speed will improve the surface roughness. As the workpiece speed increases, the surface topography shows a more pronounced stockpile of material, which is ameliorated by an increase in grinding wheel speed. As the rotational speed of the workpiece increases, the number of abrasive grains involved in the process per unit of time decreases, and the surface removal of the workpiece is less effective, while the increase in the rotational speed of the grinding wheel has the opposite effect. The grinding deformation of thin-walled bearings is mainly induced by machining heat and stress. As the rotational speed increases, the heat flux in the grinding zone increases. More heat flux flows into the surface of the workpiece, causing an increase in thermal stresses on the inner surface of the bearing collar, leading to greater deformation. The temperature in the grinding area can be reduced during machining, realizing a reduction in deformation. The research content contributes to the balance between high quality and low distortion in machining processes. Full article

The thin-walled rings of the RV reducer main bearings are prone to structural elastic deformation, which can significantly change the bearing mechanical characteristics. According to the actual assembly state of the RV reducer, the simulation model of the planetary frame–main bearings–pin gear housing is established considering the ring deformation. The model was used to calculate and comparatively analyze the ring deformation and contact characteristics of thin-walled bearings under rigid and flexible conditions, on the basis of which the mechanism of ring deformation was described, and the effects of load conditions, ring thickness and radial clearance on ring deformation, flexible contact characteristics, and ultimate carrying capacity were analyzed. The results show that the distribution of contact loads is the main factor affecting the ring deformation. The ring deformation can optimize the bearing contact characteristics, and the greater the deformation, the more pronounced the optimization effect. However, excessive ring deformation makes the contact ellipse more susceptible to truncation, which, in turn, reduces the ultimate carrying capacity. This study indicates a 38.2% decrease in the carrying capacity of the flexible ring model compared to that of the rigid ring model. In this paper, the effect of ring deformation on bearing mechanical characteristics is deeply discussed. The research results have important guiding significance for the structural optimization design of thin-walled bearings. Full article

In this paper, a practical issue of the application of cubic boron nitride (CBN) cutting tools for the machining of steel 100Cr6 thin-walled bearing rings is addressed. Three geometries of the commercially available CBN cutting inserts were tested at different machining parameters. The effect of geometry was assessed in terms of surface integrity, considering 2D profile parameters, 3D topography of the surface, and residual stresses in the surface layer. The results were sometimes contradictory, since the same cutting inserts provided the largest and the lowest values of the topography parameters, dependent on different cutting conditions. In general, CBN cutting inserts with XCEL geometry ensured the smallest profile parameters Ra and Rz, and the spatial parameters of Smr1 exhibited the largest values among all tested tools, suggesting reduced wear resistance. Residual stresses analysis did not reveal any inacceptable or potentially dangerous surface layer state after machining. Full article

As an emerging foundation structure for offshore wind turbines, bucket foundations with superior bearing capacities and efficient construction procedures have attracted significant attention in China. Thick-walled bucket foundations with concrete skirts can effectively reduce the cost and prevent the buckling problem of steel skirts during construction, transportation, and installation. However, great challenges are encountered during the sinking process, and the accurate calculation of sinking resistance is a critical process. Static-pressure tests of thin-walled and thick-walled models in sand were performed to measure the penetration resistance and soil pressure at the sidewalls and ends. The horizontal-soil-pressure coefficients of different models were calculated, and the end and skin-friction coefficients in the cone-penetration test method are recommended. The drag-reduction effects of the anti-drag ring and pressure-pull-out loading method were examined, and the drag-reduction effect was evident for the bucket foundation. The drag-reduction effect of the pressure-pull-out loading method is mainly reflected in the end zone. Full article

The failure of harmonic gear drive is mainly caused by the fatigue fracture of flexible wheels and the fatigue damage of flexible bearings. In this paper, the stress sensitivity and fatigue life characteristics of flexible wheels with thin-walled vulnerable components are studied. Firstly, the structure of the flexible wheel of a B3-80 general harmonic gear reducer is designed, the finite element model of the flexible wheel is established by using ANSYS finite element software, and the finite element analysis results are compared with the theoretical calculations to verify the correctness of the model. Finally, by changing the cylinder length, smooth cylinder wall thickness and load, the maximum equivalent stress curves of the flexible gear ring, smooth cylinder and flexible wheel bottom are obtained, and the influence law of structural parameters on the stress characteristics of flexible wheel is obtained. At the same time, the influence laws of flexible wheel cylinder length and smooth cylinder wall thickness on the fatigue life of flexible wheel is studied, which provides a theoretical basis for the structural optimization design of the cup flexible wheel. Full article

Ecologically extreme habitats at a species’ distribution edges bear significance for biota under adverse climatic conditions and climate change. Range-edge populations adjust their functional traits to the special local ecological conditions, leading to increased intraspecific variability in their morpho-anatomical structure and, consequently, favor population survival in the absence of competitors. On the basis of wood anatomical traits, such as tracheid lumen area (CA), cell wall thickness (CWTrad), cell diameter-to-radial cell wall thickness ratio (CD/CWT), and the number of tracheids in the radial tracheid files (TNo), we investigated the xylem adjustment of Pinus sylvestris L. populations from six ecologically extreme habitats from the Eastern Carpathians and the Pannonian Basin. Results indicated significant differences among all studied sites in case of all wood anatomical traits as signs of the local adaptation of trees. Peat bog populations adapted their wood anatomical traits to the generally hydric, cool and anaerobic conditions of the peat bogs, exhibiting smaller CA and proportionally thick CWTrad to ensure the hydraulic safety of the stem, whereas, on the lowland site, trees were characterized by a more effective water-conducting system, developing larger CA with relatively thin CWTrad with lower carbon-per-conduit-costs at the expense of higher vulnerability to cavitation. Radial tree ring growth and TNo also differed markedly among sites, following the temperature and groundwater constraints of the habitats. Wood anatomical variability among tree rings and the corresponding short-term climate response of populations differed from the adaptive responses of the trees to the ecological characteristics of the habitat. In addition to the different phylogeographic origin evidenced in former studies, phenotypic differentiation by the habitat type of the studied populations linked to the variance in morpho-anatomical traits have contributed to the survival of the peripheral Scots pine populations at the species’ range margins. Full article

Because both the inner and outer rings rotate, the intershaft bearings used in gas turbines do not have fixed bearing housings. As a result, the vibration of intershaft bearings cannot be measured directly. Therefore, a vibration signal can only be collected through indirect measurement. First, it must be transferred to adjacent bearings through the shafting. Then, it should be transferred by the elastic supports and complex structure of the thin-walled strut. The vibration signal is severely weakened during transmission under the influences of the transfer path. In the meantime, in the vibration of other components, a huge amount of noise is produced by the air flow, and the variable speeds of the inner and outer rings of the intershaft bearings make it harder to analyze the signal. Hence, it is very difficult to extract the vibration fault features of intershaft bearings. To deal with the variable speed of dual rotors, as well as the weak signal, a fault feature extraction scheme for the weak fault signals of intershaft bearings is proposed in this paper. This scheme is based on linear prediction, spectral kurtosis, and order tracking in the rotation speed difference domain. First, a prewhitening process, based on linear prediction, is applied to the fault signal of the intershaft bearings to eliminate the stationary component. Thus, the remaining components, including the impulse signal of faulty bearings and nonstationary noise, can retain the features of the vibrational bearings, in addition to reducing the noise. Second, the optimal center frequency and bandwidth of the band-pass filter, applied to resonant demodulation, are selected by spectral kurtosis. Subsequently, the enveloped signal containing the features of the faults found in the intershaft bearings is obtained by resonance demodulation. The quasi-stationary signal in the angle domain is acquired by the even angle resampling of the nonstationary envelope signal, as a result of the variable speed. The final order spectrum is obtained through a Fourier transform. Fault diagnosis can be conducted for the intershaft bearings by comparing this spectrum with the feature order of the bearing fault. Experiments were conducted to verify the validity of the proposed scheme. Full article

Thin-walled integrated flexible support structures are the major trend in the development of current rolling bearing technology. A thin-walled, integrated, squirrel-cage flexible support roller bearing, quasi-dynamic iterative finite element analysis (FEA) model is established in this paper. The FEA model is used to calculate the structural deformation of the thin-wall rings and support structures; the dynamic characteristics of the bearing are analyzed using the noncircular bearing modified quasi-dynamic model. The influence of the integrated flexible support structure on the internal load distribution and the dynamic characteristics of the roller bearing are analyzed. The results indicate that with the support of a flexible squirrel-cage, the maximum contact load is decreased by 14.2%, the loading region is enlarged by 25%, the cage slide ratio is reduced by 24%, and the fatigue life is increased by more than 50%. In addition, as the ring wall thickness increased, the results increasingly approached those under a rigid assumption. Full article