Search

Because of the excellent static and fatigue performance, the interference-fit bolted structure has a wide application prospect in the joint field. In this paper, an improved spring-mass stiffness analytical prediction model is established for the interference-fit bolted single-lap laminated composite structure. The influences of interference-fit percentage, bolt preload, secondary bending and interface frictions are considered in the model. Combined with experimental research, the value of secondary bending moment coefficient ε is studied, and the correctness of the analytical model is verified. Based on the improved stiffness model, parametric research and regression analysis on the interference-fit percentage, preload, friction, laminate width and material properties are carried out and show that the overall structure stiffness is obviously affected by ε value, laminate width and laminates properties. The stiffness decreases with the increase of ε and increases with the increase of laminate width. And as the key factors, the interference-fit percentage mainly affects the joint local friction and bolt shear stiffness, the preload and friction coefficient mainly affect the local friction, and the laminates sizes and properties directly affect the overall structural stiffness.

In the traditional specification of interference fits, loads on the joint such as the torque and axial force are taken into account. However, radial and cantilever loads must also be considered. As an example, the fit of a conical gear on a shaft with complex loading is analyzed.

In this article, the rotor stress is analysed for a high-speed permanent magnet (PM) machine (HSPMM) with segmented magnets retained by a carbon-fibre sleeve. The influence of rotor PM segmentation is firstly considered in the stress analysis. It is found that when the segmented magnets are under tensile stress, significant sleeve stress concentration will occur due to magnet edging effect. By contrast, the PMs will benefit from the segmentation with reduced tangential stress. This stress reduction effect is enhanced when the number of PM segments is larger. Furthermore, the influence of PM segmentation on the worst operating scenario is determined. In order to avoid stress concentration due to PM segmentation, the design guidelines are then given by investigating the influence of sleeve thickness and interference fit. A new design scheme of sleeve thickness is proposed based on the identified worst case scenarios. Finally, a 6-slot 4-pole high speed PM machine with segmented magnets retained by carbon-fibre sleeve is prototyped and tested at the speed of 90 krpm. The rotor stability indirectly indicts the validity of the theoretical analysis and design scheme.

The bolted flange joints with spigot (short for bolted joints) are widely used in the rotor system of aero-engine. The current models of the bolted joint usually ignore the spigot, therefore cannot account for the effect of spigot on joint's mechanical characteristics. In this paper, a new analytical model of bolted joint is proposed to describe its nonlinearity under bending moment. The model takes into account the sticking and sliding statuses of spigot by introducing a Jenkins element, therefore is able to describe the joint's damping effectively. By performing a comparison study with the finite contact element model, the accuracy of the proposed model is validated. Meantime, the comparison study highlights the important role of spigot on the hysteresis nonlinearity of the bolted joint. After that, a dynamical model of the bolted rotor is developed, in which the proposed bolted joint model is introduced by considering the influence of rotor's whirl motion. Based on the dynamical model, the dynamic characteristics of the bolted rotor are investigated in detail. The results show that the bolted joint mainly produces stiffness loss and damping nonlinearity into the rotor system. The stiffness loss occurs in any loading conditions and leads to a decrease of the rotor's critical speed. While the damping nonlinearity is mainly excited under large unbalance, it may induce a self-excited components in rotor's response at super-critical speed. The influence of the bolted joint on rotor dynamics can be reduced by decreasing flange length, friction coefficient and interference fit of the spigot.

The vibration of ceramic motorized spindle determines the machining quality of CNC machine tools. The dynamic characteristics of a motorized spindle were explored under the influence of interference fit and thermal displacement. Using heat transfer theory and bearing Harris theory, the temperature field model of motorized spindle was established, which aims to find the relationship of thermal displacement and interference. In addition, the dynamic and thermal factors were coupled to the dynamic model of the ceramic motorized spindle rotor system, of which the variation rules of bearing stiffness and rotor vibration characteristics were calculated and analyzed. The accuracy of the motorized spindle rotor system dynamic model was verified by experiments. The results show that the interference fit of shaft and bearing decreases with the rotating speed increase under the combined influence of centrifugal force, load and thermal displacement. The vibration was calculated by the dynamic model of motorized spindle rotor system considering dynamic and thermal factors. The maximum error was 3.9 %, which is well consistent with the experimental results. The dynamic characteristics of ceramic motorized spindle can be improved by appropriately increasing the degree of interference tightness at high speed.

The decrease of stress amplitude is generally believed as the mechanism of fatigue life enhancement in interference fit joints under cyclic loading for each load cycle. In order to exactly estimate it, a new analytical model was presented. In this model, influences of mass, geometry, and plastic deformation are considered to modify and improve the spring model, and, moreover, the stress amplitude at the smallest crossing section is investigated. Taking these factors into account, stress amplitude decrease of various interference values can be calculated more accurately; therefore, the analytical solutions have good agreement with the finite element numerical and experimental results under different interference values and load levels. The analytical model indicates that the decrease ratio of stress amplitude is of a certain value for a specific interference value with the external load under the critical value. Furthermore, the decrease ratio of stress amplitude mainly depends on the stiffness of the pin and plate, which is mostly affected by the geometric shapes and plastic deformation ranges of the pin and plate. In addition, raising the interference value leads to larger stress amplitude reduction since the plastic deformation areas expand with the increment of interference values.

Cold forging tools fail mainly due to loss of dimensions (as a result of abrasive wear and plastic deformation) and fatigue failure. Since tooling costs represent a considerable share of the total cost in forging processes, improving fatigue life is a crucial aspect in the design of forging tools. The present study aimed to improve the fatigue life of a specific cold forging tool currently employed in the mass production of an automotive part. The stresses in the die were evaluated by means of finite element simulations, which were able to predict both the crack nucleation spot and its propagation direction, as observed in the tools employed in the production line. There is compelling evidence in the literature that fatigue life of a die is influenced by the amount of interference fit (preloading) to which it is subjected. Therefore, a slight alteration in the preloading profile was proposed, and the finite element analysis was repeated. Numerical results predicted a change from 597 MPa to 170 MPa in the highest principal stress. The design modification was then implemented in the production line and the expected mean life increased from 17,563 to 71,323 parts produced per tool. Overall, the procedure herein described may serve as a valuable tool for the design of cold working tools less prone to fatigue failure.

Wind turbines (WT) must be further optimized concerning availability and reliability. One of the major reasons of WT downtime is the failure of gearbox bearings. Some of these failures occur, due to the ring creep phenomenon, which is mostly detected in the planetary bearings. The ring creep phenomenon describes a relative movement of the outer ring to the planetary gear. In order to improve the understanding of ring creep, the finite element method (FEM) is used to simulate ring creep in planetary gears. First, a sensitivity analysis is carried out on a small bearing size (NU205), to characterize relevant influence parameters for ring creep—considered parameters are teeth module, coefficient of friction, interference fit and normal tooth forces. Secondly, a full-scale planetary bearing (SL185030) of a 1MW WT is simulated and verified with experimental data.

Gears are commonly used in transmission systems to adjust velocity and torque. An integral gear or an interference fit could be used in a gearbox. Integral gears are mostly preferred as driving gear for a compact design to reduce the weight of the system. Interference fit makes the replacement of damaged gear possible and re-use of the shaft compared to the integral shaft. However, internal pressure occurs between mating surfaces of the components mated. This internal pressure affects the stress distribution at the root and bottom land of the gear. In this case, gear parameters should be re-considered to assure gear life while reducing the size of the gear. In this study, interference fitted gear-shaft assembly was examined numerically. The effects of rim thickness, profile shifting, module and fit tolerance on bending stress occurring at the root of the gear were investigated to optimize gear design parameters. Finite element models were in good agreement with analytical solutions. Results showed that the rim thickness of the gear is the main parameter in terms of tangential stress occurring at the bottom land of the gear. Positive profile shifting reduces the tangential stress while the pitch diameter of the gear remains constant. Also, lower tolerance class could be selected to moderate stress for small rim thickness.

The main goal of the present paper is a numerical study of the fatigue strength indicators in filled holes using the example of a repair patch on an aircraft panel. The stress state characteristics of the first hole were considered in most detail being the most load-bearing and therefore the most susceptible to the formation of fatigue cracks. The analysis of the finite element mesh density in the calculated holes was carried out to stabilize the obtained values of the equivalent stresses in the contact elements. The acquired data was further processed to obtain the dependencies of the fatigue safety margins reduced to a symmetric cycle in normal and shear stresses for a filled hole with a clearance fit, an interference fit and for a mixed type of bolt setting. The results were used to determine a preferable type of fit for the bolted joint of the first hole in the patched panel for the compressed and tensioned zone.

Tie-bolt rotors are commonly applied in aeroengines and gas turbines, and interference fits ensure accurate positioning for disk assembling. This paper presents experimental and numerical studies on the stiffness and damping properties of a tie-bolt rotor with interference fits under different preloads. An FE model incorporating thin-layer elements is used to carry out model updating to predict the contact stiffness and damping characteristics. A two-step model updating approach of the tie-bolt rotor using the response surface optimization is implemented. Finally, a quasistatic FE simulation concerning the interference fits and sensitivity analysis is performed to validate the experimental results. Press fit induces a bilinear contact stiffness. Also, modal damping demonstrates a more sensitive and nonmonotonic behavior versus preload.

Reference blocks for loading the bearing rings on the car wheelset axle journals have been developed and manufactured, and a hydraulic test rig for loading bearing rings that simulates their press fitting on the axle has been certified. A mathematical model of a method for evaluating mechanical stresses in a bearing ring using acoustoelastic method with chord-type sounding has been created and solved, with the variation of the angle between the wave propagation direction and the axis of the principal mechanical stresses taken into account. The acoustoelasticity coefficient of a longitudinal wave in ShKh15 steel was determined experimentally when loading the bearing ring. Interference fit measurements of bearing rings were performed with the loading reference blocks using acoustoelasticity method.

Experimental and finite element research was conducted on the bolted interference fit of a single-lap laminated structure to reveal the damage propagation mechanism and strength change law. A typical single-lap statically loading experiment was performed, and a finite element damage prediction model was built based on intralaminar progress damage theory. The model was programmed with a user subroutine and an interlaminar cohesive zone method. The deformation and damage propagation of the specimen were analyzed, and the failure mechanism of intralaminar and interlaminar damage during loading was discussed. The effect of secondary bending moment on load translation and damage distribution was revealed. The experimental and simulated load-displacement curves were compared to validate the developed model’s reliability, and the ultimate bearing strengths under different fit percentages were predicted. An optimal percentage was also recommended.

In this article, a high-speed Halbach-array permanent magnet (PM) rotor for ironless stator axial-flux permanent magnet (AFPM) machine is proposed and researched with consideration of the multiphysics constraints, including the electromagnetic characteristics, mechanical strength, and rotor dynamics. Considering the severity of attractive force between twin rotors, the complex repulsive force among PM segments of Halbach-array and centrifugal force, the new hybrid sleeve, and PM fixation method are proposed to improve the rotor mechanical strength. Then, the rotor stress is analyzed by numerical analysis and three-dimensional (3-D) finite-element analysis (FEA). Furtherly, the sleeve thickness and interference fit are optimized by 3-D FEA. The rotor dynamics and bearing arrangement are analyzed to validate the effectiveness of the high-speed Halbach-array PM rotor. A 50-kW, 9000 r/min ironless stator AFPM machine prototype with Halbach-array PM rotor is manufactured and tested. The measured results show that the output power is up to 53.8 kW at 9000 r/min. The feasibility of high-speed Halbach-array PM rotor and accuracy of analysis method are validated by both simulated and measured results.

Steadily increasing traffic volumes and traffic loads lead to a continuously growing demand for bridge rehabilitation, strengthening and replacement projects. For existing steel girder bridges with non-composite concrete decks, the traffic load capacity can often be increased significantly if composite action can be created afterwards. Different kinds of shear connectors are more or less suitable for post-installation. Coiled spring pins are one type of interference fit connector that can be installed from below the bridge deck during traffic, in order to minimize the impact on road users. This paper describes an experimental study on the static capacity and stiffness of coiled spring pins used as shear connectors at steel-concrete interfaces. Six push-out test series are presented, with a total of 28 tests, together with an alternative type of test set-up. The results show that the failure of the coiled spring pins is very ductile and that the load capacity is predictable and sufficient for a cost-effective application. The tests also indicate a significantly lower stiffness of the connectors in comparison to welded headed studs of similar dimensions, which might be of great importance if an existing shear connection is strengthened.

In this paper, the premature failure of the railway wheel shaft of power locomotive operated three million kilometres in China was investigated. Series of macroscopic and microscopic analysis was conducted to identify the damage degree and failure mechanism of the axle thoroughly, and the root causes of the unexpected failure were fully obtained. The results showed that the different extent damage (fretting damage, fatigue crack and corrosion) occurred in the interference fit of the wheel seats, gear seats and bearing seats without any material defect. In particular, plentiful cracks distributed on the wheel seat were sprouted in the subsurface and exhibited multi-source characteristics, which were fretting fatigue failure caused by interference fit under alternating loads of rotation and bending. The main reason of fatigue crack initiation is that there were numerous tangle and a pile-up of dislocations in the sub-surface of wheel seat position, which resulted in stress concentration at the grain boundary and phase boundary, and when it exceeded the strength limit of the material, the micro-crack would initiate and propagate. Therefore, to reduce the stress concentration at the wheel seat portion, the structure of the axle need to be further optimized, and the surface be strengthened also crucial for resisting the fretting damage.

The joining of machine parts by plastic forming is a common method for transmitting forces and torque. In drive trains, the ‘knurled interference fit’ has a high transmission capacity through the combination of frictional connection and form fit. In the present study, the shaft specimen made of C45 steel material is joined with an inner knurled hub made of 16MnCr5 case hardened steel. The influence of the joining process parameters on the torsional fatigue strength of the shaft-hub connection is investigated by means of experimental studies. The most important parameter is the chamfer angle of the knurled hub, which determines the rate of strain hardening in the material and differs between the cutting and forming joining processes. This study shows that knurled interference fit connections joined by forming achieve a higher fatigue strength and a higher maximum static torque than connections joined by cutting.

The contact stiffness of the spindle/tool holder is essential for the cutting stability of the spindle system because the elastic connection of the spindle/tool holder interface determines the dynamic characteristics of the spindle system. To predict the dynamic characteristics of the spindle system at the design stage, an analytical model of the contact stiffness of the spindle/tool holder interface was proposed based on the fractal theory and the multi-scale contact mechanics model to consider the combined effect of the cutting force and drawbar force on the contact stiffness. The fractal theory was used to characterize the micro-morphology of rough surfaces and the fractal parameters were identified by the power spectrum method. For the contact of two rough curved surfaces, the surface contact coefficient was introduced into the multi-scale contact mechanics model to correct the contact stiffness, the actual contact area and the contact stress. To verify the validity of the method, the experiments were conducted and the results showed that the modeling error of the contact stiffness was reduced from 25.13% to 4.72% by the proposed method. Finally, the effect of such factors as the cutting force, the mean roughness, the material properties, the preload and the temperature variation on the contact stiffness was discussed. The contact stiffness of spindle/tool holder interface increased with the cutting force and the drawbar force and that the contact stiffness decreased with the mean roughness. Moreover, the shear contact stiffness increased with the equivalent elastic modulus, the interference fit and the temperature. The conclusion was drawn that the model can be used to predict the contact stiffness of the spindle/tool holder interface at the design stage.

In machines and technological equipment for transmitting significant axial forces and torques, the connection of parts by interference fit is widely used. Such joints allow the transmission of significant axial forces and torques. An interference fit is used to connect various structural elements to the shaft instead of key, bolt and welded joints. They are more economical and rational in comparison with, for example, keyed joints, and the risk of a significant stress concentration in the places of keyed grooves also disappears. The strength of the connection in stationary fit is achieved due to the elastic, and sometimes also plastic deformation of the parts to be joined that occurs during the assembly process. The strength and relative immobility of such joints is ensured by the forces of friction between the mating parts, due to the magnitude of the interference fit. The aim of this work is to assess the dependence of the deflected mode of different types of profile joints with interference. The connections of round bushings with round, elliptical and hexagonal holes with shafts of the corresponding shape were investigated. Based on the ANSYS PC, the results were obtained, presented in the form of tables and graphs for the total displacements, contact pressures and equivalent stresses. The dependence of the deflected mode of the profile compounds of the indicated types on the thin-walled factor is shown. The practical significance of the obtained results consists in assessing the strength of the interference fit having a different shaft shape and their suitability for use.

In the present work, the finite element analysis of interference-fit rotor-stator assembly of orbital motor has been carried out. The main drawback of a running-fit orbital motor is the generation of gaps between the rotor and the stator under working conditions. Gaps generated at the transition contacts lead to fluid leakages from the High-Pressure Zone to the Low-Pressure Zone. These leakages cause a reduction in pressure differential. Due to this loss in pressure, the output torque as well as the overall efficiency is affected. Therefore, in order to overcome this drawback, interference is provided in the rotor-stator assembly. In the present work, the interference is provided by increasing the radius of the rollers. The contact analysis is carried out in ANSYS Workbench. The values of stresses and deformation for two different positions of the rotor is obtained.

Micropitting is a surface fatigue phenomenon that occurs in Hertzian type of rolling and sliding contact that operates in elastohydrodynamic or boundary lubrication regimes and can progress both in terms of depth and extent. If micropitting continues to propagate, it may result in reducing gear tooth accuracy, increasing dynamic loads and noise. Eventually, it can develop into macropitting and other modes of gear failure such as flank initiated bending fatigue. Micropitting has become a particular problem in the gear surface fatigue. Usually micropitting initiates in the dedendum of the driver and driven at the asperities on the surface. However, the authors found for some gears with interference fit connections of their conical surface, micropitting on the pinion occurs in the addendum. This study attempted to find the reason using a 3D&ndash, TCA method based on ISO/TR 15144-1 to predict the micropitting and try to understand the key influence likely to affect micropitting location.

Developing a method for disassembly damage evaluation is of great significance for the key components in maintenance and remanufacturing. Disassembly of the interference fit joint between the shaft and impeller, which could inevitably bring damages to the parts’ surface, was investigated. The ferromagnetic materials FV520B (impeller) and 40CrNiMo7 (shaft) were used in the disassembly experiments. Experiments showed that different damage degrees appeared on the disassembled interface as a result of single sliding friction under different loads. The stress concentration and plastic deformation stimulated changes in magnetic domains, which led to the distortion of surface spontaneous magnetic field and the induction of metal magnetic memory (MMM) signals. The tangential components of MMM signals had peak-trough features with zero-crossing points, and the normal components showed peak features. The visible features of the distorted MMM signals could locate the position of the defects. The average damage depth Sa, peak-trough difference Wpp and peak area S had been proposed as characteristic values. The linear relationship between Sa and Wpp, Sa and S was further obtained, respectively. It indicated that the MMM technique was capable of quantitatively evaluating the disassembly damage of ferromagnetic parts, which also provided a reference for the remanufacturability assessment and the selection of repairing processes in remanufacturing engineering.

Most mechanical joints are in one way or another exposed to some tear, wear, corrosion and fatigue, and likely to fail over time. If the contacting surfaces in a connection are exposed to tangential loading due to vibrations, small amplitude displacements called fretting can be induced at the surface, and might result in crack nucleation and possible propagation. The review and analysis reported herein are based on study of a wide range of reported literature during the last 25 years, and it looks into which methods, techniques and tools that have been used in those studies, including laboratory and full-scale testing, especially around fretting fatigue issues in interference fit joints, and pre-tension issues in pre-loaded bolts. In modelling of mechanical joints, the main techniques can be categorized under either stochastic (or probabilistic) type, where the random variation is usually based on fluctuations observed in historical data for a selected period of time using standard time-series techniques, or deterministic techniques, with analytical and numerical models and methods, which are widely applied. Analytical techniques typically include models like; Newton’s laws of motion, Laplace transformation methods, Lagrange differential equations, D’Alambert’s principle of virtual work, Hamilton’s principle, Fourier series and transform, Duhamel’s integral and Lame’s equations. Today, computers are widely used to find approximate solutions to complex engineering problems by combining the above-mentioned methods. A large number of these combined methods, also referred to as numerical methods, fall under finite element analysis (FEA). One way to reduce fretting issues in mechanical connections could be to increase the research and investigation effort on expanding pin solutions, which are different from the traditional press and shrink fit methods.

This paper aims to reveal the effect of different fasteners on the mechanical behavior and failure mechanism of composite interference-fit joints under assembly and quasi-static loading conditions. Composite single-lap and double-lap joints joined by conventional bolt and sleeved fasteners were focused on and their joint deformation and failure were characterized by the means of digital image correlation (DIC) and scanning electron microscope (SEM). Differences in failure load, bearing strength, joint stiffness, joint deformation and failure mode under different fastener fit types including neat-fit, interference-fit and interference-fit with sleeved fasteners were evaluated. Results show that the interference-fit with sleeved fasteners significantly improves the bearing performance of the joints. Under the same interference-fit, the initial failure load and ultimate bearing strength of sleeved fasteners for the composite double-lap joints are 33% and 12% greater than conventional bolt respectively. Moreover, the interference-fit with sleeved fasteners strengthens the joint bending stiffness and further alleviates the surface strain concentration compared with the interference-fit with conventional bolt. The conclusions in this article have a guiding significance for the design of composite interference-fit joints.

The bolted joint has frequently been used to join different components together for the composite materials. However, the effect of tolerance fit on mechanical properties of the composite bolted joint is still ambiguous. In this paper, a three-dimensional numerical model is established and validated by reference experiment for the single-lap composite bolted joint. Then the High Dimension Model Representation (HDMR) using Sobol method is employed to analyse the global sensitivity of tolerance fit, bolt clamping force and friction of contact interfaces. The sensitivity index indicates that the tolerance of composite hole is the most crucial parameter for the mechanical properties of composite bolted joint. Finally, the interval values of tolerance behaviours between bolt shank and laminate hole are investigated numerically based on Six Sigma analysis. The tolerance is analysed by considering the influences of perfect fit, clearance fit and interference fit on mechanical properties. This work provides a meaningful reference for selecting the tolerance fit for the composite bolted joint.

The performance of high-speed and high-precision machine tool spindle is quite sensitive to the variation of system parameters. How to accurately predict the influences of key parameters on spindle characteristics is important for designers to achieve required machining accuracy. In the assembly of spindle system, the interference fit, which is always used to connect bearing and shaft, affects the performances of spindle system directly. Therefore, the quantitative investigation on the effects of interference fit on spindle characteristics are of great practical significance. In this paper, the effect mechanism of interference fit on spindle bearing system is explored and used to modify the analytical spindle bearing model. Firstly, the internal geometric relationships among the assembly bearing parts and shaft is analyzed under the influence of assembly deformation and centrifugal expansion. Then, the static and dynamic characteristics of spindle bearing system, including the bearing stiffness, maximum loosing speed, spindle stiffness as well as modal characteristics, are predicted under different interference fit values based on the modified spindle bearing model. The results show that the interference fit will stiffen the bearing and spindle system and result in obvious increments on bearing stiffness, spindle stiffness as well as the natural frequencies. A specially designed spindle test rig is built to verify the simulation results, and the variation of spindle stiffness and natural frequencies are measured under different interference fit values. The maximum error of the system natural frequencies between the analytical results and the experimental data is 7.36%, which confirmed the accuracy of the proposed analytical model.

The fatigue behavior of aluminum alloy 7050-T7451 single lap four-bolted joints was studied by high-frequency fatigue test and finite element (FE) methods. The fatigue test results showed that a better enhancement of fatigue life was achieved for the joints with high-locked bolts by employing the combinations of cold expansion, interference fit, and clamping force. The fractography revealed that fatigue cracks propagated tortuously; more fatigue micro-cliffs, tearing ridges, lamellar structure were observed, and fatigue striation spacing was simultaneously reduced. The evaluation of residual stress conducted by FE methods confirmed the experimental results and locations of fatigue crack initiation. The extension of fatigue lives can be attributed to the evolution of fatigue damage and effect of beneficial compressive residual stresses around the hole, resulting in the delay of crack initiation, crack deflection, and plasticity-induced crack closure.

This attempt aims at investigating the Interference Fit Process as a procedure to arrest a detectable crack size in mechanical part. The 7075-T6 Aluminum alloy cracked SENT specimen is considered in the current work. A 2D- FE analysis is implemented to simulate the stress distribution around the expanded hole after Interference Fit Process. Lemaitre-Chaboche model was considered for describing the material behaviour. Both, fatigue life improvement and compressive residual stress distribution, arising from the Interference Fit Process, are predicted. Different crack lengths, different interference fit sizes and different crack arrest hole (CAH) diameters are investigated. In order to optimize the Interference Fit Technique's process parameters and study their effects and their interactions, the Response Surface Methodology (RSM) is implemented. Results show that higher fatigue life improvement is obtained at hole diameter equal to 6 mm, an Interference Fit Size equal to 0.2 mm and an initial crack size equal to 20 mm. The Design of Experiments (DoE) procedure can be used with the Interference Fit Process as an efficient tool to ensure the safety behaviour of cracked components.

According to the statistics, failure of gearbox often leads to the longest downtime and maximum economic loss for wind turbine. Operational experience reveals that damage morphology often occurs on planetary gear trains. Based on real cases, the hypothesis that failure developing process of planetary gear is divided into two stages including fretting wear and fatigue source generation has been proposed. For the fretting wear stage, the research work focuses on testing the hardness difference between gear inner surface and bearing outer ring, analyzing the influence of interference fit tolerance on fretting slip distance, and exploring the influence of gear hub thickness on fretting slip distance. The relevant technical improvement measures are proposed and following experimental data have shown these measures are quite effective. At the stage of fatigue source generation, the roundness error of gear inner surface and the profile error of tooth surface can affect the radial clearance of the meshing gear pair. As a result, uneven load region on gear inner surface appears. Following quantitative analysis of comprehensive stress on the uneven load region reveals the formation mechanism of symmetrical fatigue source, which has been verified by the real failure case eventually.

Bearing failures are one of the most common failure modes in the rotating machinery and equipment. Angular contact ball bearings are widely used considering their ability to carry the loads in both axial and radial directions, durability and low friction. The smooth functioning of these bearings greatly depends on the bearing load rating, material, type of fit with which it is assembled, the operating temperature and proper installation in the assembly. This paper presents the analysis of a failure of an angular contact ball bearing used in the gas motor system of an electrohydraulic control actuator used for launch vehicle attitude control. Detailed investigation of the failure is carried out by thermal and structural modeling of the bearing assembly, and the failure cause is identified as the combination of design error, hardware deviations and improper assembly operation which led to bearing misalignment and very high loading of the first row of balls resulting in excessive heating. The failure theory explains all the observations on the parts of the failed bearing. The physics of failure is understood, corrective actions to avoid the failure are addressed, and the strategies for prevention of similar failures are evolved.

Load capacity of keyway couplings is usually calculated according to standards (e.g. DIN6892, DIN743) based on nominal stress and simplifying assumptions dating back to several decades. Detailed modeling of keyway couplings is still a research topic, because of the complex mechanical behaviour involved. Moreover, the current standards apply only to usual geometries the designer sometimes needs to depart from, especially for the sake of compacity. This is the case in gearmotors, where the input pinion is directly fixed on the electric motor shaft. This requires, for small diameter pinions, that the pinion shaft be inserted in the hollow motor shaft end. In the design investigated hereunder, a special key is built in an opening in the hollow shaft wall. This design is substantially different from usual shaft-hub connections; it combines a geometrical notch with an interference fit, and is submitted to a peculiar stress distribution. This article explains the detailed investigations made on such a connection. After summarizing the different possible failure modes on classical keyway connections, it explains how a simple interference fit behaves under an external load. Despite its inherent limitations, a FE model gives valuable insight into the connection behaviour : especially the influence of the interference fit, the load combination and the progressive stress stabilization after a few revolutions, due to the combination of friction and relative deformations. Static test results are then presented, and the challenges of a realistic fatigue tests are analyzed. A simplified dimensioning strategy is finally set out, which is more suited to practical application in the design office.

In mechanical engineering the following profile connections are applied most often: with three sides (P-3); with three cut off sides (PC-3); with four cut off sides (PC-4) and with five sides (P-5 and PC-5). Despite considerable results, in the field of studying of stresses and deformations at contact interaction of solid bodies of various forms there is an unresolved number of tasks, which are of scientific and practical value. As the analysis of theoretical and experimental studies of motionless detachable and non-detachable connections (cylindrical, profile) has shown, there are unresolved tasks, in particular regarding the choice of geometrical form of contour curves, the magnitude of interference fit of motionless, non-detachable profile connections with equiaxial contour. The working capacity and reliability polygon profile connections with interference fit is defined by their strength, that is ability of elements to resist strain when in use. For the purpose of determination of working capacity of polygon profile connections with interference fit with respect to strength, stresses and deformations arising in hub with polygon profile opening from the action of polygon profile shaft installed in a nave with interference fit. The article considers the technique of conducting experimental studies by strain-gauging method for the purpose of assessing the influence of structural parameters and external loadings on stress-strain state of parts of the connection. Based on the experimental results tables of comparative characteristics of the recommended types of interference fits for P-3 profile connections and also the recommended interference fits for the corresponding n values of P-3 profile shaft-nave connections applied for tooth gearings were composed.

The proper interference fit between the joined parts is a prerequisite for an effective pressure joint. The main purpose of the pressure joint is to transfer tangential, radial and axial loads between the joined parts. In order to provide proper functioning of the machine assembly (whose component parts are connected by the pressure joints), i.e. the transfer of loads without skidding, it is essential to determine the pressure joints interference fit parameters. The new methodology for the conveyor idlers pressure joints quality control is presented in this paper. The procedure for the analytical determination of the expected disassembling force (limiting value) in the pressure joints between the shaft – rolling bearing and the bearing – idler shell is described in detail. The analytically calculated boundary values are compared with the experimental ones. According to the presented criteria, the evaluation of the conveyor idler fits quality was performed and reliable conclusions were successfully adopted.

In the research article, Friction welding was done by joining two different boiler grade materials using an external tool. This research was carried to certify and upgrade mechanical and metallurgical properties by metal joining method. Taguchi L 9 optimization technique is used to analyze that most significant input parameter that produce capital joint strength and a set of observations are splitted into specific components by ANOVA. In this study, compressive strength is considered as an output specification that proves the capital peerless strength of the samples. This investigation was carried out by comparing with supporting block samples from the conditions clearance fit and interference fit. By comparing supporting block condition in both clearance and interference fits exhibit the welding research area detected as 2355.30 MPa and 2371.41 MPa respectively.

Interference fit joints have been widely used in many engineering constructions, in particular in electric motors. It is of particular importance to calculate the load capacity of press-fit joints, especially in the overload ranges of construction to estimate the safety factor. The article presents a FEM numerical simulation of pressing the shaft into the hub, taking into account various types of fits. The results of numerical simulations presented in the article were positively verified with the MTS measuring device, which confirmed the correctness of the numerical model. So far, the load-bearing capacity of press-fit joints has been calculated from Lame’s formulas. The results of the load capacity of the joints obtained by the FEM simulation were compared with the results obtained from Lame’s formula. The comparison shows that when designing interference fit joints, attention should be paid to the fact that the press-in process, depending on the type of fit, may be elastic-plastic. Plastic deformations in the contact zone of the joint affect its load-bearing capacity. Therefore, the design of press-fit joints should not be based on Lame’s formulas, which do not take into account the range of plastic work of the material.

A bushing is usually assembled with the small end of a connecting rod in an engine by an interference fit. Inappropriate interference or insufficient stiffness of the small end will cause loosening of bushing. Since the bushing loosening often occurred in the development process of the studied V-type diesel engine, the pressing force applied to push the bushing out of the small end was used to evaluate the tightness of the connection between the bushing and the small end. In this paper, the influence of bushing thickness and interference on the pressing force of the bushing of the connecting rod small end in the V-type diesel engine was investigated by finite element method. Considering the strength of the bushing and the stiffness of the connecting rod small end, the suitable bushing thickness and interference for this connecting rod small end were obtained and verified in practice.

Since high-performance composite materials were widely used in various fields, composite fasteners’ connection technology has been a research hotspot. In this paper, a new type of interference-fit fastener was proposed and manufactured. Pull-through resistance tests were conducted to explore the pull-out performance of the fastener. The installation and pull-out process were analyzed by a finite element method . The simulated pull-out force well matched the results of the tests. The main failure modes of the composite plate are matrix damage and delamination. The simulation results showed that the extended length of the expansion sleeve, the length of the reducer segment, the extension length of the nut, and the interference size greatly influence the joint’s performance. Based on the response surface method (RSM), the structural parameters that affect the fastener’s pre-tightening and pull-out performance were optimized. The optimal parameter combination of the interference-fit fastener was obtained.

Purpose Shrink fit is an important method used in mechanical transmission, but the design of these connections is not sufficiently precise due to lack of knowledge regarding the effects of many parameters. The paper aims to discuss these issues. Design/methodology/approach This paper presents the torque capacity and contact stress analysis for a new shrink disc by numerical analysis and experimental methods. Torque capacity analysis aims to predict the effectiveness of mechanical transmission, and to check the structural safety. Stress-strain curves are measured using the universal testing machine, and Bilinear Kinematic Hardening rate-independent plasticity model characterises the elastic-plastic response of the materials. Findings The numerical result shows that there is no plastic deformation at the interference regions, and the maximum equivalent strain happens on the inner ring. The stress of outer ring is decreased with radius increasing, and shows a periodic variation along the circumference, but stress concentration happens at the threaded holes. Finally, the torque capacity of the shrink disc system is measured through a developed test machine, and the torque capacity difference between numerical and experimental results is about 3.3 per cent. Originality/value This paper presents a numerical and experimental carrying capacity analysis for a shrink disc. Plasticity model characterises the materials’ elastic-plastic response based testing. A test machine is designed to measure the torque capacity; the error is about 3.3 per cent.

Assembling wood structure involves fastenings in jointing wood members. The strength and stability of wood structure strongly depend on these fastenings that hold wood members together. Nails are one of the most common mechanical fastenings used in wood construction. Wood is a cellular and orthotropic bio-material. For utmost rigidity, strength, and service of wood-nailed joint, the nail requires joint designs adapted to the maximum strength properties of wood along and across the grain. The traditional model for prediction of withdrawal load of nails driven into side grain of wood was purely empirical, which was built on a statistical approach. A model based on the Coulomb’s friction law, the contact pressure of interference fit, Hankinson’s off-axis baring strength, and assumed honeycomb microstructure of wood cell was proposed and validated. When compared with experimental data of nail withdrawal load, this model not only showed better prediction of nail withdrawal load than the traditional model but also bears a physical meaning.

In aircraft structures, a variety of lug joints are casted extensively to couple primary structural components. These lug joints are normally fabricated by a single pin or bolt type of fasteners, which leads to a simple joint that is easy to assemble and disassemble. The lug can act as a pivot since clamping of the joint is normally not allowed or acceptable. However, the elastic stress concentration for attachment lugs is very high, and this high stress concentration at the edge of the hole influences crack initiation and crack growth life. The analysis of these problems becomes more complex when there is a loss of contact between the pin and the lug which ends up in contact stress non-linear moving boundary value problems. Integrity of these lug joints becomes primary concern, since their failure can cause a catastrophic failure of the structure. This has led to mandatory implementation of structural health monitoring (SHM) concept at these censorious locations during the design and operational phase of the flight vehicles. The interference fits in particular, tend to reduce the alternating part of the stress variation at critical locations at the expense of increase in mean stress associated with pre-loading condition. There is a reasonable premise for expecting a better fatigue strength and fatigue life from interference fits. This paper addresses prognostic analysis of both interference and clearance fit lug joints to estimate the residual life of these joints and feed into the analysis of SHM methodology.

Positive displacement motor (PDM), which is prone to high temperature fatigue failure, can be weakened in its application in deep and superdeep well. In order to study the forced state, deformation regularity and thermal hysteresis of PDM motor, the paper established the three-dimensional thermal-mechanical coupled Finite element model (FEM). Based on the theoretical research, experimental study and numerical simulation, the study found that the displacement of stator lining shows a sinusoidal variation under internal pressure, when adapting the general form of sine function to fitting inner contour line deformation function. Then the paper analyzed the hysteresis heat generating mechanism of the motor, learning that hysteresis thermogenous of stator lining occurs due to the viscoelastic of rubber material and cyclic loading of stator lining. A heartburn happens gradually in the center of the thickest part of the stator lining as temperature increases, which means work efficiency and service life of PDM will be decreased when used in deep or superdeep well. In this paper, we established a theory equation for the choice of interference fit and motor linetype optimization design, showing hysteresis heat generating analyzing model and method are reasonable enough to significantly improve PDM’s structure and help better use PDM in deep and surdeep well.

The hypercompressor is one of the core facilities in low density polyethylene production, with a discharge pressure of approximately 300 MPa. A packing cup is the basic unit of cylinder packing, assembled by the interference fit between an inner cup and an outer cup. Because the shrink-fitting prestresses the packing cup, serious design is needed to gain a favorable stress state, for example, a tri-axial compressive stress state. The traditional method of designing the interference fit value for packing cups depends on the shrink-fit theory for thickwalled cylinder subject to internal and external pressure. According to the traditional method, critical points are at the inner radii of the inner and external cup. In this study, the finite element method (FEM) has been implemented to determine a more accurate stress level of packing cups. Different critical points have been found at the edge of lapped sealing surfaces between two adjacent packing cups. The maximum Von Mises equivalent stress in a packing cup increases after a decline with the rise of the interference fit value. The maximum equivalent stress initially occurs at the bore of the inner cup, then at the edge of lapped mating surfaces, and finally at the bore of the outer cup, as the interference radius increases. The traditional method neglects the influence of axial preloading on the interference mating pressure. As a result, it predicts a lower equivalent stress at the bore of the external cup. A higher interference fit value accepted by the traditional method may not be feasible as it might already make packing cups yield at the edge of mating surfaces or the bore of the external cup. Along with fatigue analysis, the feasible range of interference fit value has been modified by utilizing FEM. The modified range tends to be narrower and safer than the one derived from the traditional method, after getting rid of shrink-fit values that could result in yielding in a real packing cup.

The interference-fit technology is an effective way to enhance fatigue life of mechanical structures. However, for composites, oversized interference-fit percentage causes damages and then decreases the joint performance directly. Influence of percentages on stress and damage around Carbon Fiber Reinforced Plastics interference-fit hole is analyzed in this paper. The progressive damage theory is introduced into a three-dimensional finite-element model, which consists of the mixed failure criteria combining Hashin criteria and maximum stress criteria and the corresponding property degradation rules. A nonlinear shear stress–strain relationship is also built to solve the nonlinear material behavior. Three groups of 0.4%, 0.8%, and 1.2% interference-fit percentages are analyzed. Corresponding pin installation experiments are conducted to validate the accuracy of the model. The inserting force, stress distribution, and damage initialization around the hole are investigated and discussed in this model.

The wide application of composite materials in aerospace raises a new challenge for the joining technology. Though interference-fit can enhance joint strength, potential delamination damage also emerges for oversized percentage. A delamination analytical model during the interference-fit pin installation process is established in this paper. It consists of the critical delamination force (CDF) induced by mode I delamination and the pin-hole friction. The establishment of CDF model is based on fracture mechanics, classical bending plate theory and the mechanics of composites, and the friction model is built with classical anisotropic plate theory and friction law. Cohesive element (CE) based delamination simulation with bilinear softening constitutive law is made, and corresponding pin installation experiments are also conducted. The effect of interference-fit percentages and residual layers on CDF was analyzed and the critical interference percentage below which delamination-free hole can be obtained was also proposed. Finite-element delamination results and experimental delamination specimens were analyzed and the rationality of the model was testified. Keywords: Composite structure, Interference-fit, Installation process, Delamination mechanism

In a strip winding process, the sleeve is a hollow cylinder that is mounted between a strip coil and a mandrel to maintain uniform coil shape when the strip coil is very thin, but its deformation behavior has not been investigated before. Thus, a finite element (FE) model was presented to calculate the stress distribution in a sleeve and strip coil when 1 — 3 mm-thick stainless steel was wound around the sleeve. The FE model was developed by extending a previous model by adding a sleeve between the mandrel and strip, and by modifying the boundary and interaction conditions. The strip winding process was divided into an initial process and a steady-state process. During the initial process, the minimum and maximum pressure required on the belt wrapper to maintain coil shape by self-friction of the strip was calculated by the FE model when the belt wrapper is ejected at the end of the initial process. After the initial process, an analytical model of the steady-state process was established to calculate the stress distribution and was compared with the FE model to validate it. The suggested analytical model took 11 s to give the same stress distribution that the FE model took 30 d to produce.

Interference on the rolling elements of bearings is necessary to avoid slippage at high rotation speeds or at low bearing load and exact deviation of control surfaces of the control systems of the aircraft. The aim of this work is to reveal and study the influence of interference on the rolling elements of a ball bearing for radial and axial displacements of the bearing rings. In this work was carried out a review of methods and mathematical models for calculating the bearings; performed their analysis based on which a method of calculation of the bearing was selected to conduct our research. The selected methodology takes into account many different parameters and factors, moreover, it was experimentally confirmed with sufficiently high accuracy. The calculation was performed numerically by the method of iterations. The following bearing and parameters were adopted as baseline for the research: bearing № 126126, axial load Fa = 3000 N, radial load Fr = 750...20000 N, interference δ = 0...0.03 mm, the shaft speed n = 10000 rpm. Graphs of interdependence between the radial and axial displacements of the rings and the magnitude of interference of rolling element were drawn according to the results of the calculations. Analysis of the graphical interdependency has shown that increasing interference on the balls decreases the axial and radial displacement of the bearing rings linearly. The results obtained were compared with the results of similar studies of angular contact ball bearings used in machine tool spindles. It should be noted that in these works under interference is understood the provisional value of the axial force acting in the bearings which are installed in the spindle full-length scheme. Since the works are not given data on the magnitude of interference fit on the rolling elements, to compare the results of studies is not possible. It may be noted that interdependence on the displacement of the rings and stiffness coefficients are correlated, which gives an indication of the reliability of the results. It may be noted that interdependence on the displacement of the rings and stiffness coefficients are correlated, which gives an indication of the reliability of the results.

A semi-empirical fatigue life prediction model for riveted lap joints representative of the aircraft fuselage skin connections is developed. The effect of the interference fit between the rivet and the hole is taken into account utilizing fatigue test results for 2024-T3 Alclad aluminium alloy coupons with an open and filled hole. The effect of contact surface friction is considered based on comparisons between the fatigue lives of lap joints from 2024-T3 Alclad sheets and universal rivets with the Alclad contact surface and the fatigue lives of similar joints with the Teflon interfoil which eliminates friction between the sheets. Dependencies between coefficients incorporated into the model to account for the above mentioned effects and several quantities related to the amount of rivet squeezing, and thus representative of the riveting process, are provided. The fatigue life is assumed to be controlled by the local stress amplitude at the critical location of a joint. Analyses of the fatigue test results for the 2024-T3 riveted joints prove that the local stress estimated using the superposition approach can adequately represent the combined effect of the applied loading, interference between the rivet and the hole and faying surface friction condition on the fatigue life. The adequacy of the proposed model is substantiated by a good agreement between the fatigue lives predicted and observed for lap joints from D16 aluminium alloy sheets and round head rivets.

Permissible internal pressure in dies for cold extrusion may be increased by the use of one or two shrink rings. The design essentially boils down to defining the diametrical interference fit of the die/ring assembly. There are two methods of design: analytical one based on Lame’s solution and numerical one based on finite element modelling (FEM). None of these methods includes roughness of the interface surfaces of the die insert and the shrink ring. However, when designing the pre-stressed micro-dies, the interface roughness cannot be disregarded and the classical design of the diameter interference must be corrected. In this paper, a semi-physical modelling of interface roughness (SPMIR) is used as novel method which determines the interference correction value. A set of FEM models created on the base of Abbot-Firestone curves, determined from the roughness profile, enables determination of a contact surface stiffness curve and further the interference correction. Relative correction of the die diameter interference increases with the diameter decrease, which might be recognized as a pre-stressed micro-die assembling scale effect. In the experimental part, three miniature dies, with interface diameter 2.8 mm and different levels of interface surface roughness, Ra=0.16, Ra=0.43, Ra=0.60, have been manufactured by WEDM. Relative interference corrections calculated by the SPMIR method reached respectively 17.6, 27.9 and 43.3 %. A practical design advice has been formulated as follows: interference correction based on the interface surface topology is recommended for micro-dies with the interface diameter less than 10, 15 and 25 mm, for the three levels of the surface roughness investigated.

The analysis of interference-fit joints process and theirs strength, by finite element method (FEM) in FEMAP v. 11.2 numerical system is presented. The results of the analysis are compared with the numerical results obtained with the Lame calculations. All results were also verified experimentally with the MTS measurement system.