Interference Fit Research Articles

Vibration Characteristics of a Rotor System with Coupling of Insufficient Interference Fit of Disc-Shaft and Pedestal Looseness

Vibration Characteristics of a Rotor System with Coupling of Insufficient Interference Fit of Disc-Shaft and Pedestal Looseness

Experimental measurements of femoral primary stability in two cementless posterior-stabilized knee replacement implants

Sufficient primary stability through interference fit is required for bone ingrowth and subsequent long-term fixation of cementless knee replacement implants, and can be evaluated in experimental testing. In this study, primary stability of a novel posterior-stabilized (PS) femoral component (Attune PS) and a contemporary PS component (Triathlon PS) were analyzed, and compared to previous outcomes of cruciate-retaining (CR) implants. Potential bone ingrowth was evaluated by measuring micromotions over the implant−bone interface in six cadaveric femur pairs under two loading conditions using digital image correlation, for a paired comparison of the PS implants. Push-off forces required to achieve implant removal under high-flexion were determined as a measure of implant fixation. Achieved interference fit was determined by reconstructing the implant positions through use of separate implant and resected bone geometries. Lower overall micromotions and a higher average push-off force were measured in the Attune PS implant, indicating increased initial fixation compared to the Triathlon PS design. Interference fit was significantly higher for the Attune PS and was related to lower gait micromotions in Triathlon and overall PS groups. Based on reported clinical results and the comparison with available CR implant results, both PS implants are expected to provide sufficient initial clinical stability.

Analysis of Interference-Fit Joints

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.

Design of adaptive optics by interference fitting: Theoretical background

Interference-fit joints are typically adopted to produce permanent assemblies among mechanical parts. The resulting contact pressure is generally used for element fixing or to allow load transmission. Nevertheless, some special designs take advantage of the contact pressure to induce desiderata deformation or to mitigate the stress field inside the structure. Biased interference fitting between a planar mirror and an external ring could be used to induce the required curvature to realize new adaptive lens for optical aberration correction. Recently, thermally-actuated deformable mirror on this principle based, was proposed and prototyped. Although the feasibility and utility of such innovative lens was demonstrated, no comprehensive theory was developed to describe mirror behavior and predict their curvature. Nowadays, the use of approximated numerical approach, such as the finite element method, is the only way to study the interaction between biased and interference fitted bodies. The paper aims to give the theoretical background for the correct design of adaptive lens actuated by interference fitting. A new formulation for the curvature prediction is proposed and compared with finite element analysis and available experimental measurements.

Comparison of Initial Stability of Oblong, Large Circular, and Multiple-Plug "Snowman" Osteochondral Autografts for Elongated Focal Cartilage Lesions: A Biomechanical Study in a Porcine Model.

Background:Distal femoral osteochondral allograft transplantation (OAT) is an effective treatment of osteochondral lesions in the knee measuring >2 cm2 in select patients. Prior studies have demonstrated that the morphology of the plug can affect graft-host interference fit. To our knowledge, there are no data comparing the initial biomechanical stability of standard cylindrical plugs with multiple-plug and oblong-plug morphologies.Hypothesis:Large cylindrical single-plug (LCSP) and oblong single-plug (OSP) grafts will have greater pull-out strength, and therefore greater initial stability, than multiple-plug (MP) grafts in a cadaveric porcine femur model.Study Design:Controlled laboratory study.Methods:A total of 55 porcine distal femurs were divided into 3 groups—LCSP (n = 18), OSP (n = 19), and MP (n = 18)—according to the plug morphology used. The method of graft harvesting and implantation was based on technique guides for the respective implant systems. The sizes (length × width × depth) of the osteochondral defects created in each of the groups were approximately 20.2 × 20.2 × 9.4–mm for the LCSP group, 14.4 × 30.5 × 7.9–mm for the OSP group, and 14.8 × 14.8 × 9.9–mm for the MP group. Tensile testing was performed on each graft to determine pull-out strength.Results:The pull-out strength was significantly lower in the OSP group (65.7 N) versus the LCSP (133 N; P = .0005) and the MP (117.6 N; P = .001) groups. There was no statistically significant difference in pull-out strength between the LCSP and MP groups (P = .42). There were no statistically significant differences in displacement at maximum load among any 2 of the 3 groups.Conclusion:These findings suggest that while initial stability may play a role in the clinical outcomes of osteochondral allograft (OCA) implantation, the biological milieu in vivo for each graft setting perhaps has a greater impact on the success of an OAT procedure. Further study is needed on the relationship between OCA biomechanics and clinical outcomes of OAT.

Research on Complex Product Parts Matching by using Improved Taguchi Method

With the development of intelligent manufacturing, the key strategic of complex equipment is becoming more and more obvious. How to realize the assembly of complex products has become the focus of intelligent manufacturing. This paper puts forward the improved Taguchi method to dimension chains measures, by using different quality loss function to different dimension chains, the cores are the Nominal-is-best, non-core is measured with the improved Smaller-is-better to improve convergence perusal and increase matching rate; General adopt Smaller-is-better to enhance assembly accuracy, reduce interference fit and assembly cost. Then the dimension chains quantitative model of complicated product assembly by using the signal-to-noise ratio and different weights is built up. The model contains modeling assumption, the objective function and the matching model. And this model is regard as the fitness function of genetic algorithm. Finally, the feasibility and efficiency of the scheme are verified by the case study.

505 Failed Femoral Nail with Significant Operative Technical Difficulty: A Practical Solution to Achieve Metalwork Extraction Using Conical Screw Remover

Abstract Introduction There is a greater risk of delayed healing and revision surgery in atypical femoral fractures (AFFs). Although non-union in reamed intra-medullary (IM) nailing is relatively uncommon, it can lead to fracture of the nail and present a considerable challenge to the treating surgeon. Case Report We present a case of AFF treated with IM nail fixation. Metalwork failure of the nail prompted removal of distal locking screws and plating of the fracture site at 8 months. Failure of the plate-bone interface 3 months later led to further revision surgery to remove the broken metalwork. We focus on the significant operative difficulty encountered during removal of the failed IM metalwork and provide a novel practical solution to overcome this particular challenge - insertion of a conical cannulated screw remover under fluoroscopy guidance to create an interference fit with the distal segment of the broken nail. Discussion This case is an example of significant and unexpected intra-operative technical difficulty, requiring improvisation and teamwork to manage. We introduce an accessible and uncomplicated alternative to the existing techniques for removal of a broken femoral nail and in doing so hope to benefit peers and colleagues should they encounter similar difficulties in the future.

Leakage analysis of B shape ring self-energized seal in high pressure polythene polymerizer due to the aging of its nonmetallic ring

B shape ring with metal and nonmetallic materials is often used in the high-pressure polythene polymerizer for the self-energized seal. However, many factories reported that leakages often occurred when pressure is lower than 30 MPa, especially during the shutdown after a long period of operation. In this paper, the nonmetallic material Valqua 6502 were aged at 270 °C for 60 days, which is close to the working conditions of polymerizer. The compression and resilience abilities were tested and compared with those before aging. It reveals that the temperature aging reduces both compression and resilience abilities of the nonmetallic materials. FEM model was worked out for the simulation of sealing performance, which includes working conditions such as the assembly of the self-energized structure, the start up with temperature and pressure rise and the shutdown with temperature and pressure drop. It reveals that the sealing performance is not only influenced by the aging of nonmetallic ring, but also related with the interference fit to nonmetallic ring and clearance fit to the metal ring. Another kind of nonmetallic material XX300 was also aged as comparison, which performed better than the currently used one. With parameter studies, optimal interference and clearance fit were worked out for XX300 but failed for 6502. Therefore, when B shape ring with nonmetallic and metal materials works under high temperature and high pressure, the aging of the nonmetallic material should be considered to avoid decreasing its deformation and resilience ability and harming the sealing performance.

Evaluating load distribution at the bearing-housing interface using thin film pressure sensors

The objective of this investigation was to utilize thin film pressure sensors to evaluate the pressure distribution between rolling element bearings and a housing. A test rig was constructed to place thin film sensors around the perimeter of a test bearing inside of a housing. High precision drive shafts were manufactured that produce a light and heavy interference fit with each of the test bearings. Pressure map results are used to evaluate the effect of internal clearance on the load distribution of different bearing types. The thin film sensor system was also used to investigate the circumferential load distribution on the housing. The presented apparatus and test method could be used to validate bearing fit selection and housing design.

Torque capacity of the multilayer interference fit based on a friction coefficient prediction model

This paper proposes the theoretical model of a multilayer interference fit and gives out the relational expression between radial interference and friction coefficient. Taking the typical wind turbine's shrink disk of a three-layer interference fit structure as an example, special experimental equipment is developed to test the torque capacity. Based on experimental results and the theoretical model, the mathematical expressions of radial interference and assembly stroke for friction coefficient are obtained by polynomial fitting, and the prediction model of friction coefficient is established. The three-dimensional finite element model of a shrink disk is constructed by applying the friction coefficient prediction model. With the mathematical expressions of radial interference and assembly stroke for the torque capacity, the rules of main dimension parameters and torque capacity are analyzed. The maximum relative error between experiment and simulation is 8.2%, which shows the feasibility of finite element simulation. The results of our study have certain guidance for the prediction of friction coefficient and the manufacture of the multilayer interference fit.

Design of a novel midstream fluid waste sample collection device for patients

Reducing the contamination rates in mid-stream urine samples is a challenge. A novel design for a mid-stream urine sample collection device, which uses a novel mechanism to separate the mid-stream flow from the fore-stream and end-stream flows based on flow speed, is presented. The device, supplied in two parts, is designed to be clipped to a toilet and used in a seated position, which improves ease of use for disabled patients. As there is no mixing of the flow types during use, it is hypothesised that contamination rates should be lower than many competing designs. The all-polymer design is easy to use by both men and women, due to the addition of a form-fitting funnel and is designed to collect samples directly into containers of the same standard currently issued, allowing easy and hygienic collection. Due to its complex shape, the main body of the device is produced by a non-conventional injection moulding process. The holder can be produced using standard injection moulding technology. The two parts are designed to be assembled together by the user by means of a simple interference fit, which removes the cost of assembly altogether.

Research on quality detection method for axis-hole interference fit based on laser ultrasound

The interference fit quality determines the equipment’s service performance. In this work, interference fit assembly quality was evaluated using a laser ultrasonic method, including the assembly state of the interference fit. The power spectral density was used to calculate the power of the guided waves, and an interference assembly state evaluation method was proposed. Contact edge micro-cracks were identified by acquiring the full-field waveform propagation diagram, and these cracks were located by coupling the scanning area with the crack location. The center coordinate error for crack detection, which can basically determine the exact crack location, ranged between 0.09 mm and 0.15 mm. The length and width measurement errors ranged from 0.01 mm to 0.04 mm and 0.02 mm to 0.09 mm, respectively. The relationship curve between the guided wave power and interference was obtained experimentally. This method provides a new method for detection of the interference assembly structure state and the micro-cracks.

A Novel Parametric Design Method of Three-section Bioabsorbable Interface Screw

Bioabsorbable interface screw is a kind of fixation instrument which uses interference fit to produce tightening force. The mechanical properties of interface screws, which are mainly used for cruciate ligament reconstruction surgery, have a strong correlation with thread parameters. Due to the different contact stresses caused by the different contact environments of each section of the interface screw after knee ligament reconstruction, this paper proposed a parametric design method for the three-section interface screw. In this study, the cross-section perpendicular to the axis was used as the reference plane for modeling, and a mathematical model of the structural parameters of each cross-section was established. Finally, through the python module of the open design platform GRASSHOPPER, the mathematical model established was applied to the parametric design of the interface screw.

Multi-objective intelligent cooperative design for interference fit of the conical sleeve

Multi-objective intelligent cooperative design for interference fit of the conical sleeve

Dual pitch screw design provides equivalent fixation to upsized screw diameter in revision pedicle screw instrumentation: a cadaveric biomechanical study

Background ContextThere are situations that require the replacement of pedicle screws. They are often exchanged when loose or broken or to accommodate a different sized rod or pedicle screw system. Traditionally, pedicle screws are replaced by up-sizing the core diameter until an interference fit is obtained. However, this method carries a risk of pedicle screw breach. PurposeTo determine if dual pitch screws, with cancellous pitch in the vertebral body and cortical pitch throughout the pedicle, allows for in-line screw revision without upsizing screw diameter. Study DesignCadaveric biomechanical Study Patient SampleNot applicable Outcome MeasuresNot applicable MethodsPedicle screws were tested in the lumbar vertebrae from eleven cadavers. Standard pitch 5.5 mm screws were inserted and loaded using a "break-in" protocol. Screws were removed and replaced with one of four screw types: 5.5 mm Standard Pitch, 5.5 mm Dual Pitch, 6.0 mm Standard Pitch, or 6.0 mm Dual Pitch. Failure testing was done using a stepwise increasing cyclic loading protocol for 100 cycles at each increasing load level. The loading consisted of a combined axial and bending load simulating the load seen by the most inferior screw. ResultsFailure was consistent, with the tip of the screw displacing inferiorly into the vertebral body while simultaneously pulling out. Failure strength was lowest in the 5.5mm Standard (135.8±29.4N) followed by 6.0mm Standard (141.8±38.6N), 5.5mm Dual (158.1±53.8N), and 6.0mm Dual (173.6±52.1N, p=.023). There was no difference in the failure strength between the 5.5mm Dual and 6.0mm Standard. Lumbar level (p=.701) and donor spine (p=.062) were not associated with failure strength. ConclusionsAfter pedicle screw removal, screws with a larger core diameter or with a dual pitch have similar failure strengths. Dual pitch screws may allow for in-line revision of screws without upsizing screw diameter, minimizing the risk of pedicle breach or fracture. Clinical SignificanceDual pitch screws, with cancellous pitch in the vertebral body and cortical pitch through the pedicle, allows for in-line revision of pedicle screws without upsizing screw diameter; reducing the risk of pedicle breach or fracture when exchanging screws.

Determinants of the primary stability of cementless acetabular cup implants: A 3D finite element study

Primary stability of cementless implants is crucial for the surgical success and long–term stability. However, primary stability is difficult to quantify in vivo and the biomechanical phenomena occurring during the press–fit insertion of an acetabular cup (AC) implant are still poorly understood. The aim of this study is to investigate the influence of the cortical and trabecular bone Young's moduli Ec and Et, the interference fit IF and the sliding friction coefficient of the bone–implant interface μ on the primary stability of an AC implant. For each parameter combination, the insertion of the AC implant into the hip cavity and consequent pull–out are simulated with a 3D finite element model of a human hemi–pelvis. The primary stability is assessed by determining the polar gap and the maximum pull–out force. The polar gap increases along with all considered parameters. The pull–out force shows a continuous increase with Ec and Et and a non-linear variation as a function of μ and IF is obtained. For μ > 0.6 and IF > 1.4 mm the primary stability decreases, and a combination of smaller μ and IF lead to a better fixation. Based on the patient's bone stiffness, optimal combinations of μ and IF can be identified. The results are in good qualitative agreement with previous studies and provide a better understanding of the determinants of the AC implant primary stability. They suggest a guideline for the optimal choice of implant surface roughness and IF based on the patient's bone quality.

Interference and thickness design of bushing of connecting rod small end for Anti-loosening

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.

Accounting method for residual technological stresses in modeling the stress-deformed state of a railway wheel disk. Report 1

The work is devoted to development of a method for accounting residual technological stresses in wheel disks, which will provide both the versatility of the approach and the accuracy of calculations. The analysis of stresses in the wheel disk from the action of assembly (interference between the hub and the axle) and operational loads is carried out on basis of the results of finite element modeling. Verification of adequacy of the used model was made by comparing the calculated information with the experimental data of JSC “VNIIZHT”. The analysis of calculated and experimental values of radial stresses was carried out for the most loaded (critical) zones of the disk during operation – the zones of its interface with the rim and the hub. It was found that by setting the interference fit value to be greater than the actual one, it is possible to obtain the formation of additional stresses in the wheel, which, with a sufficient degree of accuracy, reflect the effect of residual technological stresses on its stress-strain state. On the example of calculating a wheel with a flat-conical disk (GOST 10791 – 2011), it is shown that an increase in the interference fit value by 60 % (from 0.25 mm to 0.4 mm per diameter) makes it possible to adequately predict the magnitude of stresses in the most critical disk elements. The maximum relative deviations of the calculated values of radial stresses from the experimental ones, both along the outer and inner sides of the wheel, do not exceed 14 %. Despite the simplicity of implementation, the proposed method provides an increase in the accuracy of predicting the strength characteristics of wheels, as well as the possibility of using it for various standard wheel sizes.

APPLICATION OF MECHATRONIC MODULES IN HEXAPODS TO AUTOMATION OF JOINTS ASSEMBLING


 
 
 
 The paper deals with the advantages of using mechanisms with parallel kinematics for the assembly of interference fits. The analysis of applicability of various types of actuators in hexapods is carried out, their main advantages and disadvantages are revealed.
 The main features of the construction of mechatronic systems with electromechanical and electrohydraulic drives are considered, the analysis of energy transitions in each type of drive is carried out.
 Comparative assessments of the technical characteristics of the actuators are carried out: in terms of load capacity, accuracy and speed.
 
 
 

A new model for stress analysis in pin–Plate interference fit joints under tension loading

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.