Thread Friction Research Articles

The prediction of bolted joint loosening state under transverse load based on a data-driven model

The impact of transverse load results in the loosening of bolted joints. The loosening condition is determined based on the transverse load and relevant parameters of the bolted joint. To efficiently forecast the loosening state of bolts under various transverse loads and relevant parameters, this study proposes a predictive model for the loosening state of bolted joints. Initially, the relationship between the loosening criteria and relevant parameters is established according to the bolt’s force conditions. Through elementary effect analysis, the high-dimensional representation model is improved, breaking down the loosening criteria function with high-dimensional parameter inputs into a series of low-dimensional functions. Subsequently, the prediction of the loosening state is achieved by training artificial neural networks to approximate multiple low-dimensional functions. The improved predictive model is utilized to determine the critical load for bolted joint loosening. Validation indicates the accuracy of the proposed model. Notably, the influence of the bearing friction coefficient and preload on the critical transverse load is more pronounced compared to the thread friction coefficient.

The Tightening and Untightening Modeling and Simulation of Bolted Joints

Although bolted joints may appear simple and are easy to manipulate, they are challenging to model and analyze due to their complex structural patterns and statically indeterminate nature. Ensuring the structural integrity of these joints requires maintaining proper bolt preload and clamping force, which is crucial for preventing failures such as overload, excessive bearing stress, fatigue, and stripping caused by seizing or galling. Achieving the necessary clamping force involves carefully controlling the input tightening torque, which is divided into the pitch torque and the friction torques at the bolt or nut bearing surfaces and in the engaged threads. The resulting clamping force is critical for generating the required force within the bolt. However, the achieved bolt force depends on several factors, such as friction at the joint’s contact surfaces, grip length, and the relative rotation between the bolt and nut during tightening. Friction at the contact surfaces, particularly beneath the bolt head or nut and between the threads, consumes a significant portion of the applied tightening torque—approximately 90%. This paper explores the three existing bolt internal pitch, bearing, and thread friction torques that are generated by the external applied torque in a bolted joint, as well as their contributions and variations throughout a loading cycle composed of three phases: tightening, settling, and untightening. An analytical model is developed to determine these torque components, and its results are compared with those obtained from finite element (FE) modeling and experimental testing from previous studies. Finally, this study examines the torque–tension relationship during bolt tightening, offering insights into the required accuracy of bolt and clamped member stiffness. The bolt samples used in this study include M12 × 1.75 and M36 × 4 hex bolts.

A methodology for the selection of low friction/anti-seize coating in applying bolted joints of ITER blanket modules

The application of bolted joints with the Spiralock®/Selflock® technology for remote handling system in fusion machines leads to develop a methodology for selection a low friction/anti-seize coating in applying sliding surfaces of high-loaded threaded fasteners. This study discusses the analytical engineering method for calculation the maximum/minimum allowable friction coefficients in the thread and on the bearing surface during the tightening/untightening procedure. Calculations were made to determine the maximum/minimum allowable coefficient of friction in threaded pairs used for the ITER Blanket Module Connections and enhanced flux First Wall Panel fasteners (bolts with a regular metric thread/nuts with a self-locking thread, Spiralock®/Selflock® technology) of the ITER fusion experimental reactor under maximum torque conditions of the robot manipulator (remote handling system) and tensile load (preload) generated in the bolt during the tightening/untightening procedure. Design features of the Spiralock® technology were derived for calculation the working ranges of thread friction coefficient in the threaded pairs of the Blanket Module Connection and enhanced Heat Flux First Wall Panels fasteners at different coefficient of thread proportionality values (ζ=0.45–1.00). The lowest thread friction coefficients were obtained by the coefficient of thread proportionality ζ=1.00: 0.022≤μth≤0.171 for the M24 × 3 SB Electrical strap central bolts, 0.013≤μth≤0.047 for the М52 × 4 Outboard Flexible Cartridge central bolts, 0.010≤μth≤0.055 for the M64 × 4 Inboard Flexible Cartridge central bolts. The new method of determining the total tightening torque of the M24 × 3, M52 × 4, M64 × 4 bolted joints fastened to the Spiralock® female thread under conditions of elastoplastic, plastic deformation was applied to assess the suitability the solid lubricating coating MoS2 (VNIINP-212) under preload force Fa=10–1200 kN. The performed design verification indicated the significant differences in the calculated tightening torque obtained according to the standard and proposed method for the Spiralock® female thread by the plastic deformation of the tip of bolt thread and change of sliding friction coefficient depending on the contact pressure.

Probabilistic analysis of bolted joint anti-loosening under cyclic transverse load

The loosening of bolted joints under cyclic transverse load is a crucial failure mode, and the uncertainty of the relevant parameters of the bolted joint will affect the loosening state. However, there are few bolt-loosening probability analysis and evaluation methods based on parameter uncertainty in previous studies. In this paper, different loosening states are analyzed based on the relationship between pitch torque, thread friction torque, and bearing friction torque. Considering the uncertainty of process parameters, a probabilistic analysis method of the bolted joint anti-loosening under cyclic transverse load is proposed. In the proposed method, the finite element model verified by the fastening experiment is used to verify the accuracy of the bolted joints’ loosening criterion. Then, the loosening criterion is used as the Limit State Function (LSF). According to the LSF, an Adaptive Kriging-Kernel Density Importance Sampling (AK-KDIS) method is proposed for solving the anti-loosening reliability. This method combines adaptive Kriging model with the importance sampling method, effectively reducing the number of sampling samples and the number of LSF calls. The classical and robust Quasi-Monte Carlo (QMC) method is also used to evaluate the reliability of anti-loosening to verify the accuracy of the proposed AK-KDIS method. Finally, the practical application of probabilistic analysis of anti-loosening is presented, and the effectiveness of the proposed method is analyzed in detail. The results indicate that the AK-KDIS method has higher efficiency while ensuring calculation accuracy compared with the QMC method.

Simultaneous Surgery of the Clitoral Hood-Labia Minora Complex with the Central Neurovascular Pedicle Retained.

Hypertrophy of the labia minora with clitoral hood redundancy always occurs simultaneously and should be considered in its entirety. This study investigated a new simultaneous procedure for the clitoral hood-labia minora complex (CLC) that retains the central neurovascular pedicle. This retrospective observational study, conducted between January 2021 and August 2022, included 29 patients with labia minora hypertrophy and clitoral hood redundancy who underwent a surgery wherein procedures on the CLC were performed simultaneously. A divisional design to separate the medial and lateral labia minora and to remove the skin and subcutaneous tissue asymmetrically, while retaining the central neurovascular pedicle and the natural margin of labia minora, was employed. Postoperatively, all patients were followed up via the Internet or at the outpatient clinic. The follow-up included observing postoperative outcomes and any complications and completing the satisfaction questionnaires. All the patients who underwent surgery showed good wound healing without discomfort of thread friction. Postoperatively, the labia minora had a natural appearance and retained sexual sensitivity. The scarring on the surgical incision was not evident. Hematoma and evident bilateral asymmetry occurred in one patient each. The satisfaction rate within 14 days and after 3 months of surgery was 96.6% and 92.6%, respectively. This method uses a hidden incision, to remove the hypertrophic tissue and retain the natural edge and shape of the labia minora. Qualitatively, the patients were highly satisfied. This method was safe, effective, and easy to implement. This journal requires that authors assign a level of evidence to each article. For a full description of these Evidence-Based Medicine ratings, please refer to the Table of Contents or the online Instructions to Authors www.springer.com/00266 .

Research on the relationship between the tightening torque and the preload of composite bolted structures

Bolted joints are widely used in assembly of composite structures that transmit large loads. The relationship between torque ( T) and preload ( F) is needed to be obtained when using the torque method to tighten bolts. In this paper, the T- F relationship in the process of bolt tightening composite laminates was analyzed through bolt tightening experiments. The variation behavior of friction coefficient in this process was also studied. On this basis, a progressive damage finite element model was established using the improved LaRC05 criterion to analyze the stress and damage of the composite laminate during tightening. The various stages in the bolt tightening were divided and the mechanical properties of each stage were analyzed. The results of the study showed that the thread friction coefficient μth and the bearing friction coefficient μb change with the preload during the tightening process. Its behavior can be described using an exponential function. Serious stress concentration and assembly damage can be formed in the direct extrusion area of the outer edge of the locknut when the composite laminate is bolted. The bolt tightening process of composite laminates can be divided into five stages. Research conclusions are valuable for understanding composite structures and formulating the bolt tightening process.

Hyperstatic mechanics analysis of guideway assembly and motion errors prediction method under thread friction coefficient uncertainties

A method of hyperstatic mechanics analysis of guideway assembly and motion errors prediction under thread friction coefficient uncertainties is proposed. Based on the probability distribution characteristics and uncertainty analysis of the friction coefficient, the hyperstatic mechanic's equations of guideway assembly are established. By the geometric relation between the guideway profile curve and the motion errors, the motion straightness and angle errors (SAEs) are predicted. The results show that the guideway assembly can offset a part of the manufacturing error wavelength, which makes an important contribution to the error averaging effect. Combined with the error test results, the prediction accuracy of motion errors is above 81%, which verifies the effectiveness of the proposed method.

An experimental and comparative study of the self-loosening of bolted-joints under cyclic transverse loading

The capabilities of analytic models in predicting the experimental critical displacements of the self-loosening of bolted-joints were investigated experimentally and numerically. The experimental loosening rates were determined in a Junker test bench at a constant transverse displacement amplitude (0.45 mm) and under varying initial clamp force and clamp length and controlled bearing and thread friction coefficients. The analytic critical displacements were then calculated using experimental parameters. In addition, a three-dimensional accompanying finite element (FE) model was developed in order to calculate the ratio of spring constants engaging the thread to spring. The results showed relatively low capabilities of present analytic model in the prediction of the critical displacements of the self-loosening of bolted-joints. The efforts to modify the nut reaction moment and the inclination compliance of bolt head portion in the investigated equations however resulted moderate increase in the correct predictions. On the other side, the use of the reaction moment determined by FE model increased the correct prediction from 58.3 to 73.4%. The accuracy of the equations was further increased by the use of an appropriate kw value, but the increase in this case was only ~4%.

Определение коэффициентов трения в резьбовых соединениях из углерод-углеродных композиционных материалов

Experimental studies were carried out to estimate the friction coefficients for a screw-nut threaded pair made of spatially reinforced carbon-carbon composite materials (CCCM). Quantitative values were obtained for the thread friction coefficient and nut end friction coefficient. The ultimate screw-in torque for the CCCM threaded pair was determined, and its failure mode at a destructive screw-in torque was established. The laboratory tests were carried out to measure the tightening force. The nut screw-in torque was measured using a torque wrench.

Effect of Component Twist on Friction in a Bolted Joint

This paper presents an analysis of the assembly and disassembly processes for components in a bolted joint. The analysis shows a small amount of torsional elastic twist in joint components from applied torque during assembly and disassembly significantly affects thread and nut bearing friction. It reveals that after the assembly process, the nut bearing interface friction torque alone acts to counter not only the torque associated with bolt stretch, also known as the inherent self-loosening torque, but thread interface friction torque as well. Previous models and analyses of bolted joints have missed this point. Further, analysis of the disassembly process with applied removal torque reveals thread friction does not act to counter self-loosening and removal torque until sometime after nut bearing interface slip occurs. Only then do both thread friction and nut bearing friction counter self-loosening torque and removal torque. This is the state commonly assumed after the assembly process and for the duration of the disassembly process. The analysis presented reveals the effects of elastic twist of components in a bolted joint on thread friction and nut bearing friction and provides improved understanding of the state and behavior of bolted joints.

Investigation of dynamic friction during impact tightening of bolted joints

The impact tightening process of bolted joints differs from continuous tightening. To expand knowledge about impact tightening processes, this paper investigates friction and frictional variances regarding different lubrications and rotational speeds of the impact wrench. Therefore, bearing and thread friction are measured independently by an introduced new test bench. During tightening the bearing and thread coefficient of friction decrease both by approximately 80%, but only the variance of the thread friction decreases to about a third of the starting value. As the effect of the rotational speed on friction is very large, lubrication has a comparatively small effect.The found behavior is a basis for future investigations and simulation of the phenomena in frictional contacts of impact-tightened bolted joints.

Investigation of the thread coefficient of friction when impact tightening bolted joints

The friction conditions in bolted joints are decisive for the quality of the tightening process and therefore for the quality of the joint. One of the many influences on the tribological systems in bolted joints is the tightening process, which in case of the impact tightening process has not yet been researched fully yet. This paper aims to investigate the differences in thread friction between manual and impact tightening during the tightening process and in relation to the thread friction during the loosening process. A full factorial study with the factors preload and tightening tool, with two factor levels each, was conducted. The measurements were analyzed qualitatively and a linear regression model was derived. The results show for the tests with the torque wrench as expected the approximatively same coefficient of friction (COF) for tightening and loosening of the bolted joint. Whereas for the impact wrench it is shown that the COF while tightening is in average 70% higher than the corresponding coefficient of friction while loosening. To depict the correlation of the tightening thread COF with the loosening thread COF a factor λ is introduced and is going to be investigated in further research.

Threaded fasteners with applied medium or high strength threadlockers: effect of different tightening procedures on the tribological response

ABSTRACTThreaded joints are widely used in the automotive industry, where threadlockers can be applied to prevent self-loosening and to possibly achieve a friction drop upon tightening. This study deals with this topic, investigating threadlocker tribological response before polymerization takes place. These lubricating properties are usually not considered in adhesive datasheets, but can be highly beneficial from the point of view of the achievable preload, thus preventing self-loosening. The topic was tackled experimentally, running an extensive campaign that involved a medium and a strong threadlocker (LOCTITE 243 and LOCTITE 270, respectively), used for tightening zinc-plated and black-oxidized screws. The testing procedure was inspired by a protocol being used by most manufacturers in the automotive field: in particular, the impacts of pre-tightening speed and of the time interval between pre-tightening and final tightening were investigated. The retrieved results indicate a lubricating effect of the medium threadlocker with achievable friction coefficients in the order of 0.11. Moreover, for both the threadlockers, a generally decreasing trend for the thread friction upon tightening for increasing time interval before tightening was observed. This is a particularly original outcome that could have remarkable implications for optimizing the assembly tasks of large sets of bolts.

Tightening behavior of bolted joint with non-parallel bearing surface

Non-parallel bearing surface resulting from accumulation of geometric deviations is often unavoidable in tightening process of bolted joint, which has a significant influence on the tightening accuracy. In this study, the mechanism of preload deviation caused by non-parallel bearing surface is proposed by analytical model. Then the tightening behaviors of non-parallel bolted joint with different geometric parameters are analyzed through parametric FEA. Finally, the bolt tightening experiment is carried out, which verified the theoretical hypothesis and the FEA model. The results show that the extra thread friction torque generated by lateral pressing in mating threads resulting from bending moment is the cause of preload deviation. Larger inclination angle of bearing surface, shorter grip length of bolted joint and smaller fitting clearance between internal and external threads will increase this preload deviation.

Effects of tightening speed on torque coefficient in lag screw timber joints with steel side plates

To investigate the effects of tightening speed on the torque coefficient in lag screw timber joints with steel side plates, tightening tests were conducted on main timber members made from Cryptomeria japonica, Chamaecyparis obtusa and Pseudotsuga menziesii, under four tightening speed conditions (1, 4, 10, and 20 rpm). Major stick-slip behavior was observed in C. obtusa based on the relationship of tightening angle with clamp force, tightening torque, and thread torque at tightening speeds of 1 and 4 rpm. In addition, tightening speed’s effects on the torque coefficient (K) varied depending on the wood species of the main member. In P. menziesii, K was not affected by the tightening speed: the ratio of torque expended on tightening was 25% on average, and the ratio of torque expended on bearing surface friction was higher than the ratio of torque expended on thread friction.

Determination of the best distribution and effective interval using statistical characterization of uncertain variables

Abstract In this paper, an algorithm for estimating the best distribution about data containing uncertainties is proposed. The proposed algorithm combines sequence statistical modeling (SSM) and a method for determining the minimum experimental data. SSM is a method for selecting the best distribution about data using a goodness of fit (GoF) test and a comparison of the likelihood. The method used to determine the minimum experimental data determines the minimum data needed to an estimate the best distribution. The SSM presented herein is a method for selecting a suitable data distribution when considering only a parametric distribution. Thus, in this paper, the SSM was improved in order to select the correct distribution of both parametric and non-parametric distributions simultaneously. In addition, with the existing method for determining the minimum data, the data should be added based on actual experiments when the results data show an insufficient number, and there is a limitation in that the designers cannot broadly identify the data required. To overcome this limitation, SSM and random sampling are applied to the method to determine the minimum data, and thereby, ensure that the designer knows the approximate minimum data needed. To verify the validity of the proposed algorithm, it was applied to a real world case study on determining multiple statistical parameters in the bolt fastening problem. The sequence of verification methods used is as follows: First, the best distribution of the bearing surface and thread friction coefficient estimated by the proposed algorithm and based on a normal distribution are selected as comparison targets. Second, the bearing surface and thread friction coefficient data are sampled within the 95% confidence interval of the two distributions. Third, the reliability of the sampled friction coefficient data are compared using a Monte-Carlo simulation and an equation to calculate the bolt fastening force. In this study, the effectiveness of the proposed algorithm is validated. Highlights The algorithm to determine appropriate probability distribution of data is proposed. The sequential statistical modeling is improved to consider both parametric and non-parametric distribution. The method to determine minimum data is improved to verify sufficiency of data without actual experiments. The effectiveness and validation of the proposed algorithm is verified using the bolt-fastening data.

Preload, Coefficient of Friction, and Thread Friction in an Implant-Abutment-Screw Complex.

To examine the screw preload, coefficient of friction (COF), and tightening torque needed to overcome the thread friction of an implant-abutment-screw complex. In a customized load frame, 25 new implant-abutment-screw complexes including uncoated titanium alloy screws were torqued and untorqued 10 times each, applying 25 Ncm. Mean preload values decreased significantly from 209.8 N to 129.5 N according to the number of repetitions. The overall COF increased correspondingly. There was no comparable trend for the thread friction component. These results suggest that the application of a used implant-abutment-screw complex may be unfavorable for obtaining optimal screw preload.

Investigations of friction-relevant parameters to ensure reliable bolted joints

During the process of torque-controlled tightening of bolted joints, the reliability of load transmission is limited by the achieved accurate preload. The preload is mainly influenced by head‐ and thread friction. The knowledge of reliable coefficients of friction and the dependence on assembly parameters are essential. Although a variety of friction coefficients were published but the overall ranges ask for more precision. So called windows of friction coefficients are available in known guidelines, to define permissible scattering. However, there are practical doubts about useful friction coefficients, especially if newly developed lubricants, corrosion‐resistant coatings and securing devices against bolt-loosening are used. In this study, different parameters of a bolted joint connection, such as lubrication, the surface protection of the screw connection or used security systems, have been investigated on their frictional influence. To make a reliable conclusion about the coefficients of friction, only a measured examination like DIN EN ISO 16047:2013-01 can help. By means of a designed test bench those values could be detected by measurement and supplemented with the collected data of vibration test results at the TH Koln. On this way practically useful coefficients of friction and their scattering have been made available.

Ultrasonic tightening control of a screw joint: A comparison of the clamp force accuracy from different tightening methods

Clamp force and its accuracy are investigated using torque, angle, gradient, and clamp force/elongation control. Phosphated, lightly oiled M14 and M10 bolts are tightened. A PowerMACS 4000 system with a QST62-350CT nutrunner is used in the experimental setup. An ultrasonic signal processing unit using a piezoelectric sensor fitted to the socket is used for signal generation and processing when evaluating clamp force. The ultrasonic clamp force control is based on a novel method for assuring correct echo and high repeatability measurements in the tightening system. Torque and angle are extracted from the tool control system. During the experiments a load cell is used to measure the clamp force in the joint. Combined head and thread friction is calculated at final torque and clamp force. The results show that the lowest scatter (3 s) in clamp force, approximately 2.9% can be obtained using ultrasonic clamp force control and the highest, approximately 18% when using torque control. The results are also compared to tightening factors described in VDI2230.

A Mathematical Model for Temperature Induced Loosening due to Radial Expansion of Rectangle Thread Bolted Joints

This paper proposed a mathematical model to investigate the radial expansion induced loosening of rectangle thread bolted joints that were subjected to cyclic temperature variation, which could cause slippage between contact pairs of engaged threads and bolt bearing. Firstly, integral equations were derived for the shear stress components caused by expansion difference, as well as the bearing and thread friction torque components, which depended on the temperature variation. Secondly, the relationship of displacement components was developed based on quasi-static hypotheses. Then, treating the rotation of bolt as plastic elongation, the bolt tension's evolution was obtained by using a one-dimensional bolted joint model. Numerical results showed that the temperature variation decreased the bearing and thread friction torque components, which could lead bolted joint to loosen. Finally, the effects of some associated factors on the progress were discussed.