Nut Threads Research Articles

A two-scale method to include essential behavior of bolted connections in structures including elevated temperatures

A two-scale method is proposed to simulate the essential behavior of bolted connections in structures including elevated temperatures. It is presented, verified, and validated for the structural behavior of two plates, connected by a bolt, under a variety of loads and elevated temperatures. The method consists of a global-scale model that simulates the structure (here the two plates) by volume finite elements, and in which the bolt is modelled by a spring. The spring properties are provided by a small-scale model, in which the bolt is modelled by volume elements, and for which the boundary conditions are retrieved from the global-scale model. To ensure the small-scale model to be as computationally efficient as possible, simplifications are discussed regarding the material model and the modelling of the threads. For the latter, this leads to the experimentally validated application of a non-threaded shank with its stress area. It is shown that a non-linear elastic spring is needed for the bolt in the global-scale model, so the post-peak behavior of the structure can be described efficiently. All types of bolted connection failure as given by design standards are simulated by the two-scale method, which is successfully validated (except for net section failure) by experiments, and verified by a detailed system model, which models the structure in full detail. The sensitivity to the size of the part of the plate used in the small-scale model is also studied. Finally, multi-directional load cases, also for elevated temperatures, are studied with the two-scale method and verified with the detailed system model. As a result, a computationally efficient finite element modelling approach is provided for all possible combined load actions (except for nut thread failure and net section failure) and temperatures. The two-scale method is shown to be insightful, for it contains a functional separation of scales, revealing their relationships, and consequently, local small-scale non-convergence can be handled. Not presented in this paper, but the two-scale method can be used in e.g. computationally expensive two-way coupled fire-structure simulations, where it is beneficial for distributed computing and densely packed bolt configurations with stiff plates, for which a single small-scale model may be representative of several connections.

A Comparative Analysis of YOLOv8 and YOLOv5 for Nut Thread Classification - Deep Learning Approach

Abstract: This research provides valuable and compelling insights into the performance comparison of YOLOv8 and YOLOv5 for Thread and No thread detection. The findings underscore the significant impact of architectural improvements and model advancements, resulting in higher precision and accuracy in object detection tasks. Furthermore, the successful implementation of LabelImg and Beautiful Soup demonstrates their remarkable effectiveness in dataset annotation and collection, crucial contributors to the overall success of the study. As a result, these results lay a solid foundation for future advancements in object detection techniques, with wide-ranging applications across diverse domains, encompassing industrial automation, surveillance systems, and beyond.

Optimal design of prestressed bolt thread

The design of bolt and nut thread comes in many variations, typically the designs are specified in standards like the metric ISO thread. The thread design is important for the connection strength, and bolted connections are used for many applications. In the present paper focus is on the strength of prestressed bolts, that is, where the preload is typically more than 75% of the proof strength. The objective is in the present work to reduce the stress concentration in the thread. The stress is found numerically using a full 3D finite element model, and a simplified 2D axisymmetric model. It is shown that the 2D model is sufficient for evaluating the maximum stress. Applying a symmetric design it is shown that a reduction in the maximum stress in the thread of 14% can be achieved. Allowing for an unsymmetrical thread design the maximum stress is reduced by 33%. With the unsymmetrical design some of the stress reduction is due to a more evenly load distribution along the thread. geometrically, all optimized designs are such that they can be manufactured by the same methods as a standard ISO thread.

Farklı Et Kalınlıklarına Sahip Soğuk Şekillendirilmiş Kare İçi Boş Kesitli Elemanlara Monte Edilen Kör Perçin Somunlarının (BRN'ler) Çekme Kapasitesi Üzerine Deneysel Çalışma

In this study, pull-out tests of blind rivet nuts (BRNs) mounted on cold-formed square hollow section (SHS) webs with 100×100 mm nominal cross-section dimensions and different wall thicknesses (2.0 to 5.0 mm) were performed, and the effect of different wall thicknesses and BRN thread sizes on the test results was experimentally investigated. M10 and M12 stainless steel BRNs were mounted on SHSs using a standard riveter tool, and the test elements were prepared for the experiment. Load–displacement curves and the final damage modes were obtained for each test specimen. The results show that the pull-out capacity depends on both the SHS wall thickness and rivet nut thread size. Although the pull-out capacity increased in both thread sizes with the increase in wall thickness parameters, the effect of thread size is negligible in the case of 2.5, 3.0, and 4.0 wall thickness. In addition, when a connection is created using a BRN, the design should consider the stripped thread strength in addition to the pull-out capacity.

Time-varying contact characteristics of the planetary roller screw mechanism considering nonuniform surface waviness

The nonuniform surface waviness of the thread raceway is inevitably generated due to the vibration of the machine tool. In this paper, the surface waviness in the helical direction is decomposed into circumferential and axial surface waviness, and a time-varying contact model considering the nonuniform surface waviness is proposed for investigating time-varying contact characteristics of the planetary roller screw mechanism. The effects of the surface waviness of the screw, roller and nut thread raceway on the axial clearance and contact force are investigated through the analysis of examples in detail. The results show that axial clearances and contact forces at the screw-roller and roller-nut interfaces are time-varying rather than time-invariant.

Гайка для стопорения резьбы

Abstract. In engineering products, a significant part of the connections are formed using threaded connections, the functioning of which largely determines the reliability of mechanisms and assemblies. To preserve the invariability of the tightening of threaded connections during the operation of vehicles, a nut is presented, in which the internal thread is divided into two parts with different geometric parameters. Nut thread profiles made with different profile heights are described. The first profile height is equal to the height of the initial contour with sharp vertices, and the other one is equal to the standardized height and rounded vertices. When assembling the connection between the increased working height of the nut thread profile and the internal diameter of the bolt thread, the necessary tightness is provided. In the zone of the upper section of the outer diameter of the thread of the nut, the metal is elastically deformed, therefore, when the bolt and nut are connected, an interference is formed with an increase in the coefficient of friction, which determines the operational reliability of the connection. The optimal ratio of the lengths of sections with different profile heights has been determined to ensure the necessary increase in the locking properties of threaded connections, depending on the specific operating conditions of vehicles. Conducted laboratory studies on a specially made stand showed the reliability of the initial scientific hypothesis, suggesting that the stability of tightening a threaded connection depends on changes in physical parameters associated with the distortion of the crystal lattice and changes in the density of dislocations that occur in the process of thread formation using a particular technology and during its operation. . A technique for accelerated testing based on the creation of an additional unscrewing torque has been developed, which can significantly reduce the amount of testing and predict the time after which it is necessary to re-tighten the connection. The nut is designed for repeated use during reassembly with retention of locking properties during the repair of various technical devices, including cars. The technology for the production of the proposed nut is simple and economical and involves the use of universal screw-cutting equipment available at any repair company. In further studies, it is planned to conduct long-term operational tests of vehicles in order to confirm the reliability of the proposed nut for thread locking at the same time as achieving the simplicity of the product and high manufacturability.

Особенности расчета параметров метчиков для нарезания точных резьб на станках с ЧПУ

The analysis of the features of the taps when cutting precise metric threads by the synchronous method on CNC machines is given. The layout of the tolerance fields of the average diameter of the tap and nut threads is constructed, which allows to ensure the accuracy, controllability and durability of the cutting tool. The formula for calculating the average diameter of the tap thread has been defined.

Optimization of laser texture geometry and resulting functionality of nickel aluminium bronze for landing gear applications

Nickel-aluminium bronze (NAB) is adopted in certain crucial applications such as nut threads of actuator screw assembly in nose landing gear, which forms the critical weakest link for landing gear operation. Surface engineering of such critical aircraft parts made of softer materials is required to improve their safety design life. This paper reports optimization of nanosecond laser parameters for enhancing the quality characteristics of surface textures formed on NAB. These characteristics include micro-texture depth, aspect ratio, average surface roughness, maximum height of the profile and kurtosis. Texture diameter and width was computed using an optical microscope. Dimples and grooves with minimum damage were obtained at higher laser power (18 W), moderate scanning speed (500 mm/s) and moderate frequency (50 kHz). The quality ellipse was obtained at moderate power of 14 W, higher scanning speed of 800 mm/s and moderate frequency of 50 kHz. However, the quality of textures deteriorated at moderate laser power (14 W), lowest scanning speed (100 mm/s) and moderate frequency (50 kHz).

Forgácsoló szerszám tervezése golyósanya menetesztergálásához

Jelen cikk a golyósanya menetfelületének különböző megmunkálási lehetőségeit ismerteti. A nagy menetemelkedésű golyósanyák forgácsolással történő megmunkálásának egyik hátránya, hogy módosított szerszámprofilt előállítása szükséges, hogy elkerüljük a szerszámtartó és a munkadarab ütközését. Profilos forgácsolólapkák alkalmazásával azonban lehetséges a golyósanya menetprofiljának előállítása esztergálási technológiával. A technológia alkalmazhatóságát a koncepcionális tervek alapján készült szerszámmal és kísérleti megmunkálással igazoljuk, amelyek eredményeit a cikk végén ismertetjük.

Three-dimensional finite element analysis for prevailing torque of bolt-nut connection having slight pitch difference

In a vast industrial field, the bolt-nut connection is widely used and unitized as an important machine component. In order to improve safety and for cost reduction, cheap bolt-nut connections with excellent anti-loosening performance are always needed. In this paper, the slight pitch difference is considered between the nut and bolt threads to improve the anti-loosening by focusing on the prevailing torque Tp. In the first place, during the nut screwing process, the bolt axial force Fa caused by the pitch difference is examined because previously Fa was studied by the axisymmetric FEM simulation as a substitute of the prevailing torque Tp. Next, the prevailing torque Tp is directly analyzed by changing the pitch difference through the 3D FEM simulation. The obtained prevailing torque needed for the nut rotation is in consonance with the measured value experimentally. By considering manufacturing error sometimes included, finally, the real pitch difference or of the nut is identified from the number of nut thread in contact with the bolt thread, which is measured experimentally. Then, the correctness of this α is confirmed through the prevailing torque obtained by 3D FEM simulation.

Numerical Analysis of Stress Distribution in Offshore Wind Turbine M72 Bolted Connections

The use of bolted joints to connect the transition piece and monopile is nowadays widely applied in the offshore wind industry. Traditionally, grouted connections were used in the early generation of offshore wind turbines, but the experienced failures in such connections led to an increased tendency towards bolted flange connections to join the transition piece and monopile in the new generation of offshore wind turbines. The bolts used for this purpose have high strength and huge sizes, and are subjected to a preload that is applied during the tightening process. The present study is focused on the analysis of preload effects on stress distribution in M72 bolted connections by considering different friction coefficients between the bolt and nut threads. The bolt is considered to be made of grade 10.9 steel, whereas the nut is assumed to be made of grade 8.8 steel, which is a softer material. Using the finite element commercial software package Abaqus, numerical models were developed and analysed to establish trends for stress distribution and plastic strains during the bolt tightening process, and to quantify stress concentration factors in individual engaged threads.

Contact Analysis of Thread Pairs in a Planetary Roller Screw Based on Finite Element Method

This paper investigates the contact characteristics of the thread pairs in the planetary roller screw mechanism. Firstly, the analytical model of thread contact based on Hertz contact theory is established. Secondly, the contact models of the screw and roller threads and of the roller and nut threads based on FE method are developed. The correctness of the numerical results is verified via the comparison with analytical results, the relative error between the two sets of results is less than or equal to 2%. Lastly, according to FE model, the contact state, contact positions and contact stresses of thread pairs at the screw-roller interface and at the roller-nut interface are derived.

Fatigue strength of metric steel screws depending on pre-load and nut type

The fatigue properties of metric steel screws are investigated experimentally regarding the impact of the length of thread engagement, the nut thread type and the nut material. The load capacity of the screw up to fatigue failure depends significantly on the load distribution resulting from the varied parameters by an impact of the applied pre-load. An over-elastic pre-load of the screw-nut connection leads to a significantly higher load capacity due to a homogenization of the load introduction and load-induced compressive residual stresses at the thread root. The numerical simulations for determining the load distribution and the calculation of local stresses and strains lead to a lifetime evaluation.

Conceptional cutting tool design for internal thread turning

This article describes the different machining methods of the ball nut thread. One of the disadvantages of machining high pitch ball nuts by grinding process is to produce a modified tool profile to avoid collisions between the tool holder and the workpiece. However, by using profiled lathe inserts, it is possible to produce the thread profile of the ball nut using turning technology. The applicability of the technology is verified by tooling and experimental machining based on conceptual designs, the results of which are described at the end of the article.

Microstructural evolution and deformation behavior of copper alloy during rheoforging process

A complete rheo-forming process was carried out to investigate the rheoforging process of C3771 lead brass valve, starting from the semi-solid billet preparation to rheoforging experiments and material performance tests. The near-spherical micro-grains with mean equivalent diameter of 56.3 μm, shape factor of 0.78 were obtained when the raw C3771 lead brass were rotary swaged to a radial strain of 0.22 and then heated to 895 °C for 5 min. The Forge 3D software was used to analyze the temperature, strain and strain rate distribution of copper valve for obtain the reasonable process parameters during the subsequent rheoforging process. The experiment results showed that near-spherical micro-grains were stretched and refined to about 35.7–43.4 μm in different positions due to the dynamic recrystallization during the rheoforging process. The cap thread and nut thread failure torque of the so-produced valve are also discovered to be higher than the traditionally forged copper valve with dendrite micro-grains, with an enhancement of the cap and thread failure torque of 42.2 % and 28 %, respectively.

Real-Time Image-Based Defect Inspection System of Internal Thread for Nut

The most important components of the internal nut thread inspection process are measuring the pitch and pitch diameter value and comparing these with their respective specifications, as a test nut is considered to be abnormal when its pitch or pitch diameter does not meet specifications. This paper focuses on defects arising when the pitch diameter does not meet its specification. Because conventional contact strategies are not suited to the real-time inspection of internal thread defects, there have been a number of recent attempts to develop noncontact methods for real-time measurement. Some approaches have applied laser triangulation techniques in which reflected light is used to measure the z-axis depth on an object’s surface. Although point lasers have been shown to be highly precise in measuring pitch diameter, the optical architecture involved in these approaches is complicated and, as the laser must be scanned in a pointwise manner to derive cross-sectional measurements, the measurement process is too long to be compatible with real-time defect inspection. In this papere, an image-based method employing a line laser projector was used to develop a real-time image-based nut pitch diameter defect inspection system. The proposed method, which improves upon the conventional, widely used template-matching method for rapid defect detection, was shown to be effective through experimental validation.

Self-loosening behavior of bolt in curvic coupling due to materials ratcheting at thread root

This article presents the bolt self-loosening mechanism in curvic coupling due to the structural ratcheting under cyclic loading. Finite element simulations are carried out under several loading conditions with different preloads and cyclic torque loadings on curvic coupling. To avoid relative rotation between bolt and nut in simulation, the surface between the threads of bolt and nut are connected together. The finite element analysis results reveal that the local cyclic plasticity occurring near the roots of the engaged threads resulted in cyclic strain ratcheting. The structural ratcheting causes the gradual loss of clamping force with loading cycles in bolts and the stresses to redistribute in the curvic coupling. Either the structural ratcheting behavior or the fatigue strength of the curvic coupling is more sensitive to the magnitude of the torque load in contrast to the magnitude of the preload of the bolt. Comparatively, the large preload of the bolt or the low magnitude of the torque load is benefit for improving the structural integrity in curvic coupling under the bolt self-loosening.

Tension Test for Axially Vibrated Prestressing Fine‐Rolled Screw‐Threaded Steel Bars Based on Thread‐Contact Connection

The interface between anchor plate and anchorage nut can be considered as a coupling spring whose stiffness is essentially the contact stiffness related to normal force at the contact surface, thus removing the usual assumption of fixed connection. The nut threads and steel bar are also connected with a coupling spring with the stiffness determined based on the threads treated as cantilever components. An analytical model was developed to assess the axial vibration of an anchorage system consisting of prestressing fine‐rolled screw‐threaded steel bars (P/S FSSBs). Both laboratory model and field tests show that the contact stiffness between anchor plate and anchorage nut has good a linear relationship with the effective tension of prestressed tendons. The vibration model was used to obtain the natural frequency and tensile force of a P/S FSSB. It is shown to be feasible and practical. According to the analytical model and test method presented in this paper, the proposed tension tester for P/S FSSBs possesses the features of repeated use, rapid testing, and minimized impact on the construction and is thus suggested for wider practical applications.

New non-destructive dynamic tensile testing of prestressing fine-rolled screw-threaded steel bars

This paper presents a new non-destructive dynamic tensile test for fine-rolled screw-threaded steel bars (FSSBs) in prestressed concrete box-girder bridges. In this study, the anchorage nut and anchor plate are connected by a coupling spring, so are the steel bar and nut threads. A discrete dynamic model of a spring–mass system was therefore established to evaluate the bending vibration of the anchorage system. The tensile force in prestressing FSSBs can be determined indirectly using the measured natural frequency of the exposed section. Based on the force transmission characteristics of threads, a frequency correction equation is proposed to correct the test error in the tensile force. The laboratory model and field tests of multiple bridges show that the proposed test method for tensile force is feasible and practical. The proposed tension test method is rapid, non-destructive, and can be used repeatedly. It has no impact on the construction and offers potential wide applications. The study results are significant in terms of the testing and analysis of the induced tensions in mechanical components and similar structures of civil engineering.

Projection welding of nuts involving the use of electromechanical and pneumatic electrode force

The projection welding of nuts performed using the pneumatic (electrode) force system (PFS) was subjected to thorough numerical and experimental analysis, enabling the identification of the window of welding parameters taking into consideration boundary conditions including expulsion, torsional strength and the deformation of the nut thread. The welding process was subjected to optimisation involving the use of a new, i.e. electromechanical (electrode) force system (EFS). The optimisation-related approach involved the reduction of welding current and the extension of a welding current flow time in comparison with those obtained when using the pneumatic force system. It was assumed that the acceptance criterion would be the breaking torque not lower than that obtained under the most favourable welding conditions performed using the PFS. The research work involved comparative numerical calculations (performed using the SORPAS software) in relation to both, i.e. the PFS and EFS. The technological welding tests were performed using inverter welding machines (1 kHz) provided with various (electrode) force systems. The research work also included metallographic tests, hardness measurements and torsional strength tests. As a result of the application of EFS and a special innovative hybrid algorithm for controlling the electrode clamps, a wider and higher weld core was obtained. The depth of “penetration” into the sheet was greater. As a result, the welded joint has a higher resistance (by 30%). Technological welding tests for the new EFS system were carried out for a 25% lower welding current compared with PFS. Despite the lower welding current for EFS, the welding energy is slightly lower but the welding quality for EPS is significantly higher.