Pre-tightening Force Research Articles

Static test and theoretical study on semirigid pin joint for modular steel reticulated shell

SummaryIn order to realize the modularity and rapid assembly of steel reticulated shells in the construction site, a new type of simple assembled joint named semirigid pin joint is proposed for modular steel reticulated shell in this paper. While on the premise of meeting the stiffness and strength requirement, complicated procedures such as tightening nuts and controlling pretightening force are avoided in this joint. In addition, the joints can adapt to the complex curvature changes of reticulated shells. When it is connected in the middle of the member, the new joint can realize the connection of arc members. First, experiments were carried out on different screw rod diameters, wing plate pin diameters, and the number of wing plate pins. Different failure modes and M–Φ curves of semirigid pin joints were obtained. The stiffness and strength of the joints were studied. Second, a three‐dimensional finite element model of the joint was established by ABAQUS, and the comparison between the simulated results and the experimental results proved the accuracy of the finite element numerical analysis. On this basis, the antirotation stiffness, strength, and failure mode of the new joint with different parameters were compared and discussed, and the influence law of each parameter on the mechanical properties of the new joint was obtained. Finally, based on the power function model, a theoretical analysis model for estimating the M–Φ curve of the joint was established. Compared with the results of the experiments, the results indicated that the prediction formula has high accuracy.

Workspace Analysis of Cable-driven Continuum Manipulator with Cable-constrained Synchronous Rotating Mechanism

In this paper, a cable-driven continuum manipulator with cable-constrained synchronous rotating mechanism (CCSRM) is studied. The purpose of this paper is to give the workspace for the cable-driven continuum manipulator, where the friction effects and the allowable range of cable tension are considered. The problem of solving workspace is transformed into a linear programming problem, which is solved by dual-simplex algorithm. On this basis, the influence of the pre-tightening force of the connecting cable on the workspace is analyzed. In addition, the tension of the motor on each driving cable is optimized to minimize the control error. Finally, the load range that the manipulator can withstand within the workspace is analyzed.

Effects of Different Friction Coefficients on Input Torque Distribution in the Bolt Tightening Process Based on the Energy Method

Abstract Bolted joints are one of the most common fastening methods in engineering applications. To meet the requirements of structural parts, the torque method is often used for controlling the bolted joint performance. However, only a few investigations have been carried out on the conversion efficiency of bolt torque to the tensile force, leading to uncertainty and potential safety hazards during the bolt tightening. In order to study the input torque distribution and overcome problems caused by the Motosh method and experimental investigations, a new energy-based torque distribution model is established in the present study. In the proposed model, numerous affecting parameters, including the connector compression work, effective bearing radius, effective thread contact radius, and spiral angle are considered. Then a parameterized thread mesh model using finite element technology is proposed to analyze the influence of different bolt friction coefficients on the bolt tightening process. Based on 16 types of tightening analyses, it is concluded that as bolt friction coefficient increases, the corresponding torque conversion rate decreases from 14.45% to 7.89%. Compared with the Motosh method, the torque conversion rate obtained by the proposed method is relatively large, which makes the actual pre-tightening force larger than the design value. However, there is still a possibility of bolt failure.

Research on the reliable test range of four-point supported piezoelectric dynamometer

PurposeThe purpose of this paper is to improve the reliability of the force measurement system by determining the reliable test range of dynamometer.Design/methodology/approachBased on the principle of leverage and moment balance, a general force distribution model is applicable in where the test point is located either inside or outside the support region of four three-component force links of dynamometer is established. After corroborating the correctness of the model through verification experiments, the boundary conditions that each three-component force link should satisfy are analyzed by considering the characteristic of the dynamometer components comprehensively. Furthermore, the reliable test range of dynamometer is determined, followed by a calibration experiment to verify its rationality.FindingsThe relationships between the reliable test range and the tested force, the bolt pre-tightening force and the bearing capacity of quartz wafers are clarified. Further, the experimental calibration results show that when the test point is within the reliable test range, the three-directional output voltage of dynamometer has excellent linearity and repeatability. The nonlinearity and repeatability in X-, Y- and Z-directions are all less than 1.1%.Originality/valueA general mathematical model of force distribution of four three-component force links is constructed, which provides a theoretical basic for the mechanical analysis of multi-sensors’ dynamometer. Comprehensively considering the performance of dynamometer components, the value of measured force and the pre-tightening force, the simultaneous equations of reliable test range are deduced, which limits the boundary of allowable test position of piezoelectric dynamometer.

Compressive stress-hydrothermal aging behavior and constitutive model of shield tunnel EPDM rubber material

The damage and aging of the ethylene-propylene-diene monomer (EPDM) rubber material significantly impact the attenuation of the shield tunnel's waterproof performance. Furthermore, the compressive stress acting on the rubber material will further exacerbate this consequence. Therefore, it is necessary to explore the time-dependent properties of rubber under compressive stress. In this study, the EPDM rubber was subjected to compressive stress-hydrothermal aging (CS-HA) test at different pre-compression strains, temperatures, and time according to the application environment of the shield tunnel. The rule of compression set (CS) and the variation rule of mechanical properties of rubber materials after aging were investigated, and the reasons for these rules were analyzed. According to the rule of rubber material performance degradation, a constitutive model of EPDM rubber for shield tunnel segment squeezing environment was proposed. Using compression set as the index of material performance deterioration degree, the time and temperature conversion relationship between laboratory aging and service environment aging of the EPDM rubber segment joint was obtained. Furthermore, based on the constitutive model and related parameter expressions proposed in this paper, the attenuation rule of rubber mechanical properties and residual properties was obtained. It was proposed that the service performance of EPDM rubber under compressive stress should be considered when setting the pre-tightening force during the construction of the shield tunnel, and a reasonable pre-compression force should be adopted. This work provides an effective test method and constitutive model for predicting the time-dependent characteristics of the mechanical properties of rubber materials under compressive stress.

Initial losing behavior of pre-tightening force for threaded fastener during repeated tightening

The clamping force of the bolted joint is a key factor in maintaining its service performance. However, when the torque wrench is removed after tightening, there will always be a certain degree of loss in the pre-tightening force. Herein, the stress state of the bolt and the nut during tightening and service was analyzed. The repeatability experiment of the threaded fasteners during repeated tightening was carried out to investigate the pre-tightening force loss after the removal of torque wrench (initial loss) and the pre-tightening force loss in a period of service (service loss). Different forms of lubrication was considered, namely without lubrication, thread lubrication and nut surface lubrication. The influence of the pre-tightening force, repeated tightening and lubrication on the initial loss and the service loss was analyzed according to the experimental results. It showed that the pre-tightening force and its loss have a large dispersion. At the first tightening, the pre-tightening force may increase after the initial loss stage. When the lubricant is used, the service loss has a significant positive correlation with its pre-tightening force. The use of lubricant at the threads is easier to lead the service loss of pre-tightening force.

Methodology for optimization of preload in a bolted-flange connection based on Markov theory

The bolted-flange connection is one of the most popular detachable mechanical joints in mechanical flange connection. It is well known that bolted-flange joints need to be tightened to meet the assembly performance in practical engineering applications. However, the dispersion of the pre-tightening force caused by the elastic interaction between the bolts has a serious impact on the sealing and safety of the product, and therefore the optimization of bolt preload has always been a hot spot in the assembly research field. Combining mathematical theory and experimental data, this paper proposes an optimization model for uniformly distributed preload based on the Markov theory. The torque method was utilized to fasten the bolt-flange joint. The bolt pre-tightening force in the final state was collected and used as sample data. A state transition model was constructed to determine the state transition matrix. Ultimately, an iterative model of the preload was deduced, and the rationality of the model was verified through experimentation. The proposed optimization method of bolt preload can be applied to determine the initial preload of each bolt. This method improves the assembly efficiency and accuracy, which provides a theoretical approach to effectively guide the tightening work of bolted-flange connections.

Recent Patents on Bearing Pre-tightening

Background: Bearing has been widely used in automotive, aerospace, electronics industry and other fields. Its pre-tightening technology is one of the most critical technologies. It has an important influence on the accuracy, speed, stiffness and temperature rise of the spindle. Proper pre-tightening force can eliminate bearing clearance and improve machining accuracy and efficiency of machine tools. Therefore, the development trend of bearing pre-tightening mechanism has been paid more and more attention. Objective: In order to improve the processing efficiency and processing accuracy of the bearing system, the structure and function of the bearing pre-tensioning device are continuously enhanced. Methods: This paper retraces various current representative patents relative to the mechanism of bearing pre-tightening. Results: Through the investigation of a number of patents of bearing pre-tightening devices, the principles and effects of different bearing pre-tightening devices are classified and reviewed. Besides, the future development trend of bearing pre-tightening devices is discussed. Conclusion: The optimization of the bearing pre-tightening device is conducive to improving processing efficiency and quality. A controllable pre-tightening force is the research direction, and more related patents will be invented in the future.

A stiffness degradation model of bolted joint based on fourth polynomial pressure distribution

This paper proposed a new friction mechanical model based on the Coulomb friction law to describe the nonlinear stiffness degradation of bolted joints. Several different contact pressure distributions are analyzed, and the results show that the fourth polynomial distribution has a better effect on characterizing the contact pressure distribution of the bolted interface. Then, a new density function of friction shear stress is obtained through mathematical deduction. There is an interesting discovery that the new density function curve is similar to the truncated power-law spectrum curve. In addition, a method of parameter identification is proposed, and multiple sets of parameters are identified for the subsequent model verification. Finally, the correlation between the theoretical value and the experimental data under different pre-tightening forces is analyzed. The results show the accuracy improvement of the new model compared with the existing model. The new model has better mechanism rationality and can be applied to stiffness degradation analysis.

Dynamics modeling and analysis of cable-driven segmented manipulator considering friction effects

In this paper, a new cable-driven segmented manipulator is studied, which maintains a nearly piecewise constant curvature under the constraint of a cable-constrained synchronous rotating mechanism. The main purpose of this paper is to present a refined dynamics model for the cable-driven segmented manipulator system considering friction effects and deformation of the cables. First, the arbitrary-Lagrangian–Eulerian method is introduced for the modeling of the driving cables, and the friction between the cables and the manipulator is described by the LuGre model. Second, the dynamics model and algorithm for the 2D segmented manipulator system considering friction effects and deformation of the cables is established using Lagrange’s equation of the first kind and Baumgarte’s stabilization method. Finally, a single-segment manipulator and a multi-segment manipulator are simulated successively, and an example of the manipulator circumventing an obstacle is simulated. The control errors caused by friction and deformation of the cables are analyzed, and the influences of the joint angle and the cable pre-tightening force on the control errors are discussed. In addition, the control errors of different segments are compared and analyzed, and reduced by adjusting the pre-tightening force of the cables.

Full-Stress Anchoring Technology and Application of Bolts in the Coal Roadway

The traditional anchoring method of bolts has insufficient control over the surrounding rock of the coal roadway. Based on this background, full-stress anchoring technology of bolts was proposed. Firstly, a mechanical relationship model of a bolt-drawing, anchoring interface was established to obtain the equations of the axial force and obtain shear stress distribution as well as the decreasing-load transfer law of the anchoring section of bolts. Through studying the prestress-loading experimental device of bolts, we found that increasing the initial preload could increase the axial force under the same conditions and the retarded anchoring section could control the axial-force loss of bolts in the middle of the anchoring section. Under the full-stress anchoring mode, the effect of applying a pre-tightening force was better than that of applying a pre-tightening force under traditional anchoring methods. Moreover, FLAC3D (Fast Lagrangian Analysis of Continua 3D; ITASCA (Ita sca International Inc), Minnesota, USA) numerical simulation calculation was performed. Under the full-stress anchoring mode of bolts, the increased anchoring length reduced the damage of the anchoring section, with a wider control range of the rock formation and higher strength of the compressive-stress anchoring zone. Based on the above research, four methods for applying the full-stress anchoring technology of bolts in engineering were proposed. The full-stress anchoring technology of bolts in the coal roadway has been applied in the support project of the return-air roadway at working face 3204 of the Taitou Coking Coal Mine of the Xiangning Coking Coal Group, Shanxi. The maximum moving distance of the roof and floor of the roadway was reduced from 200 to 42 mm, and the maximum moving distance on both coal sides was reduced from 330 to 86 mm. The full-stress anchoring technology of bolts was able to control the surrounding rock in the coal roadway.

Experimental and numerical study on the anti-sliding performance of full-lock coil cable clamps

The full-lock coil cable clamp node is an important joint in cable structures, and its sliding will reduce the bearing capacity and stability of the structure. Based on cable clamp node slide resistance tests and finite element analyses, the bolt pre-tightening force, cable tensioning sequence, and parameters such as the cable diameter were investigated to determine their influence on the cable clamp slide resistance. The stress distribution and variation in cable in the process of cable clamp sliding with steel wire was obtained. The main conclusions are as follows. (1) The bolt fastening force is basically proportional to the ultimate anti-slide bearing capacity of the cable clamp. The reduction coefficients for an 80 mm cable with initial fastening forces of 125 kN, 175 kN, and 225 kN are 0.49, 0.56, and 0.61, respectively. (2) Tensioning the cable first and then tightening the bolt can effectively improve the ultimate anti sliding bearing capacity of the cable clamp. The ultimate anti sliding bearing capacity of the cable clamp tested in this paper is increased by 38%. (3) Under the condition of the same initial fastening force, with increasing cable diameter, the sliding bearing capacity decreases linearly. (4) During cable clamp sliding, the stress of the cable in the slide direction of the cable clamp decreases, while the stress of the cable on the other side increases. (5) A calculation equation for the slide resistance ultimate bearing capacity of full-lock coil cable clamps considering the cable diameter and cable clamp length is obtained.

Research on optimizing the axial force of thread connection of engine connecting rod

The connecting-rod (abbreviate as conrod) bolt is a key part of the crank conrod mechanism, however, due to the structural characteristics of the thread connection, uneven loading between thread teeth and stress concentration at the root of thread teeth are common. In this paper, a finite element model of the conrod bolt was established based on the mesh convergence criterion. The finite element model of the conrod bolt was verfied by Akira Yamamoto analytical method. The influence of thread pitch, pre-tightening force and thread connection length on the distribution of axial stress of the thread was studied, and the stress concentration at the first thread was more serious. To improve the stress distribution of the first thread, the Spiralock anti-loosening thread was replaced to the standard conrod bolt and taken as the research object. The results show that the axial stress distribution of the Spiralock anti-loosing thread is more uniform, the fatigue strength and life are also improved.

Features of the study of threaded joints using the finite element method

A significant number of computer programs exist today for various engineering calculations, research and development of equipment elements. The SolidWorks software has become widespread for such work, which allows you to minimize time, facilitate the performance of the necessary work, as well as analyze the strength, stiffness, stability and endurance of products of a wide range of complexity and purpose. The program uses the finite element method, which has both a number of advantages and certain disadvantages.
 To investigate the possibilities of such a program, a model of a threaded connection of sucker rods has been built. Simulation of make-up torque for threaded connections remains problematic when modeling in SolidWorks Simulation. There are several ways to simulate the make-up moment during the study of the stress-strain state of threaded connections. To solve problems in an axisymmetric setting, the optimal method is to overlap the ends of the nipple and coupling by the required amount. The use of an axisymmetric model in the process of simulation does not impair the results obtained in comparison with 3D models. But it speeds up the calculation process, allows you to build a fine mesh of finite elements and get more accurate results.
 The paper presents an algorithm for calculating the tension of the threaded connections of sucker rods, which can be applied to threaded connections of drill string elements with some adjustments. The only difference will be in the formula for determining the make-up moment, from which the value of the pre-tightening force and the areas of dangerous sections are derived. Also, in the work, a simulation study was carried out using the selected method using the example of a threaded connection of sucker rods with a diameter of 19 mm. A diagram of displacements and distribution of equivalent stresses in a threaded connection was obtained and the possibility of determining specific parameters at certain points of the model under study was shown with subsequent automated construction of their graphical dependencies.

Embedment Effect on Eliminating Damage of CFRP Pull-riveting Process by Simulation Study

The rivet joints have been widely applied in aerospace and vehicle fields. During the joining process of the carbon fiber reinforced plastic (CFRP) laminates, the pre-tightening force of pulling-rivet was the key factor to ensure the connection performance. To predict the impact of clamping loads on stress and failure of laminates, the value of stress and damage evolution of the wall of a hole under the pre-tightening force were simulated by the finite element method. The results of the simulation showed that excessive clamping force led to the damage and failure of CFRP in the hole edge. Connection performance together with progressive failure process and failure modes of CFRP laminates with various pre-tightening forces were investigated. A kind of metal embedded parts embedded in the laminates was designed to reduce the damage by the simulation study. Simulation results showed that embedment reduced the failure and damage efficiently. The embedment reduced about 64% of the maximum stress.

Structure bolt tightening force and loosening monitoring by conductive MXene/FPC pressure sensor with high sensitivity and wide sensing range

Mxenes can be used in a variety of applications due to their multifunctional chemical properties. It has received increasing attention as a piezoresistive sensor. However, the stability and pressure monitoring range of the reported MXene sensors are limited, thereby limiting these scalability and effectiveness. In contrast, this paper presents a conductive MXene/FPC based pressure sensor overcomes the aforementioned shortcoming in that its pressure monitoring range and stability are improved by one order of magnitude. Therefore, this study aims to validate the use of MXene sensor for detecting bolt loosening. First, the mechanical properties of MXene were tested, including pressure test, vibration test and so on. The mechanical parameters of MXene are obtained. Secondly, the bolt structure embedded with MXene sensor is tested by torque loading and bolt looseness monitoring under vibration environment. The experimental results show that it has a linear pressure monitoring range of 0−120Mpa, the sensitivity of the sensor is up to 1.3 Mpa −1, and can remain stable after more than 63,000 cycles. Through monitoring the change of resistance ΔR/R0, the pressure of bolt pre tightening force transmitted to the joint surface can be accurately sensed. In the vibration environment, when the excitation frequency is 20 Hz, the bolt structure resonates, and ΔR/R0 increases from 0.28 to 0.6; when the bolt looses in about 100 s, the ΔR/R0 increases from 0.3 to 0.68 indicates that MXene can respond to bolt loosening in time. Thus, the sensor can be used in the whole life health monitoring of bolted structure completely.

Research on coordination design method of main bearing assembly structure based on the maximum radial deformation of bearing bush

Aiming at the difficulty of control and evaluation of main bearing deformation in the coordination design of the main bearing assembly structure for a high-speed diesel engine, taking MRD (the MRD means the maximum radial deformation of the bearing bush) of the bearing bush as an index to evaluate the out-of-round deformation of the bearing bush was proposed in this paper. The numerical calculation method of the MRD was given and the correctness of the method was experimentally verified. And the influence rules of different design parameters on the MRD were analyzed. On this basis, the coordination multi-objective optimization research of the main bearing assembly structure was carried out, and the optimization results were analyzed based on the influence rules of different design parameters on the reliability indexes. The results show that, when the pre-tightening force of the vertical bolt and the bearing bush interference are 240 kN and 0.17 mm respectively, the MRD reaches the minimum value. If the two values continue to increase, redundant loads can be generated, leading to the increase of the MRD. After optimization, the engine block strength coordination and bearing cap strength coordination had increased by 2.47% and 10.48%, respectively, and the deformation coordination and contact coordination had increased by 46.15% and 14.84%, respectively.

Design of Remote Monitoring System for Pre-Tightening Force of Anchor Bolts

Given the broad monitoring range and long monitoring time of anchor bolt loosening of draught fan, and harsh site environment in offshore wind power projects, a remote temperature and pressure monitoring system was designed in this study to realize the real-time wide-range monitoring of anchor bolt loosening of draught fans. The strain pressure transducer and platinum thermistor were used at the test end to acquire the pressure and temperature data, respectively. stm32f103 was used as the master controller in the acquisition system, hierarchical networking was conducted via Modbus protocol, and the long-distance transmission was realized by a fiber optical transceiver. LabVIEW was used by the upper computer to establish the client side to implement the data acquisition, storage and real-time monitoring.

Liquid water transport and mechanical performance of electrospun gas diffusion layers

ABSTRACT Self-humidification is becoming a popular strategy for water management in proton exchange membrane fuel cells (PEMFCs), owing to the advantages of decreased volume, cost, and parasitic power of the hydrogen fuel cell engine. Membrane dehydration is one of the key issues that seriously affect the performance and lifespan of PEMFCs under low humidity conditions. In this work, an electrospinning approach was employed to fabricate gas diffusion layers (e-GDLs) composed of nanosized carbon fibers with a nanoscale pore structure. Further, a vapor deposition of Dow Corning Sylgard 184 was utilized to apply a hydrophobic coating to enhance the hydrophobicity of the e-GDL. The fabricated e-GDL can help alleviate the dehydration of the catalyst-coated membrane by increasing the breakthrough pressure. The breakthrough pressure of the e-GDL is five folds higher than that of the current commercial GDL, owing to the combined effects of the nanostructure and enhanced hydrophobicity. This superior characteristic is expected to effectively alleviate membrane dehydration under low humidity conditions. In addition, the e-GDL has excellent elastic deformability, which can effectively alleviate the irreversible damage caused by the pre-tightening force in the stack assembly process, thus enhancing the durability and lifetime of PEMFCs.

АНАЛІЗ НАПРУЖЕНО-ДЕФОРМОВАНОГО СТАНУ ФІТИНГОВОГО СТИКУ ПАНЕЛЕЙ ВІД'ЄМНОЇ ЧАСТИНИ КРИЛА ТА ЦЕНТРОПЛАНА ТРАНСПОРТНОГО ЛІТАКА

Fitting joints are widely used in aircraft structures, and they are responsible for the interconnection of important components. The stress-strain state analysis of the fitting joint must be carried out before the performance analysis of the fitting joint. With the help of 3D modeling software (CATIA) and finite element analysis software (ANSYS), the stress-strain state of each component in the fitting joint of outer wing section was calculated in this paper. In the CATIA, the solid model is simplified and segmented according to the size of the cross section and the height of the center of gravity of the model. In the ANSYS, the beam elements are used to replace the simplified segmented model to obtain the internal force distribution of the solid model and to determine the magnitude and change law of the stress applied to the end of the solid model. When calculating the force transmitted by the fastener, the pre-tightening force of the bolt and the interaction between the surfaces of the component are taken into account, so as to simulate the real force situation well. Therefore, it is a very feasible method to use the CATIA and ANSYS to obtain the stress-strain state of components in the fitting joint of center wing section and outer wing section.The results show that under the working conditions of the fitting joint (130Mpa), the fitting of outer wing section with center section has a maximum stress of 245.79Mpa and a maximum strain of 0.0035, the stringer of outer wing section has a maximum stress of 293.17Mpa and a maximum strain of 0.0047, the lower panel of outer wing section has a maximum stress of 289.53Mpa and a maximum strain of 0.0042. The connecting bolts (M8 and M6) have a maximum stress of 686.81Mpa and a maximum strain of 0.0063, which meets the design requirements. In addition, according to the analysis results of the stress-strain state of the fitting joint of outer wing section, the force distribution of the bolts in the fitting joint of outer wing section with center section was obtained in this paper. It has been confirmed that due to the different positions and force areas of the bolts, the force distribution between rows of bolts is uneven, and the first row of bolts has a more force.