Pre-tightening Force Research Articles

Effects of Bias Voltage and Target Current on Microstructure and Load Measurement Performance of ZnO Piezoelectric Coatings Applied to Bolt in Transformer

Electrical accidents caused by bolt looseness in transformers have been frequently reported in recent years. The monitoring, and warning of, axial force as an indicator of looseness is one of the key issues affecting the operation and maintenance of transformers. Traditional ultrasonic testing and a patch-type ultrasonic method, using piezoelectric probes and coupling agents, showed poor repeatability and accuracy in detecting the bolt pre-tightening force, because of the uncertainty of the contact interface produced via manual operation. A permanent thin-film pressure sensor (PMTS), which provides accurate and in-situ stress detection, is more suitable for bolts, to reveal the pretightening force. The key is depositing a nano-zinc oxide (ZnO) piezoelectric film with an excellent measurement performance, which could be tuned using deposition parameters. This paper investigates the effects of the current and bias voltage on the crystal structure and performance of ZnO piezoelectric films. The results show that the crystallinity degree and resistance decrease with the increase in bias voltage, while the target current could increase the crystallinity. However, a high current also brings large particles in the coating surface, which greatly decrease the resistance. The cause is expected to be related to the ion energy, which could be affected by the bias voltage and current. The PMTS deposited with an optimized bias voltage and current revealed excellent measurement performance, and is expected to be applied to the bolt, to detect the pretightening force.

Study on failure characteristics of fiber reinforced composite structural connections

In this paper, the three-dimensional progressive damage finite element models of composite bolted connection and adhesive-bolt hybrid connection were constructed, and the accuracy of the model is verified by comparing with the experimental results. The energy-based B-K criterion was used to simulate the damage and evolution of the adhesive layer, and the effects of bolt hole diameter, pre-tightening force and layup sequence on the failure characteristics of composite mechanical connections were analyzed. The results show that, in the bolted connection model, the final failure mode is typically extrusion damage near the bolt hole, with matrix failure being the primary form of failure. Appropriately increasing the diameter of the bolt hole or applying an appropriate pre-tightening force can both enhance the connection strength. Maximal strength of the connection structure is achieved when the first layer in the connection area is oriented at 0°, whereas if the first layer is oriented at 90°, the connection's bearing capacity is minimally reduced. In the adhesive-bolt hybrid connection model, the fiber and matrix damage of the four plies closest to the adhesive layer mainly spread along the 45°direction, and the damage is mainly matrix tensile damage.

Multi sensor fusion methods for state of charge estimation of smart lithium-ion batteries

Multi-dimensional sensing is the key characteristic of next generation smart batteries. But the existing researches on multi-sensor fusion methods haven't focused on algorithm mechanism, the global optimal solution has not been built, the superiority has not been proved theoretically. For the first time, this research built the global optimal structure of multi-sensor fusion state estimation algorithm. Specifically, the state of charge (SoC) estimation problem of lithium iron phosphate (LFP) batteries is studied, cooperating with voltage signal, expansion force (EF) signal is introduced. Firstly, a normalization algorithm is introduced to overcome the drift of EF under different cycles and different pre-tightening force. Secondly, the non-monotonic relationship of LFP battery's EF-SoC curve is addressed with a forced monotone transformation method in the transition areas. Then the global optimal multi-sensor fusion method is built, theoretical reductions are carried out to prove the higher precision of multi-sensor fusion methods compared to single-signal methods. Experiments are conducted to verify the effectiveness of the methods, even under the most serious situations, the fusion methods exhibit powerful correction ability, and the root mean square error can be controlled within 3 %. Moreover, the proposed algorithms shows strong tolerance to error sources.

Experimental investigation on 4D printed intelligent assembly cushion with adjustable pre-tightening force

In order to design an intelligent assembly cushion with an adjustable pre-tightening force, a reentrant honeycomb structure was printed by additive manufacturing to realize the active and intelligent assembly process of filling gaps. The thermo-mechanical deformation experiments of the reentrant honeycomb structure were conducted at different pre-compressions, constrained displacements, and recovery temperatures. The recovery force and the force recovery ratio under semi-constrained conditions are explored emphatically. The results show that pre-compression, constrained displacement, and recovery temperature affect the recovery force and force recovery ratio under semi-constrained conditions. The recovery force and force recovery ratio increase with pre-compression, decrease with constrained displacement, and increase with recovery temperature below the glass transition temperature. Based on these results, the adjustability of the recovery force of a reentrant honeycomb cushion can be controlled by changing the thermo-mechanical deformation processes. Finally, the reentrant honeycomb cushion is applied to the mimetic assembly environment for corresponding testing, achieving the design of an active and intelligent assembly cushion with an adjustable pre-tightening force.

Design Method for Automatic Assembly Production Line of Electric Valves in Space Propulsion Systems

This article proposes a design method for a valve automatic assembly production line in response to the automation assembly requirements of electric valve products in space propulsion systems and the engineering problems of inaccurate loading force control and low valve measurement accuracy in existing process methods. This method can achieve five assembly processes during the assembly process of electric valves, including pre-tightening force control, valve-core stroke measurement, performance testing, and shell structure welding. The article introduces the design of platform components such as process execution, positioning, and transportation, as well as the design and operation process of workstations. By combining the design of a three-axis motion mechanism, a small turntable, and a robotic arm, the product can achieve professional, positioning, full process automation, and equipment miniaturization design across multiple workstations. Through the design of precise control of loading force and non-contact optical measurement method of moving structure, compared with the original method, the parameters affecting product performance are precisely controlled and the precision is improved. And the multivariable decoupling of valve product performance is realized by this method. Through application verification, this automatic assembly production line can significantly improve the assembly efficiency of electric valve products and solve difficult problems in product engineering.

Investigation of the effect of pre-tightening forces on bolted connection for FRP-steel joints

This paper experimentally and numerically investigates the effect of pre-tightening forces on bolted connection for double-lap FRP-steel joints, considering varied levels of pre-tightening forces. In the experimental phase of this study, six bolted double-lap pull-pull specimens with varying pre-tightening degrees (preloaded of 0, 3, 6, 7, 8, and 9 N·m, respectively) were examined. Test results indicated that all specimens exhibited bearing failure of FRP plates and the load capacity was significantly influenced by the pre-tightening forces applied through bolts. The highest loading capacity (27.1 kN) was recorded for the specimen with a preloaded of 6 N·m. In order to study the stress distribution of FRP plate for the bolted specimens, three-dimensional finite element (FE) models were conducted. Based on the FE analyzing results, the pre-tightening coefficient Pc (the coefficient of the preload increment per pre-tightening torque of bolts) of 750 m−1 was concluded and further proved by the analysis of the stress in contact zones for specimens preloaded by 0, 3, and 6 N·m.

Thickness and Strength Analysis of Prestressed Anchor (Cable) Compression Arch Based on Safe Co-Mining of Deep Coal and Gas

The stability of the gas extraction roadway is very important for the safe mining of coal and gas. The compression arch formed by the combined action of the prestressed bolt (cable) support and surrounding rock has been widely used in the engineering practice of the gas extraction roadway. It is of great engineering application value to analyze the influence of prestressed bolt (cable) parameters on the compression arch. In this paper, combined with the engineering practice of the deep roadway in Huainan and Huaibei mining area of Anhui Province, the mechanical parameters of surrounding rock are measured via field coring and the laboratory. The numerical simulation software FLAC3D is used to analyze the typical position of fractured mudstone, mudstone, sandy mudstone and muddy sandstone under the bolt pre-tightening force of F = 50 kN, 70 kN and 100 kN; the bolt spacing of a × b = 400 mm × 400 mm, 500 mm × 500 mm and 600 mm × 600 mm; the bolt length of L = 1500 mm, 2000 mm, 2600 mm and 3000 mm; and the distribution characteristics of additional compressive stress on the surface of the side. The influence of the different lithology and bolt parameters on the thickness and strength of the compression arch was analyzed, and on this basis, prestressed anchor cables with a pre-tightening force of F = 80 kN, 100 kN and 120 kN and length of L = 3000 mm, 4000 mm and 6000 mm were applied, and their influence on the thickness and strength of the compression arch was analyzed. The results show that the bolt pre-tightening force (F) and the bolt length (L) have a significant effect on the thickness of the compression arch, while the surrounding rock lithology, the bolt spacing (a × b), the anchor cable pre-tightening force (F) and the anchor cable length (L) have no obvious effect on the thickness of the compression arch. The surrounding rock lithology, the bolt pre-tightening force (F), the bolt length (L), the bolt spacing (a × b), the anchor cable pre-tightening force (F) and the anchor cable length (L) have a significant effect on the strength of the compression arch.

Research on Non-contact Bolt Preload Monitoring Based on DIC

Bolt preload is a key parameter of the reliability of bolt connection. Traditional bolt preload detection generally uses torque wrench or high-precision strain sensor. In this paper, a new method of non-contact preload monitoring is realized by measuring the digital image of bolt elongation. A bolt tensile test device is designed, and the results of laser triangulation and three-dimensional point tracking are compared with those of optical measurement. The embedded load cell is used to monitor the bolt preload. The test results of M18 bolts with different bolt lengths and grades are evaluated. and it is found that the test values are close to the theoretical calculation, which can be used to predict the pretightening force.

Design of a Tomato Sorting Device Based on the Multisine-FSR Composite Measurement

The ripeness of tomatoes is crucial to determining their shelf life and quality. Most of the current methods for picking and sorting tomatoes take a long time, so this paper aims to design a device for sorting tomatoes based on force and bioelectrical impedance measurement. A force sensor installed on each of its four fingers may be used as an impedance measurement electrode. When picking tomatoes, the electrical impedance analysis circuit is first connected for pre-grasping. By applying a certain pre-tightening force, the FSR sensor on the end effector finger can be tightly attached to the tomato and establish an electric current pathway. Then, the electrical parameters of the tomato are measured to determine its maturity, and some of the electrical parameters are used for force monitoring compensation. Then, a force analysis is conducted to consider the resistance of the FSR under current stress. According to the principle of complex impedance circuit voltage division, the voltage signal on the tomato is determined. At the same time, the specific value of the grasping force at this time is determined based on the calibration of the pre-experiment and the compensation during the detection process, achieving real-time detection of the grasping force. The bioelectricity parameters of tomatoes can not only judge the ripeness of tomatoes, but also compensate for the force measurement stage to achieve more accurate non-destructive sorting. The experimental results showed that within 0.6 s of stable grasping, this system could complete tomato ripeness detection, improve the overall tomato sorting efficiency, and achieve 95% accuracy in identifying ripeness through impedance.

General prediction model of residual pretightening force of bolt group with one-step and multi-step pretightening and analysis of influencing factors from the perspective of elastic interaction

PurposeThe purpose is to predict the distribution of the residual pretightening force of the bolt group under the action of any initial pretightening force, and to achieve the final residual pretightening force as the target to solve the initial pretightening force value to be applied.Design/methodology/approachBased on the finite element method and the elastic interaction theory between bolt group, this paper establishes a prediction model for the residual pretightening force distribution of bolt group for one-step pretightening and multi-step pretightening of gasketless flange connection systems. In addition, using the general modeling method given in this paper, the prediction model of residual pretightening force of long plate bolt connection system is established, and compared with reference, which fully proves the effectiveness and universality of the general prediction model of residual pretightening force of bolt group.FindingsThe appropriate pretightening sequence, increasing the number of pretightening steps and variable amplitude loading can effectively reduce the influence of elastic interaction and improve the uniformity of residual pretightening force of the bolt group. And the selection of material, number of bolts and connected thickness of bolt connection system also has a great influence on the distribution of residual pretightening force of bolt groups.Originality/valueThe general prediction model for the residual pretightening force of bolt group of connecting structural components considering elastic interaction given in this paper can provide a reference for the design and optimization of the bolt assembly process of the rotor system and the casing system in aero-engine and the prediction of the performance of the connecting system.

Analysis of Sealing Characteristics of Lip Seal Rings for Deep-Sea Separable Pressure Vessels

Deep-sea pressure vessels are specialized pressure vessels designed for automatic deployment from underwater to the surface. These vessels find extensive applications in underwater life-saving and transportation. Their interiors are furnished with a pair of sealing rings, one of which is lip-shaped, and the other is a convex shape, to ensure a dependable seal. With increasing water depth, the sealing rings experience augmented pressure, resulting in a gradual pressing of the rings into the sealing groove. Using ANSYS workbench finite element software, a two-dimensional axisymmetric lip seal finite element model using forces for overall constraint was established, the complete process of progressive pressing into the sealing groove was simulated, and the deformation, contact stress, maximum shear stress, and von Mises stress distribution was also simulated. We also conducted a comparative analysis of lip seals under low and high-water pressure sealing conditions. The findings of the study indicate that when subjected to a combined effect of the installation pre-tightening force and the working water pressure, the lip seal experiences complete compression into the sealing groove at a specific water depth. When subjected to the simultaneous influence of water pressure on the sealing ring material and friction force on the contact surface, two extremes of contact stress manifest in the primary sealing zone of the lip seal. These extremes have the capacity to elevate the contact stress and the effective sealing width, ultimately leading to an improvement in the sealing performance. Concurrently, as the water pressure gradually increases, the inner concave circle of the sealing ring experiences stretching, leading to a reduction in stress concentration, equivalent stress, and shear stress to a considerable extent. This mechanism ensures that the lip-shaped sealing ring retains sufficient strength. This study offers a viable solution for conducting sealing studies on deep-sea separable pressure vessels.

Optimal phase compensation for a rotor-AMB system considering interface contact

Rotor-Active magnetic bearing (rotor-AMB) systems offer significant advantages in power consumption and are increasingly being applied in fluid machinery. However, in such machinery, the impeller and the rotor are commonly connected by bolt fastening. Once a certain pre-tightening force is applied to the bolted connection and the interface contact between the rotor and the impeller is formed, the flexible modal vibration will be excited when the rotor is levitated. The conventional Proportional-Integral-Derivative (PID) controller is limited in this vibration suppression and it is essential to increase the damping at bending mode to inhibit vibration. However, the calculation of the optimal phase compensated is based on the rotor-AMB model considering interface contact. In this work, the effect of the interface contact is equivalent to massless spring units, and the disturbance generated by spring units is acted upon the mechatronic system in the way of positive feedback. The detailed description of the transfer function from the disturbance to rotor deformation at fourth bending mode is obtained by theoretical model and system identification. The optimal phase of the system needed to inhibit the disturbance is determined by minimizing the gain of the transfer function at fourth bending mode. A combination of PID control and phase compensation is implemented in the experiment. The results show that the optimal phase is 50° as the calculation and the optimal phase compensation control can sufficiently inhibit the modal vibration.

A novel bonded-type 3-degree-of-freedom ultrasonic motor: design, simulation, and experimental investigation

Most of 3-degree-of-freedom (3-DOF) ultrasonic motors generally have the problems of low positioning accuracy, difficulty to apply preload, and excessive longitudinal dimension, leading to the limitation in industrial application. To address these issues, a novel bonded-type 3-DOF ultrasonic motor, consists of a convex cylindrical stator, a pre-tightening force structure, and a hemispherical rotor, is proposed in this study. A quadratically polarized toroidal piezoelectric ceramic is bonded to the upper surface of the stator. Three vibration modes of the stator are excited by applying different excitation signals on the piezoelectric ceramic. By coupling any two of the three vibration modes, the elliptical motion of the driving feet of the convex cylindrical stator around the x, y, and z axes are excited, respectively. A novel pre-tightening force application method is proposed to adjust the contact between the stator and rotor. Under the action of friction, the elliptical motion of the driving feet in three directions drives the rotor to rotate around three axes, respectively. The vibration modes of the stator are first simulated by using the finite element method. In addition, the optimal structural dimensions of the stator and the elliptical motion trajectories of the driving feet are calculated. Finally, a prototype of the proposed 3-DOF ultrasonic motor is fabricated and experimentally investigated. The experimental results show that the no-load rotary velocities of the motor prototype in the three rotation directions are 25 r min−1, 22 r min−1, and 380 r min−1, respectively, its start/stop response time are 4.1 ms/3.9 ms, 6.3 ms/7.5 ms, and 6.1 ms/7.9 ms, respectively, and its angular displacement resolutions are 4.3 μrad, 5.1 μrad, and 10.2 μrad, respectively, when the excitation voltage is 250 VPP. The proposed motor holds the advantages of compact structure, adjustable preload, and high positioning accuracy, and presents a broad application prospect in the fields of robot joint technology, optical tracking system, and laser communication.

Numerical simulation of damage evolution of bolted connectors considering fretting fatigue effect

ABSTRACT In engineering, the failure of bolted connector is mainly caused by multi-axis non-proportional fretting fatigue damage. A three-dimensional finite element model of bolted connector is established in this paper, and a damage constitutive model suitable for multi-axial fatigue analysis is established based on the critical plane SWT (Smith Watson-Topper) method and continuous damage mechanics theory. A material subroutine UMAT is developed to describe the damage model and realizes the visualization of the damage evolution process caused by the fretting fatigue effect. Based on the test, the validity of the program is verified, the fretting fatigue characteristics and damage evolution characteristics of the bolted connector are analyzed. The results show that (i) the damage evolution analysis method can make up for the deficiency that the critical plane SWT method is only used for simple components and can be applied to the damage evolution analysis and fatigue life evaluation of three-dimensional complex structures. (ii) The crack initiation position of the connecting plate does not change with the magnitude of the tensile load and pre tightening force. In the process of losing the bolt preload from 1 to 0.8 times, the connected parts will be damaged faster as the preload 20 decreases.

High-fidelity Modelling Approach for Investigating the Tightening Torque Effect in Thread Connection

Accurate replication of the torque-tightening effect is important when simulating the mechanical behavior of composite joints using the finite element (FE) approach. In this study, a parametric mesh construction strategy was developed to automatically build a high-fidelity 3D FE model with lift angle to simulate bolt thread interactions. An experimental approach was proposed to calibrate the FE model. The relation between tightening torque and the axial force was studied by the FE method, experiment, and engineering algorithm. Results showed that traditional empirical formula overestimate the clamping force. By using the proposed model to calculate the axial force of the bolt, the accuracy of the axial force can be significantly improved when analyzing the composite bolted joints. Finally, parametric simulations were performed to investigate the influence of coefficients of friction at thread interfaces and the nut/washer interfaces. The pre-tightening force was significantly influenced by the frictional coefficients at these interfaces. Results indicated that increasing the coefficient of friction (CoF) at the nut/washer interface from 0.1 to 0.2 can lead up to 28% reduction in the clamping force, while this increase was 23% for the threads interfaces.

Cause Analysis and Treatment of Abnormal Vibration of Hydraulic Generator Unit Caused by Coupling Defect

When a hydropower station 25MW hydropower unit is operated with load after overhaul, the upper bracket vibration will exceed the standard. To find out the cause of the problem and eliminate the fault, the mechanical, electromagnetic, and hydraulic aspects are mainly analyzed and checked. The results show that the excessive vibration of the upper bracket of the unit is caused by the incomplete pre-tightening force between the coupling bolts of the turbine and generator of the unit, as well as the improper location and thickness of the padding. It is characterized by a vibration component whose frequency is between the rotational frequency and twice the rotational frequency. By fully pre-tightening the coupling bolts and restoring the original padding position and thickness, the vibration of the upper bracket, upper guide swing, and other data are significantly improved, and the desired purpose is achieved. The cause analysis and fault treatment of the abnormal vibration of the hydro-generator unit can provide some reference for diagnosing other similar faults.

Research on vibration characteristics of silicon nitride 6206 full-ceramic bearing with different pre-tightening force and oil supply rate

Research on vibration characteristics of silicon nitride 6206 full-ceramic bearing with different pre-tightening force and oil supply rate

Experiment and Numerical Simulation of Strength and Stress Distribution Behaviors of Anchored Rock Mass in a Roadway

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock.

Experimental Study on Mechanical Properties of Automatic Anchoring Preloaded Energy Absorbing Anchor Rods

In order to enhance the anti-impact mechanical properties of the roadway support system, an automatic anchoring pre-tightening energy absorbing anchor composed of rod body, tray, constant resistance energy absorber, energy-absorbing casing bulging block, pre-tightening force warning washer, and nut and anchorage force warning stopper was designed and developed for the special requirements of rock burst roadway support. The anchor can automatically judge the anchoring force and pre-tightening force of the anchor, and also has the functions of energy absorption and early warning. The static load tensile test and impact test are used to study the mechanical properties of the energy absorbing anchor, such as the displacement distance, energy absorption, and impact time, and they are then compared with the mechanical properties of the conventional anchor. It is concluded that under static load, the yielding distance of the energy absorbing anchor is 1.67 times that of conventional anchor. The absorbed energy is 1.61 times that of the conventional anchor. Under the impact load, the displacement distance of the energy absorbing anchor is 2.02 times that of the conventional anchor. The absorbed energy is 1.85 times that of the conventional anchor, and the anti-impact time is 1.47 times that of the conventional anchor. The energy absorbing anchor increases the constant resistance deformation stage of the energy absorber during the deformation process, so that the anchor has better deformation ability, energy absorption, and anti-impact ability than the conventional anchor, and it can thus effectively guide and control the release and transformation of surrounding rock deformation energy.

Analysis of the contact resistance of the symmetrical double side cathode solid oxide fuel cell

In recent years, all research on symmetrical double side cathode solid oxide fuel cell (SDSC-SOFC) has mainly focused on electrochemical and mechanical properties. However, there is a lack of research on the contact resistance of SDSC-SOFC. The sintering model of SDSC-SOFC is established first, and then based on the sintering model, the impact of the pre-tightening force is considered. The effects of end plate thickness and pre-tightening force on contact resistance are analyzed. In order to improve the mass power density of SDSC-SOFC, an end plate thickness of 30 mm is recommended. The average contact resistance of the cathode decreases with the increase of the pre-tightening force, but the decreasing rate is reduced. When the pre-tightening force is greater than 400 N, the impact of the pre-tightening force on the average cathode contact resistance can be ignored.