Preload Force Research Articles

Mechanism and control of preload force loss of precast structural joint bolts under freeze–Thaw environments

Bolt-connected precast buildings are increasingly prevalent, especially due to their efficient force transfer and accelerated construction processes. However, in cold climates, special attention must be directed towards the effects of freeze-thaw (F-T) damage on concrete at bolt connection sites. This study conducted an accelerated F-t-test to investigate how concrete F-T damage influences the preload force of the connection bolts. The changes in bolt preload forces across F-T cycles were monitored using advanced fiber optic sensing technology. To mitigate preload force loss, silicone rubber sleeves were introduced into the bolts. Results indicate a correlation between initial preload force and subsequent preload loss, with lower initial preloads leading to greater losses. Additionally, the concrete's frost resistance significantly affects preload force loss, with less resistant specimens showing marked preload decreases. A notable risk of brittle damage arises after 3 to 6 F-T cycles if a 4 mm gap between the bolt and concrete exists, attributed to water freezing and expansion within the gap. Concrete specimens subjected to our proposed mitigation strategies effectively withstand over 140 F-T cycles, substantially lowering crack damage risks.

Establishment of rigid-flexible coupling model of leaf spring detector detection arm and the optimization of its accuracy

A pipeline through-diameter detector is vital in pipeline detection. Still, the commonly used through-diameter detector is a generally complex structure, sizeable structural size, not suitable for small pipe diameters, significant deformation of the pipeline, as well as high-precision detection requirements (Zhang et al., 2019). In this paper, the rigid-flexible coupling system and accuracy optimization of the detection arm of the leaf spring detector is proposed to improve the detection accuracy under the rigid-flexible coupling state. Under the condition of rigid-flexible coupling, the process and stage of over-convex defects are studied, the effects of different motion speeds, different preload forces, and different defect L/D ratios on the detection accuracy are analyzed, and the fitting values of the defects of the leaf spring detector detecting arm are obtained under the motion condition, which needs to be corrected for the right values to reduce the error and improve the detection accuracy under the condition of rigid-flexible coupling.

Fabrication and characterization of smart titanium alloy bolt based on high-frequency piezoelectric thin-film.

We reported here on the fabrication and characterization of a smart titanium alloy bolt based on a high-frequency piezoelectric thin-film sensor. The thin-film sensor was directly deposited on a titanium alloy bolt head with radio frequency magnetron sputtering and characterized by a scanning electron microscope and an atomic force microscope. The ultrasonic characteristics of the smart bolt, which include a pure and broad frequency spectrum peaked at 14.81MHz, high measurement accuracy below 3%, and high repeatability free from some interference from bolt detection position change, were fully characterized. No obvious frequency shift was observed with the increase in axial preload. Based on the mono-wave method [TOF (time of flight) of longitudinal mode wave], TOF change increased linearly with preload force in the range of 0-20kN. With the increase in temperature from 22 to 150°C, the TOF linearly increases while the longitudinal wave velocity linearly decreases. The results indicate the prepared smart titanium alloy bolt is suitable as a smart aviation and automotive fastener.

Simulation and experimental study on contact pressure distribution of contact interface in single and double bolted connection structures

Bolted joints play an important role in aerospace, machinery manufacturing, weapons and other fields, and the contact pressure distribution at the connection interface seriously affects the service performance of the bolts. Contact pressure analysis is an essential basis and reference for structural design, calibration, inspection, and safety monitoring of bolted connection structures. Considering the preload force and frictional contact between the joint components, a block mapping hexahedron mesh generation and finite element modeling method for bolted connections is presented, and the finite element models of single and double bolted structures are constructed. Then, an experimental test platform for measuring contact pressure distribution is constructed. Comparison of finite element analysis results with experimental results for the contact pressure distribution in the single and double-bolted joints; the root mean squared error of contact pressure distribution is less than 5%, which verifies the effectiveness of the finite element models. After that, the models are used to study the contact pressure distribution in single-bolted joints and contact pressure coupling effect of double-bolted joints, and the normal stress distribution features within members and contact pressure distribution contour are revealed for single and double-bolted joint. Finally, the finite element models are adopted to investigate the effects of the clamping length, preload, material properties, hole clearance, and bolt size on contact pressure distribution in single-bolted joints. The coupling effect of contact pressure distribution in double-bolted joints under different preloads and geometric parameters are also examined.

Investigation of the leakage in the flow distribution pair of radial piston hydraulic motors through CFD analysis and experiments

The internal leakage of a radial piston motor (RPM) is an unavoidable structural characteristic, and the amount of internal leakage has a critical effect on the volumetric efficiency of the motor. Using the distribution plate as the force body, an equation for the balance between the preload spring force and the hydrodynamic force is analytically derived, the variation range of the clearance of the flow distribution pair (FDP) is determined, and a model for the internal leakage flow of the FDP is developed. Based on computational fluid dynamics (CFD) simulations, the effects of the oil film thickness, inlet pressure, motor speed, and oil temperature on the leakage volume are investigated. An efficiency test system for RPMs is built and tests are performed on motor prototypes. The experimental results show that the error between experimental and simulation results decreases gradually with increasing motor speed. When the motor runs at the rated speed, the error is stable within 5%. The experimental results verify the correctness of both the theoretical and CFD models. The CFD analysis method can be used as a technical means to optimize the motor volumetric efficiency and the preload spring design.

Influence of temperature and preload force on capacitance and electromechanical impedance of lead zirconate titanate piezoelectric wafer active sensors for structural health monitoring of bolts

This study focuses on the effect of temperature and preload force on capacitance and electromechanical impedance of lead zirconate titanate piezoelectric wafer active sensors for structural health monitoring of bolts. We explain the influence of temperature on the basis of the phenomenological thermodynamic theory of ferroelectricity by Landau, Ginsburg and Devonshire. The article illustrates the effect of damping the radial deformation of piezoelectric sensors on the capacitance and electromechanical impedance spectra in structural health monitoring of bolts. We also explains the similarities between the effects of temperature and preload force on the electromechanical impedance spectra. We establish a clear correlation between the mechanical strain in the region of the sensor (here due to a preload force), the capacitance and the electromechanical impedance spectra and thus show that piezoelectric sensors made of lead–zirconate–titanate can be used excellently in areas of variable mechanical strain. The article enhances the understanding of the measurement method and facilitates the transfer of the measurement method to other problems in structural health monitoring. Furthermore, the acquired knowledge serves as a solid basis for verifying the plausibility of data sets containing electromechanical impedance spectra.

Fatigue strength assessment of preloaded cross-toothed flange connections based on the FKM guidelines

Cross-toothed flange connections are used in drivetrains for form-fit coupling of shafts. They belong to the group of non-shiftable couplings. Compared to frictional connections, tooth flange connections can transmit significantly higher torques in the same space. In contrast to other tooth couplings, the crossed tooth flange coupling investigated here is characterized by a particularly complex load distribution. The preload force, which is necessary to transmit operational loads, is generated by tensioning bolts, which can be located centrally or decentralized. Thus, the stress condition in the notch of the coupling is always determined by a superposition of stresses from preload force and operating loads.Extensive experimental and simulative investigations were carried out as a part of a research project. In addition to the development of a pragmatic, specially adapted calculation concept for cross-toothed couplings for practice, the experimental tests were accompanied by calculations with the FKM guideline “Analytical Strength Assessment” and the FKM guideline “non-linear”, The determination of local stresses was carried out with the help of elasticity theoretical and elastic-plastic FE full-contact calculations based on experimentally determined material data.This article deals with the possibilities of calculations based on the FE simulation results using the above mentioned FKM guidelines. The experimentally determined load-carrying capacity is critically compared to the calculation results. The focus is on the implementation of the fatigue strength analysis in the context of the corresponding boundary conditions. Topics such as the assumed knee point of the Wöhler curve to the fatigue strength range are discussed as well as the evaluation options for elastic-plastic FE results for the guideline „non-linear”.

High-strength preload indicator inner washer forward design method

The preload indicator bolt assembly is a fastener that achieves the desired preload effect by simply tightening the preload nut within a specified range without additional measuring tools. The inner washer is a critical component in this assembly, with its outer diameter and height serving as crucial design parameters. In this paper, an equivalent mechanical model is established for the preload indicator bolt assembly. Utilizing this model, an iterative search process is developed to determine the optimal outer diameter and height of the inner washer. The analytical relationship between the bolt preload force and nut displacement is compared and validated against finite element analysis and experimental results, yielding favorable agreement. Notably, the nut tightening angle can vary within the range of 187°–242°, while the preload force exhibits a minimal variation of only ±2% for type 10-0A bolt connection (Bolt diameter and bolt pitch are φ16 mm and 1.41 mm, respectively. The material of bolt, inner ring, and flat ring are GH4169, 40CrNiMoA, and 30CrMo, respectively). This feature significantly simplifies the installation process of the preload indicator bolt assembly in real-world applications, offering great convenience. The increment in tension force on preloaded bolts under external loads exhibits an almost identical trend for both connection methods. Under the same preload force and the same eccentric working load conditions, the thickness of the connected components follows the same trend as their contact area.

Effect of preload forces on multidimensional signal dynamic behaviours for battery early safety warning

Providing early safety warning for batteries in real-world applications is challenging. In this study, comprehensive thermal abuse experiments are conducted to clarify the multidimensional signal evolution of battery failure under various preload forces. The time-sequence relationship among expansion force, voltage, and temperature during thermal abuse under five categorised stages is revealed. Three characteristic peaks are identified for the expansion force, which correspond to venting, internal short-circuiting, and thermal runaway. In particular, an abnormal expansion force signal can be detected at temperatures as low as 42.4 °C, followed by battery thermal runaway in approximately 6.5 min. Moreover, reducing the preload force can improve the effectiveness of the early-warning method via the expansion force. Specifically, reducing the preload force from 6000 to 1000 N prolongs the warning time (i.e., 227 to 398 s) before thermal runaway is triggered. Based on the results, a notable expansion force early-warning method is proposed that can successfully enable early safety warning approximately 375 s ahead of battery thermal runaway and effectively prevent failure propagation with module validation. This study provides a practical reference for the development of timely and accurate early-warning strategies as well as guidance for the design of safer battery systems.

Design and experiment on mechanized batch harvesting of Shiitake mushrooms

Shiitake mushroom must be harvested in time or its commercial value will be reduced. At present, manual harvesting is time-consuming and labor-intensive, and the robotic selective harvesting is far from mature and marketable. Based on the analysis of manual harvesting, a mechanized batch-based harvesting method for the stick cultivation of shiitake mushrooms is proposed as an alternative harvest method in the scenario of large-scale factory production. The feasibility of the simplified picking method was verified by a data acquisition system with integrated force sensor and inertial measurement unit, and the picking force and picking action during manual picking were measured. A mechanized harvesting scheme by picking rings with forward forces to the mushroom stalk was proposed, and its finite element analysis concluded that the mushroom could be picked without damaging the mushroom by using a 5/10 size latex tube. A new mushroom Batch Harvesting Picker (BHP) was designed, including a pushing mechanism, a guiding mechanism, and a harvesting mechanism. By analyzing the causes of harvesting failure and mushroom damage, the stick surface profiling unit were improved by multi-body dynamics simulation. The simulation results show that when the preload force of the reset spring of the harvesting mechanism is set to 30 N, the least pressure on the mushroom stick is 8.97 N, and the picking ring working closer along the surface of stick. The experiment of BHP showed that the harvesting success rate is 98.93 %, the harvesting damage rate is 3.31 %, and the average harvesting time of a single mushroom stick is 9.8 s, which improved the harvesting efficiency of single stick by 2.2–6.6 times compared with the manual harvesting process, which proved the feasibility and efficiency of this batch harvesting scheme in large-scale factory production of shiitake mushrooms.

Research Progress on Influencing Factors of Bolted Joint Structure Loosening

Loosening of bolted joint structure is a critical failure mode mainly caused by the slippage and friction behaviours on the thread and bearing surfaces. Domestic and foreign scholars have conducted a series of studies on the loosening mechanism and anti-loosening methods of bolted joint structures; however, there are fewer summaries on the influencing factors of loosening of bolted joint structures. This paper takes the phenomenon of loosening of bolted joint structure as the research object, summarizes the research method of loosening of bolt joint structure and the influencing factors, and summarizes the influencing law of loosening of bolted joint structure in four aspects, namely, preload force, external load factors, structural factors, and operating temperature, to provide references for the design of anti-loosening of bolted joint structure.

Research on the design and application of wind turbine mechanical parts based on parametric modeling

Abstract Based on ANSYS finite element analysis software, a parametric modeling interface for wind turbine blades and pitch bearings is developed using parametric design language. The parametric modeling interface is used to quickly establish a simplified finite element model of the blade and pitch bearing so as to optimize the design of the blade structure, calculate the maximum tensile stress of the bearing and bolt connection, and analyze the relationship between the working stress of the bearing and bolt and the bolt preload. The analysis and calculation results guide the safety and reliability of wind turbine parts design. After analysis, the optimization of blade structure is mainly in the region of leaf root enhancement, the number of layers laid in the cross-section of No. 1-3 has no major modification, the bi-directional cloth in the cross-section of No. 3-6 is increased by 55 layers, 5 layers reduce the cross-section of No. 7-8, and the cross-section of No. 16-23, 1 layer of the bi-directional cloth is increased in order to improve the strength of the tip of the blade and the resistance to bending capacity. The preload force applied to the pitch bearing during the actual installation process is generally 50% to 70% of the yield limit of the bolt material. The pitch bearings have the best load-carrying capacity under ultimate loads, with the ditch curvature radius coefficient and clearance generally around 0.530 and −0.12mm.

Design, Manufacturing, and Testing of a Non‐Preload Variable Friction Damper for Seismic Application of Buildings

Friction dampers are widely used due to their simple structure, remarkable energy dissipation capacity, and frequency independence. However, existing friction dampers are prone to relaxing the preload force during long‐term service, which can lead to cold bonding or cold solidification. To overcome this critical shortcoming, a novel non‐preload variable friction damper (NVFD) was firstly proposed. The construction of the proposed NVFD is provided in detail. Furthermore, restoring the force model through the amplification factors of friction force and inertial mass was derived based on the principle of the proposed NVFD. Then, pseudo‐static tests with various parameters were conducted. Finally, a single‐degree‐of‐freedom (SDOF) structure was employed to compare the effectiveness of this paper’s new NVFD with a conventional friction damper (FD) under various earthquake levels. The results show that non‐preload characteristics avoided the problems of large preloads by traditional friction dampers; thus, the NVFD had stable and reliable variable friction performance, which can effectively adapt to different hazard levels.

Three-dimensional mechanical characteristics analysis of bolted joints and loosening mechanism

Bolted joints are widely used in various industries. However, in challenging conditions such as shock, vibration, and temperature fluctuations, threads can loosen, leading to equipment damage and accidents. Scholars have introduced self-locking thread designs like wedge-shaped self-locking threads and stepped threads to improve anti-loosening performances. While experiments support their effectiveness, previous research primarily focused on optimizing thread structure parameters, and the studies of loosening mechanism are not in-depth enough, which restricts the development of anti-loosening bolted joints. This paper proposes a parametric modeling approach to create 3D elastic–plastic finite element models of bolted joints with different thread profiles. This approach allows for a comprehensive analysis of structural behavior, stress distribution, and load conditions, enabling the in-depth examination of the mechanical properties for thread loosening. A novel arc-lock anti-loosening threads design is proposed. Arc-lock threads are found to provide superior load distribution uniformity, increased normal force, and enhanced frictional resistance. Furthermore, the correctness of the finite element results is validated through photoelastic experiments and transverse vibration experiments. Results show that under a preload force of 225.5kN, the assembly of M24 Grade 10.9 bolts with Grade 10 nuts exhibit RMSE (Root Mean Square Error) values of 11.25, 9.02, and 8.76 for regular threads, wedge-shaped threads and arc-lock threads, respectively. Arc-lock threads demonstrate a more uniform stress distribution. In transverse vibration experiments under fully tightened conditions, regular threads loosened at the 2326th vibration cycle, while wedge-shaped self-locking threads and arc-lock threads maintained the preload percentages of 91.24% and 93.51%, respectively. These findings offer a scientific basis for understanding anti-loosening mechanisms in bolted joints and inform anti-loosening thread design.

Non-destructive detection of high-strength wind turbine bolt looseness using digital image correlation

Looseness of high-strength wind turbine bolts is one of the main types of mechanical failure that threaten the quality and safety of wind turbines, and how to non-destructively detect bolt loosening is essential to accurate assessment of operational reliability of wind turbine structures. Therefore, to address the issue of looseness detection of high-strength wind turbine bolts, this paper proposes a non-destructive detection method based on digital image correlation (DIC). Firstly, the mathematical relationships between the inplane displacement component of the bolt’s nut surface, the bolt’s preload force loss and the bolt loosening angle are both deduced theoretically. Then, experimental measurements are respectively conducted with DIC with different small bolt loosening angles. The results show that the bolt loosening angle detection method based on DIC has a detection accuracy of over 95%, and the bolt’s preload force loss evaluated by the deduced relationship has a good agreement with the empirical value. Therefore, the proposed DIC-based bolt loosening angle detection method can meet the requirements of engineering inspection, and can achieve quantitative assessment of preload forces loss of wind turbine bolt.

Effect of fiber annealing temperature on twisted and coiled UHMWPE actuator performance

Twisted and coiled polymer (TCP) actuators are flexible, wearable, and cost effective. However, the effects of annealing temperature on the properties of these devices are poorly understood. Thus, TCPs were prepared using ultra-high molecular weight polyethylene (UHMWPE) fibers and NiCr string and characterized. High-temperature annealing caused internal crystal-phase transformation, and annealing at 130 °C yielded a coiled fiber with optimized mechanical properties. Electromechanical tests confirmed that TCPs prepared from UHMWPE fibers annealed at 130 °C exhibited the best performance. Additionally, the voltage, displacement, tensile force, and temperature variation in the TCP fibers were recorded under different driving currents and pre-load forces to determine the optimal working conditions, and 1200-cycle life-span tests were carried out for validation. Finally, the driving performance of a TCP array was explored, and the range of motion, pressure, and possibility of lifting weights were tested using a model finger. Overall, the TCP array can be used as a soft actuated dexterous hand robot.

Fatigue enhancement and hardening effect through ultrasonic vibration‐assisted ball‐burnishing process on AISI 1045 steel

AbstractThis paper aims to present a study of the effects of ball burnishing with vibration assistance on the bending fatigue endurance of cylindrical specimens subjected to bending stress and obtain the best input parameters. The specimens were burnished through six different combinations of preload force, number of passes, and vibration assistance, finding that burnishing while applying a 90‐N preload, five passes, and the addition of vibration assistance results in larger fatigue strength. In terms of roughness, it has been proved that vibration‐assisted ball burnishing reduces the mean roughness up to 90%, while enhancing the skewness and kurtosis parameters. The softening effect while deforming, caused by the vibration assistance, helped to reconstruct the surface, obtaining higher depths of affectation and hardening. Fatigue strength was improved by a 6.54% by only adding vibration assistance to the ball‐burnishing process.

Application of SLAM in bolt tightening monitoring process based on intelligent data algorithm analysis

Abstract In this paper, firstly, according to the requirements of static monitoring of bolt tightening quality, the bolt tightening process can be divided into four stages: snug, elastic deformation, yielding and plastic deformation, and the SLAM technology is applied to bolt monitoring modeling and building engineering modeling. Next, the pre-tightening force for the bolt is measured using the waveform expansion method, and the bolt tightening index can be determined. Then, all the collected bolt data are randomly combined into two categories of loosening and tightening to form a training data set, and the improved intelligent data algorithm is used to train and predict them. The results show a linear correlation between tightening degree x |τ ɛ| and preload force change ΔF under 0.31kN and 0.22kN loading gradients, and the linear correlation coefficient of the fitted curve is greater than 0.9215. The results of the data analysis verify the correctness of the theoretical analysis.

Rendering Perceived Terrain Stiffness in VR Via Preload Variation Against Body-Weight.

PreloadStep is a novel platform that creates the illusion of walking on different types of terrain in Virtual Reality without requiring users to wear any special instrumentation. PreloadStep works by compressing a set of springs between two plates, with the amount of compression determining the perceived stiffness of the virtual terrain. The platform can render perception of stiffness by applying preload forces up to 824 N in different portions of the terrain, capable of changing stiffness illusion even while a user is standing on it. The effectiveness of PreloadStep was tested in two perception studies (perception thresholds and haptic-visual congruence studies) and an example application, with the results indicating that it is a promising method for creating engaging virtual terrain experiences.

Characteristics and Experimental Research on Performance of the Seal Structure of Deepwater Collet Connector

The sealing reliability of collet connectors is essential within underwater production systems. This paper is based on the lens gasket sealing mechanism and Hertzian contact theory, establishing mechanical models for the core sealing components in preloaded and working states and analyzing the minimum required axial preload force for sealing. According to the sealing principles of the connector, the force characteristics of each sealing element are analyzed in both preloaded and working states. The interplay of forces between these elements is subsequently determined. Furthermore, the amplification of axial preload force within the sealing structure is confirmed through simulations of contact characteristics. Finally, the accuracy of theoretical and simulated results is confirmed through experimental validation.