Bolt Torque Research Articles

Experimental study of the effect of fastening bolts on PEMEC performance

The fastening bolt is one of the important parts of the stacked structure proton exchange membrane electrolyzer (PEMEC), and the bolt tightening behavior has a significant impact on the electrochemical performance of the PEMEC. In this paper, we use a transparent visualization system to explore the effect of tightening bolt behavior on the performance of PEMEC. Pressure sensitive paper was used to record the contact pressure distribution map of PEMEC under different bolt tightening methods, and a high-speed camera was used to record the state of gas-liquid two-phase flow inside PEMEC under different bolt tightening methods. Both of them are used to verify the effect of bolt tightening behavior on the performance of PEMEC. The experimental results show that the contact pressure of PEMEC increases with the increase of bolt torque, and the electrochemical performance first increases and then decreases with the increase of bolt torque. The optimum bolt torque is 3.5 N m for a square PEMEC with an end plate size of 100 mm × 100 mm and a membrane size of 50 mm × 50 mm × 0.17 mm. The PEMEC performance increases with the increase of bolt tightening steps, and the optimal tightening step for the system is three steps. In addition, symmetrical tightening of bolts is beneficial for improving electrochemical performance, and there is an optimal tightening sequence in the system. This paper illustrates the relationship between tightened bolts and PEMEC electrochemical performance, showing the relationship between bolt tightening and the gas-liquid two-phase flow state inside PEMEC. The research results can provide a reference for optimizing the assembly and installation process of PEMEC.

The Analysis of Loosening of Bolt Connection Due to Structural Vibration Through Changes in Dynamic Characteristics

Bolted joints are generally used to connect two or more mechanical structures due to their ease of assembly and disassembly for maintenance. However, the problem of vibration is one of the main challenges when the tightness of the bolted joints is insufficient, causing failures such as looseness and resulting in disconnection. Looseness is the most common cause of dynamically loaded bolted joint structure failure. This study tested a simple bolt joint structure to observe the looseness indication of the bolt joint after it was vibrated using a shaker in a single-frequency excitation. A freely fixed beam consisting of two beams connected by a bolt and subjected to varying bolt tightening torques. Then the response measurement is carried out by recording the FRF graph obtained from loosening and tightening bolt torque effects. Modal parameters such as personal frequency and damping ratio were collected through experimental modal analysis (EMA). It was found that the structure’s vibration could change the conditions of loosening or lower tightening torque indicated by shifting the structure’s natural frequency. In addition, the damping characteristics are also affected by changes in the tightening torque. Especially when conditions are loose, the damping ratio becomes much higher than that of tightening.

Quality control method of steel structure construction based on digital twin technology

Background: The quality of construction is crucial in evaluating steel structure. However, traditional quality control methods for steel structure construction have been criticized for their lack of intelligence, resulting in a heavier reliance on manual experience and post-construction inspections to address quality issues. This shortcoming makes quality management inefficient and labor-intensive. To address this issue, this paper proposes a smart quality control method based on digital twin technology. Methods: In this framework, data collection is used for subsequent quality control throughout the construction process. To improve pre-construction quality control, a mixed reality (MR) system is used to guide and train personnel. During the steel structure construction process, the Markov method is used to analyze and predict real-time data. Results: To test the effectiveness of the proposed method, ten sets of parallel tests were conducted to predict whether the bolt torque value was normal or not, resulting in an 80% accuracy rate. Conclusions: The proposed method for steel structure construction quality control was effectively certified, achieving active prevention and real-time control of quality problems and improving the overall intelligence level of quality control.

Design, construction, and performance of a próton exchange membrane water electrolyzer (PEM-WE)

This work presents the design and construction of a proton exchange membrane water electrolyzer (PEM-WE) for H2 production. The evaluation of the flow regimen in the flow channels was performed by computational fluid dynamic anlysis (CFD). The cell components were machined by computer numerical control (CNC) milling. The electrode membrane assembly (MEA) manufacturing consisted of a Nafion® 117 membrane and electrodes with an active area of 100 cm2. Electrocatalysts were deposited using the electrospray technique with a metal loading of 1 mg of Pt cm−2 in the cathode zone and 2 mg IrO∙cm−2 in the anode region. The different components were assembled to the six cell stack PEM-WE, which was held with a bolt torque of 1.7 N∙m. The PEM-WE stack was characterized in a potential range from to 11.8–15 V at a temperature interval ranging from 30 °C to 70 °C. Deionized water was supplied at 300 mL∙min−1. The best performance was registered when operating at 15 V and 70 °C, for an efficiency of 59.65%. The hydrogen production amount was 42 NL∙ h−1, and theamount of power consumed was 132 W∙h.

Electromechanical Impedance Temperature Compensation and Bolt Loosening Monitoring Based on Modified Unet and Multitask Learning

Bolts are frequently subjected to loosening due to time varying external loads during service. The electromechanical impedance (EMI) technique based on piezoelectric ceramic wafers (PZT) is sensitive to the initial bolt preload looseness. However, the change in environmental temperature has a great effect on EMI monitoring. Deep convolutional neural network (CNN) is a promising technique for EMI monitoring. Nevertheless, it is difficult to train a deep CNN with limited training data to accurately identify damages under a wide range of temperature variations. To this end, this study proposes a multitask CNN for identifying bolts loosening. The network consists of a temperature compensation subnetwork to compensate for the temperature effect, and a lightweight damage identification subnetwork to identify bolt loosening states. The temperature compensation subnetwork is a modified Unet, and both the impedance and temperature are used as its input. The damage identification subnetwork is connected in series behind the temperature compensation subnetwork. A multiloss function is proposed in which a TV regularizer is used. Experimental results show that the validation accuracy of the multitask network is 97.71% when the network is trained by only about 30 samples from each loosening state. Moreover, the generalization abilities of the proposed multitask model to unexpected temperatures and bolt torques are investigated. The model is interpreted by the integrated gradients method, and is also compared with single-task damage identification CNNs. It is proved that the multitask network trained by limited samples can achieve accurate damage identification in temperature varying environments.

Study on the method for detecting contact state of bolted joint surface based on laser ultrasonic

The contact state of the bolt joint surface has an important influence on the contact stiffness, damping, and other properties of the equipment. To obtain the contact state of the bolt joint surface, the method to detect the contact state of the bolt joint surface based on laser ultrasonic technology is proposed in this paper. The reflectivity under different working conditions is obtained by the reflection amplitude of the longitudinal wave before and after bolt tightening. The relationship between reflectivity and bolt torque is studied. The results show methods proposed in this paper can effectively detect the contact state of the bolt joint surface, and it provides a basis for the study of the mechanical properties of the contact surface.

In-process Jet Engine Bolt Torque Measurement Solved in Collaborative R&D Project

In-process Jet Engine Bolt Torque Measurement Solved in Collaborative R&D Project

Estimation of thermal contact conductance of spacecraft heat sink bolted joints

Efficient thermal management is one of the key steps required to minimize failure and enhance the lifespan of electronic packages deployed in space applications. Precise and accurate knowledge of thermal contact conductance at the electronics package — heat sink interface is a key input required to achieve the efficient design of heat sinks for the mentioned application. In this study, a novel non-intrusive method for estimating the spatially varying thermal contact conductance for thin-plate bolted joints used in spacecraft thermal control systems is presented. A five bolt configuration joining the electronics package base plate to the heat sink plate is considered. Different bolt torques and their effect on the interface thermal contact conductance between the plates are investigated. Using pressure-sensitive films, the actual contact area and its spatial variation is determined for each torque level in the range of 1.5 N m to 9.0 N m and the contact interface is divided into three regions. Heat transfer experiments are carried out in vacuum at a pressure of 1×10−6 mbar for different combinations of bolt torques, heat load and heat sink temperatures. The thermal contact conductance values over the three regions are simultaneously estimated using an inverse parameter estimation technique. To improve the computational accuracy of the estimation process, a two stage stochastic optimization technique using the Monte-Carlo random sampling algorithm is used and the obtained estimates are compared. With an increase in applied bolt torque from 1.5 N m to 6.0 N m, the actual contact area and the area weighted interface thermal contact conductance are found to increase by 72.26% and 138.82%, respectively. Furthermore, the stochastic estimates of the spatially varying thermal contact conductance obtained using the developed methodology are found to follow a normal distribution with the average limit of standard deviation being ±7.34%, ±6.26% and ±13.22% of the mean values for the considered three regions respectively.

Artificial Intelligence (AI)-Based Evaluation of Bolt Loosening Using Vibro-Acoustic Modulation (VAM) Features from a Combination of Simulation and Experiments

The detection of bolt loosening using vibro-acoustic modulation (VAM) has been increasingly investigated in the past decade. However, conventional nonlinear coefficients, derived from theoretical analysis, are usually based on the assumption of ideal wave–surface interactions at the joint interfaces. Such coefficients show a poor correlation with the tightening torque when the joint is under the combined influences of structural and material nonlinearities. A reliable inspection method of residual bolt torque is proposed in this study using support vector regression (SVR) with acoustic features from VAM. By considering the material intrinsic nonlinearity (MIN) and dissipative nonlinearity (DN), the responses of aluminum–aluminum and composite–composite bolted joints during the VAM test were accurately simulated. The SVRs were subsequently established based on the database built by combining simulated and experimental nonlinear spectral features when the joints were inspected at different scenarios. The results show that the evaluation of residual torque using the SVR models driven by the acoustic nonlinear responses had higher accuracy compared to the conventional nonlinear coefficients. Requiring limited experimental data, the proposed method can achieve a reliable inspection of bolt torque by including the simulated data in the machine training.

Evaluation of Axial Preload in Different-Frequency Smart Bolts by Laser Ultrasound.

We report here on a laser ultrasonic system to indirectly evaluate the preload force of different-frequency piezoelectric bolts. This newly developed system enables us to achieve the goal of non-contact excitation and synchronously collects the laser-induced ultrasonic signal by the combination of a smart piezoelectric sensor and a magnetically mounted transducer connector. A numerical model based on the finite element method (FEM) was developed to simulate the propagation and displacement distribution of laser-generated ultrasonic waves along the axial direction. The measured A-scan waveform basically coincided with the counterpart obtained from a theoretical simulation, confirming the effectiveness of the proposed system to measure a bolt. By comparison, a laser spot diameter of 6 mm was the optimal beam diameter for the excitation of the ultrasonic wave in the bolt. The linear relationship between time of flight (TOF) of the ultrasonic longitudinal wave and bolt torque was almost independent from the center frequency of the smart bolt. By contrast, a piezoelectric patch centered at 5 MHz was more suitable as an ultrasonic sensor in terms of the nonlinear effects component suppression and linear fitting degree between TOF and torque. The results indicate that the proposed system based on a surface-mounted piezoelectric sensor is a promising system for evaluating the axial preload change of connector and fastener and is an additional potential laser ultrasonic system for nondestructive tests.

Development of a novel buckling-restrained damper with additional friction energy dissipation: Component tests and structural verification

Aiming at solving the issue of the conventional buckling-restrained brace, i.e., the fixed yield strength and residual deformation, a novel buckling-restrained damper with additional friction energy dissipation (BFD) was proposed and tested in the present study. By fabricating an inner core with a small yield segment (SYS) and a large yield segment (LYS) connected in series and setting a friction device in parallel with the SYS, the dual stiffness and stable energy dissipation capacity of the BFD were achieved. Low-cycle fatigue tests were conducted on nine BFD specimens to investigate the influences of the length of the LYS, the length of the slotted holes, the bolt torque and the loading protocol on the hysteretic behavior of the BFD. The experimental results demonstrated that the strength of the BFD increased with the maximum strain of the LYS, whereas the low-cycle fatigue life of the BFD was negatively affected by the maximum strain of the LYS. The friction energy dissipation device could enhance the energy dissipation capability of the BFD throughout the working process. Moreover, the results from the numerical case study determined that the BFD could effectively control the displacement response of the SDOF system under different earthquake magnitudes.

Experimental Research on the Load Transfer Mechanism of Tie Plates for 400 km/h High-Speed Turnouts

Based on the research and development demand of the 400 km/h high-speed turnout, a new type of elastic iron tie plate based on stiffness optimization is proposed. The new elastic iron tie plate is expected to reduce the stiffness unevenness and effectively solve the problems in the use of existing elastic iron tie plates. However, the new plate uses rubber bosses instead of rubber washers. There are certain differences in the force transmission mechanism from the original tie plate because of the change in structure of the new tie plate. In this paper, a series of experiments are designed to quantitatively compare and analyze the overall stiffness characteristics of different tie-plate structures and the differences in bolt force transmission and distribution laws. The main conclusions are as follows. The laws of vertical load transfer and distribution in the new tie plate are remarkably different from those for the original tie plate because of the differences in their structures. Under the rated bolt torque, the force transferred to the upper surface of the tie plate through the rubber boss in the new tie plate is less than that in the original tie-plate structure by 5.18 kN in the assembled state. Further, the new structure also has lower tie plate precompression; hence, the influence on the stiffness characteristics of the tie plate is less than that in the original structure. However, the steel sleeve deflection in the new tie plate is greater than that in the original tie plate; that is, a larger proportion of the bolt preload force is borne by the steel sleeve, thus making the vulcanized rubber under the steel sleeve more vulnerable to shear damage. If put into actual use, the tie plate bolt torque will be somewhat different from the rated torque; because of the difference in the torques coupled with the different vertical load transfer mechanisms between the new and the original tie-plate structures, the precompression and the proportion of the bolt preload force borne by the steel sleeves of the two tie plates will also show different degrees of deviation corresponding to different deviations of the tie plate bolt torque. Therefore, the new tie plate structure needs to be further optimized to make the transfer mechanism of preload force of bolt as consistent with the original tie plate as possible. In addition, the vibration and deformation characteristics and long-term service performance of the new type of plate under the condition of vehicle passing will be studied through a small-scale field trial and systematic dynamic tests.

Temperature compensation to guided wave-based monitoring of bolt loosening using an attention-based multi-task network

Online monitoring of bolt torque is critical to ensure the safe operation of bolted structures. Guided waves have been intensively explored for bolt loosening monitoring. Nevertheless, guided waves are excessively sensitive to fluctuation of ambient temperature. As a result of the complexity of wave transmitting across a bolted joint, it is highly challenging to compensate for the effect of temperature. To this end, an attention-based multi-task network is developed towards accurate detection of bolt loosening in multi-bolt connections over a wide range of temperature variation. By integrating improved attention gate modules in a modified U-Net architecture, an attention U-Net is configured for temperature compensation. A two-layer convolutional subnetwork is connected in series behind the attention U-Net to identify bolt loosening. Experimental validation is carried out on a bolt jointed lap plate simulating a real aircraft structure. The results have proved that the developed multi-task network achieves temperature compensation and accurate bolt loosening identification. To further understand the multi-task network, the Integrated Gradients method and a simplified structure of the bolt lap plate are used to interpret the developed network. It is proved that the A0 mode is sensitive to bolt loosening, while the S0 mode is not.

Investigation into the transmission of guided waves across bolt jointed plates

Bolt joints are extensively used in aerospace and civil engineering. Online monitoring of bolt looseness is crucial to ensure the function and safety of these structures. Understanding the interaction between guided waves and the joint interfaces can aid in the design and optimization of such monitoring systems, and hence becomes important. However, the influence of contact area on guided wave energy passing through these jointed plates is still not clear. In this paper, a semi-analytic method, which combines finite element models with a wave superposition method, is proposed to predict the transmission of guided waves in joint interfaces. The wave mode conversions in the contact area are included. The model was validated by comparison with independent finite element models. In addition, the influence of the contact length on transmission coefficients of guided waves passing through the joint interface is investigated. The results were experimentally validated by wire electrical discharge machined specimens with various contact areas. Then, the transmitted guided wave and the contact area in a bolt jointed plate under different torques were measured experimentally and compared with the present method. The results of the two different experiments agree well with those predicted using the semi-analytic method, respectively. In particular, the experimental results of the bolt jointed plate show that the direct S0 wave packet energy decreases with the bolt preload, which can be explained by the proposed model. Thus, the proposed semi-analytic method demonstrates efficiency in the prediction of the power transmission coefficient and has potential applications in the selection of excitation frequencies in the online monitoring of jointed structures. On this basis, a normalized power transmission coefficient can be directly calculated by the energy of the first S0 wave packet in the received signal to monitor bolt torque.

Performance and design optimization of different numbers and bolt torque for air-cooled open-cathode proton exchange membrane fuel cells

Air-cooled open-cathode polymer electrolyte fuel cells have attracted increasing attention in the field of portable energy equipment. This study explores the influence of the number of single cells, and bolt torque on stack performance based on the measurements of polarization curves, the single-cell voltage, and temperature distribution. The stack bolt torque and the number of single cells present a linear relationship and should be reasonably matched to improve the stack performance. Remarkably, the more cells, the greater bolt torque is required to achieve better stack performance. The results show that the optimal range of the number of single cells for the air-cooled open-cathode polymer electrolyte fuel cells is 20–25. When the cell number increases to 32–40, stack operating temperature exceeds the optimal range, thus reducing the output power and mass power density. A novel modularized design for the stack with the optimal number of single cells is firstly proposed which effectively improves the thermal management and power performance index of the stack. The work conducted could provide the reference and guidance for the stack design and accelerate the application of air-cooled open-cathode fuel cells.

A Review of Fibre Reinforced Polymer Structures

This paper reviews Fibre Reinforced Polymer (FRP) composites in Civil Engineering applications. Three FRP types are used in Structural Engineering: FRP profiles for new construction, FRP rebars and FRP strengthening systems. Basic materials (fibres and resins), manufacturing processes and material properties are discussed. The focus of the paper is on all-FRP new-build structures and their joints. All-FRP structures use pultruded FRP profiles. Their connections and joints use bolting, bonding or a combination of both. For plate-to-pate connections, effects of geometry, fibre direction, type and rate of loading, bolt torque and bolt hole clearance, and washers on failure modes and strength are reviewed. FRP beam-columns joints are also reviewed. The joints are divided into five categories: web cleated, web and flange cleated, high strength, plate bolted and box profile joints. The effect of both static and cyclic loading on joints is studied. The joints’ failure modes are also discussed.

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.

Metal inserts for performance improvement in glass fiber‐reinforced polymer nanocomposite joints under accelerated aging conditions

AbstractIn the present work, the accelerated aging of glass/epoxy composite bolted joints was carried out for performance evaluation. The woven glass fiber was used as reinforcement and an optimum wt% of nanoclay as filler was used to counter the accelerated aging attack. The bolted joint specimen and its testing fixture were designed as per ASTM D5961 considering width to hole diameter ratio (W/D) and edge to hole diameter ratio (E/D) as 6 and 5, respectively. The specimens were tested with and without the metal inserts. The specimens were given a cyclic exposure of 8 h of ultraviolet radiation (at 60°C) followed by 4 h of condensation (at 50°C), for a maximum of 500 h. The bolt torque of 0, 2, and 4 Nm were used for the failure analysis of the joint. The metal insert and nanoclay particles proved to be positive contributors for the performance of bolted joints under accelerated aging conditions.

Effects of bolt torque and gasket geometric parameters on open-cathode polymer electrolyte fuel cells

Open-cathode polymer electrolyte fuel cells with compact design have attracted increasing attention in the field of portable energy equipment. In view of the open cathode design, these cells usually exhibit large ohmic and mass transfer resistances. Such resistances can be reduced by using optimized bolt torque as well as gasket. The present study explores the effects of bolt torque and gasket geometric parameters on cell performance based on various measurements of polarization curve, high-frequency impedance, electrochemical impedance spectroscopy, and pressure distribution indentation. Remarkably, a performance improvement of 20.1% is achieved with the increase of torque (1.0–5.0 N·m) due to the decrease of ohmic resistance. However, excess torque (5.5 N·m) results in a 1.3% power reduction due to the increased mass transfer resistance. For the gasket of the cell, reducing the gasket thickness (0.65–0.48 mm) and width (2.5–1.5 mm) leads to the decrease of ohmic resistance and improvement of the cell performance by 3.4%~11.1%. However, the gasket with the minimum thickness (0.40 mm) suffers from a serious mass transfer issue. The relationship between the GDL compression, gasket, and sealing groove is quantitatively introduced to explain how the geometric parameters of the gasket affect the cell performance. Additionally, the longitudinal and transverse deformation of the gasket is considered. It is concluded that the applied torque, GDL compression, gasket, and sealing groove should be reasonably matched to reduce the ohmic resistance and avoid mass transfer limitation.

Aging of bolted joints prepared from electron‐beam‐cured multiwalled carbon nanotube‐based nanocomposites with variable torques

AbstractWe evaluate the behavior of a bolted joint prepared from electron beam (EB)‐cured carbon/epoxy nanocomposites under accelerated weathering environment at varying bolt tightening torques. For strength improvement, different weight percentages (wt%) of multiwalled carbon nanotubes (MWCNTs) in the range 0.1–0.5 wt% were incorporated into the composite laminates; 0.3 wt% of MWCNT had the maximum tensile strength. The properties of EB‐cured composites were compared with those of thermally cured ones. For accelerated weathering, cyclic exposure of ultraviolet (UV) radiation as well as condensation at elevated temperatures was conducted for 1000 h on the nanocomposite specimens. The chemical, physical, thermal, and mechanical properties of the nanocomposites were studied under accelerated aging conditions. To determine the failure loads in the bolted joints, specimens were prepared as per ASTM D5961. It was found that after 1000 h of aging, there was only 5% reduction in the ultimate failure load for joints prepared with the addition of MWCNTs. It was also found that the bolt torque had a positive effect on the performance of the joints. The experimental results were validated with progressive damage analysis using the characteristic curve method along with the Hashin damage criteria.