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We investigate the propagation characteristics of two temporally separated soliton pulses with the same spectra, under the influence of stimulated Raman scattering, within a single-mode optical fiber. This analysis explores the behavior of the interacting solitons while propagating in different chalcogenide materials, exhibiting new features and promising prospects for soliton transmission in optical communication systems. Our study included all the interaction parameters constituting the nonlinear Schrödinger equation (NLSE). We have examined the relationship between the Kerr nonlinearity, interpulse and intrapulse Raman effects, and material-dependent collision length featuring a key aspect in logic design and phase control in mode-locking systems. We have also systematically shown the manifestation of the Raman response function from the Raman gain curve, which our mathematical model (the Lorentzian model) provides, that exhibits a near agreement with experimental data. Our findings reveal significant differences from the typical behavior of two-soliton interaction only due to Kerr nonlinearity. Furthermore, we have investigated the mechanism of the net energy transfer between the interacting solitons as an integral phenomenon involved in multiple soliton propagation. These results provide an insightful understanding of the associated nonlinear effects in high-power soliton transmission systems and are foreseen to possess the potential for designing advanced optical switches and mode-locked lasers. [ABSTRACT FROM AUTHOR]

Topological insulators with high spin–orbit coupling and helically spin-momentum-locked topological surface states (TSSs) can serve as efficient spin current generators for modern spintronics applications. We used the industrial-friendly DC magnetron sputtering technique to fabricate magnetic heterostructures consisting of Bi2Te3 (BT) as a topological insulator and Co60Fe20B20 (CFB) as a magnetic layer and studied the temperature-dependent spin pumping, utilizing out-of-plane ferromagnetic resonance spectroscopy. These results demonstrate that the effective spin-mixing conductance is significantly affected by the contribution of two-magnon scattering (TMS). It is found that the TMS-free effective spin-mixing conductance increases with decreasing temperature. Additionally, results from magneto-transport measurements indicate that the surface coherence length of BT is in accordance with the temperature-dependent effective spin-mixing conductance. This enhancement of effective mixing conductance correlated with the enhancement in the contribution of the TSSs as evaluated using the weak-anti-localization effect. This study provides a deeper understanding of the temperature-dependent spin dynamics in sputtered BT/CFB heterostructures which can serve as a guide for further exploration of such bilayers for topological-based spintronic applications. [ABSTRACT FROM AUTHOR]

Pre-tightening torque has a significant impact on the performance of a bolt-clamped high-frequency piezoelectric ultrasonic transducer widely used in wire bonding. To develop a vibratory response-based method for the determination of optimal pre-tightening torque, the vibration amplitude signals of the transducer under different excitation conditions were monitored, and the characteristic parameters of the response, involving the resonance frequency, settling time within the initial transient response, and vibration amplitude of the steady-state stage, were extracted. Based on a series of in-depth tests, analyses, and discussions, the influences that the pre-tightening torque has on the vibratory response properties were investigated. Then, the experimental measurement and the random forest method were combined to determine the optimal pre-tightening torque. The performance test results show that the developed method can give the optimal pre-tightening torque according to the desired vibrational response properties, and it is feasible, effective, and reliable as well as improves the adaptability and flexibility of the high-frequency ultrasonic transducer in the application. [ABSTRACT FROM AUTHOR]

Virtual trial assembly (VTA) using 3D laser scanning as the digital carrier can overcome the shortcomings of time‐consuming and costly physical preassembly. However, its application in large steel structures with bolted connections remains limited. First, this study introduces a novel approach for acquiring multiscale point cloud data of large steel members using terrestrial laser scanners (TLSs) and hand‐held scanner (HHS). This approach considers both the global data and the local details of the steel members. Additionally, a precise registration method based on magnetic 3D targets is proposed for multiscale point clouds, which enables the registration accuracy of multisource point clouds to reach submillimeter precision. Subsequently, a novel algorithm for feature point screening is introduced, which utilizes a dichotomous point cloud grid approach to identify and extract a significant quantity of bolt holes effectively. This approach enables fully automated and fast extraction of the point cloud on the cylindrical inner surface of the holes. Finally, the bounding box and Procrustes analysis approach are employed to perform VTA using the point cloud of the cylindrical bolt holes as the assembled features. The accuracy and feasibility of the above method are verified by a down‐scale modeling experiment and project test, which provide technical support for the VTA of large steel truss structures. [ABSTRACT FROM AUTHOR]

The results of an experimental investigation of a new dry connection for reinforced concrete slab elements are presented. Seven full-scale slabs were tested; one slab was monolithic and used as a control specimen, while the other six were assembled using top and bottom steel plates joined by steel bolts with high tensile strength. Two connection scenarios were investigated – a simple bolted connection and a connection with a shear key. The parameters studied were the use of stirrups at the connection section, the step size of the shear key, the bolt diameter and the number of bolts. The test results showed that using a shear key at the assembled section in demountable slabs was more efficient than the simple bolted connection, providing higher flexural stiffness, greater load capacity and less deflection. However, increasing the shear key step size improved the flexural performance of the demountable slabs. In addition, adding stirrups in the assembled section enhanced the flexural stiffness and the total load capacity of the demountable slabs. Predictions of the moment capacity and deflection of the demountable slabs showed reasonably good agreement with the experimental results but, to be generalised, additional calibrated data from experiments are required. [ABSTRACT FROM AUTHOR]

The experimental study presented in this paper aimed to investigate the effects of bolt number and their pattern on the failure time of minimally fire-protected glulam beam bolted connections. Four full-size glulam beam-end connection configurations reinforced perpendicular to wood grain with self-tapping screws (STS) were experimentally tested under exposure to elevated temperatures that followed the CAN/ULC S101 (Standard methods of fire endurance tests of building construction and materials. Underwriters Laboratories of Canada, Fifth edition, Ottawa, Canada, 2019) standard fire time–temperature curve. All metal connecting components (i.e., bolt heads and nuts and steel plate edges) were fire protected using wood plugs and strips, respectively. Throughout the duration of fire tests, all specimens were subjected to monotonic load causing bending moment equivalent to the maximum moment design capacity of the weakest unreinforced connection configuration. Fire test results show that the failure time of all four proposed wood–steel–wood connection configurations surpassed the 45-min mark, which is the minimum prescribed fire resistance rating for timber connections in applicable codes, with the two configurations that employed six bolts sustained the applied load for more than 60 min in standard fire conditions. Increasing the number of bolts from four to six enhanced the failure time of the proposed connection configurations with time increments more than those due to changing the bolt pattern. Most importantly, test results confirm that reinforcing the connections with STS fully curtailed wood splitting and averted row shear failure that is frequently encountered in similar but unreinforced connection configurations. [ABSTRACT FROM AUTHOR]

High-strength carbon steel bolts were fractured by the tension, shear, or combined failure mode in semirigid and flexible beam-to-column connections as observed from natural fire incidents and full-scale fire tests. This phenomenon is attributed to the temperature-sensitivity of quenching and tempering procedures on these bolts. However, provided that these bolts are replaced by stainless steel bolts in these connections, the connection performance of the latter can be better improved compared to that of the former. Accordingly, this paper documents an experimental investigation of low-carbon austenitic high-strength A4L-80 bolts after fire exposure to determine the temperature-based stress-strain curves. The residual properties of Young's modulus, yield and ultimate strengths, and ultimate strain obtained from the experimentally measured stress-strain curves were compared with those of base materials regarding A4L-80 and carbon steel bolts including Grade 8.8, 10.9, and 12.9. Considering the limitations of prediction accuracy of reduction models of base materials in the existing standards and design manuals, reduction models after fire exposure were proposed for five mechanical parameters (Young's modulus, yield and ultimate strengths, ultimate strain, and strain-hardening exponent in the Ramberg-Osgood model). In combination with the currently proposed reduction models, the temperature-dependent constituent model of A4L-80 was formulated using five mechanical parameters at ambient temperature. It is concluded that austenitic high-strength bolts after fire exposure are capable of providing a more pronounced enhancement to the fire resistance of semirigid connections than carbon steel bolts, and the formulated material model showed good consistency with stress-strain curves acquired from experimental tests. Finally, a finite element model (FEM) with this material model was established based on the previous experimental study of web angle cleat connections with A4L-80 after fire, according to which the moment-rotation curves obtained from FEM can correspond well to those done from tests in previous study. This confirms the further validation and prediction accuracy of the formulated material model. [ABSTRACT FROM AUTHOR]

Bolted joints are widely used in various engineering structures. The bolted joint may become loosening under long-term oscillating load, and cause reciprocating friction between the contact interfaces. Acoustic emission (AE) is a phenomenon of rapid release of transient elastic waves, which will be generated continuously during the reciprocating friction. The friction conditions will affect the characteristics of the contact interface and the related AE signals. Therefore, analyzing the quantitative relationship between friction conditions and AE signal is significant for applying AE technique in bolt loosening monitoring. However, researches on the relationship between AE Vrms and friction operating parameters are mostly focused on rotating machineries currently, whether the obtained conclusions are suitable for bolted joints is not clear. This paper finds that the commonly used quantitative relationship between the AE Vrms and friction operating parameters is not suitable for bolted joint structures by comparing the theoretical and experimental AE Vrms. The relationship is then modified through exponential parameter fitting and verified using the same experiments in this paper. The results show that the modified equation can accurately describe the quantitative relationship between the AE Vrms and the friction operating parameters, thus revealing the mechanism of acoustic emission signals generated during the gross-slip. [ABSTRACT FROM AUTHOR]

Summary: A novel proposal for an assembled bolted joint between a precast reinforced concrete beam and column is presented in this paper. In order to evaluate the behavior of the joint, a comprehensive experiment was carried out on a full‐scale precast concrete beam‐column joint based on bolted connection subjected to pseudo‐static loading. The experiment aims to investigate the failure mode, load carrying capacity, and energy dissipation characteristics of the joint. To further understand the performance of the joint, a finite element model was developed using ABAQUS. The difference in failure mode and ultimate bearing capacity between the bolted joints and cast‐in‐situ joints were analyzed in conjunction with the experimental results. Moreover, the impact of various parameters on the performance of the bolted joints was quantified. The characteristics of the bolted joints, such as the span‐depth ratio, reinforcement ratio of the beam, the stirrup ratio at the beam‐column junction, T‐end length, and the bolt strength grade, were meticulously analyzed through an examination of bearing capacity curve, stiffness degradation patterns, and energy dissipation capability. The results show that, in comparison with the traditional cast‐in‐situ joints, the damage failure extent exhibited by the bolted joints is notably smaller, thereby rendering it more advantageous for seismic restoration and replacement. Furthermore, the span‐depth ratio, reinforcement ratio of the beam, and the stirrup ratio have a greater influence on the seismic performance of bolted joints than the T‐end length and bolt strength grade. [ABSTRACT FROM AUTHOR]

The nonlinear vibrations of composite cylindrical–cylindrical shells with bolt loosening connections are investigated. First, a theoretical model of such a combined shell is developed, with a multisegmental virtual material ring technique being adopted to replicate the partial bolt looseness in the bolted connection zone of two single shells. Furthermore, to consider the nonlinear vibration issue of such a bolted connection zone affected by external excitation amplitude, the equivalent Young’s modulus of the virtual material is defined, and the equation of motion is derived to solve nonlinear vibration parameters. Finally, three single composite cylindrical shells are connected with 12 bolts to form two combined shell specimens, and experimental tests are carried out to validate the model and examine the nonlinear vibration characteristics of such combined shells. Also, the impact of partial bolt loosening parameters on the nonlinear vibration behaviors is investigated with some important findings being summarized. The analysis methods, modeling techniques, test methods and important conclusions proposed in this study provide a useful reference for the study of the vibration issues of bolted composite shells. [ABSTRACT FROM AUTHOR]

Bolted joint behaviour is a key parameter in predicting transmission tower performance. Various types of joints are based on the number of bolts and their configuration. However, a few types of these joints were tested or modelled. In the present study, the load-deformation response of transmission tower joints as a joint behaviour was predicted using a simplified numerical model. Then, available experimental load-deformation responses of joints were used to verify the results of the proposed model. In the last step, the joint behaviours of a 400 kV transmission tower were predicted with the proposed numerical model. Then, the evaluation of the tower’s response was done with a numerical model in ABAQUS under testing loading conditions. Lastly, the deformation of a full-scale tested tower was compared with the numerical results. The numerical model results show a good agreement with the experimental results. The ultimate strength and its corresponding displacement at the full-scale model are predicted with an error of about 4%. Moreover, the failure mode of the transmission tower was not affected by the behaviour of the joints. [ABSTRACT FROM AUTHOR]

AbstractComposite materials are widely used in various aircraft due to their high specific strength, stiffness, corrosion resistance, and robust design flexibility. However, when subjected to complex loading conditions, composite structures are susceptible to damage, necessitating prompt repair upon aircraft return. Analyzing the re-damage process of repaired structures is crucial for assessing aircraft structural reliability, lifespan, and determining whether a repeat flight is warranted. In this study, a prediction method was proposed for re-damage behavior through meso-modeling and energy analysis of the repaired composite bolted joint. First, this article established a meso-mechanical model for composite laminates, analyzed force transfer characteristics at the fiber − matrix interface, and derived equations for stress field. Additionally, a strain energy distribution model was developed for composite bolted repaired joint near fibers and repaired area, proposing a damage prediction method based on the strain energy criterion. This method could anticipate the location, type, sequence, and magnitude of damage. Finally, simulation calculations yielded mechanical characteristics of the repaired area under typical load conditions, while loading tests verified the feasibility of the prediction method. This study offered an effective means of predicting performance degradation in composite structures and provided a vital direction for optimal spacecraft structure repairing methods and parameters. [ABSTRACT FROM AUTHOR]

Highlights In this paper, the mechanical properties, damage modes, and bolt load distribution of the bonded‐bolted hybrid three‐bolt joint were investigated by a combination of experiments and numerical simulations. Acoustic emission (AE) was used to monitor the tensile process of the connection in real time, and the K‐means clustering algorithm was used to realize the cluster analysis of the damage modes. A numerical simulation model of the tensile process of the joint was established using ABAQUS simulation software. The progressive damage evolution of composite laminates, and adhesive layer was characterized by using the VUMAT subroutine, the B‐K failure criterion, and cohesive element with zero thickness, respectively. The results show that four main damage modes occur in composite laminates during tension: matrix cracking, delamination, fiber pull‐out, and fiber breakage, with corresponding peak frequency ranges of (0–80 kHz), (80–210 kHz), (210–330 kHz), and (330–375 kHz), respectively. The adhesive layer between the laminates mainly exhibits peeling failure because of the secondary bending effect. In the load‐bearing process, the adhesive layer was loaded first and failed, and the bolt loading was delayed. Meanwhile, the results of bolt load distribution showed that the bolts and the adhesive layer at both ends carried greater loads. Damage modes and damage evolution of the bonded‐bolted hybrid joint in tension were analyzed by combining acoustic emission technology and numerical simulation. The simulation of delamination damage in composite laminates was carried out by inserting zero‐thickness cohesive elements into the laminates, and the delamination damage between the carbon fiber layup and the adjacent glass fiber layup was analyzed. The effect of the inclusion of the adhesive layer on the mechanical properties of the joint and the distribution of the bolt load was analyzed. [ABSTRACT FROM AUTHOR]

Highlights It is important to study damage evolution as well as failure of carbon fiber reinforced polymer (CFRP) plates bolted joints. Therefore, the quasi‐static tensile test on single‐lap and double‐lap CFRP plates bolted joints was conducted. Meanwhile, the tensile strength prediction model for titanium alloy bolted joint of CFRP plates was established based on the improved 3D Hashin failure criterion, then a theoretical model was proposed to accurately predict the load distributions and tilt angle of bolted joints. Thus, the load–displacement curves were divided into four stages, and load distributions at different stage points as well as the relationship between tilt angle of bolt and load variation were obtained. The damage evolution of single‐lap and double‐lap at different stage points was analyzed respectively, and failure mechanisms were revealed based on load distribution. The results show that the ultimate failure of single‐lap is caused by the intrusion of bolt head into CFRP plates, while double‐lap is caused by the compression deformation of central plate. The numerical simulation works are in high agreement with the experimental results. Calculate the load distribution at single‐lap and double‐lap bolted joints. Obtain the relationship between bolts tilt angle and load variation. Analysis of damage evolution in bolt‐hole wall of carbon fiber reinforced polymer (CFRP) plates. Using loads to reveal the failure mechanisms of single‐lap and double‐lap bolted joints of CFRP plates. [ABSTRACT FROM AUTHOR]

• A dynamic model of bolted joint rotor system considering rubbing and pedestal looseness fault is established. • The effect of the rubbing fault on dynamic properties of the bolted joint was evaluated. • The effect of the rubbing-pedestal-looseness coupled fault on dynamic properties of the bolted joint was studied. • Experimental studies is conducted on a bolted joint rotor-bearing test rig with pedestal and rubbing device. Rotor-stator rub and pedestal looseness are common faults in rotating machinery, such as large gas turbines that typically use bolted joint structures to fasten adjacent disks together. It is of great significance to investigate the vibration behaviors of the bolted joint rotor-bearing system with pedestal looseness and rubbing coupled fault, which can provide proofs for the fault diagnosis. In the present work, a dynamic model of the bolted joint rotor-bearing system with coupled fault is developed by using the finite element (FE) method, and then the vibration characteristic analysis is carried out. The rotor shafts that connected by the bolted joint element (BJE) are discretized as two sets of Timoshenko beam elements. The BJE is composed with four springs (two linear translational springs and two rotational springs with piecewise-linear stiffness). The interactions of rotor-stator contact are then modeled based on the Hertz contact theory and Coulomb's friction law, and the bearing forces are also calculated based on the Hertz contact theory. Moreover, the pedestal looseness fault is modeled through the piecewise-linear stiffness spring. The equations of motions of the bolted joint rotor-bearing system with coupled fault are then developed through FE theory and solved by the Newmark method. The dynamic responses are then calculated, and the frequency spectrums, bending stiffness of bolted joint, and vibration responses under different rotation speeds under the coupled fault are analyzed. The experimental study is finally conducted based on a bolted joint rotor test rig. Simulation results are in agreement with experiment results. The research results can provide a basis for understanding the rotor dynamic features of a bolted joint rotor system with coupled faults of rubbing and pedestal looseness. [ABSTRACT FROM AUTHOR]

Traditional vibro-acoustic modulation methods for bolt looseness detection often use a probe wave with single frequency. However, using a single frequency probe wave not only reduces the detection accuracy but also increases the difficulty of selecting the frequency of the probe wave. To overcome these drawbacks, this paper proposes a bolt looseness detection method based the vibro-acoustic modulation using a frequency sweep probe wave. For the low-frequency pump wave, the excitation frequency is set as the resonant frequency of the bolted joint to enhance the modulation effect. For the high-frequency probe wave, a frequency sweep excitation is used to replace the single frequency excitation, which improves the detection accuracy and overcomes the difficulty of selecting the probe frequency. A signal processing method is proposed to extract modulation information from the complex response signal obtained under a frequency sweep excitation. A nonlinear modulation index is defined using the extracted modulation information to quantify the loosening level of bolts. An experimental setup is designed to implement the vibro-acoustic modulation detection method on a bolted joint. Experimental results demonstrate that the proposed method is effective for detecting bolt looseness and has high detection sensitivity and accuracy for the early bolt loosening. [ABSTRACT FROM AUTHOR]

Based on the shortcomings of traditional bolts in the process of supporting surrounding rock, the structural composition and working principle of new bolts have been studied in detail. The working principle of the new bolt is divided into the elastic deformation stage and slip stage, and the energy constitutive equation of the corresponding stage is analysed. Then, Abaqus software is used to numerically simulate the working state of the bolt under static tension. With increasing drawing load, the maximum axial stress of the bolt and the von Mises stress of the surrounding rock first increased and then tended to stabilize, and the maximum axial displacement of the bolt gradually increased. The axial stress of the bolt was concentrated at the damping module, and the stress was mainly concentrated at the front damping module. The deformation of the bolt is mainly concentrated in the damping module of the first section, and the deformation of the bolt decreases rapidly with increasing anchoring depth. On-site pull-out tests confirmed that the drawing force of the new bolt increased by 128% and 24% compared with that of the pipe bolt and the left handed without longitudinal rebar bolt, respectively. The novel bolt has the characteristics of high strength and large displacement, which allows it to support the surrounding rock well and has good application prospects. [ABSTRACT FROM AUTHOR]

In this paper, the effects of interference-fit sizes and service environment temperature on the preload and relaxation of CFRP bolted joints are investigated based on an ultrasonic monitoring method. Specimens of different interference-fit sizes were subjected to insertion, preloading and preloading force monitoring for up to 200 h. To describe the preloading relaxation response of CFRP bolted joints, a comprehensive relaxation mechanics model is proposed. Experimental results demonstrate that this model accurately describe the variations in bolted preloading force under interference-fit conditions and thermal-oxygen environments. During the preloading process, a portion the axial force in interference-fit bolted joints is dissipated by interfacial frictional force and the magnitude of the frictional force is influenced by the interference-fit sizes. The interference-fit will lead to a tightly coupled interface, causing interface friction between the bolt-shank and the joint-holes, which can lead to a weakening transformation ability from tightening torque to axial force. Compared to clearance-fit condition, interference-fit can suppress the preloading relaxation effect of CFRP bolted joints to a certain extent. With an increase in interference-fit percentage (from 0% to 1.2%), the preloading relaxation coefficient rises from 94.4% to 95.7%. The additional interfacial friction effectively suppresses the creep deformation of composites. However, with an increase in the service temperature, the relaxation behavior of preloading forces in CFRP bolted joint significantly intensifies. As the environmental temperature rises from 25 ℃ to 150 ℃, the preloading relaxation coefficient decreases from 95.0% to 79.8%. High-temperature environments can lead changes in the material properties of composite and interface friction characteristics, even potentially leading to damage. [ABSTRACT FROM AUTHOR]

Bolted joints play a more and more important role in the structure with lighter weight and heavier load. This paper aims to provide an overview of different experimental approaches for the dynamic behavior of structures in the presence of bolted joints, especially the energy dissipation or damping at frictional interfaces. The comprehension of energy dissipation mechanisms due to friction is provided first, while the key parameters and the measurement techniques, such as the excitation force, the preload of the bolt, or the pressure at the interfaces, are briefly introduced. Secondly, the round-robin systems aim to measure the hysteresis parameters of the frictional joints under tangential loads are reviewed, summarizing the basic theory and the strategies to apply the excitation force or acquire the response in different testing systems. Followed by parameter identification strategies for bolted structures, the test rigs with one or more simplified bolted joints are summarized to give an insight into the understanding of typical characteristics of bolted structures, which are affected by the presence of friction. More complex test rigs hosting real-like or actual engineering structures with bolted lap or flange joints are also introduced to show the identification process of the dynamic characteristics of bolted connections employed in specific applications. Based on the review paper, researchers can get the basic knowledge about the experimental systems of the bolted structures, especially several classical round robin systems, such as the Gaul resonator and widely used Brake-Reuß beam system. Readers can take advantage of this background for more creative and effective future studies, make more progress on the study of assembled structures and understand the influence of bolting frictional connections on the dynamic response better. [ABSTRACT FROM AUTHOR]

There are many examples of steel structures subjected to severe environmental conditions with bolted connections directly exposed to climatic agents such as steel bridges, mining transfer towers, wind towers etc. In this experimental research, non‐slip joints with M16 and M20 bolts have been studied. The specimens were subjected to fourteen 12 h freeze‐thaw cycles, with periodic immersion in water and temperature oscillation. Subsequently, the connections were subjected to a slip test under monotonic load. The results were compared with other equal joints not subjected to freeze‐thaw cycles and kept at room temperature for the same time. Some interesting conclusions are extracted from this piece of research. It was observed that freeze‐thaw cycles negatively affect the slip resistance of non‐slip joints with GB+ZE surfaces, even with a slight increase in clamping force. Samples with SR and GB surfaces increase in their slip resistance was observed. [ABSTRACT FROM AUTHOR]

This paper presents the first seismic tests on a full-scale all-composite frame structure, constituted by pultruded glass fiber–reinforced polymer (GFRP) profiles, to the best of the authors' knowledge. These tests were performed in the scope of the FRP-Quake project, which aimed to provide an in-depth understanding of the dynamic and seismic behavior of all-GFRP structures, and to develop structural systems with adequate seismic resistance. Therefore, an extensive research program was conducted, from the material and component scales to the structural full-scale, which encompassed the development of appropriate beam-to-column bolted connection systems. The experimental campaign presented in this paper was composed of shaking table tests on a full-scale, two-story, three-dimensional (3D) frame of I section pultruded GFRP profiles connected with bolted stainless steel parts. First, modal identification tests were performed, which show the influence of adding floor masses, bracings, or both on the dynamic characteristics of the structure, which were accurately predicted with relatively simple linear finite-element (FE) models. Then, the frame structure was subjected to 18 base displacement histories with increasing intensity, which was based on the design earthquake for mainland Portugal. The results showed that the structure maintained its integrity for intensities up to 37% higher than the normative requirements. This showed the feasibility of using this type of all-GFRP structures in seismic areas. [ABSTRACT FROM AUTHOR]

This study investigated the effects of threaded bolt fasteners on the initial and final stiffness of bolted joints in special steel modular construction. A comprehensive set of 246 specimens, including 4, 7.6, and 12 mm thick plates with 20 and 30 mm diameter bolts and different end spacings, were tested. The results revealed that connections with threaded bolts exhibited lower initial stiffness compared to pure shaft connections. This study introduced a novel formula that significantly improved simulation results for bolted joints, surpassing previous modeling approaches. Following the American Society for Testing and Materials (ASTM) definition, the "elastic" stiffness values obtained from the laboratory tests were compared with those of Eurocode provisions. Additionally, ad hoc formulas were proposed for the stiffness of shank, lap connection with partially threaded, and fully threaded bolts. These results offer valuable insights for enhancing the stiffness of bolted shear connections. [ABSTRACT FROM AUTHOR]

In this study, the relaxation of the initial tightening preload of bolted carbon fiber reinforced thermoplastic sheet molding compound (CFRTP‐SMC) joints was experimentally investigated under different temperatures and initial preload conditions. The influence of preload relaxation on the bolted structures was evaluated using static bearing tests, whereas the failure modes during the test were verified based on metallographic observations. The experimental results indicate that the speed of the preload relaxation can be accelerated by increasing the temperature and initial preload. The static bearing strength of the bolted SMC material decreased with a continuous increase in the preload loss. Furthermore, the existence of a lateral preload protected the material around the assembly hole from buckling, resulting in a higher static bearing strength. The shielding effect of the preload was weakened after the relaxation of the initial preload. Highlights: Elevated temperature and initial preload can expedite the relaxation process.Preload loss will result in a declined static bearing performance.Initial tightening preload can protect the bolted SMC material from buckling. [ABSTRACT FROM AUTHOR]

There exist issues of ill-adaptability and low-accuracy in ultrasonic bolt stress measurement based on acoustic elasticity and scattering attenuation. Therefore, a bolt axial stress measurement method based on ultrasound multi-feature fusion is proposed in this paper. Firstly, ultrasound characteristic parameters based on the theory of acoustic elasticity are extracted, including the difference of time-of-flight (TOF) and the longitudinal wave attenuation coefficient in polycrystalline materials within the Rayleigh scattering range. Then, following the dimension reduction principle, the difference of TOF, attenuation coefficient, and clamping length are chosen as the input feature vectors for the fusion model. Subsequently, the SVR model is employed to establish a multi-feature fusion model for bolt axial stress measurement. Calibration and measurement experiments are conducted using the constructed experimental platform. Comparative analysis between the traditional measurement methods and the proposed method reveals that the SVR model can adapt to measurements of bolts with different lengths, overcoming the limitations of traditional methods. Furthermore, the measurement results of different fusion algorithms show that SVR yields significantly lower average relative errors in the measurement of the three bolts (3.35%, 4.44%, and 4.48%) compared to BP and RBF algorithms. This indicates higher measurement accuracy and immunity to low-stress effects. [ABSTRACT FROM AUTHOR]

This experimental study aimed to investigate the structural fire behaviour of damaged glulam beam connections retrofitted using self-tapping screws (STS). Four full-size glulam beam-end bolted connections with wood–steel–wood connection configurations using four or six bolts arranged in two different bolt patterns were examined. All connections were retrofitted using STS after being deliberately damaged through physical testing until failure. In a subsequent stage, the retrofitted connections were experimentally tested under standard fire exposure while subjected to the maximum design load of the weakest, undamaged, unreinforced connection configuration. The influence of the application of STS in terms of preventing wood-splitting propagation and maintaining reasonable fire resistance for the retrofitted connections was experimentally investigated and proven in this study. Results show that the retrofitted glulam beam connections maintained a minimum of approximately 67% of the failure time of identical but undamaged, unreinforced connections under standard fire exposure. [ABSTRACT FROM AUTHOR]

In this paper, we present a bolt preload monitoring system, including the system architecture and algorithms. We show how Finite Element Method (FEM) simulations aided the design and how we processed signals to achieve experimental validation. The preload is measured using a Piezoelectric Micromachined Ultrasonic Transducer (PMUT) in pulse-echo mode, by detecting the Change in Time-of-Flight (CTOF) of the acoustic wave generated by the PMUT, between no-load and load conditions. We performed FEM simulations to analyze the wave propagation inside the bolt and understand the effect of different configurations and parameters, such as transducer bandwidth, transducer position (head/tip), presence or absence of threads, as well as the frequency of the acoustic waves. In order to couple the PMUT to the bolt, a novel assembly process involving the deposition of an elastomeric acoustic impedance matching layer was developed. We achieved, for the first time with PMUTs, an experimental measure of bolt preload from the CTOF, with a good signal-to-noise ratio. Due to its low cost and small size, this system has great potential for use in the field for continuous monitoring throughout the operative life of the bolt. [ABSTRACT FROM AUTHOR]

Using bolts as shear connectors of the steel–concrete composite beams enables prefabricated assembly and makes it possible to demountable and reuse the prefabricated components. However, studies on the fire resistance of prefabricated demountable composite beams (PDCBs) connected by bolts are limited. In this paper, four full-scale fire resistance tests were conducted to investigate the fire resistance of PDCBs connected by shear bolts with profiled sheet ribs parallel to the steel beam. Experimental observations, heating curves, deformation curves, and critical temperatures of specimens were obtained through fire-resistant tests. Test results show that the shear failure of bolted connectors occurred in the partially connected PDCBs instead of in the fully connected ones. Under the same load ratio, the fire resistance limit of PDCBs with fire protection was 4.4 times that of PDCBs without fire protection. The temperatures of the upper flanges of the steel beams in the PDCBs were overestimated by the existing codes. Moreover, numerical heat transfer analysis was carried out to investigate the effect of concrete slab thickness, concrete moisture content and steel beam upper flange dimensions on the temperature distribution of the steel beam upper flange. Finally, based on the results, relevant recommendations are made for the method of calculating the temperature of the steel beam upper flange in the PDCBs. [ABSTRACT FROM AUTHOR]

A finite element analysis (FEA) was conducted to examine the behaviour of single-lap quasi-isotropic (QI) and cross-ply (CP) hybrid bolted/bonded (HBB) configurations subjected to tensile shear loading. Several critical design factors influencing the composite joint strength, failure conditions, and load-sharing mechanisms that would optimise the joining performance were assessed. The study of the stress concentration around the holes and along the adhesive layer highlights the fact that the HBB joints benefit from significantly lower stresses compared to only bolted joints, especially for CP configurations. The simulation results confirmed the redundancy of the middle bolt in a three-bolt HBB joint. The stiffness and plastic behaviour of the adhesive were found to be important factors that define the transition of the behaviour of the joint from a bolted type, where load sharing is predominant, to a bonded joint. The load-sharing potential, known as an indicator of the joint's performance, is improved by reducing the overlap length, using a low-stiffness, high-plasticity adhesive, and using thicker laminates in the QI layup configuration. Enhancing both the ratio of the edge distance to the hole diameter and washer size proves advantageous in reducing stresses within the adhesive layer, thereby improving the joint strength. [ABSTRACT FROM AUTHOR]

Residual drifts are an important measure of post-earthquake functionality in bridges and buildings, and can determine whether the structure remains fit for its intended purpose or not. This study aims at investigating numerically, through finite element (FE) analysis in ABAQUS, the cyclic response of exterior steel I beam-hollow column connection using welded shape memory alloys (SMA) bolts and seat angles. This is followed by validating the numerical model using an accredited experimental data available in the literature through different techniques, (1) SMA bolts, (2) SMA angles, (3) SMA bolts and angles. The parameters investigated included: SMA type, SMA angle thickness, SMA bolt diameter, SMA angle stiffener and SMA angle direction. The cyclic performance of the steel connection was enhanced further by varying the bolt diameter, plate thickness, angle type and direction. The results revealed that the connections equipped with a combination of SMA plates and SMA angles reduced the residual drift by up to 94%, and doubled the self-centering capability compared to conventional steel connections. Moreover, the parametric analysis showed that Fe-based SMA members could be a good alternative to NiTi based SMA members for improving the self-centering capability and reducing the residual drifts of conventional steel connections. [ABSTRACT FROM AUTHOR]

• Develop an original FE-analytical model of bolt tightening with elastic of bearing cap. • Propose a new assembly accuracy prediction method of planetary gear train. • Consider gear-shaft-bearing-bolt coupling effects on assembly accuracy. • Explore bolt tightening effects on shaft error motion and assembly accuracy. • Carry out the assembly accuracy and vibration tests to verify the proposed method. Planetary gear train (PGT) is a complex transmission system composed of gears, shafts, bearings and bolted joints, of which the assembly accuracy affects the transmission accuracy and dynamic behavior. In this paper, a new assembly accuracy prediction method is proposed for PGT considering gear-shaft-bearing-bolt coupling effects. The new method is formulated by establishing three models for bolt assembly, shaft error motion and assembly accuracy (transmission error) of PGT. The model for bolt assembly is an original FE-analytical model to analyze the bolt assembly effect on elastic deformation of bearing cap, which is developed by finite element (FE) method and analytical method for addressing the elastic effect of bearing cap and elastic interaction between bolts. The models for shaft error motion and assembly accuracy are performed by the three-dimensional contact analysis with errors and preload of bearing cap based on analytical method and kinematic geometry relationship. Combining the three models, the assembly accuracy can be predicted by simulations. The simulations indicate that the proper bolt assembly parameters can alleviate the influence of manufacturing errors on assembly accuracy. The assembly accuracy tests of PGT are conducted. The results well agree with the simulations', and the assembly accuracy is improved by the proper bolt assembly parameters. [ABSTRACT FROM AUTHOR]

The advantages of carbon nanotubes (CNTs) in fortifying the glass fiber reinforced polymeric (GFRP) composites are discussed in this paper. Bolted steel straps are utilized at the edges of composite plate to establish clamped conditions in the test setup. To minimize uncertainties caused by bolt attachments, a genetic algorithm-based model updating approach has been implemented by introducing artificial linear springs at the margins to achieve a better balance between theory and reality. The accuracy of the plate's results (natural frequencies and mode shapes) is verified, and the mechanical properties of randomly dispersed CNTs are incorporated in the formulations of folded plates. Remarkably, the motion equations are brought forward by the first order shear deformation theory (FSDT). Thereafter, two-directional generalized differential quadrature (2D-GDQ) technique is employed to determine natural frequencies from available motion, continuity, and boundary equations. The results of the folded plate are validated first by an experimental modal testing and finally some effective parameters such as folding angle, CNT weight ratio, boundary condition and flange-shape length are examined. [ABSTRACT FROM AUTHOR]

This paper proposes the double-endplates replaceable beam-column joint (DEBJ) based on the seismic design concept of replaceable beam. Compared to the common extended endplate bolted joint (CEBJ), the DEBJ is easy to be connected and replaced after earthquakes, and it can achieve plastic hinge outward movement in steel frame. Due to double endplates and different failure modes, the current moment-rotation models for CEBJ cannot be used for DEBJ. Therefore, based on the classical model used for traditional endplate joints, a theoretical moment-rotation model for DEBJ is developed, and the calculation methods on ultimate bending moment and initial rotational stiffness are deduced. A parametric study is performed for DEBJ based on a test-validated finite element (FE) model developed in this paper. The predicted moment-rotation curves calculated from proposed theoretical model is validated by the experimental results on endplate joints and FE results on DEBJ. The results show that the established theoretical model proposed in this paper can predict the moment-rotation relation curves of DEBJ and the common extended endplate bolted joint (CEBJ) accurately, the predicted results by established theoretical model are in good agreement with experimental and FE results according to the comparison. It is revealed that the established model has universality to some extent. [ABSTRACT FROM AUTHOR]

This paper presents the experimental results of a study investigating the behavior of bolted glued-laminated (glulam) timber brace connections with slotted-in steel plates under monotonic and cyclic loading. A total of 12 brace specimens with one or two slotted-in steel plates and two different bolt sizes were studied with the aim to determine the ductility of the connections and brace assemblies. The use of self-tapping screws as perpendicular-to-grain reinforcement to prevent splitting and enhance brace ductility was also investigated. The results of the study showed that both connections in a brace can experience significant plastic deformations if the connections exhibit a postyield hardening response. In braces with connections that exhibited postyield softening, plastic deformations were limited to one of the brace connections, resulting in lower brace ductility ratios. The use of self-tapping screws was found to be effective at preventing splitting and increasing the connection yield and ultimate strengths, while also increasing the brace ductility when compared with an identical connection without reinforcement tested under cyclic loading. [ABSTRACT FROM AUTHOR]

Incident particles in the Klein tunnel phenomenon in quantum mechanics can pass a very high potential barrier. Introducing the concept of tunneling into the analysis of phononic crystals can broaden the application prospects. In this study, the structure of the unit cell is designed, and the low frequency (< 1 kHz) valley locked waveguide is realized through the creation of a phononic crystal plate with a topological phase transition interface. The defect immunity of the topological waveguide is verified, that is, the wave can propagate along the original path in the cases of impurities and disorder. Then, the tunneling phenomenon is introduced into the topological valley-locked waveguide to analyze the wave propagation, and its potential applications (such as signal separators and logic gates) are further explored by designing phononic crystal plates. This research has broad application prospects in information processing and vibration control, and potential applications in other directions are also worth exploring. [ABSTRACT FROM AUTHOR]

Removable joint technology is commonly used in composite laminates for various load-bearing structures. However, existing research primarily focuses on bolted joints, there is relatively limited research on screwed joints in composite materials. This study investigates the influence of connected layer thickness and hole diameter on the tensile behavior of threaded joints in carbon fiber-reinforced polymer (CFRP) laminates. After fabricating different CFRP screwed joint specimens, tensile tests were conducted. The digital image correlation (DIC) technique captured the deformation process. The experiment results indicate a significant increase in load-bearing capacity with the increase in diameter. For instance, joints with an 8 mm diameter exhibited a load-bearing capacity of 10.82 kN. The increase in the connected layer thickness correspondingly enhanced the load-bearing capacity of the joint. The joint with a thickness of 7 mm had the highest load-bearing capacity of 8.83 kN. Besides, with the increase in the thickness of the connected layer, the failure mode transitioned from shear failure in the connected layer to screw pull-out. The tilt angle of the screw during the pull-out process also decreases with the increase in the connected layer thickness. Strain and out-of-plane displacement measurements under ultimate load conditions verify these observations. [ABSTRACT FROM AUTHOR]

Current steel construction research for offshore wind energy This report begins with an overview of current and future developments in offshore wind energy. The focus is on steel support structures. The so‐called monopiles dominate here. Jacket constructions made of tubular sections are used to a much lesser extent. Due to the high dynamic demands and the simultaneously adverse environmental conditions at sea, steel construction‐specific questions arise for research. The Institute of Steel Construction of Leibniz University Hannover has been focussing on these topics for 25 years now. This article addresses three topics typical of steel construction: Connection technology, stability and fatigue. First, it deals with yield point‐controlled tightening of prestressed bolted joints with high‐strength bolts. Then the non‐linear numerical determination the load bearing capacity of shell structures under axial and circumferential pressure, as required for the design of so‐called suction buckets, will be reported on. Finally, research is presented considering the quantification of corrosion on fatigue strength. [ABSTRACT FROM AUTHOR]

Background: Ultra high molecular weight polyethylene composites are fiber based composites used in armor applications. While some characterization has been conducted experimentally, this study varies multiple parameters simultaneously to investigate material response under a wide range of conditions. Objective: This work focuses on characterizing the response of Dyneema® HB26 hard laminate composites under high-speed impacts to examine the influence of plate diameter, clamping pressure, and plate spacing on target performance. Additionally, micro Computer Tomography scans are used to nondestructively evaluate the damage evolution in the targets. Methods: These scan results are used in concert with more traditional armor performance metrics to evaluate the effect of various parameters using the method of orthogonal array analysis. This technique allows for multiple variables to be investigated in the same test series, saving time and budget while still providing quality results across a range of variables and variable values. Results: We conclude that of the parameters investigated, the plate spacing parameter has the largest effect on performance, followed by the plate diameter. Bolt torque was found to not have a significant impact on results, indicating that an edge clamping pressure is not critical to material response. Additionally, by examining the high resolution scans, we can quantify the damage with an effective damage angle and that this angle is a good predictor of performance. Conclusion: Finally a damage theory involving the effective bending strength of the plates is discussed as an explanation for all of the results observed in this test series. [ABSTRACT FROM AUTHOR]

The deep mining of coal resources is accompanied by severe environmental challenges and various potential engineering hazards. The implementation of NPR (negative Poisson's ratio) bolts are capable of controlling large deformations in the surrounding rock effectively. This paper focuses on studying the mechanical properties of the NPR bolt under static disturbance load. The deep nonlinear mechanical experimental system was used to study the mechanical behavior of rock samples with different anchored types (unanchored/PR anchored/2G NPR anchored) under static disturbance load. The whole process of rock samples was taken by high-speed camera to obtain the real-time failure characteristics under static disturbance load. At the same time, the acoustic emission signal was collected to obtain the key characteristic parameters of acoustic emission such as acoustic emission count, energy, and frequency. The deformation at the failure of the samples was calculated and analyzed by digital speckle software. The findings indicate that the failure mode of rock is influenced by different types of anchoring. The peak failure strength of 2G NPR bolt anchored rock samples exhibits an increase of 6.5% when compared to the unanchored rock samples. The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 62.16% and 62.90%, respectively. The maximum deformation of bearing capacity exhibits an increase of 59.27%, while the failure time demonstrates a delay of 42.86%. The peak failure strength of the 2G NPR bolt anchored ones under static disturbance load exhibits an increase of 5.94% when compared to the rock anchored by PR (Poisson's ratio) bolt. The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 47.16% and 43.86%, respectively. The maximum deformation of the bearing capacity exhibits an increase of 50.43%, and the failure time demonstrates a delay of 32%. After anchoring by 2G NPR bolt, anchoring support effectively reduces the risk of damage caused by static disturbance load. These results demonstrate that the support effect of 2G NPR bolt materials surpasses that of PR bolt. [ABSTRACT FROM AUTHOR]

The bolts and connections of each working part of a rice combine harvester can suffer from severe instantaneous impacts and alternating loads, and these strong impacts and loads cause instantaneous fracture and fatigue failure of the bolt face and even the loosening, detachment, and fracture of the bolt. The main vibration directions and the most complex vibration parts of the bolts and connections in the main working parts of a combine harvester under time-variable multiload excitation were obtained through the analysis of response signals in terms of time-domain and frequency–domain characteristics via a vibration response experiment. This study revealed that the random peak value of the vibrating screen is 12.5622, which is the severe impact and collision standard. For the vibrating screen, the local peak in the 4-Y direction was the main load of the destroying bolt connection (the impact reached 60.57 m/s2, 96.91 m/s2) and the vibration energy intensity in the 4-Z direction was mainly concentrated at 12.42 m/s2, which is the maximum vibration energy value in the three directions (the peak vibration value reached 109~115.68 m/s2), so the bolted connections of the vibrating screen are the most vulnerable to destruction. Therefore, a kinetic model and a microscopic response model of a vibrating screen were established via the centralized mass method to explore the kinetic response characteristics of bolted structures subjected to multiple excitation loads, thus providing a mathematical model for identifying the features of bolted connections based on static characteristics. [ABSTRACT FROM AUTHOR]

Friction-type bolted joints are widely used in both the civil and aerospace industries. Uncontrolled excessive bolt clamping force can cause damage to the laminated fiber-reinforced polymeric (FRP) composite through the thickness and damage the joint before applying the service loads. The effect of the friction coefficient (between 0 and 0.3), bolt clearance, joint type, and other parameters on failure modes and the maximum bolt clamping force of the carbon FRP lapped joint is studied. A three-dimensional finite element (FE) model consisting of a bolt, a washer, a laminate FRP composite plate, and steel plates was developed for the simulation of the double- (3DD) and single (3DS)-lapped bolted joint. The FE model was validated by using experimental results and was able to predict the experimental results by a difference of between 2.2 and 6.7%. The joint capacity of the clamping force was found to be greatly increased by adopting the double lap technique, which involves placing an FRP composite plate between two steel plates. Also, it was recommended to use an internal washer diameter less than or equal to the FRP composite plate hole diameter since a larger washer clearance can produce higher contact pressure and reduce the resistance by 22%. In addition, reducing the bolt head diameter can lead to a 65% reduction in the 3DS joint clamping strength. [ABSTRACT FROM AUTHOR]

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Structural connections are one of the most important parts influencing the overall performance of a wooden structure. The way of design of these can lead both to increasing and decreasing internal stresses occurring in the load-carrying elements and total deformations of the structure. Typical mechanical joints in wooden structures are defined as plastic hinges or, at best, semi-rigid. The innovative hybrid proposed in the paper with adhesive added between elements can be much stiffer than a typical connection, which can lead to assuming rigid joint and significant reduction in stresses and deformations of a structure. The research comprised 30 specimens in three groups (10 per each group: reference - without adhesive, hybrid with one-component PUR - polyurethane adhesive and hybrid with one-component PVAc - polyvinyl acetate adhesive) tested on the MTS 809 testing machine up to failure. An innovative idea was to connect elements initially by applying an accurately predicted tightening torque value to bolts. This resulted in obtaining enough clamping pressure between elements for adhesive curing, with none other equipment. The load was applied in parallel-to-grain wood direction. The results showed that utilising hybrid connection caused, both for PUR and PVAc adhesive, a huge increase in stiffness. When comparing to the reference no-adhesive, bolted connection, this was 2365% stiffer (nearly 24 times). Load-carrying capacity was higher too, however, the increase was not that significant and was at the level of 14.4% and 27.1%, for PUR and PVAc adhesives, consecutively. Worth noting is that the hybrid connection could continue to work after adhesive failure with 60% higher stiffness than the reference one and its load-carrying capacity was only 10% lower than the reference. Hybrid connections of this type can potentially serve as structural joints because of the innovative concept of combining components. Steel plates can be covered with adhesive and then inserted between wooden parts. Next, the tightened bolts can work as clamps producing enough pressure for adhesive curing, enabling the joint to be assembled directly on the construction site. Despite the mentioned advantages, before providing the connections' design methods, the idea needs to be tested towards various effects influencing wooden structures. Incorporating numerical modelling can be extremely important too. [ABSTRACT FROM AUTHOR]

Summary: Vision‐based bolt defect detection methods based on feature changes have been reported. However, the robustness of key feature extraction and bolt detection requires improvement. This paper proposes a robust missing and loose bolt defect detection approach. The key features—reference points for perspective correction and the straight lines of the bolt edges—are extracted from the masks obtained by semantic segmentation models. The true and false bolt discrimination approach based on the mask shape can help improve bolt object detection accuracy. Overlapping between the bolt bounding boxes in the reference and detection images indicates missing bolts. The rotation angles reveal loosened bolts. The proposed approach was tested on fabricated bolted joint specimens and a steel railway bridge. The results suggest that these improvements ensure defect detection accuracy, with a miss rate of only 1% for missing bolt detection. Moreover, a loosened bolt with only 3° rotation is successfully detected. This approach has promising potential applicability in automatically detecting bolt defects in large steel structures. [ABSTRACT FROM AUTHOR]

Rubber-like materials such as sealant with recent developments in formulation are widely used in various structural components, especially in aerospace industry with many applications such as the sealing of bolted joints on aircraft. The objective of this paper is to assess the load transfer distribution in bolted-sealed joints through an approach coupling both experimental and numerical tests. Quasi-static and relaxation tests under uniaxial and pure shear loading were carried out to determine the parameters of phenomenological hyperelastic laws and of the generalized Maxwell model for the sealant PR 1782 C2. The fastener is an alloy steel bolt with a protruding head when the substrates are made from aluminum 2024-T3. Experimental and numerical quasi-static tests were then performed on double-lap bonded and bolted-sealed joints under in-plane loading. The numerical tests are done using 2D and 3D Finite Element (FE) models; they involve the visco-hyperelastic behavior previously assessed for the sealant. Accounting for visco-hyperelasticity makes it possible to better estimate the load transfer between bolt and sealant layer. Typically, the bolt load transfer rate is derived from numerical output for different sealant thicknesses. In the considered geometrical joint configuration, the sealant load contribution is between 7% and 13% according to the sealant thickness. Methodology and results provide a solid basis for the fatigue strength prediction of bolted-sealed joints. [ABSTRACT FROM AUTHOR]

• Specific modal vibration caused by bolted joint in rotor-AMBs system. • Accurate macroscopical rotor-AMBs mechatronic model with microscopic contact model. • Modelling of partial separation in the contact interface due to the AMBs supporting. • A novel time-variant additional stiffness matrix related to contact status. • Influence of bolted joint parameters on system response validated by experiments. Rotor-active magnetic bearings (rotor-AMBs) systems nowadays have been widely used in fluid machinery and the impeller and the shaft are commonly connected by bolted joint. However, when a certain pre-tightening force is applied to the bolted joint and the interface contact between the shaft and the impeller is formed, causing flexible modal vibrations when rotor is levitated. The mechanism of this modal vibration needs to be revealed to ensure stable operation of the machine. In traditional modelling, the effect of the interface contact is equated to an additional stiffness matrix by massless spring units, whose certain contact stiffness is uniformly distributed over the interface. Particularly, the calculation of contact stiffness and the effect of AMBs are neglected, resulting in the inaccurate response compared to experiments. Based on traditional modelling, we consider that there is partial separation in the contact interface due to the AMBs supporting and a novel additional stiffness matrix related to contact status is proposed by calculating the real-time contact area. The contact stiffness is calculated by microscopic contact model based on fractal theory and surface topography measurement. Finally, numerical simulation shows that the interface contact influences the system robustness and the unstable mode is excited. The increase of pre-tightening torque and contact radius both will increase the steady vibration amplitude, with the former being the major contributor. Moreover, the influence and order of the vibration are quantitatively validated by the experiments. [ABSTRACT FROM AUTHOR]