Friction Devices Research Articles

Hybrid-self-centring damper for industrial structure: Development and experimental validation

The seismic resilience of industrial structures has become an increasingly important issue considering the significant role played by industrial structures in social operation and post-earthquake rescue. This study presented a hybrid-self-centring damper (HSCD) incorporating the variable friction device (VFD) and tapered strip device (TSD) for tunable hysteretic behaviour to improve the seismic resilience of industrial structures. The notion of the proposed HSCD was first illustrated, followed by an experimental study on eight test specimens to understand the behaviour of the proposed damper. The test results confirmed that the proposed HSCD exhibited the expected energy dissipation sequence with excellent self-centring ability. The energy dissipation sequence of the proposed HSCD can be achieved by successive inelasticity consisting of the VFD and TSD, and the hysteretic behaviour can be flexibly adjusted by modulating the essential parameters. Detailed finite element models validated by the experimental results were developed to take insights into the behaviour of the proposed damper. To facilitate the design in the seismic application of the proposed HSCD, the hysteretic model and nonlinear-spring-based simplified model verified by test results were developed to quantify the hysteretic behaviour of the proposed damper.

Seismic performance of friction damped posttensioned steel frame equipped with SMA strands

The post-tensioned friction dissipating (PTFD) connection for steel frames has drawn significant attention from researchers due to its excellent seismic performance. A simplified numerical algorithm suitable for modeling the SMA strands is proposed. The simplified numerical model of the SMA-PTFD is established. Parametric analysis is performed based on hysteresis analysis and transient dynamic analysis to reveal the influence of SMA strands on the seismic performance of SMA-PTFD frames. The changing rule of seismic response of SMA-PTFD frames, along with the fmax for SMA strands and the Fmax for the friction device, is systematically investigated. The value of the objective function can be reduced by about 50 % when the fmax is increased from 1 kN to 13 kN. The fundamental frequency is 1.25 Hz for three analyzed conditions. The value of the second frequency is significantly affected by Fmax. The values of the second frequency are 1.5 Hz, 1.58 Hz, and 1.42 Hz. The characteristics of seismic response, including displacement and cable force, are deeply studied. The seismic response is also investigated in the frequency domain. The results presented in this work reveal the collaborative energy dissipation mechanism of the friction device and SMA strands.

Quasi-static cyclic tests of FRP-confined steel-reinforced HPFRCC circular columns

This study presents a novel composite component comprising of steel-reinforced high-performance fiber reinforced cementitious composites (HPFRCC) circular columns confined by fiber-reinforced polymer (FRP), with the goal of improving the mechanical behavior of conventional reinforced concrete (RC) columns. Quasi-static cyclic loading tests were conducted to investigate various aspects of the column specimens, including failure phenomena, load-displacement response, sectional compression-bending performance, plastic hinge length, and lateral strain distributions in the FRP jacket, etc. A self-designed frictional force measurement device was employed to accurately measure the actual force borne by the specimen. The experiment results revealed that FRP confinement effectively improved the load-bearing capacity and deformation capacity of the specimens and delayed the deterioration of the sectional compression-bending performance. The superior tensile ductility of HPFRCC led to increased yielding displacement and peak load compared to FRP-confined concrete specimen, although this enhancement was limited. Furthermore, the peak load of the FRP-confined HPFRCC specimen increased with axial load, while the sectional compression-bending performance after the peak load remained relatively stable until approaching the collapse prevention (CP) limit state.

Embroidery Triboelectric Nanogenerator for Energy Harvesting.

Triboelectric nanogenerators (TENGs) are devices that efficiently transform mechanical energy into electrical energy by utilizing the triboelectric effect and electrostatic induction. Embroidery triboelectric nanogenerators (ETENGs) offer a distinct prospect to incorporate energy harvesting capabilities into textile-based products. This research work introduces an embroidered triboelectric nanogenerator that is made using polyester and nylon 66 yarn. The ETENG is developed by using different embroidery parameters and its characteristics are obtained using a specialized tapping and friction device. Nine ETENGs were made, each with different stitch lengths and line spacings for the polyester yarn. Friction and tapping tests were performed to assess the electrical outputs, which included measurements of short circuit current, open circuit voltage, and capacitor charging. One sample wearable embroidered energy harvester collected 307.5 μJ (24.8 V) of energy under a 1.5 Hz sliding motion over 300 s and 72 μJ (12 V) of energy through human walking over 120 s. Another ETENG sample generated 4.5 μJ (3 V) into a 1 μF capacitor using a tapping device with a 2 Hz frequency and a 50 mm separation distance over a duration of 520 s. Measurement of the current was also performed at different pressures to check the effect of pressure and validate the different options of the triboelectric/electrostatic characterization device. In summary, this research explains the influence of embroidery parameters on the performance of ETENG (Embroidery Triboelectric Nanogenerator) and provides valuable information for energy harvesting applications.

In situ SEM side observation of asperity behavior during sliding contact

The performance and evolution characteristics of the friction interface are crucial for the design optimization of material friction and wear, as well as the revelation of the mechanism of seismic sliding motion. To understand the friction behavior of rough surfaces, it is essential to understand the physical process of interaction among asperities. However, visualizing the contact of asperities is challenging because materials are typically opaque, and the dimensions of asperities are usually in the micron range. This study developed an in-situ scanning electron microscope friction device and a micro speckle fabrication method to measure the strain field of regular asperities from the side, and synchronously measure the macroscopic friction coefficient. In-situ friction experiments were conducted on brass and silicon materials. The results indicate that directly correlating the friction coefficient with the deformation and failure images of asperities can effectively explain the evolution process and differences in friction coefficient for the two materials, validating the performance of the device. Different failure modes of asperities were observed, including severe plastic deformation in brass asperities and fracture-producing large particles in silicon asperities. The critical transition of asperity failure modes in the experiments was analyzed based on a theoretical model. The phase diagram of asperity failure modes and friction coefficient evolution was plotted, providing potential explanation for the evolution of friction coefficient in friction experiments on randomly rough surfaces. The developed device in this study can be used for non-transparent materials and helps reveal the microscopic mechanisms behind experimental phenomena.

Pseudo‐dynamic testing, repairability, and resilience assessment of a large‐scale steel structure equipped with self‐centering column bases

AbstractRecent destructive seismic events have underlined the need for increasing research efforts devoted to the development of innovative seismic‐resilient structures able to reduce seismic‐induced direct and indirect losses. Regarding steel Moment Resisting Frames (MRFs), the inclusion of Friction Devices (FDs) in Beam‐to‐Column Joints (BCJs) has emerged as an effective solution to dissipate the seismic input energy while ensuring a damage‐free behavior. Additionally, recent studies have demonstrated the benefits of implementing similar damage‐free solutions for Column Bases (CBs). In this context, the authors have recently experimentally investigated a Self‐Centering CB (SC‐CB) aimed at residual drift reduction. Previous experimental tests only focused on the response of isolated SC‐CBs under cyclic loads. Conversely, the present paper advances the research through an experimental campaign on a large‐scale steel structure equipped with the proposed SC‐CBs, providing valuable insights into the global structural response and improved repairability. A set of eight Pseudo‐Dynamic (PsD) tests were conducted considering different records and configurations of the structure. The experimental results highlighted the effectiveness of the SC‐CBs in minimizing the residual interstory drifts and protecting the first‐story columns from damage, thus enhancing the structure's resilience. Moreover, the consecutive PsD tests allowed investigating the effectiveness of the reparation process in restoring the seismic performance of the ‘undamaged’ structure. An advanced numerical model was developed in OpenSees and validated against the global and component‐level experimental results. Incremental Dynamic Analyses were finally performed to investigate the influence of the SC‐CBs on the structure's seismic response while accounting for the record‐to‐record variability.

Experimental lap-shear tests on friction dampers with single and double slotted holes

Several experimental lap shear tests have been performed to assess the initial values of the slip resistance and their evolution during a cyclic loading history. Both friction dampers with parallel slotted holes and double slotted holes have been investigated. Friction devices with shims made of a previously tested material, called M4, have been tested and the tribological behaviour, the degradation of the friction coefficient, the influence of the bolts’ preload and the effect of Belleville washers have also been investigated. Moreover, a phenomenological model for the force-displacement response has been calibrated for the modelling of the cyclic response of the friction device. This is particularly important for the development of non-linear dynamic analyses of seismic resistant frames equipped with friction joints aiming at an accurate prediction of the structural response during a seismic event. Finally, a quality control of the friction properties of different batches of friction shims has been performed by means of the Fisher-Berens and Snedecor tests.

Analysis of technical solutions for a high-power drive of a pumping unit intended for hydraulic fracturing of reservoir bridges in oil and gas isolated cavities

In order to simplify the design and increase the reliability of a high-power drive, the possibilities of using various high-speed two-shaft double-flow mechanical gear shift transmissions in a pumping unit designed for hydraulic fracturing of reservoir bridges in oil and gas isolated cavities are considered. Keywords:power drive, gear shift transmission, friction device, planetary gearbox, hydraulic pump, power flow au@vstu.ru

Steel Beam-to-Column Friction Joint under a Column Loss Scenario

FREEDAM joints have been recently seismically prequalified for applications in European seismically prone countries. Despite their excellent seismic response, FREEDAM joints are not purposely conceived for exceptional loading conditions, such as in the case of a column loss scenario. Therefore, a comprehensive parametric numerical study has been carried out to investigate the robustness of this type of joint, varying the geometry of the beam–column assembly and the associated friction device. The results of the performed finite-element simulations allowed the identification of the critical components of the joints such as the upper T-stub connecting the upper beam flange to the column. This component is characterized by significant demand, due to the concentration of tensile and shear forces when catenary action develops in the beam. In order to enhance the ductility of the beam-to-column joint under large imposed rotations, the details of the upper T-stub connection were modified and numerically analyzed. The obtained results allowed for the verifying of the effectiveness of the amended details as well as characterizing the evolution of the tensile forces in the bolts.

Current-carrying tribological behavior of copper alloy matrix and molybdenum alloy coating at high current density

Improving the current-carrying friction and wear resistance of copper alloy current-carrying friction subsets effectively is a hot topic. In this paper, a method of preparing high melting point molybdenum-based coating on copper alloy surfaces by laser cladding technology is presented. A large current (106 A/m2) comparison experiment is carried out with a self-made current-carrying friction device, and the failure mechanism is analyzed. The results show that the molybdenum-based coating significantly improves the adhesion problem between the friction partner and the copper alloy substrate, while the thickness of the stress layer caused by the current-carrying friction is reduced by about 7 times. The molybdenum-based coating significantly reduces the surface arc rate and has a lower friction interface temperature, thus retaining the Al2O3 self-lubricating phase. The research in this paper is expected to provide extended research ideas for the surface protection of current-carrying friction subsets of copper alloys.

Mechanics and validation tests of a post-tensioned self-centering brace with adjusted stiffness and deformation capacities using disc springs

Self-centering braces have been developed to reduce the residual deformation of steel frames in earthquakes. The brace has a higher elastic axial stiffness before the activation, which may result in a higher base shear for frame design. This work was aimed to develop a new post-tensioned self-centering brace (PT-SCB) with adjusted stiffness and deformation capabilities such that the brace could be designed based on a specified yield or ultimate frame drift. Combining disc springs and one of the compression members together in the original SCB could achieve new structural characteristics, providing an alternative to tune the axial stiffness and deformation. This work first introduces the mechanics and deformation mechanism of the proposed SCB and performs a parametric study to investigate the effect of disc spring stacks on the hysteretic response of SCBs. A test program is then conducted on cyclic tests of disc spring stacks in different serial and parallel combinations and two PT-SCBs. Each 3800 mm-long brace is composed of high-strength steel tendons, compression steel members, disc spring stacks, and bolted friction device. The hysteretic responses of the new SCB with different design parameters are used to validate the mechanics and ability of the axial stiffness and deformation adjustment.

Prototype Test of Resilient Friction Materials for Seismic Dampers

In recent decades, low-yielding seismic devices based on the use of friction dampers have emerged as an excellent solution for the development of building structures with improved reparability and resilience. Achieving an optimal design for such low-yielding seismic devices requires precise control of bolt preloading levels and predictability of the friction coefficient (CoF) between the damper interfaces. While various types of friction devices exist that are capable of providing significant energy dissipation, ongoing research is focused on the development of novel friction materials that exhibit a stable hysteretic response, high CoF values, minimal differences between static and dynamic CoF, and predictable slip resistance. In this context, an experimental campaign was conducted at the STRENGTH Laboratory of the University of Salerno to evaluate the behaviour of new friction shims employing specially developed metal alloys. Specifically, the influence of the characteristics of the contact surfaces in the sliding area on the behaviour and performance of the friction device was analysed. The tests followed the loading protocol recommended by EN12159 for seismic device qualification. Monitored parameters included preloading force values and the evolution of slip resistance. The friction value was determined, along with its degradation over time. Finally, the material’s performance in terms of hysteretic behaviour was assessed, providing a comparison of the tested specimens in terms of slip force degradation and energy dissipation capacity.

Seismic performance of self-centering braced rocking frame with novel self-centering friction dampers characterized by low-secondary stiffness

Research has demonstrated that self-centering energy dissipation dampers (SCEDs) are effective devices for reducing the residual deformation of structures after a strong earthquake. However, the equivalent damping ratio of SCEDs is relatively lower than that of conventional dampers such as viscous dampers, BRBs, or friction dampers. According to displacement spectrums, the lower damping ratio could result in a lower natural period and higher equivalent stiffness of structures for a given displacement target, and thus the structures could attract more earthquake action to the structures. To alleviate the problem, a novel self-centering damper composed of elastic post-buckling plates and adjustable friction devices (PBSCFD) was proposed and used as the self-centering braces for a self-centering braced rocking frame (SBRF) structure for example. First, the theoretical force-displacement relationship of the PBSCFD was derived based on its configuration and work principle, and then a scaled PBSCFD was manufactured and tested to investigate its mechanical properties and verify the theoretical constitutive model. Subsequently, the SBRF structure with PBSCFDs was designed by the direct displacement-based seismic design method (DDBD), and its seismic performance was examined by elastic–plastic time-history analysis. Finally, the effects of the secondary stiffness ratio of the self-centering braces on seismic mitigation of the SBRF structure were investigated. The results show that PBSCFDs is characterized by classic self-centering behavior with low secondary stiffness, which can be designed to obtain significant control effects on the base/interstorey shear and interstorey drift ratio of the SBRF structure under rare and extremely rare earthquake compared to the conventional SCEDs with significant secondary stiffness.

Experimental, mathematical model, and simulation of a dual-system self-centering energy dissipative brace equipped with SMA and variable friction device

The application of shape memory alloy (SMA) in seismic-resistant devices has received extensive attention due to its unique superelastic and shape memory effect. The poor energy dissipative capacity, insufficient reliability, and small bearing capacity are the main challenges that hinder the application of the developed SMA braces and dampers. The new system of self-centering energy dissipative (SCED) brace was proposed, fabricated, and tested, and the numerical model was defined and verified. The dates manifest that the load-displacement curve of the new dual-system SCED brace displays a typical flag shape. The new dual-system SCED brace exhibits the desirable energy dissipative ability and self-centering capacity and the theoretical and FE model established in this research can preferably express the hysteretic performance. The FE parametric analysis shows that the SMA screw preload has a small effect on the hysteretic curve of the new system brace, but it plays a decisive role in the shape of the hysteretic curve under small deformation. Furthermore, the bearing capacity and stiffness of the dual-system SCED brace can be adjusted by designing key parameters. The research shows that the new dual-system SCED device compensates for the shortcomings of the existing SMA braces and dampers, and it is a very promising and recommended self-centering energy dissipative device to use the wedge block system as the main energy dissipative system and SMA system as the main self-centering system.

Resilience Assessment of a two‐storey Steel Structure equipped with Innovative Connections

AbstractIn the last few decades, increasing research efforts have been devoted to the definition of innovative seismic resilient design strategies with the aim of reducing direct and indirect losses. Among others, the use of Friction Devices (FDs) for Beam‐to‐Column joints (BCJs) has emerged as an effective solution to ensure the damage‐free behaviour of steel Moment Resisting Frames (MRFs). Additionally, more recent research studies have revealed the benefits of replacing traditional full‐strength Column Bases (CBs) with innovative CBs promoting the residual drift reduction of steel MRFs. Additionally, several research studies developed and investigated structures that could be easily repaired after an extreme event, promoting a functional recovery of the structures and able to reinstate the original seismic performance in a short time. However, experimental research on suitable structural repair techniques is still marginal and the lack of confidence in the performance of repaired structures are relevant issues contributing to the high demolition rates. In this direction, an experimental campaign has been performed on a large‐scale steel structure equipped with BCJs with FDs and innovative CBs. Several pseudo‐dynamic tests have been performed and at the end of each test, the structure have been repaired by simply loosening the bolts of the FDs. Results demonstrated the effectiveness of repairing methodology.

Seismic assessment of the steel Moment Resisting Frame equipped with friction beam‐to‐column joints

AbstractSupplementary dissipative devices are viable solutions to enhance the seismic response of building structures. In particular, friction devices are low‐cost and easy‐to‐maintain systems that can be easily inserted into moment‐resisting beam‐to‐column joints of steel Moment Resisting Frames. The effectiveness of dissipative friction joints has been widely demonstrated in many research project. In Europe, the first building equipped with such devices will be fabricated in Italy within the framework of the ongoing RFCS DREAMERS project. The preliminary seismic assessment of this prototype building using the framework of performance‐based earthquake engineering method at different performance levels is summarized in the present paper. To this end, nonlinear dynamic analyses are carried out on three‐dimensional (3‐D) models of the prototype developed in “OpenSees”. The results show that this type of structure can be free of damage under earthquakes corresponding to significant damage and near collapse limit states.

К РАЗРАБОТКЕ ВЫСОКОЭФФЕКТИВНЫХ ПОРИСТЫХ ПОРОШКОВЫХ ФРИКЦИОННЫХ ПОКРЫТИЙ ДЛЯ РАБОТЫ В МАСЛЕ

The issues of development and research of new high-performance porous powder friction coatings for operation in oil with increased coefficient of friction and wear resistance, obtained by plasma spraying, are considered in relation to cones of synchronizers of gearboxes and disks of friction and brake units. The characteristics of the developed porous powder coatings and the technological parameters of their production for friction devices of transmissions of tracked vehicles with a high specific power are given.

A novel self-centering friction damper with elastic post-buckling plates to retrofit bridge bents

The self-centering energy dissipation dampers (SCEDs) have been demonstrated in mitigating the residual deformation of structures under strong ground motions. However, existing researches show that the damping force demand of SCEDs is higher than conventional dampers such as viscous dampers, BRBs or friction dampers for same design displacement of self-centering retrofitted structures, which could lead to higher base shear and acceleration responses of structures. In order to alleviate the problem, a novel self-centering damper composed of elastic post-buckling plates and adjustable friction devices (PBSCFD) was proposed. Compared with conventional SCEDs, the proposed PBSCFD has low secondary stiffness and adjustable energy dissipation capacity, which is beneficial to control the additional internal force of members adjacent to the damper in self-centering retrofitted structures. Based on the configuration and working principle of the PBSCFD, the theoretical force-displacement relationship of the damper was derived. Subsequently, a scaled PBSCFD was manufactured and tested under quasi-static loading to investigate its mechanical properties and to verify the theoretical constitutive model. In order to demonstrate the seismic performance of PBSCFDs, the double-column bridge bent retrofitted with PBSCFDs was designed by direct displacement-based seismic design method (DDBD), and its seismic performance was examined by elastic-plastic time-history analysis. Finally, effects of secondary stiffness ratio of self-centering dampers on seismic mitigation of self-centering retrofitted bridge bent were investigated. The results show that PBSCFDs have certain advantages in controlling the base shear and acceleration of the retrofitted bridge bent compared to conventional SCEDs with significant secondary stiffness.

Development of designs and research of the main tribotechnical parameters of friction pairs with plasma powder friction coatings and a steel counterbody when operating in oil for friction devices

Designs are developed and studies of the main tribotechnical parameters of friction pairs with plasma powder friction coatings and a steel counterbody when operating in oil for disc and cone friction devices are carried out. The threedimensional image shows the dependence of the dynamic coefficient of friction on the sliding speeds and specific loads for the considered friction devices. Keywords: friction in oil, tribological parameters, coefficient of friction, wear, sliding speed, specific load, temperature, friction machine, new friction material, steel counterbody. au@vstu.ru

Power stand with a combined loading device for testing motor-wheels and their control systems

The article describes the implemented design of a prototype single-drum power bench with a combined load device and an automated measurement system for testing motor-wheels and their control systems. Algorithms for testing motor-wheels with a diameter of 100 to 700 mm and a power of up to 5 kW are proposed, providing a clamping force to the running drum up to 1500 N. The results of testing a motor-wheel, a control system for small vehicles using friction and inertial loading devices are presented. Keywords: electric transport, power stand, motor-wheel, tests, electric drive control systems, traction characteristic, acceleration characteristic, ADC