Elastomeric Pads Research Articles

Parametric study for shear failure of bearing pads due to hurricane-induced wave loadings

The increasing frequency of extreme weather events, such as hurricanes and rising sea levels due to climate change, presents significant challenges to coastal infrastructure. With 42% of bridges in the United States exceeding 50 years of age, which surpasses their intended service life, there is a pressing need to assess their structural integrity, especially in coastal regions. This study focuses on evaluating the structural performance of bearing pads in coastal bridges under hurricane-induced wave loadings. Utilizing a combination of physics-based models (PBM), nonlinear modal time history analysis, and numerical validation, the research examines the hysteresis response of eight distinct bearing pad configurations. The findings indicate that reinforced circular bearing pads exhibit significantly greater shear displacements compared to plain elastomeric pads, underscoring the critical influence of shape factors on shear response. Fragility functions developed in the study illustrate the probability of shear failure, with reinforced circular pads showing a 28% higher likelihood of exceedance compared to rectangular plain pads. These results highlight the necessity for advanced design methodologies specifically for bearing pads to enhance the resilience of coastal infrastructure against severe hydrodynamic forces induced by hurricanes.

Study on vibration isolation design using elastomeric pads and its application

Study on vibration isolation design using elastomeric pads and its application

Preparation and performance study of silicon modified polyurethane-based magnetorheological elastomeric polishing pad

Abstract By employing Magnetorheological Elastomers (MREs) as polishing pads for chemical mechanical polishing (CMP), the magnetorheological properties are utilized to effectively control the flexible removal of materials in CMP. This study presents a method for preparing a Silicon modified Polyurethane (SPU)-based MRE polishing pad, aimed at demonstrating improved magnetorheological properties while preserving mechanical properties. The SPU-based MRE polishing pad was synthesized through the copolymerization of hydroxypropyl silicone oil and polyurethane prepolymers, with subsequent evaluation of its mechanical properties and polishing performance. Fourier Transform Infrared (FTIR) analysis confirmed the successful incorporation of the soft polydimethylsiloxane main chain from organosilicon into the polyurethane main chain, forming a soft segment that intertwines with the polyurethane main chain to create a soft-hard segment crosslinked structure. Comparison to Polyurethane (PU)-based MRE, SPU exhibits significantly reduced hardness but improved wear resistance, as well as enhanced resistance to acid and alkali corrosion. Due to the presence of a soft matrix, SPU shows better magnetorheological effects than PU-based MRE. Under a magnetic field intensity of 845 mT, the magnetorheological effect of PU-based MRE is only 18%, while Si-15.96 and Si-16.79 SPU-based MREs can reach 84% and 110%, respectively. Although the Material Removal Rate (MRR) of single-crystal SiC decreases after polishing with SPU compared to PU-based MRE, a higher surface quality is achieved, and the glazing degree of the polishing pad is significantly reduced. In the magnetic field-assisted polishing of single crystal SiC, the MRR increased by 38.4% when polished with an SPU-based MRE polishing pad, whereas the MRR was only 8.7% when polished with a PU-based MRE polishing pad. This study provides further evidence for the development and application of MRE in CMP.

Design and numerical simulation of the elastomeric support for the topside modules of an FPSO

Elastomeric support utilizing steel-reinforced elastomeric bearing pads (SREBPs) has been applied to offshore structures gradually. This study presented a process for designing the offshore elastomeric support. And a specific numerical method was introduced to synchronously simulate the hydrodynamic responses and structural interactions between hull and topside modules of a spread-moored floating production storage and offloading (FPSO) unit with elastomeric-supporting topside modules. Furthermore, a model test of the target FPSO was conducted in a deepwater offshore basin to validate the numerical simulation, and the numerical results were consistent with the experimental outcomes overall. The numerical results demonstrated that both bearing force and stress of the SREBPs fell within the design scope, and the maximum bearing force on vertical SREBPs was found to be around 1.3 times the weight of a corresponding topside module, considering the dynamic effects resulted from motion responses of the FPSO. Additionally, the maximum bearing force acting on anti-uplift SREBPs can refer to the peak value of a vertical SREBP's dynamic force correspondingly. The horizontal interactions between hull and topsides mainly depend on inclination of the hull, so the bearing forces of horizontal SREBPs are closely related to the severity of rolling and pitching.

Experimental Study and Seismic Response Evaluation of Chlorobutyl Rubber-Based Viscoelastic Dampers

Conventional viscoelastic devices often use high-damping elastomeric pads, typically made of patented formulations, that are bonded to steel plates. The response properties of these pads under cyclic shear deformations directly influence the load-deformation hysteretic response of the device. Chlorobutyl (CIIR) is a high-damping rubber commonly used in industrial applications. However, this study found that the damping properties of a typical CIIR rubber compound are insufficient for effective structural seismic mitigation at ambient temperatures above 0°C. The goal of this study was to develop a new composite of CIIR, referred to as modified CIIR, with improved damping properties and to compare its performance with that of the reference CIIR rubber. In the first phase of the experimental studies, the viscoelastic characteristics of the reference and modified CIIR rubber materials were evaluated using dynamic mechanical thermal analysis (DMTA) in tension mode. Prototype viscoelastic damper devices were then fabricated from both the reference and modified CIIR rubber materials and subjected to cyclic shear tests at room temperature and various loading frequencies. The results showed that the modified CIIR rubber exhibited significantly improved effective damping compared to the reference CIIR. The final component of this study involved investigating the seismic response of a 2D frame structure equipped with prototype dampers made from both reference and modified CIIR materials, using nonlinear time-history analyses. The analysis results indicated that the modified CIIR rubber can be effectively utilized in the seismic response mitigation of structures.

Reliability analysis based on load spectrum: A structural improvement of Indian Railways three-piece freight bogie elastomeric pad

Dynamic characteristics and reliability of elastomeric pads are dominant components in the design methodology to satisfy the performance parameters under dynamic operations. The fatigue life of rubber pads fitted with elastomeric pads mainly depends upon elastomers; natural rubber, chloroprene, nitrile butadiene, silicon compounds, etc., additives, accelerators, activators, fillers, anti-degradants, and manufacturing processes. The performance of the elastomeric pad is evaluated based on service operation, simulation, and laboratory testing. New and failed elastomeric (EM) pads have been examined in the Indian Rubber Manufacturer’s Research Association IRMRA laboratory for detailed failure analysis of existing EM pads. Further, chemical and physical properties are also evaluated in M&C (Metallurgical and Chemical) and Testing Directorate of Research Designs and Standards Organization (RDSO), labs respectively. The fatigue life of the EM pad is estimated based on the results extracted from the Finite Element (FE) analysis of the EM pad. An attempt is made to modify the design of the EM pad by considering the results of detailed field trials, lab testing, and FE analysis. The modified design satisfies the dynamic characteristic during FE (Structural and Thermal) analysis and lab testing.

Stress increases in crane runway girders due to rail joints

AbstractVertically acting wheel loads from overhead bridge cranes and potential additional horizontal crane loads induce two types of stresses in crane runway girders: i) global stresses due to bi‐axial bending and torsion and ii) local stresses which mainly affect the girder's web. The latter typically represent one of the most decisive criteria for the fatigue design check of welded girders and are the focus of this paper. Crane rails with foot flange are typically connected to the top flange with rail clips. These clips maintain the position of the rail in vertical and horizontal transverse direction, but they generally allow for longitudinal movement of the rail. Rails with foot flange are used with and without elastomeric bearing pads between the rail and the top flange of the girder. The local stresses in the webs of crane runway girders are strongly affected by discontinuities of the crane rails. Such discontinuities can originate from unplanned rail cracks as well as planned rail expansion joints. The current mechanical models for concentric as well as eccentric wheel loading in relevant design standards assume continuous crane rails. However, rail joints are expected to significantly increase the local stresses in the region beneath rail joints. The present paper focuses on the impact of rail joints on the local stresses in crane runway girders. The research activities comprise experimental tests as well as finite element calculations. The aim of the investigations is to develop a better understanding of the mechanical behaviour in order to avoid future fatigue damage due to an unexpected increase of local stresses at a rail joint.

A Hybrid Vibration Isolator Based on Elastomeric and Electromagnetic Restoring Force

The protection of structures and machines from ground vibrations is a deeply felt and widely studied problem. These vibrations are typically generated by the operation of machines, vehicular traffic, seismic events, shocks, explosions, etc., and are generally characterized by frequencies that are not known a priori, making the use of passive isolation systems problematic. Just away from the source, ground vibrations have a predominantly horizontal component. To meet the conflicting requirements of passive isolation systems, which should have higher stiffness when the structure is at rest and lower stiffness when the ground forces it to vibrate, active or semi-active isolation systems can be adopted. In the following article, the possibility of adopting a hybrid isolator is evaluated; it consists of shear-stressed elastomeric pads coupled with an electromagnetic actuator; the latter consists of three coils, two of which are connected to the ground and the other one to the body to be isolated. This kind of isolator has the same flexibility and adaptability as the active ones, with the advantage of ensuring its functioning even in the absence of an external energy source. Its flexibility is due to the presence of a smart element that allows one to tune the characteristics of the isolator to consider the instantaneous isolation requirements. The proposed solution allows one to modify the isolation system’s characteristics in a sufficiently wide range of displacements equal to that defined by the maximum allowed deformation of the elastomeric pads. This paper reports the description of the isolation system and an analytical model to describe its restoring force; then, an experimental setup is adopted to identify the parameters of the analytic model; finally, several simulations are reported to compare the analytical and the experimental trends of the restoring force and to characterize the isolator.

Seismic risk assessment of ageing existing reinforced concrete bridges accounting for uncertainty in bearing properties

A growing challenge in the seismic risk assessment of ageing existing bridge structures is the lack of knowledge of the key features of the structural components. In fact, the mechanical properties could change over time and the recommendations in the literature could be considerably different thus adopted modelling parameters can significantly alter the seismic response and risk estimates,e.g., expected annual losses (EAL) or mean annual frequency of collapse (MAFC). It is therefore crucial to understand the role of critical properties of structural components on seismic risk metrics before allocating further resources to estimate them more accurately.With the above in mind, this study focuses on analysing the importance of the frequently unknown properties of bridge bearings featuring un-reinforced thin elastomeric pads, typically used in bridges built in the ‘60 s and ‘70 s in Italy. For this purpose, a real case study bridge is selected and Latin Hypercube Sampling is performed to generate a large set of bearing parameters, namely the shear modulus and friction coefficient between rubber and concrete surfaces. Component-level seismic loss estimation of the bridge is performed for each bearing properties realisation, considering both the presence and absence of non-sacrificial shear keys at the cap beams. The EAL and MAFC results are scrutinised to analyse the impact of the variation in the bearing properties on such risk metrics. The main observations indicate that the influence of the shear modulus of rubber on these quantities is low, whereas the friction coefficient between concrete and rubber can lead to more impactful changes.

Momentum transfer on impact damping by liquid crystalline elastomers

The effect of elastomeric damping pads, softening the collision of hard objects, is investigated comparing the reference silicone elastomer and the polydomain nematic liquid crystalline elastomer, which has a far superior internal dissipation mechanism. We specifically focus not just on the energy dissipation, but also on the momentum conservation and transfer during the collision, because the latter determines the force exerted on the target and/or the impactor—and it is the force that does the damage during the short time of an impact, while the energy might be dissipated on a much longer time scale. To better assess the momentum transfer, we compare the collision with a very heavy object and the collision with a comparable mass, when some of the impact momentum is retained in the target receding away from the collision. We also propose a method to estimate the optimal thickness of an elastomer damping pad for minimising the energy in impactor rebound. It has been found that thicker pads introduce a large elastic rebound and the optimal thickness is therefore the thinnest possible pad that does not suffer from mechanical failure. We find good agreement between our estimate of the minimal thickness of the elastomer before the puncture through occurs and the experimental observations.

Impact of rail joints on the local stresses in crane runway girders

Vertically acting wheel loads from overhead bridge cranes and potential additional horizontal crane loads induce global stresses due to bi-axial bending and torsion and local stresses in crane runway girders which mainly affect the girder’s web. The latter typically represent one of the most decisive criteria for the fatigue design check of welded girders and are the focus of this paper. Crane rails with foot flange are typically used for moderate to high wheel loads. They are usually connected to the top flange with rail clips. Rails with foot flange are used with and without elastomeric bearing pads between the rail and the top flange of the girder. The local stresses in the webs of crane runway girders are strongly affected by discontinuities of the crane rails. Such discontinuities can originate from unplanned rail cracks as well as planned rail expansion joints. The current mechanical models for concentric as well as eccentric wheel loading in relevant design standards assume continuous crane rails. However, rail joints are expected to significantly increase the local stresses in the region beneath rail joints. The present paper focuses on the impact of rail joints on the local stresses in crane runway girders. The research activities comprise experimental tests as well as numerical parametric studies based on finite element calculations, both for rails with and without elastomeric bearing pads. The aim of the investigations is to develop a better understanding of the mechanical behaviour and to quantify the increase factor for maximum local stresses in order to avoid future fatigue damage due to an unexpected increase of local stresses at a rail joint.

Local vertical compressive stress in the crane runway beam web

In this paper, the authors analysed several variants of connections between a block rail (60 mm × 60 mm) and a crane runway beam (IKS 800-6). They compared local vertical compressive stress in the crane runway beam web, calculated using an analytical approach and numerical simulations. In the case of the continuous block rail rigidly fixed to the beam flange, satisfactory convergence was obtained. For the remaining types of connections the results based on the analytical method were different from the results of the numerical simulations. The difference resulted from the fact that the analytical method did not take into account the crane rail joint. Furthermore, the impact of the elastomeric bearing pad on the local stress value was taken into account in a simplified manner in the analytical method by increasing the effective length by approximately 30%. The local vertical compressive stress in the crane runway beam web was significantly affected by the connection between the rail and the crane runway beam, the crane rail joint type, the use of the elastomeric bearing pad, the length of the elastomeric bearing pad, and the crane rail wear.

Influence of rubber compressibility on the compressive stiffness of steel‐reinforced elastomeric bearings in finite element simulations considering the shape factor

AbstractIn finite element analysis of steel‐reinforced elastomeric bearings (SREB) under compression, modeling of rubber as a nearly or fully incompressible material requires special attention. In this study, finite element simulations of circular elastomeric pads and rectangular SREB under compression were performed to analyze the effects of rubber compressibility with respect to different pad geometries and shape factor values. The ratio of the compressive modulus for a compressible rubber to that of an incompressible rubber was also introduced based on the previously derived exact solutions as well as the ad hoc approximations. This ratio accurately represents the influence of compressibility on compressive stiffness in terms of relative compressibility (K/G) and shape factor values. Numerical results were also compared with the experimental results on rectangular SREB with moderate shape factors. Recommended values for relative compressibility of carbon black‐filled rubbers in the range of 50–200 result in underestimated compressive stiffness, especially for bearings with shape factor values greater than five. It is recommended to adjust the relative compressibility, considering the shape factor, so that the compressive stiffness does not decrease by more than 50% compared to the incompressible case.

Compression behavior of perforated steel laminated elastomeric bearing

Elastomeric bearing pads have been the economical and maintenance-free, widely used component of bridges for more than decades. Research has been ongoing for years to increase the versatility of elastomeric bearings. Recently, fibre fabrics like glass and carbon reinforced with elastomers have substantiated a lead to traditional steel reinforced elastomeric bearings by a reduction in cost and weight. This paper deals with an experimental investigation into the compressive behavior of elastomeric bearing pads reinforced with perforated steel shims of various geometries placed between traditional solid steel shims. The compressive behavior of modified elastomeric bearings was determined and compared with that of traditional steel-reinforced elastomeric bearings.

A novel viscoelastic modelling of railway track elements and experimental validation

This study presents a novel approach for the viscoelastic (VE) modelling of railway track elements that depends on the combination of strong sides of classical and fractional derivative models (FDM) of viscoelasticity. First, parameters of a recent 10 parameter fractional derivative model are identified from dynamic mechanical analysis (DMA) data for three different elastomeric pads that are used in railway system. The FDM gives accurate results in wide frequency ranges, however, the time domain representation of this model includes fractional derivatives that substantially increase the computation time. To overcome this drawback, five-armed Generalized Maxwell Model (GMM) parameters are fitted in 0.01–1000 Hz to be used in the time domain analyses. The mathematical models of two distinct types of railway superstructure are obtained and solved by the Galerkin’s method. The results of proposed framework are tested against measurements and the results of finite element model (FEM) analyses and very good agreement is observed.

Application and analysis of elastomeric supporting style for topside modules of a spread mooring FPSO

The offshore elastomeric supporting style via steel reinforced elastomeric bearing pads (SREBPs) has been in use gradually. In this study, the elastomeric supporting style used for the interfaces between topsides and stools is adopted by a spread mooring FPSO to analyze the responses of SREBPs and evaluate the applicability. Firstly, the motion responses of target FPSO are numerically simulated to check if the mooring system is safe. Then, the hydrodynamic responses are taken as the boundary conditions of hull for the multibody dynamic simulations. In the simulation, a compression spring model is proposed to equivalently replace the SREBPs. The stiffness of equivalent compression springs is obtained by linear fitting of the stiffness data from finite element analysis of SREBPs. Finally, the multibody numerical results show that the SREBPs can reach into yield state, but if there are assistant devices helping to limit the deformations, the SREBPs would work well. The largest deformations of SREBPs are observed to be sensitive to the hydrodynamic responses, so the SREBPs can still reach into yield state in extreme case. In that condition, it is recommended to bond the topsides to the stools and the numerical results confirm that it is available.

Hybrid sol-gel-derived method for the synthesis of silicon rubber composites with hBN for characteristic applications in elastomeric thermal pads

The thermal conductivity of silicone rubber is very low and does not meet the required thermal conductive applications, so inorganic fillers are added to increase heat transfer which ultimately improves the thermally conductive path. In this study, silicone rubber/hexagonal boron nitride composite was synthesized by the hydrolysis-polycondensation method to enhance the thermal conductivity of the material while retaining acceptable flexibility properties. The introduction of MQ resin reduced crosslink density, thermal stability, tensile strength, and hardness of the silicone resin composite and improved elongation. The addition of vinyl-based MQT and aluminum-based MQT resins improved the properties of the silicone rubber, while the addition of vinyl-based MQT resin reduced the crosslink density, tensile strength and hardness, and improved its elongation and thermal stability properties. While aluminum-based MQT resin did not have a significant effect on crosslink density, tensile strength, or hardness, it also improved elongation and reduced thermal stability. The high filler concentration of hexagonal boron nitride in the composite enhanced thermal conductivity up to 3.253 Wm−1 K−1, while it reduced tensile strength to 1.248 MPa and elongation to 22% but increased hardness up to 75 shore A. The addition of silicone resin improved the thermal conductivity of all MQ, vinyl-based MQT3 and aluminum-based MQT3 resin composites up to 3.661, 3.962 and 4.817 Wm−1 K−1, respectively. For the same three resins, tensile strength was increased up to 1.274, 1.290, and 1.312 MPa, elongation at break was raised to 125%, 188%, and 150%, and hardness was reduced to 69, 71, and 72 shore A, respectively. The addition of silicone resin also showed an effect on density, volatile content, flame resistance, and volume resistivity.

Strain measurements on rails of crane runway girders to predict accurate wheel loads

AbstractIn existing crane runways, data on the actual wheel loads acting on the crane rail are often missing. Therefore, approximated wheel loads have often to be assumed for static calculations of the crane runway girder. Within this paper, a method is presented that allows to calculate the actual wheel loads based on strain measurements on the crane rail. The idea is to measure strains on the rail at certain pre‐defined locations, while the crane is passing and calculate the wheel load from the measured strains. The correlation between the strains in the rail and the wheel load is determined in a numerical finite element study and in laboratory tests.The numerical studies also comprise several different geometries of crane runway girders. The objective is to verify the influences of them on the calculated strains in the rail. The results of the numeric calculations show, that the strains in the rail generally depend on the stiffness of the crane runway girder. The thickness of the upper flange and the web as well were identified as the main parameters. This behavior is also verified in laboratory tests.For the contact between the rail and the crane runway girder, two different cases have been investigated. The first analysis refers to a hard contact under compression which allows separation under tension. This configuration corresponds to cases with steel wearing plates beneath the crane rails. The second case considers an elastomeric rail pad between the rail and the crane runway girder.

Auxetic metamaterial optimisation for head impact mitigation in American football

American football has a comparatively high rate of sports-related concussions, despite mitigating strategies including the use of protective helmets. The traditional energy absorbing component, elastomeric foam pads, have limited scope for leveraging any further protection. Alternative structures and materials that exhibit novel deformation mechanics have been proposed as a route to increased energy absorption capacity. This study investigated a metamaterial based on the Miura Ori folding pattern. Eighty-one potential structural variations were conceptualised and evaluated via the Taguchi method. Twenty-seven geometries were then additively manufactured using commercially available thermoplastic polyurethane, before being impacted at multiple velocities. Experimental data were then extrapolated to predict the impact behaviour across all 81 variants. An optimised geometry was then proposed, which reduced linear accelerations across the test conditions and performed favourably when compared to current, elastomeric foam solutions. This work provides a promising foundation for future investigation.

Dynamically Tunable Friction via Subsurface Stiffness Modulation

Currently soft robots primarily rely on pneumatics and geometrical asymmetry to achieve locomotion, which limits their working range, versatility, and other untethered functionalities. In this paper, we introduce a novel approach to achieve locomotion for soft robots through dynamically tunable friction to address these challenges, which is achieved by subsurface stiffness modulation (SSM) of a stimuli-responsive component within composite structures. To demonstrate this, we design and fabricate an elastomeric pad made of polydimethylsiloxane (PDMS), which is embedded with a spiral channel filled with a low melting point alloy (LMPA). Once the LMPA strip is melted upon Joule heating, the compliance of the composite structure increases and the friction between the composite surface and the opposing surface increases. A series of experiments and finite element analysis (FEA) have been performed to characterize the frictional behavior of these composite pads and elucidate the underlying physics dominating the tunable friction. We also demonstrate that when these composite structures are properly integrated into soft crawling robots inspired by inchworms and earthworms, the differences in friction of the two ends of these robots through SSM can potentially be used to generate translational locomotion for untethered crawling robots.