Interfacial Energy Dissipation Research Articles

Energy dissipation and damage on the interface of steel and steel fiber‐reinforced concrete composite column

SummaryTo address the problems faced with steel‐reinforced concrete (SRC) in construction, such as positional conflicts between steel and steel bars or difficulty in pouring concrete, a novel “Steel and Steel Fiber‐Reinforced Concrete” (SSFRC) composite structure was proposed. Push‐out tests of 34 SSFRC composite columns were carried out in this paper to study the interfacial bond performance from the perspective of energy dissipation. Based on loading‐displacement (P‐D) curves, the interfacial energy dissipation (Wb) and energy dissipation factor (λ) were introduced, and the influence of embedded length (Le), steel fiber volume rate (ρsf), thickness of concrete cover (Css), and section type on Wb and λ were analyzed. Test results indicated that circular column is better than square column in terms of Wb and λ. The increase of Le, Css, or ρsf is beneficial to the improvement of Wb, and λ is positively correlated with ρsf and Css but negatively correlated with Le. Additionally, the interfacial damage (Da) was defined by the relationship between elastic deformation energy (Wa) and Wb. It can be concluded that the ascent of Le and Css can effectively delay the appearance of Da and inhibit the development of Da, respectively, and Da develops slowly with the increase of ρsf at the later loading stage.

A Multirate Discontinuous-Galerkin-in-Time Framework for Interface-Coupled Problems

A framework is presented to design multirate time stepping algorithms for two dissipative models with coupling across a physical interface. The coupling takes the form of boundary conditions imposed on the interface, relating the solution variables for both models to each other. The multirate aspect arises when numerical time integration is performed with different time step sizes for the component models. In this paper, we seek to identify a unified approach to develop multirate algorithms for these coupled problems. This effort is pursued though the use of discontinuous-Galerkin time stepping methods, acting as a general unified framework, with different time step sizes. The subproblems are coupled across user-defined intervals of time, called coupling windows, using polynomials that are continuous on the window. The coupling method is shown to reproduce the correct interfacial energy dissipation, discrete conservation of fluxes, and asymptotic accuracy. In principle, methods of arbitrary order are possible. As a first step, herein we focus on the presentation and analysis of monolithic methods for advection-diffusion models coupled via generalized Robin-type conditions. The monolithic methods could be computed using a Schur-complement approach. The framework and analysis herein accommodate multirate coupling for a wide variety of single-step, multistep, and multistage methods. A concrete example of Crank--Nicolson integrators coupled in a multirate fashion is also included to illustrate the ideas. We conclude with some discussion of future developments, such as different interface conditions and partitioned methods.

Highly Tough, Stretchable and Self-Healing Polyampholyte Elastomers with Dual Adhesiveness.

A new type of polyampholyte with unique viscoelastic properties can be easily synthesized by the copolymerization of butyl acrylate with dimethylaminoethyl methacrylate and acid acrylate in one pot. The elastic modulus of the as-prepared polyampholyte can be easily tuned by adjusting the ratio between the butyl acrylate and ionic monomers. The polyampholyte synthesized by a low proportion of ionic monomer showed low tensile strength and high stretchability, resulting in good conformal compliance with the biological tissues and potent energy dissipation. Due to the existence of high-intensity reversible ionic bonds in the polymer matrix, excellent self-recovery and self-healing properties were achieved on the as-prepared polyampholytes. By combining the high Coulombic interaction and interfacial energy dissipation, tough adhesiveness was obtained for the polyampholyte on various substrates. This new type of polyampholyte may have important applications in adhesives, packaging and tissue engineering.

Interfacial energy dissipation in bio-inspired graphene nanocomposites

Bio-inspired nanocomposites have been fabricated by self-assembly using graphene oxide (GO) based fillers, and their interfacial energy dissipation during cyclic deformation has been studied. The GO flakes were washed with a base solution to remove some functional groups and this base-washed GO (BwGO) obtained was also employed as a comparison to study the effect of functional groups on the interface. Raman spectroscopy was used to monitor the deformation of the fillers and to determine their stress-strain curve in the nanocomposites. The area of the hysteresis loop between the loading and unloading curves was used to calculate the interfacial energy dissipation during cyclic deformation. The presence of functional groups on GO reduced the interfacial energy dissipation in the elastic regime. The energy dissipation starts to increase with strain, and eventually when the applied strain is beyond the elastic regime, the functional groups ‘toughen’ the interface by requiring higher energy to break and also roughening the interface, similar to the behaviour of the biological composites. This work has shed light on the fabrication of bio-inspired nanocomposites and the evaluation and application of the graphene-based fillers where energy dissipation is needed, for example, in composites toughening and the damping of elastomers.

Experimental study on the interfacial bond strength and energy dissipation capacity of steel and steel fibre reinforced concrete (SSFRC) structures

In this study, to address the problems faced while constructing steel reinforced concrete (SRC) structures, such as the positional conflicts between the shaped steel and steel bars or the difficulty in pouring concrete, we propose a novel ‘Steel and Steel Fibre Reinforced Concrete’ (SSFRC) composite structure, wherein the steel reinforcement cage in SRC is replaced with steel fibres. We designed 20 square-section specimens and performed push-out tests to evaluate the bond properties between the shaped steel and steel fibre reinforced concrete experimentally. The influence of the steel fibre volume rate (ρsf), length-to-diameter ratio (Le/D0), and thickness of concrete cover (Css) on the interfacial bond strength, energy dissipation capacity, and interfacial damage were investigated. In addition, the ultimate bond strengths of SSFRC and SRC were compared. The results indicate that the novel SSFRC composite structure increases the ease of construction and has an ultimate bond strength that is similar to that of SRC. The interfacial energy dissipation increases with the increase in Le/D0, ρsf, and Css, and the steel fibres slow down the development of damage in the concrete specimens. Based on the results, we present an economical and effective method for determining the critical thickness of the concrete cover for SSFRC members. The thicker the concrete cover, the slower the interfacial damage development during the later stages of the test.

Modulating Interfacial Energy Dissipation via Potential-Controlled Ion Trapping.

As a metal (gold) surface at a given, but variable potential slides past a dielectric (mica) surface at a fixed charge, across aqueous salt solutions, two distinct dissipation regimes may be identified. In regime I, when the gold potential is such that counterions are expelled from between the surfaces, which then come to adhesive contact, the frictional dissipation is high, with coefficient of friction μ ≈ 0.8–0.9. In regime II, when hydrated counterions are trapped between the compressed surfaces, hydration lubrication is active and friction is much lower, μ = 0.05 ± 0.03. Moreover, the dissipation regime as the surfaces contact is largely retained even when the metal potential changes to the other regime, attributed to the slow kinetics of counterion expulsion from or penetration into the subnanometer intersurface gap. Our results indicate how frictional dissipation between such a conducting/nonconducting couple may be modulated by the potential applied to the metal.

Interfacial Bond Behavior of High Strength Concrete Filled Steel Tube after Exposure to Elevated Temperatures and Cooled by Fire Hydrant

For the engineering structure in case of fire, a fire hydrant is generally used for extinguishing the fire. This paper presents an experimental investigation on interfacial bond behavior of high-strength concrete-filled steel tube (HSCFST) after exposure to elevated temperatures and cooled by fire hydrant using the pull-out test of 22 specimens. According to the experimental study, the failure mechanism of HSCFST exposed to elevated temperatures and water-cooling (ETWC) was revealed, the influence of various parameters on the bond behavior was analyzed, and the calculation formula of the bond strength of HSCFST subjected to ETWC was put forward. The results show that the load-slip curves of the loading end and the free end of the specimen are basically similar, and can be divided into three types of typical curves. In the push out test, the strain on the outer surface of the steel tube is exponentially distributed with its distance from the loading end. After ETWC exposure, the bond strength of the specimen is less affected by the concrete strength, which is inversely proportional to the anchorage length, and it is basically stable after the constant temperature duration is longer than 60 min. With the increase of the maximum temperature, the ultimate bond strength increases first, then decreases and then increases, and the residual bond strength increases first and then decreases. Besides, the study indicate that cooling method has significant influence on the bond behavior, compared with natural cooling specimens, the ultimate bond strength, residual bond strength, and shear bond stiffness of water-cooling specimens are smaller, and the interfacial energy dissipation capacity is larger.

Experimental Investigation on the Interfacial Debonding between FRP Sheet and Concrete under Medium Strain Rate

Fiber-reinforced polymer (FRP) composites have been widely used to strengthen the existing reinforced concrete (RC) structures to against static and dynamic loads. During the past decades, the interfacial bond behavior between FRP and the concrete substrate under static load has been systematically investigated by experimental and numerical approaches. In contrast, the interfacial bond performance under dynamic loads, e.g., impact and explosive loading, is still far away from well known, especially taking the strain rate effect into account. In this contribution, the single-lap shear test is conducted to sixty specimens at the medium strain rate between 1.0E−4/s and 5.0E−3/s. The effects of various system parameters, including the strain rate, concrete strength, type of FRP and adhesive, on the interfacial fracture energy, peak shear stress, FRP strain distribution, interfacial shear stress, and effective bond length, are thoroughly investigated. It has been revealed that the strain rate and concrete strength can significantly affect the interfacial fracture energy and peak shear stress. The specimen with CFRP sheet possesses higher interfacial shear stress but lower fracture energy than that with BFRP sheet. The adhesive with lower elastic modulus is helpful to improve interfacial energy dissipation under dynamic load. The effective bond length decreases with concrete strength and strain rate, mainly between 75 mm and 90 mm, which is significantly shorter than that under static load. Inspired from the Kulkarni and Shah model, a new model is proposed to evaluate the interfacial fracture energy and peak shear stress with respect to the strain rate, and the estimated values agree well with the experiments.

Investigation on Direct Shear and Energy Dissipation Characteristics of Iron Tailings Powder Reinforced by Polypropylene Fiber

Resource utilization of iron tailings powder is an effective measure to reduce the dam-break risk of an iron tailings reservoir. Adding polypropylene fiber to iron tailings powder can improve its shear performance. Direct shear tests were carried out on reinforced iron tailings powder with polypropylene fiber with dosages of 0%, 0.25%, 0.5%, 0.75%, and 1%, respectively. The normal stresses during the tests were 100, 200, 300, and 400 kPa, respectively. The test results show that with the increase of polypropylene fiber dosage, the cohesive force of iron tailings powder firstly increases and then decreases gradually, and the internal friction angle firstly decreases and then increases. The back propagation (BP)neural network was used to fit the shear force (F) and shear displacement (s) of the test to obtain the F-s function relationship that satisfies the accuracy. Based on the energy dissipation theory, the direct shear energy dissipation of polypropylene-fiber-reinforced iron tailings powder was calculated. The mathematical model of energy dissipation of fiber interfacial failure was derived by the fiber distribution model. The interfacial strength parameters of polypropylene fiber were calculated based on the direct shear test data and the mathematical model of fiber interfacial energy dissipation. The test results show that the addition of polypropylene fiber from the perspective of energy dissipation can improve the shear properties of iron tailings powder.

Engineering Graphene Wrinkles for Large Enhancement of Interlaminar Friction Enabled Damping Capability.

Graphene nanoplates are hoped-for solid lubricants to reduce friction and energy dissipation in micro and nanoscale devices benefiting from their interface slips to reach an expected superlubricity. On the contrary, we propose here by introducing engineered wrinkles of graphene nanoplates to exploit and optimize the interfacial energy dissipation mechanisms between the nanoplates in graphene-based composites for enhanced vibration damping performance. Polyurethane (PU) beams with designed sandwich structures have been successfully fabricated to activate the interlaminar slips of wrinkled graphene-graphene, which significantly contribute to the dissipation of vibration energy. These engineered composite materials with extremely low graphene content (∼0.08 wt %) yield a significant increase in quasi-static and dynamic damping compared to the baseline PU beams (by 71% and 94%, respectively). Friction force images of wrinkled graphene oxide (GO) nanoplates detected via an atomic force microscope (AFM) indicate that wrinkles with large coefficients of friction (COFs) indeed play a dominant role in delaying slip occurrences. Reduction of GO further enhances the COFs of the interacting wrinkles by 7.8%, owing to the increased effective contact area and adhesive force. This work provides a new insight into how to design graphene-based composites with optimized damping properties from the microstructure perspective.

Normal Damping Model of Mechanical Joints Interfaces Considering Asperities in Lateral Contact

A mechanical interface behaves as the stiffness and damping when the interface is bearing a static normal force and a sine normal exciting force. For the interfacial normal damping, a calculating model was proposed. This proposed model studied the lateral contact (shoulder–shoulder contact) between upper and lower asperities in the elastic and elastic-perfectly plastic stages, which is neglected by other classical models. The normal force can be divided into a normal component and a tangential component when two asperities are contacting in dislocation. The relation between the loading–unloading normal component forces and deformation can be calculated, and then the strain energy dissipation between asperities can be gotten by integral. The friction energy dissipation also can be calculated based on the relation between loading–unloading tangential component forces and the slippage. Furthermore, the total interfacial energy dissipation can be obtained according to the statistical theory. Finally, the equivalent viscous damping is estimated using the vibration theory. The proposed model and classical models are compared by simulation and experiment, and it was found that the interfacial damping of the proposed model is more than the damping of the classical models. Moreover, the proposed model is consistent with the experimental results.

Frictional Energy Dissipation in Spherical Contacts Under Presliding: Effect of Elastic Mismatch, Plasticity and Phase Difference in Loading

Behavior of friction at material interfaces is inherently nonlinear causing variations and uncertainties in interfacial energy dissipation. A finite element model (FEM) of an elastic–plastic spherical contact subjected to periodic normal and tangential loads is developed to study fundamental mechanisms contributing to the frictional energy dissipation. Particular attention is devoted to three mechanisms: the elastic mismatch between contacting pairs, plastic deformations, and phase difference between the normal and tangential fluctuations in loading. Small tangential loads simulating mild vibrational environments are applied to the model and resulting friction (hysteresis) loops are used to estimate the energy loss per loading cycle. The energy losses are then correlated against the maximum tangential load as a power-law where the exponents show the degree of nonlinearity. Exponents increase significantly with in-phase loading and increasing plasticity. Although increasing elastic mismatch facilitates more dissipation during normal load fluctuations, it has negligible influence on the power-law exponents in tangential loading. Among all the configurations considered, out-of-phase loading with minimal mismatch and no plasticity lead to the smallest power-law exponents; promising linear frictional dissipation. The duration the contact remains stuck during a loading cycle is found to have a predominant influence on the power-law exponents. Thus, controlling that duration enables tunable degree of nonlinearity and magnitude in frictional energy dissipation.

Molecular dynamics simulation of mechanical behavior of osteopontin-hydroxyapatite interfaces

Bone is characterized with an optimized combination of high stiffness and toughness. The understanding of bone nanomechanics is critical to the development of new artificial biological materials with unique properties. In this work, the mechanical characteristics of the interfaces between osteopontin (OPN, a noncollagenous protein in extrafibrillar protein matrix) and hydroxyapatite (HA, a mineral nanoplatelet in mineralized collagen fibrils) were investigated using molecular dynamics method. We found that the interfacial mechanical behavior is governed by the electrostatic attraction between acidic amino acid residues in OPN and calcium in HA. Higher energy dissipation is associated with the OPN peptides with a higher number of acidic amino acid residues. When loading in the interface direction, new bonds between some acidic residues and HA surface are formed, resulting in a stick–slip type motion of OPN peptide on the HA surface and high interfacial energy dissipation. The formation of new bonds during loading is considered to be a key mechanism responsible for high fracture resistance observed in bone and other biological materials.

Dynamic Behavior of Nanocomposites Reinforced with Multi-Walled Carbon Nanotubes (MWCNTs).

The influence of multi-walled carbon nanotubes (MWCNT) on the structural dynamic behavior of MWCNT/epoxy nanocomposites was investigated. Two different types of MWCNTs, pristine MWCNT and functionalized MWCNT, were used in this study. Carboxylic acid-functionalized MWCNTs (MWCNT-COOH) were obtained by oxidation pristine MWCNTs via sonication in sulfuric-nitric acid and characterized by Fourier transform infrared spectroscopy (FTIR). Dynamic behaviors of the MWCNT reinforced nanocomposite including the natural frequency and damping ratio were determined using free vibration test. Experimental results showed that the damping ratio of the nanocomposite decreases with the increase of the MWCNT addition, while the natural frequency is increasing with the increase of the MWCNT addition. Functionalized MWCNTs improved the interfacial bonding between the nanotubes and epoxy resin resulting in the reduction of the interfacial energy dissipation ability and enhancement of the stiffness.

Effect of Meso to Micro Transition in Morphology Dependent Fracture of SiC Ceramics

Silicon carbide (SiC) is an important ceramic material usually found in polycrystalline form with grain boundary thickness ranging from a few nanometers to a few hundred nanometers and grains with multiple orientations with sizes of the order of few micrometers. The present work focuses on analyzing how the interplay between different orientations of SiC grains and different grain boundary thicknesses can be exploited for targeted improvement in the fracture resistance properties of SiC. Crack propagation simulations using the cohesive finite element method (CFEM) are performed on the finite element meshes developed on experimentally processed SiC morphologies. Analyses were performed at two different length scales: 300 μm × 60 μm (scale-1:Microscale) and 75 μm × 15 μm (scale-2:Mesoscale). Lower resolution microstructure at scale-1 does not explicitly consider the presence of grain boundaries (GBs). Higher resolution microstructure at scale-2 explicitly models GBs. Results indicate that the effect of change in grain orientation is on crack path only. The fracture resistance is not significantly affected. The presence of GBs may directly aid in strengthening a microstructure’s fracture resistance. However, indirectly it may weaken a microstructure by favoring the formation of microcracks. Significantly higher crack formation in grain interior while lower interfacial energy dissipation in comparison to interfaces indicates overall lower fracture strength of grain interiors in comparison to interfaces. If GBs are not accounted for, the second most influencing factor affecting fracture strength is the average grains size. Overall, it is mainly the GBs not the grain orientation distribution and grain size that significantly affects fracture strength.

A nanocell for quartz crystal microbalance and quartz crystal microbalance with dissipation-monitoring sensing

A novel device for nanometer-confinement of soft matter in one dimension (1D) is presented. This nanocell, with very large (up to 10(6):1) cell-radius to cell-height ratio, is tailored as an accessory for quartz crystal microbalance (QCM) and QCM with dissipation-monitoring (QCM-D) sensing to study internal and interfacial energy dissipation phenomena in highly confined (in 1D) soft matter and fluid films (patent pending). The cell consists of two macroscopic plates (diameter of 9 mm), a top (the "lid") and a bottom (the QCM-D sensor), separated by appropriate spacers with heights ranging from below 100 nm up to 10 microm. The surfaces of both the lid and the bottom plate can be mechanically or/and chemically modified, prior to cell assembly, in order to tailor desired interfacial properties for the experiment. The cell is mounted on a standard QCM-D sensor, an AT-cut quartz crystal (the quartz crystal is cut at an angle of 35 degrees from its ZX-plane), forming the bottom plate. We illustrate theoretically and experimentally, as application examples, the use of this device for studies of dynamic mass loading and internal energy dissipation processes in thin films of ethylene glycol respective thin liquid crystal films around the nematic-isotropic phase transition.

Local Packing Environment Strongly Influences the Frictional Properties of Mixed CH3- and CF3-Terminated Alkanethiol SAMs on Au(111)

Compositionally mixed, self-assembled monolayers (SAMs) derived from 16,16,16-trifluorohexadecanethiol and a normal alkanethiol, either hexadecanethiol or pentadecanethiol, were formed on Au(111) substrates. The relative composition of the films was determined using X-ray photoelectron spectroscopy and was found to approximately equal the equimolar composition of the isooctane solution from which they were formed. The frictional properties of the mixed films were measured on the nanometer scale using atomic force microscopy and were observed to decrease when the chain length of the CH(3)-terminated component was shortened by one methylene unit (i.e., when hexadecanethiol was replaced by pentadecanethiol). For comparison, the frictional properties of a mixed-chain-length CH(3)-terminated SAM derived from hexadecanethiol and pentadecanethiol in a 1:1 ratio was also examined. In contrast to the mixed CF(3)/CH(3) system, the latter mixed-chain-length system exhibited relatively higher friction when compared to single-component SAMs derived solely from either hexadecanethiol or pentadecanethiol. For both types of mixed films, the change in frictional properties that occurs as a result of modifying the position of neighboring terminal groups with respect to the surface plane is discussed in terms of the influence of local packing environments on interfacial energy dissipation (friction).

Interfacial damping characteristics of carbon nanotube-based composites

Because of their ultra small, nanometer scale size and low density, the surface area to mass ratio (specific area) of carbon nanotubes (CNTs) is extremely large. Therefore, in a nanotube-based polymeric composite structure, it is anticipated that high damping can be achieved by taking advantage of the interfacial friction between the nanotubes and the polymer resin. In addition, the CNT’s large aspect ratio and high elastic modulus features allow for the design of such composites with large differences in strain between the constituents, which could further enhance the interfacial energy dissipation ability. Despite their wonderful engineering potential, the damping properties of CNT-based composites have not been examined in any detail. The purpose of this paper is to investigate the structural damping characteristics of polymeric composites containing single-walled carbon nanotubes (SWNTs), with a focus on analyzing the interfacial interaction between the CNT and the resin materials. The system is modeled using a four-phase composite, composed of a resin, voids, and bonded and debonded nanotubes. A micromechanical model is proposed to describe interfacial debonding evolution. To characterize the overall behavior, Weibull’s statistical function is employed to describe the varying probability of nanotube debonding under uniaxial loading. To address damping effects, the concept of interfacial “stick-slip” frictional motion between the nanotubes and the resin is proposed. The developed method is extended to analyze composites with randomly oriented nanotubes. The analytical results show that the critical shear stress, nanotube weight ratio and structure deformation are the factors affecting the damping characteristic. Experiments are also performed to verify the trends predicted by the analysis. Through comparing with neat resin specimens, the study shows that one can enhance damping by adding CNT fillers into polymeric resins. It is also observed that SWNT-based composites could achieve higher damping than composites with several other types (different size, surface area, density and stiffness) of fillers. These results confirm the possible advantage of using CNTs for damping enhancement.

Friction in Adhesion

The effect of interfacial friction on adhesion was studied by using a model system, in which a thin strip of silicone elastomer was peeled from a PDMS (poly(dimethylsiloxane)) treated glass slide. The fluorescent particle tracking method revealed that the elastomer stretches and slides on glass well before the crack faces open up. Interfacial energy dissipation due to friction, which is the product of the slip displacement and the interfacial shear stress, is found to be a significant contributor to the total fracture energy at various peel configurations. These results suggest that interfacial sliding may provide a mechanism for energy dissipation in the fracture of asymmetric interfaces.