Viscoelastic Energy Dissipation Research Articles

Design and additive manufacturing of bionic hybrid structure inspired by cuttlebone to achieve superior mechanical properties and shape memory function

Lightweight porous materials with high load-bearing, damage tolerance and energy absorption (EA) as well as intelligence of shape recovery after material deformation are beneficial and critical for many applications, e.g. aerospace, automobiles, electronics, etc. Cuttlebone produced in the cuttlefish has evolved vertical walls with the optimal corrugation gradient, enabling stress homogenization, significant load bearing, and damage tolerance to protect the organism from high external pressures in the deep sea. This work illustrated that the complex hybrid wave shape in cuttlebone walls, becoming more tortuous from bottom to top, creates a lightweight, load-bearing structure with progressive failure. By mimicking the cuttlebone, a novel bionic hybrid structure (BHS) was proposed, and as a comparison, a regular corrugated structure and a straight wall structure were designed. Three types of designed structures have been successfully manufactured by laser powder bed fusion (LPBF) with NiTi powder. The LPBF-processed BHS exhibited a total porosity of 0.042% and a good dimensional accuracy with a peak deviation of 17.4 μm. Microstructural analysis indicated that the LPBF-processed BHS had a strong (001) crystallographic orientation and an average size of 9.85 μm. Mechanical analysis revealed the LPBF-processed BHS could withstand over 25 000 times its weight without significant deformation and had the highest specific EA value (5.32 J·g−1) due to the absence of stress concentration and progressive wall failure during compression. Cyclic compression testing showed that LPBF-processed BHS possessed superior viscoelastic and elasticity energy dissipation capacity. Importantly, the uniform reversible phase transition from martensite to austenite in the walls enables the structure to largely recover its pre-deformation shape when heated (over 99% recovery rate). These design strategies can serve as valuable references for the development of intelligent components that possess high mechanical efficiency and shape memory capabilities.

Максвеллівська релаксація і внутрішнє тертя в системі полівінілбутираль-полівінілхлорид

The Maxwellian relaxation and internal friction of a mixture of amorphous polymers: polyvinyl butyral (PVB) - polyvinyl chloride (PVC) are studied. It has been found that by changing the temperature (T) and content (j ) of the ingredients, it is possible to control the value of viscoelastic moduli, viscosity, damping force, and energy dissipation due to Maxwellian relaxation caused by the action of ultrasonic vibrations with a frequency (w ) of 0.4 MHz on the composite. The use of computational methods, models, and a phenomenological approach made it possible to differentiate the effects of relaxation and indicate the ways to optimally combine the desired properties of the components in the system.

Why soft contacts are stickier when breaking than when making them.

Soft solids are sticky. They attract each other and spontaneously form a large area of contact. Their force of attraction is higher when separating than when forming contact, a phenomenon known as adhesion hysteresis. The common explanation for this hysteresis is viscoelastic energy dissipation or contact aging. Here, we use experiments and simulations to show that it emerges even for perfectly elastic solids. Pinning by surface roughness triggers the stick-slip motion of the contact line, dissipating energy. We derive a simple and general parameter-free equation that quantitatively describes contact formation in the presence of roughness. Our results highlight the crucial role of surface roughness and present a fundamental shift in our understanding of soft adhesion.

Experimental Study on 3D RC Frame Structures with VE Energy Dissipation Braces Using STM32-Matlab-OpenSees Hybrid Test Platform

This study aims to reveal the control mechanism of viscoelastic (VE) energy dissipation braces with strong mechanical nonlinear characteristics on the seismic response of reinforced concrete (RC) frame structures. Firstly, a new STM32-Matlab-OpenSees joint hybrid test platform is developed by introducing OpenSees, which is convenient for structural modeling and fast for structural calculation. The overall architecture and operation of the hybrid test platform are comprehensively analyzed. Then, a series of simulated seismic hybrid tests on three-dimensional (3D) RC frame structures with VE energy dissipation braces under different seismic waves are successfully carried out. Lastly, the hybrid test results of this structure system at different working conditions are compared and analyzed comprehensively. The research results show that the developed platform breaks the boundary limitation that OpenSees relies on the framework software OpenFresco and can only be connected to specific control systems in the hybrid test. Thus, it greatly expands the application scope of flexible configuration controller and actuator categories for the hybrid test platform, and it also provides a good reference value for the establishment and implementation of similar hybrid test platforms. Under the action of various seismic waves, VE energy dissipation braces has good universality for the shock absorption of RC frame structures. The damping control effect and energy dissipation efficiency of VE energy dissipation braces are significantly different under various seismic waves. In the design of RC frame structures with VE energy dispersion braces, it is very necessary to conduct the seismic analysis of the structures under multiple ground motions with wide frequency domain. The additional position of VE energy dissipation braces should be an important analysis indicators in the optimization design of the structures.

Seismic retrofit of low-rise structures using rotational viscoelastic dampers

In this research, the efficiency of a rotational viscoelastic seismic energy dissipation device is evaluated in a theoretical framework. Unlike conventional dampers which block the bays, the main advantage of this damper lies within its vertical installation scheme that provides open space in the bay and architectural flexibility. The proposed damper consists of a steel column with viscoelastic hinges at both ends that dissipate the seismic energy. Conventional viscoelastic dampers usually act under translational deformation, whereas it acts under rotational deformations in the considered scheme. The theoretical foundation is laid for the proposed damper and is verified by comparing the results with the analytical model of the damper. The developed device is proven to be versatile in terms of stiffness and energy dissipation which can be easily adjusted. The application and efficiency of this damper is validated by retrofitting a soft-first-story structure to fulfill the enhanced performance objective. The performance of the structure under a suite of earthquakes is compared before and after the seismic retrofit in terms of maximum interstory drift ratio and residual displacement.

The effect of surface roughness on the viscoelastic energy dissipation in a particle–wall collision

The particle collision on a wall with roughness is common in nature and industries, but not well understood yet. The presence of surface roughness greatly increases the complexity of local contact and makes it difficult to predict the energy dissipation by analytical models. In this work, we investigate the energy dissipation in a dynamic particle–wall collision with regular hemisphere roughness. The finite element method (FEM) with the standard linear solid model is used to solve the problem of non-ideal geometry, and extract the law of energy dissipation due to viscoelasticity. The results show that with the existence of surface roughness, the total viscoelastic dissipation is lower than that for a smooth surface, showing a higher restitution coefficient compared to the smooth surface. Based on the maximum number of asperities that particle contacts, the dynamic collisions can be categorized as the single-contact mode and multiple-contact mode. The variation of the total energy dissipation shows opposite trends with the roughness height in the two different modes. The collision time is recognized as the key to predict the total energy dissipation. Based on FEM simulation results, a piecewise correlation is established to estimate the Hertzian collision time with regular roughness. Finally, a correlation is proposed for the total energy dissipation in a viscoelastic particle–wall collision with regular roughness, which only takes the dimensionless relaxation time as the parameter. Covering different roughness heights, particle sizes, densities, relaxation times, and Young’s modulus, all the data are well correlated with the predicted curve.

Insights into Mechanical Dynamics of Nanoscale Interfaces in Epoxy Composites Using Nanorheology Atomic Force Microscopy.

Interfacial polymer layers with nanoscale size play critical roles in dissipating the strain energy around cracks and defects in structural nanocomposites, thereby enhancing the material's fracture toughness. However, understanding how the intrinsic mechanical dynamics of the interfacial layer determine the toughening and reinforcement mechanisms in various polymer nanocomposites remains a major challenge. Here, by means of a recently developed nanorheology atomic force microscopy method, also known as nanoscale dynamic mechanical analysis (nDMA), we report direct mapping of dynamic mechanical responses at the interface of a model epoxy nanocomposite under the transition from a glassy to a rubbery state. We demonstrate a significant deviation in the dynamic moduli of the interface from matrix behavior. Interestingly, the sign of the deviation is observed to be reversed when the polymer changes from a glassy to a rubbery state, which provides an excellent explanation for the difference in the modulus reinforcement between glassy and rubbery epoxy nanocomposites. More importantly, nDMA loss tangent images unambiguously show an enhanced viscoelastic response at the interface compared to the bulk matrix in the glassy state. This observation can therefore provide important insights into the nanoscale toughening mechanism that occurs in epoxy nanocomposites due to viscoelastic energy dissipation at the interface.

An Incremental Contact Model for Rough Viscoelastic Solids

Viscoelastic dissipation is long concerned to be one of the origins of kinetic friction. In this study, the viscoelastic contact of rough solids is investigated by combining the principle of Lee and Radok and a recently developed incremental contact model. Evolutions of the real contact area and the average interfacial separation are obtained for a loading-unloading circle. For standard linear solids with Gaussian random rough surfaces, the effects of the viscoelastic reduction ratio and the loading rate on the contact responses are discussed. The viscosity of contacting solids would lead to the hysteresis of the mechanical responses to external excitation. Based on the relation between the average interfacial separation and the normal load, the viscoelastic energy dissipation is calculated and the role of surface morphology is addressed. Generally, the dissipated energy is proportional to the root-mean-square height of the rough surface, but decays for surfaces with larger root-mean-square slopes. The results of the current study are helpful for studying the friction between solids.

SIMULATION OF INTERMEDIATE VISCOELASTIC SUPPORT UNDER NON-STATIONARY VIBRATIONS OF TIMOSHENKO BEAMS

When modeling mechanical objects and their systems, mathematical models developed for an elastic domain are most often used, which in some cases can lead to significant inaccuracies in calculations. The use of mathematical models that take into account visco-elastic properties or energy dissipation allows to obtain more realistic models, which will make it possible to obtain more accurate calculation results. In the paper non-stationary loading of a mechanical system, consisting of a beam hinged at the edges, and an additional support installed in the span of the beam is considered. We use a beam deformation model, which is based on the hypotheses of S. P. Timoshenko and takes into account the inertia of rotation and shear. The system of partial differential equations describing the deformation of the beam is solved by expanding the desired functions into the corresponding Fourier series and subsequent using the integral Laplace transform. The additional support is assumed to be realistic rather than absolutely rigid, having linear elastic and viscous components. It is assumed that at the point of attachment of the additional support to the beam their displacements coincide. The reaction between the beam and the additional support is replaced by an external unknown concentrated force applied to the beam, which changes with time. The law of change in time of this unknown reaction is determined from the solution of the Volterra integral equation. A method for obtaining an integral equation for an unknown reaction is described. Analytical relations and calculation results for specific numerical parameters are given. The influence of stiffness and viscosity on the determined reaction of the additional support, as well as on the deflections of the beam at various points, is investigated. The results obtained can also be used for damping forced vibrations of mechanical systems.

A Complex Mode Method for Wind-Induced Responses of 6-Parameter Practical Viscoelastic Damping Energy Dissipation Structures Based on the Davenport Wind Speed Spectrum

Based on Davenport wind speed spectrum series, the response of six-parameter practical viscoelastic damping energy dissipation structure is studied systematically. Firstly, the differential constitutive relation of six-parameter viscoelastic damper is used to establish the equation of motion of energy dissipation structure under Davenport wind spectrum excitation. Then, the equation of motion of energy dissipation structure is transformed from the second-order differential equation to the first-order equation of motion by using complex mode method, and the frequency-domain solution and power spectral density function expression of energy dissipation structure system under wind excitation are obtained, Finally, based on the random vibration theory, the analytical solutions of the response of the energy dissipating structure system under Davenport wind spectrum excitation and the force response of the damper are obtained by using the mathematical identity. This method not only considers the results of the whole array expansion of the structure system under wind vibration excitation, but also has more simple and efficient expressions than those obtained by existing methods.

Dynamic performance and cross-level damage criteria of strengthened reinforced concrete frames with VE energy dissipation braces

Based on the low cost and superior damping performance of viscoelastic dampers, the new structural system strengthened with viscoelastic energy dissipation braces (VEDB) is proposed to upgrade the reinforced concrete frame structures with insufficient seismic capability. For the dynamic performance researches and damage evolution predictions of this structure system during earthquakes, the dynamic performance of six RCFs (reinforced concrete frames) and six VEFs (another six special reinforced concrete frames with VEDB) are studied under sinusoidal wide frequency range loading excitation horizontally. On this basis, the qualitative and quantitative relations on the damage growing at the material-level and the member-level performance deteriorating about the frame structures are conducted. Furthermore, the empirical calculation model on the cross-level damage evolution of VEFs are established and verified. Finally, a set of useful and robust cross-level judgment criteria for damage performance rates is proposed. The research found that, the installation of VEDB can significantly improve the load bearing capacity, the lateral stiffness and the energy dissipation capacity of the structures. The damage pattern of the structures is improved by VEDB, and it ensures the design criteria of “strong joints and weak members.” The empirical calculation model on the cross-level damage evolution and judgment criteria for damage performance rates proposed in this paper are useful and stable in practical engineering.

The poroviscoelastodynamic solution to Mandel's problem

Mandel's problem of quasi-static poroelasticity describes axial compression of a rectangular sample from a porous, fluid-saturated, and elastic material while allowing the pore fluid to drain from the lateral boundaries. This paper reports the closed-form analytical solution to an extension of this problem that considers dynamic response of a porous, fluid-saturated, and viscoelastic specimen with similar geometry and boundary conditions to harmonic excitation. Biot's theory of poroelastodynamics, along with frequency-domain formulation of the viscoelastic constitutive behavior, are used for this purpose. Results indicate that a quasi-static approximation of the dynamic Mandel's problem could generate significantly deviant results compared to the presented dynamic solution, even at frequencies that are substantially smaller than the first natural frequency of the specimen. In this aspect, the solution delineates the existence of four timescale categories pertaining to viscous energy dissipation within the solid and fluid phases of the tested material, as well as the specimen natural frequencies and the loading excitation frequency. Relative order of the described timescales is shown to shape the various forms that the sample frequency response may take. These variations are demonstrated via three case studies involving the brain tissue, asphalt mix, and shale. The presented poroviscoelastodynamic solution verifies previous findings from experimental studies suggesting that a disentangled exhibition of the poroelastic and viscoelastic energy dissipation mechanisms may be captured by the loss angle curves of a frequency sweep test on poroviscoelastic materials.

Temperature-Dependent Viscoelastic Energy Dissipation and Fatigue Crack Growth in Filled Silicone Elastomers

There has always been a need to investigate the mechanical properties and fracture behaviors of materials that are widely used commercially, such as filled silicone rubbers. In this work, a thorough study was performed to evaluate the temperature dependencies of viscoelastic energy dissipation and fatigue crack propagation. Small strain viscoelastic behavior was examined by using dynamic mechanical analysis (DMA), and larger strain viscoelastic dissipation was quantified by defining an effective viscoelastic phase angle from large-amplitude cyclic deformation. Pure shear mode I fatigue tests were performed for quantification of material toughness and crack propagation resistance. In addition, natural rubber with different filler levels was tested to provide a direct comparison between two important classes of filled rubber elastomers. Major differences were identified for the two elastomers. However, for both types of elastomers, a common power law relationship with an exponent of 1.5 describes the dependence of the fatigue crack growth per cycle on a normalized driving force obtained from the stored elastic energy. We found that the silicone rubber deviated from the 1.5 exponent power law relation at elevated temperature, and its prefactor in this power law was correlated to the crack morphology, with rough cracks providing a higher fatigue resistance than smooth cracks.

Thermal-Regulated Adhesion Enhancement and Fast Switching within the Viscoelastic Glass Transition Zone of a Shape Memory Polymer

The effects of temperature and preload on adhesion of an epoxy-based shape memory polymer (ESMP) were investigated experimentally. The ESMP sheet and polydimethylsiloxane (PDMS) control sample were prepared by mold casting. The adhesion measurements were carried out on a home-built adhesion tester using a hemispherical glass indenter as the counter-surface. The reduced modulus was determined by the Oliver-Pharr method and Hertz theory. The viscoelastic energy dissipation was extracted, and the effective work of adhesion was calculated by the fitting method and JKR theory. In the vicinity of glass transition temperature (Tg), the viscoelastic enhancement factor (1 + f(v, T)) is as high as 955 because of the strong viscoelastic effect of the ESMP sheet. The adhesion strength of the ESMP sheet is about 589 kPa under a relatively smaller contact displacement condition (∼44.6 μm). The strong viscoelastic effect induces more viscoelastic energy dissipation that contributes to the effective work of adhesion and leads to strong preload dependence of the adhesion. The pull-off force Fpull-off is demonstrated to linearly depend on Fm1/3Er2/3. In the sharp half glass transition zone (T > Tg), the viscoelasticity and rigidity rapidly decrease with the temperature increasing about 10 °C, leading to a 6-fold reduction in adhesion. The results indicate that the adhesion of the ESMP sheet can be significantly enhanced and meanwhile rapidly switched within the viscoelastic glass transition zone.

Multi-Timescale Simulations of Temperature Elevation for Ultrasonic Welding of CFRP with Energy Director

Ultrasonic welding is an energy-efficient technology that enables quick bonding of thermoplastic composite materials under normal temperature and pressure conditions. Here, numerical multi-timescale simulation is proposed to understand the welding principle, using numerical simulations of ultrasonic welding. The simulation results are validated by comparing with temperature measurements in welding tests. In the multi-timescale simulations, microsecond-scale simulations are performed first. The ultrasonic wave is modeled as a vibration load, and the energy dissipation per vibration at 25, 75, 125, 175, 225, and 275∘C is analyzed. Then, the time derivative of the temperature rise is obtained. In the normal scale simulations, the ultrasonic wave and holding pressure are replaced by a constant load, and the entire process of ultrasonic welding is simulated. The slope of the temperature rise is fitted to the time derivative of the temperature rise obtained from the microsecond-scale simulations, using the material constant as a parameter. Explicit multi-timescale simulations were performed to investigate the relationship between stress concentration and temperature rise due to ED geometry. The result reveals similar temperature behavior to the experimental one, indicating the validity of the multi-timescale method. It suggests that viscoelastic energy dissipation and stress concentration are responsible for the temperature spike.

Impact of α‐cellulose as a green filler on physico‐mechanical properties of a solution grade styrene‐butadiene rubber based tire‐tread compound

AbstractPhysico‐mechanical and dynamic mechanical properties of typical solution grade styrene‐butadiene rubber (S‐SBR) and polybutadiene rubber (PBR) based tire‐tread compound were investigated by partially replacing highly dispersible (HD) silica with naturally occurring α‐cellulose. Fourier transform infrared spectrum detected abundance of hydroxyl group in α‐cellulose, which has created keenness to investigate its reinforcement characteristics in an S‐SBR and PBR based compound. Scanning electron microscope and transmission electron microscope were employed to investigate the microstructure and dispersion of α‐cellulose at higher magnification. Thermo‐gravimetric analysis was performed to understand the degradation behavior of α‐cellulose. Differential scanning calorimeter was engaged to detect phase transition and degree of purity of α‐cellulose. An increase in cure rate was observed with partial replacement of HD silica by α‐cellulose. The cure rate index was increased by 13% over control one at 10% replacement of silica with α‐cellulose. It was noticed that at an optimum level of replacement (10%), α‐cellulose containing compounds exhibited lower viscoelastic energy dissipation (both loss modulus [E″] and loss tangent [tan δ]) at the slight expense of tensile moduli. Beside these, substitution of silica with α‐cellulose found to have no effect on wet grip property of the compounds.

Effect of Back‐layer on seal performance of multilayer polyethylene‐based sealant films

AbstractThis work studies effects of back‐layer materials, thickness of sealant layer, and sealing condition on seal performance of multilayer polyethylene‐based films. Multilayer films with back‐layers of high‐density polyethylene (HDPE), or low‐density polyethylene (LDPE), or linear low‐density polyethylene (LLDPE) were produced with different thicknesses of the metallocene layer. It was found that increasing the thickness of the metallocene layer improved hot tack properties. In addition, films with back‐layers of LLDPE or LDPE showed higher hot tack strength compared to those with HDPE back‐layer. Increasing sealing temperature reduced significantly the hot tack strength and its dependency on metallocene layer thickness. It was found that increasing delay time after sealing, before peeling test, increased hot tack strength, but the rate of hot tack evolution and the type of peeling behavior were considerably affected by the type of back‐layer material. The effect of dwell time was also examined, and it was observed that increasing dwell time in the studied range did not affect the hot tack evolution. The mechanisms involved in the development of hot tack evolution were discussed, and it was shown that the back‐layer effects can be explained by bulk viscoelastic energy dissipation theory.

Rate-dependent fracture behavior of tough polyelectrolyte complex hydrogels from biopolymers

Tough bio-based hydrogels based on the association of physical bonds are promising materials for use in biomedical applications due to their biocompatibility, biomimicry and biodegradability. Understanding the mechanical mechanisms at work during the fracture in such applications is indispensable. Using tough and self-healing bio-based hydrogels attained by the complexation of the negatively charged sodium hyaluronate (HA) and positively charged chitosan as a model system, an investigation of the tensile and fracture behavior over five decades of stretch velocities in physically and chemically crosslinked HA/chitosan hydrogels was systematically performed. In this study, the tensile analysis shows that the both of physically and chemically crosslinked hydrogels at small deformation are viscoelastic at a low stretch velocity, while they exhibit quasi-elastic character at a relatively high stretch velocity. In comparison to the physically and lightly chemically crosslinked HA/chitosan hydrogels exhibiting plastic-like behavior, the highly chemically crosslinked hydrogels demonstrate strong finite chain extensibility before fracture. The fracture analysis shows that the fracture energy of the highly chemically crosslinked hydrogels scales with the crack velocity as a power law relation Γ∝Vca (a= 0.15), where the exponent a can be well predicted from the viscoelastic spectrum of the bulk sample. These findings indicate that the viscoelastic energy dissipation around the crack tip dominates the fracture energy of the highly chemically crosslinked hydrogels. On the other hand, the fracture energy of the physically and lightly chemically crosslinked hydrogels is noted to increase with the crack velocity as a complex growth function, which can be effectively predicated by a viscoplastic model. The observed finding shows that the fracture energy of the physically and lightly chemically crosslinked hydrogel is dominated by the unzipping of the polyion complex structure and viscous energy dissipation due to the pulled out chains from the polymer network structure.

Bend stiffener linear viscoelastic thermo-mechanical analysis, Part II: Numerical solution and case study

The viscoelastic energy dissipated by the bend stiffener when subjected to cyclic loading increases the polyurethane temperature and may affect the system curvature distribution in a coupled manner. The steady-state thermo-mechanical mathematical formulation and material experimental characterization has been presented in a companion paper (Part I). In this work (Part II), the rate of viscoelastic mechanical energy dissipation is obtained from the steady-state mechanical formulation employing the shooting method combined with the Runge–Kutta method for the two-point boundary value problem numerical solution. The temperature field distribution within the bend stiffener volume is then estimated with the three-dimensional steady-state thermal model employing the finite difference technique with a boundary-fitted coordinate system that transforms the physical domain into a structured computational domain grid. The partial differential equations governing heat transfer are solved in the computational domain and transformed back into the physical domain by transformation relations. A detailed description of the iterative thermo-mechanical numerical solution procedure is presented and a case study carried out demonstrating the loading frequency and oscillation amplitude influence on the bend stiffener temperature field distribution. It is shown that the bend stiffener may be exposed to high internal temperatures for some loading conditions.

Force reversal and energy dissipation in composite tubes through nonlinear viscoelasticity of component materials.

Fibre-reinforced, fluid-filled structures are commonly found in nature and emulated in devices. Researchers in the field of soft robotics have used such structures to build lightweight, impact-resistant and safe robots. The polymers and biological materials in many soft actuators have these advantageous characteristics because of viscoelastic energy dissipation. Yet, the gross effects of these underlying viscoelastic properties have not been studied. We explore nonlinear viscoelasticity in soft, pressurized fibre-reinforced tubes, which are a popular type of soft actuation and a common biological architecture. Relative properties of the reinforcement and matrix materials lead to a rich parameter space connecting actuator inputs, loading response and energy dissipation. We solve a mechanical problem in which both the fibre and the matrix are nonlinearly viscoelastic, and the tube deforms into component materials' nonlinear response regimes. We show that stress relaxation of an actuator can cause the relationship between the working fluid input and the output force to reverse over time compared to the equivalent, non-dissipative case. We further show that differences in design parameter and viscoelastic material properties can affect energy dissipation throughout the use cycle. This approach bridges the gap between viscoelastic behaviour of fibre-reinforced materials and time-dependent soft robot actuation.