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Accurate modeling of material behavior is very critical for the success of magnetorheological elastomer-based semi-active control device. The material property of magnetorheological elastomer is sensitive to the frequency, magnetic field and the input strain. Additionally, these properties are unique for a particular combination of matrix and the filler loading. An experimental-based characterization approach is costly and time consuming as it demands a large amount of experimental data. This process can be simplified by adopting material modeling approach. The material modeling of magnetorheological elastomer is an extension of conventional viscoelastic constitutive relations coupled with hysteresis and magnetic field sensitive attributes. In the present study, a mathematical relation to represent the frequency, magnetic field and strain dependent behavior of magnetorheological elastomer is presented. The viscoelastic behavior is represented by a fractional zener element and the magnetic field and strain dependent attributes incorporated in the model by a magnetic spring and linearized Bouc-–Wen element, respectively. The proposed model comprised of a total of eight parameters, which are identified by minimizing the least square error between the model predicted and the experimental response. The variations of each parameter with respect to the operating conditions are represented by a generalized expression. The parameters estimated from the generalized expression are used to assess the ability of the model in describing the dynamic response of magnetorheological elastomer. The proposed model effectively predicted the stiffness characteristics with an accuracy, more than 94.3% and the corresponding accuracy in predicting the damping properties is above 90.1%. This model is capable of fitting the experimental value with a fitness value of more than 93.22%.

In this study, two types of polymeric nanocomposite blends based on poly(l-lactide) (PLLA) and a thermoplastic polyurethane were prepared by reactive and non-reactive melt mixing. Multiwalled carbon nanotubes (MWCNTs) participated in reactive melt mixing and changed in both cases the morphology of blends. Melt rheology was used to study the influence of reactive melt mixing and localization of MWCNTs in terms of melt viscoelastic properties and relaxation time spectrum. Two relaxation times were observed for both types of blends due to reptation and stress release mechanism, although blends prepared by reactive melt mixing showed another relaxation mechanism associated with the generated interphase. Solid-state viscoelasticity determined by dynamical mechanical analysis showed significant influences of both MWCNTs and reactive melt mixing on storage modulus of the blends. Thermogravimetric analysis showed several degradation steps for polymer blends that contrast with the single step determined for both pure PLLA and PLLA nanocomposites.

This paper presents material characteristics of a rigid magnetorheological (MR) foam that comprises polyurethane foam matrix and carbonyl iron particles (CIPs). Three different samples of MR foams are prepared by changing the concentration of CIPs (0, 35, and 70 g) in isotropic condition. In-depth characterization on the morphological properties, the field-dependent rheological behavior in terms of linear viscoelastic region and storage modulus, and the off-state sound absorption properties are then experimentally investigated. In the morphological observation, it is seen from the fluorescence micrographs that MR foam consists of open pore structure and the average size of the pores is decreased with the increment in CIPs content. In the rheological test of MR foam, it is identified that MR foam with the addition of 70 g of CIPs to the total of polyol and isocyanates (100 g) can enhance the storage modulus up to 112% compared with MR foam without CIPs. In the meantime, from the acoustic absorption test, it is shown that the maximum peaks of sound absorption coefficient (SAC) are shifted to the low frequency and the SAC is increased up to 229% due to the decrement in the pores size and increment in the storage modulus. The results achieved from this material characterization of MR foam provide useful guidelines for the development of new type smart materials associated with MR fluids and for the findings of appropriate applications which require controllability of both the stiffness and acoustic properties.

Changes in moisture content of single pulp fibers have an immense influence on the behavior of paper and paper products. Here, an atomic force microscopy (AFM)-based method is applied to investigate the viscoelastic properties of pulp fibers at varying relative humidity (RH) in the transverse direction. Pulp fibers have not only anisotropic properties, but also a very rough surface due to their hierarchical structure. For this reason, we have developed a specific load schedule for the AFM-based test method to overcome uncertainties and limitations due to surface roughness of the pulp fibers. The evaluation of the experimental data combines contact mechanics and viscoelastic models which consist of springs and dashpots in series or parallel describing elastic and viscous behavior. Here, it will be demonstrated that the so-called Generalized Maxwell (GM) model yields comparable results for single pulp fibers at five different RH values and in water. The moisture changes lead to a decrease in the elastic modulus but increase in the relaxation effects with increasing RH. All the determined parameters for the elastic and viscous behavior exhibit a gradual decrease with increasing RH from 10 to 75% RH. The elastic moduli decrease by a factor of 10 and the viscosities are decreasing by a factor of 10–20. In water, there is an even more pronounced decrease of the elastic moduli by a factor 100, and the viscosities decrease by at least three orders of magnitude compared to 10% RH. This indicates that the mechanical response of pulp fibers in water is significantly different than in humid air. This is also illustrated by the fact that a GM model of order two suffices to describe the material behavior in humid air but a GM model of order three is necessary to fit the material behavior in water. A possible interpretation is an additional relaxation effect of the pulp fiber wall in water.

Dynamic mechanical analysis is a method to characterize the frequency domain viscoelastic properties including storage and loss moduli. Methods have been developed to transform these properties to time domain and extract elastic modulus over strain rates, which is useful in mechanical design. However, application of these methods becomes increasingly complex for materials containing multiple thermal transitions. Neural networks can provide advantages in solving such problems. As the form of radial basis neural network satisfies the form obtained from time–temperature superposition principle, it is used in the present work with back-propagation to establish the master relation of loss modulus. The influence of regulation factor and neuron number is investigated to find the best parameter set. Then, storage modulus is divided into frequency-dependent and frequency-independent part. Both parts are individually calculated from loss modulus using Kramers–Kronig relation. The linear integral relation of viscoelasticity can transform the storage modulus into time-domain relaxation modulus, which can predict the stress response with specific strain history and temperature. The transformation is tested on ethylene–vinyl acetate. The time-domain elastic properties are extracted and compared with those from tensile tests at room temperature. The transformation achieves an average root mean square error of 3.3% and a maximum error 4.9% between strain rates 10−6 to 10−2 s−1. This process can predict the properties at a wide range of temperatures and frequencies from a single specimen and can be implemented using parallel computing, which is promising for complex material systems.

We studied the microstructure–rheology relationship of polypropylene (PP)/ethylene octene copolymer (EOC) blends by means of rheology in combination with scanning electron microscopy. The blends varying in blend ratio all prepared by melt mixing were considered. The results of the frequency sweep experiment performed on the blend sample with matrix-dispersed morphology showed a pronounced positive deviation of storage modulus values at a low frequency range from those predicted by Palierne’s viscoelastic model. This could be explained in terms of EOC droplets interconnectivity which was generated by in situ increased chain-branched entanglements. That is, the thermo-mechanically induced PP macro-radicals produced during the melt mixing could graft onto the more stable EOC macro-radicals in the interface leading to much longer-chain-branched EOC molecules, which had the capability of creating favorable entanglements for the EOC droplets conductivity.

Polyimine vitrimers are a promising class of self-healing materials for their attractive dynamic reversible properties and ease of preparation without catalysts, but they still remain some challenges to overcome, such as poor mechanical properties and thermal stability or a higher temperature to reprocess and recycle. Herein, performance-modified polyimine vitrimers, combining flexibility, good mechanical properties and thermal stability with easy reprocessed/recycle properties, were studied by introducing aromatic diamines dimer (m-xylylenediamine dimer) into the polymer networks. The incorporation of m-xylylenediamine dimer increases the molecular chain of polymer networks, which makes the material more flexible and easy reprocessed. Besides, it owns two benzene rings and endows the dynamic polymer with broaden conjugation structure, which remains the material’s thermal stabilities and mechanical properties. Results show that the polymer material exhibits flexibility at room temperature [a glass transition temperature (Tg) of 72 °C, a storage modulus of = 1.56 GPa and stress at break of = 45 MPa (dry sample) and 27 MPa (wet sample)], possesses excellent thermal stability (a mass loss of 6.3% at 300 °C) and performs viscoelastic liquid behavior in very short relaxation times at lower temperatures (from 260 s at 70 °C to 22 s at 100 °C). In addition, the obtained networks could be more easily reprocessed and remolded in shorter times and at lower temperatures under the condition of heat, water and amine solvents without adding any catalyst.

This work studies the effects of loading various functionalized multiwall carbon nanotubes (carboxyl, –COOH-MWCNTs) on the morphological and the field-dependent rheological properties of magnetorheological elastomers (MREs). A new type of MRE, which is reinforced by various loading from 0 to 1.5 wt% of COOH-MWCNT, is fabricated and experimentally investigated. The morphology of COOH-MWCNT and MRE with COOH-MWCNTs is characterized using field emission scanning electron microscopy and transmission electron microscopy. The results indicate that the COOH-MWCNTs are well embedded and dispersed randomly in the MRE structures. The rheological properties under different magnetic fields are evaluated using parallel plate rheometers. The influence of COOH-MWCNT content on the viscoelastic performance of the MRE is systematically investigated. It is found that when a higher content of COOH-MWCNT (up to 1.0 wt%) is added in the MRE, the MRE exhibits a higher MR effect of up to 17.5%. It is also shown that COOH-MWCNT acts as a reinforcing agent that leads to an enhancement in MR performance.

The additives improve the properties of magnetorheological elastomer by modifying the surface of ferromagnetic filler particles or by varying the properties of a host polymer matrix. In this study, effect of carbon nanotube additive on the viscoelastic properties of magnetorheological elastomer reinforced with optimum quantity of ferromagnetic filler is studied. Room temperature vulcanizing silicone elastomer-based test samples are prepared by mixing the elastomer with the carbon nanotube and carbonyl iron powder blend obtained from ultrasonication. Viscoelastic properties are measured by adopting the dynamic blocked transfer stiffness method. The results revealed that the properties of magnetorheological elastomer vary significantly with the inclusion of carbon nanotube. With the addition of 0.5 wt% carbon nanotube, the zero field dynamic stiffness of magnetorheological elastomer is enhanced by 36.7% and the loss factor is increased by 17.2%. The enhancement in zero field properties led to the least field-induced enhancement for magnetorheological elastomer doped with 0.5 wt% carbon nanotube. A relatively larger flexibility of pure magnetorheological elastomer samples had resulted in the maximum field-induced enhancement of 48.04%. Among the prepared test samples with carbon nanotube addition, the sample loaded with 0.25 wt% carbon nanotube exhibited a pronounced stiffness enhancement and lower loss factor. This substantiated the existence of an optimum limit for carbon nanotube additive. The present study also confirmed the feasibility of developing MRE tailor-made to suit the particular application by selecting a proper composition of matrix, filler and the additives.

The role of surface modification on rheological properties of fibrillated cellulose suspensions has been evaluated under creep, oscillatory, and rotational testing conditions. Two types of fibrillated cellulose were produced by mechanical homogenization, followed by the deposition of poly(styrene-co-maleimide) or SMI nanoparticles containing encapsulated palm oil on the fibril surfaces. During static creep testing, the modified fibrils changed into fully viscous properties, while native fibrils showed viscoelastic behavior at low stresses. A lower viscosity and reduction in hysteresis effects were experienced during steady-state rotational flow testing, together with a reduction in yield stress after modification. A study of viscoelastic properties by oscillatory testing illustrated that the cross-over point between storage and loss moduli was shifted towards lower strains by surface modification as an indication for the enhancement of liquid-like properties observed for SMI/oil nanoparticle dispersions, while the transition point was hardly affected by fibrillation. The variations in rheological properties were overruled by surface modification and reduction in hydrogen bonding interactions of modified fibrillated cellulose, whereas rheological properties of a physical mixture of native fibrillated cellulose suspension and nanoparticle dispersion remained dominated by the fibrillated cellulose.

Hygrothermal recovery (HTR), the dimensional changes in wood induced by hygrothermal treatment, was investigated using both compression and normal wood of sugi (Cryptomeria japonica). The elastic released strain of growth stress was measured on living tree surfaces; subsequently, the specimens were taken from the same position to measure HTR. HTR was measured as dimensional changes due to treatment at 20, 40, 60, 80, and 100 °C in hot water ranging from 200 min to 177 days. The intensity of HTR had a positive relationship with elastic released strain of growth stress. This result suggests that HTR is the relaxation of the viscoelastic component of growth stress accumulated during the maturation process of trees. The rate of HTR clearly showed a time–temperature dependency: higher at higher treatment temperatures and lower at lower treatment temperatures. Based on kinetic analysis, the apparent activation energy (E a) was calculated as 407 kJ/mol, which is similar to the published E a of lignin softening implying that the HTR is a lignin-related phenomenon.

Dynamic rheological properties of multiwalled carbon nanotubes-(MWCNTs) reinforced acrylonitrile butadiene styrene (ABS) composites prepared by micro twin-screw extruder with back flow channel (used for proper dispersion) are reported. Scanning electron microscopic and high-resolution transmission electron microscopic studies showed that the nanotubes were uniformly dispersed in the ABS polymer matrix. MWCNT forms a network throughout the polymer matrix and thus promotes the reinforcement. The rheological studies showed that (for 3 wt% of MWCNTs loading) the material undergoes viscous to elastic transition. At a higher MWCNTs concentration nematic gel-like phase is observed where both storage and loss modulus (G′ and G″) are nearly independent of frequency. van Gurp–Palmen plot has been used to determine the viscoelastic properties. Dynamic intersection frequency has been used to correlate the rheological properties with different wt% of MWCNTs loading in ABS. Dynamic rheological measurements revealed the viscous-like (G″ > G′) behaviour at a lower MWCNTs loading ( 3 wt%).

Subcellular mechanical characterization of the cell wall can provide important insights into the cell wall’s functional organization, especially if the characterization is not confounded by extracellular factors and intercellular boundaries. However, due to the technical challenges associated with the microscale mechanical characterization of soft biological materials, subcellular investigations of the plant cell wall under tensile loading have yet to be properly performed. This study reports the mechanical characterization of primary onion epidermal cell wall profiles using a novel cryosection-based sample preparation method and a microelectromechanical system-based tensile testing protocol. At the subcellular scale, the cell wall showed biphasic behavior similar to tissue samples. However, instead of a transition zone between the linear elastic or viscoelastic and linear plastic zones, the subcellular-scale samples showed a plateau-like trend with a sharp drop in the modulus value. The critical ranges of stress (20–40 MPa) and strain (5–12 %) of the plateau zone were identified. A strain energy of 1.3 MJ m−3 was calculated at the midpoint of the critical stress–strain range; this value was in accordance with the previously estimated hydrogen bond energy of the cell wall. Subcellular-scale samples showed very large lateral/axial deformations (0.8 ± 0.13) at fracturing. In addition, investigating the cell wall’s mechanical properties at three different water states showed that water is critical for the flow-like behavior of cell wall matrix polymers. These results at subcellular scale provide new insights into biological materials that possess a structural hierarchy at different length scales; which cannot be obtained from tissue-scale experiments.

The present article reports viscoelastic properties and melt rheology of novel nanostructured thermoplastic vulcanizates (TPVs) consisting of dispersed nanodimensional fluoroelastomer (FKM) particles into the continuous polyamide (PA6) matrix. The influence of dynamic vulcanization on the above properties of the blends was reported. The storage modulus and loss modulus were plotted against reduced frequency to understand the behavior of nanostructured TPVs. PA6/FKM TPVs showed pseudoplasticity and obeyed cross viscosity model. Insight into how the crosslink density of TPVs affects the rheological response was discussed. Also, a new relationship of zero shear viscosity (η 0) with the crosslink density of TPVs was proposed to gain insight into dynamic vulcanization. It was found that up to a certain amount of curative concentration, η 0 depends upon the crosslink density to a power equal to 3.4 and is roughly proportional to the crosslink density on further increase of curative concentration. van Gurp–Palmen plot of phase angle versus reduced complex modulus indicated the droplet–matrix morphology of the PA6/FKM blends which was further confirmed from field emission scanning electron microscopy and atomic force microscopy studies, where FKM nanoparticles (60–80 nm) were the dispersed phase. Various melt elastic properties of TPVs such as die swell, first normal stress difference, recoverable shear strain, and apparent elasticity were measured and analyzed. TPV extrudates were examined using surface finish and roughness values. TPVs exhibited smoother extrudate surface than reported earlier. Extrudate surface roughness from atomic force microscopy was used to analyze the processing behavior of TPVs.

Local failure initiation mechanisms, such as the nucleation and propagation of multiple cracks, have been investigated in energetic aggregates with a viscoelastic estane binder and crystalline RDX grains that have been subjected to dynamic thermo-mechanical loading conditions. A dislocation density-based crystalline plasticity, finite viscoelasticity, dynamic fracture nucleation and propagation, and non-linear finite-element formulations were used to study crack nucleation and propagation due to dynamic, tensile mechanical strain-rate loading conditions in RDX-Estane energetic aggregates. The interrelated effects of grain boundary (GB) misorientations, porosity, grain morphology, dislocation densities, polymer binder relaxation, and crystal-binder interactions were coupled with adiabatic plasticity heating, thermal decomposition, and viscous dissipation heating to fundamentally understand and predict aggregate behavior and local failure initiation mechanisms. The predictions indicate that local failure occurs when cracks nucleate at the peripheries of internal porosity and subsequently propagate toward the viscoelastic estane binder where crack arrest occurs at the interface, which results in large inelastic deformations and temperature accumulations at the interfaces.

The viscoelasticity of a variety of active materials is controllable, e.g., by the application of electric or thermal fields. However, their viscoelastic behavior cannot be fully explored by current methods due to limitations in their control of mechanical, electrical, and thermal fields simultaneously. To close this gap, we introduce Broadband Electromechanical Spectroscopy (BES). For the specific apparatus developed, specimens are subjected to bending and torsional moments with frequencies up to 4 kHz and amplitudes up to 10−4 Nm (the method is sufficiently general to allow for higher and wider frequency ranges). Deflection/twist is measured and moments are applied in a contactless fashion to minimize the influence of the apparatus compliance and of spurious damping. Electric fields are applied to specimens via surface electrodes at frequencies up to 10 Hz and amplitudes up to 5 MV/m. Experiments are performed under vacuum to remove noise from the surrounding air. Using BES, the dynamic stiffness and damping in bending and torsion of a ferroelectric ceramic, lead zirconate titanate, were measured at room temperature, while applying large, cyclic electric fields to induce domain switching. Results reveal large increases of the specimen’s damping capacity and softening of the modulus during domain switching. The effect occurs over wide ranges of mechanical frequencies and permits lowering of the resonance frequencies. This promises potential for using ferroelectrics for active vibration control beyond linear piezoelectricity. More generally, BES helps improve current understanding of microstructure kinetics (such as during domain switching) and how it relates to the macroscopic viscoelastic response of materials.

The literature on the time-dependent behaviour of single bast fibres such as flax and hemp is extremely poor. The aim of this extensive study is to characterise the long-term behaviour of elementary hemp fibres and to establish suitable constitutive laws. Single hemp fibres are shown to exhibit both instantaneous strain and delayed, time-dependent strain when tensile loaded under constant climate. The creep behaviour appears to be a logarithmic function of time with a high strain rate during the primary creep and a lower and constant one during the secondary creep. A large scattering both in time-dependent properties and behaviour was observed on a batch of 25 single fibres. Three main creep behaviours were observed. Type II is truly linear as a function of the logarithm of time while Type I and Type III are strongly nonlinear and can be described, respectively, by concave and convex functions. A rheological model based on an anisotropic viscoelastic law and on a truncated inverse Gaussian spectrum of viscous mechanisms was shown to successfully describe all the experimentally observed behaviours.

Clay is a soil component, a ceramic ware component, and a reinforcement in nanocomposites. Its viscoelastic behavior is relevant to vibration damping and slip rheology. The clay studied is hectorite, which is a trioctahedral magnesium-based smectite. Clay compacts with solid contents (50–53) vol% are studied in terms of the dynamic compressive properties at small static strains (3.1–3.5 %), low deformation amplitudes (5–8 μm), and low frequencies (0.2–10.0 Hz). The organic intercalation of hectorite (with basal spacing 12 A prior to intercalation) to form organoclay (nanoclay in the form of disteardimonium hectorite with basal spacing 29 A) increases both the loss tangent and the loss modulus of the solid part of the compact by up to about 27 %, while affecting the storage modulus negligibly. At 10.0 Hz, the organic intercalation increases the loss tangent of the solid part from 0.306 ± 0.009 to 0.366 ± 0.021 and increases the loss modulus of the solid part from (2.69 ± 0.08) × 104 to (3.44 ± 0.04) × 104 Pa. The organic intercalation affects the viscous behavior rather than the elastic behavior. The viscous behavior is attributed to the low-amplitude dynamic slippage at the interface between adjacent clay layers in a clay nanoplatelet and that between nanoplatelets in a clay particle. In case of organoclay, it is also due to the nanoscale viscous behavior of the organic component. The viscoelastic properties are essentially independent of the frequency. The viscous character of both unmodified clay and organoclay is weaker than that of carbon black or exfoliated graphite, but the elastic character of both unmodified clay and organoclay is stronger than that of carbon black or exfoliated graphite.

Three-dimensional viscoelastic properties of four-step three-dimensionally (3D) braided composites are studied in this paper. Based on the three-cell division scheme, a multi-scale model for 3D braided composites is proposed. A periodic boundary condition is applied to characterize the periodic structure of 3D braided composites and yarns. Given the viscoelastic parameters of resin matrix and the elastic constants of fibers, the viscoelastic properties of yarns are obtained by the finite element method and Prony Series fitting. The three-dimensional viscoelastic constitutive relationship of interior cells is derived based upon the viscoelastic properties of yarns and resin matrix. Moreover, the viscoelasticity of 3D braided composites is studied by creep experiment. The viscoelastic deformation obtained from the multi-scale method agrees well with the experimental results. The influence of the two independent micro-structural parameters, braiding angles, and fiber volume fractions, on the viscoelastic properties of 3D braided composites is investigated in detail.

Cyclic material tests were done on Divinycell PVC H100 foam to obtain out-of-plane and in-plane compression and shear material properties after foam yielding. The compression and shear stress–strain behaviors were very similar to each other except that a plateau (flow) stress occurred after yielding in compression, while the foam underwent mild strain hardening after shear yielding. The ratio of out-of-plane to in-plane stiffness and yield strength for the PVC H100 was found to be approximately 3/2 in both the compression and shear modes. After viscoplastic yielding, the foam underwent permanent damage and exhibited hysteresis, mainly in the form of viscoelasticity. Damage that occurred in the foam after it yields followed the pattern of Mullins damage, i.e., the damage was essentially fixed at a given strain amplitude, and more damage occurred with increasing the strain amplitude. Hysteresis was much more pronounced as the damage grew, suggesting that viscoelastic properties of the foam could be changing with the amount of damage.

The viscoelastic characteristics of ultra-high molecular weight polyethylene (UHMWPE) fibres are investigated, in terms of creep-induced recovery strain and force output, to evaluate their potential for producing a novel form of prestressed composite. Composite production involves subjecting fibres to tensile creep, the applied load being removed before moulding the fibres into a resin matrix. After matrix curing, the viscoelastically strained fibres impart compressive stresses to the surrounding matrix, to produce a viscoelastically prestressed polymeric matrix composite (VPPMC). Previous research has demonstrated that nylon fibre-based VPPMCs can improve mechanical properties without needing to increase mass or section dimensions. The viability of UHMWPE fibre-based VPPMCs is demonstrated through flexural stiffness tests. Compared with control (unstressed) counterparts, these VPPMCs typically show increases of 20–40 % in flexural modulus. Studies on the viscoelastic characteristics indicate that these fibres can release mechanical energy over a long-timescale and fibre core–skin interactions may have an important role.

The pomelo (Citrus maxima) is the largest and heaviest fruit of the genus Citrus and can acquire considerable potential energy as it ripens hanging up to 15 m height. Its thick foam-like structured peel presumably acts inter alia as a shock absorbing layer, protecting the fruit as it impacts on the ground upon being shed. Thereby the peel dissipates kinetic energy by being compacted. In order to elucidate the compaction mechanism of the highly heterogeneous pomelo peel, we conducted incremental stress relaxation tests. Two different models describing the stress relaxation curves, namely, the well-known Maxwell model and the Peleg model were compared and found to be suitable to describe the stress relaxation. As the Peleg model involves only two constants describing the relaxation curves it was the method of choice for interpreting the compaction of the peel samples. The inverse of k 1 reflects the initial decay rate of the relaxation process and k 2 is a measure of the samples’ solidity. The behaviour of these constants with increasing strain indicates the strong influence of the peel samples’ geometry and composition which is attributed to the fruit shape, a gradual changing density of the peel, which can be considered as a stacked array of foam layers differing in density, and the turgescence of the biological cells.

Temperature-dependent indent recovery of polymethyl methacrylate is depicted by atomic force microscopy. The viscoelastic indent recovery is predicted by a numerical model based on the Boussinesq elastic theory. From the perspective of an elastic solution, viscoelastic solution for stress and displacement field is constructed through the analysis of the elasticity–viscoelasticity corresponding theory. The findings also illustrate the effect of loading condition, elastic modulus, and viscosity on the viscoelastic recovery rate.

Viscoelastic properties of hollow particle-reinforced composites called syntactic foams are studied using a dynamic mechanical analyzer. Glass hollow particles of three different wall thicknesses are incorporated in the volume fraction range of 0.3–0.6 in vinyl ester resin matrix to fabricate twelve compositions of syntactic foams. Storage modulus, loss modulus, and glass transition temperature are measured and related to the microstructural parameters of syntactic foams. In the first step, a temperature sweep from −75 to 195 °C is applied at a fixed loading frequency of 1 Hz to obtain temperature dependent properties of syntactic foams. In the next step, selected four compositions of syntactic foams are studied for combined effect of temperature and loading frequency. A frequency sweep is applied in the range 1–100 Hz and the temperature is varied in the range 30–140 °C. Time–temperature superposition (TTS) principle is used to generate master curves for storage modulus over a wide frequency range. The room temperature loss modulus and maximum damping parameter, Tanδ, are found to have a linear relationship with the syntactic foam density. Increasing volume fraction of particles helps in improving the retention of storage modulus at high temperature in syntactic foams. Cole–Cole plot and William–Landel–Ferry equation are used to interpret the trends obtained from TTS. The correlations developed between the viscoelastic properties and material parameters help in tailoring the properties of syntactic foams as per requirements of an application.

Yarn made from natural fibers, synthetic fibers, or other types of fibrous materials is all formed by twisting an assembly of short or long fibers and its performance is significantly influenced by the physical behavior of these fibers in the yarn forming region—a small triangle area called spinning triangle. In spinning process, the fibers in spinning triangle where they are finally twisted into a yarn are subject to dynamic loads. However, earlier theoretical models are all based on the static assumptions and it cannot reflect the real status of the spinning process. Therefore, in this study, a new dynamic model of spinning triangle was developed by using finite-element method with consideration of the dynamic effects such as the inertia and damping forces of constituent fibers for a more complete and accurate description. With consideration of dynamic characteristics of fiber, earlier static model of spinning triangle can be considered as a special case of the proposed dynamic model. In order to verify the developed theoretical model, comparisons of the proposed model with earlier model and experimental measurements were carried out and good agreements were achieved. Furthermore, the dynamic behavior of fibers in spinning triangle, such as the natural frequency, mode shape, resonant response, harmonic analysis, and response under a time-varying tension, has been numerically studied. The results show that dynamic parameters have a great influence on the amplitude and attenuation of the response of constituent fibers in spinning triangle.

The application of a computerised image analysis system to simultaneously measure longitudinal and axial strain in naturally available anisotropic-viscoelastic material like leather is described. The results are used to calculate Poisson’s ratio and indicate that this parameter varies with position and orientation on the hide and depends on the degree of pre-existing fibre orientation. The origins of this dependency can be explained by a simple microstructural model. The practical implication of the findings for detecting lines of tightness (maximum fibre’s orientation) is discussed.

An ever increasing demand for material performance coupled with recent advances in the production and availability of nanoscale materials has led to a significant interest in the use of nanoscale fillers to augment and tailor material performance in nanocomposites. Specifically, the use of high aspect ratio fillers, such as carbon nanotubes and carbon nanofibers (CNF) to augment the viscoelastic performance of nanocomposites has been the focus of many studies. Previous study has shown the use of high aspect ratio fillers to significantly enhance the damping capacity at low frequencies by more than 100 %, relative to the neat epoxy. In light of the promise, this technology holds for use in engineered applications, requiring specific damping performance, there remains a fundamental lack in understanding of the precise mechanisms and thereby a lack of ability to accurately predict material performance, which is limiting application of the technology. This study looks at both the effect of the random filler orientation and the effect of filler waviness in examining the viscoelastic response of CNF-reinforced nanocomposites. Using a fundamental approach, this study employs experimental, analytical, and numerical modeling techniques to characterize the amount of strain energy transferred to the filler and the matrix, and to indirectly estimate the effective loss factor of the filler. Utilizing experimental investigation coupled with parametric inquiries using strain energy methods relative to both filler orientation and waviness, this study provides fundamental insight into the effect of imperfect geometries and random filler distributions seen in nanocomposites utilizing high aspect ratio fillers, such as CNF.

The influence of the viscous and elastic components of a visco-elastic binder phase on the extrusion behaviour of a tungsten carbide–cobalt hardmetal paste was investigated by studying the paste over a range of temperatures, 30–42 °C, where the binder changed from a semi-solid gel to a viscous liquid. The extrusion behaviour of the paste was studied by ram extrusion and quantified by the Benbow–Bridgwater (BB) method. The elastic and viscous components of the binder were studied separately by means of oscillatory and steady shear techniques in a controlled stress rheometer using rough parallel plates. The paste behaviour fitted the four parameter BB model well: the initial bulk yield stress parameter, σ0, increased linearly with the binder elastic modulus, G′, while both the velocity dependence parameters α and β were linearly related to the binder steady shear viscosity. Analysis of paste-wall slip parameters gave estimated slip layer thicknesses of 2–5 particle diameters.

The review focuses on the current studies of the deformation response and accompanying structural transformations of thermoplastic semicrystalline polymers subjected to uniaxial tension prior to the yield point. The mechanisms of strain-induced cavitation of amorphous layers and damages of crystalline lamellae are analyzed in line with novel results on the deformation behavior of solid polymers at temperatures exceeding the glass transition point. The coupling of viscoelastic and plastic deformation mechanisms with the small-strain structural transformations is critically discussed on the basis of the advanced theoretical modeling of mechanical properties of semicrystalline polymers.

The article describes the effect of hydrocarbon (HC) and coumarone-indene (CI) resin tackifiers on autohesion behavior of ethylene propylene diene polymethylene (EPDM) rubber. The viscoelastic behavior and nature of compatibility of EPDM/tackifier blends were studied by means of dynamic mechanical analysis. Furthermore, scanning electron microscopy and atomic force microscopy were used to understand the compatibility of the EPDM/tackifier blends. The HC tackifying resin modified the viscoelastic properties of the EPDM rubber in such a way that it behaved as a plasticizer at lower frequency by reducing the storage modulus and filler at higher frequency by increasing the storage modulus. On the contrary, the CI modified EPDM rubber did not show similar behavior; the modulus enhanced throughout the entire frequency range. The viscosity of the matrix was found to be highly governed by the compatibility as well as amount of tackifier present in the blend. In order to explain the tack behavior, several tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation time, self-diffusion coefficient, and monomer friction coefficient (ζ0) were investigated. The tack strength increased with HC tackifier loading up to 24 parts per hundred grams of rubber (phr), beyond which a plateau region was observed. A maximum of 196% improvement was observed at 24 phr HC loaded sample as compared to gum EPDM rubber devoid of tackifier. Conversely, there was a marginal improvement of tack strength (36%) up to 8 phr loading for the system containing CI, beyond which it dropped.

Cellulose is a fascinating biopolymer of almost inexhaustible quantity. While being a lightweight material, it shows outstanding values of strength and stiffness when present in its native form. Unsurprisingly, cellulose fibre has been rigorously investigated as a reinforcing component in biocomposites. In recent years, however, a new class of monocomponent composites based on cellulosic materials, so-called all-cellulose composites (ACCs) have emerged. These new materials promise to overcome the critical problem of fibre–matrix adhesion in biocomposites by using chemically similar or identical cellulosic materials for both matrix and reinforcement. A number of papers scattered throughout the polymer, composites and biomolecular science literature have been published describing non-derivatized and derivatized ACCs. Exceptional mechanical properties of ACCs have been reported that easily exceed those of traditional biocomposites. Several different processing routes have been applied to the manufacture of ACCs using a broad range of different solvent systems and raw materials. This article aims to provide a comprehensive review of the background chemistry and various cellulosic sources investigated, various synthesis routes, phase transformations of the cellulose, and mechanical, viscoelastic and optical properties of ACCs. The current difficulties and challenges of ACCs are clearly outlined, pointing the way forward for further exploration of this interesting subcategory of biocomposites.

Short aramid fibre reinforced vinyl ester resin based isotropic composites are fabricated with varying fibre weight fractions (20–50 wt%). The composites were evaluated for their erosion performance under a dynamic set of variables such as impingement angle (30°–90°), impact velocity (43–76 m/s), erodent size (250–600 μm) and stand-off distance (55–85 mm) following design of experiments (DOE) based on Taguchi analysis approach. The thermo-mechanical attributes such as storage modulus, loss modulus and damping properties as viscoelastic responses of the composites were investigated in the temperature range of 0–180 °C for their possible interpretations regarding reinforcement efficiency and energy dissipation aspects relevant to erosion process. An interrelation between the full-width half-maxima (FWHM) of loss modulus peak and erosion rate has emerged indicating the erosion to be mainly controlled by the fibre–matrix interfacial characteristics. The eroded surface morphology investigation by scanning electron microscopy (SEM) revealed the nature of wear-craters, material damage mode and other qualitative attributes responsible in facilitating erosion of the composites.

In a previous article, the sorption kinetics’ properties of a range of natural fibres were reported. Analysis of the sorption kinetics was made using the parallel exponential kinetics (PEK) model, and it was argued that the rate limiting step of the sorption process was determined by substrate swelling rather than being diffusion limited. The PEK model divides the sorption kinetics curve into two first-order kinetics processes (fast and slow) but there is as yet no generally accepted explanation of what these two processes represent. In this article, the PEK parameters for sorption have been further evaluated in terms of two Kelvin–Voigt elements arranged in series. The force constant in the spring of each Kelvin–Voigt elements determines the equilibrium moisture content for each of the processes, whereas the viscosity of the dashpot is represented by the time constant for each process. Determination of interfibrillar matrix modulus using the Kelvin–Voigt model gives values that are in line with what would be predicted, giving credence to this interpretation of the sorption kinetics. Possible interpretations of the fast and slow kinetics processes are discussed.

This article aims to present an improved technique for the mechanical characterization of single plant fibers. In particular, our efforts lie in resolving the difficulties involved in the testing of short plant fibers with only a few millimeters in length and tens of microns in width. Such fibers are potentially used as reinforcement phase in polymer composites. A special fiber gripping system, consisting of a pair of fiber clamps, a 3D positioning stage and two digital microscopes, was developed and combined to a small commercial mechanical tester. The resultant testing system possesses great convenience and reliability for the installation, orientation adjustment, and gripping of short plant fibers, as well as powerful control and data analysis functions. The equipment was then applied to the mechanical characterization of single bamboo fibers under air-dried state. Furthermore, the capability of this equipment for studying moisture content-related mechanical and viscoelastic properties of bamboo fibers was also successfully demonstrated.

Synergistic effect of carbon black (CB) in presence of nanofillers (nanoclay and nanofiber) on mechanical and dynamic mechanical properties was discussed in light of electrostatic interactions and the concomitant microstructural developments, in Part I of this series. These interactions enhanced filler dispersion and ensured efficient stress transfer from the matrix resulting in improvement in properties, undiminished even by continual increase in CB loading. In this part, the micromechanical processes that influence wear behavior have been addressed conjointly with dynamic mechanical properties. Tribological characteristics were studied by sliding rubber wheel samples against a steel blade, in a specially designed abrader, in both transient and steady state conditions. Wear loss was reduced in the dual filler nanocomposites by 33% (over the CB microcomposite) in less stringent and 75% under severe wear conditions. These CB filled nanocomposites also illustrated lowering of coefficient of friction and temperature build-up. This was attributed to efficient heat dissipation due to the formation of a unique microstructural architecture by the participating fillers and also an adhering transfer film on the abraders’ counterface. From viscoelastic measurements, the CB filled nanocomposites were also found to lie in the high performance window of good wet skid and low rolling resistance.

Silane-treated TiO2/high-density polyethylene (silane-TiO2/HDPE) is a potential bone substitute material with good bioactivity and mechanical properties. In this composite, 40 vol.% TiO2 particles were connected chemically with HDPE (high-density polyethylene) by silane-coupling agent. The intensive silane connection was believed to play very important role in compressive creep behavior of silane-TiO2/HDPE in our previous study. In order to deeply understand the relationship between the special structure and creep behavior, both a viscoelastic creep model named Burgers, and an empirical model called Findley power law were applied to simulate and predict the creep curves obtained in both air and saline solution. The results showed that Burgers model succeeded in simulating the creep curves but failed in long-term prediction for all dry samples, while Findley power law failed in simulating the creep curves in air but succeeded in saline solution. By analyzing the parameters obtained from Burgers model, it was believed that the structure of intense connection by silane chains resulted in the very big and gradually increased permanent viscous flow of this material with creep time. The big permanent viscous flow brought on the failure in simulating creep curves using Findley power law, and the improved permanent viscous flow during creep conduced to the positive deviation between the prediction and practical creep curve using Burgers model. The effect of saline solution around sample could not only decrease the permanent viscous flow but also stabilize it gradually, which resulted in the success in the prediction and simulation of creep curve in saline solution by the two models.

Small amounts of organoclays in different sizes and concentrations were added into thermotropic liquid crystalline polymer (TLCP) by a combination method of ultrasonication, centrifugation, and solution casting (and shear-induced phase separation). Four kinds of organoclay-modified TLCP composites were obtained. TC3 UP was a kind of organoclay which displayed a marked shear-induced phase separation phenomenon at 190 °C and higher temperatures. TC3 UP could be separated into a TLCP-rich part, TC3 white, and an organoclay-rich part, TC3 dark. TC3 white was an organoclay-modified TLCP with fully exfoliated organoclay of a uniform size of 15–25 nm well dispersed in the TLCP. TC3 dark had a typical intercalated model structure with some TLCP molecules confined in organoclay galleries. TC3 FS was an organoclay-modified TLCP with organoclay of comparable size to that of the fully extended TLCP molecule, i.e., 85 nm. The organoclay layers dispersed into the polymeric matrix as a few randomly organized organoclay layers or stacks of layers in the quiescent condition in organoclay-modified TLCPs. The larger organoclay size or higher concentration of organoclay in the composites (such as, TC3 UP and TC3 dark) caused a greater proportion of the layers or stacks be hydro-dynamically impeded in the quiescent state, resulting in the filler–filler interaction becoming important and in fact dominating the long-term viscoelasticity of the composites. Additionally, the ease with which the organoclay structure could be altered by flow was considerably enhanced, primarily because of filler–filler interactions. Organoclay size has primary effect on the liquid crystallinity of TLCP. Small or comparable organoclay size with the fully extended TLCP molecule in TC3 white and TC3 FS has weak or negligible negative influence on the liquid crystallinity of TLCP, while larger organoclay size totally damages the liquid crystallinity of TLCP. The morphologies, liquid crystallinity as well as the linear and non-linear viscoelastic behaviors of organoclay-modified TLCPs have been characterized in detail.

In recent years, many authors have researched polymer-modified asphalt blends and tried to better understand the rheological behavior of these materials. In this work, the thermomechanical response of an asphalt formulation was researched trying to find better asphalt-modified blends that allow for the construction of improved asphalt roads. The experimentation included several polymer–maltene formulations developed at different polymer concentrations and temperatures where the asphaltenes of the original asphalt were removed. Such separation was carried out because the maltene fraction represents the portion of the asphalt that chemically reacts with the polymer modifier. The rheological behavior of the blends was determined from oscillatory shear flow data. Analysis of the G′, G′′, G* moduli and phase angle (δ) as a function of oscillatory frequency for various temperatures led to the conclusion that the maltenes behaved as a pseudo-homogeneous viscoelastic material that could dissipate stress without presenting structural changes. Furthermore, all maltenes–polymer blends behaved more viscoelastically than the non-blended maltenes depending on the amount of the polymer contained in the formulation. The blend viscosity increased with polymer concentration, and this increase was seen in both the viscous and elastic moduli. Furthermore, performance grade trials were also performed according to the AASHTO TP5 to determine the failing temperature. It was noticed that the limiting temperature increased with the modifier concentration with a δ between 50° and 60°, indirect value of elasticity found to have industrial applications for asphalt pavements.

An investigation was carried out to explore the morphology and mechanical properties of diglycidyl ether of bisphenol A epoxy resin (DGEBA) with liquid natural rubber possessing hydroxyl functionality (HLNR). Though modification of epoxies by synthetic rubber has been extensively studied not much attention has been paid to liquid natural rubber. Photo depolymerisation of natural rubber enables us to synthesise low molecular weight oligomers by varying the experimental parameters. Epoxy resin was cured using nadic methyl anhydride as hardener in presence of N,N-dimethyl benzyl amine accelerator. Hydroxylated natural rubber of different concentrations is used as modifier for epoxy resin. The addition of such chemically modified liquid rubber to an anhydride hardener–epoxy resin mixture has given rise to the formation of a two-phase microstructure in the cured systems, consisting of spherical particles of liquid natural rubber strongly bonded to the surrounding matrix, there by providing the required mechanism for toughness enhancement. Subinclusions of epoxy resin were present in the elastomer domains as secondary particles (particle in particle morphology) as evidenced from the SEM (scanning electron micrograph) photomicrographs. The origin of the so-called secondary phase separation is due to the combined effect of hydrodynamics, viscoelastic effects of rubber phase, diffusion, surface tension, polymerisation reaction and phase separation. In a dynamic asymmetric system, the diffusion of the fast dynamic phase is prevented by the slow dynamic phase, and hence the growth of fast dynamic phase gets retarded due to the slow dynamic phase. In the case of low viscosity blends the growth of fast dynamic phase turns fast and hence diffusion of fast dynamic phase cannot follow geometrical growth and cannot establish local concentration equilibrium and hence double phase separation takes place. The double phase separation is responsible for the enhanced impact and toughness behaviour of the blends. The mechanical behaviour of the liquid rubber-modified epoxy resin was evaluated in terms of tensile and flexural properties.

Brittleness of materials—whether it occurs naturally or with aging—affects significantly performance and manifests itself in various properties. In the past, brittleness was defined qualitatively, but now a definition of brittleness for viscoelastic materials exists, enabling analysis of all types of polymer-based materials. The quantity brittleness, B, has been evaluated for neat thermoplastics, but here composites and metal alloys are also assessed. The physical significance of brittleness is connected to the dimensional stability of materials. The connections of brittleness to tensile elongation and to fatigue are explored while its relationship to surface properties—specifically wear by repetitive scratching—is examined more closely. The economic impact of wear results in monetary loss associated with failure and reduced service life of plastic parts—thus its connection to brittleness finds use across a broad spectrum of industrial applications which utilize plastics for manufacturing, processing, etc. We also demonstrate a correspondence between impact strength (Charpy or Izod) and brittleness of polymers. It is shown that the assumption hardness is equivalent to brittleness is inaccurate; this fact has important implications for interpreting the results of mechanical testing of viscoelastic materials.

The mechanical and the dynamic rheological behavior of solution-polymerized styrene butadiene rubber (SSBR) filled with compounding fillers organic montmorillonite (OMMT)/silica (SiO2) were studied. The mechanical properties of the vulcanizates could be improved by incorporation of low OMMT contents, and the best reinforcement effect appeared when 7 phr (parts per hundred rubber) OMMT was added. Moreover, due to the formation of the exfoliated silicate platelet in the matrix, a strong cooperative reinforcement effect to the vulcanizate could be gained for the vulcanizate containing 7 phr OMMT and 20 phr SiO2. Incorporation of SiO2 up to 50 phr to the vulcanizates with or without OMMT resulted in marked reinforcement effect, and the best mechanical properties were obtained for 7 phr OMMT filled composites. On the other hand, compounding fillers OMMT/SiO2 significantly influences the dynamic mechanical behavior of the vulcanizates. It was found that the compounding filler with a certain composition facilitated preparing SSBR vulcanizates with optimized wet traction, rolling resistance, and strength properties.

Tests are described to measure the creep and relaxation response of aramid fibres with the specific aim of determining whether the visco-elastic response is linear or non-linear. Hitherto, creep and relaxation tests have been carried out in different circumstances and at different loads, which has led to disagreement about the type of response that aramid fibres exhibit. Tests are carried out at stresses between 10% and 80% of the short-term strength of the fibres under controlled temperature and humidity conditions, and it is shown that both creep and relaxation are non-linear at stresses below 40% of the breaking load, but both are linear at stresses above this level. This result explains the contradictions in earlier work and also indicates that there may be two different processes underway in the visco-elasticity of aramids.

Studies on the gelation behaviors of the reactive blends of nylon1212 and functional elastomer were carried out. The results show that the curves of the storage modulus(G′)–frequency (ω) exhibit a gel plateau in the low ω region, and the transition from liquid-like to solid-like viscoelastic behaviors emerges with the concentration of SEBS-g-MA increasing. There exist the gelation behaviors in the blending process similar to those of crosslinking polymer. Based on Winter’s method, the gel point of blends is determined to be, φg = 17.45 wt%, and the corresponding value of tanδ is 1.44. The gel index n calculated is 0.61 and the gel strength Sg is 1.08 × 104 Pa s0.61. However, the non-reactive blends of nylon1212 and elastomer have no emergence of gelation behaviors. The morphology analysis shows that the gel point for the reactive blends is a threshold of cocontinuous morphology, and morphology analysis can also be a method to determine the gel point.

In this article we discuss the energy dissipation that occurs when the interfacial slip of nanoscale fillers is activated in a host matrix material. We consider both polymer (such as polycarbonate, PEO, PEG) and epoxy matrices. The nanoscale fillers considered are carbon nanotubes (both singlewalled and multiwalled) as well as fullerenes. The nano-composites are fabricated by using a solution mixing technique with tetra-hydro-furan as the solvent. The interfacial friction damping is quantified by performing uniaxial dynamic load tests and measuring the material storage and loss modulus. We study various effects such as impact of nanotube weight fraction, nanotube surface treatment (oxidation, epoxidation etc.), test frequency, strain amplitude, operating temperature, as well as effect of pre-strain or biased strain. The effect of geometry (i.e., aspect ratio) is also considered by comparing the damping response of fullerene-composites with that of nanotube-composites.