Viscoelastic-plastic Behavior Research Articles

A viscoelastic-plastic model for the core of various close-packings of multifilament polyamide-6 yarns

Different forms of close-packed yarns can be produced by varying the number of monofilaments in the core region, ranging from one to five. Numerous efforts have been made to model or simulate the mechanical response of close-packed yarns; however, previous studies have predominantly focused on one or two monofilaments in the core. In this study, we propose an analytical approach that combines a geometrical model with an artificial neural network (ANN) to predict the tensile behavior of close-packed yarns containing 2 to 5 monofilaments in the core region. The novelty of this hybrid model lies not only in accounting for more than two monofilaments in the core but also in extending the prediction range from elastic to viscoelastic-plastic behavior. Validation of the proposed method showed excellent agreement between experimental and theoretical results. Numerical simulations further confirmed that the results align with theoretical predictions, demonstrating the model’s accuracy in predicting the tensile behavior of close-packed yarns. This modeling approach has the potential to significantly improve the understanding and modeling of textile structures.

Investigation of Viscoelastic-Plastic Properties of Fresh Cemented Gangue Fly Ash Backfill Slurries

In underground filling mining, freshly prepared cemented gangue-fly ash backfill (CGFB) slurries are typically piped into the gobs. The rheological properties of backfill slurry during pipeline transportation have a direct impact on the transportation characteristics, which in turn affect pipeline blockage and wear. In this paper, the rheological behavior and viscoelastic-plastic properties of CGFB during pipeline transportation are investigated. The effects of different solid content and cement content on resistivity were tested experimentally, and their viscoelasticity and plasticity were analyzed. The results show that with the increase in solid phase content and cement content, the viscosity, yield stress, and energy storage modulus of the materials showed an increasing trend. The viscosity and yield stress of the material both increased, reaching 32.77% and 51.22%, respectively. It was found by the dynamic shear test that in the low-strain region, the material showed a more significant elastic nature of the solid, while in the high-strain region, the viscosity of the material gradually increased. Cement has a substantially lower resistivity than fly ash and gangue, and with the increase in solid concentration, the resistivity of the material shows an increasing trend. With the increase in cement content, the resistivity generally shows a decreasing trend, but it should be noted that the resistivity change trend may tend to stabilize after the cement content exceeds 12%. The study’s findings can aid in understanding the rheological properties of CGFB and its viscoelastic-plastic behavior during the underground filling and conveying process, which can provide a reference basis for research and application in related fields.

Performance of Asphaltic Concrete Incorporating Fly Ash under Low Temperature

One of the most common asphalt concrete pavement distresses is low temperature cracking, also known as thermal cracking. Characterizations of low temperature cracking and formulation for pavement design have taken a lot of effort. Asphalt binder has viscoelastic behaviour, so asphalt mixture behaviour changes as the temperature changes. At high and low temperatures, the asphalt binder shows viscoelastic plastic behaviour and elastic behaviour. Low temperature cracks that grow day by day due to the movement of vehicles are the most significant pavement cracks caused by cold climates. It needs early and premature repairs to build and expand low temperature cracks. The aim of this research is to perform Low Temperature Cracking analysis of asphalt materials (laboratory and analytical assessment), in light of the latest update of binder cracking temperature. The role of basic material properties in low-temperature cracking was studied in this work. As a result, statistical analysis in the cohesive failure condition revealed that the asphalt mixture aggregate's free energy was ineffective in this cohesion failure. Fly ash had been used in the other type of asphalt mixture. It was proven that the addition of fly ash as an additive can improves the low temperature resistance of the asphalt mix. The binder with 60/70 penetration grade was used. The different amount of fly ash (0%, 1%, 3% and 5%) was added to the asphalt mixture. Marshall Stability and flow, resilient modulus and dynamic creep were carried out to investigate the mechanisms of cracking at low temperature. From the results obtained, there are significant effect comes from the addition of the fly ash. The result show that the addition of 5% fly ash produce the best outcomes for the density, stability, stiffness, resilient modulus and dynamic creep. Thus, it can conclude that the existence of fly ash in the mixture is able to enhance the mechanical performance of the AC14 dense-graded asphalt.

An Extensive Review on the Viscoelastic-plastic and Fractural Mechanical Behaviour of ETFE Membranes

The present article is a review of ETFE (ethylene tetrafluoroethylene) material, with emphasis on the mechanical and fractural behaviour, considering that the material is becoming one of the most promising façades and roof materials due to its advantageous properties. This paper examines the basic chemical makeup of this copolymer and details the elastic-plastic and viscous properties through selected studies in the field. The paper also reviews the available phenomenological, continuum mechanical or rheological constitutive models focusing on the engineering application to the corresponding phenomena. A separate part of the article covers the existing fractural mechanical research on ETFE.

Development and Characterization of Freestanding Poly (Methyl Methacrylate)/Monolayer Graphene Membrane

Graphene-polymer based materials are gaining more popularity among researchers due to its mechanical properties that are found to be suitable to be used in various micro/nanoscale application requiring highly sensitive sensors. This research ventured into the fabrication and characterization process of a freestanding poly (methyl methacrylate) (PMMA) on monolayer graphene (Gr) yielding a (PMMA/Gr) membrane. In the process of transferring the chemical vapor deposition (CVD) graphene film over a cavity that was developed on a silicon substrate, the wet transfer method was used. Five repetitions of the nanoindentation testing had been carried out on the flexible membrane which resulted in a reproducible deflection, when exerted with a maximum loading of 10 mN. The indented (PMMA/Gr) membrane showed an identical elastic behavior with Young's modulus of 0.18 GPa. The highest deflection of approximately 22 μm at 1.6 mN maximum loads and the tensile stress of 0.58 MPa was obtained from the indentation testing analysis. The combination of PMMA-Graphene materials as a membrane has shown impressive changes to its mechanical properties. Besides maintaining its viscoelastic-plastic behavior which contributed to its flexibility, the presence of a graphene layer provided strong support to prevent damages to the membrane. Meanwhile, PMMA properties with low elastic modulus have contributed to the increased of the mechanical sensitivity of the membrane. Based on this research, the mechanical sensitivity of (PMMA/Gr) is reported to be 0.15 nm/Pa, which is much higher compared to a typical conventional membrane. It was proven that the hybrid (PMMA/Gr) membrane was extremely sensitive to the subjected pressures, thus, shown its potential to be applied as a micro-electro-mechanical systems (MEMS) capacitive pressure sensor.

Modeling of non-isothermic viscoelastic-plastic behavior of flexible reinforced plates

Based on a step-by-step procedure over time, a numerical-analytical model of the nonisothermal viscoelastic-plastic behavior of crisscrossed-reinforced material is constructed. The components of the composition are isotropic; their viscoelastic deformation is described by the Maxwell - Boltzmann model of the body, and instantaneous inelastic behavior is described by the relations of the theory of elastoplastic deformation with isotropic hardening. In this case, the temperature dependence of the loading function and material constants is taken into account. The conditions of the viscoelastic deformation, the beginning of unloading, neutral and active viscoelastic-plastic loading of the thermosensitive materials of the composition are formulated. Relationship between the mechanical and thermophysical characteristics of the composite material is taken into account. The structural relationships of the thermophysical component of the problem are presented. The developed mathematical model is focused on the use of explicit schemes for the numerical integration of viscoelastic-plastic and thermophysical problems. The initial-boundary problem of nonisothermal viscoelastic-plastic bending deformation of fibrous plates is formulated. The poor resistance of such thin-walled constructions to transverse shear is described in the framework of Ambardzumyan's theory. The geometric nonlinearity of the problem is taken into account in the Karman approximation. In the transverse direction, the temperature is approximated by a second-order polynomial. To reduce the three-dimensional heat conduction problem to two-dimensional relations, the method of additional boundary conditions is used. The dynamic bending of a flat-crisscrossed-reinforced fiberglass plate under the influence of an air blast wave is investigated. It is shown that in the absence of external thermal heating in the process of oscillations, this structure heats by only 2-3ºС. In such cases, the calculation can reasonably be carried out without taking into account the temperature effect. In the presence of intense thermal loading of the structure, the heat sensitivity of the materials of the composition must be taken into account. It has been demonstrated that in the presence of a temperature field inhomogeneous over the thickness of the plate, the shape and magnitude of the residual deflection significantly depend on which face surface an external dynamic load is applied to.

A compact constitutive model to describe the viscoelastic-plastic behaviour of glassy polymers: Comparison with monotonic and cyclic experiments and state-of-the-art models

A number of constitutive models have been developed for solid polymers to describe the large deformation behavior. However, most of the existing models rely on a purely elastic or hyperelastic initial response when they are incapable of accurately predicting the cyclic stress-strain hysteresis loops. In this work, therefore, a compact cyclic viscoelastic-viscoplastic constitutive model is proposed to improve the prediction of the loops below the peak yield stress. The proposed approach is based on the distinguished model by Haward and Thackray (1968) for glassy polymers, which is augmented by a few thermodynamically motivated internal state variables able to predict the missing viscous deformation behavior, including the nonlinear cyclic hardening in three dimensions. Based on the comprehensive uniaxial tension experiments, it is demonstrated that this compact formulation, along with a calibration scheme, enables accurate prediction of the shape of the hysteresis loops, as well as the representation of ratcheting behavior. A comparison is also made with state-of-the-art models that are capable of predicting the cyclic stress-strain hysteresis loops.

Modelling polymeric deformable granular materials - from experimental data to numerical models at the grain scale

Polymeric deformable granular materials are widely used in industry and the understanding and the modelling of their shaping process is a point of interest. This kind of materials often presents a viscoelasticplastic behaviour and the present study promotes a joint approach between numerical simulations and experiments in order to derive the behaviour law of such granular material. The experiment is conducted on a polystyrene powder on which a confining pressure of 7MPa and an axial pressure reaching 30MPa are applied. Between different steps of the in-situ test, the sample is scanned in an X-rays microtomograph in order to know the structure of the material depending on the density. From the tomographic images and by using specific algorithms to improve the images quality, grains are automatically identified, separated and a finite element mesh is generated. The long-term objective of this study is to derive a representative sample directly from the experiments in order to run numerical simulations using a viscoelactic or viscoelastic-plastic constitutive law and compare numerical and experimental results at the particle scale.

Damping behavior investigation and optimization of the structural layout of load-bearing biological materials

Load-bearing biological materials, such as bone and nacre, exhibit superior mechanical properties to support and/or protect biological functionalities. To achieve this, an important ability of such materials is to effectively shield external dynamic impacts. The damping behavior of the biological materials mostly stems from their architecture and also the organic portion which intrinsically shows viscoelastic-plastic behavior. The loss modulus, a crucial representative of dynamic behavior, is a key index on how strong the bio-composite is able to damp the dynamic energy within its structure. This work aims to study the damping behavior of mostly seen staggered architectures of biological materials such as regular, offset, stairwise, herringbone and random staggering patterns to highlight the optimal layout, geometry, and feature sizes of the bio-composite in which the energy dissipation within the structure is maximal. Our studies show that not only the stairwise staggering arrangement overall offers the highest loss modulus amongst other existing architectures but also the aspect ratio of the platelet leading to the maximum loss modulus is remarkably in excellent agreement with experimental observations which might explain why this kind of arrangements is extensively observed in nature. Our findings here not only gain valuable insights into the dynamic behavior of load-bearing biological materials, but also provide useful guidelines to the design of bio-inspired engineering materials.

Stress Wave Propagation in Viscoelastic-Plastic Rock-Like Materials.

Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic rock-like materials under a high-strain-rate loading and verifies the solution through an experimental test. A constitutive equation of viscoelastic-plastic rock-like materials was first established, and then kinematic and kinetic equations were then solved to derive the analytic solution for stress wave propagation in viscoelastic-plastic rock-like materials. An experimental test using the SHPB (Split Hopkinson Pressure Bar) for a concrete specimen was conducted to obtain a stress-strain curve under a high-strain-rate loading. Inverse analysis based on differential evolution was conducted to estimate undetermined variables for constitutive equations. Finally, the relationship between the attenuation factor and the strain rate in viscoelastic-plastic rock-like materials was investigated. According to the results, the frequency of the stress wave, viscosity coefficient, modulus of elasticity, and density play dominant roles in the attenuation of the stress wave. The attenuation decreases with increasing strain rate, demonstrating strongly strain-dependent attenuation in viscoelastic-plastic rock-like materials.

Viscoelastic-plastic behavior of single tomato mesocarp cells in high speed compression-holding tests

Abstract The micromechanics of isolated tomato fruit cells were investigated by microcompression-holding. Covering the cells with deionized water after isolation caused no significant volume changes, suggesting that cells suspended in water for compression testing were representative of those in the original tissue. The viscoelastic-plastic behavior of such cells was characterized by compression at 4900 ± 200 μm s− 1, then holding. Although the cells were generally not spherical initially and some cell deformation appeared to be local, the force-time data were fitted by the Hertz–Maxwell model for relaxation of viscoelastic spheres. The force at 15% deformation, instantaneous and equilibrium elastic moduli, yield strength, and first and second relaxation times were 2.5 ± 0.6 mN, 0.6 ± 0.3 MPa, 0.22 ± 0.08 MPa, 0.03 ± 0.01 MPa, 0.48 ± 0.05 s, and 0.033 ± 0.004 s, respectively. These parameters showed little sensitivity to several reasonable definitions of cell size nor to changes in the (assumed) Poisson's ratio. Industrial relevance Fresh fruit is very susceptible to damage during industrial handling (e.g. mechanical harvesting, packaging and transport). Mechanical damage to fruit, manifested at the macro scale, is caused ultimately by failure of cells at the micro scale. Viscoelastic-plastic characterization of single cells isolated from tissue is vital to macro-scale modeling, simulation and prediction of mechanical damage to fruits. The method might be extended to single cells of other fruits.

Determination of the Poisson’s ratio of viscoelastic materials based on the linear rheological model using instrumented indentation

ABSTRACTBased on the linear rheological constitutive model that is used to describe viscoelastic-plastic behavior of viscoelastic materials, a formula of the Poisson’s ratio was deduced according to the relationship between the shear creep compliance and tensile compliance. Instrumented indentation under various loading conditions and universal creep tests were performed on polyamide 12 samples to obtain the relevant rheological parameters. Results show that the Poisson’s ratio for a step load indentation can obtain a constant but overrated value. However, the Poisson’s ratio approaches an asymptotic value and an accurate value can be gained at a certain loading rate.

Study on Energy Requirement of Wood Chip Compaction

In order to utilize waste products such as sawdust and chips in the wood industry, pellets are made using compaction pressures in the range of 100 MPa or higher. During the compaction process, the density and the modulus of elasticity of the material rapidly increase. Wood materials generally show non-linear viscoelasticplastic behavior and, therefore, the pressure-deformation relationship is dependent on the loading velocity and on the time during which the material is subjected to constant deformation or load. The energy requirement of pellet production depends on many infl uencing factors and in such cases the use of dimensionless numbers in the form of similarity equation facilitates the processing of experimental results and the obtained similarity relationship has a more general validity for the users. Various fractions of different wood species were used in these experiments, and the pressure, pellet diameter, temperature were also varied. The proposed similarity equation shows a good correlation with the experimental results.

Assessment and prediction of long-term mechanical properties of adhesives with high plasticity

Long-term life prediction for adhesives based on laboratory tests requiring only days, weeks, or months, is still a demanding challenge. Testing is carried out with the intention of simulating and often accelerating time-dependent aging effects that may occur in a joint during its lifetime. Initial strength values of bonded joints, such as shear or peel properties, can often be obtained from the adhesive manufacturers or retrieved from the literature. They are useful to compare different adhesives and to demonstrate the effect of parameters such as bondline thickness, overlap length or curing conditions and, in some cases, also the surface state. On the other hand, only few data are available relative to the long-term mechanical properties of adhesives with high plasticity. Due to the specific network structure of elastomer adhesives their viscoelastic-plastic deformation behavior is strongly time- and temperature-dependent. Therefore, the main objective of this paper is to illustrate methods for investigating the viscous properties of elastomer-based adhesives and creating basic data for the design and engineering of adhesive joints with enhanced plasticity.

Friction characterisation of polymers abrasion (UHWMPE) during scratch tests: single and multi-asperity contact

An understanding of abrasion resistance and the associated surfaces deformation mechanisms is of primary importance in materials engineering and design [Wear (1998)]. Instrumented scratch testing has proven to be a useful tool for the characterisation of the abrasion resistance of material. Although most studies on scratch resistance have been conducted for metals, assuming a purely plastic behaviour, recent studies focus on the effects of elastic and visco–elastic–plastic behaviour on the scratch mechanisms [Tribol. Int. (1998)]. In this study, normal and tangential scratch forces are measured during the scratch experiments using various indenter geometry and abrasive paper, under various temperature conditions (263–293 K). To complete the characterisation of the scratch process, three-dimensional topography of the scratched surface is measured. The comparison between single point scratch and multi-asperity abrasion testing is made possible thanks to morphological analysis of the abrasive paper topography. The single point scratch tests provide a good understanding of the effect of the contact geometry and temperature on the friction coefficient. These results are then used to explain the evolution of the friction coefficient obtained with two abrasive papers under various temperature and load conditions.

A Viscoelastic-Plastic Behaviour Analysis of Expanded Polystyrene under Compressive Loading: Experiments and Modelling

Generally, when soil has poor properties (unstable or compressible soils) it is possible to use EPS foam in road construction, because this material has low density. In this case, it is necessary to investigate the mechanical properties of EPS. In this work, an experimental study and modelling investigation were performed in order to determine the EPS mechanical behaviour under compressive loading. The experimental results show that the global compression behaviour of EPS is characterised by three stages. The linear elastic stage is defined by an initial tangent modulus E* followed by a non-linear elastic part. The second stage, which is described by a plateau, is characterised by a stress threshold σs*. Finally, the densification stage corresponds to large compressive strains when the material of the cell walls is entirely compressed. Globally, the apparent density of EPS plays an important role. In fact, when the density increases Young's modulus and threshold stress increase, but the densification strain decreases. A phenomenological mechanical model is verified in order to simulate the EPS viscoelastic-plastic behaviour under compressive loading. This model, which is based on a super-position of viscoelastic and elastic-plastic behaviour, introduces six parameters determined by an identification technique. The results obtained in terms of the stress-strain curves are in a good agreement with the experimental data. Using “Castem 2000” finite element software, the numerical simulations were achieved in order to describe the mechanical behaviour of the EPS material. This shows that it is possible to use numerical simulation in order to compute EPS structure used in road laying.

Viscoelastic-plastic behaviour with mean strain changes in polypropylene

The stress-strain curves and stress-relaxation curves of polypropylene are obtained by using a closed-loop, electrohydraulic, servo-controlled testing machine. Effects of mean strain changes on deformation behaviour are examined in a tension-compression mode under strain control at room temperature (18–23 °C). The hysteresis loops of three mean strains show a steady-state response from the stress-strain curves at a strain rate of 1 × 10−3 s−1 at a strain width of 5%, at a number of cycles of N=50 and at three mean strains (ɛm=0, + 1.0 and + 2.0%). The drop of stress at the mean strain of ɛm= -1.0% is larger in magnitude than that at ɛm=+1.0%; this is caused by the higher stress level at ɛm=- 1.0% as compared with the stress level at ɛm=+1.0%. From the results of stress amplitude and the stress drop behaviour, the magnitude of stress drop is hardly affected by the mean strain.

Viscoelastic‐plastic deformation behavior of polypropylene after cyclic preloadings

AbstractStress‐relaxation behavior is studied in polypropylene samples subjected to different cyclic preloadings and to simple tension. The relaxation tests are performed under different sets of strain amplitude, number of cycles, and strain rate, using a closed‐loop, electrohydraulic, servocontrolled testing machine. The calculated stress‐strain curves are determined from a constitutive equation based on an overstress theory in which an equilibrium stress and a viscosity function are treated. The calculated results agree well with the experimental ones. It is concluded that the overstress theory explains the nonlinear viscoelastic‐plastic behavior of polypropylene.

Study of Deformation Mechanism and Strength Characteristics of Ship Structural Materials under Cyclic Loading Conditions (2nd Report)

In the previous paper by authors, fatigue limit and the stress at the transition point, the point where the deformation mechanism of the material changed from visco elastic into visco elastic-plastic behavior, of mild steel were found to be almost identical under constant-amplitude loading conditions, and the visco elastic-plastic constitutive equation which represent cyclic stress-strain response of mild steel was derived.In this paper, complete compression-to-tension load-controlled axial loading test programs-constant amplitude and random loading with an exponential distribution of stress amplitude- were performed for mild steel plane specimens. From the test results, coefficients in the visco elastic-plastic constitutive equation derived in the previous paper are given as a function of both the value of applied stress and their cycles. Then, the correlation between fatigue limit and the stress at the transition point is discussed.As a result, following four main points are obtained.1) There is a good correlation between fatigue limit and the stress at the transition point under variable-amplitude loading conditions.2) The transition point stress decreases when stresses larger than fatigue limit (corresponding to the transition point stress) are applied, and then converges to a certain value, depending on the value of the larger applied stresses and their cycles.3) Given the condition of variable amplitude loading, the transition point stress can be calculated using the derived constitutive equation.4) Using the above results, a method for determining fatigue limit under variable-amplitude loading conditions is proposed.

Effects of Stress Ratio on the Inelastic Deformation and Fatigue Damage of Graphite/Epoxy Tubes (.+-.45.DEG.)4 under Tension-Compression Loading.

Fatigue tests of graphite/epoxy laminate tubes [ ± 45°]4 were performed under tension-compression loading. The effects of stress ratio on the inelastic deformation under cyclic tension-compression are discussed. Cyclic stress-strain curves show viscoelastic-plastic behavior with cyclic hardening and softening, and are highly affected by the evolution of internal damage such as matrix cracking, delamination and fiber breakage. Development of matrix cracking and delamination causes an increase of the hysteresis loop width as the result of the decrease in the elastic modulus and the global stiffness. In particular, in the case of stress ratio R ( =σmin/σmax) < 0, salient and complex inelastic deformations were observed mainly due to the delamination and the resulting macroscopic buckling of the tubular specimens. The changes of energy dissipation per cycle and Young's modulus are found to reflect the change of the internal damage.