Viscoelastic Plastic Deformation Research Articles

牛粪压缩和应力松弛特性及其本构模型构建研究

In order to study the mechanical properties of compression and stress relaxation of manure under drainage conditions, the experiment was carried out with cattle manure as the object, and the constitutive models were improved to describe the stress-strain curves of compression and stress relaxation. The defined constitutive model was determined by parameter identification, and the influence laws of moisture content and filling mass on the compression and relaxation process were investigated. The results show that the improved Nishihara model and the five-component generalized Maxwell model can better describe the compression and stress relaxation properties of cattle manure, and the coefficients of determination of the parameters of the fitted intrinsic model are all greater than 0.9, with high fitting accuracy. The compression process was divided into three stages: exhaust, drainage, and viscoelastic-plastic deformation. The stress decay rate tended to change quickly and then slowly, and there was a negative correlation between the compressed mass, moisture content, and stress decay rate. Duncan's mean comparisons revealed that the differences in elastic modulus between different moisture content / compressed mass groups in the parameters of the cattle manure compression principal model were all significant (P<0.05). The differences in elastic modulus and coefficient of viscous attenuation between different moisture content groups in the parameters of the stress relaxation model were all significant. The study's results can provide the theoretical basis for the study and simulation of CM's compression and dewatering mechanism and provide support for the solid-liquid separator for livestock and poultry manure.

Finite elastic-viscoplastic deformation behaviour of PEO-based solid polymer electrolyte: Experimental investigation and constitutive modelling

Polyethene oxide (PEO) has emerged as a preferred candidate for solid electrolytes due to its excellent solubility towards lithium salts, stable chemical properties, high flexibility, and low cost. However, the poor knowledge of the mechanical behaviours of PEO electrolytes leads to the road facing vast challenges in developing all-solid-state lithium batteries. In this study, we conducted the uniaxial tensile tests on PEO-LiTFSI films at 20–40 °C, and the strain rate ranges from 0.001 s−1 to 0.01 s−1 while investigating the potential effect mechanisms. Based on a rheological scheme of semi-crystalline polymers, we developed a new constitutive model for simulating the stress-strain curves of PEO-based electrolytes. The results indicate that PEO-LiTFSI exhibits the finite viscoelastic-plastic deformation characteristic with a minimal elastic strain range, low elastic modulus and yield strength. Increasing LiTFSI content and temperature can reduce the crystallinity of the PEO, resulting in significant softening of the polymer electrolyte; the opposite is true with raising the strain rate. Notably, the present model can capture the mechanical response of PEO electrolytes across a range of temperatures and strain rates, and the predicted tensile curves align closely with the experimental results. In addition, the simulation reveals that subpar mechanical performance would occur for PEO-LiTFSI under the recommended electrochemical operation conditions (0.05–5 C and 50 °C).

Viscous shear flow and heating of impact-extruded composite energetic materials

Investigating the macroscopic deformation and localized heating behaviors of high-ductility composite energetic material (CEM) under impact extrusion is crucial to understand the accidental ignition phenomenon of CEM charged weapon systems with structural defects and design the advanced safe munitions. In this study, the rapid viscous shear flow and ignition responses of impact-extruded CEM are first experimentally studied and then simulated using a physically based thermomechanical model. The experimental results show that CEM sample impacted by a 6 kg and ∼2 m/s falling drop-weight could be extruded into the narrow crack with a high flow speed (∼20 m/s) and ignited. A thermomechanical model is developed to describe the continuum viscoelastic-plastic deformation and localized heating due to viscoplastic deformation in solid material, viscous flow in melted liquid and chemical reaction. By simulation, a semicircular extrusion region with a shear concentration is formed in CEM sample above the crack, and high shear stress and strain rate at this region contributes to the localized viscous shear heating and ignition of CEM. The effects of the diameter ratio between crack and sample (0.1∼0.4) on dynamic responses of CEM are further investigated. The simulated main features of CEM sample, including flow history into the crack, ignition time and location, are consistent with the experimental observations.

Enhanced Interfacial Adhesion of TiO2 Nanotubes Decorated With Ag Silver Nanoparticles Prepared by Photo-Reduction Process

Abstract In the present study, the adhesion of TiO2 nanotubes (TiO2-NTs) to thicker substrates was improved by decorating them with metallic Ag nanoparticles (NPs) using the photo-reduction process. The obtained coatings were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy, and transmission electron microscope (TEM). The XRD confirmed that all TiO2-NTs crystallized in anatase after annealing at 400 °C regardless of the anodization potential. The SEM indicated that the TiO2-NTs were uniformly distributed on the substrate with an ordered and vertically aligned morphology. It also revealed that the diameter of the TiO2-NTs reached ∼100 nm. The decoration of TiO2-NTs surface with silver nanoparticles was assessed by the TEM. Moreover, a new scratch test mode called “wear mode” was performed to evaluate the wear resistance of the coatings. Results obtained by the scratch tests proved that the decorated coating with Ag nanoparticles improved the interfacial adhesion. The friction coefficient decreased from 0.65 to 0.45 when pure TiO2 was decorated with 10 min-Ag-NPs. The wear behavior was studied using a multi-pass scratch test. It was found that the wear volume reduced with the incorporation of Ag nanoparticles. The study of the damage mechanisms showed visco-elastic plastic deformation in the pure TiO2 coating.

The mechanical creep property of shale for different loads and temperatures

The analysis of the mechanical properties and the failure mechanism of shale with the effect of temperature are of great significance to the shale gas exploitation. In this paper, triaxial creep mechanical tests and AE monitoring method for shale under step loading were carried out at different temperatures and confining pressures. The classic Poynting-Thomson creep model was improved and the modified creep model considering temperature and viscoelastic-plastic deformation were built. The test results showed that the strength of the shale was related to the confining pressures and temperatures. The creep mechanism of shale was analyzed by the acoustic emission parameters. The peak frequency of acoustic emission signals reflected the difference of the rock fracture mode. The Poynting-Thomson model was modified on the theory of nonlinear rheology, which is more suitable for creep deformation of shale. The correlation coefficient of the modified model was higher than that of the classical model. The modified model considering temperature fit the shale creep curve well and could explain the creep characteristics under the influence of temperature and stress. The new model can be widely used in the research of shale creep deformation, such as the deep exploitation of shale gas, wellbore stability and other aspects of engineering problem of shale.

A Constitutive Model of Time-Dependent Deformation Behavior for Sandstone

Considering sandstone's heterogeneity in the mesoscale and homogeneity in the macroscale, it is very difficult to describe its time-dependent behavior under stress. The mesoscale heterogeneity can affect the initiation and propagation of cracks. Clusters of cracks have a strong influence on the formation of macroscale fractures. In order to investigate the influence of crack evolution on the formation of fractures during creep deformation, a time-dependent damage model is introduced in this paper. First, the instantaneous elastoplastic damage model of sandstone was built based on the elastoplastic theory of rock and the micro-heterogeneous characteristics of sandstone. A viscoelastic plastic creep damage model was established by combining the Nishihara model and the elastoplastic damage constitutive model. The proposed models have been validated by the results of corresponding analytical solutions. To help back up the model, some conventional constant strain rate tests and multi-step creep tests were carried out to analyze the time-dependent behavior of sandstone. The results show that the proposed damage model can not only reflect the time-dependent viscoelastic deformation characteristics of sandstone, but also provide a good fit to the viscoelastic plastic deformation characteristics of sandstone's creep behavior. The damage model can also reproduce the propagation process of mesoscopic cracks in sandstone upon the damage and failure of micro-units. This research can provide an effective tool for studying the propagation of microscopic cracks in sandstone.

Fluorinated Ethylene Propylene Coatings Deposited by a Spray Process: Mechanical Properties, Scratch and Wear Behavior

To increase the lifetime of metallic molds and protect their surface from wear, a fluorinated ethylene propylene (FEP) polymer was coated onto a stainless-steel (SS304) substrate, using an air spray process followed by a heat treatment. The microstructural properties of the coating were studied using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) as well as X-ray diffraction. The mechanical properties and adhesion behavior were analyzed via a nanoindentation test and progressive scratching. According to the results, the FEP coating had a smooth and dense microstructure. The mechanical properties of the coatings, i.e., the hardness and Young’s modulus, were 57 ± 2.35 and 1.56 ± 0.07 GPa, respectively. During scratching, successive delamination stages (initiation, expansion, and propagation) were noticed, and the measured critical loads LC1 (3.36 N), LC2 (6.2 N), and LC3 (7.6 N) indicated a high adhesion of the FEP coating to SS304. The detailed wear behavior and related damage mechanisms of the FEP coating were investigated employing a multi-pass scratch test and SEM in various sliding conditions. It was found that the wear volume increased with an increase in applied load and sliding velocity. Moreover, the FEP coating revealed a low friction coefficient (around 0.13) and a low wear coefficient (3.1 × 10−4 mm3 N m−1). The investigation of the damage mechanisms of the FEP coating showed a viscoelastic plastic deformation related to FEP ductility. Finally, the coating’s resistance to corrosion was examined using electrochemical measurements in a 3.5 wt% NaCl solution. The coating was found to provide satisfactory corrosion protection to the SS304 substrate, as no corrosion was observed after 60 days of immersion.

A Refined Model of Viscoelastic-Plastic Deformation of Flexible Plates with Spatial Reinforcement Structures

A Refined Model of Viscoelastic-Plastic Deformation of Flexible Plates with Spatial Reinforcement Structures

Development and Application of a New Triaxial Testing System for Subzero Rocks

Abstract To face the challenges of coal production today, the mechanical behaviors of rock in subzero and disturbed environments are critical in the geomechanics of coal mining and artificial freezing engineering. Disturbances significantly affect the long-term mechanical properties and nonlinear viscoelastic-plastic deformation characteristics of frozen soft rock. This article summarizes current rock triaxial test systems, which cannot concurrently solve the problems of subzero temperatures, creep, disturbance, and high sampling rates. Based on existing equipment limitations and the current research aims, an innovative, applicable, and scalable measurement/control system based on National Instruments hardware is integrated into LabVIEW to design and construct a new triaxial testing system capable of achieving both dynamic disturbances and subzero temperatures. The testing system can produce a basic environment with confining pressures up to 30 MPa, axial forces up to 500 kN, and lowest temperatures of −30°C. The system has a 51.2 kS/s sampling using 5-channel closed-loop control. By changing the transfer valve between the supercharger and the servo valve, both conventional triaxial compression and creep tests can be carried out. The triaxial creep tests are performed on frozen rock specimens under step loading and graded disturbances to analyze the creep deformation characteristics and failure modes of the specimens. The results show that at low stress levels, the disturbance load closes and reorganizes microcracks in the rock specimens, reducing the specimen deformation rate. With increasing stress levels or disturbance intensities, the specimen cracks expand rapidly, the creep rate increases, the disturbance energy stored in the rock specimen releases, and the specimens rapidly fail. Therefore, this disturbance creep phenomenon must be considered, and timely support should be provided for exposed frozen rock wall to guarantee construction safety. Moreover, the test results also verify that the design of the new testing system is reliable, feasible, and useful.

Vibration compaction process model for rockfill materials considering viscoelastic-plastic deformation

Compaction technology has been developed over the past three decades. However, the absence of an effective model that can rapidly and accurately simulate the compaction process limits the further development of compaction technology. In this paper, we propose a vibration compaction process model to simulate the compaction of rockfill materials. A viscoelastic-plastic dynamic compaction deformation formula for rockfill materials was proposed and, considering the horizontal movement of the roller, this formula was utilized for simulating pass-by-pass compaction by dividing the rockfill materials into equal-width blocks. Furthermore, an inversion method based on neural networks was proposed to determine the model parameters of real-world rockfill materials through field test results. Then, the effects of number of roller passes and vibration frequency were analyzed. The experimental results verified that the proposed model could effectively simulate the roller-soil interaction and rockfill material deformation characteristics and could thus provide a theoretical basis for intelligent compaction.

Dynamic response properties of polymer bonded explosives under different excitation by deceleration

Based on the experimental method of projectile penetration into the concrete target, different excitation by deceleration of polymer bonded explosives (PBXs) was achieved by controlling the length of steel pillars behind PBXs. A series of impact tests were conducted to study the mechanical response of PBXs with different initial densities under different excitation by deceleration. A physical model was developed to describe the viscoelastic-plastic deformation of PBXs. The plastic part was added on the basis of the viscoelastic statistical crack mechanical model (Visco-SCRAM) model, and the compaction behavior of charge in different environments was characterized based on the Heckel compaction equation. The model was implemented in LS-DYNA, and the simulation results were verified by the experiments. The dynamic mechanical behavior of PBXs under different excitation by deceleration was studied from the macroscopic and mesoscale aspects. The stress curves, strain curves, the density change and the interaction between particles in deceleration environment were predicted. After comparison and analysis, the dynamic response law of the charge in the penetrating process was obtained. Macroscopic responses along with mesoscale modeling results are significantly important to have a better understanding of deformation mechanisms of PBXs.

A hybrid lamination model for simulation of woven fabric reinforced thermoplastic composites solid-state thermo-stamping

Solid-state thermo-stamping of fabric reinforced composites has attracted extensive attention for its efficiency and potential energy saving in recent years. In this paper, a hybrid lamination model is proposed to describe the forming behavior of woven fabric reinforced thermoplastic composites (WFRTP) during solid-state thermo-stamping process. The woven carbon fiber (CF)/ Polyetheretherketone (PEEK) sheet/prepreg is modelled as laminate structure with woven reinforcement layers (shell elements) embedded in thermoplastic resin layer (solid elements). More specifically, a hypoelastic constitutive model is used to represent the anisotropic mechanical behavior of fabric reinforcement under large deformation, while the fabric model is calibrated and validated by uniaxial bias extension (UBE) test and tensile test of woven fabric. A phenomenological model is adopted to describe the viscoelastic-plastic deformation behavior of thermoplastic resin, while the resin model is calibrated by tensile tests of PEEK. The applicability of the hybrid model is demonstrated through comparing numerical results of UBE tests and Erichsen tests with their corresponding experiment results. The hybrid lamination model provides a theoretical foundation for numerical simulation of WFRTP solid-state thermo-stamping.

The Refined Model of Viscoelastic-Plastic Deformation of Reinforced Cylindrical Shells

The paper formulates the initial-boundary-value problem of the viscoelastic-plastic bending behavior of cylindrical circular shells cross-reinforced along equidistant surfaces. The instant elastoplastic deformation of the shell composition components is described by the governing equations of the theory of plastic flow with isotropic hardening. The viscoelastic deformation of these materials is described by the defining relations of the Maxwell - Boltzmann model of body. The geometric nonlinearity of the problem is taken into account in the Karman approximation. The used system of two-dimensional resolving equations and the corresponding initial and boundary conditions make it possible to determine displacements and stress-strain state (including residual one) in materials of the composition of flexible cylindrical shells with varying degrees of accuracy. In this case, the weak resistance of the considered composite structures to transverse shears is taken into account. In the first approximation, the equations are used, the initial and boundary conditions correspond to the relations of the widely used non-classical Reddy theory. A numerical solution of the initial-boundary-value problem posed is constructed using an explicit step-by-step "cross" scheme. The elastoplastic and viscoelastic-plastic dynamic deformation of a relatively thin long circular cylindrical shell is investigated. The structure is rationally reinforced in the circumferential direction and is loaded with an internal pressure of an explosive type. It has been demonstrated that under intense short-term loading even of a relatively thin cylindrical reinforced shell by internal pressure, the traditional Reddy theory does not guarantee that the maximum residual deflection and the intensity of residual deformations of the components of the composition are accurate to within 10% compared to calculations performed by the refined theory. The difference in the results of the corresponding calculations increases with an increase in the relative thickness of the composite shell. It was found that after plastic deformation of a long reinforced cylindrical shell in its residual state, not only appear zones of edge effects, but also a local zone of an intense deformation located in the vicinity of the central section of the shell. The length of the local central zone is comparable with the length of the zones of edge effects. It is shown that the amplitude of the transverse vibrations of the reinforced shell in the vicinity of the initial moment of time significantly (by an order of magnitude) exceeds the value of the maximum modulus of the residual deflection. Therefore, the calculations performed in the framework of the theory of elastoplastic deformation of composition materials do not allow a very approximate determination of the magnitude of the residual displacements and the magnitude of the residual deformed state of the components of the composition of the cylindrical shell.

A macro–micro viscoelastic-plastic constitutive model for saturated frozen soil

A macro–micro creep constitutive model of viscoelastic-plastic deformation characteristics for three-phase saturated frozen soils is derived in this paper based on micromechanics, considering the influences of ice content and temperature. First, creep tests of saturated frozen soils are performed, and the mechanism of creep deformation is discussed from a micro perspective. Then, the micro-scale and macro-scale information are connected by establishing a relationship between the macroscopic strain energy rate and strain energy rate of the ice particles, soil matrix, and unfrozen water. The viscoelastic stress tensor for the three phases of materials is derived using the visoelastic correspondence principle and the micromechanics method. Thus, the macro-micro viscoelastic constitutive model for saturated frozen soils is obtained. Based on this analysis, the viscoelastic-plastic constitutive model is further considered for the viscoplastic properties of the soil matrix and ice particles. In addition, the corresponding relationship between viscoplastic and viscoelastic is established based on the “equivalent” method. Therefore, the macro-micro creep constitutive model of viscoelastic-plastic deformation characteristics for three-phase saturated frozen soils is finally derived. The model parameters are determined based on the creep tests of frozen soils and the model is verified using creep test results for saturated frozen soil. It is also determined that the proposed model can illustrate the influence of temperature and ice content on the creep of saturated frozen soils.

Viscoelastic—Plastic Deformation of Plates with Spatial Reinforcement Structures

A mathematical model of viscoelastic-plastic bending deformation of spatially reinforced plates is developed based on the time step method. The viscoelastic behavior of the components of the composition is described by the Maxwell-Boltzmann equations, and plastic behavior by flow theory with isotropic hardening. The low resistance of composite plates to transverse shear is taken into account within the framework of Reddy’s theory, and the geometric nonlinearity of the problem is considered in the von Karman approximation. The corresponding initial-boundary-value problem is solved using a leapfrog numerical scheme. The dynamic viscoelastic-plastic bending of spatially reinforced fiberglass rectangular plates subjected to air blast wave loading is investigated. It is shown that for relatively thick plates, replacing a flat reinforcement structure by a spatial reinforcement structure leads to a significant decrease in the maximum and residual deflections and strain intensity of the binder material, and for relatively thin plates, this replacement is ineffective. It is found that in the initial stage of deformation, the amplitude of oscillation of the composite plate far exceeds the residual deflection.

A refined model of viscoelastic-plastic deformation of flexible plates with spatial reinforcement structures

A refined model of viscoelastic-plastic deformation of flexible plates with spatial reinforcement structures has been developed. Strains of the composition materials are assumed to be small and decomposed into plastic and viscoelastic components. Instant plastic deformation of these materials is described by the flow theory with isotropic hardening. Viscoelastic deformation obeys the equations of a linear model of a five-constant body. The geometric nonlinearity of the problem is taken into account in the Karman approximation. The possible weak resistance of composite plates to lateral shear is modeled in the framework of a refined theory of bending. This allows one to determine the displacements of plate points and the stress-strain state in the components of the composition with varying degrees of accuracy. In a first approximation, from the obtained equations and boundary conditions, we obtain relations corresponding to the traditional nonclassical Reddy theory. A numerical solution to the formulated initial-boundary-value problem is sought according to an explicit “cross-type” scheme The viscoelastic-plastic dynamic deformation of rectangular, relatively thin fiberglass plates under the influence of an explosive type load is investigated. The plates have a traditional plane-cross (orthogonal) or spatial reinforcement structure. It is shown that even in the case of relatively thin composite plates the Reddy theory is unacceptable for adequate calculations of their dynamic viscoelastic-plastic deformation. It has been demonstrated that the magnitude and shape of the residual deflections depend not only on the reinforcement structure, but also on the magnitude of the viscoelastic characteristics of the materials of the composition components. It was found that, after dynamic inelastic deformation, the composite plate can have a corrugated residual shape with folds oriented in the longitudinal direction. It is shown that even in the case of a relatively thin plate, replacing the planar-cross reinforcement structure with a spatial structure can significantly reduce the amount of residual deflection and the intensity of residual deformation in the binder material and some fiber families. For relatively thick plates, the effect of such a replacement of the reinforcing structures manifests itself much more.

Viscoelastic-Plastic Deformation of Plates with Spatial Reinforcement Structures

Viscoelastic-Plastic Deformation of Plates with Spatial Reinforcement Structures

Modelling the viscoelastic-plastic deformation of flexible reinforced plates with account of weak resistance to transverse shear

Modelling the viscoelastic-plastic deformation of flexible reinforced plates with account of weak resistance to transverse shear

Numerical simulations of microcrack-related damage and ignition behavior of mild-impacted polymer bonded explosives

A physical model is developed to describe the viscoelastic-plastic deformation, cracking damage, and ignition behavior of polymer-bonded explosives (PBXs) under mild impact. This model improves on the viscoelastic-statistical crack mechanical model (Visco-SCRAM) in several respects. (i) The proposed model introduces rate-dependent plasticity into the framework which is more suitable for explosives with relatively high binder content. (ii) Damage evolution is calculated by the generalized Griffith instability criterion with the dominant (most unstable) crack size rather than the averaged crack size over all crack orientations. (iii) The fast burning of cracks following ignition and the effects of gaseous products on crack opening are considered. The predicted uniaxial and triaxial stress-strain responses of PBX9501 sample under dynamic compression loading are presented to illustrate the main features of the materials. For an uncovered cylindrical PBX charge impacted by a flat-nosed rod, the simulated results show that a triangular-shaped dead zone is formed beneath the front of the rod. The cracks in the dead zone are stable due to friction-locked stress state, whereas the cracks near the front edges of dead zone become unstable and turn into hotspots due to high-shear effects.

A coupled one-dimensional viscoelastic-plastic model for aquitard consolidation caused by hydraulic head variations in aquifers

Accurate and practical calculation of aquitard consolidation is required for a reliable analysis of land subsidence caused by groundwater overexploitation in a multilayered aquifer system because aquitards are generally more compressible than aquifers are. This study proposes a coupled one-dimensional viscoelastic–plastic consolidation model that considers the combined effect of changes in soil parameters and body force to simulate aquitard consolidation caused by hydraulic head variations in neighbouring aquifers. The proposed model uses variable total stress and simultaneously solves hydraulic head and vertical soil displacement. The constitutive relation based on the Voigt model with different elastic moduli of the spring in normally consolidated and overconsolidated soils is used to describe the viscoelastic–plastic deformation mechanism of aquitards. In addition, the proposed model considers the combined effect of variations in hydraulic conductivity, elastic moduli, and body force on the calculation of aquitard consolidation. Three hypothetical scenarios with various hydraulic head variations in aquifers are used to examine the coupled one-dimensional viscoelastic–plastic consolidation model. The results show that neglecting plasticity and viscosity of soil causes aquitard consolidation to be respectively underestimated and overestimated. In addition, ignoring body force variation underestimates aquitard consolidation, whereas neglecting soil parameters variation overestimates aquitard consolidation. Two real case scenarios are also studied to further demonstrate the applicability of the coupled one-dimensional viscoelastic–plastic consolidation model. Copyright © 2015 John Wiley & Sons, Ltd.