Thermo-viscoelastic Properties Research Articles

Accurate and efficient determination of glass thermo-viscoelastic properties using creep compliance master curve construction approach

An accurate and efficient method for determining the thermo-viscoelastic properties of glass was proposed using a creep compliance master curve construction approach based on the time-temperature superposition principle. This method mainly involved obtaining creep compliance at multiple temperatures, constructing the master curve, and converting into relaxation modulus. By applying this method, the shear relaxation modulus and Williams-Landel-Ferry constants were successfully obtained for K9 glass. A smooth creep compliance master curve at 590 °C was constructed covering a vast timescale up to 2.6×105 seconds, despite a single curve's duration being only 619 seconds. Consequently, the derived relaxation modulus encompassed a broad range of relaxation times spanning six orders of magnitude. The high accuracy of the determined thermo-viscoelastic properties was firmly validated across all tested temperatures. Furthermore, the detrimental impact of friction on the method's accuracy can be effectively minimized by selecting a suitably large height-to-diameter ratio for the cylindrical glass specimen.

Investigation of the applicable temperature range of time-temperature superposition principle for thermo-viscoelastic properties of optical glasses

Investigation of the applicable temperature range of time-temperature superposition principle for thermo-viscoelastic properties of optical glasses

Bottom‐up analysis framework for the continuous multidirectional carbon fiber‐reinforced PEEK composite laminates

AbstractThe continuous carbon fiber‐reinforced polyether ether ketone (CCF/PEEK) composites have been widely utilized in aerospace structures due to their excellent properties. However, the main load‐bearing structure in the next‐generation aircraft needs to withstand high temperatures up to 200°C, and the mechanical properties of CCF/PEEK composites show significant time‐/temperature‐dependence due to the viscoelastic nature of the PEEK matrix. Therefore, accurate predictions of the mechanical performance of CCF/PEEK composites under high‐temperature service conditions are the key issue for structural safety and life assessments and have therefore become a recent research focus. To address these challenges, this study established a bottom‐up analysis framework for the CCF/PEEK composites and employed the theoretical model and the finite‐element representative volume element (FE‐RVE) method to investigate the anisotropic viscoelastic properties of CCF/PEEK composites. We first built an anisotropic viscoelastic model of the unidirectional CCF/PEEK composites by integrating the generalized Maxwell into the bridging model. Upon this foundation, we further developed a viscoelastic laminate model capable of accurately predicting the thermoviscoelastic properties of multidirectional laminates. To verify the developed model, different kinds of FE‐RVEs were built and analyzed. Overall, there is good agreement among the model predictions, the FE‐RVE simulations, and the experimental results within a temperature range of 25–250°C. The developed model can be used to design the high‐temperature performance of CCF/PEEK composites with different fiber volume fractions, laminated configurations, or loading directions.Highlights An anisotropic viscoelastic model of the unidirectional (UD) continuous carbon fiber‐reinforced polyether ether ketone (CCF/PEEK) composites is built. The viscoelastic laminate composite model is developed based on the UD CCF/PEEK composites model. The finite element representative volume element (FE‐RVE) simulation with fibers in a hexagonal or random array has better accuracy compared with the experimental results. The FE‐RVE simulation and the experimental results verified the developed model from 25°C to 250°C.

Curing-dependent thermo-viscoelastic and shrinkage behaviour of photopolymers

This study investigates the influence of curing on the thermo-viscoelastic properties and chemical shrinkage of a commercially available photopolymer resin used in SLA and DLP 3D printing and presents a modelling approach for predicting material properties. UV rheometer and DMA measurements were performed to investigate the viscoelastic properties of the photopolymer material as a function of temperature, degree of cure, and frequency. Time–temperature and time-cure superposition principles were applied to the experimental results. In addition, the chemical shrinkage behaviour was studied by the UV rheometer as a function of the degree of cure and temperature, and a model equation was proposed based on these parameters. Our experimental findings have led to the development of constitutive equations for the complete material behaviour.

Using asymptotic homogenization to determine effective thermo-viscoelastic properties of fibrous composites with interphase layer

In this paper, we apply the method of asymptotic homogenization in parametric space in order to determine thermo-viscoelastic properties of materials composed of cylindrical fibers surrounding by an intermediate layer separating them from viscoelastic matrix. We use the Maxwell model of viscoelasticity. The volumetric fraction and physical properties of the layer can vary. There is a possibility of a contrast between the properties of fibers, the layer, and the matrix. Our approach allows us to treat temperature as a parameter and study the response of mechanical characteristics on the change in temperature. We perform the Fourier transform of governing equations and then implement asymptotic homogenization of the resulting equations in parametric space. Microscopic boundary value problem is defined on a periodic cell consisting of a fiber surrounded by a layer and embedded in the matrix. Macroscopic equations are derived for the complex Young’s and shear moduli. Effective viscoelastic properties of the material are computed for different values of the frequency of harmonic oscillations and for various temperatures. This paper discusses how effective storage and loss Young’s and shear moduli depend on volumetric fraction and mechanical properties of the material of the layer. The obtained results can provide information on how concentration, structure and properties of inclusions can affect the effective storage and loss Young’s and shear moduli.

Mechanistic modelling of grid-reinforced milled-and-overlaid asphalt pavements

ABSTRACT This study was motivated by the need for a mechanistic-empirical (ME) design method applicable to asphalt pavements after mill-and-overlay repairs that include reinforcing grids; the focus was solely on the mechanistic component. A new model, based on layered theory, was developed – coupling in one single framework the following features: elastic layers for representing subgrade and unbound layers, fragmented layers for representing existing aged and densely cracked asphalt concrete (AC), imperfect bonding conditions for representing any differential slippage between adjoining layers, thermo-viscoelastic layer properties for representing new AC, and moving loads for representing traffic conditions. Grid effects were modelled as a combination of three contributions: the presence of an additional thin high-modulus elastic layer within the pavement system, the influence of a grid on interlayer bonding between layer above and below it, and the influence of a grid on the properties of the surrounding AC. These contributions require new grid-related modelling inputs that are physically meaningful and generic – not limited to any specific product. A secondary objective of the work was to generate some initial intuition on the mechanistic effects of interlayer grids. Accordingly, the new model was demonstrated in a parametric investigation covering a synthetic milled-and-overlaid structure with and without reinforcement. Findings from this demonstration provided an initial validation for the new model, given the conformity to findings from experimental studies. Overall, the new model is deemed a candidate computational engine for a ME design applicable to new and rehabilitated asphalt pavement systems. Furthermore, it can serve as an analysis tool to guide manufacturers on improving their products or showcasing existing capabilities in a quantified manner. Lastly, the new model can support the design of experimental setups for assessing grid effects within asphalt pavement systems, and therefore ensure the collection of usable measurements for subsequent mechanistic interpretation.

A hygro-thermo-mechanical constitutive model for shape memory polymers filled with nano-carbon powder

ABSTRACT The nano-carbon powders are often used as fillers to endow the shape memory polymers (SMPs) with electroconductivity. It has been found that the shape memory effects (SMEs) of SMPs filled with nano-carbon powder can be triggered both by temperature and by water. To reveal the driving mechanism of SMEs, a constitutive model for describing the thermally activated and moisture activated SMEs of these shape memory polymer composite (SMPCs) is developed here. Because both of the SMEs share the same driving mechanism, the variable moisture is incorporated into the framework of a thermo-mechanical modeling approach to disclose the effect of moisture on the thermoviscoelastic properties. The SMPCs are regarded as isotropic materials and the effect of carbon powder on the mechanical properties of the matrix is also considered in the paper. Because the complete recovery may not be reached even they are exposed to the stimulus environment long enough, the blocking mechanism is also considered here. This is the mainly new contribution compared to the early work. Using the method of parameter determination presented here, the effectiveness of the proposed hygro-thermo-mechanical constitutive model is confirmed by comparing the model results with the test data of uniaxial deformation from the literature.

Thermo-viscoelastic properties in a non-simple three-dimensional material based on fractional derivative Kelvin–Voigt model

This paper provides a connection between the theories of thermoelasticity with fractional order, two-temperature, Kelvin–Voigt viscoelasticity and heat conduction with three-phase lags. The proposed model is used to study the thermoelastic vibrations in a homogeneous isotropic three-dimensional solid whose surface is traction free and subject to a time-dependent thermal loading. The problem has been addressed using Laplace and double Fourier transform methods to remove the time variable as well as two space variables. To obtain the numerical results of the investigated fields in the physical domain, we applied a numerical inverse method. We have also concluded some special cases of interest from this work. Furthermore, the results are displayed graphically to illustrate the influence of viscosity, phase lags, two-temperature and fractional-order parameters on all physical fields.

Thermo-Viscoelastic Response of 3D Braided Composites Based on a Novel FsMsFE Method.

A homogenization-based five-step multi-scale finite element (FsMsFE) simulation framework is developed to describe the time-temperature-dependent viscoelastic behavior of 3D braided four-directional composites. The current analysis was performed via three-scale finite element models, the fiber/matrix (microscopic) representative unit cell (RUC) model, the yarn/matrix (mesoscopic) representative unit cell model, and the macroscopic solid model with homogeneous property. Coupling the time-temperature equivalence principle, multi-phase finite element approach, Laplace transformation and Prony series fitting technology, the character of the stress relaxation behaviors at three scales subject to variation in temperature is investigated, and the equivalent time-dependent thermal expansion coefficients (TTEC), the equivalent time-dependent thermal relaxation modulus (TTRM) under micro-scale and meso-scale were predicted. Furthermore, the impacts of temperature, structural parameters and relaxation time on the time-dependent thermo-viscoelastic properties of 3D braided four-directional composites were studied.

Effect of network structure on thermo-viscoelastic properties of the optical glasses

Effect of network structure on thermo-viscoelastic properties of the optical glasses

A novel model of fractional thermal and plasma transfer within a non-metallic plate

While in several publications the thermo-viscoelastic properties of solids have been documented, no attempt has been made to examine the action of coupled thermal and plasma wave in viscoelastic materials. In this paper, a new mathematical model for thermal and plasma transfer in an organic semiconductor was constructed with a time-fractional derivative of order

Changes in thermoviscoelastic and biochemical properties of Atroncau blancu and roxu Afuega'l Pitu cheese (PDO) during ripening

Thermoviscoelastic and biochemical properties of Afuega'l Pitu cheese blancu (B) and roxu (R), a Spanish acid-curd cheese made from cow’s milk, were determined at 3, 15, 30 and 60 days of ripening. The contents of fat (>45 g/100 g total solids, TS) and NaCl (<3 g/100 g TS) were similar between varieties and did not change with ripening. Total solids, pH, nitrogen fractions and fat acidity increased with ripening time in B and R samples. Lactose content was higher in B than in R cheeses at 3 d, was degraded gradually throughout ripening but did not disappear totally in both cheeses at 60 d. Viscoelastic parameters were determined in the linear viscoelastic region (LVER) by stress sweeps (6.3 rad/s, 20 °C): the stress amplitude (σmax) and complex modulus (G*) increased, while strain amplitude (γmax) decreased up to 60 d. Mechanical spectra were also determined, in the LVER, at 20 °C, 50 °C and 75 °C, showing that all samples behaved as “true gels” (elastic modulus, G' > viscous modulus, G''), irrespective of temperature. The best gel properties (low values of loss factor, tanδ = G''/G', and minor frequency dependence, i.e., low n', n'' exponents), were observed at 20 °C for B30 and R30. The viscoelastic parameters (G0' and G0'') increased with ripening time, irrespective of the temperature, and for a fixed ripening time they were lower at higher temperature. At 75 °C, all samples exhibited notable frequency dependence (n'' ≫ n'), resulting in shear-induced gelation at low frequencies (high oscillation times) which was consistent with data in thermal profiles from 70 °C to 90 °C.

Hyperbolic thermal-plasma wave propagation in semiconductor of organic material

Although the thermo-viscoelastic properties of solids have been reported in many articles, no effort has been made to investigate the coupled thermo-viscoelastic and plasma wave behavior of semiconductors based on the photothermal theory. In this work, a new mathematical model of heat and plasma transport has been constructed for semiconductor of viscoelastic material. Some fundamental theorems on the linear coupled and generalized theories can be easily obtained as special cases. A two-dimensional problem is viewed for a half-space of an organic semiconductor plate whose surface is traction free and subjected to an arbitrary time-dependent heat flux. Laplace and Fourier integral transforms are utilized. The carrier density, temperature, thermal stress, and displacement distributions have been obtained through the use of the theoretical model together with plasma and thermo-viscoelastic effects. The inversion technique for Fourier and Laplace transforms is carried out using a numerical technique based on Fourier series expansions. Comparisons are made with the results anticipated through the coupled idea and generalized theory. The influence of the some parameters on all the regarded fields is examined for different theories.

Modeling the thermoviscoelasticity of transversely isotropic shape memory polymer composites

Shape memory polymer composites (SMPCs) are emerging smart materials of great application potential due to high deformability and good shape memory properties, with improved mechanical properties compared to pure polymers. In the paper, a micromechanical model is developed to predict the thermoviscoelastic and shape memory properties of such composite systems. First of all, we extend the Mori–Tanaka method into Carson domain based on the Correspondence Principle in viscoelasticity. Thus, the relaxation moduli of SMPCs at different temperatures can be obtained by the thermoviscoelastic properties of the matrix and the reinforcement in the transformed Carson domain. Next the inversion of the relaxation moduli from the Carson domain to the time (physical) domain is accomplished numerically by a multi-precision algorithm. Then, the three-element fractional Zener model is employed to describe the temperature-dependent relaxation modulus and the constitutive relations of SMPCs, and the analytical solutions to the partially constrained shape recovery behaviors are obtained, as well as the stress–strain relations of the material at different temperatures. The overall micromechanical model is then implemented into Mathematica, and the simulation results are compared to and agree well with the experimental results of two different kinds of SMPCs. The paper provides an efficient method on predicting the complex behaviors of transversely isotropic SMPCs.

Thermo-viscoelastic Modeling of Nonequilibrium Material Behavior of Glass in Nonisothermal Glass Molding

Nonisothermal Glass Molding (NGM) has become a viable replicative manufacturing technology for the cost-efficient production of complex precision optical components made of glass. During the pressing stage in NGM, glass materials undergo a huge temperature change in the glass transition range. In this range, glass exhibits thermo-viscoelastic responses, and the temperature drop through the glass transition leads glass structure to depart from an equilibrium to a nonequilibrium state. Thermo-viscoelastic properties of the nonequilibrium glass material greatly depend on temperature and thermal history. This paper presents a phenomenological constitutive model developed for modeling the thermo-viscoelastic responses of nonequilibrium glass. We propose a direct incorporation of the temperature -and thermal history effects into each parameter of the phenomenological model. This novelty allows the model to describe the nonequilibrium phenomena and to study temperature-dependent viscoelasticity of glass without assuming thermo-rheologically simple characteristics. Furthermore, the phenomenological model enables the coupling of structural -and stress relaxation phenomena. The model validation conducted for creep experiments demonstrates an enhancement in numerical predictions of the nonequilibrium material behaviors of glass over wide ranges of temperature and thermal history.

Force recovery evaluation of thermo-induced shape-memory polymer stent: material, process and thermo-viscoelastic characterization

Due to their functional and biological benefits, shape memory polymer (SMP) stents have attracted the attention of researchers in the biomedical science area. The highlights of this article are the evaluation of stent performance including radial force recovery and recovery start temperature (RST) in a constrained state. The effects of polyurethane (PU) mechanical properties and fabrication method are investigated on thermo-viscoelastic properties, sample defect and shape recovery of PU and polycaprolactone (PCL) blend. Thereafter, three tubular stents fabricated with the different diameter to thickness (d/t) ratio and their mechanical behavior are examined in loading, relaxation, and unloading. Finally, the radial force recovery of the stents is measured after stimulation in temperatures up to 45 °C. Emerging more peaks in the delta tangent graph implies that samples fabricated with solution-mixing has a better viscoelastic behavior and shows fewer defects compared to the melt-mixing ones. The fabrication method was much more effective on enhancement of the storage and loss modulus compared to double increasing of Young’s modulus of applied PU from 4.3 to 9 MPa. Moreover, an increase in the stent’s d/t from 15 to 10 causes not only an increase in the radial stiffness and force recovery but also leads to the reduction of irreversible deformation and RST. The results of this research reveals the importance of the dimensional and geometric design of SMP stents in controlling the force recovery and RST.

Microstructure evolution and mechanical behaviors of alumina-based ceramic shell for directional solidification of turbine blades

The high temperature mechanical behaviors of Al2O3-based ceramic shell for the directional solidification of turbine blades were investigated. Isothermal uniaxial compression tests of ceramic shell samples were conducted on a Gleeble-1500D mechanical simulator with an innovative auxiliary thermal system. The microstructures of sintered, heat-treated, and tested samples were characterized using scanning electron microscope and X-ray powder diffraction. The experimental stress–strain results of heat-treated samples were obtained. The eutectic mixture region composed of ZrO2 and SiO2 that regenerated by the decomposition reaction of excess zirconium silicate appears in the samples after heat treatment at 1500. The fracture type of CST25 and CST700 is brittle fracture, but CST1100 and CST1400 have thermo-viscoelastic and viscoplastic properties under stress conditions at high temperatures (>1100). The evolution of zirconium silicate decomposition reaction during the directional solidification process is analyzed. The SiO2 particles provide the major viscosity source of the ceramic shell at high temperatures. The thermo-viscodamage constitutive model of Al2O3-based ceramic shell for the directional solidification of single crystal superalloy is established.

Large Shape Transforming 4D Auxetic Structures

Three-dimensional (3D) printing of active materials is a rapidly growing research area over the last few years. Numerous works have shown potential to revolutionize the field of four-dimensional (4D) printing and active self-deploying structures. Conventional manufacturing technologies restrict the geometric complexity of active structures. 3D printing allows the fabrication of complex active structures with no assembly required. In this study, we propose active 3D printed auxetic meta-materials that are capable of achieving area changes up to 200%. With these meta-materials, we design geometrically complex active structures that can be programmed into versatile shapes and recover their original shape given an external stimulus. We simulate the proposed meta-materials based on thermoviscoelastic material properties obtained by experimental characterization. A reduced beam model is constructed to predict forces and deformations of complex active structures. Excellent correlation is found between finite element simulation and experimental data from a 3-point bending test. Rectilinear tiling of the proposed meta-materials achieves the desired shape transformation. To demonstrate versatile programming, a selected meta-material is tiled into a complex contour, programmed into an arbitrary shape, and recovers as predicted. Simulation results verify this behavior. Such programmability in conjunction with 3D printing may be further exploited for applications such as biomedical devices, civil structures, and aerospace.

Micromechanics-based thermo-viscoelastic properties prediction of fiber reinforced polymers with graded interphases and slightly weakened interfaces

A three-dimensional (3D) micromechanical study is performed for effective viscoelastic properties prediction of fiber reinforced polymers (FRPs) containing elastic, transversely isotropic/isotropic ellipsoidal fibers surrounded by graded interphases, embedded in an isotropic, viscoelastic matrix. Based on mean-field homogenization theory, an improved double-inclusion model for FRPs considering graded interphase and imperfect interface is established. Applying two-step homogenization technology, elastic-viscoelastic corresponding approach and Time-Temperature Superposition Principle (TTSP), effective thermo-viscoelastic moduli of FRPs are obtained with respect to the grading and geometric parameters. By solving the interface damage tensors numerically, the mathematical errors in the previously used analytical expressions are avoided, and the entire prediction scheme is extended to fillers at any aspect ratio. Comparing the results for composites with 3D randomly dispersed fibers with existing semi-analytical solutions, the accuracy and efficiency of the proposed method is verified. Parameters analyses are conducted, which indicate that the established model and the proposed method should be of great help for predicting mechanical properties of FRPs and designing micro-composites.

Softenable composite boom for reconfigurable and self-deployable structures

ABSTRACTThis article investigates (experimentally and numerically) the time and temperature-dependent folding and unfolding behavior, including the structural nonlinearity, of thin-walled softenable composite structures. The composites are fabricated with woven fabric fibers and a heat softenable material of the shape memory polymer (SMP) resin. A numerical model is developed. The model is based on the elastic properties of the woven fabric fibers, their fabric geometry, and the thermo-viscoelastic properties of the SMP resin. A thin-walled cylindrical boom, which can be flexibly folded into an arbitrary configuration and be self-deployed, is fabricated using the heat softenable composite. The viscoelasticity and the shape memory behaviors are investigated during the folding and unfolding of the boom at elevated temperatures.