Modulus Data Research Articles

Detailed experimental and theoretical investigation of the thermomechanical properties of epoxy composites containing paraffin microcapsules for thermal management

AbstractMicroencapsulated phase change materials (PCMs) are being increasingly employed as functional fillers in polymer matrices for thermal management. Therefore, the effect of PCM microcapsules on the rheological, microstructural, thermal and mechanical properties of the host polymer matrices must be understood. This work concerned the preparation of epoxy polymers filled with PCM microcapsules (MC) in various concentrations and their subsequent characterization. The MC phase increases the viscosity of epoxy before curing, thereby reducing castability and hindering elimination of air bubbles. The latter was reflected in an increase in porosity for highly filled compositions, as elucidated by density measurements and microscopic investigation. SEM micrographs showed that the adhesion between the capsule shell and the epoxy matrix was not optimal. The interfacial weakness and the intrinsic low stiffness and strength of MC caused a reduction in mechanical properties, as evidenced by the Nicolais‐Narkis and Pukanszky models. On the other hand, at zero or low deformation levels, the interface presents no gaps and is able to transfer load and heat, as demonstrated by the data of elastic modulus, modeled with the Halpin‐Tsai and Lewis‐Nielsen models, and those of thermal conductivity, in excellent agreement with the Pal model. POLYM. ENG. SCI., 2020. © 2020 Society of Plastics Engineers

Uncertainty Quantification of Simplified Viscoelastic Continuum Damage Fatigue Model using the Bayesian Inference-Based Markov Chain Monte Carlo Method

The simplified viscoelastic continuum damage model (S-VECD) has been widely accepted as a computationally efficient and a rigorous mechanistic model to predict the fatigue resistance of asphalt concrete. It operates in a deterministic framework, but in actual practice, there are multiple sources of uncertainty such as specimen preparation errors and measurement errors which need to be probabilistically characterized. In this study, a Bayesian inference-based Markov Chain Monte Carlo method is used to quantify the uncertainty in the S-VECD model. The dynamic modulus and cyclic fatigue test data from 32 specimens are used for parameter estimation and predictive envelope calculation of the dynamic modulus, damage characterization and failure criterion model. These parameter distributions are then propagated to quantify the uncertainty in fatigue prediction. The predictive envelope for each model is further used to analyze the decrease in variance with the increase in the number of replicates. Finally, the proposed methodology is implemented to compare three asphalt concrete mixtures from standard testing. The major findings of this study are: (1) the parameters in the dynamic modulus and damage characterization model have relatively strong correlation which indicates the necessity of Bayesian techniques; (2) the uncertainty of the damage characteristic curve for a single specimen propagated from parameter uncertainties of the dynamic modulus model is negligible compared to the difference in the replicates; (3) four replicates of the cyclic fatigue test are recommended considering the balance between the uncertainty of fatigue prediction and the testing efficiency; and (4) more replicates are needed to confidently detect the difference between different mixtures if their fatigue performance is close.

An Initial Effort to Create a Superficial Femoral Artery Ultrasound Phantom Using 3-Dimensional Printing

Three-dimensional (3D) printing of anatomical structures has yielded valuable models for simulation, education, and surgical planning applications. Applications for 3D printing have continued to expand to include some ultrasound applications. The goal of this effort was to evaluate if a 3D printed model of a superficial femoral artery (SFA) would have realistic ultrasound characteristics. A computed tomography scan was 3D reconstructed and segmented using TeraRecon Aquarius Intuition software (TeraRecon, Foster City, California) to obtain an atherosclerotic SFA geometry. Both the lumen geometry and calcified plaque geometry of the SFA were exported as a stereolithographic (STL) file. The STL file was printed with An Object350 Connex 3D System using 2 different materials selected based on published elastic modulus data. VeroWhite was selected for the calcified plaque and TangoPlus Clear was selected for the artery wall. After printing, the SFA model was imaged in a water bath with a Phillips IU22 duplex ultrasound console and L12-9 ultrasound probe. Ultrasound imaging of the SFA model yielded grayscale views of artery geometry. Lumen geometry of the SFA model was similar to the actual artery geometry. Ultrasound was able to discern between the 3D print materials and visualize regions with stenosis. Suboptimal ultrasound parameters of echogenicity and wave velocity noted to differ from biological tissue. Total 3D print material cost was estimated at below $20. Although the 3D printed model did not have fully accurate ultrasound characteristics, it still provided realistic imaging. With further research, 3D printed models may offer a low-cost alternative for ultrasound phantoms.

Bicontinuous Cubic and Hexagonal Columnar Liquid Crystalline Ion-Conductors at Room Temperature in Ion-Doped Dendritic Amphiphiles

A bicontinuous cubic (Cubbi) liquid crystalline (LC) phase consisting of three dimensional (3D) conducting networks is a promising structural platform for ion-conductors. For practical applications using this fascinating LC structure, it is necessary to suppress crystallization at room temperature (RT). Herein, we report the Cubbi structure at RT and the morphology–dependent conduction behavior in ionic samples of a non-crystallizable dendritic amphiphile. In the molecular design, branched alkyl chains were used as an ionophobic part instead of crystallizable linear alkyl chains. Two ionic samples with Cubbi and hexagonal columnar (Colhex) LC phases at RT were prepared by adding different amounts of lithium salt to the amphiphile. Impedance analysis demonstrated that the Cubbi phase contributed to the faster ion-conduction to a larger extent than the Colhex phase due to the 3D ionic networks of the Cubbi phase. In addition, the temperature–dependent impedance and electric modulus data provided information regarding the phase transition from microphase-separated phase to molecularly mixed liquid phase.

Dielectric Response of ZnTe–Ti/Al Schottky Junctions with CdTe Quantum Dots Studied by Impedance Spectroscopy

The electrical properties of ZnTe–Ti/Al Schottky junctions were investigated by the impedance spectroscopy (IS) method. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were also performed. The studied samples were the CdTe quantum dot structures embedded in ZnTe matrix and a reference ZnTe sample without quantum dots. C-V characteristics confirmed the presence of quantum dots (QDs) in the structures. Electric modulus and impedance data were analyzed. IS studies proved that long-range conductivity governs the relaxation processes in the junctions. For both samples, the data were fitted with a simple RC circuit composed of a depletion layer capacitance in parallel with bulk resistance and a series resistance of contacts. The activation energy of the relaxation process observed for the reference sample obtained from the Arrhenius plot of the resistance, imaginary impedance, and electric modulus equals 0.4 eV at zero bias. For the quantum dot sample, the value of activation energy determined with the help of the same methods equals 0.2 eV. In conclusion, it was assumed that the relaxation processes for the reference sample are attributed to the trap present in ZnTe host material, whereas those observed for the QD structure are assigned to the deep level associated with defects located close to the QDs created during their growth.

A DEM method for simulating rubber tyres

Recently, recycled rubber tyres were found to be an economical and environmental-friendly reinforcement material in geotechnical engineering. Although the use of rubber tyre-reinforced soil has become increasingly popular, there is still a lack of a robust and systematic method to model rubber tyres when using the discrete-element method (DEM) to investigate the stress-strain responses. In this paper, DEM rubber tyres are simulated by bonding regular-packed balls, and numerically tested under tensile force using the particle flow code in three dimensions. When comparing the effects of different packings on the sample, using Young's modulus and Poisson's ratio, it was found that only body-centred-cubic packing could achieve a Poisson's ratio of 0·5 representing no volume change during the deformation of rubber. The difference between uniaxial compression and tension simulations was also compared as well as the influences of particle overlapping, particle radius and sample aspect ratio on the mechanical response of the tyre model. Finally, the DEM parameters were set to match the experimental Young's modulus data. This proposed DEM rubber tyre strips model could be a basis to study other rubber reinforcements such as tyre chips and shreds, irregular rubber buffings and granulated rubber.

Computer Modeling on the Effect of the Multistep Nanoimprinting Process in Elastic Deformation Recovery of COC (Cyclic Olefin Copolymer)

The effect of the multistep imprint in elastic deformation recovery was studied numerically with more than one roll and different depth ratios. As well as effect hold-on time on the elastic deformation recovery of polymer Cyclic Olefin Copolymer (COC) material was studied using Generalized Maxwell (GM) constitutive model and their parameters in finite element simulation software of ABAQUS were presented. Firstly, the modified Genetic Algorithm (GA) was employed to obtain a Prony series of the viscoelastic model in terms of experimental data of the complex modulus for COC. To evaluate the elastic recovery of the microstructure, the cross-sectional area of micro-channel before and after hot-imprinting was computed and compared numerically. The simulated results were analysed and clearly showed an improvement in the elastic recovery rate of the microstructure area as the multi-step of rolling was employed.

Combined Occupancy of Gadolinium at the Lattice Sites of β‐Ca3(PO4)2 and t‐ZrO2 Crystal Structures

An in situ aqueous precipitation with the aid of Gd3+ as a stabilizer has been used to attain a series of β‐Ca3(PO4)2/t‐ZrO2 composites. Analytical characterization techniques were used to investigate the formation of desired composite during progressive heat treatments. The transformation of calcium deficient apatite to β‐Ca3(PO4)2, which usually occurs at ≈ 780 °C for pure systems, is delayed to beyond 1100 °C, depending upon the concentration of Gd3+/Zr4+ used in the synthesis. Gd3+ prefers to accommodate at the lattice sites of both β‐Ca3(PO4)2 and t‐ZrO2. Gd3+ ensures limited occupancy at the Ca2+(1), Ca2+(2), and Ca2+(3) of β‐Ca3(PO4)2 while t‐ZrO2 consumes the excess Gd3+. Phase pure β‐Ca3(PO4)2/t‐ZrO2 composite mixtures devoid of any secondary phase alongside enhanced structural stability were accomplished at 1500 °C. The micrographs of the composite specimen revealed good sintering behaviour, and the Youngs modulus and hardness data determined from indentation displayed significant variations depending on the phase content of the individual components in the composite system.

Investigation on the low temperature properties of asphalt binder: Glass transition temperature and modulus shift factor

This paper investigates the effect of the glass transition temperature, Tg, and the use of modulus shift factors bT on the measured rheological properties of asphalt binders at low temperatures. First, temperature-frequency (T-f) sweep tests are performed with the Dynamic Shear Rheometer (DSR) on asphalt binder, and, the corresponding Tg is calculated. Next, modulus shift factors bT is applied to the modulus data measured at temperatures below Tg in the Cole-Cole plot. Finally, a visual comparison of master curves and the parameter assessment of 2 Spring 2 Parabolic 1 Dashpot (2S2P1D) model are used to evaluate the effect of bT. A significant increase in dynamic shear modulus is observed when the DSR test is performed below Tg, while bT can take into account this phenomenon on the shape of the curves in the Cole-Cole plot. Hence, the combined use of the horizontal shift factor, aT, and modulus shift factor, bT, is recommended when the DSR tests are performed at temperatures lower than the corresponding asphalt binders Tg.

Study of structural changes in thermoplastics using dynamic mechanical analysis

Diffuse coplanar surface barrier discharge (DCSBD) is an innovative plasma source that finds application in industrial practice and also in the surface treatment of various types of materials. The presented paper deals with the investigation of structural changes in selected thermoplastic materials that have occurred after their treatment with plasma discharge. The structural changes were investigated by using dynamic mechanical analysis, where the changes between the unmodified material samples and the thermoplastic material samples exposed to the plasma discharge, were compared, based on the obtained data of the storage modulus, the loss modulus and the loss tangent. For the experiment, thermoplastic materials were chosen, which are widely represented in the production of packaging materials, namely polypropylene (PP), polyethylene (PE), polyethylene terephthalate (PET).

Quintessence behavior via matter creation cosmology

We study the matter creation cosmology as an alternative theory to explain the dark energy phenomena. We discuss the matter-dominated Universe in a flat Friedmann-Robertson-Walker line element by adopting the thermodynamics of open systems, in which the matter creation irreversible processes may take place at a cosmological scale. We propose a new form of the matter creation rate, varGamma =3alpha H_0+3beta H+3gamma ; frac{ddot{a}}{{dot{a}}}, which generalizes some of the previous models in the literature. Exact solutions of the field equations are found and discussed the evolution of the Universe. Constraints on the model parameters are obtained from Markov Chain Monte Carlo (MCMC) analysis using the Supernova distance modulus data, observational measurements of Hubble parameter, Baryon acoustic oscillation data. The trajectories of the evolution of the scale factor, deceleration parameter and equation of state parameter are plotted by using best-fit values of the parameters. It is observed that the model shows accelerating behavior and behaves quintessence like (omega >-1). The age of the Universe is obtained which is in good agreement with varLambda CDM model. We examine the model using two independent diagnostic parameters, namely statefinder and textit{Om}. We apply Akaike information criterion (AIC) and Bayesian information criterion (BIC) to discriminate the model based on the penalization associated to the number of parameters. The analysis shows that the model has close resemblance to the varLambda CDM cosmology. We also discuss the thermodynamics of the model and find that the model satisfies the generalized second law of thermodynamics with certain constraints.

Effect of Structural Water on the Dielectric Properties of Hydrated Tungsten Trioxide

Layered hydrated tungsten trioxide with orthorhombic phase is prepared by a hydrothermal method in an acidic environment. Dielectric studies reveal the presence of space charge and ionic polarizations in the as-prepared samples at different temperatures and frequencies. The scaling behavior shows the gradual shifting of space charge to ionic polarization at 343 K. Impedance along with phase measures a shift from purely resistive to capacitive for the sample with an increase in frequency above 343 K. Modular dispersion spectra suggest that electrical transport and conductivity relaxation occur in the material. Nyquist plots are drawn from impedance and modulus data and the activation energies calculated show a transition from metallic to insulating around 343 K. Comparison of variation of imaginary parts of impedance and modulus with frequency shows the movement of grain boundaries to grain, which supports the transition.

Viscoelastic behavior corresponding to reptative relaxation times across the λ-transition for liquid elemental sulfur.

Continued interest regarding the rheometric measurements of molten sulfur has persisted due to the need for industrial-scale transportation and handling of the material in a liquid phase. This has allowed for extended research developments to attain a fundamental understanding of the fluid. This work reports novel high temperature modulus data over the λ-transition region for liquid elemental sulfur, measured through the use of a modified Anton-Paar Modular Compact Rheometer 302. From these measurements, further insight was gained on the viscoelastic behavior and reptative relaxation times for liquid elemental sulfur. The slow relaxation time, τs, related to reptative behavior, was found to be between 0.24 s and 0.28 s at 190 °C. Utilizing the Maxwell relation, this was determined to correspond to an estimated viscosity range from 72 000 × 10-3 Pa s to 95 000 × 10-3 Pa s, which is in agreement with previous viscosity studies on liquid sulfur. A Cole-Cole plot of the experimental data also displayed characteristics of Debye-like relaxation, suggesting that the slow relaxation process was related to local S-S bond scission and recombination in sulfur chains and was not a relaxation coinciding with a polymeric chain mode. Finally, consecutive heating and cooling of the sulfur sample gave replicate values up to 210 °C on the third heating cycle, where an apparent structural change took place possibly due to cycling over the secondary transition, producing a thermal history, or sulfur reactions with trace impurities. This 210 °C temperature was found to have some recurrence within the literature.

Dielectric relaxation in zinc-borotellurite glasses doped with alkali, transition and rare earth oxides

A batch of zinc borotellurite glasses doped with Li2O, W2O3 and rare earth ions were synthesized with varied composition and investigated for dielectric properties in the frequency range from 50Hz to 15MHz and temperature from 300K to 620K. Electric moduli and impedance were estimated. Dielectric relaxation time from both impedance and moduli data were determined. Activation energy for relaxation time has been determined. Nature of the phase of the glasses has been understood in terms of cole-cole plots. Normalized moduli plots were made to learn temperature dependance of relaxation processes. For the first time, glasses of the present composition have been exposed for detailed dielectric relaxation studies.

Complex Modulus Testing and Rheological Modeling of Cold-Recycled Mixtures

Abstract This research compares the rheological behavior of different cold-recycled mixtures (CRMs) produced in-place through full-depth reclamation. Reclaimed asphalt pavement (RAP) obtained from the milling of the old asphalt layers was blended with reclaimed unbound aggregate from the existing subgrade. Asphalt emulsion, foamed asphalt, and portland cement were employed as stabilizing agents. The complex modulus was measured on cylindrical cores, applying a sinusoidal strain with an amplitude of 30 microstrain at testing temperatures ranging from 0°C to 50°C and frequencies ranging from 0.1 to 20 Hz. The Huet-Sayegh (HS) rheological model was applied to simulate the experimental data. The results showed that the behavior of CRM is thermo- and frequency-dependent and that the time-temperature superposition principle can be applied. The HS model provides an excellent fitting of the dynamic modulus data, whereas fitting of the loss angle data was improved, introducing a temperature- and frequency-independent correction. The RAP influences the rheological behavior, but viscous dissipation is mainly due to the asphalt-stabilizing agents (emulsion residue or foamed asphalt).

Evaluation of variability characteristics of mechanical parameters of artificially frozen clay in deep alluvium

The uncertain mechanical parameters of artificial frozen soil in deep alluvium are the key factors for computing the stochastic stress fields and stochastic deformation fields of artificial freezing engineering. In this study, a series of mechanical parameters tests for the artificially frozen clay are carried out, and the statistical data of elastic modulus, strength and Poisson ratio of frozen clay under three different low temperature conditions (−20 °C, −15 °C and −10 °C) are obtained. The experimental semi-variogram values of the mechanical parameters for artificially frozen clay under different temperature conditions are calculated and analyzed. The results show that the test data meets the requirements of the coefficient of variation analysis and the elastic modulus, strength and poisson ratio basically meet the normal distribution. The variability of the mechanical parameters for artificially frozen clay is basically in the degree of moderate to weak variability. The optimal theoretical variation function model of basic mechanical parameters of frozen clay is Gaussian model. The correlation of soil parameters calculated by Gauss model at smaller distances is greater than that of Exponential model and Spherical model. The mechanical parameters of artificially frozen clay are strongly dependent in spatial range. This study can improve our understanding of the variation characteristics of uncertain mechanical parameters for artificial frozen soil in deep alluvium and provide a theoretical basis and reference for the stochastic mechanical analysis of artificial freezing engineering.

Thermal stability and ionic conduction characteristics of lithium germanate glasses

A report is given of the systematic investigation on the glass stability and conduction characteristics of binary lithium germanate glasses in the series, mol% xLi2O-(100-x)GeO2, 5 ≤ x ≤ 30. The glass stability (against devitrification) parameters along with density and glass transition temperature reveal an extremum around 15 mol% of Li2O, a signature of the germanate anomaly. The analysis of impedance data in conductivity and modulus formalisms reflect different aspects of the structural changes as the amount of Li2O increases. The lithium ion conductivity increases with the increase in the Li2O concentration while the activation energy for ionic motion does not change much from mol% 5 to 10 Li2O and decreases monotonically from mol% 10 to 30 Li2O indicating the absence of germanate anomaly. However, the data in modulus formalism does not scale to a master curve for all the glasses suggesting the germanate anomaly. Modeling of the modulus data using the Kohlrausch-Williams-Watts (KWW) function depicts the germanate anomaly in the stretched exponential parameter (β) at 15 mol% Li2O. Raman spectra of the glasses reveal the preferential formation of Q2 units at low alkali concentration along with the formation of ring structures of several Ge tetrahedra and/or the formation of higher coordinated Ge species around the anomalous composition region. A correlation of these structural changes with the conduction characteristics of the glasses is also discussed.

Microfibrillated lignocellulose (MFLC) and nanopaper films from unbleached kraft softwood pulp

Microfibrillated cellulose (MFC) is an important industrial nanocellulose product and material component. New MFC grades can widen the materials property range and improve product tailoring. Microfibrillated lignocellulose (MFLC) is investigated, with the hypothesis that there is an optimum in lignin content of unbleached wood pulp fibre with respect to nanofibril yield. A series of kraft fibres with falling Kappa numbers (lower lignin content) was prepared. Fibres were beaten and fibrillated into MFLC by high-pressure microfluidization. Nano-sized fractions of fibrils were separated using centrifugation. Lignin content and carbohydrate analysis, total charge, FE-SEM, TEM microscopy and suspension rheology characterization were carried out. Fibres with Kappa number 65 (11% lignin) combined high lignin content with ease of fibrillation. This confirms an optimum in nanofibril yield as a function of lignin content, and mechanisms are discussed. MFLC from these fibres contained a 40–60 wt% fraction of nano-sized fibrils with widths in the range of 2.5–70 nm. Despite the large size distribution, data for modulus and tensile strength of MFLC films with 11% lignin were as high as 14 GPa and 240 MPa. MFLC films showed improved water contact angle of 84–88°, compared to neat MFC films (< 50°). All MFLC films showed substantial optical transmittance, and the fraction of haze scattering strongly correlated with defect content in the form of coarse fibrils.Graphic abstract

Local process-dependent structural and mechanical properties of extrusion blow molded high-density polyethylene hollow parts

Although applied for several decades, production of hollow plastic parts by extrusion blow molding (EBM) is still over-dimensioned. To overcome this issue, a thorough investigation of the process-structure-property relationship is required. In this study, the local process-structure-property relationship for high-density polyethylene EBM containers is analyzed with differential scanning calorimetry and dynamic mechanic analysis microindentation. Local process-dependent crystallinity and complex modulus data at various processing conditions are supplemented with wide-angle X-ray diffraction and transmission electron microscopy (TEM). The crystallinities and the complex moduli clearly show lower values close to the mold side than at the inner side and the middle of the cross-section, which reflects the temperature gradient during processing. Additionally, the orientation of the polymer chain (c-axis) reveals a low level of biaxiality with a slight tendency towards transverse direction. The biaxiality increases for low mold temperature and high draw ratio. Finally, biaxiality is confirmed with TEM, which reveals no preferred lamellar orientation.

Investigation on modulus of elasticity of fly ash-ground granulated blast furnace slag blended geopolymer concrete

Alkali-activated geopolymer binder is an upcoming alternative to Ordinary Portland Cement (OPC) binders because of its environment-friendly nature. Production of Cement liberates large amounts of CO2 into the environment leading to global warming and in the other direction scarcity of natural resources for cement production necessitates the introduction of Geopolymer Concrete (GPC) to the construction industry. The present paper investigates the mechanical behaviour of Geopolymer GPC synthesized by fly ash and Ground Granulated Blast Furnace Slag (GGBS) at ambient curing conditions. To predict the values, experimental data of Modulus of Elasticity (MOE) values are compared with codes and previous literature. The Equation was proposed to calculate MOE based on the experimental compressive strength of GPC. The experimental data is evidently representing the predicted values are almost equal to laboratory tested values. It was recognized that the equations originate in various codes and published papers are predicted the superior result of the MOE than those find with the proposed equation.