Dynamic Mechanical Analysis Method Research Articles

Multiplet relaxation transitions in fluorurethane coating after climate aging

The relaxation transition from a glassy to a highly elastic state (α-transition) of a fluoropolyurethane coating deposited on the surface of VPS-48/778 glass fiber reinforced plastic was studied using the method of dynamic mechanical analysis. It is shown that the relaxation maximum of the dynamic loss modulus in the initial state is a superposition of α1-, α2-, α3-transitions, corresponding, respectively, to transitions from the glassy to highly elastic state of VE-69 enamel and EP-0215 epoxy primer. The transition temperature α1, which is the glass transition temperature of fluoropolyurethane VE-69, after 3 years of exposure decreases in proportion to the average annual air temperature of the region. The transition temperatures α2 and α3 after full-scale exposure due to post-curing increased by 13−15°C and acquired stable values α2 = 99 ± 1°C, α3 = 122.5 ± 0.5°C, regardless of the climatic conditions of the tests.

Repercussion of fiber content on the mechanical, thermal, and thermomechanical properties of natural fibers reinforced thermoplastic composites for automotive application

Natural fibers are becoming very popular as a reinforcement in composite materials owing to their benefits, such as low-price, lightweight, availability, and environmental friendliness. In this study, abaca fiber-reinforced polypropylene (PP) and high-density polyethylene (HDPE) composites were created with the help of the injection molding method. Prior to composite fabrication, abaca fibers were chemically treated with a 5 wt% caustic soda (NaOH) solution to improve the bonding between the abaca fibers and the matrix and to enhance their properties. Scanning electron microscopy (SEM) was utilized to assess the fiber surface microstructures before as well as after the chemical treatment, along with the fractured surfaces of tensile specimens. The mechanical properties, such as tensile, bending, and impact strength, of abaca/PP and abaca/HDPE composites were evaluated and compared. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) methods were utilized to investigate the thermal behavior of composites. Also, the dynamic mechanical analysis (DMA) method was utilized to explore the thermomechanical properties of the fabricated composites. The outcomes of the experimental findings showed that abaca/PP composite with 10 and 20 wt% fibers is the best choice of material to be used in the automobile industry.

Comparative Study on Mechanical Response in Rigid Pavement Structures of Static and Dynamic Finite Element Models

The safety of airport runways is important to guarantee aircraft taking-off, landing, and taxiing, and the comparison of the mechanical response of pavement structures under dynamic and static loading by LS-DYNA has rarely been studied. The purpose of this work is to separate two analysis methods to investigate the mechanical response of rigid airport pavements. Firstly, a tire–road coupling model of an airfield was established to evaluate the suitability of dynamic and static analyses. Then, the effects of landing pitch angles, sinking speeds, and tire pressures on the effective stress, effective strain, and z-displacement of the runway were investigated for both dynamic and static analysis. Finally, the significance of influence factors was analyzed by regression analysis in Statistical Product and Service Solutions (SPSS). The results indicated that the effective stress, effective strain, and z-displacement of the runway increased with a decrease in the landing pitch angle, which also increased with an increase in the sinking speed and tire pressure. It was demonstrated that the difference in pavement mechanical response between dynamic and static analyses progressively widened at high tire pressure and sinking speed. In other words, the static analysis method can be adopted to assess the dynamic mechanical behavior when the landing pitch angle is large and the tire pressure is small. Among the various factors of mechanical response, the effect of tire pressure was the most obvious, followed by sinking speed and landing pitch angle. The work proposes a new approach to understanding the mechanical behavior of runways under complicated and varied conditions, evaluates the applicability of the dynamic and static mechanical analysis methods, identifies key factors in the dynamic and static mechanical analysis of rigid runways, and provides technical support for improving and maintaining the impact resistance of pavement facilities.

Characterization Methods to Determine Interpenetrating Polymer Network (IPN) in Hydrogels.

Significant developments have been achieved with the invention of hydrogels. They are effective in many fields such as wastewater treatment, food, agriculture, pharmaceutical applications, and drug delivery. Although hydrogels have been used successfully in these areas, there is a need to make them better for future applications. Interpenetrating polymer networks (IPNs) can be created to make hydrogels more adjustable and suitable for a specific purpose. IPN formation is an innovative approach for polymeric systems. It brings two or more polymer networks together with entanglements. The properties of IPNs are controlled by its chemistry, crosslinking density, and morphology. Therefore, it is necessary to understand characterization methods in order to detect the formation of IPN structure and to develop the properties of hydrogels. In recent studies, IPN structure in hydrogels has been determined via chemical, physical, and mechanical methods such as Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (XRD), and rheology methods. In this paper, these characterization methods will be explained, recent studies will be scrutinized, and the effectiveness of these methods to confirm IPN formation will be evaluated.

Fatigue behavior of polymethyl methacrylate/acrylonitrile butadiene styrene blends including blend composition, stress ratio, frequency, and holding pressure effects

In engineering applications, polymer materials are expected to exhibit superior fatigue life and balanced mechanical properties as essential performance criteria. The blending method is an important alternative in improving the performance criteria of ABS polymer in service. Thermogravimetric Analysis (TGA), Differential Scanning Calorimetry (DSC), Fourier Transform Infrared Spectroscopy (FTIR), and Dynamic Mechanical Analysis (DMA) methods were used for characterization. The effects of the PMMA fraction on the mechanical and fatigue behavior of PMMA/ABS blends were investigated by tensile and fatigue tests. Also, the influence of blend composition, stress amplitudes, stress ratio, holding pressure, and loading frequency on fatigue life is considered. The study improved yield strength, tensile strength, and elongation at break values of blends compared to ABS. In addition, 115 % and 75 % improvements were achieved in fatigue cycles at high and low-stress amplitudes with blends, respectively, for tension/tension loading. Similar improvements were obtained for fully reverse loading at 218 %. Thus, it was determined that the PMMA/ABS blend exhibited superior fatigue life in both tension/tension and fully reverse loading situations. Finally, it has been understood that PMMA/ABS blends can be designed to have mechanical properties and fatigue life behavior that can meet different requirements in conditions for engineering applications.

Spectral analysis and dynamic properties of polyurethanes dyed with rhodamine 6G and rhodamine B as matrices of a solid-state laser element

A comparison was carried out of the nature of intermolecular interactions, elastic properties and gas permeability of the crosslinked polyurethanes doped with xanthene dyes and original polyurethane using IR spectroscopy, dynamic mechanical analysis (DMA) and electron paramagnetic resonance (EPR). The introduced dye can be considered as useful microimpurity which, however, can affect the efficiency of the laser. In IR spectra of polyurethanes the complex band of stretching vibrations of C=O groups is sensitive to the nature of intermolecular interaction of urethane groups. From the analysis of that band it is shown that in the presence of dyes, self-association of urethane groups within the hard segment predominates and the interaction of urethane groups with the oligoether component decreases, which can contribute to increasing the mobility of the flexible component. A decrease in the dynamic storage modulus (E’) and a decrease in the glass transition temperature (Tc) of polyurethanes in the presence of dyes is shown by the DMA method. The results of both DMA and IR spectroscopy indicate a greater increase in the mobility of the elastic component with the introduction of the rhodamine B dye, covalently bound to the polyurethane chain. According to nitroxyl paramagnetic probe data the introduction of both rhodamine B and rhodamine 6G dyes into polyurethanes increases their permeability to vapors of low-molecular weight compounds, but rhodamine 6G has a more prominent effect on this characteristic. This is consistent with DMA data indicating a greater increase in the Mc value in the presence of rhodamine 6G in polyurethane. The obtained results make it possible to determine the optimal composition of the active laser medium and are important in assessing the radiation resistance of the polymer matrix. Its increase is facilitated by a decrease in the storage modulus and an increase in the gas permeability of the polymer, leading to a decrease in pressure in the area of local heating.

Characterization of viscoelastic properties of yarn materials: Dynamic mechanical analysis in the transversal direction

Abstract Warp knitting creates very challenging dynamics due to its high production speeds. On the one hand, this makes it method of choice for many products in various fields. On the other hand, not all materials are suitable for such high productivity. With the current generation of machines being limited to only achieve their maximum speed of around 4,400 min−1 with highly elastic yarns, it is desired to gain a deeper insight into yarn behavior in such highly dynamic environments. Among other influences, resonance effects gain high significance as they may result in high loads on the used materials; therefore, yarn breakages interrupt the production and decrease the quality of the product. To extend the material choice, especially high-performance fibers, for high productivity, a deep understanding of the intrinsic properties of the yarn is required. In particular, the viscoelastic properties are of importance. This study proposes a method to determine these characteristics using the dynamic mechanical analysis method. For the purpose of finding the damping in the transversal direction to the yarn axis, the variant of free oscillation is chosen. For the trials, a high-speed camera is suspended above a testing rig. On this rig, a yarn sample is clamped and then displaced from its rest position. The resulting oscillation is recorded and later extracted from the video. From the decrement of the maxima of the amplitude and corresponding time intervals, the damping factor is determined. It decreases with higher initial deflection. Summarised the developed trial setup proved suitable for the determination of the viscoelastic properties in transversal direction.

Determination of the ignorable boundary condition and standard sample for a novel in-situ dynamic mechanical analysis method on soft matter

An in-situ Dynamic Mechanical Analysis (DMA) method for soft matter developed by our group [Wu. et.al. 2022] encounters the problem of irregular samples, which significantly vary in shape and size in practice, therefore a standard sample “large enough” to ignore the boundary and size effects is necessary to determine the baseline of test and build the correspondence between this new method to classical mechanical tests. In this work, we use finite element analysis to approach the optimal size of a brick sample where the stress on the boundaries in three spatial directions are ignorable, and certified the results by testing a series of silicone gel samples on the in-situ DMA device. The stress-strain of tensile and compression are characterized. The material properties of gel are chosen to be close to the biological soft tissue. The size of 40mm(L)×40mm(W)×20mm(H) is determined to be the optimal result.

Structure, and Mechanical and Thermal Properties of Vinyl-Polydimethylsiloxane/Zinc Dimethacrylate/Isobutylene-Isoprene Rubber Composites

The vinyl-polydimethylsiloxane (v-PDMS) composite reinforced by micron size ZDMA particles previously showed high modulus, thermal stability, solvent-proofness, and good processing ability. However, its poor damping properties limited usages. Thus, incorporation of new polymers into the composite was imperative to improve its loss factors. With a similar solubility parameter and good damping properties, isobutylene-isoprene rubber (IIR) was melt-blended in, then heat-pressed and cross-linked. The v-PDMS/ZDMA/IIR composites gotten were characterized by scanning electric microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), mechanical tests, dynamic mechanical analysis (DMA) and thermal gravimetric analysis (TGA) methods. The IR spectra of the composites illustrated that the incorporation of IIR was successful. The SEM observation showed good dispersion of the IIR, and the increasing deformation on the surface with growing dosage of IIR. The incorporation of IIR rubber decreased the composite’s modulus sharply and also the tensile strength, but improved the elongation and damping properties of the v-PDMS/ZDMA composites at low temperature. The TGA test results in N2 gas showed the composites had good thermal stability below 350 °C, then deteriorated at higher temperature owing to the decomposition of the IIR at 400 °C. The decomposition activation energy at 400 °C was determined by the Kissinger method.

Measurements and estimation of frequency-dependent multi-scale viscoelastic damping properties of materials

The state-of-art viscoelastic property measurement and estimation methods at different frequencies/length scales inherently couple structural effects or sometimes lose accuracy for relevant parameters at smaller length scales in the material. We report a unified approach to measuring and estimating the frequency-dependent viscoelastic damping properties across different frequency scales independently of the specimen size effect and boundary conditions. The Dynamic Mechanical Analysis (DMA) method with three-point bending configuration is extended to higher-fidelity modeling in terms of time–frequency scales and material micro-mechanical scales together. The methodology demonstrates ways to identify the possible sources of undesired dynamics in the measurement process and eliminate those effects. It includes exciter tip contact dynamics in three-point bending configuration, anharmonic energy transfer to different frequencies (fractal bifurcation), and unmodelled artifacts or noise. Critically reviewing the standard DMA procedure with normal mode synthesis, this paper proposes a time–frequency Fourier spectral method that resolves a broader frequency range that extends to even acoustic/ultrasonic wave regimes of viscoelastic damping. An algorithm proposed in this paper with the advanced viscoelastic model with multi-parameters (standard linear solid model) estimates the fundamental material parameters at small length scales, which is more insightful to obtain a frequency-dependent correlation of material response to general dynamic loading. Stiffness and damping properties are estimated from measured data and validated for self-consistencies via different controls regarding static preload, specimen resonance, filtered noise, and model fidelity across the frequency range, and certain consistency and convergence properties of a series solution. The unified approach with a single test will be helpful in the design and evaluation of a wide variety of materials and their applications in vibration and acoustic problems. The proposed technique further demonstrates a novel way to extend low-frequency measurement to high-frequency response modeling.

Irradiation effects and photostability of aerosil-filled polyurethane as a matrix for laser solid-state elements

Photooxidation processes during irradiation of the aerosil-filled polyurethane films, based on oligooxypropylene glycol, toluene diisocyanate and trimethylolpropane, for a use as the active media of solid-state lasers were investigated by means of the IR-spectroscopy and dynamic mechanical analysis (DMA) methods, depending on the inorganic dopant concentration (5 and 7 wt%). The IR-spectroscopic experiments showed that the introduction of aerosil slowed down these processes. Data from dynamic mechanical studies indicated that irradiation of aerosil-filled polyurethane matrices caused an increase in its structural heterogeneity and a drop of the elastic modulus. During irradiation of the polyurethane material with 7 wt% of aerosil, a partial destruction of the nanofiller spatial network was possible due to dispersion of the irradiation energy by the nanoparticles. The obtained results demonstrated a positive effect of the aerosil nanofiller on the polyurethane material stability under irradiation with an ultra-high pressure mercury lamp.

Isothermal curing analysis and properties of ultra heat‐resistant polyimide composites by DMA method

AbstractThe isothermal curing process of T700 carbon fiber/P450 polyimide prepreg is characterized by dynamic mechanical analysis method and the gelation points are analyzed by torsional braid analysis theory. The growth mechanisms of the mechanical property at different constant temperatures are investigated by the relative mechanical growth rate of storage modulus and the curing kinetics models are established. The theories of Flory and Hsich are used to calculate the activation energy during the curing reaction of prepreg. The results indicates that the gelation times which are detected by the method of torsional braid analysis at 300, 310, 330, and 350°C were 293.7, 213.8, 104.1, and 45.4 min, respectively. The activation energies of curing reaction are calculated by Flory theory and Hsich theory, they are 112.35 and 119.96 kJ/mol, respectively. The feasibly of curing system 300°C × 4 h + 330°C × 2 h + 350°C × 2 h + 370°C × 2 h is verified by the mechanical properties and the heat resistance of polyimide composite.

Composite Films Based on Methyl Cellulose Mixtures with Poly(urethane-imide) Obtained from Their Solutions in Dimethylacetamide

Composite films of methyl cellulose and poly(urethane-imide) are obtained. At the poly(urethane-imide) content in the films above 50% phase separation of the polymers is observed. Using the methods of dynamic mechanical analysis and X-ray diffraction the structural organization of the films is studied, the temperatures of relaxation transitions are determined, and the mechanical characteristics of the composite films are investigated.

Contributing Factors of Uneven Climatic Aging for Polymeric Composite Materials: Methods and Modelling

Regarding a wide variety of PCMs, the materials' strength properties which decrease no more than 20% after 30 years of operation are of special interest. One of the important regularities of the climatic aging of PCMs is the formation of gradients of mechanical parameters across the thickness of the plates. The occurrence of gradients must be taken into account when modeling the strength of PCMs for long periods of operation. At present, there is no scientific basis for the reliable prediction of the physical-mechanical characteristics of PCMs for a long period of operation in the world of science. Nevertheless, "climatic qualification" has been a universally recognized practice of substantiating the safe operation of PCMs for various branches of mechanical engineering. In this review, the influence of solar radiation, temperature, and moisture according to gradients of mechanical parameters across the thickness of the PCMs are analyzed according to the data of dynamic mechanical analysis, linear dilatometry, profilometry, acoustic emission, and other methods. In addition, the mechanisms of uneven climatic PCM aging are revealed. Finally, the problems of theoretical modeling of uneven climatic aging of composites are identified.

Dynamic Characteristics of a Novel Right-Angle Viscoelastic Damper (RVD) Using Polyurethane Damping Materials

Excessive plastic deformation may occur at the beam-column joints under seismic action and lead to connection failure, increasing the possibility of collapse of the entire frame structure. In order to improve the seismic performance of assembled steel structure joints, a right-angle viscoelastic joint damper with polyurethane as the core energy dissipation material is proposed in this paper. First, the temperature scanning tests of polyurethane materials were carried out based on the dynamic mechanical analysis method. Second, the dynamic mechanical test and numerical simulation analysis of the designed right-angle viscoelastic damper were performed to reveal the dynamic energy dissipation characteristics of the right-angle damper. Finally, the dynamic time-history damping analysis was performed on the steel frame structure equipped with RVDs. The results show that the TA value of polyurethane material reached its peak at 2.0 Hz, which is the ideal frequency for the material’s damping ability. The right-angle damper made of polyurethane material has a softening nonlinear characteristic, and the peak value of the loss factor was obtained at 2.0 Hz, which is consistent with the results of the dynamic performance of the polyurethane material. The numerical simulation results demonstrate that stress on the steel plates and viscoelastic layers is reasonable. When the excitation level did not exceed 9 mm displacement amplitude, the energy input to the damper was dissipated by polyurethane, and the steel plates never showed plastic deformation. The time-history analysis of the steel structure shows that the dampers designed in this paper have a good control effect on the interstory displacement, acceleration, and interstory shear force of the structure. The research results lay the necessary foundation for the engineering application of polyurethane materials in the field of beam-column joints vibration damping.

Study of temperature fields in samples of polymer materials using dynamic mechanical analysis

The goal of the study is to reveal the dependence of the glass transition temperature on conditions of its determination. We present the results of studying temperature fields in the samples of polymer materials by the method of dynamic mechanical analysis. Changes in the glass transition temperature of the poly­mer casting VSE-34 and the temperature profile in the polymer matrix ED-20/DAFS were analyzed. Stan­dard melting samples were used to correct the test results using the correction function. It is shown that the most significant temperature deviations are observed when measured in argon and helium media with heating rates of 1, 2, 5, and 5 K/min. The temperature distribution over the polymer casting sample is highly non-uniform. The difference between the temperature in the middle and at a distance of 1/4 from the edge of the sample equals 16°C (medium — argon, heating rate — 5 K/min). Moreover, at a heating rate of 1 K/min, abnormally low values of the glass transition index were marked. The results obtained can be used to improve the measurement procedure, reduce test duration and refine the results of tests in various gaseous media.

Послойный динамический модуль сдвига в поперечном сечении древесностружечной плиты

The research results are aimed at the formation of ideas concerning the features of molecular motion of the components of the outer and inner layers of the particle board material in the temperature range from room temperature to 275–300 °C, as well as at revealing the fact of binder undercuring in the inner layers. The paper provides data on the temperature dependences of the dynamic shear modulus of the outer and inner layers of the particle board material, obtained by dynamic mechanical analysis using a torsion pendulum. We found significant differences in the nature of the dependencies for samples taken at different distances from the surface layers. The material of the outer layers is characterized by the typical pattern of a continuous irregularly consistent decrease in the dynamic shear modulus with increasing temperature, which is common to most polymeric and composite materials. A short-term intermittent increase in the dynamic shear modulus relative to neighboring areas was detected in the inner layers at 140±5 °C, which is not typical for materials in a stable state. There is also a tendency for the dynamic shear modulus of the particle board material to decrease at room temperature with distance from the outer layers, due to the heterogeneous fractional composition and differences in the nature of chemical cross-linking during hot pressing. It has been assumed that the detected anomalous increase in the dynamic shear modulus in the inner layers of the material at 140±5 °С is a symptom of the binder post-treatment process directly in conditions of its heating when measuring the dynamic shear modulus by dynamic mechanical analysis. Thus, it is concluded that the particle board sample shows maximum curing of the thermosetting binder in the layers, which are 4.5–5.0 mm distant from both surfaces. Partial undercuring of the binder occurs in the inner layers, which are more than 5.5 mm away from the surfaces. Thus, it is shown that the method of dynamic mechanical analysis can be used as a tool to control the presence in the inner layers of the particle board material of the components of thermosetting binder, undercured in the hot pressing process, which will help to obtain a material with more stable characteristics.

Long-Term Performance Evolution of RIOHTrack Pavement Surface Layer Based on DMA Method.

Asphalt mixture is a typical viscoelastic material, and its road performance will change with the action of environment and load during actual service. This study conducted experimental research on the surface course asphalt mixture of three categories and six typical structures of RIOHTrack based on the Dynamic Mechanical Analysis method. Moreover, this study explored the performance evolution law of asphalt mixture under the coupling action of load and environment in the process of loading from 0 million to 54 million standard axle times. Results demonstrated that the phase transition characteristic temperature of the surface course materials of the three types of typical structures showed a trend of first increasing and then decreasing with the accumulation of load and environmental effects, indicating the presence of two stages of the dual coupling effect of environmental aging and load rolling on the asphalt mixture during service. In addition, the results suggested that the phase transition characteristic temperature, modulus, and phase angle of the surface layer materials have obvious material differences and structure dependencies.

Local deformation on damping performance of integral-forming aluminum foam sandwich

Damping performances of porous metals are generally measured by dynamic mechanical analysis (DMA) method which has strictly dimensional requirements on specimens especially on their thickness. In this work, based on sinusoidal excitation and Fourier transform, a new set of test equipment suitable for evaluating damping performances of large-scale porous metals was constructed. On this basis, the influence of local compression deformation on the damping performances of the newly developed integrated-forming aluminum foam sandwich (IFAFS) was investigated by means of single-point excitation method. Damping performances of different regions were obtained through partition measurement and the reasons were discussed which are beneficial to evaluate damping performances of IFAFS after local deformation.

An experimental investigation on the thermal and mechanical characterization of boron/flax/PLA sustainable composite

The current study deals with the effect of boron compounds, zinc borate (ZB), borax: boric acid combines (BxBc), and ulexite which are used to improve fire resistance, on the thermal, microstructural, and mechanical properties of the flax/PLA biocomposites. For this purpose, the mechanical properties of the biocomposites were determined by tensile, impact, and three-point bending tests. Thermogravimetric analysis and the UL-94 burn test were conducted to determine the thermal properties of composites, such as thermal stability and flammability. Thermo-mechanical properties and viscoelastic characteristics of biocomposites were determined by the dynamic mechanical thermal analysis method. Test results showed that ulexite addition could significantly reduce the burning rate by 80%. However, although mechanical properties were adversely affected by the incorporation of boron compounds resulting in a drop of up to 20%, it is believed that boron compound-filled flax/PLA composites have mechanical and thermal properties that can be considered as an alternative material, especially for the automotive industry.