Dynamic Mechanical Analysis Tests Research Articles

Experimental measurements through ultrasounds for viscoelasticity analysis

Among the different methodologies useful to determinate polymers viscoelastic properties in literature, it is possible to find some different techniques based on the ultrasounds pulse-echo methods which show several limits in the properties estimation of the tested materials. In this scenario, the proposed manuscript focuses on an innovative non-destructive technique of viscoelastic materials by means of ultrasounds, which could be suitably employed on polymers. The developed procedure is aimed to evaluate the material response in terms of loss factor within different temperatures and induced excitation frequencies. To carry out the viscoelasticity analysis through ultrasounds, a bench has been set up and the data acquisition has been performed by means of the pulse-echo method on three different tires tread specimens and, then, a post-process algorithm has been implemented in order to determine the viscoelastic behavior in terms of loss factor. The comparison of the achieved results with the temperature sweep master curves, which were determined by means of standard Dynamic Mechanical Analysis (D.M.A.) testing on the same polymers, has provided an indication of the goodness of the proposed procedure.

Role of initial stored energy on hydrogen microalloying of ZrCoAl(Nb) bulk metallic glasses

In this paper, the role of primary stored energy and structural heterogeneity on the subsequent effects of hydrogen microalloying in glassy alloys was studied. For this purpose, two bulk metallic glasses with different chemical compositions and initial stored energy, i.e. Zr60Co30Al10 and Zr55Co30Al10Nb5, were fabricated in a hydrogen-induced environment. Dynamic mechanical analysis and nanoindentation tests were carried out to evaluate relaxation behavior and mechanical properties of bulk metallic glasses, respectively. The nanoindentation results indicated declining serrations in load–displacement curves of hydrogen-affected samples. This event was related to the annihilation of localized deformation in hydrogen-affected samples under the external load. Moreover, the dynamic mechanical analysis showed that the hydrogen microalloying process improved the plasticity behavior of metallic glasses by activating fast β′ relaxation. Finally, the results unveiled that the higher initial structural heterogeneity and stored energy in the bulk metallic glass with the alloying composition of Zr55Co30Al10Nb5 led to the improvement of microalloying effects on the corresponding properties.

Experimental Study on Dynamic Properties of a Recycled Composite Sleeper and Its Theoretical Model

As a symmetrical structure in track system, the dynamic properties of recycled composite sleepers are important factors affecting the vibration characteristics of track structure. To study the viscoelastic dynamic properties of the composite sleeper, dynamic mechanical analysis (DMA) tests of a composite sleeper at −5 to 30 °C and 1–60 Hz were first carried out, and then the time-temperature superposition (TTS) and the Williams–Landel–Ferry (WLF) formula were used to predict the dynamic properties of a composite sleeper at a wider frequency range. Finally, the generalized Maxwell model was adopted to characterize the dynamic properties of the composite sleeper, which provides parameters and theoretical models for dynamic analysis. The research results show that the composite sleeper has obvious viscoelasticity. Its modulus is large at low temperature or high frequency. On the contrary, the modulus is small at high temperature or low frequency. Under the test conditions, its complex modulus ranges from 1500 to 2700 MPa. The loss factor is in the range of 0.08–0.13. Using the generalized Maxwell model (n = 4), which can better reflect the dynamic properties of the composite sleeper.

Effect of diesel and microwave on the properties of crumb rubber and its modified binders

Some novel methods are introduced to improve thermal storage stability and pavement performance of crumb rubber modified binder. In this paper, the objective was to investigate the effects of compound activation on the molecular structure and physical properties of crumb rubber, as well as rheological properties and thermal storage stability of crumb rubber modified binders. Two activation methods, with and without diesel pre-swelling, and six microwave radiation intensities were designed in this study. Fourier transform infrared spectroscopy (FTIR) test, swelling equilibrium test and dynamic mechanical thermal analyzer (DMA) test were performed to evaluate the characteristic functional groups and physical properties of crumb rubbers before and after activation. Additionally, rheological properties test at various service temperatures and thermal storage stability test were carried out on the crumb rubber modified binders. The results show that certain microwave radiation intensity would break the C-S and C=S bonds and reduces the cross-linking density of crumb rubber. Activation mode was the main factor affecting high temperature stability, fatigue life and low temperature relaxation property rather than microwave radiation intensity compared with control one. In addition, thermal storage stabilities of activated crumb rubber modified binders were better than control one. The more radiation intensity, the improvement effect of thermal storage stability is. Synthesizes each kind of property, diesel pre-swelling and microwave radiation intensity of 1.2 kJ/g was a preferable combination in this study.

Flexible epoxy graphene thermoset with excellent weather and corrosion resistance

The chemical-bonding-dispersed method was used to develop a functional graphene oxide/epoxy nanocomposite coating with multifunctional properties and long-term stability for anticorrosion and weather resistance purposes. This study compared relevant properties before and after ultraviolet (UV) irradiation of the chemical-bonding-dispersed nanocomposite, a physically blended composite, and a neat polymer by using Fourier-transform infrared spectroscopy, X-ray diffraction, transmission electron microscopy, ultraviolet aging, contact angle testing, electrochemical corrosion studies, dynamic mechanical analyzer testing, thermogravimetric analysis, flexibility testing, and an adhesion test. The as-prepared nanocomposite prevented the yellowing of epoxy resin, demonstrating the nanocomposite’s durability under UV light. Furthermore, the nanocomposite exhibited excellent anticorrosion properties. Anticorrosion performance with a corrosion rate of 6.10 × 10−3 mil/year and a corrosion efficiency of 99.99 % was attained with a thin-film coating of approximately 10 μm, and it retained a corrosion rate of 1.50 × 10-2 mil/year with a corrosion efficiency of 99.98 %. The results of the long-term durability tests performed using the electrochemical impedance spectrum indicated that the chemical-bonding-dispersed nanocomposite was superior to the physically blended dispersed composite and pure epoxy coating. The nanocomposite coating retained its high impedance over long-term durability tests, with a charge transfer resistance of 8.73 × 107 Ω·cm2 after 90 days. This study demonstrated the durability of the anticorrosion, mechanical, thermal, and degradation properties of the designed coating material before and after UV irradiation.

Investigation of the influence of carbon black on the rheology and electromechanical properties of ethylene butene copolymer

In this scientific article, the potential of producing a highly capable sensor by the addition of electric conductive carbon black (CB) to polymer composite was studied, and the effects of various carbon black content on ethylene-butene copolymer (EBC) on rheological and electromechanical were investigated. Electric conductive composites have many attempts at producing original material in technology as a sensor. The amount of (0, 4.07, 6.31, 8.71, and 11.28) volume % of CB was introduced to EBC using Brabender, mixed, and homogenized for 5 min at 180 °C. The dynamic mechanical analysis (DMA) and electromechanical test show that the addition of CB to the EBC would increase the viscosity, modulus, while electric resistance significantly decreased and changed greatly with elongation. The modulus increased from 8.9 to 15 MPa by increase of from 15 to 25 wt% of CB while the gauge factor decreases for about five times by increasing the CB from 15 to 25 wt% under 5 N force. These works demonstrate the possibility of producing strain sensors using a cheap and versatile technique, with potential health and electromechanical sensors.

Electrochemical and dynamic mechanical studies of newly synthesized polyurethane/SiO2-Al2O3 mixed oxide nanocomposite coated steel immersed in 3.5% NaCl solution

SiO2-Al2O3 mixed oxide nanoparticles were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffractometry (XRD) analysis. The anticorrosion behaviour of PU/SiO2-Al2O3 nanocomposite coating was investigated by SECM, polarization studies and EIS for 1 h, 240 h, 480 h, and 720 h of immersion in 3.5% NaCl solution. EIS studies showed a pronounced protection performance for PU/SiO2-Al2O3 coating in 3.5% NaCl. SECM analysis measured lower current for the PU/SiO2-Al2O3 at the scratch of the coated surface compared to PU coating. Dynamic mechanical analysis (DMA) test provided valuable information about the protective performance of the PU/SiO2-Al2O3 nanocomposite coated surface. The formation of thin films of oxides and chlorides of Si and Al blocks the penetration corrosive ion in the coating/metal interface was investigated by FE-SEM/EDX. It was revealed that the mixed oxide nanoparticles (SiO2-Al2O3) enhanced mechanical as well as barrier properties of the polyurethane coating against corrosion.

Enhanced mechanical and thermal properties of polyamide 6/p (N-(4-F-phenylmaleimide)–alt-styrene) composites based on interfacial complexation inducing crystal transformation

Improving complexation at the interfaces and regulating the crystal transformation behaviors of polyamide 6 (PA6) composites with high mechanical and thermal properties are essential for the industrial applications of PA6. In this work, the effects of adding p (N-(4-F-phenylmaleimide)-alt-styrene) (PFS) on the crystal transformation, thermostability, thermal conductivity, and mechanical properties of PA6 were investigated and discussed systematically. The resu---lts from heat deflection temperature (HDT), dynamic mechanical analysis (DMA) and thermal conductivity tests indicate that PFS greatly increases the HDT, glass-transition temperature (Tg), and thermal conductivity of PA6. Simultaneously, when the content of PFS is 10%, the tensile strength and flexural moduli of PA6/PFS composites are increased by 10.5 and 17.8% compared with that of pure PA6, respectively. The results from differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) show that PFS induces the transformation of PA6 from γ to α crystals by interfacial complexation. This work offers a facile approach for producing materials with high thermal and mechanical performances that can be potentially used in automobiles, electronics, and related technologies.

Effect of wood and graphite fillers on the glass fiber reinforced composite

Glass fiber reinforced polymer is the most popular composite used in engineering applications. The objective of this study is twofold. First, to develop glass fiber reinforced composites with synthetic and natural fillers, namely graphite and various wood fillers. Second, to characterize the mechanical and thermomechanical properties of such filler composites. This study clearly demonstrated that graphite filled glass fiber composites exhibit more mechanical and thermomechanical strengths compared the composite without a filler. Thermomechanical properties were studied by using dynamic mechanical analysis (DMA) test to know the viscoelastic behaviour of the composite materials.

Superior improvement in thermo-mechanical properties of polyurethane based on glycidyl azide polymer/polyethylene adipate

In this study, to improve the thermo-mechanical properties of glycidyl azide polymer (GAP)-based elastomers, polyethylene adipate (PEA) with different molecular weights was successfully synthesized using a solvent-free method. GAP was synthesized by cationic ring-opening polymerization of epichlorohydrin and then azidation. The structure of PEA and GAP was characterized by FTIR, 1HNMR, and GPC. The compatibility of GAP/PEA at various weight ratio blends was investigated by differential scanning calorimetry. The result indicated GAP/PEA is compatible, and addition of PEA to GAP leads to the decrease in glass transition temperature. The copolyurethane elastomers were prepared by cross-linking GAP and PEA at various weight ratios using isophorone diisocyanate and N100 as curing agent. The thermo-mechanical properties were evaluated by dynamic mechanical analysis and tensile test. Based on the results, with increasing weight ratios of PEA, the copolyurethane elastomers displayed an increase in tensile strength (6.97 MPa) and elongation (792%) in comparison with GAP.

Mechanical and viscoelastic properties of SiO2/epoxy nanocomposites post-cured at different temperatures

ABSTRACT Response :In this investigation, an experimental study has been carried to determine the effects of post-curing temperature (Tc) on the mechanical and viscoelastic properties of SiO2/epoxy nanocomposites. The nanocomposites were prepared through ultrasonic mixing with a dispersion of 2, 4, 6, and 8 wt.% SiO2 nanoparticles and post cured at 75, 100, 125, and 150 °‌‌C. The viscoelastic properties were determined using dynamic mechanical analysis tests. The glass transition temperature (Tg) increased with an increase in Tc for pristine epoxy and nanocomposites; however, the increase in the value of Tg for pristine epoxy is less than nanocomposites. The results show that the Tc below the Tg of pristine epoxy improves the tensile properties; however, for Tc above Tg have a detrimental effect on the properties of nanocomposites. With the increase in Tc above Tg, the fracture toughness and fracture energy decrease for nanocomposites.

Effects of hygrothermal aging on the thermomechanical properties of a carbon fiber reinforced epoxy sheet molding compound: An experimental research

AbstractCarbon fiber sheet molding compounds (C‐SMCs) are discontinuous fiber reinforced composite materials. Among them, epoxy‐based C‐SMCs are becoming relevant materials due to their high thermomechanical performance and better formability than continuous fiber reinforced composites. The thermomechanical performance of epoxy resins and epoxy based continuous carbon fiber composites have shown to be influenced by hygrothermal aging. In this work, this influence is studied for an epoxy‐based C‐SMC. Epoxy‐based C‐SMC samples were hygrothermally aged by means of accelerated conditioning, exposing them to 65% relative humidity, and 80°C in a climatic chamber. The equilibrium moisture content, as well as the moisture diffusion coefficient has been determined. The thermomechanical properties of epoxy C‐SMC have been analyzed by dynamic mechanical analysis, tensile, 3‐point bending, and short beam tests in dry and aged samples. The results showed that epoxy C‐SMC is affected by hygrothermal aging in the cases of moisture intake and its effects on Tg value, but interestingly, the hygrothermal aging did not generate any degradation effects in the mechanical response of epoxy C‐SMC.

A comparative study on the thermomechanical and electrical properties of carbide/or graphite/epoxy-reinforced composites

Three series of epoxy composite systems were fabricated and tested varying the filler type and content. An epoxy resin was employed as the matrix, while boron carbide (B4C), titanium carbide (TiC), and graphite (C) microparticles were the reinforcing phases. The behavior of these systems under the influence of time-varying mechanical stress was investigated via dynamic mechanical analysis (DMA), while their thermal response was examined by means of differential scanning calorimetry (DSC). Furthermore, systems’ morphology was investigated via scanning electron microscopy, whereas their dielectric properties were examined using broadband dielectric spectroscopy. Storage modulus, loss tangent, dielectric permittivity, and electrical conductivity were studied with parameters filler type, content, and temperature. Glass transition temperature was also determined using DMA and DSC tests. The present work examines the reinforcing ability of the employed fillers, upon the dynamic mechanical properties as well as on the electrical properties and the energy storing ability of their epoxy composites, which have been prepared under identical filler loadings and fabrication conditions. Moreover, the optimum thermomechanical or electrical performance is determined as a function of the reinforcing phase type and content.

Expanded Polycarbonate (EPC)-A New Generation of High-Temperature Engineering Bead Foams.

Bead foams serve in a wide variety of applications, from insulation and packaging to midsoles in shoes. However, the currently used materials are limited to somewhat low temperature or exhibit significant changes in modulus in the temperature range of many applications due to their glass transition. By comparison, polycarbonate (PC) exhibits almost constant mechanics for temperatures up to 130 °C. Therefore, it appears as an advantageous base material for bead foams. The aim of the publication is to provide comprehensive data on the properties of expanded PC (EPC) in comparison to already commercially available expanded polypropylene, EPP, and expanded polyethylene-terephthalate, EPET. A special focus is set on the thermo-mechanical properties as these are the most lacking features in current materials. In this frame, dynamic mechanical analysis, and tensile, bending, compression and impact tests at room temperature (RT), 80 °C, and 110 °C are conducted for the three materials of the same density. Already at RT, EPC exhibits superior mechanics compared to its peers, which becomes more pronounced toward higher temperature. This comes from the low sensitivity of properties to temperature as EPC is used below its glass transition. In summary, EPC proves to be an outstanding foam material over a broad range of temperatures for structural applications.

Ohmic heating and mechanical stability of carbon fabric/green epoxy composites after incorporation of fly ash particles

The objective of present research was to study the Ohmic heating and mechanical stability of carbon fabric/green epoxy laminated composites after incorporation of 0.5, 1 and 3 wt % unmilled and milled fly ash particles. The Ohmic heating behavior was analyzed by estimating temperature response rapidity, maximum temperature, and electric power efficiency from time-temperature curves of the composites when constant voltage of 5 V was applied for the duration of 120 s. The composites filled with 0.5 wt % milled fly ash showed rapid heating, high temperature generation and less power consumption. Later, the effect of 15, 30 and 60 min Ohmic heating action on structural and mechanical stability of 0.5 wt % fly ash filled composites was examined from DSC, SEM, tensile testing, dynamic mechanical analysis and creep testing. The composites filled with milled fly ash showed superior mechanical and viscoelastic stability than unmilled fly ash composites. This indicated faster heat transportation characteristics by milled fly ash particles to avoid local matrix melting around carbon fibres during Ohmic heating. The marginal loss in mechanical properties was found due to increased agglomeration tendency of fly ash particles under Ohmic heating.

Poro-mechanical model of strain hysteresis due to cyclic water freezing in partially saturated porous media

The paper presents a novel mathematical model of coupled hygro-thermo-mechanical processes in a porous material, partially saturated with liquid water and exposed to temperatures below the freezing point of pore water. Water – ice phase change is modelled by means of a non-equilibrium approach considering both water supercooling and a hysteresis of ice content during freezing and thawing of moist porous materials. The hysteresis results in different crystallization pressure and material strains during freezing and thawing processes at a given temperature. The latter effect is modelled by means of the effective stress principle, considering crystallization pressure of ice in the material pores. Methods used for discretization of the model equations and their numerical solution are described.The model is applied for solving the numerical example dealing with laboratory Dynamic Mechanical Analysis test of two different cement mortars saturated with water and exposed to temperatures below the freezing point of water (down to −15 °C) where hysteresis of strains was observed. The results are used for experimental validation of the proposed model. Then, for a 1-D case concerning water freezing-thawing of a wall, the effects on the simulation results of the phase-change model parameters, of the material hygro-thermal state, of the supercooling phenomenon and finally of the rate of temperature variation, are analyzed and discussed.

Synthesis, characterization, and photopolymerization of (meth)acrylate‐functional polyisobutylene macromers produced by cleavage/alkylation of butyl rubber

AbstractLinear, multi‐functional polyisobutylene (PIB) macromers bearing pendent and terminal (meth)acrylate moieties were prepared via electrophilic cleavage/alkylation of butyl rubber in the presence of (3‐bromopropoxy)benzene, followed by displacement of the resulting bromide moieties with potassium (meth)acrylate. Number average functionality (Fn) ranged from 2.8–7.9; functional equivalent weights ranged from 2.3–4.7 kg/mol. For comparison, a three‐arm, end‐functional PIB triacrylate with equivalent weight of 3.3 kg/mol was also synthesized via living polymerization and end quenching with 4‐phenoxy‐1‐butyl acrylate. All polymers were photocured using Darocur 1173 photoinitiator, and curing kinetics were monitored by real time Fourier‐transform infrared spectroscopy. All systems reached ~100% conversion by 1,800 s, but the linear macromers displayed slower curing rates compared to the PIB triacrylate. The curing rate of linear macromers increased as molecular weight decreased. Cured networks were characterized using dynamic mechanical analysis and tensile testing. Tensile strength varied from 0.15–0.80 MPa. Young's modulus varied from 0.13–1.8 MPa. Strain at break for most networks ranged from 34–54%, but the network derived from the lowest molecular weight PIB reached 113% at failure. Percent extractables, measured using solvent extraction, was about 2% for linear macromers and about 4% for PIB triacrylate.

Assessment of moisture barrier, mechanical, and thermal property of base/nanophased carbon-epoxy composites in seawater

Polymeric composites absorb moisture by quick surface absorption followed by slow diffusion through the matrix in humid environment. Moisture absorption damages the matrix and interface of fiber reinforced polymer (FRP) composites and consequently, weakens their mechanical and thermal properties. Effects of seawater on mechanical and thermal behavior of base and nanophased carbon fiber reinforced epoxy polymer (CFRP) composites were investigated in this study. It was observed that moisture barrier property of carbon/epoxy composites can be improved by adding a small amount (1 to 3% by weight) of nanoclay as filler. Base and nanophased carbon/epoxy composite panels were fabricated by the vacuum assisted resin transfer molding (VARTM) process and samples were prepared from these panels for mechanical and thermal testing according to ASTM standards. Some of these samples were exposed to seawater for 180 days. Moisture intake by the samples was measured every 10 days for 90 days by which time samples reached a saturated state. Mechanical and thermal behavior of base and nanoclay-infused carbon/epoxy composites with exposure to seawater for 180 days were compared with those with no exposure to seawater for 180 days. Mechanical characterization was performed by compression test. Thermal characterizations were carried out by dynamic mechanical analysis, thermo-gravimetric analysis, and thermo-mechanical analysis tests. Results showed that the 2 wt% nanoclay loading is optimum in terms of moisture barrier capability, compression, and thermal properties. After 90-day exposure to seawater, the 2 wt% nanophased composite absorbed 0.39% moisture compared to 0.67% moisture absorption by the base carbon/epoxy composite. Compressive strength and modulus were decreased by 8.20% and 7.11% respectively, for 2 wt% nanophased composites submerged in seawater for 180 days compared with identical samples with no exposure to seawater. Corresponding data from thermal characterization tests indicate storage modulus and glass transition temperature to be 6.59% and 6.1 °C lower respectively, and the coefficient of thermal expansion to be increased by about 6% for the 2 wt% conditioned sample. SEM study revealed that the nanophased composites exhibited a better bonding between the fiber and matrix compared to the base one even after exposure in the seawater. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for enhanced durability of the nanophased carbon/epoxy composite in seawater compared to the base one in the same condition.

Experimental characterization of the hygrothermal ageing effects on the bulk mechanical properties and lap-shear strength of the novel bio-based epichlorohydrin/cardanol adhesive

ABSTRACT In the present paper, the effects of hygrothermal ageing on the bulk mechanical properties and lap-shear strength of the novel bio-based epichlorohydrin/cardanol adhesive have been studied by tension tests, fracture toughness tests and single-lap shear tests on bonded CFRP and aluminum specimens. The thermomechanical properties of the adhesive have been characterized using dynamic mechanical analysis tests. Ageing of the specimens has been realized inside an environmental chamber under the conditions of 70°C/85%RH until saturation. The glass transition temperature of the adhesive is reduced by 13.8%. The results from the tension tests reveal that ageing has caused a reduction of Young’s modulus by 13.4% and of tensile strength by 34.9%. Fracture toughness is reduced by 3.2% while the plasticity caused by the ageing has led to a less brittle behavior. Contrary to the bulk mechanical properties, the lap-shear strength of both the CFRP and aluminum joints is not affected. These findings reveal that although Tg and tensile properties of the bio-adhesive are significantly reduced by the ageing, the fracture toughness and lap-shear strength, which largely determine the adhesion capacity of the adhesive, are not affected.

Bio‐Based Polymers Obtained from Modified Fatty Acids and Soybean Oil with Tailorable Physical and Mechanical Performance

AbstractThe impending world oil shortage, global climate changes, and environmental pollution encourage the use of natural renewable resources to produce substitutes for petroleum‐derived polymers. In this work, two series of bio‐based thermoset polymers are prepared by free radical polymerization of commercially available acrylated epoxidized soybean oil (AESO) with different amounts of methacrylated oleic (MOA) or lauric (MLA) acids. The characterization of the resulting cured bio‐based copolymers is performed by infrared spectroscopy, dynamic mechanical analysis, thermogravimetric analysis, and tensile tests. Experimental results show that heat resistance index, storage modulus, and crosslinking density increase as the content of AESO in the samples increases, whereas the corresponding glass transition temperatures (Tg) decrease slightly. Samples containing MLA present higher tensile modulus and strength than polymers made from MOA or 100% AESO. All materials are insoluble in water and common organic solvents, show high transparency and water contact angles among 67° and 86.3°, and at least some of the samples demonstrate stress relaxation capacity.Practical Applications: The properties of the bio‐based polymers obtained in this work can be adapted to different potential applications by selecting both the amount and type of constituents. Their tailorable physical and mechanical performance, malleability at elevated temperatures, moderate wettable surfaces, easy preparation, high content of bio‐carbon, and environmental benefits make these novel bio‐based polymers great candidates not only for structural applications but also as protective or decorative coatings.