Mechanical Loss Factor Research Articles

Effects of Multiple Extrusions on Structure-property Performance of Natural Fiber High-density Polyethylene Biocomposites

Detailed analysis of the effects of multiple extrusions on physical, mechanical, micro-structural as well as dynamic mechanical thermal properties of natural fiber high-density polyethylene (HDPE) composites is reported. Composite materials containing HDPE, wood flour, and Maleic Anhydride polyethylene (MAPE) were manufactured and subjected to a recycling process consisting of up to four times grinding and reprocessing under industrial conditions. A wide range of analytical methods including bending tests, modulus of elasticity, impact strength, Scanning electron microscopy (SEM), fiber length measurement, water absorption tests, and dynamic mechanical thermal analysis (DMTA) were employed to understand the effects of recycling on natural fiber-HDPE composites. The results revealed that the recycled composites had lower bending strength and modulus of elasticity values, as compared to the reference counterparts. Also, the once recycled composites showed higher impact strength. Results, as well, indicated that generally the recycled composites had lower water absorption values as compared to the reference ones. The results obtained from DMTA exhibited a decrease in storage modulus and an increase in mechanical loss factor (tan δ) for all composites subjected to recycling. Alterations in phase transition temperatures and intensities were also monitored and the possible reasons were analyzed.

The influence of combined active fillers on the properties of elastomeric materials for eco-friendly tyres

Reinforcing of elastomers by the addition of various nanofillers has led to significant improvements in elastomer properties, and therefore, to the increase of potentials for use as suitable materials for special applications. The aim of this study was to investigate the effects of combinations of two active fillers (carbon black and synthesized silica (50/0; 35/15; 25/25; 15/35; 0/50; phr)) on the morphology, curing, as well as thermal, dynamic-mechanical and mechanical properties of nanocomposites based on the styrene-butadiene rubber as the network precursor. Based on SEM results, the largest agglomerates were observed in the structure of the nanocomposite containing 25 phr of carbon black and 25 phr of SiO2. Determination of curing characteristics indicated that the minimum torque at 100, 150 and 160?C had higher magnitudes for the compounds with silica filler, which is in accordance with the tendency of SiO2 to form filler-filler interactions. Values of the scorch time and the optimal time of crosslinking increased by increasing the silica phr content in the fillers mixture. It could be thus supposed that the fraction of occluded and trapped chains in the structure of elastomer reinforced by SiO2 is higher due to the almost 2-fold higher value of the silica NDBP number as compared to the NDBP number of carbon black particles. On the basis of MDSC results, it was assessed that the addition of combined active fillers had negligible effects on the glass transition temperature, registered at about -47?C for all tested samples. The obtained DMA data, concerning storage moduli in the temperature range from -20 to 0?C, (characteristic for "Payne" effect) are very significant for predictions of the properties of the tyre tread such as the slip resistance on the road on ice and in the wet conditions. The increase of silica content in the combined filler induced a decrease of the dynamic mechanical loss factor of prepared nanocomposites in the temperature range from 40 to 80?C. The obtained results are very important for the structuring of elastomeric materials aimed for production of tyres with reduced rolling resistance and fuel consumption. The elastomer containing the highest content of carbon black showed the highest value of the tensile strength (21.8 MPa). The abrasion resistance of the synthesized nanocomposites increased as the silica content was reduced in the combined fillers.

Irreversibility effects in piezoelectric wafer active sensors after exposure to high temperature

This paper presents an experimental and analytical study of irreversible change in piezoelectric wafer active sensor (PWAS) electromechanical (E/M) impedance and admittance signature under high temperature exposure. After elevated to high temperatures, change in the material properties of PWAS can be quantified through irreversible changes in its E/M impedance and admittance signature. For the experimental study, circular PWAS transducers were exposed to temperatures between 50 °C and 250 °C at 50 °C intervals. E/M impedance and admittance data were obtained before and after each heating cycle. Irreversible temperature sensitivity of PWAS resonance and anti-resonance frequency was estimated as 0.0246 kHz °C−1 and 0.0327 kHz °C−1 respectively. PWAS transducer material properties relevant to impedance or admittance signature such as dielectric constant, dielectric loss factor, mechanical loss factor, and in plane piezoelectric constant were determined experimentally at room temperature before and after the elevated temperature tests. The in-plane piezoelectric coefficient was measured by using optical-fiber strain transducer system. It was found that the dielectric constant and in-plane piezoelectric coefficient increased linearly with temperature. Dielectric loss also increases with temperature but remains within 0.2% of initial room temperature value. Change in dielectric properties and piezoelectric constant may be explained by depinning of domains or by domain wall motion. The piezoelectric material degradation was investigated microstructurally and crystallographically by using scanning electron microscope and x-ray diffraction method respectively. There were no noticeable changes in microstructure, crystal structure, unit cell dimension, or symmetry. The degraded PWAS material properties were determined by matching impedance and admittance spectrums from experimental results with a closed form circular PWAS analytical model. Analytical results showed that impedance and admittance strongly depend on elastic coefficient, dielectric constant, mechanical loss factor, dielectric loss tangent and in plane piezoelectric constant. These properties were found to be susceptible to change after high temperature exposure.

Rheological Behaviors of Graphene Oxide/Polyacrylonitrile Spinning Solutions

The rheological behaviors of polyacrylonitrile (PAN) in NaSCN aqueous solutions containing different amount of Graphene oxide (GO) were investigated through both steady-state and dynamic rheological measurements. The parameters such as apparent viscosity (ηα), flow activation energy (Eη), structural viscosity index (Δη), storage modulus (G’), loss modulus (G’’) and mechanical loss factor (tanδ) were measured to illustrate the rheological behaviors of these solutions. The results showed that the apparent viscosity decreased with adding appropriate amount of GO, while the structural viscosity index, the flow activation energy and the mechanical loss factor of GO/PAN spinning solutions increased. Accordingly, a possible mechanism of GO effect on rheological behaviors of PAN solution was proposed in this work.

Aramid hybrid composite laminates reinforced with inorganic fullerene-like tungsten disulfide nanoparticles

Abstract Combination of phenolic resin with poly (vinyl butyral), PVB, is often used as impregnation of aramid fabrics in prepregs for the ballistic protection products. In this study an effect of inorganic fullerene-like tungsten disulfide nanoparticles (IF-WS 2 ) in aramid/phenolic resin/PVB composite for improving its viscoelastic and mechanical properties is examined. The effect of IF-WS 2 on mechanical properties improvement was first proved by nanoindentation on thin film samples PVB/IF-WS 2 . The quality of aramid fabrics impregnation with PVB/phenolic resin/IF-WS 2, and the nanoparticles dispersion were analyzed by scanning electron microscope with energy dispersive spectrometer. Viscoelastic properties of the composites were examined by dynamic mechanical thermal analysis, observing the storage and loss modulus, mechanical loss factor and glass transition temperature versus temperature and frequency. Time-temperature superposition principle was applied for the construction of master curves. IF-WS 2 causes increase of glass transition temperature and improvement in mechanical properties of examined composites.

Material Selection of an Elastomer Capable of Absorbing Vibrations Actuated by a 4D Movie Theater

The objective was to investigate possible vibration isolator solutions for a 4D entertainment theater. The paper focused on resolving a vibration leakage issue experienced by customers of Company A which manufactures tactile motion actuators for 4D theater entertainment purposes. The investigation started by utilizing Cambridge Engineering Selector software to determine the value of the mechanical loss factor for given materials. Elastomers had the best mechanical loss coefficient, specifically polyurethanes. While considering the specifications provided by Company A, certain parameters such as nominal load withstanding and prices were considered. After investigating the materials thoroughly, Sorbothane showed the best performance along with suitable prices. The vibrational system investigated resulted in a frequency ratio of 6, and a transmissibility of 2.86% at normal conditions, which indicates that the material selected was suitable. Sorbothane material at shore 00 and durometer 50 showed its capability to withstand maximum nominal loading at 635 kg (1400 lbs). This was 57% higher than the targeted loading. The mechanical loss factor was 0.52 at 50-Hz excitation frequency, which was high enough to dissipate excessive vibrations.

Investigations of thickness-shear mode elastic constant and damping of shunted piezoelectric materials with a coupling resonator**Project supported by the National Defense Foundation of China (Grant No. 9149A12050414JW02180).

Shear-mode piezoelectric materials have been widely used to shunt the damping of vibrations where utilizing surface or interface shear stresses. The thick-shear mode (TSM) elastic constant and the mechanical loss factor can change correspondingly when piezoelectric materials are shunted to different electrical circuits. This phenomenon makes it possible to control the performance of a shear-mode piezoelectric damping system through designing the shunt circuit. However, due to the difficulties in directly measuring the TSM elastic constant and the mechanical loss factor of piezoelectric materials, the relationships between those parameters and the shunt circuits have rarely been investigated. In this paper, a coupling TSM electro–mechanical resonant system is proposed to indirectly measure the variations of the TSM elastic constant and the mechanical loss factor of piezoelectric materials. The main idea is to transform the variations of the TSM elastic constant and the mechanical loss factor into the changes of the easily observed resonant frequency and electrical quality factor of the coupling electro–mechanical resonator. Based on this model, the formular relationships are set up theoretically with Mason equivalent circuit method and they are validated with finite element (FE) analyses. Finally, a prototype of the coupling electro–mechanical resonator is fabricated with two shear-mode PZT5A plates to investigate the TSM elastic constants and the mechanical loss factors of different circuit-shunted cases of the piezoelectric plate. Both the resonant frequency shifts and the bandwidth changes observed in experiments are in good consistence with the theoretical and FE analyses under the same shunt conditions. The proposed coupling resonator and the obtained relationships are validated with but not limited to PZT5A.

Inorganic fullerene-like IF-WS2/PVB nanocomposites of improved thermo-mechanical and tribological properties

The subject of this research is to explore the possibility of preparation of nanocomposite material of improved thermo-mechanical and tribological properties, using inorganic fullerene-like tungsten disulfide nanostructures (IF-WS2) as reinforcement in poly(vinyl butyral) (PVB). This paper also reports investigation of the effects of using different solvents in preparation of PVB/IF-WS2 nanocomposite on the thermo-mechanical behavior of the resulting material. PVB was dissolved in ethanol, isopropanol, n-butanol and ethyl acetate. IF-WS2 nanoparticles were added to these PVB solutions and dispersed by different deagglomeration techniques. Samples were dried and thin films were obtained. Their microstructure and the quality of IF-WS2 dispersion and deagglomeration in PVB matrix was analyzed by scanning electron microscope (SEM). The reinforcing effect of IF-WS2 is examined by determining hardness, reduced modulus of elasticity and coefficient of friction, by nanoindentation and nanoscratch test, in terms of the different solvents applied in preparation of the samples, mode of stirring and different contents of IF-WS2. The glass transition temperature (Tg) was determined for the prepared samples using differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). Storage modulus and mechanical loss factor were observed in a defined temperature range using DMA.

Amphoteric Response of Loss Factor for Bimodal Magnetic Elastomers by Magnetic Fields

We have investigated the mechanical loss factor for bimodal magnetic elastomers containing magnetic and nonmagnetic particles. The bimodal magnetic elastomer exhibited amphoteric response of loss factor by magnetic fields depending on the strain amplitude; i.e. negative response at low strains and significant positive response at high strains. The mechanism of amphoteric response seen in bimodal magnetic elastomers is discussed.

The effects of wood flour content and coupling agent on the dynamic mechanical and relaxation properties of wood-plastic composites

This research studied the influence of formulations of wood-plastic composites on dynamic mechanical properties—storage modulus (E′), loss modulus (E′′) and mechanical loss factor (tan δ)—according to dynamic mechanical analysis spectra. The specimens were made with wood flour, high-density polyethylene (HDPE) and maleic anhydride polypropylene as a coupling agent. Generally, the presence of fillers and a coupling agent in polymer affect the relaxation processes and produce a more complex morphology, thereby influencing the mechanical and viscoelastic properties of the composites. In this work, the addition of a higher content of wood flour resulted in higher values of E′, indicating a better stiffness, but tan δ decreased. The bonding agent significantly improved E′, which can be attributed to an enhanced interface between the wood and the HDPE. Coupled products had better E′ retention at elevated temperatures than uncoupled samples. The addition of wood flour and a coupling agent increased the value of E′, but did not significantly change the range of relaxation transition.

Dynamic mechanical properties and thermal stability of furfuryl alcohol and nano-SiO2 treated poplar wood

Wood polymer nanocomposites (WPNC) were prepared from the furfuryl alcohol and nano-SiO2 using a method of vacuum impregnation. Dynamic mechanical properties in storage modulus and mechanical loss factor, as well as the thermal stability of the WPNC were evaluated. The interface interaction between the organic and inorganic compounds was also studied by the scanning electron microscope and energy dispersive X-ray spectrometer. The dynamic mechanical analysis showed the improvement in the storage modulus and mechanical loss factor of WPNC as a result of the strong interfacial interaction between the organic and inorganic matrix. Additionally, with an increase in nanoparticles content in the composites, the thermo-stability of WPNC improved significantly.

Wood-Like Material from Thermoplastic Polymer and Landfill Bio-Materials: Dma, Tga and Solvent Resistance Properties

The aim of this work is to explore the potential application of chemically modified olive husk residue (OHR) as naturally occurring fillers to reinforce (Nylon-12) thermoplastic to produce a cost-effective wood like material. The Nylon-12/OHR composite material was fabricated via melt mixing of the Nylon-12 followed by the addition of chemically treated OHR at 180 and 50 rev.min−1 using Brabender internal mixer. The composites were characterized with respect to their dynamic mechanical properties, namely storage and viscous moduli (E′, E”), and mechanical loss factors (tan δ) using dynamic mechanical analyzer (DMA). The thermal stability of the samples with and without chemically treated OHR were examined using thermo-gravimetric analyzer (TGA). The chemical resistance of the composites was evaluated by immersing the samples in acidic and basic media and by exposing the samples to thermo-oxidative ageing (TOA) at 80C for 72h. The influence of TOA and immersion medium on the percentage weight loss, impact strength and hardness of the composites were reported. The effect of TOA and the solvent attack on the microstructure of the fractured samples was viewed by scanning electron microscope (SEM).

Method to characterize the damping behavior of thin passively constrained layer laminates using dynamic mechanical analysis (DMA) in shear mode

In order to characterize the damping behavior of thin passively constrained layer damping (CLD) loudspeaker membranes, usually the whole loudspeaker has to be built. Therefore, a method was established to characterize the damping performance of these membranes with thicknesses below 50 μm at the film level using dynamic mechanical analysis (DMA).Since in the CLD design damping is provided via shear deformation of the middle damping layer, a test was set up to determine the mechanical loss factor tan δ (f,T) in DMA shear mode. Subsequently, results from 1-200 Hz were extrapolated to application-relevant frequencies of up to 1000 Hz via time-temperature superposition. Finally, the damping behavior was rated by the frequency dependent integrated average of the mechanical loss factor tA¯.Furthermore, in experiments with different constraining and damping layers, it was found that the damping performance was maintained as long as the adhesion between them was sufficiently strong.

An indirect method to measure the variation of elastic constant c33 of piezoelectric ceramics shunted to circuit under thickness mode

Academic interest in the use of piezoelectric shunt damping technology in the field of vibration and noise control has been on the rise in recent years. The experimental observation of the variation of elastic constants of piezoelectric materials shunted to different circuits is a fundamental problem of this technology. The existing methods to measure the elastic constants of piezoelectric ceramics are either unsuited or complicated for such a purpose. In this paper, a modified resonator measurement method is proposed to indirectly measure the variation of elastic constant c33 of piezoelectric ceramics shunted to circuit under thickness mode. The main idea is transforming the change of c33 into the change of the electrical resonant frequency of a single-oscillator model which is easier to be observed. Mason equivalent circuit and ANSYS finite element simulation are employed for the analysis of the admittance and resonant frequency of the proposed system. Based on the proposed method, the variation of the elastic constant c33 has been investigated when the piezoelectric ceramic wafer (PZT-5H) is shunted to a resistor, a capacitor, and a resistor connected in series with an inductor respectively. The variations of the resonant frequency measured in the experiment are highly consistent with those of c33. Besides, the measurement of variation of mechanical loss factor with a shunt resistor is also discussed in this paper.

The effect of temperature on creep behavior of wood-plastic composites

The creep properties of wood-plastic composites limit their application, particularly in temperature variations affecting long-term performance. In this study, the effect of temperature was studied based on dynamic mechanical analysis spectra and isochrones and a newly developed stress-temperature incorporated creep equation. According to the dynamic mechanical analysis spectra, the addition of a higher content of wood flour resulted in higher moduli, indicating increased stiffness and lower mechanical loss factor. According to the isochrones, the creep strain of wood-plastic composites increased with elevated temperatures and stresses at the same time point. Moreover, the strain increased almost linearly with increasing stress at lower temperatures but became nonlinear with elevated temperature. With these findings, a stress-temperature incorporated creep equation was developed based on short-term creep tests. This empirical equation incorporates the effect of temperature in a power law equation. Good agreement was observed between the equation and experimental results.

Effects of extrusion temperature on the rheological, dynamic mechanical and tensile properties of kenaf fiber/HDPE composites

The effects of extrusion processing temperature on the rheological, dynamic mechanical analysis and tensile properties of kenaf fiber/high-density polyethylene (HDPE) composites were investigated for low and high processing temperatures. The rheological data showed that the complex viscosity, storage and loss modulus were higher with high processing temperature. Complex viscosities of pure HDPE and 3.4wt% composite with zero shear viscosity of ⩽2340Pas were shown to exhibit Newtonian behavior while composites of 8.5 and 17.5wt% with zero shear viscosity ⩾30,970Pas displayed non-Newtonian behavior. The Han plots revealed the sensitivity of rheological properties with changes in processing temperature. An increase in storage and loss modulus and a decrease in mechanical loss factor were observed for 17.5wt% composites at high processing temperature and not observed at low processing temperature. Processing at high temperature was found to improve the tensile modulus of composites but displayed diminished properties when processed at low processing temperature especially at high fiber content. At both low and high processing temperatures, the tensile strength and strain of the composite decreased with increased content of the fiber.

Dynamic Mechanical Properties and Tensile Behavior of Oil Palm Ash Filled Natural Rubber Vulcanizates

The potential of utilizing low cost filler, i.e. oil palm ash (OPA) as a new filler in natural rubber (NR) compounds using conventional laboratory-sized two roll mills. The NR compound was cross-linked using sulphuric system. The variations of tensile and dynamic properties were examined in the NR vulcanizates with the OPA filling at low loading. In the view of reinforcement, the tensile strength and elongation at break was improved with the low loading of OPA (<10 phr). Dynamic mechanical properties of OPA filled NR vulcanizates was investigated with respect to the storage modulus and mechanical loss factor (Tan δ). Result showed that the storage modulus of the OPA filled NR vulcanizates became higher than that of gum NR vulcanizates whereas the peak height of tan δmax was reduced as the OPA loading was increased. This phenomenon manifested a strong rubber-filler interaction with the low loading of OPA.

Properties of natural rubber/recycled ethylene–propylene–diene rubber blends prepared using various vulcanizing systems

The role of various vulcanizing systems on the curing characteristics, mechanical properties, morphology and dynamic mechanical analysis of natural rubber and recycled ethylene–propylene–diene rubber blends was investigated. Accelerated sulfur-vulcanizing systems (semi-EV and EV), peroxide, and mixed sulfur/peroxide-vulcanizing systems (semi-EV/peroxide and EV/peroxide) were observed and compared. The blends were processed on a two-roll mill, and a fixed amount of carbon black was also incorporated. Amongst the blends, accelerated sulfur-vulcanizing systems exhibited higher torques, state of cure, tensile strength and elongation-at-break, in comparison with the peroxide-vulcanizing system, whereas the tensile modulus, hardness and cross-link density showed lower trend. In the mixed sulfur/peroxide-vulcanizing systems, it showed intermediate behavior to the individual sulfur- or peroxide-vulcanizing systems. This was associated to the interference of peroxide during the cross-linking formation. SEM micrographs of semi-EV-vulcanizing system exhibited more roughness and cracking path indicating that higher energy was required towards the fractured surface. The high cross-link density observed from the swelling study could be verified from the storage modulus (E′) where peroxide vulcanized blends provided a predominant degree of cross-linking followed by semi-EV, semi-EV/peroxide, EV and EV/peroxide-vulcanizing systems, respectively. The glass transition temperature (Tg) depicted at maximum peak of mechanical loss factor (tanδmax), indicating that semi-EV-vulcanizing system showed highest Tg value. The Tg values can be ordered as semi-EV > peroxide > semi-EV/peroxide > EV > EV/peroxide-vulcanizing systems. The Tg of rubber vulcanizates can be increased due to the restriction of molecular movement such as cross-link density.

The Effect of Hydrochloric Acid Treatment on Properties of Oil Palm Ash-filled Natural Rubber Composites

The properties of non-treated and hydrochloric acid (HCl)-treated oil palm ash (OPA)-filled natural rubber (NR) composites were investigated in terms of swelling behavior, rubber-filler interaction, ageing resistance, dynamic mechanical analysis, and thermal stability. The incorporation of OPA resulted in a lower degree of swelling in the NR composites, which was even lower after HCl treatment. Concerning the rubber-filler interaction, the HCl-treated OPA had better interfacial interaction with the NR matrix than that of non-treated OPA, resulting in higher crosslink density and improved ageing resistance. The dynamic mechanical properties of NR composites were better with the incorporation of HCl-treated OPA compared to non-treated OPA, in that they showed a higher storage modulus and lower mechanical loss factor. Thermogravimetry analysis revealed that the HCl treatment process did not affect the thermal stability of OPA-filled NR composites.

Effect of imidazolium ionic liquid type on the properties of nitrile rubber composites

We investigated the influence of hydrophilic and hydrophobic imidazolium ionic liquids on the curing kinetic, mechanical, morphological and ionic conductivity properties of nitrile rubber composites. Two room temperature ionic liquids with a common cation—1-ethyl-3-methylimidazolium thiocyanate (EMIM SCN; hydrophilic) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI; hydrophobic)—were used. Magnesium–aluminium layered double hydroxide (MgAl-LDH; also known as hydrotalcite) was added to carboxylated acrylonitrile–butadiene rubber (XNBR) whereas fumed silica Aerosil 380 was used in acrylonitrile–butadiene rubber (NBR) as reinforcing fillers. NBR compounds were vulcanized with a conventional sulfur-based crosslinking system whereas XNBR compounds were cured with MgAl-LDH. The optimum cure time reduction and tensile properties improvement were obtained when both ionic liquids were added at 5 parts per hundred rubber (phr). The results revealed that EMIM SCN and EMIM TFSI induced an increase in the AC conductivity of nitrile rubber composites from 10−10 to 10−8 and to 10−7 S cm−1, respectively (at 15 phr ionic liquid concentration). The presence of ionic liquids in NBR slightly affected the glass transition temperature (Tg) whereas the presence of EMIM TFSI in XNBR contributed to a shift in Tg towards lower temperatures from −23 to −31 °C, at 15 phr loading, which can be attributed to the plasticizing behaviour of EMIM TFSI in the XNBR/MgAl-LDH system. Dynamic mechanical analysis was also carried out and the related parameters, such as the mechanical loss factor and storage modulus, were determined. © 2013 Society of Chemical Industry