Tangent Delta Research Articles

Odd harmonics and third to fifth harmonic ratios of leakage currents as diagnostic tools to study the ageing of glass insulators

This paper reports an investigation into the leakage current harmonic components of 45 units of glass insulator samples. The insulator units comprise 5 groups of insulators: new insulators and naturally field-aged insulators with different ageing periods->30, 20, 15, and <;10 years from a 132 kV transmission line. Experiments were conducted at different electrical stresses (0.17, 0.24, and 0.34 kV/cm) and salt-fog conductivities (900 and 1500 μS/cm). The results suggest that the insulator samples' leakage current (LC) waveform and the total harmonic distortion (THD) correspond well with degree of ageing. Fast Fourier Transform (FFT) analysis performed on the stored waveforms showed a strong correlation between the ratio of the third to fifth harmonic amplitudes with the degree of ageing and in-service period of the naturally field-aged insulators. Furthermore, this investigation revealed a pattern between the groups of insulator samples in respect to their ageing. These findings were further validated with traditional Dielectric Dissipation Factor tests carried out on the insulators, and the results also correlated well with the samples' degree of ageing as well as service period. In addition, neural networks were trained to recognize the insulator samples' degree of ageing. This study found that, alternative to the diagnosis of insulator ageing through the measurement of loss angles or tangent delta, LC harmonics can be used as diagnostic tools and for the on-line monitoring of in-service aged transmission line ceramic glass insulators based on odd harmonics and third to fifth harmonic ratios.

Viscoelastic behaviour of porous sintered steels compact

This paper describes the viscoelastic behaviour of sintered steels with porosities of 12, 20 and 33%, using a dynamic mechanical analyser. Test specimens were prepared from premix powders of 100–150 μm size by a process of die compaction, delubrication and sintering. The influences of test temperature and vibrational frequency on storage and loss modulus and tangent delta have been investigated. The investigated operating temperature and frequency was varied from 25 to 280°C and from 10 to 50 Hz respectively.

Effect of fiber surface-treatments on the properties of poly(lactic acid)/ramie composites

Abstract Ramie fiber reinforced poly(lactic acid) (PLA) composites were prepared by a two-roll mill. Ramie was treated by alkali and silane (3-aminopropyltriethoxy silane and γ-glycidoxypropyltrimethoxy silane). Effect of surface treatment on the properties of the composites was studied. The tensile, flexural and impact strength of the composites have a significant improvement. Dynamic mechanical analysis (DMA) results show that the storage moduli of the composites with treated ramie increase with respect to the plain PLA and the composites with untreated fiber whereas tangent delta decreases. The Vicat softening temperature of the composites with treated fiber is greatly higher than that of the composites with untreated fiber. The results of thermogravimetric analysis (TGA) show that fiber treatment can improve the degradation temperature of the composites. Moreover, the morphology of fracture surface evaluated by scanning electron microscopy (SEM) indicates that surface treatment can get better adhesion between the fiber and the matrix.

The dynamic-mechanical behavior of epoxy matrix composites reinforced with ramie fibers

The exceptional tensile strength of ramie fiber has motivated investigations on its application as reinforcement in polymeric composites. In this study the temperature variation of the dynamic-mechanical parameters of epoxy matrix composites incorporated with up to 30% in volume of ramie fiber were investigated by DMA tests. The parameters were the storage modulus, loss modulus and tangent delta. The investigation was conducted in the temperature from 20 to 200°C in an equipment operating in its flexural mode at 1 Hz under nitrogen. The results showed that the incorporation of ramie fiber tends to increase the viscoelastic stiffness of the epoxy matrix. It was also observed sensible changes in the structure damping capacity when the fraction of fiber is increased in the composite. These results indicate that the segmental mobility of the epoxy chains is affected by interaction with ramie fibers in the composite.

Studies of molecular dynamics of carboxylated acrylonitrile-butadiene rubber composites containing in situ synthesized silica particles

The molecular dynamics of carboxylated acrylonitrile-butadiene rubber – silica hybrid materials was investigated. Silica hybrids were formed in situ rubber matrix using varied amounts of N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (DAMS), serving also as a cross-linker. Filler–filler and filler–rubber interactions were present, due to the specific nature of these materials. It was found that the amounts of added aminosilane determined the cross-linking density of obtained materials and was the highest with 20 phr DAMS used. The cross-links had ionic nature. Dielectric relaxation spectroscopy (DRS) revealed β, α and α′ relaxation processes. The β relaxation, correlated with the mobility of polymer side groups, was influenced by the weak interaction between both acrylonitrile and carboxylic groups of the rubber and silanol groups of silica. The activation energy for that relaxation was similar for all materials (∼32 kJ mol −1). Both DRS and dynamical mechanical analysis (DMA) demonstrated that the amount of in situ formed silica filler did not significantly influence either the temperature of the α relaxation (correlated with glass transition) or its activation energy. Therefore, that relaxation was caused by free polymer chains, not attached to the silica particles. Similar values of glass transition temperature ( T g) for all hybrids were confirmed by DSC. It appeared that the amplitude of tangent delta (DMA) within T g was dependent on silica amount. Detected at higher temperature α′ relaxation resulted from the presence of domains, where polymer chains were affected by silica network, geometrical restrictions and morphology of the silica-rich domains.

PP-EPDM thermoplastic vulcanisates (TPVs) by electron induced reactive processing

Reactive processing combines melt mixing process and chemical reaction simultaneously. TPVs are produced by such reactive processing. Polymer modification with high energy electrons is based on generation of excited atoms or mol- ecules and ions for subsequent molecular changes via radical induced chemical reactions. In the present study, electron induced reactive processing is used for the development of TPVs. A 1.5 MeV electron accelerator was directly coupled to an internal mixer in order to induce chemical reactions by energy input via high energy electrons under dynamic conditions of melt mixing of polypropylene (PP) and ethylene propylene diene monomer rubber (EPDM). The influence of absorbed dose (25 to 100 kGy) as well as electron energy (1.5 and 0.6 MeV) and electron treatment time (15 to 60 s) have been stud- ied. Increased values of both tensile strength and elongation at break of the TPVs indicate in-situ compatibilisation of PP and EPDM as well as cross-linking in the EPDM phase upon electron induced reactive processing. Dynamic mechanical analyses showed a decrease in value of glass transition temperature peak of EPDM in tangent delta curve with increasing dose. This also indicates higher degree of cross-linking in EPDM phase, which is further supported by a gel content that is higher than the EPDM content itself in the blend.

Measurements of Complex Permittivity at Millimeter-Wave Frequencies With an End-Loaded Cavity Resonator

A novel cavity resonator method is proposed for measuring the complex permittivity of a dielectric plate in the millimeter-wave region. In this method, the dielectric plate is loaded at the end of the cavity resonator. The relative permittivity epsiv' and loss tangent delta are determined from measured resonant frequency and unloaded Q of the TE011 mode. This structure prevents excessive lowering of the resonant frequency due to the placement of the dielectric plate sample in the cavity. The suppression of spurious modes and the design of the cavity resonator are discussed. The values of epsiv' and tandelta were measured in the millimeter-wave range for low-temperature co-fired ceramic (LTCC), Al2O3 , and sapphire plates. The temperature dependence of the complex permittivity of the LTCC plate was measured at 34 GHz. The measurement accuracies are estimated to be within 0.6% for epsiv', and within 10% for of 10-3.

Effect of the structure of silane‐coupling agent on dynamic mechanical properties of dental resin‐nanocomposites

AbstractThis work was aimed at the study by dynamic mechanical analysis (DMA) of dental composites consisted of a Bis‐GMA/TEGDMA (50/50 wt/wt) matrix and silica nanoparticles (Aerosil OX50) as filler, silanized with various silanes. The silanes used were 3‐[(1,3(2)‐dimethacryloyloxypropyl)‐2 (3)‐oxycarbonylamido] propyltriethoxy‐silane (UDMS), 3‐methacryloxypropyl‐trimethoxysilane (MPS), octyltrimethoxysilane (OTMS), blends of UDMS/OTMS (50/50 wt/wt), or MPS/OTMS (50/50 wt/wt). The total amount of silane was kept constant at 10% by weight fraction relative to the filler weight. The silanized nanoparticles were mixed with the dimethacrylate matrix (60% filler by weight fraction). The composites were light cured and tested by DMA for the determination of storage modulus (E′), loss modulus (E″), tangent delta (tan δ), and glass transition temperature (Tg). Measurements were performed in samples immediately after curing and samples stored in water at 37°C for 1, 7, 30, or 120 days. OTMS‐composite in which OTMS does not form covalent bond with the dimethacrylate matrix showed lower elastic modulus both in dry and wet conditions. The ability of bifunctional UDMS for crosslinking was found not to increase the elastic behavior of the composite, as it was expected, compared with that of MPS‐composite, because of the high amount of the silane used. After immersion in water the elastic modulus of OTMS‐composite remained constant, while that of the other composites increased after 1 day and then remained constant up to 120 days. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Dynamic mechanical thermal analysis, forming and mold fabrication studies for hot-embossing of a polyimide microfluidic platform

In this study, we have explored the hot-embossing of polyimide films through dynamic mechanical thermal analysis (DMTA), forming and mold fabrication studies. First, the relationship between the formability and the temperature for the polyimide film was investigated by DMTA and hot-embossing tests. The DMA results represented that, as a polyimide goes through its glass transition, it exhibited dramatic decreases in storage elastic modulus, storage shear modulus and viscosity as well as the peak of tangent delta, and continued to show strong dependence on frequency and temperature. The filling characteristics of the polyimide film investigated by hot-embossing tests showed a sharp increase in the replicated depth near the glass transition temperature. Second, silicon microfluidic platforms and molds were prepared by electron beam lithography (EBL) combined with inductively coupled plasma (ICP). An ICP etching condition to prevent reverse taper of a microstructure was investigated, and Si microfluidic channels and high aspect-ratio microstructures with nearly vertical sidewall were structured. Finally, the channel structures could be successfully replicated on the polyimide surface by hot-embossing with the Si mold prepared by using EBL combined with ICP plasma etching.

Nanoindentation and the dynamic characterization of viscoelastic solids

Using a high-damping thermoplastic as a standard reference material, the purpose of this work is to compare measured values of the complex modulus as determined by dynamic nanoindentation and dynamic mechanical analysis (DMA). Experiments were performed at approximately 22 °C and seven frequencies over the range 1–50 Hz. The indentation measurements were performed using a 103 µm diameter flat punch and a newly developed test method that optimizes the accuracy and precision of the measured stiffness and damping. As determined by dynamic nanoindentation, values of the storage modulus and loss factor (tangent delta) ranged from 4.2 to 10.2 MPa, and 0.28 to 1.05, respectively. Over the range 1–25 Hz, DMA confirmed the nanoindentation results to within 15% or better. Collectively, these data and the testing methods used to generate them should help future investigators make more accurate and precise measurements of the dynamic properties of viscoelastic solids using nanoindentation.

EFEITO DA INCORPORAÇÃO DE FIBRAS DE COCO NO COMPORTAMENTO DINÂMICO-MECÂNICO DE COMPÓSITOS COM MATRIZ POLIÉSTER

A study on the temperature variation of the dynamic-mechanical parameters of polyester matrix composites incorporated with continuous coir fibers was carried out. Different weight percentages, up to 40 wt.% of coir fibers, were mixed with orthophtalic polyester resin and, after press-molding, cured for 24 hours at room temperature. Dynamicmechanical, DMA, tests were conducted to obtain the storage modulus and the loss modulus as well as the tangent delta for each type of composite with different amounts of coir fibers. The DMA results revealed that the incorporation of coir fiber decreases the viscoelastic stiffness of the composite with polyester matrix. This reduction in stiffness is associated with a low interfacial shear stress, which makes it difficult for the mechanical load transfer from the matrix to the fiber. Modifications in the glass transition temperature and in the α relaxation peak also occurred with the amount of incorporated coir fiber. In particular, the damping response of the composite, associated with the value of the tangent delta, decreases with the amount of incorporated fiber owing to the fact that only part of the applied stress was used to deform the fiber/matrix interface.

A Study on Formability of a Polyimide Film by Using Visco-Elasticity Measurement and Hot-Embossing Tests

This study explores the dynamic mechanical properties (e.g., storage shear modulus, loss tangent and shear viscosity) and formability of a polyimide film by visco-elasticity measurement and hot-embossing tests. The variations of storage shear modulus, tangent delta and the shear viscosity were measured as a function of the temperature for two frequencies. As a polyimide goes through its glass transition, it exhibits dramatic decreases in shear modulus and viscosity as well as the peak of tangent delta, and continues to show strong dependence on frequency and temperature. Moreover, the filling characteristics (e.g., surface appearance, replicated depth and surface roughness) of polyimide were investigated by hot-embossing tests at different temperatures using a mold with an aspect ratio of 2.5:1.

Preparation and damping properties of fly ash filled epoxy composites

With the purpose of characterizing the high damping properties of the promising low density epoxy/fly ash composites, a series of epoxy composites filled with fly ash of different volume fraction are prepared in this work. Damping tests of cured epoxy composites are performed in the temperature range from −40 to 150 °C and in the frequency range from 10 to 800 Hz by using a tension-compression mode. The results show that the values of tangent delta (tan δ) reach their peak values at the glass transition temperatures for the composites with 30–50 vol.% fly ash, and the tan δ values attenuate slowly with the increase of frequency, which indicates that the damping properties of such composites are better than those of other composites. Scanning electron microscopy is used to observe the fractured surfaces of the composites and clarify the dispersion and distribution of fly ash particulates in the matrix. In addition, the thermogravimetric curves are also employed to characterize the heat-resistant performance of the composites.

Study on Dynamic Mechanic Properties of Thermosetting/Thermoplastic System Used as the Matrix of Advanced Composite

Resin matrixes for aeronautic advanced composites based on thermoplastic PEK-C (modified polyetherketone) and blending epoxies of DGEBA (diglycidyl ether of bisphenol A) and TGMDA (tetraglycidyl methylenedianiline) are analyzed by DMTA in this paper. The effects of blending ratios and high-temperature post-curing processes on DMTA properties are investigated. The results show that epoxies exhibit different curing features with the existence of high viscous thermoplastic, by contrarily the neat epoxies systems cure according to a random copolymerization rule. The primary peak of tangent delta of DMTA mainly attributes to segment motions of thermoplastic in a blend and the secondary peak mainly for those of the DGEBA cured networks. The higher the ratio of TGMDA to DGEBA is the more obviously the separation degree of tangent delta peaks adopt. Increasing the amount of TGMDA is helpful for separating of phases in the blends. High temperature post-curing promotes separating of phases. In a blend the continuous phase mainly consists of a mass of thermoplastic and some TGMDA, DGEBA mainly collects in dispersed phases.

エラストマーにおけるフィラーの最近の技術動向 カーボンブラック開発の動向

The particle size, structure and surface activity of carbon black are important factors in controlling rubber compound properties. In accordance with technical analyses advances, several new parameters are proposed in carbon black characterization. Aggregate size distribution control is an effective measure to adjust the tangent delta (tan δ) of rubber compounds. The hydrogen content (Hc) of carbon black is used for a simplified parameter of surface activity. The amount of Hc is used to quantify reinforcement and electrical conductivity for a rubber compound. AFM analysis is used to explain the carbon black surface nano-structure, and to examine the interaction with rubber molecules. These new parameters are used in combination with conventional characteristics to improve carbon black. Rigorous control of carbon black properties satisfies the customers' demands for diversified rubber products.

Effects of epoxy content on dynamic mechanical behaviour of PEI‐toughened dicyanate–novolac epoxy blends

AbstractBy varying the cyanate/epoxy ratio, three polyetherimide(PEI)‐modified bisphenol A dicyanate–novolac epoxy resin blends with different epoxy contents were prepared. The effects of epoxy content on the dynamic mechanical behaviour of those blends were investigated by dynamic mechanical thermal analysis. The results showed that the glass transition temperature of the cyanate–epoxy network (Tg1) in the modified blend decreases with epoxy content. When the epoxy content increases, both the width of the glass transition of the cyanate–epoxy network and its peak density are depressed substantially. Although the tangent delta peak value of PEI is basically independent of epoxy content, the Tg of PEI (Tg2) decreases with epoxy content. Tg1 is independent of the PEI loading. When Tg1 is lower than Tg2, however, the Tg1 in the blend with revised phase structure is substantially lower than other blends. Copyright © 2004 Society of Chemical Industry

Evaluation of Isobutylene-Based Elastomers in a Model Winter Tire Tread

Abstract The performance of butyl, chlorobutyl, bromobutyl, and brominated isobutylene-co-para-methylstyrene (BIMS) rubbers were evaluated versus a solution-polymerized styrene-butadiene rubber with 20% bound styrene in model winter tire tread formulations containing natural rubber and butadiene rubber. Isobutylene-based elastomer performance was compared in carbon black-filled and silane-coupled silica-filled systems. Based on laboratory dynamic properties predictive of wet and winter traction, and on DIN abrasion index values, BIMS is the elastomer of choice affording increased tangent delta values between 0 °C and −40 °C, and the highest DIN abrasion index values of the isobutylene-based elastomers. Evaluation of BIMS / NR / BR blends in model compounds show its utility as a tread polymer for improving winter performance.

217 高分子系複合材料の制振特性のマイクロメカニックス解析

A tangent delta of a polymeric material, which influences the vibration damping capacity strongle, is high in value nearby the glass transition temperature of the material. Therefore, when the constituents of a polymer-based composite material are various in their glass transition temperatures, the magnitude of the macroscopic tangent delta of such a composite is expected to be high in wider range in temperature. In the present study, a shape memory polymer (SMP) particle/SMP matrix is used as a sample material and its macroscopic complex modulus and tangent delta are derived explicitly by using the equivalent inclusion method and the Mori-Tanaka's theorem. For the case of a four mode type of distribution of the glass transition temperatures of particles, the value of the macroscopic tangent delta becomes higher than that of the monolithic SMP at any temperature and it becomes constant in the temperature range from 20°C to 60°C.

Fracture behavior of NR and SBR vulcanizates filled with ground rubber having uniform particle size

AbstractThe use of recycled rubber including ground scrap vulcanizates in rubber compounds was studied. When ground rubber was incorporated into rubber compounds, the physical properties, especially the tensile strength, were deteriorated compared to the virgin rubber compound. Also, incorporating ground rubber caused a change of the cure behavior via migration of sulfur or an accelerator between the virgin rubber matrix and the ground rubber vulcanizate. In this study, the fracture behavior and abrasion property of carbon black‐filled SBR and NR compounds containing ground rubber vulcanizate were investigated. Also, the effect of the particle size or loading volume of ground rubber powder on those properties was studied. Four different sizes, 420–600, 177–250, 125–150, and 75–88 μm, of ambient ground rubber powder recycled from waste tire were selected and used in the compounding. The loading amounts of ground rubber powder were 10, 30, and 50 phr. The flex crack growth of SBR‐ and NR‐based compounds was altered by the addition of ground rubber particles. More delayed crack growth was observed with an increasing loading volume and decreasing particle size of the ground rubber powders, and this behavior was more prominent in SBR than in NR compounds. Tangent delta, a direct measure of internal energy dissipation, increased with an increasing loading volume of the ground rubber particles. The abrasion rate of ground rubber‐filled compounds was more dependent on the size of the abrasion pattern than on the loading level or particle size of the ground rubber powders. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2491–2500, 2002

Experimental investigation on the viscoelastic properties of porous metals

Sintered bronze and iron samples with the porosity range from 11 to 39% were subjected to rate-dependent testing and a temperature scan under a three-point bending condition. The samples were tested to the elastic limit. The influence of temperature and frequency were studied on two material parameters: the storage modulus and tangent delta. The temperature is found to be of inverse effect on the storage modulus, and the tangent delta shows a peak value at a particular frequency for different samples.