Transient effects in dynamic modulus measurement of silicone elastomers 1. Zero mean strain measurements

The strain‐dependent dynamic storage modulus of a poly(dimethyl‐siloxane‐co‐methylvinyl‐siloxane‐co‐methylphenyl‐siloxane) based silicone elastomer, which is reinforced with fumed silica and crosslinked with peroxide, is investigated. The dependence of the resulting dynamic storage modulus on the duration of cycling at a particular test condition is investigated and compared to static stress relaxation measurements in the same strain range. The dynamic modulus results are shown to depend on the time of cycling at the current test conditions as well as the time of cycling at prior conditions of lower strains. The relaxation is shown to be related to the time of cycling rather than the number of cycles performed. The pattern of behavior of the relaxation of the dynamic modulus with respect to peak strain amplitude is different than that observed in a static stress relaxation test, both of which show significant nonlinear effects in strain. The observed phenomena are interpreted in terms of the role of the polymer phase on the dynamic behavior of the elastomer material. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1001–1009, 2005     

Silks cope with stress by tuning their mechanical properties under load

We compare the nonlinear mechanical properties of silks under load with the quasi-static and isothermal dynamic mechanical properties of nylon as well as human hair. For silk and nylon, the dynamic storage modulus increases with increasing static load, while the quasi-static modulus decreases considerably through yield. However, the modulus of hair decreases irreversibly for both loading conditions. For silk, the increase in storage modulus is only partially reversible after high-loading and is accompanied by a non-recoverable strain. For nylon, the dynamic modulus increase is largely reversible after increased static loading up to a second high stress yield point, where modulus then decreases. Taken together, our data suggest that the dynamic modulus increases with increasing order in the silk and nylon structures under static load, whereas the morphology of hair is gradually degraded under load.     

Separability behavior in viscoelastic properties of EPDM gum vulcanizate

Dynamic mechanical properties of EPDM gum vulcanizates were studied using the dynamic viscoelastometer, Rheovibron. A small sinusoidal strain was superimposed on a static strain and its effect on dynamic mechanical properties were analyzed. The results are discussed in terms of total strain which takes the static strain into account. Separability of time and strain effects for loss modulus and the nonseparability for storage modulus are discussed. A critical strain was identified after which the stress dissipation mechanism changes. © 1994 John Wiley & Sons, Inc.     

Transient effects in dynamic modulus measurement of silicone rubber,part 2: Effect of mean strains and strain history

The strain‐dependent dynamic storage modulus of a poly(dimethyl‐siloxane‐co‐methylvinyl‐siloxane‐co‐methylphenyl‐siloxane)‐based silicone elastomer (PVMQ), which is reinforced with fumed silica and crosslinked with peroxide, is investigated. The time dependence of the dynamic storage modulus on the magnitude of the mean strain at a particular test condition is investigated. The dynamic modulus results are shown to depend on the time of cycling as well as the relative magnitudes of the dynamic and mean strains. The relaxation of the force required to maintain the mean strain is observed to depend on the magnitude of the dynamic strains and the data are shown to be consistent with static stress relaxation experiments in the limit of zero dynamic strain. Recovery of the dynamic modulus from the exposure to higher strain cycling is seen to be facilitated by dynamic cycling with higher cycling strains yielding faster recovery rates. The observed phenomena are interpreted in terms of the role of entanglements in the polymer phase on the dynamic behavior of the elastomer material. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2197–2204, 2007     

RPA分析硫黄用量对天然橡胶动态性能的影响

用橡胶加工分析仪(RPA)分析硫黄用量对NR动态性能的影响。结果表明:不同硫黄用量的混炼胶的动态模量随频率的升高和温度的降低而增加,损耗因子降低;应变超过28%,混炼胶的储能模量下降。不同硫黄用量的硫化胶随交联密度的提高,动态性能对频率的依赖性变小,对应变的依赖性变强;而温度越高,硫化胶的"橡胶弹性"越明显。     

Effect of the textural characteristics of the new silicas on the dynamic properties of styrene-butadiene rubber (SBR) vulcanizates

It is possible to obtain silicas with different textural characteristics from natural silicates by means of an acid treatment, where the textural characteristics of the new silicas obtained are greatly influenced by the reaction conditions. The mechanodynamical behavior of compounds filled with these silicas and based on Styrenebutadiene rubber (SBR) matrices was studied. The influence of the textural characteristics on dynamic properties is explained in terms of the stiffness, porosity, and structure of the silica particles. Silicas obtained at drastic reaction conditions yield compounds with a higher storage modulus, E′, at low strain amplitudes, but with a lower storage modulus at high strain amplitudes. The maximum loss factor, tanδ, is a function of the silica external surface area.     

Tensile and dynamic mechanical properties of improved ultrathin polymeric films

Tensile and dynamic mechanical properties of improved ultrathin polymeric films for magnetic tapes are presented. These films include poly(ethylene terephthalate) or PET, poly(ethylene naphthalate) or PEN, and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes; thinner tensilized‐type PET, PEN, and ARAMID were recently used as alternate substrates with improved material properties. The thickness of the films ranges from 6.2 to 4.8 μm. Young's modulus of elasticity, F5 value, strain‐at‐yield, breaking strength, and strain‐at‐break were obtained at low strain rates by using a tensile machine. Storage (or elastic) modulus, E′, and the loss tangent, tan δ, which is a measurement of viscous energy dissipation, are measured by using a dynamic mechanical analyzer at temperature ranges of ?50 to 150°C (for PET), and ?50 to 210°C (for PEN and ARAMID), and at a frequency range of 0.016 to 29 Hz. Frequency–temperature superposition was used to predict the dynamic mechanical behavior of the films over a 28 decade frequency range. Results show that ARAMID and tensilized films tend to have higher strength and moduli than standard PET and PEN. The rates of decrease of storage modulus as a function of temperature are lower for PET films than those for PEN and ARAMID films. Storage modulus for PEN films are higher than that for PET films at high frequencies, but this relationship reverses at low frequencies. ARAMID has the highest modulus and strength among the films in this study. The relationship between polymeric structure and mechanical properties are also discussed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2225–2244, 2002     

Dynamic mechanical characterization of PC/MWCNT composites under variable temperature conditions

A dynamic mechanical analysis has been performed on composite materials of polycarbonates (PC) and multi-walled carbon nanotubes (MWCNT) for evaluation of their mechanical hardness and storage modulus under the combined effects of variable loading frequencies and temperature conditions. The PC-based engineering machine components that are subjected to variable external loads and temperature conditions are not durable owing to the viscoelastic properties of PC. Composites of PC with MWCNT (2, 5 and 10 wt%) were fabricated and their mechanical characterization tests revealed that with increase in MWCNT composition both storage modulus and hardness enhanced significantly in comparison to pure PC. For 10 wt% PC/MWCNT composite, the average storage modulus increased in the range of 40–92%, while the average hardness was enhanced in a range of 88–121% for the combined effect of temperature range of 30–90 °C and loading frequency range of 30–230 Hz. With increase in temperature, the maxima of storage moduli and hardness for these composites shifted toward higher loading frequencies, indicating that these composites can be used for wider loading frequency range. Therefore, the experimental results of this paper have shown that the mechanical properties of PC-based composite materials with minor MWCNT compositions are enhanced significantly and hence can be used for automotive and aerospace engine parts where loading frequencies are high and temperature conditions are variable.     

Dynamic viscoelastic properties of CaCO3 filled,closed cell microcellular copoly (ethylene/octene) vulcanisates Effect of blowing agent,temperature, and strain

Abstract

Dynamic mechanical analysis of precipitate CaCO₃ filled, closed cell microcellular ethylene–octene copolymer vulcanisates has been studied as a function of temperature and double strain amplitude. Experiments were carried out over the temperature range – 100 to 100°C. Strain dependent isothermal dynamic mechanical analysis was performed for double strain amplitude 0·09–5%. The log of storage modulus bears a simple relationship with the log of density for both solid and closed cell microcellular rubber. The slope of the line is found to be temperature dependent. The relative storage modulus decreases with decreasing relative density. The eect of blowing agent and filler loading on storage modulus and loss tangent were also studied. Cole–Cole plots of microcellular vulcanisates show a circular arc relationship with density. Plots of loss tangent against storage modulus were found to exhibit a linear relationship. Hysteresis and strain work also bear a linear relationship.     

应用于3D打印技术的ABS/纳米二氧化钛复合材料制备及力学性能研究

以丙烯腈-丁二烯-苯乙烯共聚物(ABS)为基体及自制的纳米二氧化钛(nano-TiO2)为改性剂,利用加热混制法制备ABS/nano-TiO2复合材料,混炼时以不同质量分数的nano-TiO2进行混炼。针对复合材料的动态力学性能(储能模量和损耗模量)和静态力学性能(拉伸强度、杨氏模量和硬度),对混制挤压成型的线材及3D打印的试样进行对比分析。通过扫描电子显微镜(SEM)分析可知,二氧化钛粉末为纳米级,能量色散X射线光谱(EDS)分析表明,元素含量和种类与设计一致。结果显示,通过添加nano-TiO2,可以提高ABS的拉伸强度、硬度、储能模量及损耗模量;且随着温度增加,ABS/nano-TiO2复合材料的储能模量降低,而损耗模量增加。研究结果可知,添加nano-TiO2可以提升ABS/nano-TiO2复合材料的力学性能,且经3D打印成型试样的各项性能保持稳定。     

Influence of cure schedule and solvent exposure on the dynamic mechanical behavior of a vinyl ester resin containing glass fibers

This study deals with the dynamic mechanical properties of a glass-reinforced vinyl ester resin. The viscoelastic parameters of the loss factor and the storage modulus as a function of the cure temperature were used as a criterion to determine the optimum cure conditions to be employed. It is shown that the cure temperature usually used to cure these resins is not enough to reach the maximum glass transition temperature, and, therefore, an additional postcure should be used. The influence of several solvents on the dynamic mechanical behavior of these resins cured following the cure pathway proposed by the supplier was also analyzed. This behavior was compared with the solvent uptake at various exposure times, and the changes observed were related to the crosslink density as well as to the chemical structure of both the resin and the solvent. Finally, the effects of varying the exposure temperature were also investigated for the resin exposed to a liquid which simulates petroleum fluid. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2595–2602, 1998     

Effects of types of fillers on the molecular relaxation characteristics,dynamic mechanical,and physical properties of rubber vulcanizates

The dynamic mechanical, and physical properties of bromobutyl rubber were investigated to determine the effect of particle size and of the structure of carbon black and silica. Filler loading was so adjusted that all the experimental compositions had the same hardness level. The results indicate that the type and loading of filler have no significant effect on the molecular relaxation transition. However, elastomer having a desirable storage modulus with low sensitivity to temperature change can be developed using filler with smaller particle size. Higher elongation at break, and better tensile strength, energy density at break, and fatigue life could be obtained by using finer particle or high structure black than with the low structure and higher particle size black. Finer particle size filler loaded systems exhibit pronounced strain dependence, higher thixotropic change, and delayed recovery in dynamic mechanical properties compared to that exhibited by large particle size filler.     

Impact of functionalised dispersing agents on the mechanical and viscoelastic properties of pigment coating

The effect of poly(acrylic acid) – poly(styrene sulphonic acid) (AA-SSA) and poly(acrylic acid) – poly(2-acrylamido-2-methylpropane sulphonic acid) (AA-AMPS) dispersing agents on the viscoelastic and mechanical properties of precipitated calcium carbonate-latex composites used was investigated. Four different formulations were prepared using carboxylated styrene butadiene (SBR) and styrene-acrylate (SA) latexes. Pore space was characterised using mercury porosimetry. The storage modulus and loss factor were evaluated through dynamic mechanical thermal analysis (DMTA) low frequency single cantilever bending mode. The ultimate tensile strength and the Young modulus were also measured. At low latex contents, storage modulus was found to be higher for SBR latex composites. At high latex content, the SA storage modulus was found to be higher. It is suggested that at lower latex content, the viscoelastic properties are function of physical microstructure, which at low latex is influenced by the latex glass transition temperature (Tg). Softer latex spreads more on the pigment surface providing higher stiffness, since pigments are held together by latex bridges. At higher latex content, the composite stiffness tends to be more dependent on the stiffness of the pure latex. The AA-SSA dispersant creates strong pigment–latex interfacial adhesion in dry composites, which is reflected in high elastic modulus and tensile strength. The AA-AMPS dispersant formulations had greater resistance to water. Due to the compatibility between the AMPS blocks and the SBR latex within the composite, higher storage modulus stability in water saturated composites is measured (at room temperature 56% of the storage modulus is preserved).     

Glass bead-filled polypropylene part I: Rheological and mechanical properties

Five glass bead-filled polypropylene composites were rheologically characterized at 240°C using two rotational rheometers to obtain low shear-rate data and a capillary rheometer to obtain high shear-rate data. Both steady and dynamic properties were measured at low shear rates. Each composite was also injection molded into tensile and flexural test bars for a mechanical properties profile at 25°C. The tensile modulus was determined from a simple extensional deformation whereas the flexural modulus was determined from a three-point-bend test. The relative shear viscosity and relative loss modulus are different nonlinear functions of the volume fraction of beads at a constant shear rate, while the relative storage modulus appears to be a linear function of bead fraction. The relative viscosity decreases with increasing shear rate and the zero shear-rate data are in very good agreement with the Guth-Gold equation. The relative tensile modulus and relative flexural modulus are each linear functions of bead fraction over the entire range of filler concentration, 0-29 vol percent. From these data it is concluded that a simple correspondence between slow viscous flow and small strain elasticity does not exist for these composites.     

Constitutive relationships for the mechanical properties of anisotropic,partially crystalline polymers

Constitutive relationships are presented to relate the directional dependence of the mechanical properties of anisotropic, partially crystalline polymers to (a) the percent crystallinity, (b) characteristics of the crystalline and amorphous orientation distribution, and (c) the mechanical properties of the crystalline and amorphous components. These relationships were tested with structural and dynamic mechanical data obtained for isotactic polypropylene films in various states of crystalline and amorphous orientation. The dynamic mechanical properties of the crystalline and amorphous components were treated as parameters and evaluated from dynamic mechanical measurements along the longitudinal and transverse direction of three different film samples. These mechanical parameters, and the associated structural parameters, were in turn used to predict the dynamic mechanical spectra for a fourth, independent, film sample. The predicted values for the storage and loss modulus, along various directions of loading, were within 10 percent of the measured values over the temperature range of ?80°C to 80°C.     

The effect of ultra-high molecular weight polyethylene fiber on the mechanical properties of acrylic bone cement

The effects of the addition of ultra-high molecular weight polyethylene fiber (UHMWPE) on the mechanical properties of standard surgical Simplex-P radiopaque bone cement have been investigated. It was found that the tensile strength and tensile modulus were apparently not improved by the incorporation of UHMWPE in the acrylic bone cement. The results of bending strength and bending modulus indicated that a reinforcing effect is obtained at UHMWPE contents as low as 1 wt%, and then levelled off with increasing UHMWPE contents. When the UHMWPE contents as low as 2 wt%, the values of compressive strength and modulus seemed approximate the same; whereas the values of compressive strength and modulus decreased with increasing UHMWPE contents. From the results of dynamic mechanical analysis (DMA), the values of dynamic storage modulus of bone cement increased at UHMWPE fiber as low as 2 wt%, but beyond that UHMWPE content the value of the dynamic storage modulus decreased with increasing UHMWPE contents. The same results were also found for the dynamic loss modulus. When methyl methacrylate was grafted onto UHMWPE by plasma and UV irradiation treatment, it was found that by adding the treated UHMWPE fiber in acrylic bone cement had a significant reinforcing effect on the mechanical properties of bone cement.     

The strain sensing and thermal–mechanical behavior of flexible multi-walled carbon nanotube/polystyrene composite films

The strain sensing and thermal–mechanical behaviors of well dispersed multi-walled carbon nanotube/polystyrene (MWCNT/PS) composite films with different wt.% of carbon nanotubes were analyzed. The thermal–mechanical properties are studied using a dynamical mechanical analyzer and the results give their storage modulus (E′) and loss modulus (E″) as a function of temperature. We found an increase in E′ of up to 122% at 80 °C for a 6 wt.% MWCNT/PS composite compared to PS. The glass transition temperature increased significantly with an increase in MWCNTs concentration. The strain sensing behavior of the films is measured by applying an axial load over film which is attached to a brass specimen. The composite films exhibit excellent strain sensing behavior for different MWCNT contents. The result shows that an electromechanical response of the composite films varies linearly with applied strain even at high strains.     

Dynamic mechanical behavior of flexible graphite made from exfoliated graphite

The low-frequency dynamic mechanical properties of low density flexible graphite (0.027–0.089 g/cm³, obtained by compressing exfoliated graphite at 0.3–1.7 MPa without a binder) are different in flexure and compression. The storage and loss moduli and the loss tangent are higher under flexure than compression. Under flexure, the storage modulus is essentially unaffected by increasing the static strain while the loss tangent and loss modulus decrease. Under compression, both storage and loss moduli increase with increasing static strain, while the loss tangent slightly decreases. The storage and loss moduli are higher and the loss tangent is lower for out-of-plane compression than for in-plane compression. The storage and loss moduli increase with increasing fabrication pressure, while the loss tangent decreases. Energy dissipation is much more effective under flexure than compression. Flexure appears to provide more sliding of the graphite layers than compression. For the highest energy dissipation under flexure, a low static strain is recommended; for high energy dissipation under compression, a high static strain is recommended.     

Complex evaluation of the thermostability of aromatic fibres

The change in the mechanical properties of the aromatic fibres Armos, Arimid-T, and Togilen in heat treatment was investigated. The change in the strain properties was examined in detail for the first time: the strain modulus and strain energy causing breakage of the fibres during thermochemical aging. It was shown that the intensity of thermochemical aging, estimated by the relative change in the strength and elongation, and strain energy to break differed significantly and should be taken into consideration as a function of the conditions of use of the fibres. Of all fibres investigated, the smallest relative change in the mechanical properties was observed in Arimid-T fibre, and the most important change was observed in Armos and SHM (synthetic high-polymer material) fibres.St. Petersburg Academy of Technology and Design. Translated from Khimicheskie Volokna, No. 6, pp. 43–47, November–December, 1993.