Viscoelastic composite

Viscoelastic characteristics of composite materials usually result from a viscoelastic-matrix material such as epoxy resin. General stress analysis of viscoelastic composites was discussed by Schapery [6-54]. An important application to laminated plates was made by Sims [6-55]. 

R. A. Schapery, Stress Analysis of Viscoelastic Composite Materials, in Composite Materials Workshop, S. W. Tsai, J. C. Hatpin, and Nicholas J. Pagano (Editors), St Louis, Missouri, 13-21 July 1967, Technomic, Westport, Connecticut, 1968, pp. 153-192. Also Journal of Composite Materials, July 1967, pp. 228-267. 

Figure 12 Three-dimensional plot of the tear energy of a viscoelastic composite as a function of temp, and strain rate. Source Ref. 39.

Volume fraction viscoelasticity Composite modulus hardness ... 

Roscoe60 and Laws and McLaughlin30 have considered the problem of linearly viscoelastic elements, where the extremum theorems of elasticity theory do not apply. Roscoe considers linear viscoelasticity and uses the complex modulus comparing the material with an elastic one of the same phase geometry. He shows that the real parts of the overall moduli of the viscoelastic composite are not less than the corresponding overall moduli of the elastic composite when its phases have moduli equal to the real parts of the moduli of the corresponding phases in the viscoelastic composite. Similarly for the imaginary parts. 

The scope of the series covers the entire spectrum of solid mechanics. Thus it includes the foundation of mechanics variational formulations computational mechanics statics, kinematics and dynamics of rigid and elastic bodies vibrations of solids and structures dynamical systems and chaos the theories of elasticity, plasticity and viscoelasticity composite materials rods, beams, shells and membranes structural control and stability soils, rocks and geomechanics fracture tribology experimental mechanics biomechanics and machine design. 

TG-DTA Characterisation of carbon black [149], flammability evaluation [64], polymer degradation studies [65], ageing studies [70-72], product control [77, 81], combustion performance [83], safety evaluation [83], antioxidation activity [68], pyrolysis of rubbers [82], thermal stability [67, 69, 76, 77], interfacial junctions in viscoelastic composites [78], weathering [72], vulcanisation [73], oxidative behaviour [79], materials evaluation [80], failure analyses [81],... 

Hypochlorite hard surface and drain cleaner compositions exhibiting enhanced extensional viscosity are mentioned in U.S. Patents 5,728,665 and 5,916,859. The viscoelastic compositions are intended for use with trigger sprayers and the hexa-decyl amineoxide/organic counterion compositions provide low bleach odor and reduced spray misting. The patent contains extensional viscosity data in support of the claims. Viscosity as a function of shear rate at various Cm diphenyloxide disulfonate concentrations is shown in Figure 4.5. Examples of steady shear and extensional viscosity as a function of shear rate and extensional rate are shown in Figure 4.6 and Figure 4.7. 

Schapery RA, Sicking DL (1995) On nonlinear constitutive equations for elastic and viscoelastic composites with growing damage. In Baer A (ed) Mechanical behavior of materials. Delft University Press, Delft, pp 45-76... 

Zhang J, Zheng GT (2007) The biot model and its application in viscoelastic composite structures. J Vib Acoust 129 533-540... 

There is a large body of literature on the purely elastic interaction of non-pris-matic structural elements within a deformed composite solid (e.g. 63-70) this literature also forms part of the theoretical foundation of the behavior of viscoelastic composite solids. While not generally discussing these foundations three groups of model descriptions of multi-phase materials will be singled out ... 

Bradshaw, R.D. Characterization and modeling of viscoelastic composite laminates with nonisothermal physical aging, in Mechanical Engineering. Northwestern University, Evanston (1997)... 

Polymer-based rocket propellants are generally referred to as composite propellants, and often identified by the elastomer used, eg, urethane propellants or carboxy- (CTPB) or hydroxy- (HTPB) terrninated polybutadiene propellants. The cross-linked polymers act as a viscoelastic matrix to provide mechanical strength, and as a fuel to react with the oxidizers present. Ammonium perchlorate and ammonium nitrate are the most common oxidizers used nitramines such as HMX or RDX may be added to react with the fuels and increase the impulse produced. Many other substances may be added including metallic fuels, plasticizers, stabilizers, catalysts, ballistic modifiers, and bonding agents. Typical components are Hsted in Table 1. 

Colloidal State. The principal outcome of many of the composition studies has been the delineation of the asphalt system as a colloidal system at ambient or normal service conditions. This particular concept was proposed in 1924 and described the system as an oil medium in which the asphaltene fraction was dispersed. The transition from a coUoid to a Newtonian Hquid is dependent on temperature, hardness, shear rate, chemical nature, etc. At normal service temperatures asphalt is viscoelastic, and viscous at higher temperatures. The disperse phase is a micelle composed of the molecular species that make up the asphaltenes and the higher molecular weight aromatic components of the petrolenes or the maltenes (ie, the nonasphaltene components). Complete peptization of the micelle seems probable if the system contains sufficient aromatic constituents, in relation to the concentration of asphaltenes, to allow the asphaltenes to remain in the dispersed phase. 

Fiber-reinforced composite materials such as boron-epoxy and graphite-epoxy are usually treated as linear elastic materials because the essentially linear elastic fibers provide the majority of the strength and stiffness. Refinement of that approximation requires consideration of some form of plasticity, viscoelasticity, or both (viscoplasticity). Very little work has been done to implement those models or idealizations of composite material behavior in structural applications. 

DavkJ Ford Sims, Viscoelastic Creep and Relaxation Behavior of Laminated Composite Plates, Ph.O. dissertation. Department of Mechanical Engineering and Solid Mechanics Center, Institute of Technology, Southern Methodist University, Dallas, Texas, 1972. (Also available from Xerox University Microfilms as Order 72-27,298.)... 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

The treatment of blends as a two phase system opened up an interesting field of modifying the composite properties by the use of a (third component within the interface boundaries, which is termed as compatibilizers [1]. Such modifications are still being extended to the formation of microgel out of the interaction between the two blend partners having a reactive for functionalities. This type of interchain crosslinking does not require any compatibilizer to enhance the blend properties and also allows the blends to be reprocessed by further addition of a curative to achieve still further improved properties [3,4]. Such interchain crosslinking is believed to reduce the viscoelastic mismatch between the blend partners and, thus, facilitates smooth extrusion [5,6]. 

Lipatov et al. [116,124-127] who simulated the polymeric composite behavior with a view to estimate the effect of the interphase characteristics on composite properties preferred to break the problem up into two parts. First they considered a polymer-polymer composition. The viscoelastic properties of different polymers are different. One of the polymers was represented by a cube with side a, the second polymer (the binder) coated the cube as a homogeneous film of thickness d. The concentration of d-thick layers is proportional to the specific surface area of cubes with side a, that is, the thickness d remains constant while the length of the side may vary. The calculation is based on the Takayanagi model [128]. From geometric considerations the parameters of the Takayanagi model are related with the cube side and film thickness by the formulas ... 

In [343] it was shown, with regard to the hydrodynamic effect of fillers on the viscoelastic properties of composites, that the dynamic functions must obey the following equations ... 

From the results obtained in [344] it follows that the composites with PMF are more likely to develop a secondary network and a considerable deformation is needed to break it. As the authors of [344] note, at low frequencies the Gr(to) relationship for Specimens Nos. 4 and 5 (Table 16) has the form typical of a viscoelastic body. This kind of behavior has been attributed to the formation of the spatial skeleton of filler owing to the overlap of the thin boundary layers of polymer. The authors also note that only plastic deformations occurred in shear flow. 

Lipatov, Y. S. Relacation and Viscoelastic Properties of Heterogeneous Polymeric Compositions. Vol. 22, pp. 1 —59. 

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