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Results for “linear viscoelasticity”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Measurement of the linear viscoelastic behavior of antimisting kerosene

Measurements of dynamic viscoelastic properties in very small oscillating shear deformations was made on solutions of a jet fuel, Jet A, containing an antimisting polymeric additive, FM-9. A few measurements were also made on solutions of FM-9 in a mixed solvent of mineral oil, Tetralin, and 0-terphenyl. Two samples of FM-9 had approximate number-average molecular weights of 12,000,000 and 8,100,000 as deduced from analysis of the measurements. The ranges of variables were 2.42 to 4.03 g/1 in concentration (0.3 to 0.5% by weight), 1 to 35 in temperature, 1.3 to 9.4 cp in solvent viscosity, and 103 to 6100 Hz in frequency. Measurements in the Jet A solvent were made both with and without a modifying carrier. The results were compared with the Zimm theory and the viscoelastic behavior was found to resemble rather closely that of ordinary non-polar polymers in theta solvents. The relation of the results to the antithixotropic behavior of such solutions a high shear rates is discussed in terms of intramolecular and intermolecular interactions.

Ferry, J. D.↗
NASA NTRS1983

A non-linear viscoelastic characterisation method for matrix resin composites

Lifetime prediction of matrix resin composites is an important problem because of their viscoelastic character. If the Time-Temperature-Stress-Superposition principle is valid, results from short time tests at high stress levels can give the necessary information for the prediction of long time behavior. At such stress levels the viscoelastic response is nonlinear. In this contribution the basis of a computer routine is presented starting from a thermodynamical formulation given by Schapery. This method gives in an accurate way the different material parameters in that nonlinear constitutive equation for different stresses and temperatures.

Hiel, C. C.↗
NASA NTRS1989

Non linear viscoelasticity applied for the study of durability of polymer matrix composites

A methodology is described for the durability analysis of polymer matrix composites, based on nonlinear viscoelasticity theory. The durability analysis is performed on the basis of a certain number of tests carried out on limited and, if possible, short time scale by the use of accelerating factors. The method was applied to thermomatrix composites under uniaxial and biaxial loadings, showing satisfactory agreement between the life-time predictions and the published data on real-time behavior.

Cardon, A.↗
NASA NTRS1993

Reply to the comment by Y. Ricard, R. Sabadini, and G. Spada

We welcome this opportunity which Drs. Ricard, Sabadini and Spada (RSS) have offered us to elaborate on some points concerning the connection between convective circulations and rotational dynamics. The relationship of the linear viscoelastic normal-mode theory to other approaches, such as viscous and the non-linear viscoelastic treatments, can be found in Moser et al. (1993). We will address the issues raised by RSS by first going over the reference system. This will be followed by a discussion concerning long-term polar wander and relative angular momentum. We will also go over the issues concerning the off-diagonal terms in the total moment of inertia and polar wander.

Moser, Jiri↗
NASA NTRS1990

Instability of fiber-reinforced viscoelastic composite plates to in-plane compressive loads

This study analyzes the stability behavior of unidirectional fiber-reinforced composite plates with viscoelastic material behavior subject to in-plane biaxial compressive edge loads. To predict the effective time-dependent material properties, elastic fibers embedded in a linearly viscoelastic matrix are examined. The micromechanical relations developed for a transversely isotropic medium are discussed along with the correspondence principle of linear viscoelasticity. It is concluded that the stability boundary obtained for a viscoelastic plate is lower (more critical) than its elastic counterpart, and the transverse shear deformation effects are more pronounced in viscoelastic plates than in their elastic counterparts.

Chandiramani, N. K.↗
NASA NTRS1987

Linear and nonlinear mechanical properties of a series of epoxy resins

The linear viscoelastic properties have been measured for a series of bisphenol-A-based epoxy resins cured with the diamine DDS. The linear viscoelastic master curves were constructed via time-temperature superposition of frequency dependent G-prime and G-double-prime isotherms. The G-double-prime master curves exhibited two sub-Tg transitions. Superposition of isotherms in the glass-to-rubber transition (i.e., alpha) and the beta transition at -60 C was achieved by simple horizontal shifts in the log frequency axis; however, in the region between alpha and beta, superposition could not be effected by simple horizontal shifts along the log frequency axis. The different temperature dependency of the alpha and beta relaxation mechanisms causes a complex response of G-double-prime in the so called alpha-prime region. A novel numerical procedure has been developed to extract the complete relaxation spectra and its temperature dependence from the G-prime and G-double-prime isothermal data in the alpha-prime region.

Curliss, D. B.↗
NASA NTRS1989

Recent results concerning the stability of viscoelastic shear deformable plates under compressive edge loading

Some recent results obtained by the authors are summarized concerning the stability of transversely isotropic flat panels whose materials exhibit a viscoelastic behavior and whose edges are subjected to in-plane biaxial compressive loads. Two transversely isotropic type materials, largely used in advanced technology, are considered: (1) the pyrolytic-graphite type, used in the thermal protection of aerospace vehicles, and (2) the type corresponding to unidirectional fiber-reinforced composites. In the former case, the planes of isotropy are parallel at each point to the midplane of the plate. In the latter case, they are normal to the fiber directions. The micromechanical relations developed by Aboudi (1984, 1986, 1987) are considered in conjunction with the correspondence principle of linear viscoelastic theory in order to predict the macroscopic viscoelastic properties of a material composed of uniaxial elastic fibers embedded in a linear viscoelastic matrix.

Librescu, L.↗
NASA NTRS1979

Viscoelastic properties of entangled polymers - Ternary blends of monodisperse homopolymers

In a previous publication from this laboratory, the Rouse-Bueche-Zimm molecular theory of viscoelasticity has been extended by using a transient network model to apply to binary blends of monodisperse polymers with chain entanglements. The dynamics of the entanglements were modeled both by the enhanced frictional coefficients and by the additional elastic couplings. It was recognized that entanglements not only may form between chains of the same lengths (intracomponent entanglements) but also between those of different lengths (intercomponent entanglements). At a given intercomponent entanglement, the longer chain was assumed to have the frictional coefficient of the shorter chain. Similarly, for blends consisting of several monodisperse components with different molecular weights, such modifications are also required to predict their linear viscoelastic behavior. The frequency of these interactions is assumed to be proportional to the weight ratio of the respective component chains in the blend. Equations of motion are formulated for each component and solved numerically for the relaxation time spectra. Linear viscoelastic properties such as the dynamic mechanical moduli, stress relaxation moduli, and zero-shear viscosity can then be computed for these systems by linear summation of those of the components.

Soong, D.↗
NASA NTRS1991

Composite propellant technology research: Mechanical property characterization

Proof for the existence of a single Poisson's ratio function in isotropic linear viscoelastic materials is presented. An in-depth discussion is given of three dimensional viscoelastic material properties and their relationships to linear isotropic and orthotropic viscoelastic materials. A discussion of the alternate invariant definition as used by Abaqus and how it relates to the form used by Dr. S. Peng is presented.

Bower, Mark V.↗
NASA NTRS1975

Thermomechanical coupling in fatigue fracture of viscoelastic materials

Subcritical crack growth in a linear viscoelastic material subjected to cyclic loading is investigated starting with the thermodynamic power balance. Physically, it is supposed that the subcritical slow crack growth is due to local weakening of the material in the neighborhood of the crack tip. Under fatigue loading it is assumed that all energy dissipation goes into heat and that this heat build-up is the dominant irreversible process governing crack growth. The cycle averaged temperature distribution around the crack tip is obtained from local application of the first law of thermodynamics (i.e., conservation of energy). The analysis leads to the solution of a nonlinear integro-differential equation for crack length as a function of time which is coupled with the local energy equation. A regular perturbation technique is used to obtain an analytical solution which compares very well with experimental results.

Hufferd, W. L.↗