Viscoelastic Properties Of Composites Research Articles

Multiscale modeling of viscoelastic properties of polymer nanocomposites

AbstractA methodology for simple multiscale modeling of mechanical properties of polymer nanocomposites has been developed. This methodology consists of three steps: (1) obtaining from molecular dynamics simulations the viscoelastic properties of the bulklike polymer and approximating the position‐dependent shear modulus of the interfacial polymer on the basis of the polymer‐bead mean‐square displacements as a function of the distance from the nanoparticle surface, (2) using bulk‐ and interfacial‐polymer properties obtained from molecular dynamics simulations and performing stress–relaxation simulations of the nanocomposites with material‐point‐method simulations to extract the nanocomposite viscoelastic properties, and (3) performing direct validation of the average composite viscoelastic properties obtained from material‐point‐method simulations with those obtained from the molecular dynamics simulations of the nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1005‐1013, 2005

Influence of Gradual Interphase on Overall Elastic and Viscoelastic Properties of Particulate Composites

The overall elastic and viscoelastic properties of particulate composites with graded interphase have been analyzed analytically. The localization relation for a coated particle with a graded interphase in the radial direction has been firstly derived, and the effective elastic moduli of such composites are then estimated by the mean field theory and generalized self-consistent method respectively. The effective storage and loss moduli of the composite are also determined through the dynamic correspondence principle. The results show that the nature of the interphase (soft and hard) can have important influence on the prediction for effective elastic and viscoelastic properties of the composite, especially for a soft graded interphase, the predictions based on a uniform interphase model overestimates largely the effective elastic and viscoelastic moduli of the composite.

Effect of processing conditions on mechanical and viscoelastic properties of biocomposites

AbstractTo study the effects of processing conditions on the viscoelastic and mechanical properties of biodegradable composites, we prepared several composites based on sisal fibers and biodegradable polymers. The effects of processing conditions such as the speed of rotation, temperature, and time of mixing were investigated. The mechanical and viscoelastic properties of these composites were affected by the processing conditions. This was principally due to the modification of the initial aspect ratio of the natural fibers as a result of the shear stresses that developed in the mixer during the compounding. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1637–1642, 2003

Dynamic mechanical properties and interphase fiber/matrix evaluation of unidirectional glass fiber/epoxy composites

Storage modulus, loss modulus, and loss factor of unidirectional fiber composites of epoxy resin with glass fiber were determined with a Perkin Elmer DMA-7 equipment in three point bending mode. The fibers were coated with two different types of epoxy resins and the relationship between the thickness of coating and the composite viscoelastic properties were determined. A simple micromechanical model was used to analyze the data.

Shear creep of orthogonally reinforced spherofibrous composites

Models of composites with three-dimensional structure, a proposed problem solving method, and Rabotnov's creep operators were used assuming purely elastic deformation of the composite along the orientation of the fibers to determine the viscoelastic properties of composites on inclined surfaces in a three-dimensional stressed state. The formulas used in viscoelasticity theory in the elastic region of component deformation lead to results in satisfactory accord with the reported experimental elastic properties of composites with three-dimensional structure.

Viscoelastic Minimum Principles Revisited

A problem of viscoelastic counterparts for the elastic minimum theorems is considered. A theorem is proved that gives a general algorithm for the construction of such viscoelastic minimum functionals. The established results are applied for the theoretical evaluation of the effective properties of inhomogeneous viscoelastic materials. As an example, simple bounds on the effective properties of viscoelastic composites are obtained.

Study of carbon fibre surface treatments by dynamic mechanical analysis

Dynamic mechanical and thermal analysis (DMTA) has been used to study the effects of surface treatment of carbon fibres on the viscoelastic properties of composites containing them. The fibres were treated by dip-coating, electro-polymerization, and plasma polymerization, and the behaviour of these fibres is compared with that of fibres treated by ordinary commercial oxidation and sizing procedures. Analysis of the experimental results is made both in terms of conventional approaches to viscoelastic behaviour and of the power-law analysis of the glass transition in an attempt to obtain suitable parameters for the evaluation of the effects of surface treatment.

Composite materials with viscoelastic interphase: creep and relaxation

The effect of viscoelastic interphase between elastic constituents of composites is investigated on the basis of a correspondence principle relating effective elastic and viscoelastic properties of composites, which has been previously established. Previously derived results for thermoelastic properties of unidirectional fiber composites and spherical particle composites with elastic interphase are utilized in this fashion to obtain corresponding viscoelastic effective properties. The analysis shows that significant viscoelastic effect in such unidirectional composites is confined to axial and transverse shear relaxation and creep and in particulate composites to any shear loading. The viscoelastic effect is negligible for all inputs which do not include such shear components.

Role of Adhesion in Viscoelastic Properties of Rubber-Tire Cord Composites

Abstract Dynamic mechanical measurements have been carried out on samples of rubber and PET cord-rubber composites, with and without adhesive, as a function of strain amplitude, temperature, pretension, angle of strain application and time of cycling. The results show that mechanical loss and dynamic modulus depend on these variables as well as the presence and type of adhesive at the cord-rubber interface. Based on these results, we conclude that adhesion plays a significant role in the viscoelastic properties of a composite and it is an important factor along with the properties of components in the analysis of tire performance in terms of composite properties. This study clearly shows that the maximum adhesion may not be the optimum adhesion in tire technology. The most relevant question, i.e., the determination of the optimum level of adhesion for a specific tire, however, remains unanswered. The viscoelastic properties of the composites decrease with time of cycling but the rate of decrease depends upon the level of adhesion in the starting material. This result could be important in the development of a more realistic dynamic adhesion test. Attempts to use the viscoelastic experiments with small amplitude, high frequency strain to determine the onset of fracture in the composite specimen appears to be promising. Work is in progress to determine the potential of this method in the analysis of adhesion.

Mechanical dispersion of crosslinked polymers reinforced with randomly distributed short fiber

The dynamic viscoelastic properties of composites reinforced with randomly distributed short glass and carbon fibers were studied in relation to the dependence on the fiber length, the mixing ratio of glass fibers of different length, and the kind of polymer matrix. Although the composite reinforced with glass fiber of 0.05 mm in length shows only one dispersion (α) corresponding to the primary transition of polymer matrix, those reinforced with 3- and 10-mm glass fibers, and those reinforced with the mixture of 10- and 0.05-mm glass fibers are characterized by two additional dispersions (α′ and α″) which appear on the lower frequency side or higher temperature side of the α-dispersion. The composite reinforced with 3-mm carbon fiber does not show the additional dispersions. The α′- and α″-dispersions appear irrespective of the kind of matrix polymer.