Temperature effects viscoelasticity

The coefficient is related to the abrasion speed relation at constant energy and temperature. It is negative showing that at a constant temperature the abrasion would decrease with increasing speed, emphasizing the viscoelastic nature of abrasion. The coefficient bj is positive and can be taken as the temperature effect due to both energy and speed. 

Fig. 3.14. The data is for a very broad range of times and temperatures. The superposition principle is based on the observation that time (rate of change of strain, or strain rate) is inversely proportional to the temperature effect in most polymers. That is, an equivalent viscoelastic response occurs at a high temperature and normal measurement times and at a lower temperature and longer times. The individual responses can be shifted using the WLF equation to produce a modulus-time master curve at a specified temperature, as shown in Fig. 3.15. The WLF equation is as shown by Eq. 3.31 for shifting the viscosity. The method works for semicrystalline polymers. It works for amorphous polymers at temperatures (T) greater than Tg + 100 °C. Shifting the stress relaxation modulus using the shift factor a, works in a similar manner.

Temperature variations during the formation of LDPE foam sheet were investigated. A thermal model was coupled with a viscoelastic growth model, and an iterative finite difference technique was used to solve unsteady heat transfer equations and viscoelastic growth equations. The heat transfer characteristic time became comparable to the expansion time when the sheet thickness decreased to the millimetre range, during which foam thickness and density became sensitive to temperature effects. 12 refs. USA... 

Finally, it is instructive to compare the temperature effect on the tensile strength of the SBS and SIS block polymers. As noted previously (Figure 6) the tensile strength of an elastomer vulcanizate can be related to the difference between the test temperature and the Tg of the elastomer, in accordance with the viscoelastic theory of tensile strength. Since the Tg values for polyisoprene ( — 65°C) and polybutadiene ( —95°C) differ... 

However, there are, as always, complications both Tb and temperature effect is of importance the continuing plastic deformation results locally in high heat dissipation, which, due to the low heat conduction of polymers, is not transported to the environment. An estimation of the local temperature increase can be made with ... 

With polymers, complications may potentially arise due to the material viscoelastic response. For glassy amorphous polymers tested far below their glass transition temperature, such viscoelastic effects were not found, however, to induce a significant departure from this theoretical prediction of the boundary between partial slip and gross slip conditions [56]. 

Katsuta, K. and Kinsella, J. E. 1990. Effects of temperature on viscoelastic properties and activation energies of whey protein gels./. FoodSci. 55 1296-1302. 

Note also that infinitesimal temperature changes are not required in this approach. An interesting particular case is that one which external forces are absent. In this situation, the deformation (expansion or contraction) of the viscoelastic system can be due only to temperature effects. In the case of a temperature jump AT, Eq. (16.44b) leads to the relation... 

Aim of this paper is to investigate if the rate and temperature effects on the fracture parameters obtained by the EWF approach under plane stress condition are in some way related to the viscoelastic nature of the selected material (semicrystalline PET). 

The first two terms on the right-hand side of equation [12.6] are viscoelastic terms proposed by Schapery, where e represents uniaxial kinematic (or total) strain at time t, o is the Cauchy stress at time t, is the instantaneous compliance and AD(r[i ) is a transient creep compliance function. The factor g defines stress and temperature effects on the instantaneous elastic compliance and is a measure of state dependent reduction (or increase) in stiffness. Transient compliance factor gi has a similar meaning, operating on the creep compliance component. The factor gj accounts for the influence of loading rate on creep. The function i ) represents a reduced timescale parameter defined by ... 

Temperature effect is usually considered in the study of viscoelastic materials. In order to describe the mechanical behavior of polymer bonded explosives (PBX) under... 

As expected, test temperatin-e will have a dramatic effect on the FCP kinetics of polymers owing considerably to their temperature-dependent viscoelastic nature. Indeed, studies of polystyrene and acrylonitrile-butadiene-styrene (ABS) have shown that FCP rates for given AX level generally decrease with decreasing test temperature (80). By contrast, a minimum FCP resistance was noted in polycarbonate and polysulfone at intermediate test temperatures (81,82). A complex test-temperatin-e response was also noted in studies on the influence... 

The technique also measures the modulus (stiffness) and damping (energy dissipation) properties of materials as they are deformed under periodic stress. Such measurements provide quantitative and qualitative information about the performance of the materials. The technique can be used to evaluate elastomers, viscous thermoset liquids, composite coatings, and adhesives, and materials that exhibit time, frequency, and temperature effects or mechanical properties because of their viscoelastic behaviour. 

Previously we have referred only indirectly to the effect of temperature on viscoelastic behaviour. From a practical viewpoint, however, the temperature dependence of polymer properties is of paramount importance because plastics and rubbers show very large changes in properties with changing temperature. 

Time and Temperature Effects The viscoelastic characteristics of stress-strain behavior of glassy amorphous polymers can be approached through considering that the stress at any time t is the sum of all the little stresses, 5g, each of which is the result of many incremental relaxing stresses each started at a progressively different time, f. Each 5o produces an incremental strain, 5e, and... 

Abstract Rubber materials are viscoelastic systems whose properties, broadly speaking, are complex functions of time, strain, strain rate, temperature (and composition if they are inhomogeneous). Material functions are mathematical relationships that intend to describe the behavior of a material, either a solid or a liquid, when submitted to a range of strains or strain rates, with obviously temperature effects. For viscoelastic materials, such as rubber gum and compounds, these functions obviously encompass both the linear and the nonlinear domains. Providing material functions are considered in their full complexity, in other terms with respect to a multiparametric approach, they provide information about the processing behavior and the mechanical properties of rubber systems. 

Effect of Temperature on Viscoelastic Properties of Amorphous Polymers... 

Recently, Matadi Boumbimba et al. [12] proposed a temperature- and frequency-dependent version of the rule of mixtures to describe the viscoelastic response, in terms of storage modulus, of PMMA/Cloisite 20A and SOB. In the present work, to predict the effective viscoelastic response of polymer-based nanocomposites, the elastic-viscoelastic correspondence principle [11] is applied to our micromechanical model. The two implicit equations (5) become ... 

Viscoelasticity Time-temperature effects under dynamic/cyclic loading Specific heat, thermal conductivity and thermal expansion Optical properties Chemical resistance Water absorption Important process design parameters Colour, reflectance and opacity Resistance to chemical reactions during and after processing Measures material-solvent interaction... 

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