Mechanical behavior of polymers

The preceding example of superpositioning is an illustration of the principle of time-temperature equivalency. We referred to this in the last chapter in connection with the mechanical behavior of polymer samples and shall take up the... 

The mechanical behavior of polymers, as well as many other topics in polymer engineering, are presented in an up-to-date way in a book by McCrum et al. (1998). 

Many polymers are not completely amorphous but are more or less crystalline. The degree of Crystallinity and the morphology of the crystalline material have profound effects on the mechanical behavior of polymers, and since these factors can be varied over a wide range, the mechanical properties of crystalline polymers take on a bewildering array of possibilities. 

Alfrey, T. 1948. Mechanical Behavior of Polymers. Interscience, New York. 

Kotaka,T., Osaki,K. Normal stresses, non-Newtonian flow, and dynamic mechanical behavior of polymer solutions. J. Polymer ScL Pt.C 15,453-479 (1966). 

The factors controlling the mechanical behavior of polymer-coupling agent-metal oxide systems have been discussed in terms of the weakest link in a chain concept. Determination of the locus of failure and thus the weak link is not usually reliable by visual inspection, and surface roughness can cause misleading spectroscopic results if failure is near an interface. 

The temperature increase of a pellet by this rather simplified treatment can be calculated knowing p, cp, estimating dLp/dt, and thus A p, and evaluating experimentally (F/Ap)(Tp). This treatment is similar to that of Kim and Gogos in its ability to estimate pellet heating by PED in a simple fashion, needing only the experimental evaluation of the large deformation mechanical behavior of polymer solids. 

In this chapter we study the characteristics that determine the crystallinity of polymers, crystalline morphology, and the factors affecting the crystallization and melting of polymers. We describe the amorphous state, focusing on the glass transition, a fundamental property for defining the mechanical behavior of polymers. The entire description refers exclusively to synthetic polymers. 

The Influence of Vacuole Formation and Growth on the Mechanical Behavior of Polymers... 

The mechanical behavior of polymers is well recognized to be rate dependent. Transitions from ductile to brittle mode can be induced by increasing the test speed. The isotactic PP homopolymer with high molecular weight is ductile at low speed tensile tests. It is brittle at tension under high test speeds at room temperature. Grein et al. (62) determined the variation of Kiq with test speed for the a-PP CT samples (Fig. 11.22). The force-displacement (F-J) curves and the schematic diagrams of the fracture surfaces of CT samples are presented in Fig. 11.23. At a very low test speed of 1 mm s , the F-d curve exhibits a typical ductile behavior as expected. At 10 mm s, the F-d curve stiU displays some nonlinearity before the load reaches its maximum value, but this is substantially suppressed as test speeds increase further. The samples fail in brittle mode at test speeds >500 mm s . From Fig. 11.22, the Kiq values maintain at 3.2 MPam at test velocities from 1 to... 

In this work, the plastic deformation and the damage of ternary PP/PA6/POE were studied as completely as possible, and the mechanisms of plastic deformation were revealed by microscopic observation. The results obtained are original and will be helpful to well understand the mechanical behavior of polymer blends under large deformation. 

While we do not want to give a sophisticated model including all the effects found in the mechanical behavior of polymers, we restrict ourselves to the simplest case, namely to an elastic small-strain model at constant temperature. Therefore, the governing variables are the linear strain tensor [Eq. (13)] derived from the spatial gradient of the displacement field u, and the microstructural parameter k and its gradient. The free energy density is assumed to be a function of the form of Eq. (14). 

The above discussion clearly indicates that stereo regularity, chain flexibility, polarity, and other steric factors have profound influence on crystallizability and melting points and, hence, as we shall see later, play an important role in the thermal and mechanical behavior of polymers. 

Petrich, R. P. (1972), Impact Reinforcement of Poly(vinyl chloride), paper presented at SPE RETEC meeting, Cleveland, Ohio, March 7, 1972 (also presented at Polymer Conference Series, Mechanical Behavior of Polymers, University of Utah, June 1974). 

FIGURE 11.7 Mechanical behavior of polymers. (Reproduced from Encyclopedia pf Materials Science and Engineering, ed. byM.B. Sever, Cambridge, MA MET Press, 1986, p. 2917.)... 

Luo, J.-J. and Daniel, I. M. Characterization and modeling of mechanical behavior of polymer/clay nanocomposites. Composites Science and Technology 2003 63 1607-16. 

We have already referred to various kinds of data on mechanical behavior of polymers. We are now going to consider methods of acquisition of such information. The most fi equently used are the so-called quasistatic methods which involve relatively slow loading. Tension, compression, and flexure belong here. The quasistatic methods have to be distinguished from so-called transient tests which include stress relaxation and creep. There are also impact tests and dynamic mechanical procedures which will be defined later. 

Traditionally—and that started with metals—one distinguishes two types of mechanical behavior of polymers brittle and ductile. It will be clear to us after discussion of the free volume concept in Subsection 24.1.3 that brittle behavior will dominate at low temperatures when the free... 

It should be remembered that the moduli and compliances under discussion are functions of frequency. The quantities E, D etc. should thus be written E (a>), D (a>), and so forth. The frequency dependence of these quantities is governed by the same distribution of relaxation or retardation times as is stress relaxation, creep or other time-dependent mechanical phenomena. Single relaxation or retardation times cannot depict the frequency dependence of the dynamic mechanical behavior of polymers. 

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

The mechanical behavior of polymer composites is not only defined by short-term properties such as stiffness, strength, and toughness but also long-term properties such as creep, stress relaxation, and fatigue. All such properties, vhich are affected by temperature and type of environment, can be modified through the addition of fillers. 

Time-temperature equivalence n. Because an increase in temperature accelerates molecular motions, mechanical behavior of polymers at one temperature can be used to predict those at another by means of a shift factor equal to the ratio of relaxation time at the second temperature to that at the first. The principle can be used to combine measurements made at many temperatures into a single master curve for a reference temperature over many decades of time. 

Prediction of the long term mechanical behavior of polymers is still one of the great unsolved problems in the plastic industry, and this contribution provides a step in this direction. 

The difference in the mechanism of influence phosphororganic compoimds on mechanical behavior of polymers, most likely, is connected from them above molecule by structure. Block-copolyester BSP-7F it is worse "diphenylol" than a block-copolymer on mechanical to characteristics for this reason. 

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