Craze structural parameter

Craze structural parameter S(x) Craze surface stress distribution... 

Then, using Eqs. 17 and 18, the numerical value of the craze structural parameter S is experimentally known ... 

Fig. 47. Craze structural parameter versus craze material volume fraction v, from Eq. 20. The numerical values of = 0.048 0.007 leads to = 0.3 0.08, and indicates that the craze material volume fraction is not effected by the toluene vapors. From Ref. by permission of the publishers, Butterworth and Co. Ltd.

Crystallinity and disorder are important structural parameters for understanding relationships between structure and physical properties. Flaws and distortions are the main features that limit the ultimate properties of textile fibers. Some of these crazes, cracks and voids are revealed under the electron microscope, either on the surface or in cross sections stained with heavy metals (J, 2). However, these staining techniques (that reveal the main morphological features) make it much more difficult to determine the degree of distortion of the crystalline fraction. Theoretically, line profile studies permit separation of effects due to crystalline size from those due to structural distortions. However, the lack of peaks in semicrystalline fiber x-ray patterns hinders that approach. 

Fig. 46. Craze structural paraincier S. as defined by Eq. 17 and as determined by means of Eq. 19. This parameter includes craze fibril volume fraction and the tensile modulus of the bulk. The dashed i ojc encloses the values of for all the crazes in air, whereas the dots correspond to the crazes...

Molecular Criterion for Craze/Yield Behavior from Chain Structure Parameters... 

In terms of tonnage, polyolefins are by far the most important polymeric materials for structural applications, and there is consequently enormous interest in optimising their fracture properties. A rational approach to this requires detailed understanding of the relationships between macroscopic fracture and molecular parameters such as the molar mass, M, and external variables such as temperature, T, and test speed, v. Considerable effort is therefore also devoted to characterising the irreversible processes (crazing and shear deformation) that accompany crack initiation and propagation in these polymers, some examples of which will given. 

The selection of the dominant deformation mechanism in the matrix depends not only on the properties of this matrix material but also on the test temperature, strain rate, as well as the size, shape, and internal morphology of the rubber particles (BucknaU 1977, 1997, 2000 Michler 2005 Michler and Balta-Calleja 2012 Michler and Starke 1996). The properties of the matrix material, defined by its chemical structure and composition, determine not rally the type of the local yield zones and plastic deformation mechanisms active but also the critical parameters for toughening. In amorphous polymers which tend to form fibrillated crazes upon deformation, the particle diameter, D, is of primary importance. Several authors postulated that in some other amorphous and semiciystalline polymers with the dominant formation of dUatational shear bands or extensive shear yielding, the other critical parameter can be the interparticle distance (ID) (the thickness of the matrix ligaments between particles) rather than the particle diameter. 

As it is known [1], the main characteristics of local plasticity zone ( shear lips or crazes) are its length and critical opening 6. Both indicated parameters are connected with polymer structure fractal dimension d. The authors of Ref. [2] obtained the following relationship between 6 and d. ... 

Although the Eq. (5.3) gives for polymers good correspondence to experiment in the case of both crazes [6] and local shear zones [9], but it does not connect the parameter q with any structural characteristics of polymers. 

With the knowledge about the structure of the plastic zone in front of the crack tip, one may write down a simple equation for the surface parameter, known also as material resistance 2w. The total expended work equals that consumed on drawing the fibrils in the craze up to their maximum length at the point of break. As was discussed in the previous section, fibrils elongate by an incorporation of fresh material at the craze surface, which occurs under a constant tensile stress. Hence, we may formulate... 

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