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Fracture stretch zone

Fractography shows that between fatigue striations and final dimple or cleavage fracture by overload there is a featureless zone known as stretched-zone. This zone... [Pg.586]

Alle the deformation zones contain a finite and equal number of extended chains in their most highly stretched strands. This surprising conformity of the deformation zones may well be the consequence of the imposed plane-strain fracture condition which impedes lateral contraction of the material. However, no quantitative explanation has been presented as yet. A plausible explanation would be to assume that due to the hindered lateral contraction additional tensile stresses are transferred to the most extended strand with each additional chain pulled out of the matrix [112]. [Pg.346]

Fig. 8.1. Toughening mechanisms in rubber-modified polymers (1) shear band formation near rubber particles (2) fracture of rubber particles after cavitation (3) stretching, (4) debonding and (5) tearing of rubber particles (6) transparticle fracture (7) debonding of hard particles (8) crack deflection by hard particles (9) voided/cavitated rubber particles (10) crazing (II) plastic zone at craze tip (12) diffuse shear yielding (13) shear band/craze interaction. After Garg and Mai (1988a). Fig. 8.1. Toughening mechanisms in rubber-modified polymers (1) shear band formation near rubber particles (2) fracture of rubber particles after cavitation (3) stretching, (4) debonding and (5) tearing of rubber particles (6) transparticle fracture (7) debonding of hard particles (8) crack deflection by hard particles (9) voided/cavitated rubber particles (10) crazing (II) plastic zone at craze tip (12) diffuse shear yielding (13) shear band/craze interaction. After Garg and Mai (1988a).
Fig. 13.35 A longitudinal section from the neck portion of a tensUe fracture zone of Nylon-66 with a weight fraction of rubber of 0.19, showing the elongated sausage-like stretched cavities, after cavitation in the rubber (Muratoglu et al. (1995b) courtesy of Elsevier). Fig. 13.35 A longitudinal section from the neck portion of a tensUe fracture zone of Nylon-66 with a weight fraction of rubber of 0.19, showing the elongated sausage-like stretched cavities, after cavitation in the rubber (Muratoglu et al. (1995b) courtesy of Elsevier).
Toughening mechanisms due to the elastomer spheres include shear-band formation, fracture of rubber particles, stretching, debonding and tearing of rubber particles, rubber cavitation, transparticle fi acture, crazing, formation of a plastic zone at the craze tip, diffuse shear-yielding, as well as shear band/craze interaction. [Pg.565]

Even the most brittle polymers demonstrate some localized plastic deformation - in front of the crack tip, there exists a small plastic zone where stretching of chains, chain scission, and crack propagation appear in a small volume. The size of that plastic zone is too small to manifest in macroscopic plastic yielding and the crack propagates in a brittle manner. The relative low energy absorbed by the sample on its fracture is almost entirely that dissipated inside the small plastic zone. [Pg.1206]

Micro plastic zones occur even in the brittle fracture of polymers in front of the crack tip. Crazes are localized bands of plastically deformed polymer material, which always appear perpendicular to the stretching direction. They are constituted hy polymer fibrils of about 5 -15 nm diameter, which are stretched in the loading direction and separated by elongated voids with diameters up to about 50 nm. The craze-bulk interface is relatively sharp and only about 10 nm thick. Crazing is connected with volume increase of the material. In Part II, Figs. 1.4 and 1.5 and those figures that follow show typical examples of crazes in PS. Crazes in other polymers can also possess a coarser internal structure. [Pg.22]

In contrast to metals, plastics are mostly subject to a purely physical process in which time-dependent diffusion and swelling processes play a considerable role. At first, fine crazes are observed at the surface from which fracture will later develop. Crazes are crack-like damage zones within which no complete material separation takes place as is seen in cracks, but where load transfer is still possible via fibrillated or homogeneously stretched material between the craze walls. Such crazes represent weak points under impact load and can develop into true cracks under long-lasting load that will lead to fracture. Such craze formation is visible to the eye in transparent plastics and sometimes also in unfilled, non-transparent plastics [13]. [Pg.692]

Stretched fibrils The final fracture zone can include stretched fibrils and other features indicative of ductile cracking. It is important to note that ESC is not a chemical attack mechanism therefore, features that are normally associated with chemically induced molecular degradation will not normally be present. [Pg.37]

The term micromechanics covers aU processes on mesoscopic, microscopic, and nanometer scales that occur inside a material in response to an external loading (2). These processes include reactions of macromolecules, such as stretching or scission of molecular segments, reptation (snake-like) movement, micro3neld-ing, microcavitation, forming of crazes, shear bands or deformation zones up to crack initiation, propagation, emd fracture. [Pg.664]


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See also in sourсe #XX -- [ Pg.162 , Pg.163 ]




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