Particle cavitation

Particle cavitation It is produced by the beam of the elementary particles, e.g. a proton, rupturing a liquid, as in the case of a bubble chamber. 

It can be said that acoustic and hydrodynamic cavitation are the result of the tensions prevailing in a liquid, while optic and particle cavitation are the consequence of the local deposition of energy. The classification scheme for the phenomena of cavitation has been shown schematically in Fig. 2.1. Once the cavities are generated, subsequent expansion of the minute cavity may be achieved by reducing the ambient pressure using static or dynamic means. The surrounding... 

Rubber particle cavitation, 20 353 Rubber particles, morphology of,... 

These differences were correlated with the size of the rubber particles in the systems the smaller the diameter of the dispersed phase (e.g. the lower the interparticular distance), the higher the benefits of a /3-nucleation (Fig. 25b). For the grades with the smallest particle sizes, it might be attributed to an easier plastic deformation of the matrix once the damage mechanisms initiated (by particle cavitation) as a result of the smaller matrix ligaments between the rubber phase. 

To answer this question, a special testing procedure has been implemented. It allows the comparison of the resistance to fracture of both non-nucleated and -modified grades, once the particle cavitation initiated. It consists of ... 

This is a simplification of the process occurring in a curing resin-hardener system and a detailed discussion may be found in Pascault et al (2002), Williams et al (1997) and Inoue (1995). The main parameter that it is important to control in the reactive phase separation is the diameter of the elastomer particle. This is because the toughness of the resulting network is controlled by the energy-absorbing mechanisms such as particle cavitation and rubber bridging of cracks. Also of importance is the limitation of the effect of the rubber dispersed phase on the critical properties of the cured epoxy resin such as the stiffness and Tg. This will be affected by the extent to which the rubber dissolves in the matrix-rich phase. 

Finally, it should be noted that stress-whitening arises because these voids, created by cavitation and debonded particles, scatter light. Hence, it is observed that the most intense stress-whitening is present in the recipe that undergoes the greatest extent of particle cavitation and debonding. 

It is interesting that, upon rubber modification, the CET resin matrix can no longer form dilatation bands (18). Only rubber-particle cavitation and matrix shear yielding are detected. This observation implies that a dilatational stress component is required to trigger the formation of dilatation bands. In other words, upon rubber-particle cavitation, the dilatational stress component in the matrix is reduced. This suppresses the formation of dilatation bands. This conjecture finds support in the work of Glad (27), who investigated thin-film deformation of epoxy resins with various cross-link densities and could not find any signs of dilatation bands in his study. 

Figure 12. Results of simultaneous SAXS and tensile testing of acrylic sheet materials. (a) Results for the AS material show the formation of crazes during deformation. (b) Results for RTAS-8 show that the deformation processes that induce yielding are dominated by particle cavitation. The contour scattering patterns were obtained at the points indicated on the stress-strain curves.

In many practical cases, the ratio Gp/GM is smaller than 0.1 (16), yielding a stress concentration, a00, of 1.8 or more. This value is more than 85% of the maximum possible stress concentration (of 2.04, as for voids). In the case of stiffer particles, the stress concentration can be increased by cavitation of the particles (a decrease of the ratio Gp/GM). Relief of the initial thermal stress and of the hydrostatic stress inside the particles can be considered another advantage of particle cavitation (17). The effect of particle cavitation is discussed in more detail by Lazzeri and Bucknall (18). 

If fibrillated crazes (case a) coexist with homogeneous deformation (cases b or c), the homogeneous mechanisms and rubber-particle cavitation precede the formation of crazes. 

A special type of agitation is due to cavitation. This is the formation of vapor cavities in a liquid by local negative pressures, and the subsequent collapse of these cavities. The latter phenomenon generates shock waves that can disrupt nearby particles. Cavitation can be induced by ultrasonic waves, and ultrasound generators are useful for making emulsions in small quantities. 

There is experimental evidence, for many rubber-toughened polymers, that the rubber particles cavitate early in the deformation. The degree of cross-linking is kept relatively low in the polybutadiene phase of ABS to aid cavitation, and sometimes silicone oil is added for the same reason. Figure 4.12 shows both the conventional stress-strain curve and the volumetric strain versus tensile strain for rubber-modified polystyrene. When the polystyrene yields, the volume strain increases at a higher rate. Majority of the dilatational strain is due to cavitation in the rubber phase. 

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