PSI - Issue 6

V.A. Morozov et al. / Procedia Structural Integrity 6 (2017) 154–160 Morozov et al. / Structural Integrity Procedia 00 (2017) 000–000

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In the process of the destruction of a major amount of energy is spent on the plastic deformation in the sources of destruction. Destruction sources are usually represented focus of the parabolas in which there is a significant deformation. The more rough fracture surface, the higher the energy spent on the propagation of cracks. By type of fracture surfaces can be judged about the features of energy-absorbing mechanisms. When initiating a defect most of the energy is absorbed due to plastic deformation. The destruction of the mirror area corresponding to the slow rate of advance of the crack fracture surface is relatively smooth. To maintain a crack promotion process in this area requires relatively little energy. The next area of increased roughness is composed of randomly arranged geometric figures wrong acute forms of high-dispersion characteristic dimensions. Behind this region, the PMMA destruction surface becomes similar to the metal fracture in the case of viscous (cup) failure. A large number of cups in the form of parabolas require more energy for spreading the crack. The growth of the absorbed energy on the fracture surface leads to an increase in the size of the cups, which indicates a decrease in the viscosity fraction on the fracture surface. The classic view of the destruction of PMMA is a parabola, and the mechanism of its formation gives an idea about the whole process of destruction: the occurrence of breaking, interrupted the development process, further initiation of destruction in the areas of defects, the occurrence of secondary damage and their relationship with the front main crack propagating usually at di ff erent level. When the crack propagates in PMMA from the loading surface to the free surface, the nature of the destruction changes: 1- the mirror region, 2 - the areas of increased roughness and 3 - the parabolic region, respectively. With further propagation of the crack, these basic types of fractures periodically alternate. Typical types of fractures are represented in Fig. 9. The change in the character of the destruction is clearly observed in the same figure.

Fig. 9. Areas of destruction in PMMA in the direction from the loaded surface to free: 1 - mirror, 2 - area of increased roughness, 3 - parabolic.

For fluoroplast, areas of mirror and increased roughness are observed, and parabolic is practically absent - there are only small areas (Fig. 10).

Fig. 10. Areas of destruction in fluoroplast in the direction from the loaded surface to free.