PSI - Issue 20

Victor Petrov et al. / Procedia Structural Integrity 20 (2019) 87–92 Victor Petrov et al. / Structural Integrity Procedia 00 (2019) 000–000

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transportation, including automotive, railway and aerospace equipment, has faced a number of problems associated with the necessity of taking into account thermal and dynamic loads and effect of accumulated energy in the material on the process of fracture. Modern science has the means of fractographic analysis, experimental and numerical modeling, which allow to fully understand the mechanisms underlying the processes of dynamic fracture of materials as shown by Bratov(2009) and bv HaYa D(2010). However, in most cases, numerical calculation does not replace analytical solutions, and the latter can shed light on the true physical nature of the fracture process, which allows to take into account the structure of the material at different scale levels with much less time and effort as discovered by Lepov(2017). In addition, polymer materials themselves are of considerable practical interest. In particular, organic glass polymethylmethacrylate (PMMA) is widely used in electrical engineering as an insulating material in the manufacture of electrical and physical equipment, as well as in defense technology, as it is radio transparent in a wide range of frequencies. Before the widespread use of metal glasses and ceramics, it was also used as a structural material. Therefore, studies of the characteristics of its dynamic fracture are quite relevant as pointed by Md Raziun (2016) and Stukhlyak (2014).

Nomenclature A, B

correction coefficients (m 2 and m 3 )

d

structural size

K, k

Boltzmann constant

K Ic

is the stress intensity factor at failure.

T

temperature

U 0 W

activation energy of a spontaneous rupture of polymer chains at σ = 0

striker impact energy

X

crack length

structure - sensitive Zhurkov’s coefficient



reduced stress (the ratio of the applied load to the cross-sectional area of the sample) principal tensile stress in neighborhoods of the crack vertex (r = 0)

 R



ultimate strength of "defect-free" material

 c

durability at a given tensile 



period between the thermal fluctuations

 0

Materials and equipment

Since polymer materials are viscoelastic solids, their ability to inelastic and plastic deformation drops sharply due to the formation of intermolecular "bridges"at high loading rates and low test temperatures. But for PMMA, the movements of individual lateral groups of macromolecules at the initial stages of deformation are replaced by the movement of the spinal links of the macromolecule by Golovin(2005) – at the final, so PMMA slightly changes its properties with a decrease in temperature within the range from -183° to 60° C (in particular, impact viscosity). Coupled with optical transparency sensitive to internal stresses, it is an ideal material for modeling complex crack dynamics under stress concentration and impulse loading conditions. This made it possible to develop a number of theoretical models and energy criteria by Petrov (2011) on the basis of experimental data obtained in the course of studies on static-dynamic loading of samples using a high-speed camera SPR-1 by Petrov at al. (2002) (Fig. 1). In the experiment, a sample under static tension is subjected to a wedging impact on the lateral incision. The loading scheme is shown in Fig.2.