PSI - Issue 39

Viktor Morozov et al. / Procedia Structural Integrity 39 (2022) 432–440 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Approach for investigation of the cracks generation process in the continuous matter first time purposed by Griffith (1920) and Irwin (1957) and later improved by Cherepanov (1967) allowed formalizing condition which determines the growth of the cracks in the matter. It demonstrated that for a particular case of the linearly elastic solids, such an approach leads to well-known outcomes. Application of the general condition to a few cases of the plastic and linear viscous-elastic solids was also considered by Cherepanov (1967). Simulation of the crack propagation over time and, therefore, calculation of failure parameters or construction durability is possible only after laboratory study of the crack propagation in a wide range of its velocities. In present days such investigations with optical techniques are performed with a row of transparent materials utilized for the simulation of the brittle failure. Poly (methyl methacrylate) (PMMA) is a good example of such a model material. In papers by Vavakin and Salganik (1971), Aleshin et al. (1981), Williams et al. (1968), Williams (1972), Green and Pratt (1974), Efimov and Sher (2001) its cracking resistance was studied. Vavakin and Salganik (1971), Aleshin et al. (1981), Williams et al. (1968), Williams (1972) investigated the propagation of a slow crack in the range of velocities from 10 -7 up to 10 -2 m/s. Paper by Green and Pratt (1974) dedicated to the range of velocities from 100 up to 500 m/s. Efimov and Sher (2001) determinate dynamic cracking resistance profiles for the same material (a grade of PMMA) in a range of velocities from 10 -5 up to 300 m/s and discussed features of the crack propagation in various areas of this range. Application of a rather large tensile load may cause a brittle failure of polymers. Such brittle failure may be described with a homogeneous deformation till destruction. The nature of destruction depends on the technique of the experiment significantly. So, brittle fracture observed for rather low temperatures and short loading actin time (or a high rate of deformation). The transparent nature of glass-like polymers such as PMMA is a key feature for this study. This property allows visual observation and control of the crack propagation through the material. Electrical-physical techniques (Atroshenko et al. (2002), Imbert at al. (2015), Nairne (1774), Morozov et al. (2016), Atroshenko et al. (2018), Bratov and Petrov (2007)), especially based on the electric explosion of wires (Imbert at al. (2015), Nairne (1774), Morozov et al. (2016)), have now special attention among methods of high-rated loading deformation and failure of materials. Atroshenko et al. (2002) and (2018) as well as Bratov and Petrov (2007) performed an investigation of the nature of the failure of PMMA samples under the action of dynamic loading generated with the magnetic-pulse technique. Loading setup in that researches granted equilibrium distribution of the pressure on the surfaces of crack. Atroshenko et al. (2018) utilized incubation time criterion for numerical simulation of the crack propagation. This criterion was implemented in ANSYS software and utilized to perform numerical simulations of classical experimental studies by Ravi-Chandar and Knauss (1984, 4 parts) on the dynamic failure of materials. In these experiments, the plate with an artificial cut simulating the crack affected with dynamic loading was applied to the surfaces of the cut. Loading consisted of a sequence of two trapezoidal pulses. This lead to generation, propagation, shutdown and secondary re-generation of the crack. Dependence of the crack length by the time investigated. Outcomes of the FEM simulation of cracks propagation have a good correspondence to the studied cracks length change. This demonstrated the relevance of the incubation time criterion to the explanation of generation, propagation and shutdown of the dynamically loaded cracks. Bratov and Petrov (2007) provided results of experiments on quasi-static and pure-dynamic loading of the “ALTUGLAS EI CH25” composition samples. PMMA matrix of that composition was filled with rubber particles to achieve an impact-prove material. The main topic of that research was to study with laboratory tests and numerical simulations the cracking resistance of the material under the action of static and dynamic loadings. Pules magnetic field was utilized to perform high-rate loading. Analysis of failure performed and its connections to the loading parameters and microscopic properties of materials revealed. Utilization of the innovative method of tests allowed authors to estimate the viscous state of the fracture under extremal short loading and compare these results to the known dynamic properties of the tested material. Theoretical analysis was based on both tests result and incubation time criterion. Experimental studies utilizing the EEW method allow to achieve reliable data on the of tested materials in conditions of the high-rated loading and deformation change. This clarifies our understanding of the mechanisms of high-rated loading deformation and failure of materials and grants successful simulation of these processes. Klepaczko et al. (2008) and Morozov et al. (2020) provided analysis of fracture of PMMA and fluoroplastic samples under the effect of various stress rates. Therefore, a deep understanding of the high-rated failure process requires a more detailed study of cracks generation and dependence between fracture and propagation of the shock wave through the material.