PSI - Issue 36

Valeriy Kharchenko et al. / Procedia Structural Integrity 36 (2022) 145–152 Valeriy Kharchenko, Eugene Kondryakov, Andriy Kravchuk et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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state occurs in many technological operations and during the service of equipment in various industries Campbell et al. (1970), Pierron et al. (1995). Under dynamic loads such as forging, metal forming, high-speed machining, accidents, and ballistic loads, materials are more prone to shear failure with rapid loss of load-bearing capacity. Therefore, for high-strength and armor sheet steels, in addition to uniaxial tensile tests, additional tests are performed. Shear failure analysis is of great importance to ensure the safe operation of structural elements and improve existing regulations. The lack of standardized techniques for the investigation of the deformation and fracture of materials during dynamic shear is due to the complexity of their implementation in laboratory conditions. A large number of loading methods and specimens have been developed for dynamic shear tests. The most widely used techniques involve the use of impact testing machines Meyer et al. (2000), horizontal shear systems Wright (2002), air guns Klepaczko (1994), impact on an inclined plate, etc. Using special designs, the shear deformation can be limited by the cross-sectional size due to geometric inhomogeneity as follows: cap-shaped specimens Pursche et al. (2011), specimens with a double shear zone Xu et al. (2017), with a cylindrical or flat hat Clos et al. (2003), stepped or dumbbell-like specimens Wei et al. (2000), with a single or double edge Kalthoff (2000), shear under compression or tension Dorogoy et al. (2015) and compact specimens of simple shear Gray et al. (2016). In some other specimens, the shear occurs due to asymmetry or inhomogeneity of the stress-strain state in the material, for instance: compression/shear Meyer (1991), truncated cone Yu et al. (2003), punching Dowling et al. (1970), identification Meyer et al. (1986). The different types of specimens for shear tests are described in detail in Dodd et al. (2012) and Meyer et al. (2011). One of the main problems in dynamic testing is to achieve conditions of pure shear. Under shock load, the mechanical behavior of the material is subjected to the double effect of the strain rate and the stress state. The investigation of the independent effect of the strain rate requires the separation of these effects, i.e. the stress state with a shear advantage. However, a combined stress state of shear-compression or shear-tension is usually obtained. At high values of μ of the material, it is impossible to avoid the influence of the stress state. Thus, in such tests, it is not possible to investigate the influence of the strain rate. Another problem is the comparability and compliance of the material properties under different load conditions. The accuracy of the experimental data depends on both the test equipment and the type of specimen. At high strain rates, especially due to inertial effects and the propagation of stress waves in the material, each change in the specimen geometry and the loading technique can make significant variations in the specimen behavior and the results obtained. Therefore, to avoid such problems, it is desirable to test one type of specimen within the widest possible range of strain rates Rittel et al. (2002). However, there are only a few studies in this field. One type of specimen that allows one to obtain pure shear conditions and testing over a wide range of strain rates is the two-shear specimen by Ferguson Ferguson et al. (1967), and subsequently modified and used by many scientists Stepanov (1991), Xu et al. (2017), Stepanov et al. (2000), Peirs et al. (2010). The mechanisms of deformation and fracture of material under shear loading are rather complex. They require the investigation in more detail. The integrated experimental and computational approach should be used. 2. Numerical Simulation The processes occurring under dynamic shear loading are rather complex, thus it is difficult to consider numerical modeling. A lot of attention is paid to the issue, and material deformation models are improved to investigate the material behavior under dynamic shear conditions. Complex experimental and numerical investigations can provide the information for the modernization of the material deformation and fracture models, as well as the specification of these models parameters for various materials. Here special specimens with two shear zones have been developed (Fig.1). The variation in the shear zone length L makes it possible to change the strain rate within these zones at a constant loading rate. For this type of specimen, the following dependencies can be used for the determination of strain rate ̇( ) , shear stress τ(t) and shear strain γ(t) :