PSI - Issue 28

1976 Yuri Petrov et al. / Procedia Structural Integrity 28 (2020) 1975–1980 Yuri Petrov/ Structural Integrity Procedia 00 (2019) 000–000 Chandar and Knauss (1984a) and ! − ̇ curves can be nonunique for a given material or even non-existent (Kalthoff (1983), Dally et al. (1985)). In this paper the crack propagation phenomenon is numerically investigated using incubation time fracture criterion and finite element method in a two-dimensional statement. The fracture model is based on the incubation time parameter – a material property characterizing microstructural fracture processes preceding and eventually causing macroscopic fracture event (Petrov (1996)). The model does not involve any critical SIF values or SIF-involving dependencies and thus the above-mentioned ambiguities can be avoided. Crack propagation under dynamic loading conditions was studied. Experiments by Ravi-Chandar and Knauss (1984a,b,c), where crack propagated due to short pulses applied to the crack faces, were numerically simulated using finite element method with integrated incubation time fracture condition. Experimental dependence of the stress intensity factor (SIF) on the crack velocity was numerically obtained showing possibility to numerically address SIF scattering phenomenon observed in the tests. Nomenclature ! stress intensity factor (mode-I) crack tip position ̇ crack velocity ( , ) stress in material at point and time fracture process zone !" ultimate static stress intensity factor " ultimate static stress 2

incubation time material density , Lame parameters 1⃗ displacement vector # displacement vector component #$ stress tensor components Γ # specimen boundary notation # spatial coordinate coordinate couple notation time Young’s modulus Poisson’s ratio 2. Incubation time fracture criterion

The incubation time fracture criterion was originally proposed in works by Petrov and Utkin (1989) and Petrov (1991). The incubation time fracture model implies that macroscopic fracture event requires specific time – the incubation time – to develop from microscopic fracture processes such as microcracking and defect movement and coalescence. The incubation time is regarded as a material parameter to be evaluated from available dynamic fracture experiments for a given material. According to the incubation time model fracture at point and time is controlled by the following inequality: