PSI - Issue 16

Yuri Lapusta et al. / Procedia Structural Integrity 16 (2019) 105–112 Yuri Lapusta, Oleksandr Andreikiv, Nataliya Yadzhak / Structural Integrity Procedia

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In delayed fracture mechanics, it is assumed that the durability of a construction element N consists of two components:

i N

 initiation period of a macrocrack  period of its subcritical growth

subcr N . To describe this process a range of mathematical models is proposed (Andreikiv and Darchuk (1992)). In this study, we consider the residual life of a cracked plate. It has to be mentioned that there are no limitations concerning the initial crack length. The initial crack can be  physically short – the crack length is commeasurable with the size of a structural element  mechanically short – the crack is longer than a physically short crack but its size does not meet the self-similarity condition (Panasyuk (1988))  macrocrack – the crack length meets the self-similarity condition. Numerous experimental investigations have been conducted for bodies with macrocracks (Andreikiv et al. (2017)) that meet the self-similarity conditions for static loading. However, those experiments have shown that the propagation process of those cracks is being described nonuniquely by the stress intensity factors in the case of long term loading. This means that for long-term loading the self-similarity conditions should differ from those for statics. Thus, the process of delayed fracture should be described using other parameters. Earlier a computational model has been developed by Andreikiv et al. (2017,2018, 2019)) for investigation of fatigue crack propagation using the size of mechanically short cracks, which are characterized by some peculiarities including an absence of crack closure effect (Nazarchuk and Nykyforchyn (2018)). However, these cracks have to be much longer compared to physically short cracks. This paper presents another computational model that, in our view, can be used for propagation of an arbitrary crack: physically short, mechanically short, macrocrack, even crack whose size is close to zero.

Nomenclature N

number of load cycles

i N

initiation period of a macrocrack subcr N period of subcritical crack growth l crack length 

characteristic of corrosion-fatigue failure that is defined experimentally

t 

mean stress in the pre-fracture zone

l  0 l

critical crack length initial crack length

r

bending radius of a notch tip

p

load amplitude

fc  critical value of deformation max  that corresponds to spontaneous fracture fc  critical value of crack tip opening max  that corresponds to spontaneous fracture R cycle ratio p l depth of a plastic zone I K stress intensity factor for opening mode max I K maximal stress intensity factor per cycle fc K threshold stress intensity factor per cycle 0  maximal deformation value near the stress riser in the initial state