PSI - Issue 41

Slobodanka Boljanović et al. / Procedia Structural Integrity 41 (2022) 704 – 711 Slobodanka Boljanović et al. / Structural Integrity Procedia 00 (2019) 000 – 000

705

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method. Later, Boljanović and Carpinteri (20 21) developed novel fatigue design solutions for estimating the stability of a semi-elliptical flaw. Furthermore, Mikheevskiy et al. (2012) demonstrated that the progression of quarter-elliptical flaw can be evaluated using the crack growth concept developed by Noroozi et al. (2007) and the weight function method. Boljanović et al. (2019) examined the failure strength of two notches with the above flaw employing the crack growth concept proposed by Huang and Moan (2007) and the finite element method. By introducing the modified two parameter driving force concept, Boljanović and Carpinteri (2020 ) performed a damage tolerance-based analytical design of the fatigue behavior of an elliptical corner flaw. The present research work addresses a novel computational design model recommended for the fatigue assessments of a surface elliptical flaw in the areas of inspection and monitoring, with applications to the stability of plate-type configurations. Additionally, literature-based experiments show that such analytical strategy due to the incorporation of surface stress-raiser phenomenon in safety-critical design allows a precise estimation of the failure resistance life in dynamic load environment.

Nomenclature a , b

crack length in depth and surface direction C A , C B material constant in fatigue crack growth law for depth and surface direction da/dN crack growth rate in depth direction db/dN crack growth rate in surface direction K A , K B stress intensity factor in dept and surface direction m A , m B material constant in fatigue crack growth law for depth and surface direction N number of loading cycles to failure P applied force R load/stress ratio S applied stress t thickness of the plate w width of the plate

Subscripts f

failure

maximum value related to the applied load/stress

max

initial value

0

2. Failure resistance life evaluation The fatigue stability of a quarter-elliptical flaw (Fig. 1) can be explored via the crack growth concept (Zhan et al., 2014), which is extended here with respect to two critical crack directions ( a and b ), as follows:   A m A R A C e K dN da    ,   B m B R B C e K dN db    (1) where  K A ,  K B are the stress intensity factors related to crack growth rates da/dN , db/dN in the case of depth and surface direction, and C A , C B , m A , m B are material parameters experimentally obtained. Furthermore, the strength deterioration can be assessed in terms of the number N of loading cycles, by integrating crack growth rates for relevant initial (a 0 , b 0 ) and final ( a f , b f ) crack length in depth and surface direction, respectively, defined by