PSI - Issue 41

196 Yu.G Matvienko et al. / Procedia Structural Integrity 41 (2022) 192–198 Author name / Structural Integrity Procedia 00 (2019) 000–000 5 Full volume of the experimental data provides the dependencies of local strain at point of maximum strain concentration (critical point A ) �� as a function of remote stress level for all considered cycles. The distributions related to the 218th, 521st and 1017th cycles, which are practically coincide and depicted by the single straight line, are shown in Fig. 3a. Analogous dependence constructed for maximum normal strain �� at critical point A , obtained for 1418th cycle is presented in Fig. 3b. Open and filled markers indicate increasing and decreasing remote stresses, respectively.

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Fig. 3. Maximum circumferential strain versus remote stress diagram obtained for 218th, 521st and 1017th cycles (a) and normal strain versus remote stress diagram obtained for 1418th cycle (b). 3. Damage accumulation function The essence of the developed approach resides in the fact that the evolution of various deformation parameters, which are referred to the critical point located at the hole edge, can be effectively used for quantification of damage accumulation. A powerfulness of this methodology through the use of the evolution of fracture mechanics parameters for notches emanating from through-thickness open hole in plane specimens at different stages of low cycle fatigue has earlier been demonstrated by Matvienko et al. (2020, 2021, 2022). It has been shown that the explicit form of the damage accumulation function � � � , � �� can be expressed as: � � � , � � � ∑ � �� �������,� � � ���,� � ����� ��� �∆� � � � �� ��� � � �� , (4) where � is current number of loading cycle; �� � � is normalizing coefficient that must be derived from the experimental data for each specific damage indicator; � , � � is a set of experimental values of damage indicator, obtained after � cycles; � , � � �� is a value of chosen damage indicator that corresponds to maximum level of tensile remote stress for the first half cycle; � � ��� means number of loading cycle that corresponds to short crack appearance at external specimen face; ∆ � � ��� � � denotes number of loading cycles between two neighbouring points of � , � � determination. The coefficient �� � � for specimens of given geometrical dimensions is defined by mechanical properties of the material and parameters of loading program. The value of the coefficient �� � � in each specific case follows from normalization of Equation (4) taking into account that the total sum in the right-hand side must be equal to one. This