PSI - Issue 33

Yu. Matvienko et al. / Procedia Structural Integrity 33 (2021) 491–497 Author name / Structural Integrity Procedia 00 (2019) 000–000

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4. Conclusions The novel destructive method is implemented for quantitative characterization of fatigue damage accumulation near the cold-expanded hole. The developed approach employs preliminary low-cycle fatigue loading of specimens and further enlarging of initial cold-expanded hole diameter by the secondary hole drilling. A measurement of deformation response caused by local material removing in terms of in-plane displacement components is carried out by ESPI. The transition to the required principal strain values, referred to the secondary hole boundary, follows from obvious algebraic formulae. It has been established that normalized principal residual strain values, obtained at different stages of low-cycle fatigue, can be involved into the analysis as a representative damage indicator. Numerical integration of evolution curves produces the damage accumulation function within a normalizing coefficient. The required coefficient is derived as an inverse proportional value with respect to a square lying under normalized distributions of principal residual strain components over lifetime period. The proposed procedure defines an explicit form of the damage accumulation function. These functions are constructed for different stress ratios for both external specimen faces thus revealing discrepancies in damage accumulation rates. Obtained results clearly evidence that fatigue damage accumulation can be reliably characterized on a base of direct measurements of two in-plane displacement components relevant to the secondary hole edge. Moreover, these measurements can be simultaneously performed on opposite specimen’s faces without applying additional tensile load. It is of considerable importance that there is no need to employ various mechanical models for a transfer from directly measured in-plane displacement components to residual strains values in order to get the damage accumulation function. This follows from the fact that measured displacement components are related to load-free boundary of through open holes in rectangular thin plate. The approach represents the essential link in predictable joints design to reach maximal beneficial effect of cold hole expansion on the fatigue life improvement of a fastener holes. Acknowledgements The authors acknowledge the support of the Russian Science Foundation (project N 18-19-00351). References Eleonsky S. I., Pisarev V.S., Zajtsev M.D., Zichenkov M.Ch. and Abdullin M.R. Residual stresses near cold-expanded hole at different stages of high-cycle fatigue by crack compliance data. Frattura ed Integrita Strutturale, 56 (2021) 171-186; DOI: 10.3221/IGF-ESIS.56.14 Matvienko Y., Pisarev V., Eleonsky S. Investigation of fatigue damage accumulation by measurements of deformation response to narrow notch increment. Procedia Structural Integrity –2020. V. 28. – P. 584–590. Matvienko Yu.G., Pisarev V.S., Eleonsky S.I. The effect of low-cycle fatigue parameters on damage accumulation near a hole. Engineering Failure Analysis 2019; 106: Article 104175. https://doi.org/10.1016/j.engfailanal.2019.104175. Matvienko Yu.G., Pisarev V.S., Eleonsky S.I. Evolution of fracture mechanics parameters relevant to narrow notch increment as a measure of fatigue damage accumulation. International Journal of Fatigue 2021; 149 (August 2021):106310. https://doi.org/10.1016/j.ijfatigue.2021.106310 Matvienko, Y.G., Pisarev, V.S., Eleonsky, S.I., Chernov A.V. (2019). Residual stress/strain evolution due to low-cycle fatigue by removing local material volume and optical interferometric data, Fat. & Fract. of Eng. Mat. & Struct., V. 42, P. 2061–2078. doi:10.1111/ffe.13083 Matvienko Yu.G., Pisarev V.S, Eleonsky S.I. The effect of low-cycle fatigue on evolution of fracture mechanics parameters in residual stress field caused by cold hole expansion. Frattura ed Integrita Strutturale 2019; 47:303-320. https://doi:10.3221/IGF-ESIS.47.23. Pisarev, V.S., Odintsev, I.N., Eleonsky, S.I., Apalkov, A.A. (2018). Residual stress determination by optical interferometric measurements of hole diameter increments, Optics and Lasers in Engineering, 110, pp. 437–456, doi: 10.1016/j.optlaseng.2018.06.022 Reid L. Hole Cold Expansion – The Fatigue Mitigation Game Changer of the Past 50 Years. Advanced Materials Research. – 2014. V. 891– 892. – P. 679–684.