PSI - Issue 50

N. Mullahmetov Maksim et al. / Procedia Structural Integrity 50 (2023) 200–205 Mullahmetov Maksim N. et al./ Structural Integrity Procedia 00 (2022) 000 – 000

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Table 2 Values of critical distances by point and linear methods for STEF structural fiberglass

Ratio max. load to the minimum. area, MPa

Critical distance by point method, mm

Critical distance by linear method, mm

Stress concentration factor

Tensile strength,MPa

specimen

№

1 273.7

3.64 2.46 1.89 2.10 2.17

2.29 1.50 1.47 1.75 2.51

2.00 1.86 3.84 3.21 2.53

327.6 327.6 327.6 327.6 327.6

V-shape. 15x5 V-shape. 15x3 V-shape. 15x1 V-shape. 4x1 V-shape. 1x1

2 270

3 225.7 4 272.4 5 310.7

4. Conclusions From the results presented in table. 4.2, it can be seen that the forecast error varies from -12.1% to 13.1% for the point method and from -5.1% to 10.4% for the linear method. In general, it can be seen that the linear method is more accurate than the point method. At the same time, both methods demonstrate fairly good prediction accuracy. According to the theory of critical distances, an accuracy of less than 20% (10% - experimental error, 10% - modeling error) is considered satisfactory. According to the theory of critical distances, if the length of the defect is much less than the critical distance, then the defect can be considered harmless. Thus, for STEF structural fiberglass, defects smaller than approximately 0.2 0.25 mm should not reduce the strength characteristics of the material and structures. Acknowledgements The work was carried out with support of the Russian Science Foundation (Project No. 21-79 10205, https://rscf.ru/project/21-79-10205/ ) in the Perm National Research Polytechnic University. References J. Awerbuch; M.S. Madhukar 1985. Notched Strength of Composite Laminates: Predictions and Experiments — A Review. J. Reinf. Plast. Compos (1985), 4, p. 3 – 159. V.V. Vasiliev, Y.M. Tarnopolskii, 1990. Composite Materials. Academic Press, London D. Taylor, 2007. The theory of critical distances: a new perspective in fracture mechanics. Oxford, UK: Elsevier Lobanov D, S., Yankin A.S., Berdnikova N.I. Statistical evaluation of the effect of hygrothermal aging on the interlaminar shear of GFRP, Frattura ed Integrità Strutturale, 60 (2022) 146 -157. Lobanov D.S., Babushkin A.V., Luzenin A.Yu. Effect of increased temperatures on the deformation and strength characteristics of a GFRP based on a fabric of volumetric weave// Mechanics of Composite Materials, — 2018 — Vol. 54 — No. 5. — pp 655-664. J. M. Whitney, R. J. Nuismer, 1974. Stress Fracture Criteria for laminated composites containing stress concentrations, Journal of Composite Materials B. Gillham, A. Yankin, F. McNamara, C. Tomonto, D. Taylor, R. Lupoi, 2021. Application of the Theory of Critical Distances to predict the Lobanov D. S., Strungar E. M., Zubova E. M., Wildemann V. E. 2019. Studying the Development of a Technological Defect in Complex Stressed Construction CFRP Using Digital Image Correlation and Acoustic Emission Methods. Russian Journal of Nondestructive Testing, Vol. 55, No. 9, pp. 631 – 638 Strungar, E.; Lobanov, D.; Wildemann, V. 2021. Evaluation of the Sensitivity of Various Reinforcement Patterns for Structural Carbon Fibers to Open Holes during Tensile Tests. Polymers 2021, 13 , 4287. https://doi.org/10.3390/polym13244287 effect of induced and process inherent defects for SLM Ti-6Al-4V in high cycle fatigue, CIRP Annals, 70. D. Taylor, 2007. The theory of critical distances: a new perspective in fracture mechanics. Oxford, UK: Elsevier