ESTIMATING PARAMETERS OF PERMISSIBLE DEFECTS IN STRUCTURAL FIBERGLASS BASED ON THEORY OF CRITICAL DISTANCES

M.N. Mullahmetov, D.S. Lobanov, V.A. Melnikova, A.S. Yankin

Author details

M.N. Mullahmetov
Perm National Research Polytechnic University, Perm, Russian Federation
D.S. Lobanov
Perm National Research Polytechnic University, Perm, Russian Federation
V.A. Melnikova
Perm National Research Polytechnic University, Perm, Russian Federation
A.S. Yankin
Nazarbayev University, Astana, Republic of Kazakhstan

https://doi.org/10.15593/perm.mech/2023.4.08

In the process of manufacturing products from composite materials, many defects can occur: cracks, chips, scratches, dents, impact defects, air macro inclusions, and others. Such defects can significantly reduce both the static and fatigue resistance of structures. The purpose of this work is to determine the size of defects that do not affect the strength characteristics of products made of STEF composite material using the point and linear approaches of the theory of critical distances. In the course of the work, a series of tensile tests were carried out on flat specimens of STEF structural fiberglass for electrical purposes. In addition to the experiment, numerical simulation of the tensile processes of these specimens was also carried out. The studied specimens were strips without stress concentrators and with a concentrator in the form of V-shaped notches with different rounding radii at the concentrator top and notch depth. The results obtained were used to determine the material constants according to the theory of critical distances. In this case, two approaches of the theory of critical distances were used, i.e. linear and point ones. To analyze the experimental results, finite element models were built using the ANSYS software package; and numerical simulation was carried out, which resulted in the obtained linearized maximum principal stresses on the central line passing through the top of the stress concentrator. Based on the results of the work, the values of the critical distances of the composite were determined, obtained by using the point and linear methods. On the basis of the data obtained, the sizes of permissible defects in the studied fiberglass were established, which do not affect the strength characteristics of the material. The results obtained can be used to predict the strength characteristics of real products with a complex geometry, as well as to diagnose damaged structural elements.

Keywords

numerical simulationtheory of critical distancescomposite materialstension.

ОПРЕДЕЛЕНИЕ ПАРАМЕТРОВ ДОПУСТИМЫХ ДЕФЕКТОВ КОНСТРУКЦИОННОГО СТЕКЛОПЛАСТИКА НА ОСНОВЕ ТЕОРИИ КРИТИЧЕСКИХ РАССТОЯНИЙ

В процессе производства изделий из композитных материалов может возникнуть множество дефектов: трещины, сколы, царапины, вмятины, дефекты ударного характера, воздушные макровключения и другие. Такие дефекты могут существенно снизить как статическое, так и усталостное сопротивление конструкций. Целью данной работы является определение размеров дефектов, не влияющих на прочностные характеристики изделий из композитного материала СТЭФ, с использованием точечного и линейного подходов теории критических расстояний. В ходе работы были проведены серии испытаний на растяжение плоских образцов из конструкционного стеклотекстолита электротехнического назначения СТЭФ. Помимо проведенного эксперимента было осуществлено также численное моделирование процессов растяжения данных образцов. Исследуемые образцы представляли слой полоски без концентраторов напряжений и с концентратором в виде V-образных вырезов с различным радиусом скругления в вершине концентратора и глубиной выреза. Полученные результаты использовались для определения констант материала по теории критических расстояний. При этом были использованы два подхода теории критических расстояний: линейный и точечный. Для анализа результатов эксперимента были построены конечно-элементные модели с использованием программного пакета ANSYS и проведено численное моделирование, результатом которого стали полученные линеаризированые максимальные главные напряжения на центральной линии, проходящей через вершину концентратора напряжений. По результатам работы определены значения критических расстояний композита, полученные с использованием точечного и линейного методов. На основе полученных данных установлены размеры допустимых дефектов исследуемого стеклопластика, которые не оказывают влияние на прочностные характеристики материала. Полученные результаты могут быть использованы для прогнозирования прочностных характеристик реальных изделий со сложной геометрией, а также для диагностики повреждённых элементов конструкций.

Ключевые слова

численное моделированиетеория критических расстоянийкомпозиционные материалырастяжение.

Bibliography

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31.Gillham, B., Yankin, A., Shipley, H., McNamara, F., Tomonto, C., O’Donnell, G., Trimble, D., Yin, S., Taylor, D., Lupoi, R. The Analysis of Small-Scale Notches on the Fatigue Performance of SLM Ti-6Al-4V; A Theory of Critical Distances Approach // Key Engineering Materials, V.926, 2022, pp.250-267. doi:10.4028/p-h0iapl Scholar

1.Tashkinov M.A. Modelling of fracture processes in laminate composite plates with embedded delamination // Frattura ed Integrità Strutturale. – 2017. – Vol. 39. – P. 248–262; DOI: 10.3221/IGF-ESIS.39.23 Scholar
2.Repair of damage in aircraft composite sound-absorbing panels / A.N. Anoshkin, V.Yu. Zuiko, M.A. Tashkinov, V.V. Silberschmidt // Composite Structures. – 2015. – Vol. 120. – P. 153– 166. DOI: 10.1016/j.compstruct.2014.10.001 Scholar
3.Cantwell W.J., Morton J. The significance of damage and defects and their detection in composite materials: a review // The Journal of Strain Analysis for Engineering Design. – 1992. – Vol. 27(1). – P. 29–42. Scholar
4.Armstrong K.B., Cole W., Bevan G. Care and repair of advanced composites. – London: SAE International, 2005. Scholar
5.Evaluation of Repair Efficiency in Structures Made of Fibrous Polymer Composite Materials / A.N. Anoshkin [et al.] // Mechanics of Composite Materials. – 2014. – Vol. 50, № 3. – P. 311–316. Scholar
6.Strungar E., Lobanov D., Wildemann V. Evaluation of the Sensitivity of Various Reinforcement Patterns for Structural Carbon Fibers to Open Holes during Tensile Tests // Polymers. – 2021. – Vol. 13, № 24. – P. 4287. Scholar
7.Neuber H. Theory of notch stresses: principles for exact calculation of strength with reference to structural form and material. 2nd ed. – Berlin: Springer Verlag, 1958. Scholar
8.Peterson R.E. Notch sensitivity / Sines G., Waisman J.L., editors // Metal fatigue. – New York: McGraw Hill, 1959. – P. 293–306. Scholar
9.Tanaka K. Engineering formulae for fatigue strength reduction due to cracklike notches // Int. J. Fract., 1983. – Vol. 22. – P. 39–45. DOI: 10.1007/BF00942722 Scholar
10.Lazzarin P., Tovo R., Meneghetti G. Fatigue crack initiation and propagation phases near notches in metals with low notch sensitivity // Int J Fatigue. – 1997. – Vol. 19. – P. 647–57. DOI: 10.1016/S0142-1123(97)00091-1 Scholar
11.Taylor D. The theory of critical distances: a new perspective in fracture mechanics. – Oxford, UK: Elsevier, 2007. DOI: 10.1016/B978-0-08-044478-9.X5000-5 Scholar
12.A comparison of the two approaches of the theory of critical distances based on linear-elastic and elasto-plastic analyses IOP Conf. / A.I. Terekhina [et al.] // Ser.: Mater. Sci. Eng. – 2017. – Vol. 208. – P. 012042. DOI: 10.1088/1757-899X/208/1/012042 Scholar
13.Susmel L., Taylor D. The Theory of Critical Distances to estimate the static strength of notched samples of Al6082 loaded in combined tension and torsion. Part I: Material cracking behavior // Engineering Fracture Mechanics. – 2010. – Vol. 77. – P. 452–469. Scholar
14.Susmel L., Taylor D. The Theory of Critical Distances to estimate the static strength of notched samples of Al6082 loaded in combined tension and torsion. Part II: Multiaxial static assessment. Engineering Fracture Mechanics. – 2010. – Vol. 77. – P. 470–478. Scholar
15.On the use of the critical distance concept to estimate tensile strength of notched components under dynamic loading and physical explanation theory / A. Vedernikova, A. Kostina, O. Plekhov, A.M. Bragov // Theoretical and Applied Fracture Mechanics. – 2019. – Vol. 103. – P. 102280. DOI: 10.1016/j.tfamec.2019.102280 Scholar
16.Taylor D. “On the application of the Theory of Critical Distances for prediction of fracture in fibre composites” // Frattura ed Integrità Strutturale. – 2009. – Vol. 4(11). – P. 3–9. DOI: 10.3221/IGF-ESIS.11.01 Scholar
17.Alanazi N., Susmel L. The Theory of Critical Distances to Predict Static and Dynamic Strength of Notched Plain Concrete under Mixed-Mode I/II Loading // Procedia Structural Integrity. – 2020. – Vol. 28. – P. 886–895. Scholar
18.Benedetti M., Santus C. Notch fatigue and crack growth resistance of Ti-6Al-4V ELI additively manufactured via selective laser melting: A critical distance approach to defect sensitivity // Int J Fatigue. – 2019. – Vol. 121. – P. 281–292. DOI: 10.1016/j.ijfatigue.2018.12.020 Scholar
19.Theory of critical distance combined with the generalized strain energy density criterion for mixed mode fracture assessment of PMMA dental materials / Bahador Bahrami, Majid R. Ayatollahi, Saeid Ghoulia // Procedia Structural Integrity. – 2020. – Vol. 28. – P. 829–835. DOI: 10.1016/j.prost.2020.10.097 Scholar
20.Nicholas R. Gates, Ali Fatemi Multiaxial variable amplitude fatigue life analysis using the critical plane approach, Part II: Notched specimen experiments and life estimations // Int J Fatigue. – 2018. – Vol. 106. – P. 56–69. DOI: 10.1016/j.ijfatigue.2017.09.009 Scholar
21.Lanning D., Nicholas T., Haritos G. On the use of critical distance theories for the prediction of the high cycle fatigue limit stress in notched Ti-6Al-4V // Int J Fatigue. – 2005. – Vol. 27. – P. 45–57. DOI: 10.1016/j.ijfatigue.2004.06.002 Scholar
22.Lanning D., Nicholas T., Palazotto A. HCF notch predictions based on weakest-link failure models // Int J Fatigue. – 2003. – Vol. 25. – P. 835–841. DOI: 10.1016/S0142-1123(03)00156-7 Scholar
23.Fatigue life prediction of small notched Ti-6Al-4V specimens using critical distance / Y. Yamashita, Y. Ueda, H. Kuroki, M. Shinozaki // Engineering Fracture Mechanics. – 2010. – Vol. 77(9). – P. 1439–1453. DOI: 10.1016/j.engfracmech.2010.04.001 Scholar
24.Wang J., Yang X. HCF strength estimation of notched Ti-6Al-4V specimens considering the critical distance size effect // Int J Fatigue. – 2012. – Vol. 40. – P. 97–104. DOI: 10.1016/j.ijfatigue.2011.12.019 Scholar
25.Susmel L., Taylor D. A novel formulation of the theory of critical distances to estimate lifetime of notched components in the medium-cycle fatigue regime // Fatigue Fract Engng Mater Struct. – 2007. – Vol. 30(7). – P. 567–581. DOI: 10.1111/j.1460- 2695.2007.01122.x Scholar
26.Taylor D. Applications of the Theory of Critical Distances in Failure Analysis. Engineering Failure Analysis. – 2010. DOI: 10.1016/j.engfai.2010.07.002 Scholar
27.Recent advances on notch effects in metal fatigue: A review / Ding Liao, Shun Peng, Zhu José A.F.O. Correia, Abilio M.P. De Jesus, Filippo Berto // Fatigue Fract Engng Mater Struct. – 2020. – Vol. 43(4). – P. 637–659. DOI: 10.1111/jfe.13195 Scholar
28.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. – 2022. – Vol. 60. – P. 146–157. DOI: 10.3221/IGF-ESIS.60.11 Scholar
29.Strungar E.M., Lobanov D.S. Mathematical data processing according to digital image correlation method for polymer composites // Frattura ed Integrità Strutturale. - 2020. - Vol. 54. - P. 56-65. DOI: 10.3221/IGF-ESIS.54.04 Scholar
30.Application of the Theory of Critical Distances to predict the effect of induced and process inherent defects for SLM Ti-6Al-4V in high cycle fatigue / B. Gillham, A. Yankin, F. McNamara, C. Tomonto, D. Taylor, R. Lupoi // CIRP Annals. - 2021. - Vol. 70, iss. 1. - P. 171-174. DOI: 10.1016/j.cirp.2021.03.004 Scholar
31.The Analysis of Small-Scale Notches on the Fatigue Performance of SLM Ti-6Al-4V; A Theory of Critical Distances Approach / B. Gillham, A. Yankin, H. Shipley, F. McNamara, C. Tomonto, G. O'Donnell, D. Trimble, S. Yin, D. Taylor, R. Lupoi // Key Engineering Materials. - 2022. - Vol. 926. - P. 250-267. DOI: 10.4028/p-h0iapl Scholar

Article information

Published: 5 October 2023
Issue date: 5 October 2023
Issue: No. 4 (2023)