PSI - Issue 37

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Oleg Staroverov, Dmitrii Lobanov/ Structural Integrity Procedia 00 (2019) 000 – 000

Oleg Staroverov et al. / Procedia Structural Integrity 37 (2022) 804–810 © 2022 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Pedro Miguel Guimaraes Pires Moreira Keywords: Composite materials; residual strength; fatigue after impact; damage tollerance; life prediction.

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1. Introduction The use of modern composite materials allows to reduce the weight of the construction with relatively equal physical and mechanical characteristics in comparison with traditional metals and alloys. This trend is relevant for space and aviation facilities, where the proportion of composites in responsible units and parts is constantly increasing. Among all structural composites, carbon fiber-reinforced layered polymer composites stand out, which provide high strength characteristics in comparison with widespread fiberglass plastics. One of the main disadvantages of laminated composites is the relatively low strength in the transverse direction relative to the orientation of the layouts by Abrate (1991), Cantwell and Morton (1991), Safr et al. (2017). Damages resulting from the local shock transverse loads lead to cracks and delamination in the material, which are visually indeterminate, but can significantly reduce the life time of the constructure by Richardson and Wisheart (1996), Papa et al(2019), Slovikov S.V. and Lobanov D.S. (2020), Zubova E.M. et all (2020). Data on residual strength, durability, and acceptable damage are necessary for the creation and development of models of the mechanical behavior of composites. When analyzing scientific literature on similar topics, one can single out by Hinton M.J. et al (2004) in which models of fracture of layered composites are widely presented under various conditions of impact. A lot of test methods for processing experimental data and modeling mechanical behavior are given. It is noted that the databases reflecting the dependence of the residual strength, stiffness and fatigue characteristics of composite materials under complex loads need to be constantly updated and refined. The main objectives of this study were to obtain new patterns of fatigue damage accumulation after preliminary transverse local low-velocity impact, analysis of damage and fracture patterns of prototypes obtained as a result of fatigue failure. 2. Material, Equipment and methods of testing Specimens of carbon fiber composites shaped as rectangular stripes were studied. The specimens were made based on prepreg VKU-39 and binder VSE 1212 with reinforcement pattern [0º/90º] n using the autoclave molding method (Fig.1).

Fig. 1. Photo of CFRP sample

Existing standards (GOST, OST, ASTM, ISO, EN, DIN ...) and scientifically grounded methods describe the procedure for determining the main characteristics of materials under certain types of impact, such as uniaxial tension / compression, three-point bending, interlayer, cyclic tension, etc. The above standards and procedures do not allow obtaining experimental data (characteristics) describing the behavior of composite materials under complex mechanical influences. To solve the problems described, methods have been developed and tested for the experimental study of the behavior of polymer composite materials samples under by complex mechanical influences conditions. This paper studied the effects of low-rate impact bending using a falling load along the entire specimen width. This type of test is necessary for studies intended to investigate processes of deformation and failure in the conditions of