PSI - Issue 40

D.S. Lobanov et al. / Procedia Structural Integrity 40 (2022) 258–263 Lobanov D.S., Strungar E.M. / Structural Integrity Procedia 00 (2022) 000 – 000

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ray technology. In articles [J. Song et al (2019), Yifan Zhang et al (2020)], the authors analyzed the fatigue life of 2.5D woven composites with a central hole at room and elevated temperatures, and plates with holes of different diameters were also studied in tensile tests. Composites are used for complex structures where different elements are often bolted or riveted. Thus, understanding and predicting the mechanical behavior of composite structural members with holes becomes essential for the design of complex heterogeneous structures. The presence of stress concentration can lead to fracture and a significant decrease in strength. Analysis of the effect of stress concentration on the behavior of composite materials is an important topic, it is believed that they cause a relatively large decrease in strength compared to composite objects without holes [Lobanov et al (2019), Strungar et al (2020), Strungar and Wildemann (2020), Strungar and Lobanov et al (2020)]. This work is a continuation of a comprehensive study of 3D woven carbon fiber reinforced plastics under different types of loading [Hilov et al (2020), Strungar and Yankin et al (2020), Tretyakova et al (2019), Zubova et al (2020)]. The aim of this work is to study the tensile characteristics of spatially reinforced and laminated CFRPs with open hole of the same size. This study is essential for understanding the role of composite damage mechanisms, assessing hole sensitivity and comparing the performance of different reinforcement schemes. 2. Material, equipment and study methods Experimental studies were carried out using the large- scale research facilities «Complex of testing and diagnostic equipment for studying properties of structural and functional materials under complex thermomechanical loading» PNRPU. A spatially reinforced carbon fiber composite based on T26 epoxy resin and AKSA A-49 carbon fiber is considered as the material under study. Tensile tests on solid specimens without a hole in accordance with ASTM D 3039 and specimens with an open hole in accordance with ASTM D 5766 were carried out using the universal electromechanical testing system Instron 5989 (± 600 kN) with a grip displacement speed of 2 mm / min. According to the tensile testing results of specimens with an open hole and without a hole, the corresponding mechanical characteristics were determined. The comparison was carried out according to the values of the maximum stresses. A series of mechanical tests for uniaxial tension of composite specimens with a circular concentrator in the form of a hole along the axis of symmetry of the specimen was carried out (in accordance with the sketch of the specimen in Fig. 1 b, W1 = W2 = 15mm and L1 = L2 = 147mm). Specimen strip preforms are made using 3D weaving technology in various weaving methods (types 1-4), as well as layered preforms (type 5). Four weaving patterns of 3D-woven preforms are considered: orthogonal (type 1); orthogonal combined (type 2); with pairwise interlayer reinforcement (type 3); with pairwise interlayer reinforcement and longitudinal layer (type 4). The central part of rectangular specimens measuring 300x36x4 mm (LxWxh) (according to ASTM D 5766) contains a concentrator in the form of a single open hole with a diameter of 6 mm (d), specimens without a concentrator measuring 250x25x4 mm (LxWxh) (ASTM D 3039). A sketch of specimens with a hole is shown in Fig. 1. A total of 10 specimens were tested in each group.