PSI - Issue 50

Kirill Guseinov et al. / Procedia Structural Integrity 50 (2023) 105–112 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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3

through-thickness compression stresses was varied in two ways: by changing the cut angle of cubic specimens and by loading V-notched specimens at different angles in a new device.

2. Materials and Methods 2.1. Materials and specimens

The composite plates were made by hand lay-up with press moulding, similarly to Abot et al. (2011). The composites were reinforced with UWB-200-3K-Twill2/2- 100 (3K, 200 g/m2) twill carbon fabric (UMATEX®, Moscow, Russia). A mixture of epoxy, diethylene glycol and triethanoltetramine ED-20/DEG/TETA (82/8/10 by weight) was used as the polymer binder. The fire volume fraction, evaluated with the conventional burning-test method, was approximately 59%. Two types of specimens for biaxial tests were cut from the composite plate by CNC-router. The initial dimensions of the specimens were previously determined in (Abot et al. (2011), Guseinov et al. (2022)). The dimensions of the specimens for biaxial loading are shown in Figure 1.

(a)

(b)

Fig. 1. Dimensions of the cubic (a) and V-notched (b) specimens

2.2. Compression of Cubic Specimens To evaluate the interlaminar shear strength and to analyse the mechanical response under through-thickness compression of woven composites, the well-known method for determining the shear properties of composites under biaxial loading was used. Cui et al. (2018), Koerber et al. (2010) used this method for unidirectional composites, but it could be easily adopted for composite materials with fabric reinforcement. According to this test method, the desired combination of interlaminar shear and through-thickness compression stresses is obtained by varying the cutting angle of cubic specimens α during compression tests (Figure 2,a). Through -thickness compression and interlaminar shear stresses in the gauge section of the specimen are defined as follows:

2 3 sin ( ) x      ,

(1)

13 sin( ) cos( ) x        .

(2) This experimental method has some disadvantages despite the simplicity of tests implementation. Koerber et al. (2010) noted that the stress concentration was associated with friction at the specimens ends, which affected the mechanical response. It should also be noted that the uniform distribution of shear strains in cubic specimens could not be ensured due to the relatively small working section. The influence of these factors on the interlaminar shear properties of composites was evaluated in this work.