PSI - Issue 68

Robert Lowe et al. / Procedia Structural Integrity 68 (2025) 173–183 R. Lowe et al. / Structural Integrity Procedia 00 (2025) 000–000

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A piece of paper was then glued to the sample's top surface, allowing for ease of note of position during testing as shown in Fig. 1. The Mode I interlaminar fracture toughness of the composite is calculated using Equation 1, where ‘P’ denotes the load value, ‘ ’ is the sample displacement at the corresponding load, ‘b’ is the sample width, ‘a’ is the total delamination length, ‘ ∆ ’ is the correction factor corresponding to the x-intercept of the cubed root of the compliance to the delamination length. !" = & ' (#)$*%| ∆ | ) (1) Mode II testing was carried out on a Zwick-Roell Z005 UTM with a 10 kN load cell. The dimensions of the samples were 140 mm in length, 25 mm in width and 5 mm in depth. The edges of the samples were polished, and the midpoint and the compliance crack lengths were also marked (distances of 20, 30, and 40 mm into the PTFE insert from its tip) as shown in Fig. 2 and Fig. 3. The test was evaluated using a three-point bend setup. Compliance tests are carried out at half the peak load at crack lengths of 20 mm and 40 mm; finally, the sample is tested at a crack length of 30 mm, with the test continuing until advancement of the delamination is achieved (Prasad et al., 2019)(Prasad et al., 2019). The Mode II fracture toughness is calculated using Equation 2, where ‘m’ represents the compliance calibration coefficient, calculated as the slope of the linear least squares linear regression analysis of compliance against crack length cubed (ASTM D2344, n.d.). !!" = #.$ !"# $ ) % $ &' (2)

Fig. 2. A diagram showing the varying span lengths used during each step of the test with the crack insert and sample midpoint.

Fig. 3. A labelled image of the apparatus used during Mode II testing.