PSI - Issue 80

Seiji Mitsubayashi et al. / Procedia Structural Integrity 80 (2026) 423–430 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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press to melt the resin, followed by compression molding at 190 °C under a pressure of 5.0 MPa for 15 minutes. After molding, the specimen was cooled to 30 °C while maintaining the pressure. To evaluate the Mode II interlaminar fracture toughness, an End Notched Flexure (ENF) test was conducted in accordance with JIS K7086. The Mode II fracture toughness Ⅱ was calculated using Equation (1): Ⅱ ＝ 9 12 2 1 2 (2 3 +3 13 ) (1) The specimen dimensions were 20 mm in width, 3 mm in thickness, and 140 mm in length, with an initial crack length of 40 mm. The test was performed at a crosshead speed of 0.5 mm/min using a universal testing machine (AG -IS, Shimadzu Corporation, Japan). 2.4. Evaluation of mode Ⅲ interlaminar fracture toughness of CFRTP To fabricate the test specimens, twelve carbon fiber (CF) cloths (cut to 220 mm in length and 180 mm in width) and fourteen PP sheets (190 mm × 160 mm) were alternately stacked. A heat -resistant film was inserted at the mid plane to serve as an initial crack, and the surrounding layers were composed of PP sheets. The stack was heated at 190 °C for 20 minutes to melt the resin and subsequently molded at 190 °C under 0.5 MPa for 15 minutes. After molding, the specimen was cooled to 30 °C under constant pressu re and then cut in to final dimensions of 90 mm × 40 mm × 4.2 mm (length × width × thickness) . The initial crack length and the pre- crack length were set to 15 mm and 2 mm. Figure 1 (a) and (b) show a jig for Edge Crack Torsion (ECT) test, loading and boundary conditions, respectively. As shown in Figure 1 (a), the jig used in this study consisted of three support pins and one loading pin. A universal testing machine (AG-IS, Shimadzu Corporation) was used to apply the load. The ends of the pins were hemispherical with a radius of 3 mm, and the distances between the pins were 78 mm in the longitudinal direction and 34 mm in the transverse direction. The crosshead speed was set to 0.5 mm/min. The Mode III interlaminar fracture toughness was evaluated based on the Laminated Plate Theory (LPT), which incorporates classical lamination theory. The compliance and Mode III fracture toughness Ⅲ were calculated using the following equations: = = 2 4{ −(1−2 ) }( ) Ⅰ (2) Ⅲ = 2 (1−2 ) 2 {1−(1−2 )( )} (3) Here, is the crosshead displacement, is the load, and are the pin-to-pin distances in the width and length directions, respectively, is the specimen width, is the initial crack length, and is the critical load. ( ) represents the torsional stiffness of an uncracked specimen, and is defined as the ratio of the torsional stiffness of a half-thickness specimen to that of a full-thickness (uncracked) specimen. From the measured values of and , the twist angle and torque were determined, which were then used to calculate ( ) .