Evaluation of True Bonding Strength for Adhesive Bonded Carbon Fiber-Reinforced Plastics

• Published in: Materials Vol. 17; no. 2; p. 394
• Main Authors: Takamura, Maruri, Isozaki, Minori, Takeda, Shinichi, Oya, Yutaka, Koyanagi, Jun
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 01.01.2024
• Subjects: Adhesive bonding; Adhesive strength; Adhesives; Bending moments; Bond strength; bond strength test; Bonding strength; Carbon fiber reinforced plastics; Carbon fiber reinforcement; CFRP ultrasonic welding; Combined stress; Compressive strength; Fiber reinforced polymers; interfacial strength; Load; Numerical analysis; numerical simulation; Shear strength; Shear stress; Shear tests; Simulation; Stress state; Tensile tests; Test methods; Thermoplastic resins; Thermoplastics; Thickness; Vibration; Japan; bond strength test; CFRP ultrasonic welding; interfacial strength; numerical simulation
• ISSN: 1996-1944; 1996-1944
• DOI: 10.3390/ma17020394

Carbon fiber-reinforced thermoplastics (CFRTPs) have attracted attention in aerospace because of their superior specific strength and stiffness. It can be assembled by adhesive bonding; however, the existing evaluation of bonding strength is inadequate. For example, in a single-lap shear test, the weld zone fails in a combined stress state because of the bending moment. Therefore, the strength obtained experimentally is only the apparent strength. The true bonding strength was obtained via numerical analysis by outputting the local stress state at the initiation point of failure. In this study, the apparent and true bonding strengths were compared with respect to three types of strength evaluation tests to comprehensively evaluate bonding strength. Consequently, the single-lap shear test underestimates the apparent bonding strength by less than 14% of the true bonding strength. This indicates that care should be taken when determining the adhesion properties for use in numerical analyses based on experimental results. We also discussed the thickness dependence of the adhesive on the stress state and found that the developed shear test by compression reduced the discrepancy between apparent and true strength compared with the single-lap shear test and reduced the thickness dependence compared with the flatwise tensile test.