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Session: Session 10: Structural integrity of composite laminates
Session starts: Wednesday 28 June, 09:00
Presentation starts: 09:40
Room: Theatre room: plenary

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Atsushi Hosoi (Waseda University)
Shinji Ito (Waseda University)
Tsuyoshi Miyakoshi (Waseda University)
Momoka Shima (Waseda University)
Yuki Nishi (Waseda University)
Hikaru Saito (Waseda University)
Hiroyuki Kawada (Waseda University)

Abstract:
An application of carbon fiber reinforced plastic (CFRP) laminates is being expanded to rotating components such as jet engine fan blades. Since the blade members are subjected to cyclic loading exceeding 10^9 cycles during their design life, it is important to clarify the gigacycle fatigue properties of CFRP laminates and their fracture mechanisms. Thus, the objective of this study was to evaluate the gigacycle fatigue properties of CFRP laminates in transverse crack initiation. A conventional hydraulic fatigue test is too time-consuming, and accelerated tests must be conducted to evaluate gigacycle fatigue properties. In this study, accelerated fatigue tests were conducted at a test frequency of 20 kHz by ultrasonic fatigue testing. The temperature rise of the specimens due to self-heating was prevented by air cooling with dry air and intermittent operation. Therefore, the apparent test frequency was approximately 1.8 kHz. So far, no definite fatigue limit of CFRP laminates has been confirmed. It is known that the initial damage in fatigue of CFRP laminates is transverse cracks, and that its growth and increase can lead to major damage such as delamination and fiber breakage. It is possible to obtain the initial fatigue properties before macroscopic damage occurs by evaluating the initiation life of transverse cracks. In addition, a mechanical model based on a variational approach was proposed for a cross-ply laminates with transverse cracks resonated in the first-order mode by ultrasonic vibration. In this study, [0/906]s cross-ply CFRP laminates were used, and the fatigue test was conducted at a stress ratio of R = -1 by the hydraulic fatigue and the ultrasonic fatigue testing. The experimental results showed that no transverse crack initiation occurred in the giga-cycle region, suggesting the existence of the fatigue limit. The stress analysis results of the proposed model showed good agreement with the results of the finite element analysis.