Evaluation of very high cycle fatigue properties for transverse crack initiation in cross‐ply carbon fiber‐reinforced plastic laminates

This paper investigates the transverse crack initiation behaviors of carbon fiber‐reinforced plastics (CFRPs) in the high‐cycle and very high cycle regimes. To accelerate the fatigue test up to the very high cycle fatigue (VHCF) regime, an ultrasonic fatigue testing system that can apply the specimen ultrasonic load at a frequency of 20 kHz was used. The fatigue behavior of cross‐ply CFRP laminates formed with T800S/2592 prepreg was investigated. The fatigue behaviors at N = 103–107 cycles and N = 108–109 cycles were obtained by hydraulic and ultrasonic fatigue tests, respectively. The slope of the S–N diagram for transverse crack initiation showed a linear decrease in the region of N = 103–106 cycles and leveled off over N = 106 cycles. Furthermore, no cracks occurred in any specimen tested under the 90°‐layer stress σ90°max = 44 MPa up to a maximum of N = 6.56 × 109 cycles. Highlights Ultrasonic fatigue tests over N = 109 cycles were successfully performed. Fatigue behavior was obtained over a wide stress range using three different frequencies. The existence of a stress threshold for transverse crack initiation was suggested.