Experimental Investigation and Crystal Plasticity Simulation for the Fatigue Damage Behavior of C17200 Beryllium Copper Alloy in the Very High Cycle Fatigue

This study investigates the crack initiation and damage behavior of C17200 beryllium copper alloy under very high cycle fatigue (VHCF) conditions. Ultrasonic fatigue tests (20 kHz) demonstrate fatigue lives spanning 3.05 × 10 6 cycles at 400 MPa to 1 × 10 10 cycles at 240 MPa, with a distinct transition to internal crack initiation beyond 10 7 cycles. Fractographic analysis via field emission scanning electron microscopy identifies grain boundaries (GBs) and persistent slip bands as critical damage sites. Crystal plasticity finite element method simulations reveal that stress concentrations at GBs and accumulated plastic shear strain localized along 45° slip systems are the primary drivers of crack initiation and propagation, respectively. These results establish that GBs stress concentration induced by adjacent grain misorientation and preferential activation of 45° slip systems fundamentally govern VHCF failure in C17200 alloy.