Fatigue crack propagation behavior of cellulose esters

The effect of plasticizer concentration on fatigue crack propagation (FCP) rate in cellulose acetate‐propionate (CAP) was determined. Compact tension specimens were machined from 6.2 mm‐thick injection molded plaques and tested on an MTS servohydraulic testing machine using a sinusoidal waveform with a frequency of 1 Hz. Two FCP mechanisms were identified: a crazing mechanism, which dominated at low values of stress intensity factor range, Δ K , and a shear yielding mechanism, which dominated at high values of Δ K . The value of Δ K at the onset of the transition from the crazing mechanism to the shear yielding mechanism was a function of plasticizer concentration, and therefore yield strength of the CAP. The transition in crack propagation mechanism created a V‐shaped feature on the fracture surface, which could be used to weight the contributions from the two crack propagation mechanisms to the overall FCP rate.