Influence of micro-notches on the fatigue strength and crack propagation of unfilled and short carbon fiber reinforced PEEK

摘要

Short carbon fiber reinforced (SCFR) PEEK is a highly attractive material for lightweight structures; improving knowledge about the influence of local imperfections on its fatigue behavior is essential for the design of real components. To this aim, fatigue strength and crack propagation of two grades of SCFR PEEK and neat matrix were investigated by testing at different stress levels specimens with a micro-notch consisting of a small blind hole (range diameter 0.1-1mm). Overall, the presence of amicro-notch resulted in a decrease of fatigue strength compared to un-notched condition, but with different sensitivity and crack propagation patterns; while a higher fiber volume fraction enhanced fatigue strength and resistance to crack propagation, the combination of a lower fiber content and inclusion of additive particles had a negative effect. Crack propagation in the notched region was also evaluated. The average values of Paris' law exponential coefficients were similar and within the range of literature values, without apparent correlationwith reinforcement type. Preliminary investigations in the presence of the smallestmicro-notches seemto indicate the presence of a threshold size belowwhich the influence of a small notch is comparable with that of material inherent defects, but further testing is necessary. (C) 2017 Elsevier Ltd. All rights reserved.