Cyclic-fatigue crack growth in polymer composites: Data interpretation via the Hartman-Schijve methodology
Silvain Michel, A. J. Kinloch, R. Jones
Abstract
• Examines the effects of R -ratio and pre-delamination length on the fatigue of CFRP. • No one unique fatigue crack growth (FCG) rate relationship exists from the DCB tests. • Hartman-Schijve equation captures the effects of the intrinsic and extrinsic variability. • The Hartman-Schijve equation yields one unique linear ‘master’ relationship. • ‘Worst-case, upper-bound’ FCG predicted for small naturally-occurring delaminations. The European Structural Integrity Society (ESIS), Technical Committee 4 (TC4), has initiated a Round-Robin program on the Mode I delamination growth in a continuous carbon-fibre reinforced-plastic (CFRP) composite under fatigue loading, using Mode I double-cantilever (DCB) tests. The present paper shows that the Hartman-Schijve equation, determined with test data generated under R = 0.1, can be used to compute the fatigue crack growth (FCG) associated with tests performed at R = 0.3, 0.5 and 0.7, where R is the load ratio (= P min / P max ). Most importantly, the Hartman-Schijve methodology may be used to determine a worst-case upper-bound da/dN versus Δ G FCG curve for small naturally-occurring delaminations in the CFRP.