Mode I delamination fatigue crack growth in unidirectional fiber reinforced composites: Results from ESIS TC4 round-robins

• Mode I fatigue delamination propagation in unidirectionally reinforced composites was characterized.
• A round robin exercise was carried out.
• Different calculation methods for da/dN and G have an influence on in- and inter-laboratory scatter.
• Smoothening techniques reduce the amount of scatter.

Two round robins on mode I fatigue delamination propagation organized by Technical Committee 4 of the European Structural Integrity Society compared three unidirectional carbon fiber reinforced composites, one with thermoplastic (poly-ether-ether-ketone) and two with thermoset (epoxy) matrix tested at five laboratories. Different approaches for data evaluation and their effect on the in- and inter-laboratory scatter are discussed and compared. Calculated delamination rates da/dN and applied GImax from displacement controlled tests are sensitive to small scatter in the load signal, and, therefore, a new route to evaluate the crack growth rate from pairs of load and displacement data is presented.