Delamination arrest features in aircraft composite structures under static and fatigue loading

Delamination suppression is critical for large integrated composite structures as there exists no natural arrest mechanism within the laminate. As a result, one common solution is to install fasteners, clamping the laminate together in order to arrest the delamination. While this reduces the danger of critical delamination growth, research has indicated that while fasteners help limit the growth of delaminations, under certain conditions, the interlaminar cracks can extend past these fasteners. These arrest features slow and redirect the propagation of the crack, first by compressing the lamina together and second by transferring load via shear engagement of the fastener. In conjunction, work has found that fastener spacing can be increased beyond the typical spacing of 5 fastener diameters, with each additional fastener installed in series providing increasing benefit. Experimental and computational studies have indicated that the failure mode can be shifted away from delamination under both static and fatigue loading with proper arrest mechanism design. Nomenclature CLT = Classical Lamination Theory D = Fastener Diameter da dN = Crack growth per cycle ΔG = Range of G for one fatigue cycle ΔG = Gmax − Gmin G = Total Strain Energy Relapse Rate GC = Critical Total Strain Energy Release Rate GI = Mode I Strain Energy Release Rate GII = Mode II Strain Energy Release Rate GIC = Critical Mode I Strain Energy Release Rate GIIC = Critical Mode II Strain Energy Release Rate Gmax = Maximum value of G for a fatigue cycle Gmin VCCT = Minimum value of G for a fatigue cycle = Virtual Crack Closure Technique