A Mode I cohesive law characterization procedure for through-the-thickness crack propagation in composite laminates

Engineering the translaminar fracture behaviour of thin-ply composites

“…The design of the CT specimens used in this work is similar to others reported in the literature [1,26,32], which is derived from the ASTM E399 standard [33]; but with one important modification: the specimens contain a central notch which terminates with a blunted semicircular shape, instead of a sharp machined notch. This semicircular blunt notch overlaps with a 10 mm straight cut laser-engraved in each 0°ply before lamination, thus terminating in a 5 mm long laser-cut sharp notch which acts as crack initiator during the tensile test.…”

Deducing the R-curve for trans-laminar fracture from a virtual Over-height Compact Tension (OCT) test

“…On the one hand, R-curves have been reported for Mode I trans-laminar fracture e.g. in coupon tests [2][3][4][5][6][7] and observed in full-scale composite structural tests [8]. On the other hand, many existing approaches for modelling Mode I trans-laminar fracture [9][10][11][12] do not directly address R-curves and assume a constant Mode I trans-laminar fracture toughness value during fracture propagation.…”

“…Catalanotti et al [18] also applied their method to QI CP-T700/ACE Non-Crimp Fabrics. The approaches [6,10,11,18] to determine trans-laminar fracture toughness either rely on inputs from modelled notched tests [10,11], or the results from separate sets of scaled notched tensile tests [18]. The numerical prediction of R-curves for QI laminates without input parameters from the modelled fracture tests has not been reported before.…”

“…An alternative geometry to generate stable fracture in a single test is the Compact Tension configuration, for example following the ASTM E399 standard [23], originally for metals. Compact Tension specimens have been widely used for the determination of Rcurves for Mode I trans-laminar fracture in composites [3,5,6]. One limitation of that configuration is that the specimen may suffer from compressive failure at the top, bottom and rear ends.…”

“…However, the linear elastic FE analysis does not account for the material non-linearity due to the complex behaviour in the Fracture Process Zone (FPZ). Bergan et al [6] implemented their characterised cohesive law in an FE analysis, in which the crack increment was calculated numerically as the distance from the initial notch tip to the first undamaged element. DIC was used to check out-ofplane deformation and CT scans were used to check damage development, but they were not adopted for crack length measurements in Ref.…”