Mode I intralaminar fracture toughness of 2D woven carbon fibre reinforced composites: Pre-crack tip radius sensitivity

The determination of intralaminar fracture toughness for carbon fibre composites has been the subject of several studies. However, pre-crack geometry has not been extensively investigated. Here we assess the sensitivity of the mode I intralaminar fracture toughness to pre-crack tip radius, numerically and experimentally. Two sets of five scaled Double Edge Notch Tension (DENT) specimens were made from the same 2D woven carbon fibre composite laminate, one with blunt notches and another with sharp pre-cracks, and tested using the size effect method. Experimental results depicted a higher fracture toughness for the sharp pre-crack specimens. A numerical investigation was then performed on the geometric correction factor used in the data reduction, to analyse whether the differing radii affect the stress intensity at the crack tip, which may explain the difference in experimental results. However, the correction factor for the two radii, which assumes a slit crack propagating from the initial pre-crack tip, converged to the ideal slit crack solution, before reaching peak load, for all specimen sizes tested. Further investigation is required to assess the difference in experimental fracture toughness values.