High performance quasi-isotropic thin-ply carbon/glass hybrid composites with pseudo-ductile behaviour loaded off-axis

The aim of this work was to investigate the effect of loading angle variation on the pseudo-ductility of quasi-isotropic (QI) hybrid composite laminates. Previously, hybrids of thin-ply carbon fibres and standard glass fibres were found to have an excellent pseudo-ductile behaviour both in unidirectional (UD) and QI configurations when subjected to axial tension in the fibres’ orientations. In this work, the QI laminates, with 60° intervals, have been subjected to a quasi-static tensile load at various off-axis orientations – i.e. 5°, 10° and 20°. The QI hybrid composites were made by sandwiching a QI T300-carbon laminate between the two halves of a QI S-glass laminate. The results showed a pseudo-ductile behaviour with a linear elastic part and a desirable plateau for all the loading directions, however the pseudo-ductile strain decreases when increasing the off-axis angle. Comparing the 20° off-axis with the other cases, there was more active matrix cracking damage before fragmentation in the 20° off-axis plies and it failed earlier than the other samples. Acoustic emission (AE) results confirmed this, with more matrix cracking related AE signals in the 20° off-axis case compared to the other configurations.The paper has been published open accessStructural Integrity & Composite

Investigating the fatigue behaviour of quasi-isotropic pseudo-ductile thin-ply carbon/glass epoxy hybrid composites

This paper investigates the fatigue behaviour of pseudo-ductile Quasi-Isotropic (QI) interlayer hybrids with un-notched and open-hole configurations. Two different types of QI pseudo-ductile hybrids were evaluated; HighC, with carbon to glass thickness ratio of 0.29, that is made of thin-ply M46JB-carbon/epoxy and thin-ply Xstrand-glass/epoxy prepregs, and LowC, with carbon to glass thickness ratio of 0.19, that is made of thin-ply T300-carbon/epoxy and standard-ply S-glass/epoxy prepregs. The hybrid configurations were loaded at 4 Hz in tension–tension fatigue without any initial damage and at different percentages of the pseudo-yield stress (σpy) at which damage initiates. It was observed that there is no stiffness reduction, after 100,000 cycles, for a stress level of 80 % and 50 % of the σpy for the un-notched and open-hole laminates, respectively. By increasing the stress level to 90 % and 70 % of the σpy for the un-notched and open-hole laminates, respectively, there is a gradual stiffness reduction due to the appearance of matrix cracking and delamination in LowC, but no gradual reduction and no visible damage were observed for HighC. The final failure is more brittle and happens at a lower number of cycles for HighC compared with LowC. Different damage extents were observed for the investigated laminates before the final sudden failure due to variables such as the ply thickness, the cyclic energy release rate and the interfacial fracture toughness.Materials and Environmen