jmc-xavier

The effect of ply thickness on the onset of intralaminar and interlaminar damage is extremely important for the structural response of laminated composite structures. This subject has gained particular interest in recent years due to the introduction in the market of spread-tow, ultra-thin carbon-fibre reinforcements with different configurations. In the present paper, an experimental test campaign was carried out to study the structural response of aerospace-grade plain weave spread-tow fabrics (STFs) of different areal weights. The results showed that, in spite of an apparent superior longitudinal tensile strength of the thick STF, the multidirectional thin-STF laminate exhibited an improved tensile unnotched strength over the thick-STF laminate, attributed to its damage suppression capability. However, damage suppression was also responsible for similar tensile notched strengths. In compression, the thin-STF laminate performed substantially better than the thick-STF laminate in both unnotched and notched configurations. Finally, a similar bearing response was obtained in both STF laminates, in spite of a slightly higher resistance of the thin-STF laminate to the propagation of subcritical damage mechanisms.

The enhanced mechanical performance of thin-ply laminates results from their ability to delay the onset of damage typically observed in composite materials. However, in notched structures, subcritical damage growth causes beneficial stress redistributions in the vicinity of the notch, blunting the stress concentration. Precluding these damage mechanisms, as in thin-ply laminates, may potentially lead to inferior notched responses. To obviate this limitation of thin-ply laminates, a strategy based on the combination of standard grade 0� plies and thin transverse and off-axis plies is analysed in this paper. A detailed study of the effect of 0� ply blocking is carried out, with particular emphasis on the blunting mechanisms and notched response. Tests on scaled notched panels loaded in tension, with notch sizes between 6?mm and 30?mm, show that the combination of standard grade 0� ply blocks with thin transverse and off-axis plies promotes localised fibre-matrix splitting, which acts as an important notch blunting mechanism, while preventing matrix cracking and delamination. This results in an improved notched response and superior large damage capability. It is also shown that thicker 0� ply blocks provide higher stability in composite bolted joints, while the thin transverse and off-axis plies contribute for matrix-dominated damage suppression, resulting in an improved bolt-bearing response. The improvements of the large damage capability and bolt-bearing performance are obtained without compromising the superior unnotched tensile and compressive strengths intrinsic to thin-ply laminates.