Experimental evaluation of filled-hole compressive strengths of thin-ply carbon fiber / epoxy composite laminates

By experimentation, this study investigated ply thickness effects on the filled hole compression (FHC) strength of thin-ply CFRP laminates. The FHC strength of quasi-isotropic (QI) laminates increased by 26–45% with decreasing ply thickness from 0.2 to 0.05 mm. Comparing the case of 0 Nm and 7.0 Nm tightening torque, the FHC strength was more than 28–49% higher for the QI laminates with a tightening torque of 7.0 Nm. The FHC strength of thin-ply QI-CFRP (0.05 mm ply thickness) at a fastener tightening torque of 7 Nm was 675 MPa, which was greater than the un-notched compressive (UNC) strength (590 MPa). Visual observation and X-ray CT results of fractured specimens after FHC testing suggested that bearing damage of the CFRP laminates was prevented under adequate fastener tightening torque. It was inferred that the increase in the FHC strength in thin-ply CFRP was mainly contributed by the increase in the UNC and OHC strength.