Axial capacity and crushing of thin-walled metal, fibre–epoxy and composite metal–fibre tubes

Recent investigations of square hollow section (SHS) metal tubes with externally bonded carbon fibres have shown significant increases in the axial capacity and mean crushing load, compared with the metal SHS. The composite metal–fibre tubes employed carbon fibre reinforced polymer (CFRP) matrix layouts of two and four layers of carbon fibres. In this paper the same sized two and four layer CFRP SHS were manufactured independent of the metal SHS, and the axial capacity and crushing behaviour were determined experimentally. Four different tube sizes were tested, resulting in tube width to thickness ratios between 32 and 144. A photogrammetry system was employed to accurately determine the buckling and post-buckling behaviour. It is shown that the capacity and mean crush load of the composite metal–CFRP SHS exceed the sum of those for the individual metal SHS and CFRP SHS, by up to 1.8 times. This composite action results from the bond between the metal and the carbon fibres, and the mechanics with respect to buckling, capacity and crushing is discussed. The strength of metal, composite metal–CFRP and CFRP tube walls are determined using the effective width approach, and are shown to compare well with the experimental results.