Influence of manufacturing technique and autoclaving curing rate on the non-linear behaviour of thin-walled, GFRP channel columns – Experimental studies

Abstract

The target of this research is to investigate the influence of manufacturing technique and autoclaving process parameters on the buckling and post-buckling behaviour of thin-walled, GFRP laminates. We investigated the compression of channel cross-section profiles with the following dimensions of the inner perimeter: (web × flange × length of the profile): 80 mm × 38 mm × 240 mm. The nominal wall thickness of the columns was equal to 1.2 mm. The inner radius at the web-flange junction was equal to 2 mm. The material used to produce the samples was eight-layered pre-preg tape with an angle-ply, symmetric layer arrangement: [45/−45/45/−45]s. The columns were manufactured using two different techniques. The first technique was to form the channel cross-section profile by draping over an aluminium mandrel, while the second was to form square cross-section profiles, by winding around an aluminium mandrel, which are then cut into two channel-cross sections. Moreover, two curing process types were applied. The first is a nominal (suggested by the pre-preg producer) curing cycle on a hollow section aluminium mandrel, while the second is a modified curing cycle on a solid aluminium mandrel. In total, four different sets of specimens were produced and subjected to static compression. Higher buckling strength (denoting critical loads and post-buckling behaviour) is shown to be a result of internal, after curing stresses in the composite – the highest buckling resistance is achieved for the columns manufactured as square hollow sections and machined into channel sections. This solution is the most economically efficient. Additionally, the samples were 3D scanned in order to assess post-manufacturing distortions and the deviations from the nominal geometry.