Experimental and analytical investigation of the local buckling behaviour of unsymmetrically laminated thin-walled beams

The lightweight design of composite structures typically results in the configuration of thin-walled and slender components, which require consideration of structural stability. In addition to the established design criteria and calculation methods for stability analysis, the experimental validation of such methods represents a significant aspect of ensuring the reliability of design concepts. This study addresses the closed-form analytical calculation of the critical buckling load of unsymmetrically laminated composite I- and C-beams. This represents a novelty since the majority of available investigations deal with symmetrical layups. The presented methods employ the discrete plate analysis and consider individual beam segments that are simply supported at the loaded edges. Based on the analytical results, a novel experimental setup is presented, which implements the simple support of the individual unsymmetrically laminated segments in the experimental study. The buckling loads are obtained through experimental investigation employing two distinct methodologies. In contrast to global stability failure, local buckling may result in a significant load increase in the postbuckling regime, as evidenced by a parabolic curve in the force–deflection diagram. This knowledge can be used to identify the critical load experimentally. The second evaluation method is based on the loss of stiffness in the longitudinal direction of the beam at the initial stage of buckling. A comparison of the analytical and numerical calculation methods with the experimentally obtained buckling loads of unsymmetrically laminated beams demonstrates a high degree of correlation. The presented experimental setup is shown to be reliable, and the closed-form analytical methods are validated.