The buckling of CFRP composite plates in compression and shear and thin-walled composite tubes in torsion – The effects of bend-twist coupling and the applied shear direction on buckling performance

Abstract

The influence of flexural anisotropy or bend-twist coupling on the buckling performance of CFRP composite plates in compression and shear and thin-walled CFRP composite tubes in torsion is examined in this paper using the finite strip method of analysis. The finite strip formulation employed in the analysis procedure is readily able to deal with the many complexities associated with typical laminated composite construction. Lay-up configurations resulting in membrane anisotropy, flexural anisotropy and membrane-flexural coupling are all easily dealt with. The strip perturbation or buckling displacement fields are postulated to vary sinusoidally along the strip length and algebraicly across the strip width and any combination of linearly varying bi-axial tension or compression coupled with in-plane shear loading on the strip can be accommodated. The paper gives an in-depth understanding of the complex buckling mechanics associated with flexural anisotropy in polymer composite construction and highlights the importance of realising the significance of the applied in-plane shear or torque direction on buckling performance. Markedly different stability levels are shown to be in existence for the load cases of positive and negative shear in composite plates and for the clockwise and anticlockwise torsional loading of thin-walled composite tubes. This situation is, of course, not realised in isotropic metal construction or in orthotropic composite construction since such material systems are devoid of the effects of bend-twist coupling.