TORSIONAL BUCKLING AND POST-BUCKLING OF COMPOSITE GEODETIC CYLINDERS WITH SPECIAL REFERENCE TO JOINT FLEXIBILITY

Curved (geodetic) composite frameworks are being considered for battledamage tolerant helicopters. In a previous paper by the authors it was shown that it was necessary to use curved, twisted beam elements to numerically predict the correct stiffness. Unfortunately the predicted torsional buckling load of a carbon cylinder was still 30% too high. Upon further detailed experimental testing of isolated geodetic joints it was realised that joint flexibility is an important factor in the overall behaviour of the shell. When this joint flexibility is incorporated in the finite element models of the geodetic joint test specimens the differences between experiment and theory are dramatically reduced. This is also true for the complete shell where the buckling torque, calculated from linear finite element analysis, now exceeds the experimental value by about 12%, while for the non-linear analysis the discrepancy is reduced to below 7%. Compression tests of the cylindrical geodetic shell confirm that the finite element model incorporating joint flexibility produces much better results for the compression stiffness. © 1990.