| Buckling and postbuckling has been critical design parameters for many engineering structures. In recent years, this topic has continued to be of major concern due to (1) the discovery of new materials with amazingly superior properties, (2) increasingly more stringent safety requirements, (3) lighter, and more durable requirements. Such applications can be routinely found in aerospace, naval, civil, and electrical, and nuclear engineering structures and especially in the vehicle industries. Koiter is the first one to show that the imperfection-sensitivity of a structure is determined by its initial postbuckling behavior. In Koiter's 1945 general postbuckling theory, it defines the initial postbuckling behavior and imperfection sensitivity behavior by the postbuckling b coefficient. Hui and Chen (1986) were the first to show that the well-known Koiter's General Theory of Elastic Stability of 1945 can be significantly improved by evaluating the postbuckling b coefficient at the actual applied load, rather than at the classical buckling load. The reason for such significant improvement in predicting the imperfection sensitivity is due to the fact that for an imperfection-sensitive structure, the slope of the buckling load versus imperfection amplitude curve approaches negative "infinity" as the imperfection amplitude approaches to zero. Thus for "finite" amplitude of the geometric imperfection, the applied load is significantly lower than the classical buckling load, leading to significant overestimate of imperfection using Koiter's General theory of 1945. Such improvement method was demonstrated to be (1) very simple to apply with no tedious algebra, (2) significant reduction in imperfection sensitivity and (3) although it is still asymptotically valid, there exists a significant extension of validity involving larger imperfection amplitudes. Strictly speaking, Koiter's theory of 1945 is valid only for vanishingly small imperfection amplitudes. Hence such improved method is termed Hui's Postbuckling method.;This study deals with the Postbuckling and imperfection sensitivity of different kinds of cylinders by using the Hui's postbuckling method. For unstiffened cylinder and laminate cylinder, the solution of Hui's postbuckling method is compared with ABAQUS simulation result. A parameter variation of stringer/ring stiffened cylinder is also evaluated. A positive shift of the postbuckling b coefficient has been observed, which indicates a significant overestimate of the imperfection sensitivity by Koiter's general stability theory. More importantly, the valid region is significantly increased by using Hui's postbuckling method compared with the Koiter's general stability theory.;Keywords: Buckling; Postbuckling; Imperfection Sensitivity; Cylindrical Shell. |
