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An analytical model is developed to assess the compressive strength criticality of near-surface interlaminar defects in laminated composites.

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The large amplitude vibrations of a thin-walled cylindrical shell are analyzed using the Donnell's shallow-shell equations. A perturbation method is applied to reduce the nonlinear partial differential equations into a system of linear partial differential equations. The simply-supported boundary condition and the circumferential periodicity condition are satisfied. The resulting solution indicates that in addition to the fundamental modes, the response contains asymmetric modes as well as axisymmetric modes with the frequency twice that of the fundamental modes. In the previous investigations in which the Galerkins procedure was applied, only the additional axisymmetric modes were assumed. Vibrations involving a single driven mode response are investigated. The results indicate that the nonlinearity is either softening or hardening depending on the mode. The vibrations involving both a driven mode and a companion mode are also investigated. The region where the companion mode participates in the vibration is obtained and the effects due to the participation of the companion mode are studied. An experimental investigation is also conducted. The results are generally in agreement with the theory. IINon-stationary' response is detected at some frequencies for large amplitude response where the amplitude drifts from one value to another. Various nonlinear phenomena are observed and quantitative comparisons with the theoretical results are made.

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ABSTRACT-An experimental program to determine tie pi-enomenological aspects of composite-panel failure under simultaneous compressive n-plane loading and low-velocity transverse impact [C-75 m/s (0-250 ftls)] is described. Highspeed photograohy coupled with the shadow-moire techniq~e is usec to record the phenomenon of failure propagatior. The informat on gained from these records, supplemented by plate sectioning ard observatior for interior damage, has provided informaticn regarding the failure-propagation mechanism.The results show that the failure process can be divided roughly into two phases. In the first phase the plare is inpacted, and tie resulting resoonse causes interla,ninar separation. in the second phase the local damage spreads to the unaamaged portion of tie plate through a combination of laminae b~ckling and further delanination. List of Symbolsn = fringe number V = impact velocity w = out-of-plane displacement w/n = fringe constant At = time interval between frames eo = compression strain ('load')

Recent advances in shell buckling research are reviewed. Five separate subject areas are covered: elastic postbuckling behavior and imperfection sensitivity, plastic buckling, dynamic buckling, experiments and computations. Recent history of the research is presented emphasizing important advances in understanding. Areas of needed research and current trends are pointed out.

Local geometric imperfections on pipes under external pressure can lead to local buckling which under the “right” conditions can cause the initiation of a propagating buckle. This buckle, driven by the pressure, propagates up and down the pipe flattening it. The lowest pressure which can sustain a propagating buckle is called the propagation pressure and is a characteristic pressure of the pipe. Experiments have shown this pressure to be dependent on the post yield characteristics of the pipe material behavior, as well as the diameter-to-thickness ratio of the pipe. The collapse mechanism has been modeled by the collapse of a ring under external pressure. By identifying the lowest postbuckling pressure of the ring with the propagation pressure an empirical expression for the latter quantity has been established.