Showing papers by "Brian L. Wardle published in 1997"

Importance of Instability in Impact Response and Damage Resistance of Composite Shells

Abstract: The response of laminated cylindrical composite shell structures to transverse loading was studied through impact and quasi-static testing. A highly nonlinear structural instability phenomenon, closely resembling a snap-through instability, was found to have a strong influence on the loading/impact response including the resulting damage. Because of this structural instability, the behavior of convex shells under static or dynamic (i.e., impact) transverse loading is found to be much different than that for plates. These differences include trends displayed in the response parameters as well as damage extent and distribution. Convex shells with a response instability are found to have increased impact damage resistance compared with plates. A concept is proposed wherein the instability provides a mechanism, not available in plates, by which shell structures dissipate impact energy through structural deformation and thus exhibit improved impact damage resistance. Conversely, convex shells with no response instability have decreased impact damage resistance compared with plates. The differences in composite shell and plate behavior, particularly damage resistance, have important ramifications to the design of damage tolerant aerospace components and are discussed.

On the Use of Dent Depth as an Impact Damage Metric for Thin Composite Structures

Abstract: The damage resistance of thin composite structures was investigated experimentally. Specifically, surface damage in the form of dent-depth measurements are compared with internal damage states obta...

On the behavior of composite shells under transverse impact and quasi-static loading

Abstract: The impact and quasi-static response of various composite shell structures to transverse loading was studied experimentally. In particular, the effect of varying structural parameters (radius, span, and thickness) on the loading response, including damage resistance, is explored. The AS4/3501-6 graphite/epoxy composite structures considered have a [±45 n /0 n 1s layup configuration (n = 1, 2, 3) and include convex and concave shell sections, plates, and full cylinders. All structural parameters are found to affect the response, particularly characteristics of the instability associated with the convex shell behavior and the structural stiffness. Trends with regard to peak force and structural stiffness with the structural parameters are established and discussed. Specimen thickness is noted to have the greatest effect of all the parameters, but shell radius is clearly important due to the instability that it introduces. Damage resistance trends with structural parameters are established and linked to peak force. Although linked to peak force, these damage trends are also found to be dependent upon whether the peak force occurs before or after the shell instability. The results of this work establish the effects of structural parameters on the general response characteristics, including damage resistance, of composite shells under transverse loading with application to low-velocity impact. Thus, these results provide benchmark data for comparison with analytical and numerical, e.g., finite element, studies. Suggestions for areas of further work are provided.