Analysis of syntactic foam – GFRP sandwich composites for flexural loads
The use of glass microballoon (GMB) — epoxy syntactic foams as a sandwich core material is studied. The skins and foam core are fabricated and joined instantaneously unlike the procedures followed in the previous studies. Each successive layer of the sandwich is fabricated when the previous layer is in a semi-gelled state. These sandwich samples are characterized for their properties under flexural loading. The failure modes and mechanical properties are carefully investigated. The change in fabrication technique results in a significant increase in the load bearing pattern of the sandwich. In earlier studies, debonding was found to occur prematurely since the bonding between the skins and core is the weakest plane. Using the current technique, core cracking occurs first, followed by skin fiber breaking and debonding happens at the end. This ensures that the load carrying phase of the structure is extended considerably. The sandwich is also analytically studied using Reddy’s higher order shear deformation theory. A higher order theory is selected as the sandwich can no longer be considered as a thin beam and thus shear effects also need to be considered in addition to bending effects.
Experimental and analytical studies of syntactic foam core composites for impact loading
Abstract Sandwich composites with polymeric open-celled foams or honeycomb structures as core materials have been used widely in low-weight naval, aerospace and structural applications in the past. One major drawback of such foams is skin-core debonding. To overcome this, core materials with the same matrix as the skin are studied in this paper. Sandwich composites with fibre composite skins and a hollow glass particle-filled syntactic foam core are fabricated and tested under ballistic impact loading. Both the constituents have an epoxy matrix and are fabricated using a co-curing method which improves the skin-core debonding considerably. Parameters such as ballistic limit and energy absorbed by the samples are obtained for different core volume fractions and varying skin thicknesses. The effect of skin layup sequence has also been studied. It is found that samples with thicker back skins have better impact-resistant properties. The external and internal damage in the samples subject to different impact velocities is studied by visual means and CT scans. An energy-based analytical model is used to predict the ballistic limit of the samples, and to study the individual energy-absorption modes. The evolution of the contribution of the modes with time as well as the velocity profile of the projectile as it penetrates the composites are also obtained from the model. The experiments and the model show comparable ballistic limit results.
Die Populationsdynamik Von Canthocampt Us Staphylinus (Jurine) (Copepoda, Harpacticoida) Im Litoral Des Bodensees
The population dynamics of Canthocamptus staphylinus in the littoral zone of Lake Constance are described (fig. 2). Adult animals aestivate as cysts. The main part of the population emerges from the cysts in autumn. During the resting stage and the first spell after emerging, mortality is very low (fig. 3). Reproduction, expressed as numbers of ovigerous females, begins in November and reaches its maximum in January. The new generation becomes adult in May/June and encysts without previous reproduction. According to Sarvala (1979) it may be possible, that in littoral populations dormancy is induced by long day periods and temperatures of over 12° C (figs. 1, 2). In the profundal zone C. staphylinus also forms cysts, however, both light and temperature are not likely to induce this stage in depths of over 60 m.