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The South Indian Granulite Terrane (SGT) is a collage of Archaean to Neoproterozoic age granulite facies blocks that are sutured by an anastomosing network of large-scale shear systems. Besides several Neoproterozoic carbonatite complexes emplaced within the Archaean granulites, there are also smaller Paleoproterozoic (2.4 Ga, Hogenakkal) carbonatite intrusions within two NE-trending pyroxenite dikes. The Hogenakkal carbonatites, further discriminated into sövite and silicate sövite, have high Sr and Ba contents and extreme light rare earth element (LREE) enrichment with steep slopes typical of carbonatites. The C- and O-isotopic ratios [δ13CVPDB = −6.7 to −5.8‰ and δ18OVSMOW = 7.5–8.7‰ except a single18O-enriched sample (δ18O = 20.0‰)] represent unmodified mantle compositions. TheεNd values indicate two groupings for the Hogenakkal carbonatites; most samples show positiveεNd values, close to CHUR (εNd = −0.35 to 2.94) and named high-εNd group while the low-εNd group samples show negative values (−5.69 to −8.86), corresponding to depleted and enriched source components, respectively. The87Sr/86Sriratios of the two groups also can be distinguished: the high-εNd ones have low87Sr/86Sriratios (0.70161–0.70244) while the low-εNd group shows higher ratios (0.70247–0.70319). We consider the Nd–Sr ratios as primary and infer derivation from a heterogeneous mantle source. The emplacement of the Hogenakkal carbonatites may be related to Paleoproterozoic plume induced large-scale rifting and fracturing related to initiation of break-up of the Neoarchean supercontinent Kenorland. [ABSTRACT FROM PUBLISHER]

In this article, the effects of damage (delamination) on the structural vibration characteristics of spar wingskin joints (SWJs) made with curved laminated composites are investigated. Three dimensional finite element analysis is employed to evaluate the natural frequencies and corresponding mode shapes of the joint structure considered. Virtual elements are implemented in the delamination region to prevent inter element penetration. The effectiveness of the finite element analysis technique used is validated with available results. Additionally, the effects of various parameters such as delamination size, curvature effect (shallowness angle), laminate stacking sequence, overlap length, and material anisotropy (modular ratio) on the free vibration responses of the curved SWJ are analyzed in details. The present delamination modeling and simulated results could serve as guidelines in designing curved laminated composite joint structures with/without delaminations. [ABSTRACT FROM AUTHOR]

Initiation and propagation of inter-laminar delamination in adhesive bonded spar wingskin joint (SWJ) made with laminated fibre-reinforced plastic (FRP) composite curved panels have been studied employing three-dimensional finite element analyses. In-plane and out-of-plane normal and shear stress distributions are seen to be highly three-dimensional in nature. Tsai-Wu coupled stress failure criteria have been employed to identify critical locations of onset of delamination-induced damage. This occurs underneath the toe-end of the spar overlap and at the inter-laminar surface between the first and second plies of the curved FRP wingskin panel. Significant edge effects on the joint strength have been observed due to the curvature geometry of the composite wingskin panels. Non-linear finite element analyses have been carried out for study of delamination propagation using contact and multi point constraint (MPC) elements. The use of contact elements prevents inter-penetration of delaminated surfaces. Whereas, sequential release of MPC elements facilitates computation of opening, sliding and cross-sliding modes of delamination-induced strain energy release rates (SERR) by using virtual crack closure technique. Variation in delamination lengths significantly effects the variation of peel and inter-laminar shear stresses and different modes of SERRs. Variations on the two delamination fronts are seen to be quite different indicating dis-similar propagation rates. The Mode I SERR (GI) predominantly governs the delamination propagation in the SWJ. [ABSTRACT FROM PUBLISHER]