Analysis Features

• NISA II/COMPOSITES is a general purpose finite element program which is tailored specifically for the accurate and efficient analysis of a wide range of composite structures.
• Many levels of structural idealization are possible. An orthotropic material model is available for plane stress, plane strain,axisymmetric, general shell, and solid elements. The directions of orthotropy may be constant within each element, or may vary continuously form node to node.
• The heart of NISA II/COMPOSITES is a family of general laminated shell elements based on shear deformation theory and three dimensional solid elements based on elasticity theory. These elements are suited for the analysis of laminated structures with anisotropy as well as the special cases of orthotropy, transverse isotropy and isotropy.
• A single composite general shell element may be used to model an arbitrary number of layers at any given angle. The finite element discretization is just on the shell midsurface. This allows a drastic reduction in both modeling and computation time.
• A special modification of the isoparametric laminated shell element has proven to be applicable to a very general class of sandwich structures, and this analysis capability is included in NISA II/COMPOSITES as a separate family of elements.
• The element consists of thin face sheets that resist extensional and inplane shear deformation and a thick core material which resists transverse shear. The face sheets themselves can be made of laminated composites and the core may be orthotropic. Multiple cores and more than two face sheets are allowed and the construction need not be Symmetrical.
• The elements in NISA II/COMPOSITES account for the effects of transverse (interlaminar) shear deformation, material anisotropy, and all possible bending - extensional - twist - shear couplings. Thermal loads may be computed, and residual stresses due to curing may be found.
• Most plate and shell analysis are based on the classical Kirchoff theory, which assumes that lines of material points normal to the neutral surface before deformation remain normal to it after deformation. The theoretical basis of NISA II/COMPOSITES includes transverse shear effects, which are accounted for by allowing these normals to rotate relative to the deformed neutral surface.
• Consider that G/E the ratio of shearing to extensional stiffness, is fixed for an isotropic material at 1/(2 + 2v), or about 0.40 for most metals. By contrast, for a unidirectional lamina of high modulus graphite-epoxy, the value can be as low as 0.01. Thus, it is apparent that the same loading will induce significantly more transverse shear deformation in composite structures than in their metal counterparts. Indeed, it is not difficult to find composite problems where transverse shear is the dominant response mode of the structure.
• NISA II/COMPOSITES also includes the effects of rotary inertia, the counterpart of transverse shear deformation for dynamic problems. For steady state and transient dynamics, this has been shown to be an important response mode for composite structures.
• The 3D composite solid element is based on the three dimensional elasticity theory and so, conceptually, includes all the possible bending, extensional, twist and shear couplings in the element formulation. These elements are suitable for analysis of thick to moderately thick composite structures in which considerable shear deformation is present. The element can also predict the normal stress (s ) nn accurately which plane stress based elements neglect.