A Numerical Model For Post-Buckling Analysis Of Composite Shear Webs

The development of the aeronautical industry in recent times years is driving (?) new lines of research and development in the structural materials application field. Harris et al [1] show how the developments in construction using composite materials has been tracking the growth and expansion of the aviation industry, starting with the design of parts of minor structural requirements. The developments progressed with the replacement of sets of parts with considerable importance to the proper functioning of the plane and finally evolved to replacing parts critical to the performance of the aircraft.

The composite materials offer many advantages in comparison to metal made structures such as low weight, high stiffness, corrosion resistance, high static strength and fatigue. Using procedures for optimum design and low cost manufacturing processes such as resin infusion technologies, a reduction in cost can also be achieved.

Stringer-stiffened shear panels are extensively used in many aircraft structures. The fuselage is a typical example of design with this type of structure. Thus, most studies of buckling and postbuckling in composite materials structures loaded in shear are related to the design of the fuselage. In those investigations, the objective is to replace the conservative design by one that exploits the full potential of composite materials in terms of weight reduction of a fuselage.

The replacement of aluminum by composite materials implies the need of having a deep knowledge of the behaviour of these structures when they are subjected to service loads. A literature review for the type of structure analyzed is presented in Agarwal [2], Shuart and Hagaman [3], Ferley and Baker [4]. In these works, it is shown that the composite structures have completely different failure modes compared to metallic structures.

Recently a considerable effort has been dedicated towards the development of fast and reliable procedures for buckling, postbuckling and collapse analyses of fibre composite stiffened panels of future fuselage structures through the COCOMAT and POSICOSS european projects [5]. The procedures must account for degradation due to static as well as low cycle loading in the postbuckling range. It is well-known that thin-walled structures made of carbon fibre reinforced plastics are able to tolerate repeated buckling without any change in their buckling behaviour. However, it has to be found out, how deep into the postbuckling regime loading one can go without severely damaging the structure, and how this can be predicted by fast and precise simulation procedures.

Composite materials structures have five six basic failure modes: fiber breakage in tension and compression, matrix cracking in tension and compression, in plane and out of plane shear, and delamination. The residual strength of a composite structure after the initiation of the damage may be high. This is due to the fact that some failure modes may not affect significantly the overall performance of the structure. The totally different failure behaviour of composite materials compared to metallic materials requires the implementation of new methods of analysis and simulation with finite element models in order to predict the initiation and propagation of different failure modes taking place in these new generation of structures.

The method of analysis should be able to reproduce the effects of different modes