Curvilinear anisotropy: theory and application
Editors: DeWilde, W.P., Blain, W.R. and Brebbia, C.A.
Start date: 13 September 2000
Publisher: WIT Press
Place of Publication: Southampton
Laminate theory, with an off-axis stiffness calculation, is widely used in commercial EEA software. This approach is based on the volume fraction law for unidirectional composites and usually involves calculating the contribution of individual local laminate properties to the total global properties of the composite material. The assumption here is that the individual layers are either orthotropic or homogeneous in nature with local axes being different from the global axes of the loading. This type of laminate theory restricts its application to the analysis of composite materials made from layers of orthotropic plies. The overall stiffness calculation is based on the sum of the contribution of all the layers, with their appropriate orientation being taken into account.
It is quite obvious that there are limitations with this approach, as it can not simulate properties of all known materials. Some organic or natural materials are highly structured anisotropic (curvilinear) and they do not strictly follow the basic rules of unidirectional laminate theory, stated above. One such material, which has historically caused modelling difficulty, is human tooth enamel and some parts of bones etc. In these cases, some geometrical rules need to be considered which cater for these unusual properties, otherwise, EEA analysis will result in solutions that could be inaccurate and misleading.
In addition, the limitations of current modelling techniques can also limit the novel way that some components can be designed or manufactured, using relatively new and advanced materials. For example, AL-honeycombs currently used inside the blades of modern rotary winged aircraft. With improved design and analysis tools it will be possible to use this core material in new and innovative which so far has not been attempted as it cannot be modelled or analysed.