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Woven fabric reinforced composite materials: analytical modeling of mechanical properties

By: Adi Adumitroaie

1. Woven fabric reinforcements – overview The use of woven fabric reinforcements for composite materials offers some advantages, especially from the manufacturing and processing point of view: · easier manipulation · labor saving (lay-up) · better drapeability,  pliability. · damage tolerance, notch insensitivity · integral structures design · cost vs. stiffness & strength properties. Also a good level of mechanical properties is preserved, imposing this class of composites as an alternative to the traditional fibers lay-up reinforcements. At the same time, the textile industry offers a very large variety of weaving patterns to be used as reinforcements. The weave type selection has become one step of the composite material design process. For the right selection of the reinforcing weaving pattern, models of the mechanical properties of the further composite material are required for the designer (for evaluating the material strength).

2. Approach The weave types approached by the present model: · 2D woven fabrics, featuring a biaxial orthogonal threads paths under in-plane loading (tension & shear). The goal of the model is to analytically predict the composite material mechanical properties: termo-hygro-elastic material constants & strength values. Extending the present model it is possible to model the mechanical properties of: · biaxial non-orthogonal fabrics · multi-axial weaving · off-axis loading case. The main features and steps of the model: · the model is based on the selection and analyze of a geometrical Repetitive Unit Cell (RUC), that is considered as being  representative for the whole material · the right 3D geometry of the RUC is described The model makes use of a point-wise Classical Laminate Theory, followed by a homogenization model (for evaluating the material elastic constants, and higro-thermal expansion coefficients) a local stress analysis, failure detection and stiffness reduction according with the local detected failure mode, while considering an increasing external load (for evaluating the material strength).

By a proper definition of new geometrical parameters and functions, the present model solves not particular cases of weaving patterns, but it solves the general case, being meant as a flexible tool for design and analysis.

The new defined generalization parameters are: ng (the periodicity length) / ns (the phase shift between two consecutive interlacing regions) / ni (the length of the interlacing region). These parameters become user input, and based them large families of weaving patterns can be generated and analyzed.