Micropolar finite elements for thin structures of twisted-cord-reinforced composites

Twisted cord reinforced composites are widely used in industry. Because of the high in-plane stiffness in cord axial direction and low bending stiffness, they are usually considered as ideal reinforcing materials in such structures where finite deformation is unavoidable. The best examples are the belts and plies in automobile tires. With increasing interests in analysis of tires with finite element methods, the numerical simulation of belt and ply layers becomes a very important issue. In the last twenty years, Several numerical approaches have been proposed and employed to characterize the highly anisotropic behavior of composite materials reinforced with one or several layers of parallel cords with different spatial orientation. None of these current approaches, however, takes the local elongation-torsion coupling of twisted cords into account. As has been noticed for many years, the elongation-torsion coupling effect is an essential and unique characteristic of twisted cords, which distinguishes the cords from solid bars. It has been found that this coupling effect significantly influences the local stress and deformation.; In this study, the so-called micropolar theory of elasticity for thin plate and shell structures of twisted cord reinforced composite are studied, and two effective finite element approaches based on the micropolar theory are developed. One of the approaches leads to the generation of so-called Record element. A series of finite element analyses are conducted to study the characteristics of twisted cord properties and to verify the Record element. It is found that the Record element can overcome the shortcomings of ABAQUS Rebar element and be used to simulate cord-reinforced composite.