Mechanical Characterization of the Braided Composite Yarn and Bond Strength Evaluation of the Joints of the Open-Architecture Composite Structure (O-ACS)

Abstract

Open-architecture composite structures (O-ACS) can be seen as structures, optimized for weight, meant to be used as beams or columns, in applications where the stiffness to weight ratio of the structure governs the design. The transversely isotropic, braided composite yarn that is used to make O-ACS in tube form is important in making them light and strong. Characterization of this yarn’s mechanical properties was the goal of this study. Young’s modulus along the axis was found using uniaxial tensile testing. Modulus along the transverse axis was found by performing transverse compression test and using Hertzian-contact model. Poisson’s ratio was found using an image processing technique. Flexural modulus was found by performing a 3 point bend test and shear modulus was found using micromechanical modeling. Young’s modulus, Poisson’s ratio and shear modulus have also been calculated using the micromechanical model and good correlation was observed between the values found experimentally and from the micromechanical model. The bond strength of joints formed by these yarns is also an important property that would govern the progressive developments of the yarn in order to make lighter and stiffer tubes. Mode 1 type of debonding of the joints has been studied and experimental techniques for finding the maximum load to failure of the joints have been developed. Four yarns with different jacket architectures have been tested and compared on the basis of their mechanical properties and bond strength of the joints formed. Our initial work towards simulating the mode 1 and mode 2 type of debonding of the joints using finite element software and cohesive zone modeling approach, in particular, has been reported