Challenges and limitations in measuring the mechanical properties of braided composites

This publication aims to identify challenges and limitations of existing test methods applied to braided composites within the scope of extensive experimental programmes performed at Fraunhofer EMI in recent years. Following a brief introduction on braided composite mesostructure the observations made during in-plane material characterisation as well as during inter- and intra-laminar fracture tests are discussed. This includes many standard test methods for laminated composites such as coupon tension and coupon compression, cylinder compression, three rail shear, Arcan shear, double cantilever beam (DCB), end notched flexure (ENF), compact tension (CT) and compression (CC), etc. Emphasis is given to the impact of braided composite structure and size of inhomogenity on deformation and failure modes and how specific test methods are affected by these differences. Some recommendations to address limitations are presented, however main focus of the publication is the identification of challenges in existing test methods.