Compact tension and compression testing of braided composites - Challenges and limitations

The present publication aims to identify challenges and limitations of existing compact tension and compression test procedures applied to braided composites within the scope of extensive experimental programmes performed at Fraunhofer EMI in recent years. Compact tension/compression tests allow the measurement of intralaminar fracture toughness which are of particular interest for energy-based failure criteria in numerical simulations. Following a brief introduction on braided composite meso-structure the observations made during these intra-laminar fracture toughness tests are discussed. Emphasis is given to the impact of braided composite structure and size of in homogenity on test procedures and failure modes and how these differences affect the validity of the test methods. Some recommendations to address limitations are presented, however main focus of the publication is the identification of challenges in the investigated test methods.