ON THE DESIGN OF CRACK-ARRESTING LAYERS IN POLYPROPYLENE BASED MULTILAYER COMPOSITES
In natural materials, outstanding properties can be attained through an advantageous combination of different materials in intricate microstructures. Usually, a matrix material contributes high strength and stiffness (“hard phase”), while interlayer (IL) materials are often proteins with low strength and modulus (“soft phase”) but high strains at break. The combination of both phases leads to crack arresting properties, thus dramatically increasing the fracture toughness and damage tolerance of the composite. Renowned examples of such effects are nacre as well as deep-sea sponges. The same concepts shall be mimicked to increase the fracture toughness of talcum reinforced polypropylene (PP). The challenge lies in preserving specimen stiffness while also utililzing the crack arresting properties of soft ILs. In this contribution, two types of PP with different mechanical properties are used as ILs. Normalized parameters for fracture toughness and specimen stiffness are used in order to assess the overall properties of multilayer composites. The trade-offs between stiffness and toughness are illustrated, while optimized structures also demonstrate that both properties can be attained simultaneously.