PSI - Issue 47

254 2

Johannes Wiener et al. / Procedia Structural Integrity 47 (2023) 253–260 Johannes Wiener/ Structural Integrity Procedia 00 (2019) 000–000

Nomenclature � impact strength [kJ/m 2 ] � initial notch length [mm] ∆ crack extension [mm] specimen thickness [mm] parameter for estimating � [-] ( � 1 6 � under plane strain and � 1 2 � under plane stress conditions)

tensile modulus [MPa] � bending modulus [MPa] �� equivalent modulus [MPa] geometry factor [-] ( � 2 for SENB specimens) Poisson’s ratio [-] -integral [kJ/m 2 ] � uncorrected -integral [kJ/m 2 ] ��� experimental -integral [kJ/m 2 ] � plastic zone radius [mm] � yield stress [MPa] t interlayer thickness [mm] area under force displacement curve [Nmm] specimen width [mm] relative increase to fracture toughness [-] 1.1. Inspiration from nature

In nature, many materials show outstanding properties. Some well-known examples are nacre, teeth or bone, where an inorganic matrix, such as aragonite or hydroxyapatite, is combined with soft structures made of protein (Barthelat and Espinosa 2007). The basic idea is similar in most cases, where a hard but brittle matrix contributes strength and stiffness, while toughness is enhanced by the soft phase. Due to higher feasibility in polymer processing, the skeleton of deep sea-sponges is very interesting. The microstructure of these sponges consists of concentric rings of bio glass, alternating with soft protein interlayers (ILs), see Fig. 1a. The ILs serve two purposes, namely the reduction of defect size as well as neutralizing cracks in the matrix via crack arrest (Fig. 1b) and crack tip blunting (Aizenberg et al. 2005; Miserez et al. 2008; Levi et al. 1989). The aim of this contribution was to replicate these effects in engineering materials and deduce guidelines, which enable the design of optimized, biomimetic structures. For that purpose, two approaches were explored separately. In microlayer composites, layer sizes in the micron range are used, which is a close approximation of the sponge skeleton. On the other hand, multilayer composites are used with fewer, well placed ILs with thicknesses in the millimeter range. Especially for multilayer composites, advanced methods from elastic plastic fracture mechanics were required to describe the failure process in detail.