PSI - Issue 47

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

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Fig. 1. (a) Microscopic view of the skeleton of a deep-sea sponge with soft interlayers, which act as (b) crack stoppers in a matrix of bio glass (depictions created on the basis of (Wiener et al. 2020)).

1.2. Fracture mechanics as a tool to describe crack arrest at soft layers As a measure of crack driving force (CDF), the J -integral, J , from elastic plastic fracture mechanics can be used as a toughness parameter in multilayer composites. The local value directly at the crack tip, J tip , exhibits significant variation in comparison to the far field value, J far , when the crack tip approaches a soft IL (Sistaninia and Kolednik 2014, 2017). To be precise, CDF in the form of J tip increases when approaching a hard-to-soft interface (IF), which is called anti-shielding effect, and decreases at a soft-to-hard IF (shielding-effect). In a soft IL, these two effects are combined (Fig. 2) and an opportunity for crack arrest is formed at the minimum of J tip (“crack trap”). The magnitude of this crack arresting effect is greatly influenced by the ratio of mechanical properties between matrix and IL material. Literature suggests, that optimal ratios for E IL /E Matrix ≤ 0.2 and σ y , IL / σ y,Matrix ≤ 0.3 (Sistaninia and Kolednik 2014; Kolednik et al. 2019b). However, some studies also attribute significant influence to the size of the plastic zone, differences in hardening exponent, thermal expansion, etc.

Fig. 2. (a) Variation of crack driving force near a soft interlayer, which leads to (b) crack arresting properties on a macroscopic level (depiction created on the basis of (Wiener et al. 2020)).