PSI - Issue 33

Andrea Pranno et al. / Procedia Structural Integrity 33 (2021) 1103–1114 Author name / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction Today, composite materials reinforced with fibers or particles are the most used materials in recent innovative engineering applications (Ammendolea et al., 2021; Goshkoderia et al., 2020; Lonetti and Pascuzzo, 2016; Pascuzzo et al., 2020). Recent progress in the additive manufacturing field has allowed engineers and scientists to produce composite materials with innovative microstructures and extreme properties. In addition, often the researchers were inspired by materials available in nature, due to the fact that numerous natural materials show advanced properties, such as electrical, magnetic, mechanical, and thermal properties. It is widely known that the advanced properties of natural materials are given by the interplay between phenomena acting at different length scales from the nano and micro scale to the macroscopic scale. Specifically, from the mechanical point of view, numerous natural materials at the macroscopic scale can offer mechanical properties strongly superior with respect to their microstructural constituents (Slesarenko et al., 2017a, 2017b; Tran et al., 2017). In this framework, the capability of natural materials to offer superior properties and the capability of additive manufacturing to produce materials with complex microstructure are attracting the attention of the recent research lines feeding the interest of producing the so-called innovative bioinspired composite materials which can offer the same performance of the natural materials, but they can be produced with different shapes and quantities by 3D printers (Ko et al., 2019). In the past decade, the nacre microstructure has been widely studied in the light of its excellent mechanical properties, in terms of strength and toughness, given by coupling a soft organic matrix and stiff mineral platelets following a brick and mortar pattern (Jia et al., 2020). Inspired by nacre, recent innovative nacre-like composite materials have been investigated from a different point of view, but the most interesting, for our interests, is from the mechanical point of view. In the light of their heterogeneous microstructure, the nacre-like composites can be subjected to numerous nonlinear phenomena that were widely investigated in the last two decades with reference to fiber reinforced composite materials. Specifically, microstructural evolution can be induced in the fiber-reinforced composite subjected to extreme load conditions due to the occurrence of nonlinear phenomena (extensively studied in the past), such as delamination coalescence of fractures at the microscopic scale and interface debonding (Bruno et al., 2005; De Maio et al., 2020a, 2020b, 2019a; Greco et al., 2021a; Greco and Lonetti, 2009), or also because of the occurrence of geometrical nonlinearities (Aboudi and Gilat, 2006; Lonetti and Pascuzzo, 2020; Paimushin et al., 2018) and/or materials nonlinearities induced by finite deformations, or even by a combination of these nonlinearities (De Maio et al., 2020d; Greco et al., 2021b, 2018b, 2018a). To investigate, by means of numerical simulations, the macroscopic response of microstructured composite materials subjected to different nonlinear phenomena acting at the microstructural scale is necessary to model every microstructural detail requiring tremendous computational effort (De Maio et al., 2020c, 2019b, 2019a). In the past, numerous works have been published highlighting the capability of advanced and efficient modeling techniques in reducing the computation effort required to investigate the mechanical macroscopic behavior of composite material considering also the influence of the microstructural evolution, for instance, the classical homogenization methods (Greco and Luciano, 2011; Miehe et al., 2002; Rudykh and deBotton, 2012) and the multiscale methods (Belytschko et al., 2008; Greco et al., 2020a, 2020b, 2015). Since the study of the mechanical behavior of bioinspired composite materials from the numerical point of view is a recent research line, such advanced modeling techniques are not still widely used. However, in recent work by some of the authors (Greco et al., 2020c), a hybrid multiscale technique has been implemented, in a finite deformation framework, to design a bioinspired material with the best reachable combination of penetration resistance and flexibility. Numerous authors in the past highlighted that the mechanical properties of the nacre-like materials are given by the interaction between the reinforcing platelets and the soft matrix together with other mechanics operating on different length scales (Ji and Gao, 2004). Other authors, demonstrated by means of experimental tests that the soft matrix represents the main microconstituent influencing the mechanical behavior of the nacre-like microstructures is identified in (Khayer Dastjerdi et al., 2013; Meyers et al., 2008). Additional works have shown also that the interface between the soft matrix and the reinforcing stiff platelets is the weakest part of such materials and different models have been proposed to investigate the mechanical behavior of nacre-like materials affected by damage mechanisms (Abid et al., 2018; Barthelat et al., 2013; Radi et al., 2020). Definitively, the available literature with reference to the investigation of the mechanical behavior of nacre-like composite materials highlights the recent efforts made to optimize the geometrical and material parameters with the aim to improve the mechanical performances in terms of strength, penetration resistance, fracture toughness, and flexibility. On the other hand, to the authors´ best knowledge, only a few works investigate the mechanical behavior