Energy absorbing 4D printed meta-sandwich structures: load cycles and shape recovery

The International Journal of Advanced Manufacturing Technology (2023) 127:1779–1795 https://doi.org/10.1007/s00170-023-11638-0 ORIGINAL ARTICLE Energy absorbing 4D printed meta‑sandwich structures: load cycles and shape recovery Annamaria Gisario1 · Maria Pia Desole1 · Mehrshad Mehrpouya2 · Massimiliano Barletta3 Received: 12 April 2023 / Accepted: 22 May 2023 / Published online: 1 June 2023 © The Author(s) 2023 Abstract The present study investigates the behavior of solid cellular structures in polylactic acid (PLA) achieved by FDM technology (fusion deposition modelling). The geometries are permanently deformed by compressive stress and then subjected to shape recovery through the application of a thermal stimulus. The structures are submitted to medium–high and medium–low compression stresses, evaluating the mechanical properties and the absorption energy as the number of cycles varies. The study shows that the ability to absorb energy is related to the density of the model, as well as the degree of damage observed, which increases with increasing number of load cycles. The strongest geometry is the lozenge grid, which is the most reliable. It shows no damage with increasing compression cycles and keeps its capability to absorb energy almost constant. The increase in lozenge grid density leads to an improvement in both mechanical strength and absorption energy, as well as a lower incidence of microcracks in the geometry itself due to the repeated load cycles. These results open up a broad spectrum of applications of custom-designed solid cellular structures in the field of energy absorption and damping. Keywords 4D printing · Metamaterials · Energy absorbing · Springback · Shape recovery 1 Introduction Metamaterials are innovative materials artificially engineered to exhibit mechanical, thermal, acoustic, or electromagnetic behavior not found in other naturally occurring materials [1, 2, 3, 4]. Their applications can be multiple and declinable in different sectors, from civil to biomedical, from electronics to aerospace, and in the broader manufacturing sector [5, 6, 7]. Their development goes well with the growing interest in additive manufacturing technologies, which are very competitive with respect to traditional manufacturing * Massimiliano Barletta 1 Dipartimento Di Ingegneria Meccanica E Aerospaziale, Sapienza Università Di Roma, Via Eudossiana 18, 00184 Rome, Italy 2 Department of Design, Production, and Management (DPM), University of Twente, Drienerlolaan 5, 7522 NB Enschede, The Netherlands 3 Dipartimento Di Ingegneria IndustrialeElettronica E Meccanica, Università Degli Studi Roma Tre, Via Della Vasca Navale 79, 00146 Rome, Italy technologies due to the greater possibilities they offer in obtaining intricate shapes, of good quality and in reasonable times [8, 9, 10, 11, 12]. By exploiting additive manufacturing technology, it is in fact much easier to create products with complex architectures. It is possible to set up articulated addition paths of the material that generate reticular structures, with modular cavities and at the same time with mechanical properties comparable to those of a solid artefact [13]. In the conception of new reticular geometries, the study of printing supports constitutes a delicate phase of the process. An attempt is made to drastically limit their use as the presence of supports determines an increase in the cost-perpart due to the time required for their removal and surface finishing operations. It is therefore convenient to produce lattice structures making sure that the lattices themselves act as internal supports and are at the same time capable of withstanding external stresses. In recent years, the targeted design of metamaterials with lattice structures has garnered significant interest from the scientific community and has involved the use of a wide range of materials, both metallic [14, 15] and polymeric [11, 16]. The unique properties that can be obtained from lattice structures when examined from a mechanical point of view are high stiffness and mechanical strength 13 Vol.:(0123456789) 1780 The International Journal of Advanced Manufacturing Technology (2023) 127:1779–1795 or greater energy absorption in relation to reduced weight and lower density [17, 18, 19, 20]. The mechanical attributes of AM fabricated parts with lattice structures have been investigated by many researchers following various approaches. In terms of geometries, attention has been paid to structures with triangular, square, circular, or hexagonal lattices. Geometries with auxetic behavior have also been studied, with chiral and non-chiral or bio-inspired forms [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30]. Lubombo and Huneault [31], for example, investigated the stiffness and strength under uniaxial tensile and bending loading of PLA thermoplastic cellular structures fabricated by fused filament fabrication (FFF). In particular, five different filling models are examined for which a different mechanical response is highlighted. The hexagonal structure showed good performance with a twofold increase for stiffness and up to 82% for resistance under load. Honeycombs are among the most used to evaluate the performance of cellular materials, perhaps also due to their wide commercial use. In McGregor et al. [32] an in-depth study of the hexagonal lattice that is fabricated by AM using three different thermoplastic polymers is reported: (rigid polyurethane (RPU, E = 1900 MPa), additive epoxy (EPX, E = 3140 MPa), and cyanate ester (CE, E = 4200 MPa)). The mechanical behavior under compressive load of the different materials is evaluated. By varying the relative density in a sufficiently wide range (from 0.06 to 0.23), the results obtained demonstrated the possibility of varying the specific modulus and the specific strength by more than two orders of magnitude. However, a correlation was not made between geometry and the capacity of the structure to absorb energy. Also, Santos et al. [33] have studied honeycomb and auxetic structures (with negative Poisson’s ratio) by comparing the behavior of PLA (polylactic acid) and PETG (transparent polyethylene terephthalate modified with glycol). In this case, the ability of the structures to absorb energy as a function of the material and the initial load of the test is investigated. However, a limited number of geometries are analyzed in the work. It should be noted that both polymers examined in this study can be included in the category of shape memory polymers (SMPs), i.e., those intelligent polymeric materials that have the ability to return from a deformed state (temporary shape) to their original shape (permanent) following an external stimulus (trigger), such as for example a change in temperature. SMPs can in fact be profitably employed in the 3D fabrication of metamaterials with reticular structures with the aim of refe (...truncated)