Properties and applications of additively manufactured metallic cellular materials: A review

Review of Fiber-Based Three-Dimensional Printing for Applications Ranging from Nanoscale Nanoparticle Alignment to Macroscale Patterning

Four-dimensional (4D) printing of shape memory polymers is a leading research field due to the possibilities allowed by using these materials. The strain difference in the structures that is caused by the different stiffness profiles can be used to influence the shape-memory effect in the actuators. In this study, the influence of patterns on the strain is tested in polylactic acid (PLA) actuators using patterns made of different shapes. Five bioinspired geometrical shapes, namely, circles, squares, hexagons, rhombuses, and triangles, are used in the three-dimensional (3D) printing of the actuators. The use of shapes of different sizes along with combinations of different patterns in the PLA actuators is carried out to develop 40 actuators with different designs. The effects of the patterns and their characteristics are analysed and compared. The self-bending angles of the actuators range from 6.19° to 30.86°, depending on the patterns and arrangement used. To demonstrate the feasibility of utilizing the proposed designs in practical applications, a hand-like shaped gripper is developed. The results show that the gripper can grip objects with uniform and non-uniform cross-sections. The developed gripper demonstrates that the proposed concept can be implemented in various applications, including self-morphing structures and soft robotics.

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Bioinspired Pattern-Driven Single-Material 4D Printing for Self-Morphing Actuators

Honeybees are renowned for their perfectly hexagonal honeycomb, hailed as the pinnacle of biological architecture for its ability to maximize storage area while minimizing building material. However, in natural nests, workers must regularly transition between different cell sizes, merge inconsistent combs, and optimize construction in constrained geometries. These spatial obstacles pose challenges to workers building perfect hexagons, but it is unknown to what extent workers act as architects versus simple automatons during these irregular building scenarios. Using automated image analysis to extract the irregularities in natural comb building, we show that some building configurations are more difficult for the bees than others, and that workers overcome these challenges using a combination of building techniques, such as: intermediate-sized cells, regular motifs of irregular shapes, and gradual modifications of cell tilt. Remarkably, by anticipating these building challenges, workers achieve high-quality merges using limited local sensing, on par with analytical models that require global optimization. Unlike automatons building perfectly replicated hexagons, these building irregularities showcase the active role that workers take in shaping their nest and the true architectural abilities of honeybees.

Imperfect comb construction reveals the architectural abilities of honeybees

PLA toughening via bamboo-inspired 3D printed structural design

The honeybee’s comb has inspired the design of engineering honeycomb core that primarily abstract the hexagonal cell shape and exploit its mass minimizing properties to construct lightweight panels. This work explored three additional design features that are part of natural honeybee comb but have not been as well studied as design features of interest in honeycomb design: the radius at the corner of each cell, the coping at the top of the cell walls, and the interface between cell arrays. These features were first characterized in natural honeycomb using optical and X-ray techniques and then incorporated into honeycomb core design and fabricated using an additive manufacturing process. The honeycomb cores were then tested in out-of-plane compression and bending, and since all three design features added mass to the overall structure, all metrics of interest were examined per unit mass to assess performance gains despite these additions. The study concluded that the presence of an interface increases specific flexural modulus in bending, with no significant benefit in out-of-plane compression; coping radius positively impacts specific flexural strength, however, the corner radius has no significant effect in bending and actually is slightly detrimental for out-of-plane compression testing.

Bioinspired honeycomb core design: An experimental study of the role of corner radius, coping and interface

Biodiversity provides a massive library of ideas for bio-inspired design, but the sheer number of species to consider can be daunting. Current approaches for sifting through biodiversity to identify relevant biological models include searching for champion adapters that are particularly adept at solving a particular design challenge. While the champion adapter approach has benefits, it tends to focus on a narrow set of popular models while neglecting the majority of species. An alternative approach to bio-inspired design is the comparative method, which leverages biodiversity by drawing inspiration across a broad range of species. This approach uses methods in phylogenetics to map traits across evolutionary trees and compare trait variation to infer structure-function relationships. Although comparative methods have not been widely used in bio-inspired design, they have led to breakthroughs in studies on gecko-inspired adhesives and multifunctionality of butterfly wing scales. Here we outline how comparative methods can be used to complement existing approaches to bioinspired design, and we provide an example focused on bio-inspired lattices, including honeycomb and glass sponges. We demonstrate how comparative methods can lead to breakthroughs in bio-inspired applications as well as answer major questions in biology, which can strengthen collaborations with biologists and produce deeper insights into biological function.

/pdf/the-comparative-approach-to-bio-inspired-design-integrating-23oen8nn.pdf

The Comparative approach to bio-inspired design: integrating biodiversity and biologists into the design process.

Tensile and Fracture behavior of Silica Fibers from the Venus Flower Basket (Euplectella aspergillum)

Lattice-type periodic metamaterials with beam-like struts have been extensively investigated in recent years thanks to the progress in additive manufacturing technologies. However, when lattice structures are subject to large deformations, computational simulation for design and optimization remains a major challenge due to complex nonlinear and inelastic effects, such as instabilities, contacts, rate-dependence, plasticity, or damage. In this contribution, we demonstrate for the first time the efficient and accurate computational simulation of beam lattices using a finite deformation 3D beam formulation with inelastic material behavior, instability analysis, and contacts. In particular, the constitutive model captures elasto-visco-plasticity with damage/softening from the Mullins effect. Thus, the formulation can be applied to the modeling of both stiffer metallic and more flexible polymeric materials. The approach is demonstrated and experimentally validated in application to additively manufactured lattice structures made from Polyamide 12 by laser sintering and from a highly viscous polymer by vat photopolymerization. For compression tests executed until densification or with unloading and at different rates, the beam simulations are in very good agreement with experiments. These results strongly indicate that the consideration of all nonlinear and inelastic effects is crucial to accurately model the finite deformation behavior of lattice structures. It can be concluded that this can be effectively attained using inelastic beam models, which opens the perspective for simulation-based design and optimization of lattices for practical applications. 

Inelastic finite deformation beam modeling, simulation, and validation of additively manufactured lattice structures

Advances in additive manufacturing, computational design tools, and digitization techniques are converging in an exciting new era of engineering design, as humanity has never experienced before. Within this convergent domain, Bio-Inspired Design (BID) is a particularly promising area of research since the potential space for establishing structure-function correlation is vast, and the majority of it is untapped. In this chapter, bio-inspired design is first introduced, specifically in the context of the Laser Powder Bed Fusion (L-PBF) process. Practical approaches for implementing BID for L-PBF are discussed, followed by a discussion of key general design concepts that can be abstracted for BID. Examples of how BID and L-PBF have been combined are then presented, followed by a consideration of some of the most important design constraints posed by the L-PBF process that the bio-inspired designer needs to be aware of. The chapter concludes with a forward looking discussion of opportunities in this domain.

Yash Mistry

Papers

Bioinspired honeycomb core design: An experimental study of the role of corner radius, coping and interface

The Comparative approach to bio-inspired design: integrating biodiversity and biologists into the design process.

Tensile and Fracture behavior of Silica Fibers from the Venus Flower Basket (Euplectella aspergillum)

Inelastic finite deformation beam modeling, simulation, and validation of additively manufactured lattice structures

Bio-inspired design