It is widely known that the availability of lightweight structures with excellent energy absorption capacity is essential for numerous engineering applications. Inspired by many biological structures in nature, bio-inspired structures have been proved to exhibit a significant improvement over conventional structures in energy absorption capacity. Therefore, use of the biomimetic approach for designing novel lightweight structures with excellent energy absorption capacity has been increasing in engineering fields in recent years. This paper provides a comprehensive overview of recent advances in the development of bio-inspired structures for energy absorption applications. In particular, we describe the unique features and remarkable mechanical properties of biological structures such as plants and animals, which can be mimicked to design efficient energy absorbers. Next, we review and discuss the structural designs as well as the energy absorption characteristics of current bio-inspired structures with different configurations and structures, including multi-cell tubes, frusta, sandwich panels, composite plates, honeycombs, foams, building structures and lattices. These materials have been used for bio-inspired structures, including but not limited to metals, polymers, fibre-reinforced composites, concrete and glass. We also discussed the manufacturing techniques of bio-inspired structures based on conventional methods, and adaptive manufacturing (3D printing). Finally, contemporary challenges and future directions for bio-inspired structures are presented. This synopsis provides a useful platform for researchers and engineers to create novel designs of bio-inspired structures for energy absorption applications.

A review of recent research on bio-inspired structures and materials for energy absorption applications

Geometric configurations in nature could be mimicked in order to develop novel materials and structures with desirable properties. Lots of bio-inspired configurations had been introduced to tubal structures in promoting the energy-absorption performance of thin-walled structures. Nevertheless, these existing studies largely focused on hierarchical hexagonal honeycombs, and the bio-inspired hierarchical circular thin-walled structures under the out-of-plane crushing loads had not been well studied experimentally, numerically and analytically for energy absorption to date. In this study, the bionic honeycomb tubular nested structure (BHTNS) was first inspired by the micro-architecture of bamboo vascular bundles, which could be mimicked by connecting a central circular tube to other six circular tubes in a hexagonal arrangement, regardless of size or choice of materials. The energy-absorption characteristics of BHTNS under axial crushing were systematically studied by drop-weight experiment, numerical simulation, and theoretical analysis. Dynamic drop-weight impact experiments were conducted and the results showed that the specific energy absorption ( S E A ) of BHTNS was as high as 29.3 J/g. Furthermore, the parametric numerical simulation revealed the influence of diverse mean diameter D of the circular tube and length L of the junction plate on the energy-absorption characteristics. Finally, a theoretical model was also developed to predict the mean crush force P m , which was in good agreement with the numerical simulation. This work could provide a reference for an energy-absorber design with high efficiency.

Energy-absorption characteristics of a bionic honeycomb tubular nested structure inspired by bamboo under axial crushing

Honeycombs are ultra-light materials with outstanding mechanical properties, which mainly originate from their unit cell configurations rather than the properties of matrix materials. Honeycombs are triggering in numerous promising applications in the fields of architecture, automotive, railway vehicle, marine, aerospace, satellite, packaging and medical implants, etc. Here we provide an in-depth overview of some important advances in basic structural design to obtain novel honeycombs with various improved mechanical properties. Firstly, the review introduces the classical honeycomb configurations. Then, a clear classification of advanced designs is established and discussed according to the design scale. The designs on the macro scale are divided into hierarchical, graded and disordered, while the designs on the meso scale are grouped as hybrid, curved ligament and reinforced strut. Moreover, the effects of different designs on the mechanical properties of honeycomb are discussed quantitatively. Finally, we summarize the important potential designs to improve the mechanical properties of honeycombs and the challenges in further research.

Advanced honeycomb designs for improving mechanical properties: A review

Lattice structures, which are also known as architected cellular structures, have been applied in various industrial sectors, owing to their fascinated performances, such as low elastic modulus, high stiffness-to-weight ratio, low thermal expansion coefficient, and large specific surface area. The lattice structures fabricated by conventional manufacturing technologies always involve complicated process control, additional assembly steps, or other uncontrollable factors. Furthermore, limited types of unit cells can be used to construct lattice structures when using conventional processes. Fortunately, additive manufacturing technology, based on a layer-by-layer process from computer-aided design models, demonstrates the unique capability and flexibility and provides an ideal platform in manufacturing complex components like lattice structures, resulting in an effective reduction in the processing time to actual application and minimum of material waste. Therefore, additive manufacturing relieves the constraint of structure design and provides accurate fabrication for lattice structures with good quality. This work systematically presents an overview of conventional manufacturing methods and novel additive manufacturing technologies for metallic lattice structures. Afterward, the design, optimization, a variety of properties, and applications of metallic lattice structures produced by additive manufacturing are elaborated. By summarizing state-of-the-art progress of the additively manufactured metallic lattice structures, limitations and future perspectives are also discussed.

Additive manufacturing of metallic lattice structures: Unconstrained design, accurate fabrication, fascinated performances, and challenges

Energy absorption characteristics of bio-inspired hierarchical multi-cell square tubes under axial crushing

Effect of strain rate on mechanical properties of the bamboo material under quasi-static and dynamic loading condition

A Fatigue Life Prediction Approach for Laser-Directed Energy Deposition Titanium Alloys by Using Support Vector Regression Based on Pore-Induced Failures

Flax fiber-reinforced composites (FFRCs) exhibit excellent environmentally friendly qualities, such as light weight, low cost, recyclability, and excellent mechanical properties. Understanding the dynamic mechanical behavior of FFRCs could broaden their potential applications in lightweight, crashworthy, and impact-critical structures. This study presents a study on the fabrication of FFRCs by vacuum-assisted resin infusion. The dynamic stress–strain responses of the fabricated specimens at strain rates ranging from 0.006 s − 1 to 2200 s − 1 were evaluated using quasi-static tests and the Split–Hopkinson pressure bar (SHPB). The results indicated that the FFRC exhibited superior strain rate sensitivity. Final deformation photographs and scanning electron micrographs clearly revealed the damage evolution of the FFRC specimens, as well as various failure mechanisms, including fiber–matrix debonding, fiber pull-out, and fiber fracture at different strain rates. On the basis of the experimental results, a simplified Johnson–Cook model was established to describe the strain-rate dependent constitutive model of FFRC. The validation of the suggested constitutive model was embedded in the finite element simulations and could well repeat the strain wave observed from the experiment results. Finally, the quasi-static compression and drop-hammer impact of pyramidal lattice structures with FFRC cores were investigated both numerically and experimentally, proving the effectiveness of the simplified Johnson–Cook model. This study could potentially contribute to a deeper understanding of the dynamic mechanical behavior of FFRCs and provide fundamental experimental data for future engineering applications.

https://www.mdpi.com/1996-1944/12/6/854/pdf

Linwei Dang

Papers

Energy-absorption characteristics of a bionic honeycomb tubular nested structure inspired by bamboo under axial crushing

Effect of strain rate on mechanical properties of the bamboo material under quasi-static and dynamic loading condition

A Fatigue Life Prediction Approach for Laser-Directed Energy Deposition Titanium Alloys by Using Support Vector Regression Based on Pore-Induced Failures

Mechanical Behaviors of Flax Fiber-Reinforced Composites at Different Strain Rates and Rate-Dependent Constitutive Model.

Anisotropic Fatigue Performance of Directed Energy Deposited Ti-6al-4v: Effects of Build Orientation