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

Different from conventional materials, materials with negative Poisson's ratios expand laterally when stretched longitudinally. Known as ‘auxetic’ materials, the effect means they possess particularly fascinating properties, which have recently attracted considerable attention in the literature. A range of auxetic materials has been discovered, theoretically designed and fabricated. Developments in additive manufacturing (AM) techniques enable fabrication of materials with intricate cellular architectures. This paper outlines recent progress in the development of auxetic materials and structures, and their mechanical properties under quasi-static and dynamic loading are analysed and summarised. Limited experimental studies on 3D printed auxetic materials and structures are given more attention, ahead of extensively finite element (FE) simulations. A special focus is dedicated to their large, plastic deformation behaviour and energy absorption performance, which should be stressed in their engineering applications; no review paper has yet been found regarding this. Finally, this paper provides an overview of current study limitations, and some future research is envisaged in terms of auxetic materials and structures, nano-auxetics and additive manufacturing.

Large deformation and energy absorption of additively manufactured auxetic materials and structures: A review

It is widely known that the demand for lightweight structures with excellent energy absorption capacity is paramount in numerous engineering applications. Many publications have revealed that corrugated structures can collapse in a relatively controlled manner with a uniform force-displacement response and have remarkable energy absorption efficiency when compared with traditional structures without corrugations. The present work provides a comprehensive overview of recent advances in the development of corrugated structures for energy absorption applications, also considering the effects of corrugation characteristics on their crashworthiness. Such advanced energy absorbers include corrugated tubes, corrugated tapered tubes, corrugated beam and plates, corrugated honeycombs, corrugated core sandwich panels and other hybrid structures with complex corrugations. This review demonstrates that thin-walled structures with introduced corrugations can achieve more efficient and effective energy absorption. Finally, contemporary challenges of design and manufacture are discussed, as well as future directions for corrugated structures. This synopsis provides a useful platform for researchers and engineers designing corrugated structures for energy absorption applications.

Thin-walled corrugated structures: A review of crashworthiness designs and energy absorption characteristics

In this study, a novel bio-inspired honeycomb sandwich panel (BHSP) based on the microstructure of a woodpecker’s beak is proposed. Unlike a conventional honeycomb, the walls of the bio-inspired honeycomb (BH), which is used as the core of a sandwich panel, are made wavy. Finite element simulation shows that under dynamic crushing the proposed BHSPs exhibit superior energy absorption capability compared with the conventional honeycomb sandwich panel (CHSP). In particular, the specific energy absorption (SEA) of the BHSP increases by 125% and 63.7%, respectively, compared with that of the honeycomb sandwich panel with the same thickness core or the same volume core. In addition, a parametric study of the BHSPs is carried out to investigate the influences of the wave amplitude, wave number and core thickness on the energy absorption performance of the BHSPs. It is found that the BH core with a larger wave number and amplitude shows higher SEA. Furthermore, an increase in core thickness can improve the SEA. These results provide guidelines in the design of a lightweight sandwich panel for high-energy absorption capability.

Energy absorption of a bio-inspired honeycomb sandwich panel

Investigation on manufacturing and mechanical behavior of all-composite sandwich structure with Y-shaped cores

This paper systematically investigates the low-velocity impact response and resulting damage behavior of aluminum honeycomb sandwich structures with carbon fiber reinforced plastic (CFRP) face sheets by combining the experimental and numerical methods. Low-velocity impact tests are conducted to determine and quantify the effects of structural parameters, such as face sheet thickness, cell wall thickness, honeycomb core height and hexagon side length, on the impact load, energy absorption, and failure mode. To further elucidate the impact behavior, a user VUMAT subroutine is developed to predict the progressive failure behavior of composite face sheets. Numerical simulation is performed to characterize the impact response and explore the deformation/failure mechanisms. The predicted impact load, energy absorption, contact time and failure mode agree well with measured counterparts. These studies reveal the face sheet thickness has particularly significant influence on the impact resistance performance of honeycomb structures. Cell wall thickness and side length of honeycomb core have notable effect on the impact load and structural stiffness of such structures, while which do not play a great role in energy absorption. Increase in core height has comparatively little effect on initial stiffness and energy absorption but makes the second peak loads decreasing for the perforation cases.

Effect of structural parameters on low-velocity impact behavior of aluminum honeycomb sandwich structures with CFRP face sheets

Low-velocity impact response and post-impact flexural behaviour of composite sandwich structures with corrugated cores

Corrugated core sandwich structures are fabricated with carbon fiber reinforced polymer (CFRP) face sheets and aluminum alloy cores. This lightweight design concept enables sandwich structures to maximize their specific bending stiffness/strength and improve their energy absorption capability. A combined experimental and numerical study is performed to investigate the effect of impactor shape on low-velocity impact behavior. Low-velocity impact tests are conducted to study the impact resistance when impacted by conical, hemispherical and flat impactors. A user subroutine VUMAT is developed to model the CFRP face sheet behavior, in which a progressive damage model based on the Hashin failure criteria and Yeh delamination failure criteria is implemented in ABAQUS/Explicit. Reasonably good agreement is achieved when comparing impact force, absorbed energy, and failure modes between experimental measurements and numerical predictions. These studies reveal that damage, consisting of fiber damage, matrix damage and delamination of the face sheets as well as buckling of core members, depends on the impactor shape, impact energy and impact location. The investigations provide some insight into the failure mechanisms in this hybrid sandwich structure under low-velocity impact loading, which could be used in the development of novel lightweight multifunctional structures.

The effect of impactor shape on the low-velocity impact behavior of hybrid corrugated core sandwich structures

Experimental and numerical research on the low velocity impact behavior of hybrid corrugated core sandwich structures

The effects of geometric configurations of corrugated cores on the local impact response and planar compression performance of sandwich panels are presented by FEM in the present research. Five sandwich panels with various corrugated cores of different geometric configurations with the same size, weight, and materials were designed. The next step was to identify the effects of geometric configurations of the cores on the response of the sandwich panels under minor energy impact and high energy impact. Numerical simulation results of low-velocity local impact show that the geometric configuration of the core had a significant influence on energy absorption capability under minor energy impact. Sandwich panels with sinusoidal and arc-shaped cores caused lower energy absorption due to lower out-of-plane stiffness. Significant debonding occurred in the sandwich panels with sinusoidal, arc-shaped and triangular cores due to a small bonding area. Geometric configuration of the cores has no significant influence on energy absorption capability under high energy impact. Afterwards, the influence of the geometric configuration of corrugated cores on the performance of sandwich panels under planar compression was presented. Numerical results of planar compression show that sandwich panels with sinusoidal and arc-shaped cores have lower compression stiffnesses and lower ultimate strengths. A simplified analytical method for calculating ultimate strength of the five sandwich panels under lateral compression was presented, and the results matches well with the numerical results. Altogether, the trapezoidal corrugated sandwich panel has advantage in energy absorption capability under low-velocity impact and has a better performance under lateral compression among the five kinds of sandwich panels.

Wentao He

Papers

Effect of structural parameters on low-velocity impact behavior of aluminum honeycomb sandwich structures with CFRP face sheets

Low-velocity impact response and post-impact flexural behaviour of composite sandwich structures with corrugated cores

The effect of impactor shape on the low-velocity impact behavior of hybrid corrugated core sandwich structures

Experimental and numerical research on the low velocity impact behavior of hybrid corrugated core sandwich structures

Effects of geometric configurations of corrugated cores on the local impact and planar compression of sandwich panels