4D Metamaterials with Zero Poisson's Ratio, Shape Recovery, and Energy Absorption Features

Abstract

Crashworthiness is the ability of the materials or structures to absorb impact energy through plastic deformations, friction, fracture, shear, bending, and even torsion. [1] Energy absorbers have been extensively used for different applications. The most prevalent applications can be found in the automotive, railway, and aerospace industries. [2,3] It is important to reduce the mortality rate caused by car crashes in the automotive industry. When it comes to passengers' safety, some critical crashworthy elements must be considered to design proper energy absorbers. The most vital item could be the initial reaction force caused by hitting an external object. [4] The lower the initial reaction force, the safer the occupants might be. A vehicle contains structural elements like rockers, pillars, and bumpers. Among these elements, the front bumper plays a vital role when it comes to energy absorption and is the most effective parameter for vehicle safety and occupants. The front bumper usually absorbs more than half of the kinetic energy during a car crash. [4] This is the main reason for magnifying the existence of high-performance energy absorbers Distinct from the initial reaction force, the crashworthy designers have been considering various main criteria for an ideal energy absorber, including high energy absorption performance, stability, and safety. Consequently, some design approaches such as gradual energy absorption (GEA), piecemeal energy absorption (PEA), and conventional energy absorption (CEA) have been proposed. [5][6][7] The absorbers designed based on the PEA and GEA approaches show different peak force levels in force-displacement relation, whereas the CEA-based absorbers show a peak force level in their forcedisplacement relation. Xu et al. [5] proposed a structure exhibiting the GEA for subway vehicles. The proposed energy absorber exhibits multistiffness behavior under the impact, showing different peak force levels as well. Afterward, the concept of piecemeal energy absorption (PEA) was introduced by Esa et al. [6] . The PEA concept is similar to the GEA concept. Due to the flexibility of the PEA concept over the GEA, this concept is extended to diverse applications. The PEA strategy provides lower damages under low-velocity impact and higher energy absorption capacity under high-velocity impact. Apart from the GEA and PEA concepts, most energy absorbers possess a CEA response. [7] The CEA response means a gradual increase in initial reaction forces under the impact and then the fluctuations in crushing forces are caused by overcoming the energy absorber's yield strength.

4D Printing‐Encapsulated Polycaprolactone–Thermoplastic Polyurethane with High Shape Memory Performances

“…After loading, the samples were quickly cooled to 25 °C at a rate of 30°min À1 and kept for 120 s. In Figure 2, the programming steps are presented for both the bilayer and encapsulated PCL-TPU structure in bending mode. After unloading, the amount of shape fixity was calculated by measuring the amount of storage deformation according to Equation (1). A, B, C, and D are the initial height, the amount of deformation, and the height after unloading, and recovery, respectively.…”

“…Shape‐memory polymers (SMPs), as the widest and most widely utilized shape memory materials (SMMs), are a group of smart materials that can fix a temporary shape and can return to its original shape by applying proper stimulation. [ 1 ] In recent years, the 3D printing of SMPs has led to the emergence of the 4D printing term, which was first introduced by Skylar Tibbits. [ 2 ] 4D printing has attracted the attention of researchers because of its benefits and features.…”

4D printing parameters optimisation for bi-stable soft robotic gripper design

“…The ability to reassemble simple components into a complex structure that cannot be built with existing manufacturing technologies is a notable case of the design flexibility enabled by 4D printing. Robots [3], automobiles [4], healthcare [5], and aerospace [6] are just some of the emerging markets for three-dimensional (3D) printing technologies, and there has also been a notable shift towards using 4D printing technology to create soft robotics for use in a multitude of environments. The field of soft robotics is a relatively new area of study, with much of the current research being inspired by the systems in nature that have been modified over generations to achieve a certain purpose.…”

3D‐Printed Soft and Hard Meta‐Structures with Supreme Energy Absorption and Dissipation Capacities in Cyclic Loading Conditions

“…Results revealed that by increasing the thickness of structures, although the mass is increased, the energy absorption rate becomes much more considerable, enhancing the SEA. Recently, Hamzehie [ 29 ] introduced zero Poisson's ratio hard meta‐materials with reversible energy‐absorbing features fabricated by 4D printing technology. The deformation could be recovered by simply heating.…”