Mechanical response of aluminum foam sandwich structure under impact load

This study investigates the mechanical response of aluminum foam sandwich panels, sandwich cylindrical shells, and sandwich shallow shells under impact loads. First, a finite element model of the sandwich panel was established, and an impact load was applied. The numerical results were compared with theoretical and experimental results to verify the model's effectiveness. Second, the energy absorption efficiency and overall deformation of sandwich panels, sandwich cylindrical shells, and sandwich shallow shells under the same impact load were studied. The research shows that the energy absorption performance of the sandwich shells is better than that of the sandwich panels, and the overall deformation is less than that of the sandwich panels. The effect of increasing panel thickness on the two types of sandwich shell studies is based on this basis. The conclusions describe that increasing the panel thickness will significantly reduce the structure's energy absorption efficiency and deformation. Finally, the effect of single-and double-layer structure on the impact resistance of sandwich shells was studied when the total thickness of the sandwich structure was unchanged. The results show that compared with the single-layer structure, the energy absorption efficiency, overall deformation, and contact force between the projectile and structure of the double-layer structure will be reduced.

Design Method Using Response Surface Model for CFRP Corrugated Structure under Quasistatic Crushing

The development of a carbon-fiber-reinforced plastic (CFRP) part is carried out by utilizing many experimental results in deciding the design. For this reason, the development period of a CFRP structure is long and an obstacle for commercialization. In this paper, multiple regression analysis is used to derive a response surface that estimates the generated load using the shape parameters of a corrugated collision energy absorbing structure to shorten the development period. To obtain the response surface, we conducted a quasistatic crushing experiment by using the length of linear portions (pitch) and the number of stacks (thickness) of a corrugated shape as parameters. When progressive crushing mode is observed, energy absorption efficiency decreases with the increase in pitch, and increases with the increase in the number of stacks. To discuss how energy absorption efficiency changes, a comparison examination is conducted using the derived response surfaces. Results indicate that specifications with high energy absorption efficiency can be accurately selected using the response surface of primary expression. In addition, differences in deformation mode were due to the influence of the stress at the corner portion of a part.

Soft-Landing Dynamic Analysis of a Manned Lunar Lander Em-Ploying Energy Absorption Materials of Carbon Nanotube Buckypaper

With the rapid development of the aerospace field, traditional energy absorption materials are becoming more and more inadequate and cannot meet the requirements of having a light weight, high energy absorption efficiency, and high energy absorption density. Since existing studies have shown that carbon nanotube (CNT) buckypaper is a promising candidate for energy absorption, owing to its extremely high energy absorption efficiency and remarkable mass density of energy absorption, this study explores the application of buckypaper as the landing buffer material in a manned lunar lander. Firstly, coarse-grained molecular dynamics simulations were implemented to investigate the compression stress-strain relationships of buckypapers with different densities and the effect of the compression rate within the range of the landing velocity. Then, based on a self-designed manned lunar lander, buckypapers of appropriate densities were selected to be the energy absorption materials within the landing mechanisms of the lander. For comparison, suitable aluminum honeycomb materials, the most common energy absorption materials in lunar landers, were determined for the same landing mechanisms. Afterwards, the two soft-landing multibody dynamic models are established, respectively, and their soft-landing performances under three severe landing cases are analyzed, respectively. The results depicted that the landers, respectively, adopting the two energy absorption materials well, satisfy the soft-landing performance requirements in all the cases. It is worth mentioning that the lander employing the buckypaper is proved to demonstrate a better soft-landing performance, mainly reflected in reducing the mass of the energy absorption element by 8.14 kg and lowing the maximum center-of-mass overload of the lander by 0.54 g.

Sacrificial Cladding with Brittle Materials for Blast Protection

In the following work, sacrificial claddings filled with different brittle materials were investigated, from concrete foam to granular media. They were subjected to blast loading using an explosive driven shock tube, while a sensor measures the load transmission and a high speed camera records the compression of the core. From a macroscopic point of view, concrete foam and granular media can act efficiently as a crushable core but differs greatly in terms of energy dissipation mechanisms. To compare them, granular media was at first treated as a cellular material, and different key parameters (plateau stress, densification strain) were computed using the energy absorption efficiency methodology. The presented tests results, coupled with observation in literature, allow a better understanding on the crushing process of a granular media. In particular, granular media tend to work as a core even for low intensity load, contrary to more classical crushable core.

Compressive Properties of Electroless Ni-P Coating Reinforced Magnesium Alloy Foams

In this study, the open-cell Mg-2Zn-0.4Y foams were prepared by infiltration casting method. The Ni/Mg hybrid foams were prepared by electroless Ni-P coating on the foam struts to improve the compressive strength and energy absorption capacity. The compressive properties of the Mg alloy foams and Ni/Mg hybrid foams were studied by quasi-static compressive test. The experimental results show that the Ni-P coating is composed of crystallites. The Ni-P coating can significantly enhance the compressive strength, energy absorption capacity and energy absorption efficiency of the foams.

A Stretchable Pillararene-Containing Supramolecular Polymeric Material with Self-Healing Property

Constructing polymeric materials with stretchable and self-healing properties arise increasing interest in the field of tissue engineering, wearable electronics and soft actuators. Herein, a new type of supramolecular cross-linker was constructed through host-guest interaction between pillar[5]arene functionalized acrylate and pyridinium functionalized acrylate, which could form supramolecular polymeric material via photo-polymerization of n-butyl acrylate (BA). Such material exhibited excellent tensile properties, with maximum tensile strength of 3.4 MPa and strain of 3000%, respectively. Moreover, this material can effectively dissipate energy with the energy absorption efficiency of 93%, which could be applied in the field of energy absorbing materials. In addition, the material showed self-healing property after cut and responded to competitive guest.

Low-Velocity Impact Properties of Polyurethane Composites Reinforced with Warp-Knit Spacer Fabric

Eight kinds of polyurethane (PU)-matrix composite samples were prepared by impregnating the warp-knit spacer fabrics with flexible PU foam. An impact test was carried out to investigate the influence of fabric structure parameters on the compression behaviors and energy-absorption efficiency of the composites. By using finite element (FE) analysis and ANSYS software, the unit cell models of the composites were built to simulate the impact responses and get strain-stress curves. Comparison of FE simulation and experimental curves showed good consistency between them.

Bracket fungi, natural lightweight construction materials: hierarchical microstructure and compressive behavior of Fomes fomentarius fruit bodies

Bracket fungi such as Fomes fomentarius (“tinder fungus”), have strong, light and tough fruit bodies that make them interesting role-models for bio-inspired, biodegradable applications. So far, little is known about the relation between their microstructure and mechanical properties, information needed for designing novel composites. The fruit bodies (mycelia) of tinder fungus are hierarchically structured honeycomb foams. The mycelium has a transversely isotropic microstructure with open porosity on the nano- and micro-length scales. The lowest resolution porosity appears as elongated tubes that extend from beneath the woody upper surface down towards the lower side that faces the ground. The tube walls are made of a network of hollow, fibrous cells (hyphae), mainly consisting of chitin. When tested mechanically, the material shows the typical compressive stress/strain curve of foams, where an initially linear course is followed by an extended plateau region. The as-harvested material exhibits pronounced viscoelastic recovery, but the tube walls are visibly damaged. Compared with the transverse direction, the load-bearing capability and energy absorption parallel to the tube long axis are ~ 5 and ~ 10 times higher, respectively. Unexpectedly however, the energy absorption efficiency is similar for both loading directions. Buckling of the tubes and cracking of their walls are the main damage mechanisms, and the damage zones coalesce into deformation bands as it is typical for foams. Drying leads to ~ 7 times higher plateau stresses, damage becomes extensive, and the mycelium loses its viscoelastic recovery capability. Interestingly, rehydration restores the properties of the wet state. It is compelling to imagine an adaptive role to natural dry/wet conditions.