Search

The unusual properties of mechanical metamaterials are determined by the configuration of artificial periodic structures. However, the mechanical performance of conventional metamaterials is irreversible and cannot perceive and respond to the changes in the environment. In present study, a zero Poisson's ratio metamaterial with intelligent switching mechanical properties and vibration isolation effect is proposed. Based on a 4D printing method of shape memory polymer, this metamaterial is created that can sense temperature changes and switch mechanical properties. The macroscopic deformation and the morphology change of the metamaterial during compression tests are analyzed using experimental and finite element methods. The irregular buckling distortion of the metamaterial is eliminated by cylindrical design, and controllable and adjustable local deformation and stress-strain curve are achieved based on microstructure gradient design. Subsequently, this work focused on the vibration isolation performance of metamaterials, and found fascinating shock absorption performance. Compared with traditional linear spring, this metamaterial spring can effectively reduce the vibration amplitude of certain frequency bands before reaching the resonance peak, which provides a new realization method for low-frequency vibration isolation design.

To quantify the friction mechanism of the interface of the brake disk-pad pair, an analytical model of coefficient of friction (COF) is established from the perspective of contact mechanics. The model takes into account the surface topography of the disk, mechanical properties of brake pair, and the ingredients of the brake pad. As the reinforcing fillers, the effect of particle size and amount on the COF are analyzed, and the simulation results are consistent with the experimental data. The model and results presented here offer some insight into real brake pair design.

Ultrasonic welding is a versatile welding technique for the assembly of thermoplastic composite structures. The research in this paper aims at improving the manufacturing efficiency and the weld attributes, featured by welded area, weld strength and failure mechanisms, of ultrasonic spot welded joints by adopting proper sonotrodes combined with process control techniques. To achieve this goal, the research was carried out in two steps. In the first part, single-spot ultrasonic welding was performed by using sonotrodes with various diameters. The influence of the sonotrode sizes on the welding processes and weld attributes of the as-manufactured welded joints was investigated. Based on the information gathered from the first part, a novel simultaneous spot welding technique to produce two welded spots within a single step was subsequently proposed. The results in both parts indicated that the increase of the sonotrode size could significantly improve the welding efficiency. The weld attributes were also effectively enhanced by adopting proper welding force.

Metamaterials/Phononic crystals are used to control the propagation of elastic waves/sound waves, and can be used in fields such as vibration isolation, noise reduction, stealth, focusing, and acoustic wave devices. The realization of real-time, flexible and active adjustable control of elastic waves by mechanical reconstruction of metamaterials is a current research hotspot. Here, SMP metamaterials with mechanical reconstruction and self-recovery ability are proposed. Affected by the glass transition temperature of the material, the mechanical properties of the metamaterials are related to the geometric parameters of the lattice configuration and the external temperature. The metamaterials can adaptively switch mechanical properties and shapes without continuous external excitation of the physical field. The finite element method and experiments were used to analyze the deformation and self-recovery process of the metamaterials. The results show that the metamaterial can achieve mechanical programming and response recovery, and the bandgap of the metamaterial can be greatly adjusted by changing the external temperature.

The elastic metamaterials have exceptional physical properties and functions unavailable in natural materials, a major challenge is how to realize the dynamic and stable adjustment of working frequency to control elastic waves. In this work, we propose a method of creating geometrically reconfigurable and mechanically tunable multi-stable metamaterials to realize a kind of tunable elastic metamaterial with a stable state during the active regulation without continuous-consuming energy based on 4D printing technology. The underlying mechanical mechanism of dynamic and stable adjustment is investigated through theoretical model, finite element analysis and experiment. The tunable elastic metamaterial can adjust the starting/ending frequencies and broaden the frequency ranges of bandgaps and control the elastic wave propagation. The method of intelligent and active manipulation of elastic wave can be used in vibration-isolated steady-state adjustable equipment and smart wave device. Inspired by electronic technology, we implement a bi-stable logic-gate elastic metamaterial to correctly execute simple wave logic operations.

Origami has received significant interest from the science and engineering community as a design method and used to construct expandable mechanical metamaterials by folding and unfolding along the crease line. Here, we adopted a 4D printing method with shape memory polymer to create a smart origami metamaterial with tunable stress-strain curves, controllable compression twist deformation, shape programming and self-expansion, and develop its deformation theory model. The effects of unit structure parameters and temperature field on the mechanical properties and functional deformation of the metamaterial are analyzed using experiments, theory model and finite element method. The origami structure can realize the shape programming, self-expansion and mechanically tunable by control temperature, and switch between monostability and bistability by adjusting the parameters. The structure parameters, temperature field, and series combination method are used to adjust and control the stress-strain curves and compression twist deformation behavior of the metamaterials. This multifunctional metamaterial may find a wide range of applications, such as, mechanical storage, tunable shock absorption interface and soft robots.