Advanced engineering and functional ceramics are sensitive to damage cracks, which delay the wide applications of these materials in various fields. Ceramic composites with enhanced fracture toughness may trigger a paradigm for design and application of the brittle components. This paper reviews the toughening mechanisms for the nanolayered MAX phase ceramics. The main toughening mechanisms for these ternary compounds were controlled by particle toughening, phase-transformation toughening and fiber-reinforced toughening, as well as texture toughening. Based on the various toughening mechanisms in MAX phase, models of SiC particles and fibers toughening Ti₃SiC₂ are established to predict and explain the toughening mechanisms. The modeling work provides insights and guidance to fabricate MAX phase-related composites with optimized microstructures in order to achieve the desired mechanical properties required for harsh application environments.

In this work, a novel multi-span metamaterial dual-beam (MMDB) structure is proposed for the effective suppression of ultra-low-frequency vibrations in beam structures. The MMDB is composed of a periodic array of units, with each simply supported unit including beams at the top and bottom, and a spring-mass-spring resonator connecting two beams. For analyzing the dynamic behavior of the MMDB, the spectral element method (SEM) is utilized to establish a dynamic model. A comparative analysis is conducted with a traditional metamaterial dual-beam model, highlighting the advantages of the proposed MMDB. The vibration transmittance of the MMDB under base excitation is analyzed, during which the bandgap frequency beginning from zero is generated. The MMDB is further modeled by the finite element method (FEM), and the simulation results of transmittance agree well with those obtained through SEM, validating the effectiveness of the utilized approach. The band structure of the MMDB structure is further obtained and local resonance and Bragg bandgaps are simultaneously found. Subsequently, parameter study is conducted to investigate the effects of material and geometry parameters on the bandgap characteristics of the MMDB. This work provides valuable guidelines for the design of multi-layer beam structures aimed at efficiently suppressing vibrations within the ultra-low-frequency range.

Bistable energy harvesters have been extensively studied. However, theoretical research on the dynamics of bistable energy harvesters based on asymmetric bistable composite laminated plate and shell structures has not been conducted. In this paper, a theoretical model on the dynamics of an energy harvester based on an asymmetric bistable composite laminated shell is established. The dynamic snap-through, the nonlinear vibrations and the voltage output with two potential wells of the bistable energy harvester are studied. The influence of the amplitude and the frequency for the base excitation on the bistable energy harvester is studied. When the frequency for the base excitation with a suitable amplitude in the frequency sweeping is located in a specific range or the amplitude for the base excitation with a suitable frequency in the amplitude sweeping is located in a specific range, the large-amplitude dynamic snap-through, nonlinear vibrations and voltage output with two potential wells can be found to occur. The amplitude and the frequency for the base excitation interact on each other for the specific amplitude or frequency range which migrates due to the softening nonlinearity. The vibration in the process of the dynamic snap-through behaves as the chaotic vibration. The nonlinear vibrations of the bistable system behave as the periodic vibration, the quasi-periodic vibration and the chaotic vibration. This study provides a theoretical reference for the design of energy harvesters based on asymmetric bistable composite laminated plate and shell structures.