This paper investigates the deformation mechanism and energy absorption behaviour of 316 L triply periodic minimal surface (TPMS) structures with uniform and graded wall thicknesses fabricated by the selective laser melting technique. The uniform P-surface TPMS structure presents a single-level stress plateau for energy absorption and a localized diagonal shear cell failure. A graded strategy was employed to break such localized geometrical deformation to improve the overall energy absorption and to provide a double-level function. Two segments with different wall thicknesses separated by a barrier layer were designed along the compression direction while keeping the same relative density as the uniform structure. The results show that the crushing of the cells of the graded P-surface TPMS structure occurs first within the thin segment and then propagates to the thick segment. The stress–strain response shows apparent double stress plateaus. The stress level and length of each plateau can be adjusted by changing the wall thickness and position of the barrier layer between the two segments. The total energy absorption of the gradient TPMS structure was also found slightly higher than that of the uniform TPMS counterparts. The gradient design of TPMS structures may find applications where the energy absorption requires a double-level feature or a warning function.

We investigate the propagation behavior of the low-frequency topological interface state of the flexural wave in the locally resonant metastructure and analyze the tunability of the sub-wavelength interface states by the piezoelectric shunting circuit. One homogeneous thin beam is periodically attached with local resonant beams, which connect shunted piezoelectric actuators. The folding band obtained by merging two primitive unit cells into one new element can generate a Dirac point below the low-frequency locally resonant bandgap. This folding point is opened to develop one new bandgap originated from the Bragg scattering effect by breaking the mirror symmetry. Then, topological transitions are demonstrated during the distance variation between two adjacent resonances. The interface state’s existence is further confirmed by using steady and transient analysis of the heterostructure composed of two media with different topological properties. Finally, we show the relationship between the interface frequency and the capacitance ratio and research the influence of the distance parameter on the topological interface state. Because of the tunability of elastic waves by the piezoelectric shunting circuit, our design has potential for applications such as energy harvesters, filters, and physical switches.

The thermal properties of single-walled boron nitride nanotubes (BNNTs) are studied in this paper based on molecular dynamics (MD) simulations. The influence and mechanism of tubular configuration, temperature, length, diameter and chirality on the thermal conductivity of BNNTs are systematically analyzed. The results show that the thermal conductivity decreased with increasing temperatures. The values of thermal conductivity of BNNTs and boron nitride nanoribbons (BNNRs) confirm that the tubular configuration is more conducive to phonon propagation. The thermal conductivity is raised by increasing the length of BNNTs. Moreover, the thermal conductivity changes slightly with further increase of diameter and various chirality. The results share guiding significance for thermal transport characterization of nanoscale thermal conductive component based on boron nitride nanotubes.

In this article, the tensile strength, fracture strain and elastic modulus of graphene sheet (GS) containing randomly distributed vacancies are investigated using molecular dynamics simulations, and the effects of temperature and vacancy defect on these mechanical properties are analyzed. The presences of defects dramatically degrade the mechanical performance of GSs. When the number of defects is large enough the failure mechanism of the GS will change. The defects deteriorate the mechanical properties of the GSs by reducing their tensile strength, failure strain and elastic modulus. However, the discrepancies between 0.01 K and the finite temperature (300 K, 600 K and 900 K) remain almost the same as the percentage of vacancy increases.

Boron nitride nanosheets (BNNSs), a new type of wide bandgap nanomaterial, has attracted great attention due to their excellent properties and potential applications. Thus, it is necessary to have a comprehensive understanding of the mechanical properties of BNNSs in various working conditions. This paper presents an analytical model based on molecular mechanics to study the size effect and temperature effect on the Young’s modulus of BNNSs. A closed-form formulation is derived for Young’s modulus as a function of the length of B–N bonds and the out-plane displacement. It is shown that the chirality and the size of the BNNSs affect the length of BN bonds in molecular dynamic (MD) simulations. It is also found that the length of BN bonds and the out-plane displacement in a monolayer BNNS is remarkably temperature dependent. Therefore, the sizes and the temperatures can affect the Young’s modulus of BNNSs. The expressions developed in this paper are employed to investigate the Young’s modulus for zigzag and armchair BNNS with various sizes and temperatures. The present model, associating with a beam model, provides a simple method to calculate elastic properties which takes into account all bonded energies and force coefficient changes with atoms distance. The results of size effect and temperature effect are in good agreement with data of simulation performed in finite element method (FEM) simulation and MD simulation. The present study provides a molecular mechanics model to predict the Young’s modulus of a monolayer BNNS, and the present model may be applied to other two-dimensional (2D) materials in further study.