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Bio-inspired helicoidal carbon fiber reinforced polymer composite (CFRPC) laminates stacked with Bouligand configurations are considered to own great potential in engineering fields. The optimization design of helicoidal layups with single-form and combination-form of linear and nonlinear helicoidal arrangements is carried out using ABAQUS and Isight. Two single-objective optimizations and one multi-objective optimization of maximum fundamental frequency and the difference among the first four adjacent vibration frequencies of helicoidal CFRPC laminated plates are performed and the nonlinear free vibration characteristics of optimal ones are investigated for the first time. Numerical studies are carried out for 16-ply symmetrical rectangular helicoidal laminated plates under two different boundary conditions compared with quasi-isotropic counterparts. The results show that the combination-form helicoidal layup sequences can improve the linear vibration characteristics of CFRPC laminated plates. The plates stacked with the combination form of nonlinear Fibonacci and linear patterns are expected to provide better vibration characteristics. [ABSTRACT FROM AUTHOR]

In this study, molecular dynamics (MD) simulation is adopted to explore the mechanical properties and microstructure evolution of a dual-phase CoCrFeMnNi high-entropy alloy during nanoindentation. The influence of the volume fraction of the hexagonal closed-packed (hcp) phase is considered, and the P–h curves are plotted, where the indentation depths of curves initially into the plastic stage and the maximum indentation force for each curve are significantly different. At the elastic stage, the results from MD simulations are in agreement with those of the Hertz contact theory. However, the fitting coefficient k is remarkably influenced by the hcp phase volume fraction. The correlating P–h curves of plastic deformation are investigated by analyzing the instantaneous defect structures dominated by the nucleation of Shockley partial dislocations or the movements of stacking faults. Furthermore, the microstructure evolution with the increment in indentation depth is demonstrated, and it revealed that the plastic deformation is affected by the phase structure indenter that initially contacts. Unlike the slipping process for the face-centered-cube phase, a new hcp structure grain is created through dynamic recrystallization if the hcp phase is the first phase that the indenter touches. [ABSTRACT FROM AUTHOR]

Considering the impact of chemical compositions, the mechanical properties and microstructure evolution of the single-crystal FCC CoCrFeNi-based high-entropy alloys (HEAs) are investigated by using molecular dynamics simulation in nanoindentation. The addition of Cu and Mn elements would decrease the stacking faults energy resulting in the dislocation-mediated deformation. Moreover, the total number of chemical compositions of CoCrFeNi-based HEAs has critical effects on the results according to the Hertz contact theory. The plastic deformation is studied by correlating the P–h curve with the instantaneous defect structure and dominated by nucleation of Shockley partial dislocations or the motions of stacking faults. Owing to the large amount of Hirth and Stair-rod dislocations, CoCrFeNiCu HEA has the largest indentation force, next followed by CoCrFeNi and CoCrFeNiMn HEAs. Then, the influence of chemical composition on the radial distribution function is explored, and it exhibits that Cu and Mn elements are conducive to amorphization. Finally, the analysis of microstructure evolution reveals that the Mn addition would contribute to the slipping process for CoCrFeNi-based HEAs causing the decrease of indentation force and hardness. In contrast, the Cu addition results in irregular slipping mode accompanying the appearance of dislocation loops. In this simulation, the mechanical properties of single-crystal CoCrFeNi-based HEAs are strongly dependent on the chemical composition, which contributes to the composition design of high entropy alloys in the future. [ABSTRACT FROM AUTHOR]