The fatigue behaviors of high-strength bearing steel were investigated with rotating bending fatigue loading with a frequency of 52.5 Hz. It was revealed that the high-strength steel tended to initiate at interior non-metallic inclusions in a very high-cycle fatigue regime. During fractography observation, it was also seen that the inclusion acting as a failure-originating site was seldom smaller than 10 μm. Moreover, prior austenite grains could also act as the originating source of failure when inclusion was absent. The crystal plasticity finite element method (CPFEM) was adopted to simulate the residual stress distribution around non-metallic inclusions of different sizes under different loading amplitudes. The accumulated plastic strain around the inclusion suggested that the existence of inclusion may reduce material strength and lead to more fatigue damage. The value of accumulated plastic strain around different inclusion sizes also resembled the crack nucleation or propagation of the materials. The simulation results also indicated that inclusions smaller than 5 μm had little influence on fatigue lifetimes, while inclusions larger than 10 μm had a significant influence on fatigue lifetimes.

Pentamode material (PM) possesses great potential in underwater acoustic metamaterial device applications due to its broadband and solid-state merits. Previously proposed PM devices are all designed with single materials, where the additional weights for mass adjustment are connected directly to the struts for modulus adjustment. The coupling effects between them severely restrict available fabrication techniques and the realizable range of physical properties of PM devices. A multiphase PM configuration, the additional weights of which are bonded to the struts with interconnecting materials, is proposed, and a waterlike multiphase PM device based on the proposed configuration is developed to assess the validity of the multiphase PM configuration. It is revealed from both simulation and experimental results that the acoustic properties of the proposed multiphase PM device mimics water within the simulation frequency range of 3–24 kHz. The fabrication cost of the proposed multiphase PM device is reduced by 80%, and the duration is only 1/15 when compared to that of a single-phase PM device. Additionally, the multiphase PM has great advantages over single-phase PM for aspects such as withstanding higher hydrostatic pressure due to much more uniform stress distribution and broadening the realizable range of physical properties of PM devices significantly.