Mi Wang,Dewen Kong,Lingling Wang,Youbin Li,Ting Cai
The quasi-static, dynamic compression experiments and micromechanical model were employed to declare the dynamic compressive response of ZrB 2 –20%SiC composite at high-strain rates. The quasi-static compressive strengths were measured to determine the range of initial microcrack length in ZrB 2 –20%SiC composite. The effects of the strain rate on dynamic compressive strength, critical stain, as well as fracture mechanisms were discussed based on experimental results. Dynamic mechanical properties of ZrB 2 -based composites display obvious strain rate dependence. The dynamic increase factor in the compressive strength shows a rapid increase above a transition strain rate of 1228 s −1 . Moreover, a micromechanical model considering initial microcrack lengths is used to predict dynamic compressive strengths, which agree with the experimental results. Additionally, the critical strain has a linear increase tendency with the increase of strain rate. The dynamic compressive fracture mechanism of ZrB 2 –20%SiC composite is relative to the combination effect between strain rate and microstructure. The size of flaw distribution is critical below the transition strain rate resulting in bigger fragments, whereas the flaw density is primary with more and smaller fragments above the transition strain rate.
Qiqi Xue,Yihang Xiao,Xiaoyu Zhang,Xin Zhang,Wei Hong,Canhui Yang
Many biological hydrogels possess remarkable mechanical performances under both quasi-static and impact loadings, yet such mechanical robustness over a wide range of strain rates has not been achieved in synthetic hydrogels due to the lack of understanding of dynamic responses at high strain rates. Here we study the dynamic responses of tough hydrogels at high strain rates by using the Ca-alginate/polyacrylamide hydrogel as a model material and a modified split Hopkinson press bar (SHPB) system. We show that the Ca-alginate/polyacrylamide hydrogel is also much tougher than the two constituents at high strain rates. The strength of Ca-alginate/polyacrylamide hydrogel at 1.2 × 10 4 s −1 is two orders of magnitude higher than the stress at the same strain at 0.25 s −1 . We identify the fracture points by using snap rings to control the maximum compressive strains during the loading process and validate them by subsequent cyclic loading and unloading at 0.25 s −1 . We formulate a five-parameter constitutive model to describe the visco-hyperelastic behaviors and achieve satisfactory agreements between theory and experiment. We further interpret the underlying mechanisms of the strain rate-dependent deformation and fracture behaviors by comparing them with the responses of the two constituents. The importance and opportunities of studying the dynamic responses of tough hydrogels at high strain rates are discussed.
Bidirectional freeze casting combined with pressure infiltration has demonstrated significant potential as an effective approach for fabricating bioinspired lamellar composites with excellent strength and toughness. However, their dynamic mechanical response remains underexplored. In this study, B 4 C/2024Al composites with long-range ordered nacre-like architectures were fabricated using bidirectional freeze casting followed by pressure infiltration. The mechanical properties and deformation behavior under both quasi-static and dynamic compression conditions were systematically investigated. The results reveal that dynamic compressive strength and strain were significantly higher than their quasi-static counterparts, largely attributed to strain rate hardening and localized matrix melting. Compared to unidirectionally structured composites, the bidirectionally structured ones exhibited superior mechanical performance, achieving a maximum compressive strength of 1088.6 MPa at a strain rate of 3000 s −1 (40 vol% B 4 C/2024Al composite). A clear dependence of flow stress and energy absorption capability on B 4 C volume fraction was observed. As B 4 C content increased, the compressive strength rose, but dynamic strain energy density showed a decreasing trend beyond 20 vol% due to reduced ductility. Specifically, the energy density peaked at 133.08 MJ/m 3 for the 20 vol% composite and declined with further ceramic addition, indicating a trade-off between strength and impact energy absorption. The enhanced toughness under dynamic loading is primarily attributed to adiabatic shear localization in the aluminum matrix, which facilitates localized softening and strain accommodation. Additional contributions include crack deflection and branching within the hard ceramic layers, as well as plastic deformation and thermal softening-induced toughening mechanisms in the metallic phase. These findings highlight the promise of nacre-inspired B 4 C/Al composites for advanced lightweight armor systems, offering an optimized balance between strength, toughness, and energy absorption under high-strain-rate loading.
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