Biological materials exhibit superior mechanical performance owing to their hierarchically and elaborately ordered structure at multi-levels. Among them, red abalone shell (known as nacre) has been regarded as a perfect example of natural design of damage-tolerant materials. In particular, the excellent impact resistance of nacre attributed to its ‘brick-and-mortar’ microstructure has inspired new designs and fabrication of nacre-like materials has been proved to exhibit excellent mechanical properties under impact. Nacre-inspired graphene reinforced nanocomposites are promising candidates for fabricating strong, lightweight and high-impact resistance materials. This can be attributed to the excellent stiffness, impact energy delocalization, high in-plane sound speed and intrinsic strength properties of graphene.
Metal materials are highly susceptible to ultrahigh strain rate deformation when subjected to harsh conditions like space and ice dust. A number of studies on graphene/metal matrix composites with the ‘brick-and-mortar’ architecture have shown the intrinsic benefits of graphene in improving the mechanical properties of the resulting composites. Nevertheless, most of these studies were conducted under quasi-static conditions with little consideration for the deformation behavior of the composites under extreme dynamic conditions.
Deformation of metal materials is generally classified based on their strain rates. Although nanoindentation and micropillar compression are generally effective methods for studying small structures and localized deformation behaviors, their inherently low testing speed is a limiting factor. Lately, laser-induced projectile impact testing (LIPIT) has been employed to study the strain rate deformation behaviors under extreme conditions at microscale level with massive success. Therefore, it is a promising technique for evaluating the extreme rate of deformation of bioinspired graphene/metal composites.
Herein, Dr. Yifei Peng, Dr. Guohu Luo, Professor Yongxiang Hu and Professor Ding-Bang Xiong from Shanghai Jiao Tong University fabricated nacre-inspired graphene reinforced copper nanocomposites. The anisotropic extreme strain rate (~108/s) deformation behaviors of these nanocomposites were studied using LIPIT at a high speed of about 2.5 Km/s as well as post-mortem analysis. Impact tests were carried out on both vertically aligned nanocomposites with a loading direction parallel to the alignment of the graphene interface (V-MMC) and horizontally aligned nanocomposites with a loading direction perpendicular to the alignment of the graphene interface (H-MMC). Their research work is currently published in the journal, Composites Part B.
The research team showed that the pinning effect and extreme loading of graphene could result in high-density and highly stabilized stacking faults and deformation twins at the impact front. This was also observed in the ultrafine-grained copper matrix under similar dynamic and extreme conditions. The density of stacking faults and twinning as well as the volume of the severely-deformed region at the impact front in the perpendicular loading direction, was half and one-third that in the parallel impact loading direction, respectively.
Such discrepancies allowed robust comparison of the impact energy dissipation capacity in both directions. With only approximately 0.9 vol% graphene incorporated in the nacre-inspired composites, H-MMC exhibited about six times higher impact energy dissipating efficiency than V-MMC. Deformation mechanisms and energy dissipation modes were elaborately analyzed during both H-MMC and V-MMC impact orientations. The superior impact resistance performance of the resulting nanocomposite was attributed to the extraordinary impact resistance properties of both graphene and natural nacre.
In a nutshell, orientation-dependent responses of a nacre-inspired graphene/copper nanocomposite were comprehensively studied under extreme strain rate deformation. The findings revealed the crucial role of the nacre-inspired architecture design in improving the impact resistance of materials under dynamic and extreme conditions. In a statement to Advances in Engineering, Professor Ding-Bang Xiong noted that their study provided valuable insights into the design and fabrication of metal composites with outstanding mechanical properties like impact resistance under extreme conditions for different applications such as collision protection of satellites and spacecraft.
Peng, Y., Luo, G., Hu, Y., & Xiong, D. (2022). Extreme strain rate deformation of nacre-inspired graphene/copper nanocomposites under laser-induced hypersonic micro-projectile impact. Composites Part B: Engineering, 235, 109763.