Impact protection structures such as plates are highly used to provide maximum energy absorption against external impact. When the plate structures are used against the external impact in the out-of-plane direction, most of the impact energy is dissipated at the impact area whereas other plate areas will contribute little to absorb the energy, thus significantly reducing the material use efficiency of the structure. Research have revealed that the above phenomenon is due to the dynamic inertia and deformation response effects characterized by the mass and strength distribution on the plate. This means that countermeasures against the impact should take into account the various mechanisms in the mechanics. As such, there is need to understand the underlying mechanisms for effective and efficient conversion of the out-of-plane impact on the transverse response.
To address this issue, a research effort by Professor Qing Zhou and Mr. Shengduo Liu from Tsinghua University in China examined the mechanism for diverting out-of-plane impact to transverse response in plate structures. In particular, their study focused on evaluating the material distribution to determine the relationship between the intrusion in the out-of-plane direction and plastic deformation in the transverse direction. The authors devised a simple setup in which a plate structure, partitioned into two plates, was impacted by a rigid body. When the two plates came into contact, the upper plate took impact from the intruding object while the lower plate acted as a delayed defense. The influence of the thickness partition and mass distribution on the structure were investigated. Their research work is currently published in the International Journal of Impact Engineering.
In the study, the inertial effects by mass distribution and deformation on the plate were identified as the main factors influencing the range of mass activation and spread of plastic deformation on both the out-of-plane and transverse directions. For instance, energy dissipation occurred in smaller areas for stronger plate materials and spread transversely on larger range for less stronger plate materials, resulting in efficient material use. This also indicated the competing effects of the activation of inertia and deformation capabilities. However, the addition of non-structured mass on the plate influenced the range of plastic deformation by making it hard for the deformation to spread due to inertia effects.
Partitioning the plate into two was a clear demonstration that a smaller intrusion can be achieved through double-plate structure due to the optimal configuration range of the thickness partition and gaps between the plates which enabled appropriate energy transfer to the lower plate during contact. These mechanisms have the advantage of promoting the optimal design of material distribution leading to smaller intrusion and greater material use efficiency by diverting out-of-plane impact to the transverse response.
Overall, the study presents a dynamic response of thin plate structure under impact by intruding objects. Based on the findings, especially describing the relationship between the intrusion in the out-of-plane direction and plastic deformation in the transverse direction, Professor Qing Zhou observed that structures with non-symmetrical configurations are viable for protection against impact loading.
Zhou, Q., & Liu, S-D. (2019). Mechanisms of diverting out-of-plane impact to transverse response in plate structures. International Journal of Impact Engineering, 133, 103346.