Dynamic Impact Characteristics of Airdrop Cushioning Materials and a C - σ_m Curve-Based Cushioning Pad Design Method

To mitigate impact damage to airdropped supplies during landing, this study proposes a cushioning pad design method based on the C - σm (cushioning coefficient-maximum stress) curve, aiming to balance energy absorption efficiency with lightweight requirements. A medium-sized airdrop impact simulation model is established and validated via drop impact tests, and systematic dynamic impact analyses are performed on three representative cushioning materials: honeycomb paperboard, polyurethane foam, and aluminum foam. Their cushioning characteristic curves are compared, revealing that all three materials exhibit a concave C - σm profile (first decreasing, then increasing) with distinct optimal stress ranges for airdrop cushioning applications: aluminum foam for high stress (≥500 kPa), polyurethane foam for medium stress (350-450 kPa), and honeycomb paperboard for low stress (≤200 kPa). The energy absorption potential decreases with the optimal stress threshold, while cushion thickness positively correlates with the airdrop load range. In the low-stress stage, the maximum stress shows a strong functional dependence on energy density, rendering thickness effects negligible for energy absorption. Under the material fragility constraint, the C - σm curve-based graphical method can accurately determine the cushion pad's optimal thickness and bearing area. In design Case 3, optimizing the bearing area reduced the required cushion thickness from 100.5 cm to 25.0 cm, substantially decreasing the cushion volume. The findings provide reliable material-level insights and theoretical support for impact protection design in airdrop cargo, with clear guidance on selecting cushioning materials based on their intrinsic mechanical response.