Damage characterizations of lattice warp-knitted spacer flexible inflatable composites subjected to low-velocity impact

Lattice warp-knitted spacer flexible inflatable composites are a type of advanced composite material that combines several different techniques to create a material that is strong, lightweight, flexible, and able to absorb and dissipate energy. These composites are constructed using a warp-knitting technique that creates a three-dimensional lattice structure which provides flexibility and allows the material to stretch and bend without breaking. The intermediate spacer layer adds more cushioning and aids in maintaining the three-dimensional structure The inflatable aspect of the material refers to the fact that it can be inflated with air or another gas to further enhance its cushioning properties.

Lattice warp-knitted spacer flexible inflatable composites are typically much lighter and flexible than traditional composite materials, making them ideal for use in applications where weight and flexibility is a critical factor.  The aforementioned materials possess potential applications in the creation and fabrication of lightweight and pliant aerospace components, including fuselage structures, wings, and wind turbine blades. Additionally, they may be utilized in protective equipment such as body armor and helmets. Research is currently underway to enhance comprehension of the mechanical characteristics of composites that are reinforced with lattice warp-knitted spacer flexible inflatable structures. It is important to investigate the material’s response to varying levels of stress and strain, pinpointing ‘the point of failure, examining deformation patterns under different loading conditions, and assessing energy absorption and dissipation when exposed to external stimuli such as vibrations or impacts.

In a new study published in the peer-reviewed Journal Thin-Walled Structures, graduate student Tong Yang, Dr. Jiawen Xu, Dr. Yuyang Lu, Dr. Yu Liu and led by distinguished professor Pibo Ma from Jiangnan University Wuxi investigated the behavior of lattice warp-knitted spacer flexible inflatable composites when subjected to low-velocity impact. The impact resistance performance and energy absorption mechanism were analyzed for Lattice warp-knitted spacer flexible inflatable composites using experiments and numerical modeling. The fabric was knitted with high-strength polyester on a double-needle-bar warp-knitting machine with six guide bars, and it comprised two surface layers and a spacer yarn core layer. The upper and lower layers were tied with the spacer yarn. The experiments were conducted using a drop-weight impact tester, and the Lattice warp-knitted spacer flexible inflatable composites specimens were impacted at different velocities and with different impact energies. The numerical model was based on finite element analysis (FEA) and was used to predict the deformation and damage patterns of Lattice warp-knitted spacer flexible inflatable composites under different impact conditions.

The authors observed the destruction process of Lattice warp-knitted spacer flexible inflatable composites during an impact test. Initially, there was elastic deformation, which caused the inner air to gather and prevent leakage. As the elastic deformation approached its limit, the upper layer began to sustain damage. In the final stage, a portion of the impact energy was absorbed through deformation and damage of the Lattice warp-knitted spacer flexible inflatable composites, while the remaining energy was converted into kinetic energy, causing the impactor to bounce back. As the internal air pressure decreased, the flexible warp-mesh inflatable composite increased in deflection rate, peak load, and displacement. This resulted in an inverse proportionality between impact strength of composites and stiffness within a certain range. The upper layer showed an almost oval-shaped damage, with some cracks and dents. In addition, lateral views of the damaged area showed obvious irreversible deformation, coil misalignment, and fiber breakage.

In conclusion, professor Pibo Ma and co-workers demonstrated that grid warp-knit flexible inflatable composites have excellent energy absorption properties. This study showed that warp-knit flexible expandable lattice composites could be a viable alternative for wind turbine blades, airship blades, and other applications due to their superior properties such as light weight, energy absorption, and easy manufacturing process. To design more efficient inflatable structures that can withstand loads, it is important to understand the failure and damage mechanisms of lattice warp-knit flexible inflatable composites. These finding provided valuable insights for engineers and researchers who worked with Lattice warp-knitted spacer flexible inflatable composites.