Peridynamic simulation of impact damage to 3D printedlattice sandwich structure

Lattice sandwich structures often exhibit discontinuous characteristics under impact, with damage behaviors involving multiple scales, from micro-scale cell fracture to macro-scale structural collapse. Traditional methods based on continuum mechanics have difficulty in accurately describing non-continuum problems such as material interfaces and fracture behavior, so usually they can only handle single-scale problems. Besides, lattice materials have complex geometric shapes, and mesh-dependent numerical methods such as finite element analysis may suffer mesh sensitivity and may even struggle to obtain an ideal mesh. In order to effectively simulate the damage behavior of 3D printed lattice sandwich structures under projectile impact, a lattice sandwich structure modeling method based on the theory of peridynamics and micro-polar model, and by considering plastic bonds, is proposed. The simulation results of uniaxial compression and large-mass low-speed impact tests are compared with experimental results to verify the accuracy of the peridynamics model for lattice sandwich structures. This model is then used to analyze the damage patterns and failure mechanisms of lattice sandwich panels under projectile impact from low to high velocities. The results show that under low-speed impact, the failure mode of 3D printed lattice sandwich structures is mainly localized plastic deformation, which causes small-scale fractures in the lattice structure near the impact location after arriving at a certain level of strain; while under high-speed impact, it usually exhibits collapse, hole piercing, and fragment ejection, accompanied by extensive plastic deformation. The plastic yield range of 3D printed lattice sandwich structures shows different patterns under high-speed and low-speed impacts, with the plastic deformation range increasing as the impact velocity increases under low-speed impact, and decreasing under high-speed impact. This is mainly influenced by the characteristics of the lattice structure and the material crack propagation during the impact process. Under high-speed impact, the process of projectile penetration will go through four stages; i.e., panel contact, local yield, core material compression, and penetration. Because the material characteristics at each stage are different, the projectile will experience a “sharp-slow-sharp” deceleration process featured by to two acceleration peaks, with the second peak value being 50% lower than the first. Compared with high-speed impact, the projectile under low-speed impact only experiences one deceleration process, and the peak acceleration increases with increasing impact velocity. When the plastic deformation and damage process of the lattice sandwich structure cannot fully dissipate the kinetic energy of the projectile, the release of elastic strain energy in the sandwich structure will cause the projectile to bounce back. The rebound speed in this study is less than 30% of the initial velocity. The research results can provide theoretical support and new analytical methods for the design and application of lattice materials.