Fabrication and Statics Performance of Pyramidal Lattice Stitched Foam Sandwich Composites

In this study,the pyramidal lattice stitched foam sandwich composite materials were manufactured by integrating top and bottom panels with pyramidal lattice core to overcome the weak interface between the core and the skins of the sandwich structure.The influence of the reinforcing core rods on the mechanical properties including compressive,shear,and three-point bending performances of the foam sandwich compositematerialswere revealed through theoretical analysis and comparative experiments.The theoretical predictions were consistent with the experimental results.Compressive test,shear test and three-point bending test were performed.The experimental results show that the core rods can significantly improve the compressive performance and energy absorption efficiency of the pyramidal lattice stitched foam sandwich structure.The effect is related to the diameter of the core rod.The core rod with large diameter has better effect.Compared with the foamsandwich structure,the pyramidal lattice reinforcing foam composites have stronger shear and bending resistance.The failure modes and failure mechanisms of the pyramidal lattice stitched foam sandwich structure under the shear load are given.The failure modes and failure mechanisms of the pyramidal lattice stitched foam sandwich structure under the three-point bending load are also given.The study concludes that compared with the foam sandwich structure,the overall mechanical properties of the lattice stitched foam sandwich structure composites are significantly improved.

Delamination Testing of AlSi10Mg Sandwich Structures with Pyramidal Lattice Truss Core made by Laser Powder Bed Fusion

Sandwich structures possess a high bending stiffness compared to monolithic structures with a similar weight.This makes them very suitable for lightweight applications,where high stiffness to weight ratios are needed.Most common manufacturing methods of sandwich structures involve adhesive bonding of the core material with the sheets.However,adhesive bonding is prone to delamination,a failure mode that is often difficult to detect.This paper presents the results of delamination testing of fully additive manufactured(AM)AlSi10Mg sandwich structures with pyramidal lattice truss core using Laser Powder Bed Fusion(LPBF).The faces and struts are 0.5 mm thick,while the core is 2 mm thick.The inclination of the struts is 45°.To characterise the bonding strength,climbing drum peel tests and out-of-plane tensile tests are performed.Analytical formulas are derived to predict the expected failure loads and modes.The analytics and tests are supported by finite element(FE)calculations.From the analytic approach,design guidelines to avoid delamination in AM sandwich structures are derived.The study presents a critical face sheet thickness to strut diameter ratio for which the structure can delaminate.This ratio is mainly influenced by the inclination of the struts.The peel tests resulted in face yielding,which can also be inferred from the analytics and numerics.The out-of-plane tensile tests didn’t damage the structure.

Penetration of sandwich plates with hybrid-cores under oblique ballistic impact

The oblique penetration performance of lightweight hybrid-cored sand- wich plates are investigated numerically. To compose the hybrid-core, ceramic prisms are inserted into pyramidal metal lattice trusses and fixed using epoxy resin. Three-dimensional finite element simulations are carried out for the hybrid- cored sandwich impacted at 15°, 30°, 45°, and 60°obliquity by a hemispherical projectile. The ballistic limit, the energy absorbed by the constituting elements, and the critical oblique angle are quantified. The physical mechanisms underly- ing the failure and the influence of fundamental system parameters are explored. The angle of obliquity is found to have significant influence on the ballistic trajec- tory and erosion of the projectile, thus it is important for the impact response and penetration resistance of the sandwich. For oblique angles equal to or larger than 45°, the projectile moves mainly horizontally and can not effectively penetrate across the sandwich.

AEROELASTIC PROPERTIES OF SANDWICH BEAM WITH PYRAMIDAL LATTICE CORE CONSIDERING GEOMETRIC NONLINEARITY IN THE SUPERSONIC AIRFLOW

The equation of motion of sandwich beam with pyramidal lattice core in the supersonic flow considering geometric nonlinearity is formulated using Hamilton＇s principle. The piston theory is used to evaluate aerodynamic pressure. The structural aeroelastic properties are analyzed using frequency- and time-domain methods, and some interesting phenomena are observed. It is noted that the flutter of sandwich beam occurs under the coupling effect of low order modes. The critical flutter aerodynamic pressure of the sandwich beam is higher than that of the isotropic beam with the same weight, length and width. The influence of inclination angle of core truss on flutter characteristic is analyzed.