Reaserch On Failure And Damage Of Composite Orthogonal Corrugated Sandwich Structure Under Impact Load

Due to its high specific strength,specific stiffness,light weight,and versatile core material,sandwich structures are widely used in aerospace,land transportation,ocean engineering,and other fields.The impact of external objects or environmental loads pose a great threat to sandwich structure in the process of application.The impact load usually causes the perforation and cracking of sandwich structure panel,matrix cracking,local debonding and delamination of the structure.In the context of the aforementioned background,the main objective of this research is to design a composite sandwich structure with excellent impact resistance characteristics and systematically analyze its failure modes under different impact loads.Based on the principle of structural lightweight and the idea of wave resistance(Material density times wave velocity)mismatch,a new type of composite orthogonal corrugated sandwich structure was designed,which follows the “straight” to “curved” design concept to reduce the occurrence of shear failure of fiber materials under impact load,better utilize the excellent tensile properties of fiber materials,and improve their energy absorption efficiency under impact load.This sandwich structure was prepared by vacuum-assisted resin transfer molding process.The mechanical behavior and failure mode of the sandwich structure under different impact loads were revealed by combining experimental and numerical simulation methods.To enhance the accuracy of numerical simulations for structures subjected to impact loads,the strain rate effect of polyurethane foam materials and resin-based basalt fiber materials used in the sandwich structure design was experimentally studied.The results demonstrate that the three densities of polyurethane foam materials exhibit significant rate correlation at different strain rates,with the low density foam having the strongest strain rate effect.Additionally,the strain rate effect characteristics of basalt fiber strength values in different directions were obtained.It was observed that the strain rate effect differs in each direction and should be considered separately in actual numerical simulations of the strain rate effect of mechanical parameters in each direction.Finally,a three-dimensional progressive damage VUMAT subroutine,considering the strain rate effect of materials,is developed using Fortran language and Hashin failure criteria,based on the strain rate characteristics of basalt fiber materials.This subroutine provides an effective method for the numerical simulation of sandwich structures under impact loads.In order to study the energy absorption characteristics and failure modes of sandwich structures under various impact conditions,we conducted low-speed drop hammer experiments on orthogonal corrugated sandwich structures made of composite materials using Instron Dynatup 9250 HV experimental equipment.For comparison,we also prepared and tested a plate sandwich structure with the same thickness.Our results indicated that the orthogonal corrugated sandwich structure exhibited significantly higher energy absorption ratios compared to the flat plate sandwich structure under low-speed impact loads.Specifically,when the two hammer heads impacted the corrugated trough with the maximum impact energy,the orthogonal corrugated sandwich structure displayed the best energy absorption characteristics.Furthermore,numerical simulation analysis showed that more fiber tensile damage failure occurred in the corrugated fiber layer at the impact trough position,which effectively utilized the excellent tensile properties of the fiber.We also implemented the VUMAT subroutine,which considered the effect of strain rate,to reduce calculation errors in the numerical simulation.To investigate the ballistic impact characteristics and failure modes of the orthogonal corrugated sandwich structure under high-speed projectile impact,this study conducted experimental research using a first stage light gas gun experimental device.Various speeds of spherical projectile impacts were tested on the trough position of the orthogonal corrugated sandwich structure,and the ballistic limit at the trough position was obtained through fitting formula analysis.To simulate the experimental conditions,we utilized the VUMAT subroutine,which considered material strain rate effects,resulting in a 24.72% reduction in ballistic limit error compared to the numerical simulation method that did not consider these effects.Additionally,we analyzed the ballistic limit and energy absorption characteristics of the spherical projectile impacting both the orthogonal corrugated sandwich structure and flat plate sandwich structure at high speed through numerical simulation.Similar to the low-speed drop hammer impact research,the maximum ballistic limit was observed at the trough position,while the minimum ballistic limit was observed at the position between trough and crest when the projectile impacted the orthogonal corrugated sandwich structure at different positions.Combining the experimental and numerical simulation results,we observed shear failure mode occurring on the elastic-facing surface to generate the punch block,fiber tensile failure and matrix tensile failure on the corrugated surface,fiber tensile,matrix tensile,and fiber lamination failure modes on the back elastic-facing surface,and the generation of an obvious cavity in the foam core layer under the ballistic impact of the structure.To investigate the energy absorption characteristics and damage failure modes of gradient orthogonal corrugated sandwich structures under explosion impact load,we conducted underwater explosion shock wave loading experiments on three types of gradient orthogonal corrugated sandwich structures using an explosive water tank experimental device.In addition,we analyzed the energy absorption contribution rate of different parts of the sandwich structure and the transmitted stress value and damage failure of the sandwich structure with different gradients in detail through numerical simulation.Our results revealed that the foam core layer in the orthogonal corrugated sandwich structure exhibited an energy absorption ratio as high as69.4%,while the foam core layer in the plate sandwich structure exhibited an energy absorption ratio as high as 88.3%,indicating the vital role played by the foam core layer in the energy absorption of the structure.Furthermore,we observed that the positive gradient ABC corrugated sandwich structure exhibited the minimum transmitted stress value,effectively protecting the targeted equipment/structure.On the other hand,the blasting surface of the negative gradient CBA corrugated sandwich structure not only lowered the transmitted stress value but also absorbed more energy than the ABC structure while ensuring the structural integrity.Thus,the CBA corrugated sandwich structure demonstrated better protection effects while ensuring structural integrity.By considering the material strain rate effect in the calculation of the transmission stress of the column under the underwater explosion shock wave load with the VUMAT subroutine,we observed a reduction in error values of 37.86%,44.53%,and 35.77%for the ABC,BBB,and CBA corrugated sandwich structures,respectively.Our results identified that the calculation model considering material strain rate effect can effectively reduce the calculation error of numerical simulation under the loading condition of underwater explosion shock wave.The laws and conclusions obtained in this paper have significant implications for the design and optimization of lightweight sandwich structures made of composite materials.