Impact Performance Analysis And Optimal Design Of Metallic Multi-layered Corrugated Core Sandwich Panels

Sandwich structures are generally composed of two high-strength thin face sheets and a lightweight thick core layer.It endows the kinds of structures with some excellent mechanical performance,such as high specific strength,high specific stiffness,vibration and noise reduction and favorable impact-energy absorption.This is why sandwich structures are widely used in the fields of aerospace,high-speed trains and packaging,where lightweight and shock-mitigation are demanding.In recent years,attention has been paid to the employment of sandwich structures in ships.Single-layered corrugated core sandwich structures have become one of the earliest sandwich structures applied as ship structures,owing to its simple construction,easy-to-process and-maintenance.It leads to improvement in lightweight and impact protection performance of ship structures.Compared with single-layered corrugated core sandwich structures,multi-layered corrugated core sandwich structures are more designable,which makes themselves have a wide potential to be explored.Therefore,this thesis takes the multi-layered corrugated core sandwich panels as the research object.The following researches are carried out with respect to the impact performance and optimization of the sandwich panels:(1)Fabrication of metallic multi-layered corrugated core sandwich panels and the study of its out-of-plane compression behavior.According to the structural characteristics of multi-layered corrugated core sandwich panels,a brazing technology is explored to reduce its processing deformation and increase the connection strength.Six sandwich panels are designed based on the principle of equivalent areal density and total height.Quasi-static and dynamic compression experiments are conducted to investigate the effects of the stacked orientation,layer number and topology configuration of the multi-layered corrugated core on the compression behavior of the sandwich panels.Simulation model is established to further study the mechanical properties of the sandwich panels under high-speed compression.Meanwhile,the influence of corrugated core gradient on the high-speed compression characteristics of the sandwich panels is explored.The results show that stacking the corrugated core crossly and changing the core layer number would enhance the compression-resistance of the sandwich panels.Transforming the topology configuration of corrugated core from trapezoid to rectangular or reentrant trapezoid would decrease the peak stress of compression curve.The sandwich panels with multi-layered reentrant corrugated core exhibits the weakest out-of-plane compression resistance,while the one with multi-layered rectangular corrugated core has greater specific energy absorption under quasi-static compression owing to its larger densification strain,and its compression resistance is improved because of the deformation transition under dynamic compression.Under high-speed compression,the design of wall-thickness gradient enhances the cushion effect on the back face through triggering the overall buckling or reverse bending mechanism of the multi-layered corrugated core.However,the design of corrugation-angle gradient makes the core layers easier to contact with each other,which fails to improve the impact-resistance of the sandwich panels.(2)Study on the dynamic responses of metallic multi-layered corrugated core sandwich panels subjected to underwater shock loading.Sixteen sandwich panels are designed and manufactured.Experiments are conducted to identify the deformation/failure modes of the sandwich panels subjected to underwater shock loading by using a self-design explosion device.The performances of the sandwich panels with multi-layered corrugated core and the ones with air core layer are analyzed and compared under different impulse intensities.Moreover,effort is made to investigate the effects of the stacked orientation,layer number,gradation and topology configuration of the multi-layered corrugated core on the deformation/failure modes and performances of the sandwich panels under a specific impulse intensity.A fully fluid-structure coupling finite element model is established to probe into some physical characteristics which are difficult to measure during the experiments,including the process of explosive detonation and sandwich panel deformation,the pressure distribution of fluid-structure surface,the velocity response characteristics of the center points of the face sheets and the plastic energy dissipation of the structure components.The results show that within the scope of the study,the multi-layered corrugated core sandwich panels have a lower coupling strength than the air core sandwich panels with the same areal density,but the protection capacity of the latter performs is better than the former.The plastic deformation of the back faces can be reduced by changing the thickness gradient and the configuration of the corrugated core,while changing the stacked orientation,the layer number and the angle gradient of the multi-layered corrugated core are not beneficial for improving the protection capacity of the sandwich panels.The overall energy absorption of the sandwich panel increases gradually,and the multi-layered corrugated core contributes more than 70%of the energy dissipation.Changing the structural parameters of multi-layered corrugated core has no significant effect on the total plastic energy dissipated by the sandwich panels with multi-layered corrugated core,but it can alter the energy absorption distribution of their components.(3)Multi-fidelity surrogate model construction and multi-objective optimization design of the protection performance of metallic sandwich panels with graded corrugated core subjected to underwater shock loading.The established finite element model considering fully fluid-structure interaction is regarded as the high-fidelity model.Two different ways of enlarge mesh size and removing fluid mesh are respectively employed to produce low-fidelity finite element models with higher computational efficiency.An appropriate low-fidelity result is chosen to build the Co-Kriging surrogate model after comparing the trend information of the results of the two low-fidelity models,so as to fit the highly nonlinear relationship between design variables and response values.Based on the surrogate model,multivariate analyses are conducted to investigate the influence of the design variables on the response value.Thereafter,multi-objective optimization design is performed to improve the comprehensive protection performance of the multi-layered corrugated core sandwich panels with the help of a modified non dominated sorting genetic algorithm(NSGA-II).The results show that the low-fidelity numerical model with coarse mesh is more suitable for constructing the multi-fidelity surrogate model through combining with the high-fidelity model,which can realize the fast and accurate prediction of the dynamic response of graded corrugated core sandwich panels subjected to underwater shock loading.Compared with the baseline sandwich panel,the optimized design scheme can significantly improve one of the evaluation indexes by about 30%without degrading the other indexes.The research work conducted by the thesis would provide some valuable reference for the application of sandwich panels with multi-layered corrugated core in the field of marine engineering.