Investigation On The Dynamic Response And Failure Mechanism Of Layered Composite Structure Under Blast And Impact Loading

Composite materials have excellent properties such as light weight,high specific strength,anti-fatigue,corrosion resistance,invisibility and designability.And the introduction of core materials in composite sandwich structures highlights the lightweight advantages of composite materials.Therefore,a large number of applications of composite laminated and sandwich structures can be seen in aerospace,ocean engineering,traffic engineering and other important fields.Composite structures are vulnerable to out of plane impact,resulting in damage or even structural failure.For composite sandwich structures,typical impact damage modes,such as face-sheet damage initiation and propagation,core collapse,debonding between the first two,are induced as well as coupled with each other,resulting in the destruction of the overall panel.In many loading conditions,the impact of dropped objects and underwater explosion shock wave,as the current focuses,has attracted more and more attention from researchers.Based on the experimental,analytical and numerical study of composite laminated and sandwich structures under low-velocity impact and underwater explosion loading,this paper brings insight into the dynamic response process,damage characteristics and failure mechanism of composite structures under these two loading forms.And establishes theoretical model of composite sandwich panel under each loading condition to find out how to improve the impact resistance through carrying out parametric analysis.The main results are as follows:(1)Analysis of delamination propagation mechanism and prediction method for composite laminates.The drop weight tests of composite laminates under different impact energies were carried out,and the delamination was detected by ultrasonic C-scan.Based on the dynamic response and the delamination results of the tests,the numerical model was verified.And the formation process of delamination was further analyzed.By studying the distribution characteristics of delamination both in-plane and out of plane directions with energy considered,supplementing with the mechanism analysis,a feasible delamination prediction method was proposed,and the rule of delamination propagation was expounded.(2)Dynamic failure mechanism analysis of composite sandwich panels during low velocity impact penetration.Drop weight impact test was carried out on the composite sandwich panel,and the specimen was then cut to detect the cross-sectional failure.Based on the dynamic response process and final failure characteristics obtained from the tests,the numerical model considering four modes(fiber and matrix under tension and compression)of composite damage evolution until failure was verified.The response stages were discussed and divided,accompanied by failure mechanism analysis.Through the numerical analysis of asymmetric composite sandwich panels with different stacking sequence,the parametric studies were performed to improve the impact resistance.The structure optimization was discussed and pointed out combined with the failure mechanism analysis.(3)A theoretical analysis model which can accurately predict the dynamic response and failure process of composite sandwich panels under low-velocity impact penetration is developed.Based on the experimental and numerical studies of drop weight impact of composite sandwich panel,five-stage response modes were proposed.Through analyzing the deformation process,system potential energies of each stage were analyzed by using Hamilton’s principle.Shape functions which can approximately reflect the response characteristics in each stage were assumed;and the critical criteria of each stage were defined based on the deformation expressions proposed.The criteria of different failure characteristics during impact penetration of sandwich panels are established;the energy absorption and dissipation behaviors,including friction between projectile and the panel,crush and shear failure of core materials,were discussed systematically.Through applying the theoretical model,further parametric studies on core strength and face-sheet stacking sequence revealed how to perfect the composite sandwich structure for the best impact penetration resistance.(4)Study on dynamic response process and failure characteristics of composite laminates and sandwich panels under underwater blast loading.The fluid-structure interaction numerical models of composite laminates and composite foam sandwich panels under underwater shock waves loading were established.The models considered the strain rate effect and various failure criteria of each material;calculation results of each model were in good agreement with the test results referred.The effects of underwater shock waves with different peak pressure and attenuation time on the dynamic response and failure characteristics of composite laminates and sandwich panels were studied systematically.Also,the dynamic failure mechanism was analyzed in depth.Furthermore,the influence of fluid structure interaction on dynamic failure process was discussed combined with failure modes and failure map summarized.(5)Based on the one-dimensional analysis theory of fluid structure interaction,the theoretical analysis model of composite sandwich structure subjected to underwater planar shock waves loading is established.Two analytical methods used to solve the response process,either based on equation of motion or Hamilton’s principle were established respectively;the dynamic response process and cavitation characteristics obtained from the two theoretical analyses were compared with the numerical results,which revealed the limitations of the former solution and proved the good consistency with the latter theory and the simulation results.The effects of core strength and face-sheet stiffness on the response and energy absorption of composite sandwich structures under different underwater explosion shock waves were studied systematically.This paper aims at the dynamic response and failure behavior of composite sandwich structures under low-velocity impact and underwater blast loading,carries out systematic experiments,numerical simulation and theoretical analysis to study the failure mechanism of composite sandwich structures under different impact loads.The findings of the research lay a foundation for the application of composite sandwich structures in aircraft,ships and other practical engineering...