Dynamic Behavior Of Defective Brittle Solids Inside Vehicles Under Varied Shock Modes

With the progress of science and technology and the improvement of demand for national security,the modern aerospace vehicles are always used with the conditions of high speed,high dynamic pressure and high overload.Under such a severe mechanical environment,the aerospace vehicles are vulnerable to shock loading,which causes damage,failure and even explosion.It is because that the aerospace vehicles contains a large number of brittle solids,such as energetic materials in missile warheads,thermal insulation ceramics on space shuttles,and organic glass portholes in fighters.In the process of producing and manufacturing,these brittle solids inevitably leave defects inside of them,such as pores,cracks and impurities.The brittle solids with defects are sensitive to shock loading.Under shock loadings,the dynamic behaviors of the defective brittle solids inside of the aerospace vehicles can directly affect the reliability,safety and battlefield survivability of the vehicles.Therefore,polymethyl methacrylate(PMMA),one of the typical brittle solids inside of the aerospace vehicles,was chosen as the study subject in this article.And the cylindrical defect was embedded in PMMA.Based on the mathematical model of the brittle solids under shock loading,synthesizing the professional knowledge and research methods in the field of material science,solid mechanics and shock wave physics,combining the experiments and finite element simulations,the dynamic response and the evolution of the cylindrical defect in PMMA were analyzed under the nanosecond laser loading and the split hopkinson pressure bar loading.We hope that the conclusions of this research can provide some help and reference for the study on the dynamic behavior of the defective brittle solids inside of the vehicles under varied shock loadings.Aiming to overcome the shortcomings of the existing research results,such as the lack of systematicness,the lack of comparisons between different research results,and the poor consistency between numerical results and experimental results,a comprehensive and systematic research work was carried out in this paper.The innovative contributions of this work can be summarized as:1)Based on two synchronous nanosecond lasers and an ICCD camera,the laser loading-detection experiment system with ultra high time resolution was established.The high definition images of the interaction process of the stress wave and the cylindrical defect in PMMA were obtained for the first time by using this experiment system.It plays a key role in the understanding for propagation of stress waves in vehicles under the shock loadings.2)The initiation and growth laws of different cracks induced by the cylindrical defect in PMMA were first obtained by the split Hopkinson pressure bar(SHPB)and the high-speed photography experiment system.It provides a significant reference for the study of failure process of defective brittle solids inside of the vehicles under shock loadings.3)By comparing the different dynamic responses of PMMA in the nanosecond laser loading experiments and the SHPB loading experiments,loading characteristics of the two loading modes were analyzed in detail.The reasons for different experimental phenomena caused by varied loading modes were summarized.It gives us a thorough understanding of the dynamic response characteristics of defective brittle solids inside of the vehicles under varied shock modes.4)The numerical simulation results are highly consistent with the experimental results.It was proved that the mathematical models established in second chapter are self-consistent for the dynamic behaviors of defective brittle solids inside of the vehicles under varied shock modes.A set of integrated mathematical models were provided for the following research.