Protection Performance And Mechanism Of Polyurea Coated Structures Under Ballistic And Blast Loading Conditions

Polyurea coating is of great theoretical significance and engineering application prospect to armor lightweight protection of modern naval ships.In this paper,polyurea was used as enhanced protective coating of steel plate and box structures.Experiment investigation was conducted to evaluate ballistic and blast performances of polyurea coated structures.Based on experiment measurement results,effect of polyurea type and coating position on protection performance of polyurea coated structures was obtained as well as protection mechanism.Main works and conclusions are summarized as following:(1)To satisfy the requirement of ballistic and blast protections of armor structures in naval ship,experiment methods of polyurea coated structures were proposed with multiple loading and coating types,including high velocity impact,low velocity impact,external and internal explosive impact tests.Test results indicated that the optimal coating position was determined by given loading type and polyurea coating.Since strain rate was the dominant factor of polyurea coating in ballistic protection,performance enhancement effect of front coating was higher than that of back coating.However,wave impedance was the dominant factor of polyurea coating in blast protection,so performance enhancement effect of back coating was higher than that of front coating.(2)Under coating application condition of enhanced protections with the same weight and extra weight,multiple composite structures were designed with polyurea coating and steel substrate,including uncoated and coated structures with the same areal density and the same thickness substrate.The soft polyurea with low hardness and high elongation was used as protection coating.When uncoated and coated structures kept the same thickness substrate,soft coating improved ballistic and blast performances of coated structure.When uncoated and coated structures kept the same areal density,soft coating improved ballistic performance of coated structure;however,soft coating on front side could not improve blast performance of coated structure.Numerical simulation was adopted to verify results of polyurea coated structures subjected to low velocity impact.(3)To analyze the relationship of mechanical properties,protection performance and mechanism,the hard polyurea with high hardness and low elongation was first introduced as protection coating for comparison.Uncoated and coated structures with hard polyurea kept the same areal density in investigations.In ballistic tests,when polyurea coating was on front side,soft coating absorbed kinetic energy of projectile through impact-induced glass transition and lateral spreading;however,hard coating absorbed energy through large-scale brittle failure,ballistic performance improvement of which was higher than that of soft coating.When polyurea coating was on back side,pre-failure of hard coating did not contribute to energy absorption,ballistic performance improvement of which was lower than that of soft coating.In blast tests,when polyurea coating was on front side,blast performance improvement of hard coating was higher than that of soft coating.However,when polyurea coating was on back side,blast performance improvement of hard coating was lower than that of soft coating.(4)According to test results and mechanism analysis of polyurea coated structures,armor protection application technology of polyurea coating was formed.Protection performance and mechanism of polyurea coating mainly differed in loading type,material type and coating position.The major differences between projectile penetration and blast shock wave were loading strain rate and area.The major differences between soft coating and hard coating were rubber state response and glassy state response,respectively.Reasonable configuration of polyurea type,coating position and coating thickness could conditionally enhance ballistic and blast performances of polyurea coated structures simultaneously.The results and conclusions of polyurea coated structures protection performance and mechanism provide guidance for the relevant armor protection in engineering application.