| Nowadays,with the frequent military operations and the rising demand for dangerous chemicals,the number of victims caused by explosions is increasing,and the research on biological trauma is deepening.According to the data analysis in recent years,traumatic brain injury caused by blast wave has become the main threat of death.However,the current protective equipment mainly focuses on the ballistic penetration design brought by the explosion moment,and there is a lack of targeted design for shock wave protection and multi-effectiveness coupling equipment research.Therefore,how to complete the multi-damage element protection for the explosion scene including shock wave protection is the focus of the current research field.Based on the current research on multi-effect coupling materials and structures at home and abroad,based on the engineering application background of multi-damage source protection,and based on the excellent impact resistance and mechanical properties of polyurea materials,this paper carried out a comprehensive integrated experimental study from materials to structures to equipment.Through the design of new micro and nano inclusion composite PU,the influences of different kinds of micro and nano particles and different contents of the same kind of micro and nano particles on thermal properties,mechanical properties in the wide strain rate range and shock protection properties of the matrix materials were studied.The test method of material shock protection was proposed,and the bionic silica gel test system was developed.The effects of boundary and diffraction coupling in the testing of protective materials are excluded.A shock tube loading system was used to test the protective properties of materials under shock waves of different intensities.The quantization process of shock wave pressure and acceleration attenuation in biomimetic materials was obtained.On the basis of this research,a full-size shock wave protection test model of human head was developed,and the pressure and acceleration parameters of several key positions of head were measured.Finally,based on the performance test results of modified polyurea material and combined with the current requirements for lightweight and efficient helmet equipment,a new material multi-effectiveness coupling protective helmet was developed to realize efficient protection against shock wave and thermal radiation.In the thermal performance research test,TG,DSC,thermal conductivity and ultimate oxygen index were used to complete the flame retardant and heat insulation characteristics of the designed two modified polyurea materials.The results showed that the content ratio of SiO2 particles had little effect on the thermal stability of the matrix material PU,and that halloysite particles could improve the thermal stability of PU slightly.And the thermal stability increases gradually with the increase of halloysite particle content.The pyrolysis temperature of PU and its modified material is the same,both start at around 280℃,reach the optimal decomposition temperature at 400℃,and basically complete pyrolysis at close to 600℃.Compared with PU material,the thermal conductivity of PU-SiO2 increased by 13.2%,and that of PU-HP decreased by 1 1.1%,and gradually decreased with the increase of halloysite particle content.The ultimate oxygen index of the two types of modified materials increased by 2.7%and 2.5%respectively compared with PU material.The experimental results show that the thermal properties of the matrix materials are improved by SiO2 and halloysite particles,and halloysite nanoparticles are better than SiO2 particles.In the test of mechanical properties,MTS universal testing machine and Hopkinson bar test equipment,combined with DIC measurement technology,were used to complete the analysis of the stress-strain characteristics of modified polyurea material at a wide strain rate.In the quasi-static and low strain rate tensile tests,the addition of nano particles significantly changes the stress-strain characteristics,the dense section of the material disappears,the slope of the high elastic section increases,the yield stress and failure gradually decrease,and the yield point is gradually invisible.In the test of quasi-static and low strain rate compression,compared with PU material,the maximum stress does not change significantly in the study strain range,and the yield stress gradually decreases,and there is no dense section.The reduction range of SiO2 modified material is greater than that of halloysite particle modified material.In the compression test at high strain rate,the strain hardening properties of modified polyurea are enhanced,and the peak stress increases with the increase of particle content.In the shock wave protection test,the influence of the thickness of the protective material,the proportion of particle inclusion and the modification method on the shock wave protection is compared.On the basis of this,a modified multi-efficacy coupling protective helmet was designed and manufactured.The peak overpressure and peak acceleration of frontal,posterior and apex positions were taken as reference indexes,and combined with the study on the thermodynamic and mechanical properties of materials,the demonstration of shock wave protection performance of the protective helmet was completed.In the material performance test,when the thickness of PU protective material reaches 30 mm,the peak overpressure decreases by about 32.03%,the peak acceleration decreases by about 51.51%,and there is no obvious change in the rising edge time.Within 12 mm thickness of the protective material,the thickness change has a great impact on the overpressure peak,which decreases by about 28.3%.Within the range of 12 mm to 30 mm,the peak overpressure only decreases by 3.94%.In the study of two modified polyurea,it is found that the protection effect of shock wave increases with the increase of particle content.Compared with PU material,the peak overpressure of PU-SiO2 and PU-HP decreases by 8.71%and 16.77%respectively when the thickness of PU-SiO2 and the highest proportion of inclusion are 12 mm.However,the peak acceleration of the two materials did not decrease significantly.It is believed that the attenuation of peak acceleration is closely related to the thickness of the protective layer,and the particle content and type have little influence on it.The results of brain protection experiment showed that,compared with the naked head without protection,the protective effect of the two modified materials on the frontal and cranial roof test points was good,but the protective effect on the posterior skull was not obvious.The attenuation of the frontal pressure was reduced by 44.51%and 51.74%,respectively,and the attenuation of the peak acceleration was 55.80%and 57.80%,respectively.After helmet protection,the peak overpressure and peak acceleration of cranial pressure measurement points decreased to less than 40.0 g.The results show that the helmet with the new material has a good effect on shock wave protection,and the modification of halloysite particles has a better effect on shock wave protection than the modification of SiO2 particles. |
