| With the advancement of science,research on protective structures has been constantly innovated.On the one hand,the emergence of new materials has promoted the development of modern protective structures towards the direction of lighter,stronger and tougher.On the other hand,the development of various terrorist incidents and new types of weapons also raises the demands on the safety of the protective structures.Ultra high molecular weight polyethylene(UHMWPE)fiber reinforced composites are widely used in various impact resistant structures.Bulletproof vehicles,armored vehicles,ships and aircrafts equipped with UHMWPE protective structures can defend high-speed impacts from bullets and fragments;UHMWPE helmets,body armors and anti-blast clothing on modern soldiers and police officers can protect life and safety in warfare and hazardous environments.With the development of the national defense industry,the safety protection of special vehicles and personnel has become particularly import ant.The protection mechanism of UHMWPE material and composite armors against impact loads is complex.It is necessary to carry out in-depth research on the dynamic mechanical behavior of the material under impact loads,on the failure mechanism of composi te structures and on the interactions between various materials.This paper focuses on the performance of UHMWPE and composite armors under high-speed impact loads.The dynamic behavior of composite armors is tested by dynamic impact tests to study the interaction and failure mechanism between different materials.The transient responses of protective structures during impacts are analyzed by numerical simulations.To study the secondary continuous impact problem,the surface restraint effect,the uncertainty and reliability,functionally graded multilayer structures,the bionic structures and their applications against continuous impacts for UHMWPE and composite armors,the paper includes the following aspects:(1)The continuous twice impacts problem of bolted UHMWPE laminates is studied.High-speed oblique penetration and secondary debris impact test on the bolted UHMWPE laminate was carried out by a first-stage gas gun.A self-made speed probe was used to capture the photographs of the projectile with a hi gh-speed camera.The experimental results show that the impact response of the bolted UHMWPE sheet includes the bulging stage and the bolt hole bearing deformation stage.When the projectile has a certain positional offset and inclination angle,the defor mation response of the four bolt holes is different.After the projectile penetrates the target plate,the deformation response of the bolt hole is sensitive to the secondary impact parameter.Based on the results of the first penetration test,a numerical simulation model of bolted ultrahigh molecular weight polyethylene sheets is established by finite element method.Then the deformation response of the bolt holes was analyzed.The method of secondary non-penetrating impact parameter identification is studyed.(2)The surface confinement effect of segemented silicon carbide ceramics/UHMWPE composite armor is studied.The ballistic performances of composite armors under different face plate material of woven fabric,UHMWPE laminates,6061-T6 aluminum alloy and TC4 titanium alloy were tested by bullet test.The finite element model of composite armor agaisnt impacts is established,and the accuracy of the numerical model is verified by experiments.The effect of constraints on the anti-bullet properties of segemented ceramic armors is discussed.The ballistic performance of the segemented ceramic armor exhibits non-uniformity depending on the location of the strike.The segemented ceramic armor adhesive interfaces have significant boundary effects.The ceramic tile with the free surfaces undergoes interface defeat earlier under the impact of the bullet,resulting in a shorter time of the "stay" phase before the bullet invades the ceramic block.The radial constraint helps to increase the ballistic performance on the edges of the ceramic tile.The ballistic performances of segemented ceramics armor show non-uniformity with different impact positions and significant boundary effect.The residual velocity of the bullet is higher when the striking position is closer to the center of the ceramic tile than to the bonding interface.The surface constraints of different face plate materials at the same areal density are different,and the ballistic performance near the adhesive interfaces increases as the surface constraint of the face plate increases.(3)The reliability of SiC ceramic/UHMWPE composite armor is studied.The problem of the anti-ballistic uncertainty of composite armor is studied through both the bullet tests and the simulations.In the state of critical penetration,the SiC ceramic/UHMWPE composite armor was tested.At the initial velocity of the projectiles of 776 m/s and 791 m/s,the projectile was completely penetrated and partially penetrated due to the uncertainty of material and adhesive properties.In addition,it was observed in the test that the bulging deformation of UHMWPE back plate exhibited an opposite tendency to the minimum thickness.The finite element model of ceramic/UHMWPE composite armor under bullet impact was established and the accuracy of the model was verified by experiments.In order to evaluate the uncertainty of the material parameters,a penetrating state function including the impulse response was constructed,and the sensitivity analysis was performed on the uncertain material parameters.Then,the impact reliability of the composite armor is studied.Finally,the contradiction between the value of the penetration state function and the deformation of the backing plate is adjusted by the adhesive strengths.A reliability constrained optimization problem is established to achieve minimum deformation of the UHMWPE back plate without reducing the reliability.(4)Based on the inspiration of biogradient structure and multi-layer structure,the impact behavior of functionally graded multilayer structures is studied.Taking the steel-rubber multi-layer structure as an example,the influence of multi-layer parameters on anti-penetration and anti-blast performance was analyzed by numerical simulation.The results show that the mechanical properties of a multilayer structure composed of two materials are related to the gradient of the multilayer thickness.The effects of thickness and position on the anti-penetration and anti-blast performance are studied by numerical model.The multi-layer structure with obvious gradient effect is obtained by optimization with zero gradient structure.The results show that the thickness of the steel plate from thick to thin and the rubber from thin to thick are beneficial to improve the impact toughness of the multilayer structure.The thickness of the steel plate from thin to thick and the gradient of the rubber from thin to thick facilitate the energy absorption of the multilayer structure.Multilayer structure with the thickness of the steel plate from thick to thin to thick,the rubber from thin to thick can meet the requirements of anti-penetration and anti-blast performance.(5)Based on the protective mechanism of multi-layer structure of scale-footed gastropods shell,a bionic helmet structure was proposed,in which the proportion of material characteristics and size was close to the biological structure.The finite element model of the bionic helmet-gelatin anti-bullet impact and anti-explosion was established.The deformation,damage and stress superposit ion of helmet under single bullet impact,single explosion impact,continuous bullet impact and martyr explosion are studied.The head damage under explosion impact is evaluated by the penetration depth and the peak stress of the gelatin ball.The optimization of bionic helmet against multiple bullet impact and sympathetic detonation under different mass constraints is studied.The optimized bionic structure can resist multiple continuous bullet impacts and sympathetic detonation at the same time. |
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