Study of the axial density/impedance gradient composite long rod hypervelocity penetration into a four-layer Q345 target

Based on the dynamic shock response of the material and structure,the hypervelocity impact processes and mechanisms of long composite rods with axial density/impedance gradients penetration into fourlayer targets were studied through experiments and numerical simulation methods.The propagation law of the shock waves,together with the structural responses of the projectiles and targets,the formation and evolution of the fragment groups formed during the processes and their distributions were described.The damage of each target plate was quantitatively analysed by comparing the results of the experiment and numerical simulation.The results showed that the axial density/impedance gradient projectiles could decrease the impact pressure to a certain extent,and the degree of damage to the target plate decreased layer by layer when the head density/impedance of the projectile was high.When the head density/impedance of the projectile was low,the degree of target damage first increased layer by layer until the projectile was completely eroded and then it decreased.The results can provide a reference for the design and application of long rods with axial composite structure for velocities ranging from 6 to 10 Ma or greater.

Gradient carbonyl-iron/carbon-fiber reinforced composite metamaterial for ultra-broadband electromagnetic wave absorption by multi-scale integrated design

The demand of high-end electromagnetic wave absorbing materials puts forward higher requirements on comprehensive performances of small thickness,lightweight,broadband,and strong absorption.Herein,a novel multi-layer stepped metamaterial absorber with gradient electromagnetic properties is proposed.The complex permittivity and permeability of each layer are tailored via the proportion of carbonyliron and carbon-fiber dispersing into the epoxy resin.The proposed metamaterial is further optimized via adjusting the electromagnetic parameters and geometric sizes of each layer.Comparing with the four-layer composite with gradient electromagnetic properties which could only realize reflection loss(RL)of less than−6 dB in 2.0-40 GHz,the optimized stepped metamaterial with the same thickness and electromagnetic properties realizes less than−10 dB in the relevant frequency range.Additionally,the RL of less than−15 dB is achieved in the frequency range of 11.2-21.4 GHz and 28.5-40 GHz.The multiple electromagnetic wave absorption mechanism is discussed based on the experimental and simulation results,which is believed to be attributed to the synergy effect induced by multi-scale structures of the metamaterial.Therefore,combining multi-layer structures and periodic stepped structures into a novel gradient absorbing metamaterial would give new insights into designing microwave absorption devices for broadband electromagnetic protections.

Gradient honeycomb metastructure with broadband microwave absorption and effective mechanical resistance

Multifunctional metastructure integrated broadband microwave absorption and effective mechanical resistance has attracted much attention.However,multifunctional performance is limited by the lack of theoretical approaches to integrated design.Herein,a multi-layer impedance gradient honeycomb(MIGH)was designed through theoretical analysis and simulation calculation,and fabricated using 3D printing technique.A theoretical calculation strategy for impedance gradient structure was established based on the electromagnetic parameter equivalent method and the multi-layer finite iterative method.The impedance of MIGH was analyzed by the theoretical calculation strategy to resolve the broadband absorption.Intrinsic loss mechanism of matrix materials and distributions of electric fields,magnetic fields and power loss were analyzed to investigate the absorption mechanism.Experimental results indicated that a 15 mm thick designed metastructure can achieve the absorption more than 88.9%in the frequency range of 2-18 GHz.Moreover,equivalent mechanical parameters of MIGH was calculated by integral method according to the Y-shaped model.Finite Element analysis of stress distributions were carried out to predict the deformation behavior.Mechanical tests demonstrate that MIGH achieved the compression modulus of 22.89 MPa and flexure modulus of 17.05 MPa.The integration of broadband electromagnetic absorption and effective mechanical resistance was achieved by the proposed design principle and fabrication methodology.