Anti-blast Analysis And Design Of Graded Cellular Sacrificial Cladding

Graded cellular metals have attracted considerable research interest due to their designable characteristic.Introducing a density gradient is expected to improve the capacity of blast mitigation and impact resistance,which shows a wide application prospect in engineering protection and defense industries.Cellular sacrificial cladding is a kind of sandwich structures with cellular cores,in which crushable cellular materials can absorb massive explosive/impact energy.Recently,in the study of the impact resistance of cellular sacrificial cladding,a simple rigid-perfectly plastic-locking(R-PP-L)model is adopted,while the approximation is different from the actual stress-strain curve.However,whether the graded cellular materials provide superior performance of energy absorption and compaction wave attenuation has sparked some debate.In this paper,the blast mitigation behavior of density-graded cellular sacrificial cladding is investigated by using a nonlinear plastic shock model and cell-based finite element models.The dominant factor affecting the critical thickness is obtained by dimensional analysis.Besides,in order to reduce the core thickness effectively,a theoretical approach involved that a reflected wave induces a local secondary compaction is developed to improve the utilization of cellular materials,while the design of critical thickness proves to be conservative.Based on a rate-independent,rigid-plastic hardening(R-PH)idealization for more accurate prediction,a theoretical approach is employed to analyze the propagation of shock wave in linear density distributed cellular rods subjected to exponential blast impulse.The critical thickness,the minimum thickness of the core layer when the explosion energy is fully absorbed,is one of the main criteria in the design of cellular sacrificial cladding.The influences of the intensity of blast load,the cover mass and the density gradient parameter of the cellular material on the critical thickness are investigated.A design guide of density-gradient is provided which considers the critical thickness of the cellular core as well as the peak stress at the support end.The results indicate that the same intensity of explosive energy absorption,the positive gradient sacrificial cladding requires thinner core than the negative one.By increasing the gradient parameter value,the positive gradient can effectively reduce the thickness of the core layer,a higher stress level in the support brought in yet.To achieve the minimum stress peak,uniform and negative gradient density is optimal.Furthermore,a design guide for the negative gradient cellular sacrificial cladding under a particular enduring limit of stress at the support end is provided.Dimension analysis is employed to study the relationship between the dimensionless critical thickness and three dimensionless parameters,and an empirical expression is obtained by the controlling variables method,which can be used to meet the requirement of accuracy.It is revealed that the square root of the impact enhancement factor S01/2 is the dominant factor affecting the dimensionless critical thickness.The influence of density gradient parameter on thickness is relatively small and then a first order approximation is given as well.The compaction strain of the cellular metal material is dependent of impact velocity under dynamic loading.As a consequence,the thickness of core layer designed in the perspective of wave attenuation proves to be conservative.The propagation of the reflected wave in the positive gradient sacrificial cladding is studied.A numerical solution of the dynamic response is carried out.Results reveal that the thickness of the core layer can be further shortened so that the strain behind the reflected wave increase from 0.4 to near 0.7 roughly,when the stress peak at the support end does not exceed the enduring limit.Ultimately,the validity of the anti-blast analysis of graded cellular sacrificial cladding based on the nonlinear plastic shock model is verified by using cell-based finite element models,where a 2D Voronoi technique is applied.