| The future information-based warfare will propose much higher requirements on the core indicators of mortars such as firing range,firing accuracy,maneuverability and so on.Increasing the initial projectile velocity is an effective measure to increase the range,however it increases the launching load.Lightweight is beneficial to improve the performance of the maneuverability of the mortar.For example,the use of the composite base plate can reduce the weight of the mortar effectively.All of these further aggravated the force and movement of the mortar.In addition,the new generation of mortars needs to adapt to various combat environments such as mountain jungles,alpine plateaus,islands,reefs,and cities.Besides,the nonlinear dynamics of the coupling between the mortar base plate and the soil is more complicated.These make the contradiction between the maneuverability and power more prominent.The existing design theories have been difficult to solve this contradiction.Therefore,it is urgent to research the nonlinear dynamics and overall performance optimization methods of the lightweight mortar.Therefore,aiming at the feasibility of using a composite base plate on mortars,the constitutive relationship between the base plate and soil,nonlinear dynamics of mortars,lightweight design of mortar base plate,multi-objective optimization of the composite base plate,special processing technology,and firing experiment of composite base plate are deeply studied.The main research contents are as follows.A simulation experiment and experiment method for the constitutive relationship of the soil under the mortar launching load is proposed.The nonlinear constitutive relationship of the soil compaction process under the condition of multiple firing is revealed.The gas impact load under the full charge and the reduced charge is firstly analyzed.Thus,the typical characteristics and key parameters of the launching load are obtained.The correspondence of height between the drop weight and the launching load of different charges is studied.A simulation experiment scheme using electromagnets to control the impact of the falling hammer on the base plate and soil is proposed.Aspherical force transmission rod to control the impact position of the falling hammer and a protective frame to ensure the safety of the experiment are designed.The sensing system and installation structure are designed,and the dynamic response parameter experiment system is constructed,followed by the experimental research.Based on the experimental data,the constitutive relationship function of the soil from uncompacted stage to compacted stage is established using piecewise fitting.The VUMAT subroutine in ABAQUS is used to develop a soil constitutive relationship model under the launching load,which provides a solid theoretical basis for the further coupling dynamics modeling and simulation.The finite element model of a mortar is established,which considers the coupling between the base plate and the soil,the base plate structure,the weld connection,and the transmission of launching load.According to the transmission path of the launching load,the mesh models of the projectile,barrel,breech ring,gun hoop,buffer,carriage,base plate,and soil are established.By introducing the 8-node iso-parametric plate unit of Reissner-Mindlin plate theory,the model of the transition zone of the base plate is established.The solid element method is used to solve the modeling problem of the weld connection of the ribs and plates.Moreover,Rigid Body,Spring,Contact,Tie are used to simulate the connection relationship between components.The influences of the mesh density on the accuracy and efficiency of the dynamic calculation are studied.The modal analysis of the mortar is carried out by the subspace method,and the modal experiment of the base plate is carried out using the excitation method.Good consistency of the main vibration modes and natural frequencies between the calculation and experiment are achieved,which verifies the correctness of the finite element model.The experimental soil constitutive relationship is incorporated into the mortarfinite element model.The numerical calculation results are compared with the experimental results and the calculation results using the traditional soil D-P constitutive relationship.The result shows that the established experimental soil constitutive relationship and the nonlinear finite element dynamics model of the mortar can characterize the launch dynamic response of the base plate more accurately than the traditional approach.A lightweight design method for the base plate with composite material is proposed.The Latin hypercube design method is applied to obtain the variable schemes of the base plate,and the polynomial linear regression model is applied to the parameter sensitivity analysis.A topology optimization model of continuous structures with minimal flexibility considering mass constraints and balance equation constraints is established.Based on the variable density method,topology optimization of the base plate is performed in the area with the smaller principal stress response.Point cloud data processing and feature extraction techniques are comprehensively applied to reconstruct the topology optimization results.The intermediate support rods are added to complete the titanium alloy skeleton structure design of the composite base plate.Carbon fiber T700 with epoxy resin 5228 is selected as the composite material of the base plate.The composite material ply design is studied in accordance with the fiber continuity criterion.The process parameters such as the numbers,the thickness,and the order of the plies are determined.To solve the angle optimization of the composite base plate,the genetic algorithm is used to search for the optimal order of the plies.A multi-object optimization method for the launch performance of the mortar composite base plate is proposed.To overcome the expensive finite element simulation,a 5-layer BP neural network is established to replace the original simulation model.Through the target aggregation method,the high-dimensional multi-objective optimization problem with different working conditions is overcame.The stability and strength of composite base plate launched on typical soil positions achieve a great improvement.According to the structural characteristics of the composite base plate,a hybrid connection process of the titanium alloy skeleton and the composite boards is proposed,and the firing experiment is carried out.The theoretical analysis and numerical simulation of the connection process between the titanium alloy skeleton and the composite boards are studied.A "bonding+ co-curing" hybrid connection process plan is proposed.The effect of the thickness of the glue layer on the strength of the bonded joint and the feasibility of co-curing process are studied by experiments.The rigidity and firing stability of the composite base plate structure are comprehensively evaluated by the modal experiment and the mortar field firing experiment.The composite base plate designed by the method proposed in this paper can meet main performance requirements,and its weight is more than 30% lower than that of the titanium alloy base plate,which has important reference value for the lightweight design of mortars. |
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