Research On Impact Force Measurement Based On Stress Wave

With the continuous expansion of strategic requirements for high-performance vehicles in various countries,hypersonic vehicles,with wide operation range,strong penetration resistance,and high flying speed,have become researching hotspots in the 21 st century aerospace field.The aerodynamic characteristics of hypersonic vehicles are very complicated under different flight attitudes and airspeed conditions.Therefore,at the beginning of design,aerodynamic load measurement tests should be performed on key parts of the vehicle to accurately obtain the forces and moments it receives in the high-speed flow field,which is of great significance for the safe and reliable operation of the vehicle.In this paper,a hypersonic vehicle model is taken as the research object.A high supersonic aerodynamic measurement method based on the stress wave theory is proposed in view of the difficulty of short stable running time,small space and complex environment in hypersonic wind tunnel,which provides an effective reference for developing modern hypersonic aerodynamics test.Initially,the wave equation of one-dimensional stress wave is deduced based on the basic theory of stress wave,and the compatible equation of stress wave in one-dimensional bar with equal section is obtained by using the characteristic line method.According to Newton's third law,continuous conditions and compatible equations,the reflection and transmission laws of stress waves at different media surfaces and cross-sections are obtained.And then,the microelement model of variable cross-section bar was also established.The compatibility equation of stress wave propagation in one-dimensional rod with variable cross-section is derived by using the method of indefinite line.As is seen in the situation,a numerical simulation program for stress wave propagation in variable cross-section one-dimensional bars was written in LabVIEW by using finite difference theory,moreover,its correctness and reliability were verified.Additionally,the effects of the different connection modes between the hypersonic model and the stress rod on the propagation of the stress wave and the purity of the axial stress wave are analyzed,and the connection model between the vehicle model and the stress rod is also determined.Based on the engineering experience and the dispersion effect of stress waves,the structural size of the model and the stress bar are designed,and the structure of the stress bar is optimized utilizing the knowledge of material mechanics.A cylindrical equivalent model was established.Furthermore,the materials of model and stress bar were confirmed based on the reflection and transmission law of stress wave and the assumptions of rigid body model.From the aspects of sensitivity,precision and anti-interference,semiconductor strain gages were selected as the sensitive components of the stress wave balance,and their arrangement forms were determined.The overall design of the stress wave balance is completed.Finally,according to the characteristics of the hypersonic aerodynamic load and the system characteristics of the stress wave balance,the mathematical model of the stress wave balance is established and the overall scheme of dynamic calibration of the balance is determined.Three schemes for obtaining the impulse response of balance are proposed: percussion method,deconvolution method and step method,what's more,the corresponding theoretical formulas are derived.Aiming at some defects of the frequency domain deconvolution method,a new method of time domain deconvolution load identification is proposed and verified by numerical simulation program.A stress wave balance load identification experiment system was built.The experimental results show that the impulse responses obtained by the three schemes can meet the requirements of the load identification experiment.The step method has the best recognition effect and the error is only 3.17%.