Experimental Research For The Effect Of Strain-rate History On The Constitutive Relation Of Materials And Numerical Analysis On The SHB System

At the beginning of this thesis, a brief summary of the researching history , present situation and development about Hopkinson bar technique is presented and various aspects in researching the influence of strain—rate history on material constitutive relation under high strain—rate is emphatically introduced, A concise summary of development of signal recording techniques in Hopkinson bar experiment is also presented. Based on this, using high frequency response amplifier, the union of transient data A / D real time collection and computer analysis was realized with advantages of cutting down the intermediate links, simplify trigging and more convenient operation. Soft wares for data automatically processing has developed, too. In addition, effective investigation on how to overcome the noise—strong condition in Hopkinson test is conducted.Employing the improved split Hopkinson tension bar system, the constitutive relations of shape memory alloy, prestressed reinforcement and high strength aluminum under high strain—rate were experimentally studied, and it shows that except the ductile rising of shape memory alloy, all three materials emerging the behavior of strength rising and ductile descending under high strain—rate. The influence of high strain-rate history on constitutive relations of shape memory alloy and prestressed reinforcement under high strain—rate is also firstly investigated using same instrument, and results indicate that high strain-rate history will strengthen materials.Employing the Hopkinson torsion-tension combination bar system, the constitutive relations of soft aluminum under torsion-tension combined high strain—rate was obtained, The constitutive relations of Monel alloy under Dual—direction shearing high strain—rate was also investigated after special modification of above apparatus.In the numerical analysis, the formulae of dynamic response for arbitrary position in Hopkinson Bar system under arbitrary impact pulse were derived according one—dimensional(1-D) stress wave theory, and it is able to provide reference for test. Then the frequency dispersion in tension or pressure Hopkinson bar is studied using fast Fourier transform(FFT) method and dynamic finite element method(DFEM). Because of the influence of...