Design, Set Up and testing of Split Hopkinson Bar to Evaluate Flow Stress in Copper at High Strain

This paper presents a new method to investigate plastic deformation of FCC metals in high strain rates. Experimental set up includes two stages gas gun, spherical projectile and target assembly. Target assembly includes front plate, two pressure bars, FCC specimen, three frames and rigid holder. The set-up is carried out according to the following a spherical projectile, accelerated to high velocity with a two-stage gas gun, impacts and penetrates in a front plate attached to the front of input bar and results in propagation of the plane waves in the input and output bars and the specimen (FCC metal). Evaluating of effective parameters such as stress, strain and strain in the specimen rate are conducted by installing strain gauges in the pressure bars. The experimental results are compared with 3D finite element simulation. Also, the effect of projectile velocity, specimen thickness and front plate thickness are investigated. It is concluded that decreasing specimen thickness and appropriate calibration of gas gun to shot projectile to the center of front plate, are appropriate ways to achieve strain rates more than 104 s-1 in the specimen that is difficult to achieve such strain rates in conventional split Hopkinson pressure bar.