Lewis Lea

Application of photon Doppler velocimetry to direct impact Hopkinson pressure bars

Direct impact Hopkinson pressure bar systems offer many potential advantages over split Hopkinson pressure bars, including access to higher strain rates, higher strains for equivalent striker velocity and system length, lower dispersion, and faster achievement of force equilibrium. Currently, these advantages are gained at the expense of all information about the striker impacted specimen face, preventing the experimental determination of force equilibrium, and requiring approximations to be made on the sample deformation history. In this paper, we discuss an experimental method and complementary data analysis for using photon Doppler velocimetry to measure surface velocities of the striker and output bars in a direct impact bar experiment, allowing similar data to be recorded as in a split bar system. We discuss extracting velocity and force measurements, and the precision of measurements. Results obtained using the technique are compared to equivalent split bar tests, showing improved stress measurements for the lowest and highest strains in fully dense metals, and improvement for all strains in slow and non-equilibrating materials.

Research data supporting "Characterisation of high rate plasticity in the uniaxial deformation of high purity copper at elevated temperatures"

In this paper, we perform compression experiments in a uni-axial stress geometry at rates between 10,000 and 100,000 /s, at temperatures between 300 and 600K.

Measurements presented in "Measuring Structural Evolution in the Dynamic Plasticity of FCC Metals"

Example data from PDV instrumented DIHB experiments allowing low strain jump tests at uniaxial strain rates above 10,000 /s. These measurements allow the separation of instantaneous and structural contributions to metal strengths in the 10,000 to 100,000 /s regime.