DTEM In Situ Mechanical Testing: Defects Motion at High Strain Rates

Defect nucleation and motion during high strain rate experiments has not been observed in situ at the nanoscale in metals. However, imaging dislocation and twin nucleation and propagation will enhance our understanding and ability to predict dynamic behavior and spall strength. In the experiments described here we use the Dynamic TEM at the Lawrence Livermore National Laboratory which is capable of recording pictures with a 20-ns time resolution in movie mode (a short multi-frames experiment), and we developed a new TEM holder capable of deforming samples at strain rates ranging from quasistatic to 10(4) s(-1). The holder uses two piezoelectric actuators that bend rapidly to load samples and TEM specimens with small gauge sections to obtain high strain rates. The TEM specimens and their narrow gauge sections are machined from bulk specimens using a femtosecond laser. The 50-mu m wide gauge sections are ion milled to create electron transparent areas. We present high strain rate in situ mechanical test results for copper specimens.