Beyond Hopkinson's bar

Area of Science:

• Materials Science
• Mechanical Engineering
• Experimental Mechanics

Background:

• Traditional high strain rate testing methods, like the split Hopkinson pressure bar, are limited.
• Recent advancements in full-field deformation measurement techniques offer new possibilities for material characterization.

Purpose of the Study:

• To introduce and validate a new inertial impact test for high strain rate material model identification.
• To demonstrate the capability of full-field measurements combined with numerical methods for improved material parameter identification.

Main Methods:

• An inertial impact test was developed for high strain rate (up to 3000 s⁻¹) material testing.
• Quasi-isotropic composite specimens were instrumented with a grid for high-speed imaging (5 Mfps and 1 Mfps).
• The virtual fields method (VFM) was employed to process deformation, strain, and acceleration fields for parameter identification.

Main Results:

• The new test successfully generated stress-strain curves at high strain rates.
• Inertial effects were effectively exploited to enhance material parameter identification.
• Unprecedented quality in identifying stiffness parameters was achieved using the VFM.

Conclusions:

• The developed inertial impact test provides a powerful new tool for high strain rate material characterization.
• Combining advanced imaging with the VFM offers a superior approach to identifying material models under dynamic loading.
• This methodology enables more accurate and reliable material property data for engineering applications.