High Strain Rate Forming, Testing and Processing

National Laboratory: 
Pacific Northwest National Laboratory
Characterization Class: 
Mechanical Behavior of Materials
Processing/Manufacturing Class: 
Shaping and forming
Description: 

This capability at Pacific Northwest National Laboratory comprises sheet metal forming, tension/compression testing, and solid-state joining, all performed at high strain rates. These tests are instrumented with high-speed cameras and combined with digital image correlation (DIC) to determine the deformation history. Forming is done using either electrohydraulic or electromagnetic methods, so the sheet metal is deformed into dome shapes (with or without a die) and the formability at high strain rates is determined. Solid-state joining of metals is achieved by accelerating one piece toward the other and bonding them via high-velocity impact. To determine stress-strain behavior as a function of strain rate, high-rate tension/compression testing is done on a specially configured load frame.

Capability Bounds: 

All tests are done nominally at room temperature and can be imaged at up to 750,000 frames/second and post-processed with DIC software. Metal forming uses 11-in. × 11-in. sheets (up to 2-mm thick), and strain rates during forming can exceed 10,000/s. Solid-state joining typically uses thin foils and sheets. Strain rates for tension/compression tests range from 1– ~100s/s. Materials tested include aluminum (Al) alloys, magnesium (Mg) alloys, steels, and zirconium (Zr). Other materials also can be tested, depending on the application.

Unique Aspects: 

PNNL offers subject matter expertise with high-rate sheet metal forming and intermediate strain-rate testing capabilities, especially for measurements at microsecond time resolution. High-rate forming complements traditional limiting dome height (LDH) tests, while high-rate tension/compression tests are relevant to automotive crash rates and supplement quasi-static and Hopkinson bar tests.

Availability: 

Facility use is coordinated with the capability expert and via collaborative funding proposals or contracts.

Single Point of Contact: 

Name: Aashish Rohatgi
Email: aashish.rohatgi@pnnl.gov
Phone: 509-372-6047

References: 
  1. Rohatgi, A., Soulami, A., Stephens, E.V., Davies, R.W., Smith, M.T., 2014. An investigation of enhanced formability in AA5182-O Al during high-rate free-forming at room-temperature: Quantification of deformation history. Journal of Materials Processing Technology, 214, pp. 722-732. Rohatgi, A., Stephens, E.V., Soulami, A., Davies, R.W., Smith, M.T., 2011. Experimental characterization of sheet metal deformation during electro-hydraulic forming”. Journal of Materials Processing Technology, 211, pp. 1824-1833.
  2. Rohatgi, A., Stephens, E.V., Davies, R.W., Smith, M.T., Soulami, A., Ahzi, S., 2012. Electro-Hydraulic Forming of Sheet Metals: Free-forming vs. Conical-die Forming. Journal of Materials Processing Technology, 212, pp. 1070-1079.
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