Laboratory: Oak Ridge National Laboratory
Title: High Strain Rate Servo-Hydraulic Testing of Magnesium and Other Materials
Class: Characterization
Computational
Processing/Manufacturing
 Extreme Environment
 Structure
 Fabrication &
Testing
Properties
Synthesis
 Mechanical Behavior
 Shaping & Forming
of Materials
Description: The high rate test machine (HRTM) is built around a custom high-rate actuator designed
and built by MTS Corp. Capacity is 9000 lbf at static conditions and 5500 lbf at maximum
velocity of 700 in./sec. The stroke range is 15.5 inches of travel. The actuator has a single
400 gpm servo-valve supplied by two, five 5-gallon accumulators. The actuator is mounted
in a MTS 100 kip, two-post load frame. A slack adapter that allows the machine to travel up
to 7 inches before engaging and loading the specimen is attached to the actuator. This
enables the machine to accelerate up to full speed and engage the specimen at constant
velocity. Low-mass titanium alloy grips, specifically designed for high rate testing, are part
of the load train components. The objective of reducing moving mass between the sample
and load cell is to increase the Eigen frequency of the test setup, minimizing its effect on
the stress-strain curves during high strain testing. Machine transducers include a DC strain
gage load cell along with a charge amplified piezoelectric load cell (Kistler) with capacities
up to 9000 lbf.
Capability Bounds: Specifications include:
 Maximum Loading Velocity=700 in./s over an approximate 4-in. range.
 Load Capacity is 9000 lbs. static and 5500 lbs. dynamic.
 Total Stroke: 15.5 in.
 Working Stroke is approximately 7.0 inches with slack adapter in the load train.
 Control: MTS 407 servo-hydraulic controllers, with external command signal.
 In-house developed synchronization and data acquisition (DAQ) systems.
 High-speed digital imaging system (maximum Frame rate: 1,000,000 fps; threedimensional imaging capability for full field-displacement map).
Unique Aspects: Special fixtures are used for conducting strain-limited material damage evolution studies at
various strain rates. High-speed video and Digital Image Correlation are used to document
the specimen response and measure displacement data for local strain measurements and
fracture onset analysis. For the characteristic subset of loading states, material initial state
with respect to porosity, grain size, and secondary particles is assessed via metallographic
and x-ray tests. Evolving damage by void nucleation at secondary particles, void growth, and
coalescence by micro-localizations also are assessed using metallographic and x-ray tests.
Results are correlated with measurement of evolving effective material properties at the
macro level. After correlation of micromechanics and macroscopic data from selected tests,
the emphasis is on using measurements of effective material properties. The experimental
scope is limited to tests necessary to develop parameters for models based on plasticity of
voided solids, anisotropic plasticity continuum damage models, and models necessary for
July 2016
determining localization and failure parameters for finite element method (FEM)
simulations.
Availability: Available for researchers through a user program.
Capability Expert: Dr. Srdjan Simunovic, Senior Staff Scientist, [email protected], 865-241-3863
Image(s):
References: Website: http://energy.ornl.gov/Mg
http://energy.ornl.gov/ASP_new
July 2016