High Strain Rate Testing of Polymers

Technical Challenge

Polymeric materials are frequently used in impact applications where strain rates can exceed 1,000/s (i.e. helmets, protective eyewear, enclosures for electronics, etc.).  Polymeric materials (thermoplastics, thermosets, elastomers, foams) are strain-rate-dependent.  However, there is frequently little to no information about polymer behavior as a function of strain rate.

Furthermore, there are few constitutive models available in commercial finite element codes that are capable of adequately capturing the nonlinear, viscoplastic flow behavior of these materials over the wide range of strain rates needed for simulation.


 

Veryst Solution

Veryst has developed a suite of experimental and modeling capabilities ideally suited for capturing the high strain rate behavior of polymers.  One system available at Veryst, the Split Hopkinson Pressure Bar (SHPB) system, is commonly used for testing thermoplastic materials at strain rates above 1,000/s in compression.  High speed video from an SHPB test on polycarbonate is shown below. 

Data from these tests can be combined with traditional uniaxial tests with universal test frames to understand the rate-dependent response of a material. 

SHPB Machine
Veryst Engineering’s Split Hopkinson Pressure Bar

 

High speed video of a Split Hopkinson Pressure Bar test on PTFE

 

The MCalibration® software can then be used to calibrate an appropriate nonlinear, rate-dependent material model from the PolyUMod® library or a native material model within a commercial finite element code.  (Both software programs were originlly developed by Veryst and are now available through PolymerFEM.com.)  

The results of such a testing and calibration process are shown here.  This calibrated model can then be used to model polymeric components in commercial codes such as Abaqus, ANSYS, COMSOL Multiphysics, LS-DYNA, and MSC.Marc.

Polycarbonate Stress-Strain Model
Experimental data at low and high strain rates, along with predictions from a calibrated Three Network Viscoplastic (TNV) model, available in Veryst’s PolyUMod Library.

 

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