DIC Analysis of Impact Compression Test Using the Hopkinson Bar Method with HPV -X3

Significance of the topic

Accurate characterization of dynamic mechanical properties under impact loading is essential for designing safer, more reliable components in automotive, aerospace, defense and other industries. The Split Hopkinson Pressure Bar (SHPB or Hopkinson bar) method remains a standard for high-strain-rate compression testing, but meaningful interpretation of results requires high temporal and spatial resolution imaging to capture transient deformation, localization and failure. Combining high-speed imaging with Digital Image Correlation (DIC) enables full-field strain measurement during impact events, revealing onset of plasticity, strain distribution evolution and post-impact residual deformation.

Objectives and overview of the study

This application note demonstrates imaging and DIC analysis of an aluminum specimen subjected to impact-compression using the Hopkinson bar method. The key aims were to: 1) record the transient deformation with sufficient temporal resolution to resolve strain evolution during the impact pulse, and 2) obtain high-spatial-resolution DIC maps to quantify strain localization and residual plastic deformation. The HyperVision HPV-X3 high-speed camera was used to capture the event and VIC-2D software performed DIC analysis.

Methodology

• Specimen preparation: An aluminum compression specimen was prepared with a random speckle pattern applied to the camera-facing surface via a transfer sticker to enable DIC tracking.
• Hopkinson bar test: Impact-compression loading was applied using a Hopkinson bar arrangement (striker, incident/input bar, specimen, transmission/output bar, and absorption bar) to generate a short-duration high-strain-rate compressive pulse.
• Imaging protocol: High-speed imaging was performed at 500,000 frames per second (500 kfps) using the HPV-X3 camera, equipped with a close-up ring, bellows and a 105 mm macro lens. LED illumination was provided from the camera side to uniformly illuminate the speckled surface.
• DIC processing: VIC-2D (Correlated Solutions) processed the acquired image sequence to produce synchronized strain-vs-time plots and strain-distribution movies, using Lagrangian exx strain mapping in the loading direction.

Used instrumentation

• High-speed camera: HyperVision HPV-X3 (Shimadzu) — capable of up to 20 Mfps; used here at 500 kfps.
• Optics and mechanical accessories: Close-up ring, bellows and 105 mm macro lens for high-magnification imaging.
• Lighting: High-intensity LED illumination directed from the camera side to ensure high-contrast speckle images at short exposure times.
• DIC software: VIC-2D (Correlated Solutions, Inc.) for full-field strain computation and time-synchronized plotting.
• Hopkinson bar test rig: Striker bar, incident/input bar, specimen fixture, transmission/output bar and absorption bar (bar-launching device).

Main results and discussion

• Image acquisition and DIC: The HPV-X3 captured the transient compression event at 500 kfps with sufficient spatial clarity to run DIC using VIC-2D. Image frames were processed to yield exx (Lagrange) strain maps and synchronized strain-vs-time traces.
• Strain evolution: Analysis showed strain in the loading direction rising approximately linearly after load initiation. Maximum strain was reached around 120 µs after load initiation (observed between the 8th and 9th frames in the presented sequence), after which the input and transmission bars separated from the specimen.
• Residual deformation: Post-separation frames indicated residual strain remained in the specimen, demonstrating that plastic deformation occurred during the impact event.
• Temporal and spatial fidelity: The combination of the HPV-X3’s high frame rate and improved spatial resolution (reported as three times higher than previous models) allowed clear visualization of strain localization and time-resolved measurement of dynamic deformation consistent with Hopkinson-bar stress-wave timing.

Benefits and practical applications of the method

• High-speed imaging paired with DIC provides full-field, time-resolved quantitative strain data during impact, which complements traditional stress-wave measurements from strain gauges in Hopkinson-bar tests.
• Improved spatial resolution enables detection of local strain concentrations and early localization that may lead to failure — critical information for material modeling and validation of constitutive laws at high strain rates.
• Ability to observe residual plastic deformation and fracture progression supports failure analysis, material selection, and design optimization in transportation, defense and manufacturing sectors.
• The non-contact optical approach is well suited for fragile or small specimens where gauge installation would perturb the response.

Future trends and potential applications

• Higher frame rates and resolutions: Continued development of sensors and optics will push capability toward multi-Mfps imaging with greater pixel counts, improving DIC accuracy at extreme strain rates.
• 3D-DIC and multi-camera synchronization: Implementing stereo or multi-view systems for full 3D strain and out-of-plane motion measurement during Hopkinson-bar tests will yield richer datasets for constitutive model calibration.
• Integration with AI/automated analysis: Machine learning can accelerate feature detection (e.g., onset of localization, crack nucleation) and enable rapid extraction of material parameters from large high-speed datasets.
• Multimodal diagnostics: Combining high-speed DIC with high-rate thermography, acoustic emission or in-situ microstructural probes will deepen mechanistic understanding of dynamic failure processes.
• Industrial adoption: Faster, higher-resolution imaging will broaden routine use of optical DIC in industrial QA/QC for impact-sensitive components and for developing high-strain-rate-resistant materials.

Conclusion

High-speed imaging with the HyperVision HPV-X3 coupled to VIC-2D DIC effectively captured and quantified dynamic compression behavior of an aluminum specimen in a Hopkinson-bar experiment. Key outcomes included time-resolved full-field strain mapping, identification of peak strain timing (~120 µs), and evidence of residual plastic deformation after bar separation. The study highlights the importance of combining high temporal and spatial resolution imaging with robust DIC to extract meaningful mechanical data from impact tests; improvements in camera performance directly enhance the quality of DIC-based insight.

References

1. Hopkinson B. A Method of Measuring the Pressure Produced in the Detonation of High Explosives or by the Impact of Bullets. Philosophical Transactions of the Royal Society of London A. 1914;213:437–456.
2. Application Note V26. Observation of Fracture Behavior of Resin Material from an Impact Compression Test by the Hopkinson Bar Method.
3. Application Note V27. 3D-DIC Analysis of a Metal Specimen Following an Impact Compression Test by the Hopkinson Bar Method.
4. Application Note V29. Fracture Observation and Observation of Strain Distribution of Plastic Material with Hole in Impact Compression Test.