High-Speed DIC Technology: Capturing Transient Deformation in Explosion Mechanics

The 15th National Academic Conference on Explosion Mechanics was held in Shaoxing on June 28, bringing together over 2,000 experts and scholars from across the country in the fields of explosion mechanics and impact dynamics. Participants engaged in academic exchanges focusing on key topics such as engineering applications of explosion and impact dynamics, dynamic mechanical behavior and damage/fracture of materials, engineering blasting and damage assessment, energetic materials and underwater explosions, and structural dynamic response and safety protection.

XTOP3D possesses a deep understanding of the rigorous demands that explosion mechanics research places on testing equipment—specifically the need for high speed, high precision, high reliability, and robust environmental adaptability. Accordingly, during the conference, XTOP3D highlighted its high-speed Digital Image Correlation (DIC) measurement solutions tailored to this field and showcased classic application cases within the academic community of explosion mechanics to the attending experts and scholars.

High-Speed Digital Image Correlation (HS-DIC) Measurement Solution

Ultra-high-speed camera systems represent a significant advancement in explosion mechanics research. With ultra-high frame rates reaching the million-frames-per-second (fps) range, nanosecond-level exposure precision, and ultra-high resolution, these systems provide researchers with unprecedented visualization capabilities. They enable the clear capture of transient processes occurring on microsecond or even nanosecond timescales—such as the propagation of explosive shock waves, the dynamic initiation and propagation of material cracks, and the dynamic deformation and failure of structures—thereby greatly enhancing the understanding of complex transient physical phenomena.

The XTOP3D XTDIC-SPARK 3D high-speed measurement system enables ultra-high-speed measurement at rates exceeding 1 million fps with a tracking precision of up to 0.01 pixels. It synchronously records external loading or displacement data on a frame-by-frame basis, facilitating non-contact, full-field dynamic strain measurement during ultra-high-speed tests. The testing process does not interfere with the structural or kinematic characteristics of the target, ensuring that measurement results are visual, objective, and reliable.

Typical applications of high-speed DIC technology include (but are not limited to) crash testing, explosion testing, impact testing, drop testing, and vibration analysis. Below are several examples of high-speed DIC technology applied to high-speed impact deformation testing.

1. High-speed DIC for analyzing the dynamic deformation of armor-piercing projectiles during high-speed impact

Experimental methods are used to reveal the dynamic deformation behavior of armor-piercing projectiles during high-speed impact—covering stages such as target contact, penetration, and fracture—which is crucial for understanding ballistic limits and evaluating ballistic performance. By combining high-speed cameras with Digital Image Correlation (DIC) technology, the transient deformation behavior of the projectile during impact can be fully recorded.

Testing Challenges:

• Speckle patterns are prone to detaching under high-speed impact;
• Precisely synchronizing the triggering of the experimental setup (e.g., the launcher and target positioning) with the high-speed camera and light source is difficult;
• Factors such as image noise, lighting variations, and lens distortion affect measurement accuracy;

Solution:

• Generate the speckle pattern using a specialized technique, eliminating the need for primer spraying;
• Utilize a high-speed data acquisition card and ensure precise synchronization among the high-speed camera, light source, and sensors.
• The XTDIC-SPARK system enables full-resolution image calibration and testing at target resolutions and speeds, employing robust correlation algorithms to suppress noise and ensure measurement accuracy.

Test Results:

The following presents the transient deformation analysis and displacement curves for the high-speed armor-piercing projectile obtained via DIC:

2. High-speed DIC for deformation monitoring during high-speed Hopkinson bar impact tests

Hopkinson bar tests are primarily used to determine material properties—such as Young's modulus, Poisson's ratio, stress wave propagation velocity, and stress-strain relationships—under high strain rates. These measurements are fundamental to understanding material behavior under dynamic loads (e.g., collisions, explosions, and impacts). High-speed DIC is particularly well-suited for such applications, leveraging its non-contact nature to capture high-speed loading and transient responses.

Testing Challenges:

• Extremely high impact velocities and very short time windows;
• Complex and severe deformation, demanding high robustness and sub-pixel accuracy from DIC;
• Under high-speed impact, the speckle pattern must remain clearly visible and easily identifiable within the camera's field of view.

Solution:

Utilize a high-performance, high-speed camera featuring a high frame rate, high resolution, wide dynamic range, and excellent imaging capabilities;
Employ robust Digital Image Correlation (DIC) algorithms, strain-rate-sensitive deformation calculation methods, and noise suppression techniques;
Apply a specialized speckle pattern to the specimen surface to ensure that the texture remains clearly visible during the transient impact event.

Test Results:

The XTDIC-SPARK 3D high-speed measurement system successfully acquired displacement field data with high spatiotemporal resolution for the material under high-speed impact loading, revealing the spatial distribution and evolution process of the sheet's deformation.

3. High-speed DIC for analyzing transient crack evolution during high-speed compression

In engineering structures, the propagation of crack damage in materials is a critical factor affecting structural safety and reliability. This experiment employs high-speed compression testing, utilizing high-speed cameras in conjunction with Digital Image Correlation (DIC) technology to comprehensively record the transient deformation and crack propagation behavior of the material under compressive impact.

Testing Challenges:

The test involves high-speed loading, making the securing of square specimens challenging;
Monitoring deformation and forming speeds;
Analyzing crack evolution during the impact transient.

Solution:

• Square specimens are secured with screws from multiple directions to ensure they do not shift during impact;
• High-performance high-speed cameras and high-speed data acquisition cards are utilized;
• High-speed image sequences and DIC displacement/strain maps are used to analyze the dynamic crack propagation process.

Fixing method for square test specimens

Test Results:

Displacement and strain field contour plots; crack width variation plots.