Nondestructive Testing of Surface Defects Based on the Droplet Pinning Effect.

Area of Science:

• Materials Science
• Surface Science
• Physics

Background:

• Nondestructive testing (NDT) technologies have advanced diversely.
• Characterizing surface defects is crucial for material integrity.
• Existing NDT methods have limitations in sensitivity and scope.

Purpose of the Study:

• To propose a novel surface-defect NDT method utilizing the pinning effect.
• To elucidate the physics of droplet behavior on microstructured surfaces for defect detection.
• To establish a theoretical and experimental basis for surface-defect characterization.

Main Methods:

• Development of a custom high-precision solid-liquid interfacial friction measurement apparatus.
• Real-time acquisition and analysis of frictional signals during microdroplet sliding.
• Integration of multiphysics simulations to understand wetting states and defect recognition.

Main Results:

• A characteristic "rise-sudden drop" pattern in friction force curves indicates droplet pinning-depinning at surface defects.
• Optimized droplet volume and sliding velocity enhance detection efficiency, sensitivity, and reproducibility.
• The method can detect pit defects as small as 5 μm (Cassie state) or 75 μm (Wenzel state).
• Linear correlation models between defect width and pinning duration were established for different wetting states.

Conclusions:

• The proposed pinning-effect-based NDT method provides a quantitative and sensitive approach for surface-defect characterization.
• Wetting states significantly influence the detection limits of the NDT method.
• The study offers a robust theoretical and experimental framework for advanced surface inspection.