Bubble dynamics near elastoplastic plates of varying thickness and span

Bubble collapse near-rigid boundaries has been studied extensively, whereas the dynamics near deformable elastoplastic boundaries remain comparatively unexplored. Bubble collapse near deformable elastoplastic boundaries is controlled by stand-off distance and structural characteristics, yet the transition from compliant to near-rigid behavior has not been resolved within a single experimental framework. Single spark-generated bubbles are examined near fully clamped square aluminum plates using synchronized high-speed imaging and stereo digital image correlation. The tests cover stand-off distances γ = 0.40–2.00, plate thicknesses h = 0.1–5.0 mm, and clamped spans b = 100–150 mm, giving flexural rigidities D = 0.0065–818 N m. For h = 0.3 mm and b = 150 mm, the maximum bubble radius Rmax increased from 30.72 to 42.17 mm and the oscillation period Tosc from 4.925 to 7.325 ms as γ increased from 0.40 to 2.00. At γ = 1.6, increasing h reversed the terminal centroid displacement from −19.7 to +27.6 mm. Four collapse modes are identified as the boundary stiffens, namely, mushroom-shaped, compliant-boundary repulsive, transitional annular, and rigid-wall-like attractive collapse. A dimensionless boundary-compliance parameter β, defined solely by boundary and fluid properties, is proposed as an in-sample empirical coordinate that orders the four modes in a β–γ phase diagram. Attraction was observed below log10β ≈ 5, an annular transition band between about 5 and 7.2 and compliant repulsion above 7.2; these are in-sample empirical ranges for the present matrix, not established thresholds. The full-field deformation records resolved a six-stage response from shock-driven bulging to plastic settling. A phase index Π, defined from the timing of the plate-deflection extrema relative to the bubble pulsation, separates the attractive mode from the repulsion-family modes at Π = 0, showing that collapse direction is strongly associated with the rebound phase of the plate rather than with deformation amplitude alone. These results clarify how stand-off and initial plate compliance correlate with bubble evolution and loading direction on deformable structures; engineering use additionally requires strength, fatigue, and application-specific validation.