Localised Effective Bulk Modulus Elastography of Thermally Treated PVDF and a Steel–Silicone Composite with Simulation Validation

Ultrasound is a common tool for evaluating material properties, yet conventional elastography techniques often require external loading, exhibit limited spatial resolution, or struggle to detect microstructural changes in polymers. To address these limitations, this work employs Effective Bulk Modulus Elastography (EBME) to map stiffness in thermally annealed Polyvinylidene Fluoride (PVDF) samples with sub-millimetre resolution. A custom transducer–endoscope probe designed for localised, non-contact bulk modulus mapping enables high-resolution imaging without mechanical force, representing a key advancement over traditional elastography approaches. Initial tests use hard and mixed hard–soft composites, including a 0.5 mm steel sphere embedded in Dragon Skin silicone rubber, to evaluate EBME’s achievable resolution. PVDF blocks undergo controlled thermal annealing and quenching to induce microstructural variations. Each sample is placed in a water bath where an immersion transducer records ultrasound echoes; amplitude and time of flight information are used to compute local bulk modulus. The goal is to determine whether EBME can reliably detect stiffness differences arising from thermal treatment in viscoelastic polymers. The observations confirm that EBME distinguishes materials with strong stiffness contrast and is sensitive to internal microstructure, including crystalline phase distribution and speed of sound fluctuations, demonstrating its potential as a high-resolution non-destructive evaluation technique.