A Magnetorheological-Fluid-Assisted Approach for Ultrasonic Testing of Complex Additive Manufacturing Geometries

Additive manufacturing has revolutionized high-performance industries by enabling the production of components with complex geometries and internal lattice structures that cannot be fabricated using conventional manufacturing methods. However, the layer-by-layer nature of this process makes the components prone to defects such as porosity, micro-cracks, and elevated surface roughness. Moreover, the presence of intricate internal features poses a serious challenge for ultrasonic inspection, as ultrasonic waves cannot effectively penetrate deep internal regions or obtain reliable reflections from internal surfaces. In this study, magnetorheological (MR) fluid is employed as a filling medium for these cavities to establish a continuous internal pathway that enables effective ultrasonic wave propagation and integrated inspection. MR fluids, whose rheological and acoustic properties change under applied magnetic fields, allow the tuning of sound velocity and acoustic impedance and can act as a conformable mold matching the component's geometry. This work investigates the variations in sound velocity and ultrasonic attenuation in MR fluid under magnetic fields and evaluates their role in acoustic-impedance matching and wave-transmission enhancement. Experimental test specimens are fabricated, and immersion ultrasonic testing is performed using MR fluid as the coupling medium. Signal-processing techniques are applied to mitigate noise caused by particle scattering. The result demonstrate that the proposed method improve ultrasonic penetration and signal quality, offering a novel and effective approach for the nondestructive inspection of additively manufactured components.