The behaviour of geometrically-reinforced thin plates under thermoacoustic loading: A comparison of additive and subtractive manufacturing

Additive manufacturing (AM) is gaining in popularity as an approach to producing metallic components of complex geometry relatively cheaply and rapidly from digital representations. However, concerns about the impact of residual stresses induced by additive manufacturing on the distortion of parts has limited its application in some fields. Residual stresses in parts that lack rotational symmetry and, or have cross-sections with large aspect ratios could cause significant changes in the structural and dynamic performance of the parts due to changes in their shape. In this study, geometrically-reinforced thin plates of a nickel-chromium alloy have been manufactured using classical, subtractive machining processes, and additively using laser-powder bed fusion (PBF-LB). Their final shapes were measured using stereoscopic digital image correlation. Their thermoacoustic performance was investigated by subjecting them to random broadband excitation between 0 and 2000 Hz while applying a series of spatial distributions of heat so that the plates increased from room temperature to an equilibrium temperature of about 800°C and then were allowed to cool when the heating was switched off. Time-frequency spectrograms were measured during the heating and cooling over a greater frequency range (0 to 2000 Hz) than achieved previously. Mode shifting and mode switching, or jumping, was observed; however, the residual strains induced by the manufacturing processes dominated the thermoacoustic behaviour, with almost no effect from the method of manufacturing.