Monday  |  Lakeshore C  |  11:20 AM–11:40 AM

#19336, Mode Shifting due to Heating of Geometrically-Reinforced Thin Plates

Prior experimental work has confirmed predictions that non-uniform heating of geometrically-reinforced thin plates causes shifts in their natural frequencies and also switching of modes. This earlier work was performed with plates manufactured using traditional subtractive machining methods. Recently, it has been demonstrated that additive manufacturing, in the form of laser powder bed fusion, can be used to make geometrically-reinforced plates with comparable flatness to those manufactured subtractively. However, the residual stresses induced by the additive and subtractive manufacturing process are different; hence, an investigation of the effects of the manufacturing process on the frequency response of geometrically-reinforced thin plates was conducted. The rectangular plates were 1.2 mm thick with in-plane dimensions of 230 x 130 mm and were reinforced by 10 mm wide frame of thickness 4.8 mm. Additively manufactured plates were built vertically in both landscape and portrait orientations with buttress supports that were removed on completion of the build cycle. Each plate was mounted to a shaker via stinger attached to its frame and subject to heating using an array of 1 kW quartz lamps that could be individually controlled to produce a distribution of heat along the longitudinal axis of the plate. The frequency response function of each plate was measured using a laser vibrometer, and plotted as a function of time in waterfall plots, when the lamps were switched on and then off using various patterns of heating. The results show that the orientation in the build process for the additively manufactured plates had a negligible effect on the behaviour of the plates during heating and cooling. In general, the additively manufactured plates exhibited an initial increase in modal frequencies with heating and an initial decrease with cooling regardless of the distribution of heating, which was probably due to the different heat capacities of the thin plate and thick frame. The subtractively manufactured plate also exhibited this behaviour but there were also bifurcations and mergers of modes during heating and cooling; and some of these could have included the mode switching observed previously. However, it can be concluded that additive manufacturing of geometrically-reinforced thin plates appears to produce more stable behaviour in the frequency response function with temperature than subtractive manufacturing.

Eann Patterson   University of Liverpool
Melissa Weihrauch   University of Liverpool
Ceri Middleton   University of Liverpool
John Lambros   University of Illinois Urbana-Champaign