Journal of Sound and < ibration (1999) 224 (3), 411} 430 Article No. jsvi.1998.2189, available online at http://www.idealibrary.com on IMPACT TESTING OF STEREOLITHOGRAPHIC MODELS TO PREDICT NATURAL FREQUENCIES J. P. MAHN Emerson Motor Company, Motor ¹ echnology Center, 8050 = est Florissant, St. ¸ouis, MO 63136, ;.S.A. AND P. V. BAYLY Mechanical Engineering, = ashington ;niversity, St. ¸ouis, MO 63130, ;.S.A. (Received 22 December 1997, and in ,nal form 28 December 1998) Stereolithography (SLA) is a rapid-prototyping method which is used primarily to display the three-dimensional geometry of designed parts. In this paper, impact testing of SLA models is examined as a tool for the prediction of the natural frequencies of prototype aluminum parts. If the SLA model is ideal, its frequencies and those of the corresponding aluminum prototype will be related by simple ratios of material parameters and dimensions. However, the e!ects of properties of the SLA model which are non-ideal or qualitatively di!erent from aluminum have not been examined. Impact tests of SLA beams, plates, and complex shapes (models of motor end shields) were performed to quantify the e!ects of di!erences such as increased mass loading (due to the lightness of SLA parts), possible anisotropy due to the &&laminated'' nature of the model, and mismatches between the damping, non-linearity, and the Poisson ratio of the SLA material and the corresponding properties of aluminum. The natural frequencies predicted from SLA models were compared to those measured from corresponding aluminum parts. Comparisons generally showed good agreement and suggest that carefully performed impact testing of SLA models is a useful method to predict the natural frequencies of prototype parts. These predictions may be used directly in the design process, or to validate and re"ne "nite-element models.  1999 Academic Press 1. INTRODUCTION In response to the demand for quieter machines, manufacturers are increasing the amount of noise analysis performed on their products. A part of the noise analysis may include prediction of the natural frequencies of the components of the product. Current methods of prediction include "nite-element analysis (FEA). However, FEA performed on a complicated geometry can be time-consuming to model, to mesh, and to analyze. Furthermore, accurate results require the skills of an experienced analyst and even then, the accuracy of the results may be questionable. 0022-460X/99/280411#20 $30.00/0  1999 Academic Press