# Withstanding Capacity of Machine Guards: Evaluation and Validation by 3D Scanners
###### Abstract
Thus, this demonstrated that the single impact test prescribed by the standards does not provide completely reliable results to evaluate the withstanding capacity of machine guards. The effect of other test parameters was studied in [16] through finite element models to be applied on polycarbonate panels of different size and thickness. Overlap and open window sizes were varied within a specific range. Results of simulations showed a reduction in the withstanding capability to penetration for free impact areas smaller than the standardized one (450 \(\times\) 450 mm of free surface and 25 mm of side overlapping). This is probably due to the reduction of the open window for smaller sizes and therefore to a reduction of the material's ability to deform without cracks and consequently to adsorb impact energy. Results were experimentally validated by ballistic impact tests carried out at the Fraunhofer institute in Berlin on polycarbonate panels of different thickness [17]. Therefore, the influence of the test panel size is a very important issue to investigate, especially for vision panels of guards usually made by engineered plastics, such as polycarbonate polymers with wear and scratch prevention films. Statistical aspects were deeply discussed in [15] and the possibility of reducing uncertainties was discussed in [16], where it was clearly stated that with the current test standards, results are not sufficiently reliable, so different test methods and standards should be envisaged. In these works, all the uncertainty sources were explained and investigated in full detail, and the authors conclude that a single standardized test is hardly reproducible and repeatable because it is affected by local impact conditions. For all of these reasons, a review of standardized tests is required in the next years, and more testing is expected to measure the data dispersion of different test procedures [18]. In this paper, ballistic tests based on standard test rigs and with standard projectiles are performed on polycarbonate panels, but using a regression approach as in [15; 16]. Thus, a set of impact tests are executed with a proper procedure, and the regression curve is obtained. This allows to evaluate the ballistic limit of the material and to set a proper test velocity, named safe velocity, which allows to obtain a reliable result even when performing a single impact test. Then, the possibility of retrieving a plastic deformation limit to be correlated with the withstanding capacity of machine guards for a given penetrator and a given thickness is investigated through 3D scanners. A new experimental method to investigate the effect of the panel size on the withstanding capacity of machine guards to ballistic penetration is presented. The withstanding capacity evaluation is performed by analyzing the plastic deformation after ballistic penetration using 3D optical digitizing techniques to determine the maximum deformed area and the reduction of thickness after the shooting tests. In recent years, 3D scanners have been used in a wide range of industrial applications [19; 20], research activities in biomechanics [21; 22; 23], and engineering services [24; 25; 26]. The present study represents a contribution to perform a revision of standardizations for withstanding capability tests of machine guards (reduction of ejection risk) by using an innovative method based on 3D metrological scanners. In Section 2, the theoretical bases of ballistic limit evaluation are presented, together with the materials and methods used to perform the ballistic tests and the deformation analysis based on the new approach. In Section 3, the results of tests performed on non-standardized polycarbonate panels of 300 \(\times\) 300 mm in size, with an open window of 250 \(\times\) 250 mm, are shown and compared to outcomes of tests performed on standard panels (500 \(\times\) 500 mm, with 450 \(\times\) 450 mm of free surface).