The design and testing of machine safety guards useful to mitigate the ejection risk of small parts or tool tips are provided by standards such as ISO 14120. The inadequacy/suitability of the tested materials for machine guards is obtained by the perforation/not perforation of the guard in a test at the maximum foreseeable speed of a standardized projectile. This test methodology oversimplifies the actual conditions that may occur during a machining process, so research on different possible procedures are nowadays attempted.
In this paper an investigation regarding the penetration behavior of three different projectiles of a given mass for the same guard material is presented. In particular the well-known Recht & Ipson curves for the perforation of 4mm polycarbonate sheets of three different projectiles are shown. The shooting tests were performed using the gas cannon of Monte Porzio Inail laboratories (Rome), and at least five different shots velocities were taken in order to get the R&I curve for each projectile. This new testing methodology provided excellent results adopting the least square method approximation of R&I curves.
Using this new testing technique, it is also possible to obtain the confidence interval of the ballistic limit for each type of projectiles. In addition the worst case among the different projectile performances is shown.