Steel Sheets Impact Simulation for Safety Guards Design: Problems and Perspectives

Abstract

The growing need of design of safety guards for industrial workers led to the need for experimentation in the field of ballistics, typically used in the military research. In the last few years some international standards for the safety of machine tools have been developed, such as the ISO 23125: 2010, improving the ballistic protection of safety guards. But it is still possible to find in the market a large quantity of machine tools with doubtful real protective characteristics of guards. The uncontrolled projection of parts of work piece or tools can often cause very dangerous perforations of the safety guards. In such a way specific experimental tests like the ones conducted in EU, have assured the possibility to write appendices of ISO standards for safety guards design of machine tools. These tests are based on impact between a particular standardized projectile, which exemplifies an impacting fragment of variable size and energy, and a flat plate placed in the trajectory of the projectile. The penetration or buckling of the target determines the non-suitability of a particular material of a given thickness, for the design and production of safety guards. However these tests, have the following limitations: they are valid only for: a limited type of thickness and materials, a perpendicular impact with flat plates of about 500 mm × 500 mm and when the standardized penetrator is a cylinder with a prismatic head. Moreover another limitation arises for the design of real safety guards: difficulties in taking into account curved design of guards such as the ones typically used in the spindles of machine tools. Moreover it is very difficult to take into account innovative materials different from the ones provided by the standards and also it is impossible to consider projected objects whose geometry is not regular, for example fragmented parts of tools, broken as a result of a wrong manoeuvre of the machine user. The main focus of this paper is to test the applicability of numerical methods for the simulation of impacts on steel sheets of standardized penetrators for the numerical design and validation of industrial safety guards. Correlation between experimental penetration tests found in international papers and optimized numerical tests will be presented.