A new dynamic test for the identification of high speed friction law using a gas-gun device

Abstract

In the framework of metal forming, which involves high speed loads, the determination of the friction law is one of the most essential topics. Especially for Finite-element simulation the development of innovative local friction laws improves the quality of the numerical results. One of the most critical point reside in the accuracy of the identification of the governing friction law parameters. A new experimental test is based on conical extrusion. The idea is to launch a cylindrical projectile into a target provided with a conical bore prolonged with a cylindrical one. The projectile is stopped by friction forces occurring at the interface between those materials. After impact the length of extrusion is taken into account for friction law identification. The experimental set-up used is a ballistic gas-gun device capable to launch the projectile, in vacuum conditions, up to 300 m/s. The experiment is simulated by a numerical model using ABAQUS Explicit finite-element code. This code allows the implementation of various user friction laws through a FORTRAN subroutine. In order to obtain accurate results, the viscoplastic constitutive law used for both materials (projectile and target) was previously experimentally identified. The friction law identification uses a combined Monte-Carlo and Levenberg-Marquardt algorithm which provides a very precisely set of parameters law. The test presented in this paper involves two metallic materials: steel 42CrMo4 for the target and aluminum 2017 for the projectile. The friction law for the pair of materials used was validated using experimental test at different speeds of impact (149 up to 235 m/s) and the results are quite good proving a good identification of the friction law parameters.