Local identification of the stress–strain curves of metals at a high strain rate using repeated micro-impact testing

Abstract

Understanding the effect of various mechanical processes such as shot peening requires the knowledge of metal behavior at a high strain rate. The identification of this behavior is often performed using Hopkinson's bar devices. However, the resulting stress-strain curves correspond to a bulk behavior of the material and thus do not take into account the modification induced by surface preparations or surface treatments. In this paper, we have proposed a method based on local micro-impact testing to identify the stress-strain curves of metals near their surface. More precisely, this method is based on the determination of the best stress-strain curve which allows to reproduce the growth of the residual imprint at each impact for a given impact energy. The advantage of the method developed in this paper lies in its simplicity and low cost. In the first part, the repeated impact set-up is presented. Then the FEM strategy is detailed and the identification method developed. In the last part of this paper, an application to AISI1045 and AISI316L steels highlights the great interest of this method to obtain better stress-strain curves than those classically used. It points out the need to identify appropriate surface stress-strain curves when the surface behavior is concerned. As a matter of fact it should also concern other manufacturing processes such as machining or finishing.

Investigation of indentation-, impact- and scratch-induced mechanically affected zones in a copper single crystal

“…The impacts were performed using the micro-impact set-up detailed in previous studies [16,7]. This device allows one to measure with high accuracy the impact speed and thus the impact energy (Fig.…”

“…Instrumented indentation testing is the most popular technique to determine local quasi-static mechanical properties [1][2][3][4]. Standard indentation testing is unfortunately unable to identify high strain-rate-dependent mechanical properties, and in this case, impact-based methods such as dynamic indentation or microimpact testing [5][6][7] are more adequate. Identification of medium-to-large-strain mechanical properties is out of the scope of indentation and impact-based testing.…”

“…Surface treatments are usually connected with the modification of the surface properties by various actions of physical, chemical, thermal or metallurgical origin (quenching, nitriding...). However, mechanical loading may also result in modifications such as the [7], right: residual indent imprint resulting from a Brinell test (2.5 mm, 100 N) on a single-crystal copper surface ({100} face). The square-shaped imprint (not shown here) is also observed under impact loading and is a consequence of the single crystal anisotropic plastic flow.…”

Critical issues in conducting constant strain rate nanoindentation tests at higher strain rates

“…Nanoindentation is often the method of choice for performing local mechanical measurements, but in its traditional form it is rarely used above strain rates of ;0.1 s À1 . Although a great deal of recent research and development has been aimed at achieving higher indentation strain rates [1,2,3,4,5,6,7,8,9], several critical technical and theoretical issues must still be overcome before instrumented indentation testing can be used routinely to provide reliable high strain rate measurements. The remaining challenges involve both the capability of the testing systems to acquire precise, meaningful data at very high rates and how the data should be reduced to account for a variety of phenomenon that are not observed in conventional nanoindentation testing, e.g., the influence of measurement and control time constants [2].…”

“…Several different approaches to achieving high strain rate nanoindentation have recently been reported [1,2,3,4,5,6,7,8,9]. Guillonneau et al have had great success using a system based on piezoelectric displacement actuation along with a special piezo-based force transducer to increase the rate at which reliable data can be obtained [3].…”