Study of Damage distribution over the Primary Shear Zone in the Metal Cutting using Nanoindentation

In our effort to develop metal cutting as a high strain rate test, we are interested in mapping the damage distribution over the primary shear zone (PSZ). The approach is to quantify the modulus degradation via nanoindentation and use this as a measure of damage. It is shown that the hardness of the material increases and the modulus degrades as it shears through the PSZ. Introduction There are well established methods for measurement of hardness and modulus of elasticity using nanoindentation tests [1]. It is also widely known that the modulus of elasticity is related to damage [2]. Basaran has studied damage of solder joints under fatigue loading to quantify the reduction in elastic modulus using nanoindentation tests [3]. However there are no previous studies in which nanoindentation has been used to measure damage in high strain rate tests. We use ultra high speed photography and digital image correlation (DIC) for measuring the strain rate in the PSZ in orthogonal metal cutting which is illustrated in Figure 1. The strain rate in the PSZ is between 10 /s and 10 /s, depending on cutting conditions. By comparing FEA results for the strain rate distribution through the PSZ with the experimental values, the parameters of the constitutive model are refined. Since the shear strain in the PSZ is of the order of 200%, damage distribution over the PSZ should be included into the constitutive models to improve its accuracy. However, the PSZ is typically only 10 to 100 μm thick, necessitating the use of nanoindentation to detect the degradation in modulus due to damage. Approach Specimens of the nature shown in Figure 1 were prepared using a linear slide based cutting setup (Figure 2) by stopping the machining midway through a cut. The specimen is mounted and polished for metallurgical examination and nanoindentation. On an AISI 1045 steel specimen, we performed 100 nanoindents each on the workpiece and on the chip (Figure 3). The tests were performed using our Hysitron Ubi1 nanoindenter with a Berkovich indenter at two different loads of 6 mN and 10 mN. Figure 1: Schematic of orthogonal cutting showing the primary shear zone Figure 2: Close-up of the linear machining setup and the microscope which is looking at the tool while the tool is mounted on a three axes dynamometer t1