Numerical and Experimental Study of the Roughness Effects on Mechanical Properties of AISI316L by Nanoindentation

Ling Chen,Jan-Eric Ståhl,Aylin Ahadi,Jinming Zhou

doi:10.4236/mnsms.2014.44017

Abstract

Surface roughness is a commonly used criterion for characterization of surface quality in a machining operation. In the study of micro-scale mechanical properties of machined surface and cutting tool using nanoindentation method, perfect surface finish on the specimen is often required for the reliable indentation result. However, the perfect surface finish is often difficult to obtain from the machining operation due to the dynamic behavior of the machining and the limitation of the cutting tool geometry. In the presented paper, the effect of surface roughness on the nanoindentation measurements is investigated by using finite element method. A 3D finite element model with seven levels of surface roughness is developed to simulate the load-displacement behavior in an indentation process with a Berkovich indenter. The material used in the simulation is AISI 316 L stainless steel, modeled as an elastic-plastic material. The mechanical properties were calculated by combining simulations with the Oliver-Pharr method. The hardness and reduced modulus from the simulation were found to decrease with an increase of roughness. The study showed that the scatter of the load-depth curves and the deviation of the hardness and the reduced modulus are significant affected by the variation of roughness. It was also found that the height of pile-up was little affected by the surface roughness from the simulation. The combined effect of indenter tip radius and surface roughness was also investigated. The study was complemented with experimental tests and the results from these tests support the results from the simulation.

Highlights

It is well known that the mechanical properties at micro-scale level have significant impact on the performance of the machined component, such as fatigue, wear, corrosion resistance [1]
Perfect surface finish is often difficult to obtain from the machining operation due to the dynamic behavior of the machining and the limitation of the cutting tool geometry
This paper presents a fully 3D finite element model and Berkovich indenter is used to simulate the effect of roughness on nanoindentation test

Summary

Introduction

It is well known that the mechanical properties at micro-scale level have significant impact on the performance of the machined component, such as fatigue, wear, corrosion resistance [1]. In the study of micro-scale mechanical properties with nanoindentation test on machined surface and cutting tool, prefect surface finish on the test specimen is often required for the reliable result [2] [3]. Since the contact area is obtained indirectly from the depth of penetration in sample material, the natural roughness of the specimen surface can cause errors in the determination of area in the contact between indenter and specimen. This specially applies in the coating and thin film indentation, such as coated cutting tool, mold and die, in which the indentation depth is limited by their thickness [3]. Much larger indentation depth is required in the test, such as in Vickers indenter test, it always requires the contact depth larger than 20 times of roughness to eliminate the effect of roughness to some extent [1]

Methods

Results

Conclusion