Non uniform residual stress fields on sintered materials

The hole-drilling method (HDM) is a convenient and effective method for measuring residual stresses near the surface of an isotropic linear-elastic material. The measurement procedure is relatively simple, and has been standardized in ASTM Standard Test Method E837. The HDM is also versatile and can be performed in laboratory or in situ, on components ranging widely in size and shape. It is often referred to as a “semidestructive” technique, since the small hole will not, in many cases, significantly impair the structural integrity of the part being tested. The basic principle was first introduced by Mathar in 1934. Since that time, many researchers have further developed the method, culminating in the establishment of a standardized procedure ASTM E837. At least three established methods are available for estimating non-uniform residual stress fields from relaxed strain data from the incremental HDM. They are the Power Series, the Integral and the ASTM E837-08 Methods. These methods rely on finite element calculated calibration data, utilize different approaches for stabilizing and smoothing the non uniform residual stress field, and do not have the theoretical shortcomings of the two traditional methods (the Incremental Strain and the Average Strain Methods). Since the strain variations during drill depends on many factors hardly predictable and checkable a priori, it seems that the best calculation method should be evaluated for each particular experiment. This paper compares the Power Series, Integral and ASTM E837-08 methods as procedures for determining non-uniform residual stress fields using strain relaxation data from the HDM. Specimens made of AISI Maraging 300 steel by means of Selective Laser Melting are investigated and the residual stress profiles performed by means of all three stress calculation procedures are also presented and compared.