Prediction of residual stress components and their directions from pile-up morphology: An experimental study
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Indentation method has been widely used in the measurement of material mechanical properties and residual stress for its simple, fast and nondestructive characteristics. In the indentation test, because of the plastic deformation of the material, the material accumulation and subsidence occurs around the indentation. It is found that the deformation amount of the indentation, especially the maximum pile-up around the indentation after unloading, is related to the magnitude and direction of the residual stress. In this paper, an experimental study on the pile-up morphology around an indentation for determining the direction and magnitude of residual stress is reported. Nonsymmetrical morphology of spherical indenting deformation on artificially strained steel specimen was measured with a laser scanning confocal system. A unique relationship between pile-up after unloading and biaxial residual stress was set up based on the experimental results. The direction and components of nonequibiaxial residual stress can be determined by the proposed method.
I. INTRODUCTION
Residual stresses are of practical importance in bulk materials and coatings, which critically affect their mechanical integrity and reliability. Residual stress is that which remains in a body that is stationary and at equilibrium with its surroundings. It can be very detrimental to the performance of a material or the life of a component. Alternatively, beneficial residual stresses can be introduced deliberately. For instance, for a structural component undergoing an applied stress, the compressive residual stress enhances the resistance to crack propagation, whereas tensile residual stress reduces the resistance. For semiconductor devices, residual stresses may decrease their service life sharply; however, with the use of internal stresses, it is possible to considerably increase the mobility of charge carriers and thus the charge speed of the device can be increased markedly. Residual stresses are more difficult to predict than the inservice stresses on which they superimpose. For this reason, it is important to have reliable methods for the measurement of these stresses and to understand the level of information they can provide. The conventional methods for measuring residual stresses can be divided into two groups: mechanical stress-relaxation methods (including hole-drilling and saw-cutting techniques)1,2 and physical-parameter analysis methods (including ultrasonic wave, magnetic Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.270
Barkhausen noise, x-ray, and neutron diffraction).3–5 However, these methods mentioned here have their own shortcomings. For example, the destructive nature of mechanical stress-relaxation methods limits the wide application of these techniques in industry, and it is difficult to separate intrinsic microstructural effects on the physical parameters from the effects of a residual stress in physical-parameter analysis methods. Another technique fo
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