Evaluation of nonequibiaxial residual stress using Knoop indenter
- PDF / 403,342 Bytes
- 5 Pages / 584.957 x 782.986 pts Page_size
- 97 Downloads / 261 Views
The instrumented indentation test is an important alternative in quantifying residual stresses. Various indentation models have been developed to determine residual stresses, but no previous models can be applied to a nonequibiaxial residual stress state. To overcome this limitation, a Knoop indentation technique was developed to use the asymmetric characteristics of the Knoop indenter. With the ratio of conversion factors and equations for the relation between the load differences and the residual stress, a model of Knoop indentation was developed to determine the stress directionality p. This model was verified and compared through experiments on various biaxial tensile stress states. Imperfections in the Knoop tip change the conversion factor ratio. Using finite element simulations, this change in the conversion factor was expressed by a fitting equation.
I. INTRODUCTION
Residual stress is a stress state that exists in bulk material without application of an external load or other source of stress, such as a thermal gradient.1 The quantitative measurement of residual stress is considered significant for the reliability and integrity of industrial structures and facilities because residual stress affects subsequent fracture and fatigue behavior and stress-corrosion cracking.2 The instrumented indentation test is recognized as a measurement technique for residual stress because of its nondestructive characteristics and applicability from macro- to nanoscales.3,4 Numerous studies have been done to estimate residual stress using indentation methods. Tsui et al.5 and Bolshakov et al.6 used indentation tests and finite element (FE) analysis results to find that the indentation contact area is unaffected by applied stress at a given load. Using this result, Suresh and Giannakopoulos7 developed a theoretical model to estimate residual stress in the equibiaxial stress and strain fields, which was confirmed by Carlsson and Larsson.8,9 Swadener et al.10 developed another approach to determine residual stress using a spherical indenter. To consider nonequibiaxial residual stress state, Giannakopoulos11 examined the influence of surface initial stresses on instrumented sharp indentation with analytic and experimental results, and Lee and Kwon12,13 have suggested a quantitative method for evaluating nonequibiaxial residual stress using a parameter of stress directiona)
Address all correspondence to this author. e-mail: [email protected] This author was an editor of this focus issue during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2011.335 J. Mater. Res., Vol. 27, No. 1, Jan 14, 2012
http://journals.cambridge.org
Downloaded: 09 Sep 2014
ality p by modifying the influence of surface stress on the contact pressure by shear plasticity and expanding the existing equibiaxial stress model. They eliminated the pure shear stress term in the nonequibiaxial stress state and decomposed the remaine
Data Loading...
