The Digital Image Correlation Technique Applied to Hole Drilling Residual Stress Measurement 2014-01-0825
The residual stresses found in components are mainly due to thermal, mechanical and metallurgical changes of material. The manufacturing processes such as fabrication, assembly, welding, rolling, heat treatment, shot peening etc. generate residual stresses in material. The influence of residual stress can be beneficial or detrimental depending on nature and distribution of the residual stress in material. In general, the compressive residual stress can increase the fatigue life of material because it provides greater resistance for crack initiation and propagation.
A significant number of improvements for residual stress measurement techniques have occurred in last few decades. The most popular technique of residual stress measurement is based on the principle of strain gage rosette and hole drilling (ASTM E837-01, destructive). Although this technique is effective for some applications, strain gages provide the localized or averaged data and cannot capture the peak or high resolution data when this technique is applied on high strain gradient areas. The measured strains are also highly influenced by the position of strain gages around the drilled hole. The improved measurement technique of 3D-Digital Speckle Pattern Interferometry (DSPI) with hole drilling can capture the full-field, high resolution and high accuracy in-plan and out-of-plan deformation data. However, DSPI is easily affected by environmental noises and it cannot measure in-plane and out-of-plane deformation simultaneously.
The needs of Digital Image Correlation (DIC) techniques from industry have been increasing, especially in micro- and nano-scale mechanical testing applications mainly due to its relative easy implementation and utilization. Although DIC has a lower sensitivity than DSPI, it is more robust on spot measurements. Full field contour, displacement and strain data of specimens in any shape can be easily evaluated by DIC. This paper presents a new comprehensive residual stress measurement technique using 3D-DIC and hole drilling mechanism. In this, the residual stress measurement is performed in a full-field and no contact approach.