Full-Field Measurement of Residual Stresses in Composite Materials Using the Incremental Slitting and Digital Image Correlation Techniques

Abstract

Background The slitting method is a widely used destructive technique for the determination of residual stresses. Because of the rich data content of the full-field methods, optical techniques such as digital image correlation (DIC) are replacing strain gages for surface measurements. Objective The objective of the current paper is to overcome the difficulties that arise in using the DIC technique combined with the slitting method. The present noise, low signal-to-noise ratio, and systematic errors are the main impediments to the use of DIC in the slitting method. Methods An approach based on the eigenstrain concept was exploited to ascertain the optimum region of interest (ROI) for the analysis. After that, a robust procedure was implemented to utilize the DIC method while excluding the rigid body motion and rotation artifacts from the obtained displacements. Results Different slitting steps may cause dissimilar rigid body motions and rotations of the specimen. The proposed method was able to eliminate all of these different shears and stretches in the images simultaneously. The slitting experiment was conducted on a symmetric cross-ply composite specimen, and the slit progressed down to half the thickness. Although some rigid body motions were large, the method managed to exclude all of them for eight slitting steps. Conclusion A comparison made between the results of the current method and those of the strain gage technique shows that they are in acceptable agreement with each other, and this full-field method can be extended to smaller scales or other destructive techniques.

Residual Stress in Engineering Materials: A Review

“…To overcome the difficulties of implementing the DIC technique, they proposed a robust procedure based on the eigenstrain approach for using the DIC technique combined with the slitting method, while excluding the rigid body motion and rotation artifacts from the obtained displacements. [ 55 ] The results showed that different slitting increments appear to induce different rigid body motions and specimens’ rotations. The proposed method was able to eliminate all these different shears and stretches in the images simultaneously.…”

Residual stress in fiber reinforced thermosetting composites: A review of measurement techniques

“…[42,46] The latter of which has been used to investigate residual stress on a nanoscale in thin films. Recently, Salehi et al [47] applied 2D DIC with incremental slitting to investigate the macro scale residual stress in a cross-ply sample. It was found that shear effects and rigid body motion was high for some of the slitting increments.…”

A Review of Prestressed Fibre-Reinforced Polymer Matrix Composites

“…The slitting method is another destructive testing method employed in measuring residual stresses. In several studies, this is also referred to as incremental slitting [ 96 ], crack compliance or compliance [ 97 , 98 ]. The method involves making a slit in a prestressed material and measuring the resulting deformation normal to the direction of the slit by using a strain gauge.…”

“…Furthermore, the method can be applied to materials with complex shapes, and high-magnitude residual stresses at both micro and macro scales can be accurately predicted. However, the XRD method is only suitable for polycrystalline materials and the accuracy measurements can be affected by the grain size and texture [ 96 , 99 ]. The XRD method has reportedly been used to measure residual stresses in alloys [ 100 , 103 ], glass–ceramic matrix composites [ 104 ] and graphite–polymer matrix composites [ 105 ].…”