Application of Digital Image Correlation to Address Complex Motions in Thermoelastic Stress Analysis

Abstract

Abstract:A motion compensation method for thermoelastic stress analysis (TSA) is described that uses digital image correlation (DIC) to capture the displacement field on the surface of the specimen. The displacement field is used to correct the infrared (IR) images to remove the effect of the motion of the specimen from the TSA. As the DIC displacements are obtained with a relatively high spatial resolution, sharp displacement gradients and discontinuities can be corrected. The feasibility of the motion compensation method for TSA is investigated firstly by validating the approach using data obtained from an aluminium alloy plate with a central circular hole loaded in tension and comparing the results with a finite element model. It is shown that the motion compensation approach significantly improves the accuracy of TSA, particularly when high magnification optics are used. Next, the feasibility of simultaneous capture of IR and white light images is investigated. It is shown that by using the correct combination of paints, a speckle pattern can be applied to the surface to provide contrast in the white light spectrum for the DIC, but have a uniform emissivity in the IR spectrum so that there is no effect on the TSA. Thus it is possible for the motion compensation to be conducted on data collected during fatigue tests. Finally, it is demonstrated that the motion compensation technique can be applied to discontinuous motion produced by face sheet debonding in a foam cored sandwich structure loaded in a double cantilever beam (DCB) configuration. It is shown that the motion compensation technique is capable of correcting the complex and non-uniform motion for TSA in the DCB test, thereby enabling detailed thermoelastic data to be obtained from the vicinity of the crack tip.Keywords: Thermoelastic stress analysis (TSA), Motion compensation, Digital image correlation (DIC).Wang W., Fruehmann, R.K. and Dulieu-Barton, J.M., "Application of digital image correlation to address complex motions in thermoelastic stress analysis", Strain, 51, 2015, 405-418.

Data-rich characterisation of damage propagation in composite materials

“…The large variation of paint thickness is due to the surface roughness of the material; an artefact of the peel-ply fabric required during manufacture. No difference in IR response could be noted as a result of the applied speckle pattern as confirmed in [15].…”

“…As the specimen is cyclically loaded it is also necessary to account for the effects of rigid-body motion on TSA [15]. Rigid body motion during the recording of an IR video is detrimental to TSA analysis as the incident IR radiation of an individual pixel becomes a combination of the original sampling area and surrounding areas.…”

“…There have been a few publications where TSA and DIC have been combined [15,16] but not on data that has been captured together in a synchronised manner. In [15] white light images were captured separately and used to correct for the motion in the IR data to improve the accuracy of TSA.…”

“…Since the spatial resolutions of the two data types are different, the locations of the DIC and IR data are not coincident. A bilinear interpolation method was used similar to that described in [15] to resample the DIC displacement data at the IR pixel locations, so allowing the IR data to be shifted to track the deformation of the surface and allowing the two data types to be compared. This procedure was repeated iteratively for each image collected.…”

“…In [15] white light images were captured separately and used to correct for the motion in the IR data to improve the accuracy of TSA. In [16] the failure mechanisms in an adhesively bonded joint were studied using single camera DIC and TSA.…”