Application of probing hole methods to determine residual stresses in composite materials | Mekhanika | kompozitsionnykh | materialov i konstruktsii

Application of probing hole methods to determine residual stresses in composite materials

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Residual stresses can appear due to technological features of the manufacturing process, due to design features (asymmetric stacking), due to long-term force or temperature influences, etc. This work investigates the application of digital image correlation in the probing hole method to determine residual stresses in composite materials. Samples cut from a panel of a polymer composite material with asymmetric stacking were investigated, in which deformations that appeared after drilling a hole in the sample were determined. Deformation fixation was performed non-contactly, using the image correlation method. To improve the accuracy of strain fixation, a pattern was applied to the specimens. Two variants of the pattern were considered in this work: large (marker size 0.05-0.8 mm) and small (marker size 0.02-0.2 mm). Since the residual deformations were small, the coarse pattern did not produce representative results. The experimental deformations obtained were compared with numerical calculations using the finite element method. The solution of the inverse problem of elasticity theory to identify residual stresses was performed in the Comsol system using numerical finite-element modeling, the Monte Carlo method, and the Nelder-Meade method. The Monte Carlo method was used to find the global minimum of the residual stress function, and the Nelder-Meade method to refine the local minimum. The function of deviations of the calculated and experimental data was calculated in the root-mean-square approximation. Small correction values were introduced to refine the mean strain field in the experiment and to ignore the unrecoverable errors associated with the inaccuracy of the experimental data. As a result of the study, the numerical and experimental results were found to sufficiently coincide. The difference of the implemented method from other methods of measuring deformations around probing holes is the obtaining of a complete picture for all strain components.