Characterization of residual stresses in a thin-walled filament wound carbon/epoxy ring using incremental hole drilling method

The incremental hole drilling method was used to assess the curing-induced residual stresses in a filament-wound carbon/epoxy ring. In the isotropic materials, the relationship between the relaxed strains in the successive depth increments and the unknown residual stresses has a trigonometric form. However, the severe anisotropic character of a filament-wound composite ring, which results from the different mechanical properties of a single layer in the longitudinal and transverse directions as well as the dissimilar orientation of the adjacent layers, necessitated the development of a more general formulation by introducing new compliance coefficients. The calculation algorithm, which solves the inverse problem of residual-stress estimation, is based on the Integral method, which assumes that the stress in each depth increment is uniform. High tensile hoop stresses (similar to 220 MPa) were found at the inner surface of the ring. Also, a compressive hoop stress (similar to-140 MPa) was observed at the outer diameter. The residual hoop stresses were also measured by the slitting method. The results of the two techniques were very similar in trend. (C) 2014 Elsevier Ltd. All rights reserved.