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Isolation of residual shear stress effects in slitting measurement of residual normal stress in laminated composites

The conventional strain gauge slitting method is usually used to determine the residual stress component normal to the slit plane. Therefore, it is assumed that residual shear stresses released in the slit plane have no effect on the released strains measured by strain gauge. This assumption is valid when measuring released strains by back surface strain gauges. However, in the top surface measurements, it is not true and neglecting residual shear stresses could create a biased estimation of residual normal stresses. In this research, a method based on the use of two symmetrically-placed strain gauges is proposed to separate the measured strains due to residual shear stresses from those due to residual normal stresses in the slitting method. In order to validate the proposed method, two series of slitting experiments were carried out on angle-ply carbon/epoxy laminated composites. The near-surface residual normal stresses were measured using the proposed method. These stresses were also determined using strain data obtained from the back surface strain gauge. Results of both experiments showed good agreement and thus verified the validity of the proposed method for the elimination of residual shear stresses effects in the slitting method.