Stress reduction in a plate with a hole by applied induced strains
This work investigates the potential of reducing stresses in the region of stress concentration by applied induced strains. A thin 30 inch square plate with a 1 inch diameter circular hole under uniaxial load was used for this investigation.
This investigation considered first an ideal case with a few physical limitations for the purpose of probing the limits of active stress reduction. Applied induced strains were applied over the region A ≤ r ≤ 1.5A, where A is the radius of the hole. It was found that the axisymmetric applied induced strains could reduce the stress concentration factor (SCF) from 3 to 2. With non-axisymmetric applied induced strain distribution the SCF could be reduced to 1.45. Numerical optimizations based on finite element simulations were also carried out for a composite plate with a hole and similar reductions in stress concentration factors were obtained.
Next, a more realistic case, consisting of bonded and embedded piezoelectric actuators was considered. It was found that partial-thickness actuators produce large radial stresses which erase any benefits associated with axisymmetric actuation.
With non-axisymmetric actuation, the actuators with present technology limitations were found to be effective in reducing stress concentration factor for a fatigue load case. However, due to repetitive nature of the load, the energy expenditure may be large. For an extreme load case, actuators with present technology limitations were not very effective in reducing SCF. Actuators were needed to be placed over a larger area to achieve a larger reduction in SCF. Also, passive stiffening was found to be more effective in reducing stress concentration than bonded actuators with present technology limitations.