Alleviation of stress concentration with analogue reinforcement

In order to reduce the stress concentration around a hole in a plate, new, “analogue” reinforcements instead of reinforcing rings were used in this investigation. In two of these specimens, reinforcements with different volume fractions were arranged to coincide with the stress trajectories for an infinite plate with a hole under uniaxial tension, Two other specimens contained straight rectangular-grid type reinforcements with different volume fractions. These 0.005 in. thick brass reinforcements were made by using a photofabrication method. Specimens were then prepared by sandwiching these reinforcements between two epoxy resin plates. Plane specimens, i.e., without reinforcement, were also made of the same epoxy resin for comparison.

The stress concentrations at the edge of the hole under uniaxial tension were determined by photoelastic techniques. The measured stress concentration factors were compared with well known values for an infinite isotropic, homogeneous plate containing a hole. Results were also compared with published data on [90/0/90/0̅]_s 7-ply laminate composite plates, and on plates strengthened with reinforcing rings.

A definite reduction in stress concentration was observed on specimens containing analogue reinforcement.