Stresses and Strains in Thick Perforated Orthotropic Plates

Stress and strain concentrations and in-plane and out-of-plane stress constraint factors associated with a circular hole in thick, loaded orthotropic composite plates are determined by three-dimensional finite element method. The plate has essentially infinite in-plane geometry but finite thickness. Results for Sitka spruce wood are emphasized, although some for carbon-epoxy composites are included. While some results are similar to those for isotropy, there are significant consequences due to material orthotropy. Maximum stress and strain concentration factors occur at midplane for thin plates but closer to the external traction-free surfaces for thick plates. These factors decrease as the plate surface is approached and reach lower values unrepresentative of the maximum values. Differences between the midplane and/or maximum and surface stress or strain concentration factors in Sitka spruce, range from 8% if the wood grain is parallel to the vertically applied load to 15% when the grain is perpendicular to the load. These values exceed those typically reported for isotropic materials. Stress and strain concentration factors tend to differ in magnitude from each other. The combination of high local stresses and directional strength dependency of orthotropic materials can be particularly important. That maximum stress and/or strain concentrations in thick plates occur on other than the external plate surfaces where they are most readily measured is technically significant. The $E_{11}/E_{22}$ ratio in Sitka Spruce exceeds that in the carbon composite by 60%. However, when loading parallel to the strong/stiff directions, the plane-stress tensile stress concentration factors of the two materials are comparable to each other.