Defense hole design system for multiaxial stresses by combined stereolithography, photoelasticity, image processing and FEA

Reducing stress and weight of structures is one of the main goals of designers. Most engineering structures are an assembly of different parts. On most of these structures, parts are assembled by bolts, rivets, etc. The holes that are produced for such joints produce stress concentrations, which are potential sites for fracture initiation.; Defense hole theory deals with introducing auxiliary holes beside the main hole to reduce the stress concentration. In this research, a defense hole system under shear as well as general loading is investigated and an enhanced hybrid technique of stereolithography, image processing and photoelasticity is developed. This study is intended to determine the optimum defense hole system for a circular hole in an infinite plate and demonstrate the validity of the enhanced hybrid technique by optimizing defense holes. A theoretical and experimental study is conducted using a combination of finite element method (FEM) and photoelasticity, stereolithography, and image processing.; Stress concentrations associated with circular holes in pure biaxial shear-loaded plates can be reduced by up to 13.5%. This significant reduction is made possible by introducing elliptical auxiliary holes along the principal stress direction, i.e, ±45° axes with the plate axes. These holes are introduced in the areas of low stresses that appear near the main circular hole. The introduction of these holes in such places helps smooth the principal stress trajectories past the main hole. Three main goals are achieved by introducing such holes: maximum stress reduction, working as crack arrest in case a crack propagates and material reduction.; Stress concentration associated with circular holes in a shear dominant loaded plate (i.e., Uniaxial/Shear_principal ratio from zero to 0.25%) is reduced by up to 17.11%. This reduction is achieved by introducing auxiliary elliptical holes along the principal stress direction. In contrast to the pure shear case the auxiliary holes are not all of the same size, shape and location.; Maximum stress reduction and optimum defense-hole-system parameters are achieved in biaxially loaded plate in uniaxial dominant range (Tensile/Shear > 25%). For the cases under investigation, pure uniaxial load (Tensile/Shear = 200%) has the maximum stress reduction of ≅18%. This reduction is achieved by introducing auxiliary circular holes along the principal directions. (Abstract shortened by UMI.)...