Shape Optimisation of Two Closely-Spaced Holes for Fatigue Life Extension
Abstract
This report presents a set of free-form optimal shapes and the corresponding stress concentration factors for two interacting closely-spaced holes in a large biaxially loaded plate. A range of interaction distances and two distinct biaxial loading cases are considered, namely tensile field (remote principal stresses have the same sign) or mixed field (remote principal stresses have the opposite sign). The optimal shapes are obtained using the finite element analysis based gradientless shape optimisation method recently developed in AVD. In a key unexpected result, which has not previously been identified, it has been discovered that the peak stress associated with the optimal holes is independent of the interaction distance, and that the peak stress is the same as that for an optimal single hole. In both stress field cases, the absolute value of the tangential stress is piecewise constant around the hole boundary. Compared to interacting closely-spaced circular holes, which are a common feature in aircraft structures producing significant stress concentrations that often lead to premature fatigue cracking, the optimal hole shapes provide for very large reductions in peak stress (typically greater than 30%), which results in a substantial increase in fatigue life. The freeform optimal shapes are presented in a tabular form that allows them to be used readily by designers. For the tensile biaxial field, the optimal shapes are smooth and non-circular. For the mixed biaxial field case, the optimal shapes are approximately rectangular with sharp comers and curved sides and no stress singularities are present at the comers.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2003
- Accession Number
- ADA417887
Entities
People
- L. R. Rose
- Manfred Heller
- Witold Waldman
Organizations
- Defence Science and Technology Group