Residual Stress Alleviation of Aircraft Metal Structures Reinforced with Filamentary Composites.
Abstract
Residual stresses occur in composite-reinforced metal structures as a result of the elevated temperatures employed to cure various structural adhesives and the differing coefficients of thermal expansion of the materials being bonded. Methods to eliminate or reduce residual stresses were explored during this program. Residual stress level reductions were achieved in this program by modifying the manufacturing procedures used during adhesive bonding. The residual stress alleviation techniques involved various forms of mechanical constraint which were applied to the components during bonding. Nine methods were evaluated, covering a wide range in complexity. Some specimens were assembled with no tooling, while others employed complex tooling capable of generating preloads. All methods investigated during this program affected the residual stress level. In general, residual stresses were reduced by 70% or more from the stress level produced by conventional adhesive bonding procedures. The most effective method used during this study employed a steel tool capable of loading the metal component in compression prior to the bonding cycle. The other methods were slightly less effective due to the presence of elastic deformations in the vicinity of mechanical fasteners. The bonded load transfer region between the fibers and the stepped titanium load transfer fittings experiences creep deformation which can lead to delamination at the higher bonding temperatures (450 deg K, 350 deg F) and high shear stress levels produced by some assembly techniques.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1973
- Accession Number
- ADA300469
Entities
People
- J. B. Kelly
- R. R. June
Organizations
- Boeing