Repairs to Damage Tolerant Aircraft
Abstract
Results of displacement compatibility analysis, representing a variety of repair doubler and lap splice configurations, are presented to illustrate how structural repairs can degrade the fatigue initiation life and damage tolerance capability of primary transport aircraft structure. Examples show that fatigue initiation life is directly related to the peak loads induced in the first fastener rows at the edges of repair doublers. Design of repairs to an equal or better static strength capability and the associated static strength analysis will not normally highlight these peak loads which can result in considerable degradation of structural fatigue life. Critical fastener loads, based on displacement compatibility analysis accounting for fastener flexibility, are parametrically presented for a variety of skin and doubler thicknesses. Suggestions are made on how repair designs can be modified to improve fatigue initiation life and subsequent fatigue crack detectability particularly in the event of multiple-site damage. The importance of riveting quality during repairs, often not up to initial manufacturing standards, is discussed with respect to fatigue initiation life. A simplified but conservative method to generate crack growth curves is discusses with a view to easing the analytical burden for the small modifiers. It is hoped that this information, together with conservative fatigue Sn data, will help the many small repair and modification stations gain an appreciation of the fatigue and damage tolerance quality of structural repairs.
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 22, 1990
- Accession Number
- ADA225742
Entities
People
- T. Swift
Organizations
- Federal Aviation Administration