Volume 28, Issue 6 (November 2000)
Effects of Fixturing Mass on Dynamic Strain Errors in Structural Fatigue Testing
Improvements in control systems have allowed significant increases in testing frequencies for full-scale aircraft structural fatigue tests. This means that it is possible to be testing at frequencies that result in significant dynamic strains, with consequent over-testing.
This paper presents an analysis of a simple cantilever beam as a representation of a test on an aircraft wing. Using a state space formulation and the MatLab mathematical programming system, comparisons between static and dynamic strains for various locations on the beam are made for a variety of loading arrangements.
It is shown that significant dynamic strain errors will occur at testing frequencies above about 10% of the first natural frequency of the specimen itself. The errors can increase significantly due to the mass of the fixturing, and are further exacerbated by static counterbalancing.