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Considerations of environmental conditions for the fatigue evaluation of composite airframe structure

: Berg, M.; Gerharz, J.J.; Goekgoel, O.

American Society for Testing and Materials -ASTM-, Philadelphia/Pa.:
ASTM special technical publication 1012
Philadelphia/Pa., 1989 (ASTM STP 1012)
pp.29-44 : Abb.,Tab.,Lit.
Book Article
Fraunhofer LBF ()
Faserverbundkonstruktion; Festigkeitsnachweis; Kohlenstoffaserverstärktes Epoxyd; Lebensdauer; Restfestigkeit; Temperaturwechsel; Umgebungseinfluß

This paper reports on experimentally derived compensation factors to account for missing environmental history (temperature and humidity) during fatigue testing of large composite structures (components). Compensation factors are either factor by which the fatigue tests is increased or by which the required residual strength has to be increased if preloading did not include environmental history. Preconditioned coupon specimens were subjected to accelerated quasirealistic mechanical and environmental flight-by-flight loading, and other coupon specimens were loaded exactly like the composite airframe structure (that is, with less complete simulated environment). Temperature and moisture content in residual strength testing were the same for surviving coupon specimens and the composite airframe structure. Different types of laminates and specimens were used to generate predominantly matrix shear stresses or fiber normal stresses within the coupon specimens. At present design load levels, the fatigue life to be proven was reached without failures of the coupon specimens subjected to the flight-by-flight load conditions of the component test or to quasirealistic combined mechanical and environmental loading.