Static and fatigue performance of highly loaded thermoplastic fittings

Thermoplastic composites were applied to one of the more challenging and highly loaded fittings in aircraft structures, bathtub fittings. Bathtub fittings with multiple intersecting walls were designed using finite element analysis and special purpose software and were subsequently manufactured using press-forming of pre-heated flat blanks with varying thickness. Non-destructive Computed Tomography (CT) scans were used to evaluate the quality of the resulting parts. Subsequent static tests demonstrated strength 5% lower than the design strength and in close agreement with analysis predictions. Fatigue tests showed excellent performance with the failure mode not caused by the out-of-plane stresses in radius regions. A recently developed methodology for fatigue predictions based on the amount of energy dissipated per cycle was applied and was in very good agreement with the test results.