Assessment of NASYRAN and PAFEC F-111 WPF FE Models for Elastic Notch Strain Determination at FFVH #l3 and FFVH #14

The current AMRL PAFEC and NASTRAN F-111C wing pivot fitting WPF finite element FE models have been compared to assess their suitability for use in structural integrity investigations, relating to elastic notch strain predictions, at the two critical fuel flow vent holes FFVHs. Here a comparison is made between the predicted elastic strains and the measured strain data obtained from a full scale wing test. It was found that the PAFEC model accurately predicts the strain distribution around FFVH 13, however it incorrectly predicts significantly higher strains in FFVH 14 and greater bending of the wing skin above FFVH 14. In contrast, the NASTRAN model gives accurate results for the large stress gradient around both FFVH 13 14, and upper plate bending, when higher order p elements are used. Hence it is considered that while FE analyses of FFVH 13 in the F-111 WPF can be accurately completed with either the current PAFEC or NASTRAN model, only the latter is suitable at FFVH 14. Hence the NASTRAN model is the recommended model for general elastic WPF structural integrity assessments, and continued development where appropriate.