Hill Engineering is presenting at the upcoming 2018 United States Air Force Structural Integrity Program Conference (ASIP) in Phoenix, AZ. Our talk will focus on residual stress evaluation in legacy aircraft cold expanded fastener holes. The 2018 ASIP Conference is specifically designed to bring together the world leaders in the area of aircraft structural integrity, to disseminate information on state-of-the-art technologies for aircraft structures in both the military and civilian fleets. Hill Engineering’s presentation will include a summary of recent work in airframe structures, demonstrating the effect of aircraft service on the residual stress at cold expanded fastener holes. The abstract text is presented below.
Compressive residual stress treatments are known to significantly improve fatigue resistance, but the persistence of the improvements in the face of typical structural usage is unclear. A recent program was performed to quantify residual stress in aircraft structure that had seen full service life. Maps of residual stress at cold expanded fastener holes were obtained using the contour method. Residual stress data were gathered on post-service parts recovered from teardown and on mock-ups that were newly manufactured. Post-service parts consisted of sections cut from areas on the lower wing skin and spar caps of legacy aircraft. Some post-service parts had cold expansion installed on the production line while other parts had cold expansion installed during post-fielding modifications or rework scenarios. Comparisons of residual stress distributions near typical crack nucleation features provide measures of the differences between post-service and newly manufactured cold expanded holes. Observed differences may be due to differences in the cold expansion installation process or to in-field events during service. The presentation provides a summary of the program scope, observed differences in residual stress for new and post-service cold expanded holes, and the potential effect of differences on fatigue performance.
This is the 34th year of the ASIP Conference in its current format, although similar meetings occurred in the 1970s. This year also marks the 60th anniversary of the publication of the initial requirements for the US Air Force’s Aircraft Structural Integrity Program.
If you are planning to attend the conference please stop by to discuss Hill Engineering’s capabilities in fatigue analysis and designs and residual stress measurement. Please contact us for more information.