Hill Engineering Blog

ASIP Conference

Hill Engineering is presenting about fatigue analysis methods for cold expanded aircraft fastener holes at the upcoming 2016 Aircraft Structural Integrity Program (ASIP) Conference in San Antonio, TX. Cold hole expansion is a method commonly used to induce compressive residual stress around the perimeter of fastener holes, which are common in aircraft structure. The compressive residual stress has significant benefits related to fracture and fatigue of the structure. Hill Engineering’s presentation will include a summary of current analysis methods and a plan for how these methods can evolve to allow for improvements in aircraft design and sustainment. The abstract text is presented below.

The fatigue life benefits of engineered residual stress processes such as cold expansion of fastener holes and laser shock peening are well known and have been demonstrated by test in countless applications over the past few decades. Typical USAF methodologies do not directly account for the effects of residual stress and consequently often do not accurately replicate the fatigue life improvement from these processes. This has contributed to the USAF hesitation to take advantage of these benefits in damage tolerance analyses. Recent collaboration between the USAF, NRC-Canada, and multiple contractor partners have resulted in significant strides to establish and refine the analytical tools for cold expanded fastener holes and other engineered residual stress processes.

This presentation will give an overarching review of engineered residual stress tools and the contributions from the various team members in the sustainment community. The key developments to date, focus areas in work, gaps remaining, and the transportability of the analytical approaches and tools to other “deep” residual stress inducing processes will also be reviewed.

If you are planning to attend the conference please stop by to discuss Hill Engineering’s capabilities in fatigue analysis and design and residual stress measurement. Please contact us for more information.

Compressive residual stress near a cold expanded fastener hole (measured by the contour method).