Hill Engineering Blog

Residual stress in linear frictions welds

In a previous blog post we discussed, in general, issues related to residual stress in welding. In this post, we’ll follow up with a more detailed look at a specific welding application – linear friction welding of titanium alloys.

Titanium alloys are widely used in aerospace applications for their high strength to weight ratio, good corrosion resistance, and metallurgical stability. New joining methods are being implemented that allow for more efficient manufacture of titanium components. Linear friction welding (LFW) is a solid phase bonding process, which is particularly appropriate for titanium alloys. Due to the titanium’s great affinity for oxygen, nitrogen, and hydrogen, protective atmospheres must be used to prevent contamination of the welded material. LFW avoids the formation of a liquid phase during the welding process, and can therefore be carried out in air. Likewise, the typical defects caused by melting and solidification during traditional welding process such as pores, pinholes, shrinkage cracks and grain coarsening are avoided. However, as with all welding and deformation processes, understanding the weld residual stress is important. Continue reading Residual stress in linear frictions welds

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. Continue reading ASIP Conference

Residual stress analysis

Material fabrication processes like forging, rolling, extrusion, quenching, additive manufacturing, machining, and welding lock spatially varying residual stress fields into structural materials. These residual stresses can influence the way that materials perform (e.g., fatigue, fracture, distortion, and corrosion). Hill Engineering has developed expertise to support many different types of residual stress analysis, which we apply to help our customers manage residual stresses effectively in design. The following are some examples of residual stress analysis. Continue reading Residual stress analysis

Axes & Alloys mix metal with music!

Who says engineers don’t know how to have fun?

Axes & Alloys is a band comprised of six of Hill Engineering’s employees. Formed out of a shared love for all things rock n’ roll (or maybe pop, country, and some rock), the Axes got our start around three years ago, with original members Teresa (lead vocals), Adrian (guitar), and Brett (guitar). Their casual rehearsal format eventually welcomed Camille as the keyboardist, Robby as a second singer and keyboardist, and Justin as drummer. Continue reading Axes & Alloys mix metal with music!

Residual stress in welding

Welding is a very common manufacturing process that is used to join materials together to form assemblies and systems. In many cases the welded joints are large, have reduced material properties (e.g., stress corrosion cracking resistance, fracture toughness), and contain defects. The welded joints tend to be critical locations in terms of design and sustainment. For this reason, residual stress in welding is a primary concern. Hill Engineering has extensive experience with residual stress measurements and welding residual stress. Continue reading Residual stress in welding

AFGROW User Workshop

Hill Engineering is presenting about fatigue analysis as part of the AFGROW User Workshop 2016 in Layton, UT. The objective of the workshop is to provide a forum for AFGROW users to exchange information and ideas related to fracture and fatigue. Hill Engineering’s presentation will include a summary of recent work on the formulation and solving of benchmarking problems in the field of fatigue crack growth analysis. The abstract text is presented below. Continue reading AFGROW User Workshop

Welcome Frank Di Cocco

We would like to welcome Frank Di Cocco as Program Development Manager to Hill Engineering. Frank comes to Hill Engineering with more than 25 years of experience, most recently from Alcoa Technical Center. At Alcoa, Frank was the Manager of Alcoa Defense Aerospace, where he directed government and commercial aerospace programs focused on developing structures technologies. Frank brings valuable experience leading large, multi-year aerospace programs as a prime government contractor and managing diverse teams of OEM and technical specialists like Boeing, Airbus, Lockheed Martin, BAES, and Northrop Grumman. Continue reading Welcome Frank Di Cocco

Hill Engineering visits Sugar Pine Point State Park

To me, nothing says “summer” more than camping by the lake, going for a hike, roasting marshmallows over a campfire, and fatigue analysis at bedtime. On the west side of Lake Tahoe, the Ed Z’berg Sugar Pine Point State Park hosted some of Hill Engineering and their families for a fun, nature-filled weekend. Continue reading Hill Engineering visits Sugar Pine Point State Park

Happy Birthday to the Contour Method!

Today marks a major milestone in the field of residual stress measurement. The contour method, one of the most useful and advanced residual stress measurement techniques, was first successfully implemented on this date (August 16th) in 1999 by Mike Prime at Los Alamos National Laboratory. The most significant feature of the contour method is its ability to generate detailed two-dimensional residual stress maps like the one shown below. Please join us in wishing the contour method a very happy 17th birthday! Continue reading Happy Birthday to the Contour Method!