Search Results

Additive Manufacturing (AM) provides significant opportunities in aerospace applications, especially for low-volume, highly customizable parts. Besides the flexibility of part design, the approach offers significant potential of reducing product manufacturing complexity and improving in-service performance. This paper discusses an example which is in serial production at Howmet Fastening Systems. The part is a latch used in a hold-down assembly for avionics. The primary driver for the initiative was the need for increased torsional strength within the geometric constraints of the baseline design. Finite Element Analysis was used to redesign one load limiting component to improve overall torsional capability. Design for AM (DFAM) was used to successfully produce the parts without any defects with limited post-processing. Comprehensive testing included component tensile, fatigue, and microstructure characterization along with assembled part testing.

Multi-fastener lap joints are vulnerable to fretting fatigue when they are subjected to repeated loading. In general the fretting fatigue condition leads to degraded properties of metallic structures due to the presence of the surface stress concentration resulting at the sites of fretting pits. In many cases, fretting can result in premature structure failures therefore a series of counter measures are frequently taken to minimize fretting especially at the fastener holes. One of major factors that affect the fretting phenomena between the fastener and fastener hole is the surface condition of the fasteners. In this study, the influences of the surface texture and the surface plating of the fastener on the joint life were investigated by conducting double lap shear fatigue testing. It has been found that the joint fretting fatigue resistance is very sensitive to the surface texture of the fastener and as the surface roughness of the fastener is reduced the joint life increases.

Drilling fastener holes in composite is much more difficult than in aluminum or other metallic materials since individual carbon fibers fracture at irregular angles resulting in numerous microscopic voids. These voids can trap excess sealant inhibiting the intimate electrical contact between the fastener and the composite structure. As the cutting tool wears there is an increase of surface chipping and an increase in the amount of uncut fibers or resin. This condition is referred to as machining–induced micro texture. Machining–induced micro texture has been shown to be associated with the presence of arcing between the fastener and the composite structure during lightning strike tests. Lightning protection of composite structure is more complex due to the intrinsic high resistance of carbon fibers and epoxy, the multi-layer construction and the anisotropic nature of the structure.

Light weight aerospace fastening collars were manufactured from 2099 alloy which is a new generation Al-Li alloy developed by Alcoa. The collars studied in this work are threaded self-locking collars with controlled torque-off feature and are to be used in a fastener assembly with a treated pin. The mechanical properties of 2099 collars were measured and compared to the ones made of incumbent alloys such as 7075 and 2024. It was found that the 2099 collars were 16% lighter but provided the equivalent mechanical properties. In addition, the corrosion characteristics of the 2099 collars were studied using the salt spray and alternate immersion test methods. It was observed that 2099 collars exhibited an improved corrosion performance as compared to the base line 7075 collars. This paper presents the results obtained from the mechanical and corrosion testing of the Al-Li collars along with the weight saving potentials of the new product.