NASA’s next-generation launch vehicles will be enabled by high-performance composite materials and innovative manufacturing methods. As such, NASA uses adhesively bonded joints where possible instead of mechanically fastened (bolted) joints to design and manufacture structures. The adhesive joints typically are lighter and distribute loads more efficiently across an interface, while mechanically fastened joints are prone to stress concentrations around the bolts.

The (a) single and (b) DRJ Adhesively Bonded Joint architectures. All face sheets and splice plates are solid laminates composed of unidirectional laminas.
A new adhesively bonded joint concept has been developed for curved and flat panel sandwich architectures. The durable redundant joint (DRJ) offers improved reliability (safety) and additional load transfer features for sandwich structures when compared to conventional H-type joints. The DRJ uses a composite preform to connect two ends of a curved, composite sandwich panel to form, for example, a cylindrical vehicle segment.

This innovation features a joint architecture comprising redundant adhesive load paths via a laminated or woven preform composite insert. This insert, placed into the seam between sandwich panels, provides a larger total bonding area and multiple load paths for an improved distribution of load through the joint. Safety is primarily improved through two mechanisms: 1) creating an additional load path for instances when a manufacturing defect compromises one of the bonded joints and 2) creating an “inner” joint that is less susceptible to impact damage due to tool drops and transportation anomalies. Additionally, the circumferential load strains on each joint are decreased compared to a conventional double strap-type joint. The redundant load paths allow for efficient load redistribution in the case of a partial joint failure, and have been demonstrated to fail in a benign manner. The improved load transfer capability can be tailored for specific applications, and has a minimal mass increase when compared to the overall component mass.

This work was done by Eric C. Lundgren and Stanley S. Smeltzer III of Langley Research. LAR-17813-1

Topics:
Adhesives and sealants Anatomy Architecture Body regions Composite materials Head Joining Launch vehicles Manufacturing & Prototyping Manufacturing processes Medical, health and wellness Medical, health, and wellness Research and development Spacecraft Vehicles

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    This article first appeared in the September, 2014 issue of NASA Tech Briefs Magazine (Vol. 38 No. 9).

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