NASAfacts

National Aeronautics and Space Administration

AERoBOND Project 

Sustainability of the commercial air travel 

industry requires new aircraft with ultra-efficient 

structures and designs, which will depend 

largely on lightweight polymer composites 

and new assembly methods. Manufacturers 

of commercial transport aircraft are compelled 

to install thousands of redundant fasteners into 

bonded joints to prevent failures due to 

unpredictable weak bonds. 

The Adhesive-Free Bonding of Complex Composites (AERoBOND) process enables re-flow 

of matrix resin during assembly to eliminate the 

material discontinuity at the interface, thereby 

eliminating the dependence of mechanical 

performance on interfacial adhesion.

Under NASA’s Convergent Aeronautics Solutions 

project, the AERoBOND project investigated offstoichiometric epoxy polymers for fast, reliable 

assembly of epoxy matrix composite structures. 

The project goal was to demonstrate feasibility 

of the AERoBOND joining method by 

demonstrating mechanical properties greater than 

80% of conventional co-cured materials while 

reducing structure weight by 1%. The project 

consisted of three convergent research areas: 

material and process development, systems

A seven-point stress test is used to test the bonding 

of materials. 

analysis, and material and process 

modeling. Material and process development 

was the largest component of AERoBOND in 

order to formulate and characterize new 

resins, prepare carbon fiber prepregs, 

fabricate laminates, measure mechanical 

properties, analyze failure results, and select 

material and process improvements.

Rapid Assembly 

• Rapid, reliable assembly of

composite structures to reduce/

eliminate redundant fasteners

• Enables unitization without

complex tooling or processing

• Reduce part counts

• Eliminate drilling/installation

• Add no process time/steps

• No performance knockdown
The systems analysis activity estimated the potential 

reduction in part count and aircraft weight by comparing models of composite wing boxes with no fasteners 

(co-cured structure), fasteners in major joints (co-cured 

stringers), and fasteners in all joints. The materials and 

process modeling activity included a molecular model 

of the AERoBOND materials system to predict mechanical properties of resins with offset stoichiometry and a 

process model to predict the effect of resin formulation 

and processing conditions on the extent of mixing and 

degree of cure in a finished joint. 

The AERoBOND joint is equivalent to the interlaminar 

region obtained during a co-cure process, so joint performance depends on the cohesive properties of the matrix 

resin. Conventional co-cured structures, although too 

costly and complex for large-scale manufacturing, are 

trusted by manufacturers and regulators, and are certified for flight with few or no redundant fasteners. 

The AERoBOND process model is partially validated 

and available for experimental use. It allows the user to 

input AERoBOND process parameters such as material 

composition, laminate configuration, and cure cycle to 

predict the final cure state of the AERoBOND joint. A 

preliminary, multi-scale material model was developed 

to predict AERoBOND joint mechanical properties (stiffness and strength) based on the cure state of the joint 

provided by the process model. 

AERoBond Benefits 

 Systems analysis performed on a composite wing 

model at the scale of a single-aisle commercial transport aircraft indicated that more than 20,000 redundant 

fasteners per wing could be eliminated by implementing the AERoBOND joining method. 

 A total weight reduction of 15% was predicted in a wing 

box by eliminating fasteners and thinning components 

that must no longer support localized fastener loads 

and accommodate fastener dimensions. 

 Interlaminar shear fracture toughness measured by 

the end-notched flexure test was greater than 1 kJ/m2

(nearly 140% of the co-cured benchmark property), 

which is greatly in excess of the project goals for 

mechanical properties. 

The AERoBOND eliminates 

the potential for weak 

bond failure mode. 

The AERoBOND joint is 

indistinguishable from the 

matrix resin of adherends. 

NASA researchers print the experimental adhesive using a special 

prepegger tape machine. 

Rib 

Skin

Stiffener Fasteners

National Aeronautics and Space Administration 

Langley Research Center

Hampton, VA 23681

www.nasa.gov

NASA Facts 

FS-2020-10-297-LaRC