SBIR-STTR Award

To address the problems faced by the DoD regarding pi joint reliability, MAM shall utilize an innovative, aligned discontinuous fiber material format from Boston Materials inserted using ultrasonic vibrations to create toughened interfaces at the pi-joint bond line and also between plies of the laminate. By increasing the toughness at these interfaces, failures will be driven deeper into the laminate, resulting in reduced scatter and a more predictable failure mode. A significant additional benefit of reducing the scatter is that the effective design allowable will be increased, allowing for weight reductions and/or increased margins. Using the companys collective experience in developing adhesive bonding technology and bond reliability over the past three decades, MAM and their partners Boston Materials and SwRI will execute a program that demonstrates the benefits of these reinforcements and also utilizes models to gain better understanding of the interfaces. The TRUST project from DARPAs Open Manufacturing program will serve as a launch point, and the models generated by TRUST will be the baseline.

Benefit:
If Maher Advanced Manufacturing succeeds in all facets of this effort, it shall make a major impact for the DoD. Within 24 months of a Phase I contract award and follow-on Phase II, the DoD can expect: A proven method for increasing interface toughness for all bonding (not just pi-joints). Beginning to develop joint allowables that allow for parts to be properly designed without adding additional weight. A working predictive model to assist in the design of future bonded joints. Using the model as a guide, process reliability shall be able to deliver 95% process reliability with 95% confidence.

Keywords:
Confidence, Confidence, Reliability, ultrasonic horn, Bonded Joints, aligned fiber, Composite structure, toughened interfaces, Modeling

The aerospace industry has been transitioning to the use of pi joints as an assembly technique for primary structure to reduce both the weight and costs of these assemblies by eliminating the cost and weight of using fasteners. The pi-joint is a woven preform co-bonded between a skin and a stringer. While these joints are inherently weight-effective for highly loaded structural applications, the structures are susceptible to process-related variations and nonconformance issues, including variable porosity, resin pooling, and thickness variations. Maher Advanced Manufacturing has developed a process to improve the reliability of the pi-Joint through processing techniques and a new carbon fiber format. The Phase II program continues to mature this technology as well as demonstrate utility in sub-scale component demonstrations.

Benefit:
Maher Advanced Manufacturing has an improvement of at least 15% minimum increase in the resin dominated properties properties such as through thickness tensile, lateral shear, and tensile pull-off and a reduction in scatter of 44%. Maturation of the technology will enable increased utilization of pi-joint assembly of Aerostructures. This increased use will reduce costs, and increase performance of composite aircraft and vehicles in the aero defense sector, commercial aircraft, and unmanned vehicles, and urban air mobility.

Keywords:
Z-reinforcement, Composites, JOINING, Pi-joint