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Structural Engineering

Aerospace Biological Civil Geotechnical Mechanical

Safety and Certification of Discontinuous Fiber Composites (DFCs) For Aerospace Applications: Design, Testing, and Computational Modeling

Seminar Speaker
Marco Salviato, PhD
Seminar Date
Wednesday, Feb 23, 2022 - 12:00 pm
Seminar Location - Room
https://ucsd.zoom.us/j/98205861838
Speaker Bio

Dr. Salviato is an associate professor in the William E. Boeing Department of Aeronautics and Astronautics of University of Washington where he serves as the PI of the laboratory for Multiscale Analysis of Materials and Structures (MAMS). Before joining the University of Washington in 2015, Dr. Salviato obtained a Ph.D. in Theoretical and Applied Mechanics in 2013 from the University of Padova (Padova, Italy) with a doctoral dissertation focusing on the experimental characterization and computational modeling of polymer nanocomposites. He later joined the Department of Civil and Environmental Engineering at Northwestern University as postdoctoral scholar (2013-14) and research assistant professor (2014-15).

Dr. Salviato’s research and teaching interests lie in the area of Computational Mechanics and Fracture Mechanics of Quasibrittle Solids. His goal is understanding the mechanical behavior of materials and structures at multiple length-scales through the formulation of advanced computational and analytical approaches and new experimental techniques. He believes that the next-generation, damage-tolerant infrastructure will be enabled by the elimination of the old dichotomy between the concepts of “structure” and “material”. His work has been funded by several agencies and industrial sponsors including the Federal Aviation Administration, the National Science Foundation, the Air Force Research Laboratory, and Boeing.

In 2017, Dr. Salviato received the prestigious ASME Haythornthwaite Young Investigator Award for “excellence in theoretical and applied mechanics”. In 2020, he was the recipient of the DSTech Young Composites Researcher Award, an honor bestowed by the American Society for Composites on the most promising young researchers in the field of composites. In 2021, Dr Salviato published the book “Quasibrittle Fracture Mechanics and Size Effect: A First Course” (Oxford University Press) with co-authors Dr. Le (University of Minnesota) and Dr. Bažant (Northwestern University).

Composite materials are finding increasing use across the most important industrial sectors including e.g. aerospace, automotive, and wind energy. This is owed to their excellent specific mechanical properties and their taylorability paving new avenues for structural optimization and weight savings. Engineering marvels such as the Boeing 787 have already proven the benefits of composites and showed that it is possible to adopt these materials in the commercial sector. However, one of the biggest challenges for the future of composites is being able to increase production rates and manufacturing efficiency while drastically reducing costs. In fact, standard manufacturing processes for composites are labor intensive, involve the use of large and expensive autoclaves, and require costly post-machining. 

An interesting technology to mitigate the shortcomings of traditional composite manufacturing is compression or injection molding of Discontinuous Fiber Composites (DFCs). DFCs (also known as chopped fiber composites) are made of platelets cut from thermoset or thermoplastic prepregs. Thanks to the platelet form, DFCs can easily fill molds featuring very complex geometries which would not be feasible with UD or textile composites. This means that DFC parts can be produced net-shape requiring minimal post-processing. At the same time, the use of compression or injection molding enables the attainment of production rates and costs comparable to plastics, which is unprecedented in the field of composites. Finally, thanks to the mesostructure of DFCs which features several platelet interfaces which can favor the emergence of energy absorption mechanisms such matrix microcracking and delamination, DFCs feature mechanical properties comparable to ductile materials such as aluminum. This makes DFCs an interesting material candidate even in applications that have always been a prerogative of light alloys. 

Considering the numerous qualities of DFCs, it is not surprising that the aerospace and automotive industries are adopting this technology. However, one of the major roadblocks on the wide adoption of DFCs is the lack of proper design and certification guidelines capable of accounting for the specific behavior of this material. This is a very challenging tasks since the performance of DFCs is strongly dependent on the manufacturing and particularly the flow condition of the platelets. Due to the randomness of the platelet orientation, DFCs feature large Coefficients of Variation of mechanical properties. Moreover, DFCs are significantly notch insensitive which makes the prediction of the failure behavior particularly cumbersome. 

In pursuit of an established certification protocol for DFCs, this seminar will present recent experimental results and computational simulations of DFC components. A novel computational framework simulating platelets and matrix explicitly will be presented and shown to accurately capture the mesostructure of DFCs and their damage and fracturing behavior. Combining computational simulations and size effect fracture tests, it will be shown that it is possible to formulate design guidelines that mitigate the effects of the large variability of the mechanical properties of DFCs and allow turning the large notch insensitivity of these materials into an advantage.

 


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