Clarkson aerospace engineering professors win $1.43 million DURIP Equipment Grant to advance viscoelastics and viscoelastics research

Craig Merritt Marcias Martinez
Left to right: Professor Craig Merritt and Professor Marcias Martinez

Dr. Craig Merritt and Dr. Marcias Martinez of the Department of Mechanical and Aerospace Engineering recently won a $1.43 million equipment grant from the Office of Naval Research. The grant will enable the acquisition of advanced material testing equipment for polymers, composites and metals. The equipment will expand testing capabilities within the Center for Advanced Materials Processing (CAMP), Comprehensive Structural Integrity Laboratory (HolSIP), and Aero-Servo-Thermo-Visco-Elasticity Laboratory (ASTVEL). Researchers and graduate students will be able to test materials from -40°C to 1200°C, and a range of humidity levels.

This enhanced range of test environments will augment existing research on the fundamental behavior of polymers, composites, and metals; and enabling applied research that improves structures and materials in the aerospace and marine industries. Elevated temperature metals, polymers, and composites exhibit energy dissipation and a memory effect that is poorly understood but leads to marked creep and stress relaxation in components fabricated from these materials. Creep sag and compression cause dimensional problems for high-precision assemblies, or contribute to incorrect estimates of the service life of a component. These behaviors are key elements in the field of viscoelasticity.

Linear viscoelasticity was first introduced in the 1950s, and nonlinear viscoelasticity was developed in the 1970s; However, much of the field required redevelopment after a mathematical proof published in 2009 showed that some previous assumptions were incorrect. To formulate a new approach to viscoelasticity requires more elaborate experiments involving precise control of temperature and humidity. Dr. Merritt and his graduate students have pursued this redevelopment by leveraging existing testing equipment at CAMP, and specially designed test frameworks to collect necessary data across multiple polymers. In collaboration with Dr. Martinez, the current computational models implemented in ANSYS and ABAQUS were evaluated and their errors relative to exact analytical solutions were determined. The equipment provided by DURIP funding is a significant upgrade in testing capabilities over existing equipment and will provide higher quality data and more training opportunities for viscoelastic graduate students.

Practical applications of a new viscoelastic approach will appear first in aerospace and marine applications. The use of polymer composite materials has increased dramatically in both areas over the past 20 years. Polymer composites promise high strength and stiffness for much less weight compared to conventional metal structures; However, the accuracy of current predictions of composite structures is limited by the current understanding of viscoelasticity. The new approach enabled by the DURIP grant will improve strength and stiffness predictions for components such as single shear lap joints and double shear lap joints. These joints are common on aircraft wings, fuselages, and marine hulls. They also appear in the supporting structures of satellites that carry Earth-observing telescopes. Furthermore, this approach will support the endeavors being pursued by the HolSIP Laboratory for structural integrity and health monitoring of structures, and by ASTVEL in fluid structure interactions for aircraft wings.

The grant will enable DURIP CAMP and the HolSIP Laboratory and ASTVEL to begin research in allied areas involving viscoelasticity. A major area of ​​interest is hypersonic vehicle design, as these high-speed vehicles experience high temperatures in flight. The aerodynamics of these vehicles have been thoroughly studied; However, the structural effects of higher temperatures are less known. The high-temperature testing capabilities of the DURIP grant will allow the testing of composites and metals up to 1,200°C and the exploration of viscoelasticity under this temperature regime. The viscoelastic response of the structure under these conditions may lead to an understanding of the structural design of the vehicle. A second area of ​​interest is the development of advanced skin models. These models will improve medical devices that include needles and skin stitches. An example is insulin delivery pumps, which insert a needle into a patient’s tissue to deliver insulin steadily for up to 72 hours.

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