The research objectives of this award are to characterize the mechanical properties of novel steel foams and determine whether this new class of materials presents opportunities for transformative improvement of the performance of civil structures. Although other kinds of metal foams serve well established purposes in the aerospace and automotive industries, the advent of manufacturing techniques for steel foams opens the door to low cost mass production of a material suitable for civil structural application. The research program consists of experiments to characterize the structure and mechanical properties of the material and simulations to establish proof-of-concept applications of steel foams to civil structures. The target applications are energy dissipating devices to improve seismic performance of building systems and selective application of steel foam to improve the strength and ductility of thin-walled steel structural members.
If successful, this research program will spur increased research and development work leading to low-cost mass production of steel foams, and will have identified methods for improving the performance of civil structures during extreme loading events. The potential benefits accrue to society through improved structural performance and incentive for the steel industry to develop new manufacturing capabilities. The research is closely connected to the steel industry and the practice of structural design through an industrial advisory board comprising practicing engineers and steel industry professionals. A vertically integrated, collaborative research team spanning from the undergraduate to full professor levels across three institutions of higher learning, and a program of outreach targeting graduate students and high school students from under-represented groups, ensures that the project will have significant workforce development and mentorship impacts.
This project set out to bridge the gap between fundamental materials processing and production research and the application of novel material to benefit the nation’s public civil infrastructure of buildings, bridges, tunnels, etc. The particular focus was on a steel foam, a material that can be thought of as porous steel, or as analogous to typical styrofoam, but made of steel rather than plastic. Though foams made of metals are relatively well established in mechanical, aerospace, and electronic applications, steel foams are relatively new and structural engineers have not yet demonstrated that such foams can improve the performance of civil structures. Research began with a collaboration with the Fraunhofer Institute of Dresden, Germany which is an international leader in the production of metal foams. Fraunhofer provided the project with samples of a steel foam made of hollow steel spheres roughly 2 mm in diameter that had been fused together under specific conditions of temperature and pressure. This foam was roughly one fifth the weight of solid steel. In order to properly investigate structural applications of the foam, its mechanical properties first needed to be determined. An experimental campaign was therefore conducted that made several fundamental contributions: New protocols were developed for testing metal foams in tension and shear For the first time the performance of a steel foam was measured under tension and shear loadings The microstructure of the steel foam was measured statistically so that analysis could be performed leading to an understanding of how the structure of the material leads to the specific mechanical properties. Parallel to the experimental investigation of the mechanical properties of steel foam, computational modeling and hand calculations were used to explore the suitability of steel foams to two structural applications: thin-walled steel members and steel foam sandwich panels. In each case, expressions and simulations were developed that showed how using steel foam in such members would affect their stiffness and strength. Findings indicate that the more promising of the applications is a steel foam sandwich panel which can provide substantially greater stiffness and strength than a steel panel of equal weight. In addition to the basic calculations, design equations were developed that could allow designers to specify a steel foam sandwich panel for a particular structural application. In summary, this project accomplished the first ever characterization of a steel foam in terms of all mechanical properties that must be known for the design of a steel foam structural element and demonstrated specific structural elements that would perform better if made of steel foam. The research, in addition to being published in academic journals and presented at academic conferences, was communicated to members of the structural engineering design community and the steel industry through an industrial advisory board of practicing engineers and steel industry representatives.
