A novel lightweight functionally graded polymer based composite material will be developed in this project. This material will have substantially higher energy absorption in quasi-static and dynamic loading conditions compared to other lightweight materials. The proposed functionally graded material (FGM) is based on creating a dispersion of hollow micro-particles of glass according to their wall thickness in a polymeric matrix. The gradient in wall thickness will provide a better control over properties of these FGMs compared to the existing FGMs that are based on creating a gradient of particle volume fraction. The new FGM structure will be designed and optimized through extensive theoretical and experimental analysis. The experimental research will include development of processing methods, characterization of mechanical properties and development of structure-property correlations. Analytical models for two- (matrix and particles) and three-phase (matrix, particles and air voids) composite materials will be developed using homogenization techniques. These models will be applicable to hollow and solid particle filled composites and will provide significantly enhanced predictive capabilities over the currently available models.
This project is the first comprehensive attempt to unify the concept of solid and hollow particle filled composites by defining solid particles as a special case of hollow particles. The mew FGM will open up several possibilities for future research in smart composites, self healing composites, bio-compatible materials and highly damping materials. The immediate applications of the new FGMs are expected to be in higher damage withstanding structures. Future possibilities lie in automobile structures, bio-medical implants, sports equipment and self healing components. Extensive educational activities are planned for graduate, undergraduate and high school students as part of the project. The results will be disseminated widely through journal publications, conference presentations and inclusion in the relevant courses.
This NSF project was focused on developing a novel functionally graded composite foam (FGCF) with high damage absorptioncapabilities. The project outcomes are summarized as: 1. The FGCF was developed and characterized for mechanical properties. A fabrication method was developed for this kind of material system. FGCFs or similar materials can find applications in civilian and military vehicles and aerospace structures. 2. A test method was developed to characterize materials at high compression rates, which may have a wide range of implications, including testing materials that are currently used in automobiles, building, aircraft, and ship structures and determining their energy absorption capability (protective ability) under high speed compression. 3. It was found that mechanical properties at slow and high speed compression may, sometime, not show any difference. Yet, at microscopic level, the material failure mechanisms may be completely different. 4. Several ways were identified that can enhance the properties of FGCFs. Hollow particles are used to fabricating lightweight FGCFs. It was found that a combination of hollow particle wall thickness and volume fraction can help in tailoring material for desired properties. 5. A new variation of hollow particle filled composite was developed that contains carbon nanofibers. This multiscale reinforced material system is very promising and can be developed to have tailored set of mechanical as well as electrical properties since carbon nanofibers are conducting in nature. 6. Theoretical models were developed to understand the properties of hollow particle filled composites and provide predictive tools that can help in materials design according to the requirements of a given application. 7. Environmentally hazardous industrial waste material – fly ash – was explored for fabricating such lightweight composites. Fly ash is a coal combustion by product and is generated in over 70 million ton quantity every year in the USA. It was demonstrated that fly ash can be used to make such lightweight damage tolerant composite materials. 8. The work was also extended to study natural functionally graded material, that is, bone. A new failure mechanism was identified in rabbit bones at high compression rates. The difference observed in bone fracture at low and high speed compression is very important for development treatments for soldiers subjected to blast as well as for auto accident victims. These results are also important in developing damage tolerant materials such as FGCFs, which may find applications in armors and vehicle structures. 9. Training of graduate students and post-doctoral fellows is an important implication of this project. These highly skilled people can help future materials development efforts. 10. Six undergraduate students were engaged in the project. These students were trained in composite materials fabrication and various mechanical testing procedures. Many of these students have already graduated and have opted for graduate studies. 11. The project findings were widely disseminated through news items and scientific reports on various television channels. The dissemination also included news coverage on a wide range of internet based media.
