Interlayer modified prepreg systems for customized density applications

The high specific strength and specific modulus of fiber reinforced composites have allowed these materials to displace metals in many commercial applications. Consequently, composites are generally considered a low-weight alternative to metals, and research has usually been focused on reducing the weight of composite materials for an increasing number of light-weight applications. However, fiber reinforced composite materials constructed form prepreg offer those who design parts many more options involving material density than simply weight reduction. In this work it was shown that the unique layered structure of composite materials coupled with previously developed interlayer toughening techniques for prepreg could result in controlled variations in density over the length of monolithic structures. Initially, experiments were performed that explored how changes in particle size distribution effected the properties of cured laminates when using conventional rubber particles to modify the interlayer. A methodology was then developed that described how to tailor the density of a prepreg based composite using metal particles to modify the composite interlayer. The concept was proven by selectively modifying the interlayer of a series of model carbon fiber/epoxy based prepregs with metal particles of various densities. Experiments were performed which showed that the fracture toughness of the particle modified systems were either greater than or equal to the toughness of an unmodified composite. It was also shown that similar variations in density could be realized by increasing the concentration of metal particles in the composite system as opposed to changing the type of metal. Again, experiments were performed that displayed no reductions in the fracture toughness of the particle modified materials. These results led to a large scale production run of experimental metal particle modified prepreg that was used in a commercial sporting goods product development process. Results from the initial integration of the new material proved promising, and player testing was performed with the help of professional athletes. Collectively, a novel metal particle modified prepreg was developed that could be integrated into pre-existing prepreg based composite designs and tailor the density of the parts without reducing other mechanical properties.