About Machine Augmented Composites (MAC)

In describing these materials, the term "machine" is used to describe what the dictionary defines as "an instrument (such as a lever) designed to modify the application of power, force, or motion." Many of the elements contained in these new composite materials could be called "simple machines," but we use the term "machines" for brevity.

The MAC concept is best described with an example. The schematic below describes a simple stress-conversion machine that converts shear forces into tensile/compressive forces and vice versa. Note that if shear forces are applied to the machine as shown, the slanted walls change their angle, forcing the top and bottom plates to move apart. This movement causes compressive forces on any adjacent contacting material. Conversely, if compressive forces are applied to the top and the bottom faces, the machine imposes shear forces on any adjacent abutting material.

In the MAC concept, a large number of very small machines are embedded within the matrix material. A MAC material has been manufactured using appropriately small machines. The machine's walls are angled 60 degrees from the bottom. Long segments with this cross-section were extruded out of nylon. Nylon is ideal for this application because it is easy to extrude, it is compatible with many polymeric matrix materials, and it has good mechanical properties.

The optical micrograph above was taken from a thin slice of the material that was placed between crossed polarizers to highlight the difference between the machines and the matrix. The machines are made out of nylon and are hollow (filled with air). The polyester scrim cloth that was placed between the plies of the machines as a manufacturing aid is evident.

Polarized optical micrograph of a machine augmented composite

The machines cause the material to have unusual properties. In response to a compressive displacement, the material distorts in shear. This is shown on the strain conversion page. Conversely, when a shear force is applied the material modifies the force to have a compressive component. This is shown on the stress conversion page. A slightly more complicated machine is shown on the damping applications page. This machine is filled with a viscous fluid that absorbs energy as it flows.