Composite Alloy Capable of Self-Repairing Large-Scale Cracks That Have Propagated During the Component’s Service Life
This metal matrix composite is a heat-respondent, self-repairing alloy that repairs stress and fatigue cracks without needing skilled technicians and direct access. Metallic materials, such as aluminum alloys, are used in both the structural and non-structural parts of aircraft, such as the fuselage skin, frames, ribs, wing spars, fuel tanks, landing gears, wheel wells, fuel lines, shock struts, cargo doors, floor beams, seat tracks, and more. Although some properties of aluminum, such as cost and weight, are desirable for aerospace and other lightweight material applications, during operation the materials can be subjected to physical stresses due to cyclic loading, resulting in the formation of fatigue cracks, and subsequently, oftentimes fatigue failure. Repairing fatigue cracks typically requires additional materials, direct access to the crack, and the skilled application of a repair technique. In certain cases, engineers decide to replace entire components with fatigue cracks rather than repair the cracks. These cumbersome procedures are not desirable in aerospace application. Additionally, these available techniques pose challenges with regard to bonding and surface preparation.
Researchers at the University of Florida have created a self-healing, heat-respondent metal matrix composite that does not require additional materials, direct access, or skilled application. The repair bonds made by this composite are also significantly stronger than that of available technology, enhancing the performance, reliability, and success of the repaired material.
Application
Composite capable of self-repairing large-scale cracks that have developed during the component’s service life
Advantages
- Safely and effectively repairs fatigue cracks, improving material performance, reliability and success
- Minimal components needed for crack repair, reducing costs, personnel, and application time
- Simple and easy to use design, facilitating proper repairs with minimal prior training
- Metal matrix strength is significantly more reliable than available technology, enabling the safest and most efficient mending of the material
Technology
This matrix composite is comprised of an aluminum-silicon-based alloy that is reinforced with shape memory elements (SMA) for self-repair and damage mitigation. When a crack is present in the matrix material, local stresses induce phase transformations in the SMA reinforcements, causing the SMA reinforcements to stretch and bridge the crack. The cracks are forced closed when the material is heated above the reversion temperature of the SMA reinforcements. While suspended at the reversion temperature, the low melting phase of the matrix partially liquefies and acts as a healing agent by filling into the crack and then solidifying when returned to room temperature. This is a two-step crack repair method; SMA reinforcements force crack closure, and liquefaction of the matrix enables crack repair. Both steps are accomplished by heating the crack area to a pre-determined temperature.
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