Development of Metallic Sensory Alloys

The safety of aerospace vehicles is largely dependent on the ability of modern non-destructive evaluation (NDE) tools to accurately detect structural damage before a critical flaw size is reached.  However, existing NDE technologies are inherently limited by the physical response of the materials being inspected making the detection of small cracks or pre-crack damage difficult.  One innovative solution to this problem is to create a multifunctional metallic material  that can be used in structural applications and contains second phase sensory particles that significantly enhance the ability of conventional NDE techniques to detect incipient damage during use and at regularly scheduled inspections.  Ferromagnetic shape-memory alloys (FSMAs) are an ideal material for use as this second phase material as they undergo a uniform and repeatable change in both magnetic properties and crystallographic structure when strained.  These changes are more readily detected than small cracks, thereby, allowing for enhanced detection of damage by conventional NDE techniques, such as eddy current and acoustic emission.  In this study, FSMA alloys were examined for use as the sensory particles, and then a multifunctional metallic material was produced by embedding the particles within an  aluminum alloy to form a “sensory alloy.” The NDE response of the FSMA and the sensory alloy during tension/compression and fatigue loading have been investigated and will be presented.  The results show this sensory material concept will produce an acoustic emission (AE) signal amplitude an order or magnitude greater than that of aluminum, and demonstrated that a change in magnetic properties was easily detected using current Eddy current sensors.