Development of Passive and Smart Aircraft Bolts for Specialty Applications

A program is presented to design, fabricate and test the feasibility of utilizing Transformation Induced Plasticity (TRIP) steels in SMART aircraft bolt applications for damage detection and monitoring. TRIP steels offer the potential of serving as inherently SMART, high-strength structural fastener materials in critical aircraft locations since they can be formulated to change solid-state atomic arrangement(s) as a function of applied strain. Originally developed as ultra-strong and tough (fracture resistant) structural alloys, TRIP steels experience a martensitic phase transformation which can be tailored to occur within the elastic range (stress-assisted) or within the plastic range (strain-induced). The parent face-centered-cubic, austenitic phase is paramagnetic and displays no significant ferromagnetic response whereas the product, body-centered-cubic martensitic phase is ferromagnetic. The peak elastic stress in a SMART bolt can be deduced by the ferromagnetic response displayed by an elastically-loaded TRIP steel which experiences a stress assisted transformation, or the peak, post-yield, strain level can be deduced from a TRIP steel which undergoes a strain-induced transformation. Five to seven TRIP steels will be melted, fabricated to plate form and evaluated in the laboratory. Three configurations of prototype bolts of the optimize alloys, will be fabricated and simulation tested as part of the interim program.