SBIR-STTR Award

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.

Keywords:
PASSIVE SMART AIRCRAFT BOLTS DAMAGE DETECTION TRIP STEELS MONITORING

A Phase II USAF SBIR technology development proposal is presented which describes the efforts required to take the successful Phase I SMART aircraft bolt feasibility study to the Phase III commercialization stage. Essentially the task is to employ SMART metals technology for USAF applications to detect imminent strain-related failures, and to streamline inspection and maintenance efforts through non-destructive evaluation of key aircraft parts. A background section first discusses the use of metastable alloys as strain deformation sensors, with illustrative examples. A review of the TRIP steel technology presents applications directed at the use of these high-strength steels as both engineering component materials and inherent sensor materials capable of passively detecting and monitoring structural damage during service. The results of the Phase I SBIR Program and an outline of the Interim Program area also presented and discussed. Phase II efforts are primarily directed at those tasks to fully develop passive SMART bolt technology, including field testing and evaluation. The SMART bolts will be evaluated in C-130 Hercules cargo aircraft through Robins Air Force Base, Georgia. A secondary objective in the Phase II Program is the development of SMART aircraft fastener sleeves, and tasks to accomplish this goal are discussed. The Phase II Program is designed to result in the commercialization of two new aircraft products, both of which are directly transferable to commercial as well as other military sector markets.