The design and testing of subscale smart aircraft wing bolts

Abstract

Presently costly periodic inspection is vital in guaranteeing the structural integrity of aircraft. This investigation assesses the potential for significantly reducing aircraft maintenance costs without modification of aircraft structures by implementing smart wing bolts, manufactured from TRIP steel, which can be monitored for damage in situ. TRIP steels undergo a transformation from paramagnetic austenite to ferromagnetic martensite during deformation. Subscale smart aircraft wing bolts were manufactured from hot rolled TRIP steel. These wing bolts were used to demonstrate that washers incorporating embedded inductance coils can be utilized to measure the martensitic transformation occurring in the TRIP steel during bolt deformation. Early in situ warning of a critical bolt stress level was thereby facilitated, potentially reducing the costly requirement for periodic wing bolt removal and inspection. The hot rolled TRIP steels that were utilized in these subscale bolts do not however exhibit the mechanical properties required of wing bolt material. Thus warm rolled TRIP steel alloys were also investigated. The mechanical properties of the best warm rolled TRIP steel alloy tested almost matched those of AISI 4340. The warm rolled alloys were also shown to exhibit transformation before yield, allowing for earlier warning when overload occurs. Further work will be required relating to fatigue crack detection, environmental temperature fluctuation and more thorough material characterization. However, present results show that in situ early detection of wing bolt overload is feasible via the use of high alloy warm rolled TRIP steel wing bolts in combination with inductive sensor embedded washers.

An approach to interpreting metastable austenitic material sensors for fatigue analysis

“…Previous applications of metastable material sensors are known from a wide field of applications such as civil, mining or aeronautical engineering [4,[6][7][8][9]. They are summarized in table 1.…”

Invention of smart tightening tool for directly controlling the preload of bolted joints

“…Bolted joints are widely applied in the fields of mechanical engineering, civil engineering, aeronautical engineering, and among others, playing a significant role to connect two or * Author to whom any correspondence should be addressed. more separated components [1,2]. According to statistics, approximately 70% of the fasteners in a vehicle are bolted joints and the assemblies of bolted joints occupy a significant proportion in the whole assembly line of a vehicle [3].…”