Use of a Ni60Ti shape memory alloy for active jet engine chevron application: I. Thermomechanical characterization

Abstract

A shape memory alloy (SMA) with a composition of Ni 60 Ti 40 (wt%) was chosen for the fabrication of active beam elements intended for use as cyclic actuators and incorporated into a morphing aerospace structure. The active structure is a variable-geometry chevron (VGC) designed to reduce jet engine noise in the take-off flight regime while maintaining efficiency in the cruise regime. This two-part work addresses the training, characterization and derived material properties of the new nickel-rich composition, the assessment of the actuation properties of the active beam actuator and the accurate analysis of the VGC and its subcomponents using a model calibrated from the material characterization.The characterization performed in part I of this work was intended to provide quantitative information used to predict the response of SMA beam actuators of the same composition and with the same heat treatment history. Material in the form of plates was received and ASTM standard tensile testing coupons were fabricated and tested. To fully characterize the material response as an actuator, various thermomechanical experiments were performed. Properties such as actuation strain and transformation temperatures as a function of applied stress were of primary interest. Results from differential scanning calorimetry, monotonic tensile loading and constant stress thermal loading for the as-received, untrained material are first presented. These show lower transformation temperatures, higher elastic stiffnesses (60-90 GPa) and lower recoverable transformation strains (≈1.5%) when compared to equiatomic NiTi (Nitinol). Stabilization (training) cycles were applied to the tensile specimens and characterization tests were repeated for the stable (trained) material. The effects of specimen training included the saturation of cyclically generated irrecoverable plastic strains and a broadening of the thermal transformation hysteresis. A set of final derived material properties for this stable material is provided. Finally, the actuation response of a structural beam component composed of the same material given the same thermomechanical processing conditions was assessed by applying a constant bias load and a variable bias load as thermal actuation cycles were imposed.

Havacilik Ve Uzay Uygulamalarinda Şeki̇l Hafizali Alaşimlar

“…Boeing firması şekil hafızalı alaşımlardan yapılmış aktüatörler kullanarak hareketli şerit (chevron) tasarlamış ve bu tasarımı Boeing 777-300 ER ticari uçağı üzerine takılı GE90-115B jet motoru üzerinde test etmiştir [18,22]. Egzoz nozullarında kullanılan bu şeritlerin görevi hava ve sıcak gazı karıştırmak ve böylece ses oluşumunu azaltmaktır.…”

Shape Memory Alloy Actuator Design: CASMART Collaborative Best Practices

“…This was a time consuming and expensive method. Subsequently, 3D finite element modeling accurately captured the performance of the VGC [36,37]. Currently, this model is being coupled with design optimization software to reduce development times and costs for future actuator systems [38].…”

Roundrobin SMA modeling

“…Most of the macroscopic models are implemented in finite element codes and used for SMA structural analysis. Many extensions of these models are under continuous development, for example in order to take into account the effect of precipitates or the interaction between transformation and plasticity or viscoplasticity during monotonic or cyclic loading [35][36][37].…”