A morphing aerofoil with highly controllable aerodynamic performance

ABSTRACTIn this paper, a morphing carbon fibre composite aerofoil concept with an active trailing edge is proposed. This aerofoil features of camber morphing with multiple degrees of freedom. The shape morphing is enabled by an innovative structure driven by an electrical actuation system that uses linear ultrasonic motors (LUSM) with compliant runners, enabling full control of multiple degrees of freedom. The compliant runners also serve as structural components that carry the aerodynamic load and maintain a smooth skin curvature. The morphing structure with compliant truss is shown to exhibit a satisfactory flexibility and loading capacity in both numerical simulations and static loading tests. This design is capable of providing a pitching moment control independent of lift and higher L/D ratios within a wider angle-of-attack range. Such multiple morphing configurations could expand the flight envelope of future unmanned aerial vehicles. A small prototype is built to illustrate the concept, but as no off-the-shelf LUSMs can be integrated into this benchtop model, two servos are employed as actuators, providing two controlled degrees of freedom.</jats:p

Damage Evolution in 3D Woven Composite Materials Using Acoustic Emission

Fibre-reinforced composite materials are used extensively in the aerospace industry because of their high specific strength and stiffness, superior corrosion resistance and improved fatigue properties. In addition to the manufacturing costs and production rates, damage tolerance has become a major issue for the composite industry. Three-dimensional (3D) woven composites have superior through-thickness properties compared to two-dimensional (2D) laminate, for example, improved impact damage tolerance, high interlaminar fracture toughness and reduced notch sensitivity. It is a big challenge to relate acoustic emission (AE) signal events to specific damage modes developed in composites under hygro-thermo-mechanical loading [1, 2]. This study provides further insight into the AE monitoring of a 3D angle interlock (AI) glass fibre composite materials and has revealed the complex nature of the relationship between the principal characteristics of recorded AE events on the one hand and the complex damage mechanism on the other. This paper presents experimental and simulation results on the use of AE on 3D AI glass fibre composites for structural health monitoring (SHM) of transverse matrix cracks, and delamination during quasi-static tension of flat specimens. Tests were performed with piezoelectric sensors bonded on a tensile specimen acting as passive receivers of AE signals. A new set of experimental data has been generated which will be useful for validating numerical models, providing insight into the damage evolution of novel 3D AI glass fibre composites, and may ultimately lead to more effective material selection and determination of design limits.

Impact Response of Curved Composite Laminates: Effect of Radius and Thickness

From Springer Nature via Jisc Publications RouterHistory: received 2020-06-03, accepted 2020-07-13, registration 2020-07-13, pub-electronic 2020-07-25, online 2020-07-25, pub-print 2020-10Publication status: PublishedFunder: University of ManchesterAbstract: This paper presents the results of drop-weight impact testing (5 J to 30 J) on curved ±55° E-glass-epoxy laminates of varying radii and wall thickness. Three radii (75 mm, 100 mm, and 125 mm) on laminates with an effective wall thickness of 2.5 mm, and three wall thicknesses (2.5 mm, 4.1 mm, and 6.6 mm) with a radius of 100 mm were investigated. The damage pattern remained consistent, with the exception of the damage area, across the tested energies and was dominated by internal matrix cracking and multiple delaminations. However, no damage was recorded following a 5 J impact on the 2.5 mm thick laminates with 100 mm and 125 mm radii, all energy was absorbed elastically, while the laminate with a 75 mm radius of curvature developed a damage area of over 80 mm2. The thicker laminates showed a reduced overall damage area but a greater number of delaminations. The relationship between laminate thickness and delamination threshold load was found to be in line with impact testing of flat plates, varying with the laminate thickness to the 3/2 power. However, the simplified beam theory and a fracture mechanics model developed for the prediction of delamination threshold of flat plates was found to underestimate the delamination threshold load (DTL) of the curved laminates studied by about 40%. An increase in the laminate’s flexural modulus of a factor of two is required to bring the model’s predictions in line with the DTL values measured experimentally, highlighting how curvature can enhance bending stiffness and alter damage evolution. Finally, a significant finding is that the DTL of the curved plates is around 15% lower than the value measured for the whole cylindrical pipe of same specifications. Testing curved sections rather than a whole pipe could reduce effort, but further work is required to confirm this statement

Deployable Self-Regulating Centrifugally-Stiffened Decelerator (DESCENT): Design Scalability and Low Altitude Drop Test

A previous study by the authors has proposed a foldable heat shield that deploys by harnessing the re-entry kinetic energy, namely DEployable, Self-regulating, CENTrifugally-stiffened decelerator (DESCENT). The design benefits from being self-regulating and lightweight, having low requirement on thermal protection, and allowing downrange manoeuvre based on conventional attitude control devices. The present study demonstrates that the system mass can be scaled across 6 orders of magnitude using a set of relatively simple design rules, showing the potential to realise miniaturised entry probes that are simple and robust, with a possible mass-reduction of >25% to an 8 m diameter inflatable heat shield. A scaled-down test model with a stitched fabric aeroshell and on-board sensors is drop-tested at low altitude, showing satisfactory agreement with simulation, and no sign of instabilities, paving the way for future higher fidelity tests. The similarity between the low speed drop-test result and Newtonian hypersonic simulation suggests that the critical behaviour of DESCENT is dominated by its geometrical characteristics

Intra-yarn fibre hybridisation effect on homogenised elastic properties and micro and meso-stress analysis of 2D woven laminae: Two-scale FE model

In this paper, the effect of intra-yarn fibre hybridisation on the homogenised elastic properties and micro- and meso-scale matrix stress fields in 2D woven composite laminae (i.e. plain, 2/2 basket, 2/2 twill and 5-harness satin) is studied with a two-scale homogenisation scheme—employing a representative volume element model at micro-scale and a repeating unit cell model at meso-scale. The study is focused on S-glass/polypropylene/epoxy woven laminae with intra-yarn fibre hybridisation. A modified random sequential expansion algorithm generates microstructure for the micro-mechanical model, and a periodic meso-structure is used to generate the weave architecture for the meso-mechanical model. Both models are verified using analytical models. It is found that intra-yarn fibre hybridisation can significantly alter the homogenised properties as well as the micro- and meso-scale matrix stress fields—depending on the degree of hybridisation (i.e. the combination of S-glass and PP fibre volume fractions). Moreover, the homogenised lamina properties are found to be less sensitive to weave architecture and yarn thickness, but more so to the degree of intra-yarn fibre hybridisation, yarn width and yarn spacing. It is shown that the lamina properties can be tailored, and the micro- and meso-stress fields can be manipulated, by intra-yarn fibre hybridisation and weave architectures