Measurement of the fracture energy in mode I of atmospheric ice accreted on different materials using a blister test

Atmospheric ice is formed when supercooled water droplets strike an object such as a tree, aircraft or wind turbine. Its microstructure and properties vary widely according to the flow and thermal conditions prevailing. The present work was conducted in the Cranfield Icing Wind Tunnel for a european project called STORM (efficient ice protection Systems and simulation Techniques Of ice Release on propulsive systeMs). It aimed at collecting data on the fracture energy of atmospheric ice on four different materials - AL2024-T3, Ti-6Al-4V, Platinum and Alexit-411 - using a blister test. This particular test, firstly introduced by Andrews and Lockington (1983), have been adapted by Cranfield University to be able to test the ice adhesion in situ while ice is still accreting on the surface making it closer to real situation. The second part of the paper will focus on the influence of different parameters like the materials ice is accreted on, the total ambient temperature, the tunnel wind speed and the cloud liquid water content which have been investigated over a few icing condition

The effect of accretion temperature on microstructure and bending strength of atmospheric ice

Accurate determination of the mechanical response of atmospheric ice is key to understanding the risks associated with ice impact on aircraft during flight. Two types of atmospheric ice which are of particular interest to the aerospace industry are studied. Rime and Glaze ice are each manufactured in an icing wind tunnel facility under controlled conditions. Rime ice is accreted at a temperature of −20◦C, and Glaze ice is accreted at −5 ◦C. Quasi-static threepoint bend tests are performed on both types of ice to understand the effect of accretion temperature, and therefore microstructure, on strength. The results indicate that the ice accretion temperature, and thus microstructure, has a significant influence on the bending strength. On average, the bending strength of Rime ice is 9.0 ± 0.18 MPa compared to 4.4 ± 0.093 MPa for Glaze. The comparatively lower accretion temperature of Rime results in smaller grain sizes and higher bending strength. In contrast, the effective modulus appears insensitive to ice microstructure, with an average value of 3.5±0.12 GPa for Rime compared to 3.6±0.098 GPa for Glaze. Furthermore, the results indicate that both the bending strength and effective modulus are insensitive to the ice storage time.Innovate UK: 113155 Rolls-Royce pl

Experimental rig for ice accretion and adhesion strength measurement for air cycle machine system

Air cycle machines (ACM) which are part of the air-conditioning pack in every aircraft, are one such turbomachinery device that can be affected by icing issues particularly at the turbine end. Current ice protection solutions for the air cycle machines use a heating system on the downstream pipe to heat the surface, using electric resistance heaters or hot air coming from the ACM compressor stage. Both solutions require high energy, hence the need to reduce energy consumption through the development of passive energy-saving solutions. Clean Sky 2 ERICE project aims at developing an eco-friendly and cost-effective hydrophobic / ice-phobic solution able to resist ice adhesion in the ACM turbine scroll and its downstream pipe. This paper discusses the implementation of an experimental rig to reproduce the ice formation and accretion conditions within the ACM and a new shear test method to measure the ice adhesion strength on existing and new solutions in the form of coatings. The flow through the ACM turbine exhaust has also been characterized for the first time in published literature. The results from the ice accretion and adhesion tests show that hydrophobic coatings developed for the purposes of ice protection perform better than the current industry baseline material for ACM turbine scroll pipe internal surface. While these coatings could not be used to prevent accretion, they do help in reducing adhesion of ice to the surface.European Union funding: 821301. Clean Sky 2 Joint Undertakin

Measurement and FEM of ice adhesion to the downstream pipe of an air cycle machine

Ice accretion on the downstream pipe of an air cycle machine can lead to pipe blockage and turbine blade damage, and therefore de-icing is needed. Most previous studies focused on ice shedding from flat surfaces, and average interface shear strength rather than the true shear strength was usually reported. Here, the debonding of the interface between ice and cylindric surfaces of an aluminium pipe (2024-T3) was studied trying to understand the mechanism of interface fracture and to obtain the true adhesive shear strength and fracture energy. Average adhesive strength was measured first in the scrape test and the result was used to calibrate the finite element analysis. A cohesive zone model (CZM) with bilinear traction-separation law was used to simulate the interface delamination. The true shear strength σcs and mode-II energy release rate Gcs were determined by matching the numerically predicted critical force to the measured force. The influence of shear strength and shear energy release rate on the critical force was also investigated. At the interface, both the damage factor and the peak shear stress were found progressing away from the edge as the pushing force increased. Parametric studies on the influence of the length of the interface was performed. The critical force first increased and then stabilised with the increase of the length, showing the same trend as that of a theoretical model which ignored the mode-I fracture