Influence of Porosity on Ice Dynamic Tensile Behavior as Assessed by Spalling Tests

Abstract

The impact of hailstones remains a major issue due to the damage caused by hailstorms against aeronautical or space structures. During a such impact, an intense fragmentation develops in the hailstone due to dynamic tensile loading at high strain-rates which influences the mechanical loading transmitted to the impacted structure. Up to now, the work of Saletti et al. (2019) is the only survey providing a robust and reproductible set of experiments about the dynamic tensile strength of ice, however the microstructure influence was out the scope of this experimental study.Though, the hailstone microstructures are generally charaterised by a high level of porosity. It is the reason why the influence of this microstructural parameter on the dynamic behavior of polycrystalline ice needs to be investigated. The aim of this paper is to study the role of porosity on the tensile behavior of polycrystalline ice by applying the same experimental set-up and measurements processing than in Saletti et al. (2019) to low-porosity (LP) and high-porosity (HP) microstructures. To do so, spalling tests with a Hopkinson bar apparatus were conducted and fragmentation processes were carefully analyzed by means of an Ultra High Speed Camera, an Automatic Ice Texture Analyser and a micro-Computed Tomograph. The experimental results show that the tensile strength is sensitive to the applied strain rate for both types of micro-structures over the range 24 s −1 to 120 s −1 . A weakening effect of porosity is also observed, the lowly porous specimens being significantly stronger than the highly porous ones. The large 1 spherical pores present in the LP specimens are seen to contribute to this strength decrease.Although fragmentation analysis did not allow to clearly assess the role of these porosities on the crack initiation and propagation processes, the numerous clues such as the high number of cracks detected, the tortuosity of crack paths and the presence of porosities on the crack surfaces seem to validate the hypothesis of porosities playing a key role during ice fragmentation.

Internal and interfacial microstructure characterization of ice droplets on surfaces by X-ray computed tomography

“…Pore formation and porosity inside frozen droplets is rarely discussed in research focusing on icing, there are, however, two studies which have investigated porosity inside ice using XCT 18 [33,46]. In these studies, the majority of pores have a similar equivalent diameter compared to the results obtained in this study.…”

“…However, in literature, wider distributions were obtained with relatively large pores due to the different ice growth mechanisms trapping air pockets inside the ice. The first study (voxel size: 27 µm) grew ice from an ice slurry, resulting in pores with equivalent diameters in the range of 0.3 up to 3 mm [46]. The second study (voxel size:…”

Numerical and Experimental Investigations of Deicing Performance for the Pneumatic Impulse Deicing Method

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Continuous and discrete methods based on X-ray computed-tomography to model the fragmentation process in brittle solids over a wide range of strain-rates - application to three brittle materials

“…The air trapped between the snow grains during the process leads to the formation of a highly porous microstructure, with about 7 to 10 vol.% of porosity. The final microstructure is characterised by equiaxed grains, an isotropic crystallographic texture and a mean grain size of about 1-2 mm (Georges et al, 2019).…”