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A Study of the Mechanical Response of Polycrystalline Ice Subjected To A study of the mechanical response of polycrystalline ice subjected to dynamic tension loading using the spalling test technique Dominique Saletti, David Georges, Victor Gouy, Maurine Montagnat, Pascal Forquin To cite this version: Dominique Saletti, David Georges, Victor Gouy, Maurine Montagnat, Pascal Forquin. A study of the mechanical response of polycrystalline ice subjected to dynamic tension loading using the spalling test technique. International Journal of Impact Engineering, Elsevier, 2019, pp.103315. 10.1016/j.ijimpeng.2019.103315. hal-02151495 HAL Id: hal-02151495 https://hal.archives-ouvertes.fr/hal-02151495 Submitted on 13 Jun 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. ACCEPTED MANUSCRIPT Highlights • The spalling test technique is conducted to study the dynamic tensile strength of polycrystalline ice. • The results show the sensitivity of the tensile strength to the applied strain rate (from 41 s−1 to 271 s−1). • Three indicators are proposed to assess the results based on an opti- cal analysis, a measurement of the wave speed and an analysis of the transmitted pulse. • An increase of the cracking density with the strain rate is observed. 1 ACCEPTED MANUSCRIPT A study of the mechanical response of polycrystalline ice subjected to dynamic tension loading using the spalling test technique Dominique Salettia, David Georgesa,b, Victor Gouyb, Maurine Montagnatb, Pascal Forquina aUniv. Grenoble Alpes, CNRS, Grenoble INP1, 3SR, F-38000 Grenoble, France bUniv. Grenoble Alpes, CNRS, Grenoble INP1, IGE, F-38000 Grenoble, France Abstract Polycrystalline ice has been extensively investigated during the last decades regarding its mechanical behaviour for quasi-static loadings. Conversely, only few studies can be found on its dynamic behaviour and scientists suffer from a lack of experimental observation to develop relevant modelling at high strain-rate ranges. Dynamic experiments have already been conducted in compression mode using Hopkinson bar set-up. Regarding tension, experi- mental observations and measurements are scarce. The literature gives only approximated strength values. The knowledge of the latter is essential to design structures that may experience ice impact. The present study aims at providing the first reproducible experimental data of the tensile strength of polycrystalline ice subjected to dynamic tensile loading. To do so, a spalling test technique has been used for the first time on ice to apply tensile load- ing at strain-rates from 41 s−1 to 271 s−1. The experimental results show that the tensile strength is sensitive to the applied strain-rate, evolving from 1Institute of Engineering Univ. Grenoble Alpes Preprint submitted to Journal to be defined June 7, 2019 ACCEPTED MANUSCRIPT 1.9 MPa to 16.3 MPa for the highest applied loading rate. Keywords: spalling test, ice, dynamic tensile strength, strain-rate sensitivity, fracture 1 1. Introduction 2 Ice found on Earth has a hexagonal crystallographic structure and is also 3 known as ice Ih, the only stable phase at atmospheric pressure. The mechan- 4 ical behaviour of its isotropic polycrystalline form (also called granular ice) 5 has been widely investigated during the last decades but essentially regarding 6 its mechanical response to static or quasi-static loading cases (Schulson and 7 Duval [1]). In order to design structures that may experience ice impact, the 8 knowledge of the mechanical response of ice experiencing dynamic loading 9 is of main interest. To achieve this goal, some studies were conducted using 10 different techniques. Two main characterisations can be found in the litera- 11 ture, one investigating the response of the material to dynamic compression 12 loading and one looking at the response of a mechanical structure experienc- 13 ing an ice ball impact. As far as the authors know, only one study, done by 14 Lange and Ahrens [2], deals with the dynamic tensile behaviour of ice. In this 15 work, ice specimens were tested in plate impact experiments and a tensile 4 −1 16 strength of about 17 MPa is measured at a strain-rate of 10 s . Regarding 17 compression tests, a study was made by Combescure et al. [3] using a fast −2 −1 −1 18 hydraulic jack allowing applied strain-rates from 10 s to 50 s . The ul- 19 timate compressive strength was identified to be 10 ± 1.5 MPa. Shazly et al. 20 [4] investigated the compressive behaviour at a higher range of strain-rate −1 21 (60 to 1400 s ) using a classical Hopkinson pressure bar with a short cylin- 2 ACCEPTED MANUSCRIPT 22 drical specimen. The ultimate compressive strength was established to be −1 23 around 15 MPa at the lowest strain-rates (60 s ) reaching about 58.4 MPa −1 24 for the highest strain-rates(1400 s ). By changing the size of the specimen 25 and the velocity of the striker, Kim and Keune [5] loaded the ice material at −1 −1 26 strain-rates from 400 s to 2600 s . Regarding the ultimate compressive 27 strength, a mean value of 19.7 MPa was identified with values varying from 28 12 to 29 MPa. The authors stated a slight sensitivity to the strain-rate but 29 the dispersion of the results cannot allow assessing this fact firmly. 30 Some clues on the dynamic behaviour of ice can also be found from the 31 studies that used ice impact on mechanical structures (Combescure et al. 32 [3], Pernas-S´anchez et al. [6]). The results obtained from these tests are 33 mostly used to validate numerical modelling of ice ball impact on different 34 types of structures and, then, do not propose a direct identification of tensile 35 strength values for ice itself. 36 Except the work of Lange and Ahrens [2], all the studies investigating the 37 tensile strength of ice propose values at strain-rate ranges that do not exceed −3 −1 38 10 s . Both Schulson [7] and Petrovic [8] proposed a general review of 39 the mechanical properties of ice in which tension is described. According to 40 Schulson [7], the fracture in tension is due to a transgranular cleavage with a 41 maximal applied strength around 1 MPa. The same value is given by Petrovic 42 [8] and does not seem to be influenced by the applied strain-rate, at least up −3 −1 43 to 10 s . In fact, the main parameter influencing the tensile behaviour 44 of ice appears to be the grain size of the material and the temperature. The 45 tensile strength decreases when grain diameter increases, with the existence 46 of a critical grain diameter for which a brittle-to-ductile fracture transition 3 ACCEPTED MANUSCRIPT 47 occurs. This critical grain diameter appears to decrease with the increase 48 of the applied strain-rate. Despite all these pieces of information about the 49 mechanical response of polycrystalline ice to tensile loadings, the strain-rate 50 sensitivity can only be presumed: no data are available for strain-rate above −1 51 1 s . 52 Understanding the dynamic tensile behaviour of the polycrystalline ice 53 is of main interest since tension plays an important role in the damage pro- 54 cess of a material subjected to impact and having a quasi-brittle behaviour 55 (Forquin and Hild [9]) such as ice. Among all the mechanical parameters 56 that should be investigated and identified in order to get satisfying mod- 57 elling, the tensile strength is at the forefront. But experimentally speaking, 58 applying a tensile loading can be very difficult, especially with materials as 59 polycrystalline ice for which the attachment to the possible grips is tricky. 60 Specimens cannot be threaded or glued, except with water, but in that case, 61 the test has to be carefully designed in order for the failure to remain in 62 the center part of the specimen and not at the boundaries. In addition, the 63 experimental set-ups that can be found in the literature to apply dynamic −1 64 tensile loading to quasi-brittle materials are limited to a range of 1 s to −1 65 1000 s . Universal testing machines equipped with fast hydraulic jack can −1 66 reach strain-rate up to 1 s and the Split Hopkinson Tensile Bars technique −1 67 can lead to loading rates up to 200 s (Cadoni et al. [10], Saletti et al. [11]) 68 but for both cases, the specimen attachment is problematic due to likely 69 melting of ice at contact surfaces. Indeed, a stress should be applied on the 70 specimen surface transmitting the tensile forces during the test. This stress 71 could lead to a temperature variation of the specimen and melt locally the 4 ACCEPTED MANUSCRIPT 72 material, preventing the forces to be transmitted. Xia and Yao [12] made a 73 complete review of the different techniques to apply a tensile loading to brit- 74 tle materials such as rocks which have, as well as polycrystalline ice, a higher 75 strength in compression than in tension. The Brazilian test technique could 76 be employed but the authors propose here what seems to be a good candi- 77 date to tackle the issue of applying a dynamic tensile loading: the spalling 78 testing technique. This technique needs a specimen with a simple cylindri- 79 cal shape and only a simple unilateral contact with the measurement bar 80 (Klepaczko and Brara [13], Erzar and Forquin [14]).
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