The resulting wing is disk shaped, as shown experimentally by Sahouryeh et al. ( 1994), but under confined compression the curling is prevented. The wings do not grow under further loading, as shown by Dyskin et al. When the length of the curled wings is 1.0–1.5 times the diameter of the parent crack, growth stops. The growth is stable in 2-D, but in 3-D the wings curl around the primary crack (Adams & Sines, 1978 Cannon et al., 1990). Under increasing load, wings start to grow from the ends of the parent crack. (c) Winged cracks in 3-D.Ĭonsider a single penny-shaped parent crack in 3-D under uniaxial compression. (b) Opening of the representative crack due to the wedging traction R. (a) Parent crack normal N and wing crack normal n. The mechanism in 3-D is different to that of 2-D. The winged crack is modeled as a straight representative crack, where the wedging traction R shown in Figure 2b on the precrack area opens the crack.
#BUT CRACK SPLITTING SERIES#
The failure occurs when series of wing cracks extend and finally link together and split the material. The majority of wing crack models are two-dimensional a brief discussion of different wing crack models is given by Lehner and Kachanov ( 1996).Īxial splitting failure begins when a parent (or primary) crack undergoes sliding, creating wing cracks at the tips of the primary crack as illustrated in Figure 2a. One of the mechanisms proposed for modeling of axial splitting is the sliding wing crack model (ibid). Formation, growth, and interaction of cracks is considered to be the mechanism of brittle failure in uniaxial compression. When brittle materials are subjected to uniaxial compressive loading, they are known to fail by axial splitting along the direction of loading (Ashby & Hallam, 1986 Brace & Bombolakis, 1963 Nemat-Nasser & Horii, 1982). 1.2 Modeling of Splitting-Sliding Wing Crack Model (b) Coulombic shear fault under moderate across confinement. The failure modes are shown in Figure 1.īrittle failure modes under compression: (a) Splitting under uniaxial compression. Under higher confinement, failure occurs out of the loading plane by splitting through the columns, termed spalling in this case. Under moderately low confinement, the failure mode is shear-type faulting in the loading plane.
Under uniaxial compression, failure occurs by splitting along the loading direction and parallel to the columns. The failure pattern of columnar ice loaded biaxially across the columns is known to change under increasing confinement (Iliescu & Schulson, 2004 Renshaw & Schulson, 2001 Schulson & Nickolayev, 1995 Smith & Schulson, 1993 Wachter et al., 2009). The strength is sensitive to the direction of loading and the confinement ratio. The behavior in a brittle regime is considered here. 1.1 Splitting-to-Spalling Transition of Columnar Iceĭepending on the confinement and strain rate, columnar ice exhibits both ductile and brittle behavior under biaxial compression across the columns. Crack initiation in S2 ice is considered here. 45–46): S1 ice, in which the c axes are preferred in vertical orientation S2 ice, in which the c axes are randomly oriented in horizontal plane and S3 ice, which is similar to S2 ice, but the c axes are parallel in the horizontal plane. The modeling is based on the wing crack approach proposed by the author (Kolari, 2017).ĭepending on the orientation of the crystallographic c axes, natural columnar ice can be divided into three basic variants (Michel & Ramseier, 1971 Schulson & Duval, 2009, p. The primary objective is to formulate a new three-dimensional model for crack initiation in columnar ice and verify the model's ability to capture the splitting-to-spalling transition in a brittle regime. The transition of failure modes plays a significant role in the process. Simulation of the failure process based on observed physical mechanisms is of importance in the safe design of offshore structures. Spalling of columnar grains close to the ice edge has been observed to precede the development of crushed ice in the contact zone (Fransson, 2001 Kärnä & Muhonen, 1990). Ice loads exerted on structures are limited by the failure process of the ice during the interaction. Crushing of ice is an important failure mode during impact and interaction with vertical offshore structures.
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