Notch Sensitivity of First‐Year Sea Ice

Tests were carried out in Resolute NWT, Canada, (74°43′N, 95°04′W) on first‐year sea ice to determine for the first time the notch sensitivity of first‐year sea ice. A displacement feedback control was used on a soft portable testing frame to apply a calculated strain rate of 10⁻³ s⁻¹ at the extreme tensile fiber of the beam. An ice beam $0.1m\times 0.1m$ in cross section, 1.0 m long was loaded in four‐point bending, the constant moment region was 0.5 m long. In this region three identical cracks were prepared with lengths of 0 to 50% of the thickness of the beam. Beams with prepared cracks 1.5 mm long fractured at sites other than a prepared crack in nine out of 16 samples. In the 81 other beams, the crack initiated in the first prepared crack 29 times, in the second 32, and in the crack last sharpened, 20 times. The nominal failure strength was calculated using the unbroken ligament as the thickness, and it dropped to one‐half the tensile strength at $a/w=0.25$, but the fracture toughness did not drop from 190 kNm^−3/2 to 124 kNm^−3/2 until $a/w=0.5$.