Notch-acuity effects on the fracture toughness of saline ice

Abstract

ABSTRACT. Dynamic ocean-induced loading of ice has recently prompted interest in the fatigue strength of ice and, consequently, aspects of the fracture testing of ice need to be examined. One aspect in fracture testing, the effects of notch acuity on the apparent fracture toughness (J(Q) of saline ice, was investigated in this study using four groups of single-edge notched-bend specimens with different crack-(or notch-) root radii, fabricated by four different methods; namely, drilling a small hole of two different radii at the crack tip, cutting a crack with a band saw and using a hand-held razor blade to scribe a sharp crack. For this study, tests were performed on saline ice using one crack length and orientation, constant thickness and constant temperature (-25°C). The mean values and the standard deviations of the apparent fracture toughness of the specimens with blunt notches were higher than those with sharp cracks. The results presented in a plot of fracture toughness versus ..JP, where p is the crack-tip radius, provide a preliminary estimate of the required notch acuity for fracture-toughness testing of saline ice.

Fracture toughness and crack growth of brackish ice using chevron-notched specimens

“…As stated above, only a 1.5% difference was detected using FIFT instead of the test set-up used on AÍ specimens by Bubsey and others (1982) and Shannon and others (1982). Furthermore, in recent tests, a 40% increase in compliance was found when calibrating FIFT on a PMMA RTCLWL specimen compared with the compliance obtained using the stiff loading device of DeFranco and Dempsey (1991). This situation can be improved.…”

“…Stable crack growth, in the situation of continuous quasi-static growth, has not been obtained in ice. Instead, crack-jumping is observed where the crack grows abruptly over a distance and then arrests (DeFranco and Dempsey, 1990, 1991; Parsons and others, 1988, 1989) on both fresh-water and sea ice. This behavior may be attributed to a decreasing crack-growth resistance of the ice.…”

“…The third term on the righthand side of Equation (11) arises from the effect of the increasing crack-front length with crack growth. The above concept has been used both for the double torsion (DT) specimen, (Parson and others, 1989) and for the reverse tapered crack line wedge loaded (RTCLWL) geometry developed by DeFranco and Dempsey (1991) *. Figure 8 shows a plot of the normalized gsf for the DT, RTCLWL and SRCN (cf.…”

“…Figure 8 shows a plot of the normalized gsf for the DT, RTCLWL and SRCN (cf. DeFranco and Dempsey, 1991). It is instructive to note that the geometry of every specimen shows negative gsf for all crack lengths.…”

“…The stable crack-growth characteristic of sea ice and fresh-water ice is desirable for a number of reasons: it permits the crack-growth resistance, R, to be determined as a function of crack velocity, ȧ and amount of crack growth, Δa ; it permits the design of controlled experiments; it permits the toughening effect of the micro-structure on the crack growth to be determined and it permits the evaluation of the critical energy-release rate, G 1c . Crack stability and growth on ice have only lately received any attention (Parsons and others, 1988, 1989; DeFranco and Dempsey, 1990, 1991). Controlled crack propagation may often be achieved simply by the choice of the appropriate specimen geometry.…”