SAMCoT - Annual Report 2015

SAMC

• ANNUAL REPORT 2015

Fracturing of ice:

In 2015, Dr Wenjun Lu continued his research work cover-

ing the fracturing of sea ice. In addition to the frequently

observed splitting failure mode, some other important

out-of-plane failure modes were identified and studied

theoretically. Figure WP4_3 depicts the so called ‘radial

cracking’ of an ice floe under a vertical contact load that

has been studied numerically. The Figure shows how the

radial crack propagates (i.e.

= 2 ,…, 80 percent of the floe

size) within ice floes of different sizes (i.e., n=1, 4, 8 is an

increasing size number that represents the ratio between

floe size and the characteristic length of a plate on an

elastic foundation). In short, this figure shows that small

ice floes fail by radial cracking while large ice floes fail by

circumferential crack formation.

Combining with previous studies, all these different failure

modes constitute different scenarios during ice-floe ice

interactions. The ability to capture these different failure

modes will give a reasonable estimate of the ice fracturing

load depending on floe ice’s size, confinement and the inter-

action speeds. It is expected that the analytical solutions of

these different failure modes will be implemented in the

numerical simulator so as to cover a simulation over a

large temporal and spatial scale.

Apart from the fracturing of a single ice floe, the practical

advantage of parallel channel-induced fracturing events,

which are beneficial for an ice management operation, also

caught Lu’s eye. Its fracture principle is similar to other

fracture events. A series of theoretical and experimen-

tal efforts have been made to study the parallel channel

fracturing processes. The objective is to study what paral-

lel channel spacing would lead to an efficient ice manage-

ment operation (i.e. to better control the broken ice size

within neighbouring channels).

Moreover, as a preparation for the full tests in March 2016

to acquire the fracture properties of sea ice, a trial test

was carried out in March 2015 together with a preliminary

theoretical analysis on the fracture test design (see Figure

WP4_4). The trial test was conducted at Svea, Spitsbergen.

The test was theoretically designed and the equipment was

tested in the field. The Ditch Witch trencher proved to be

an effective tool for cutting large ice sheets. Based on the

experience obtained in this trial test, a new test campaign

is scheduled for March 2016. The objective of this test is

to acquire the fracture properties of sea ice (e.g., fracture

toughness, fracture energy and the traction-separation

curve). These quantities are important in describing the

fracturing process of sea ice, especially considering that

the traction-separation curve is an indispensable material

property in computational mechanics used to simulate the

fracture initiation and propagation within most materials

(e.g., concrete, metal, fibre reinforced plastics, etc.)

Figure WP4_3. Continuation of theoretical studies on different

fracture patterns of ice floes (e.g. different out-of-plane failure

scenarios are depicted depending on the floe sizes).

Figure WP4_4. A trial campaign in the field to acquire the

fracture properties of sea ice.

Photo: Sveinung Løset