Rupture of a V-thread observed in the infrared!

An Abalakov thread (also known as V-Thread) named after the Soviet climber Vitaly Abalakov is a common protection system in ice climbing.

It is used especially while rapelling since to build it, one needs only an ice screw and a piece of cord and avoid leaving expensive gear behind.

It is very safe if build properly.

According to work done by Beverly J. and Attaway W.(1), the greater the area encircled by the abalakov anchor, the more likely it is to be a stronger anchor so a long (21 cm for example) ice screw along with a 7 mm minimum diameter cord are recommended (2).

During the 2020 edition of the Grimpe en Ville festival, we had the chance to use a high-speed infrared camera from the company Telops, based in Quebec, to capture images of abalakov ruptures during a workshop led by André Laperrière . This high-tech equipment is sensitive to the temperature emitted by objects.

For this demonstration, an abalakov was constructed using a 16cm ice screw (shorter than recommended) and a thinner cord, 6mm. Building it this way allows us to apply enough force to make it give way! The abalakov was loaded using a hand puller and the applied force was measured with a dynamometer. Figure 3 shows a video of the abalakov breaking taken by a conventional camera.

Despite its relatively poor construction, this abalakov withstood up to 9.5 kN, which corresponds to 2135 pound-force (lbf). Even if this is not what is recommended, it would therefore be strong enough for rapelling! Figure 4 shows the same abalakov filmed with the high speed infrared camera. The video was slowed down considerably.

Figure 5 presents additional information revealed by the thermal camera. A temperature increase is observed on the tensioned knot, at the point of attachment of the carabiner, as well as on the section of cord under pressure behind the ice column. When the column of ice gives way, we can see a temperature elevation of 2-3 °C at the place where the string applied pressure.

Figure 6 shows the increase in temperature as a function of time at three places in the image: the cord around the ice (top), the knot (center) and the attachment point connecting the cord to the carabiner (bottom). The double fisherman’s knot shows a significant increase in temperature (+ 7 °C). Although the temperature increases in the two other places, the cord and the carabiner, the tempereture rise is less important than at the knot where there is a lot of friction generated. With an abalakov constructed with a longer ice screw, it would have been interesting to see if and where the cord would have given way. Considering the increase in temperature at the knot, it is conceivable that it would have given way there.

The use of a high speed thermal camera makes it possible to visualize invisible processes and to better understand specific aspects of abalakov! Additional data obtained with this camera would allow further analysis.

References:

1. « Ice Climbing Anchor Strength: An In-Depth Analysis » by J. Marc Beverly, Stephen W. Attaway 2009
2. https://www.petzl.com/US/en/Sport/Rappelling-on-an-abalakov?ActivityName=Ice-climbing