Pykrete Pykrete Norton Juster Category="Composite materials"Pykrete is a Composite material made of approximately 14% Sawdust (or, less frequently, Wood pulp) and 86% Ice by weight, invented by Max Perutz and proposed during World War II by Geoffrey Pyke to the Royal Navy as a candidate material for making a huge, unsinkable aircraft carrier, Project Habbakuk, actually more of a Floating island than a ship in the traditional sense. Pykrete has some interesting properties, notably its relatively slow melting rate (due to low thermal conductivity), and its vastly improved strength and toughness over pure ice, actually closer to Concrete. Pykrete is slightly harder to form than concrete, as it expands while freezing, but can be repaired and maintained from the sea's most abundant raw material.

History

Pyke managed to convince Lord Mountbatten of the worth of his project some time around 1942, and trials were made in two locations in Alberta in Canada. Blocks of Pykrete were attacked with various explosives and it was found that a charge corresponding to a torpedo warhead would have made only a minor dent in the planned Habbakuk carrier.

At the Quebec Conference of 1943 Mountbatten brought a block of Pykrete along to demonstrate its potential to the bevy of admirals and generals who had come along with Winston Churchill and Franklin D. Roosevelt. Mountbatten entered the project meeting with two blocks and placed them on the ground. One was a normal ice block and the other was Pykrete. He then drew his service pistol and shot at the first block. It shattered and splintered. Next, he fired at the Pykrete to give an idea of the resistance of that kind of ice to projectiles. The bullet ricocheted off the block, grazing the trouser leg of Admiral Ernest King and ending up in the wall. The Admiral was impressed by Mountbatten's unorthodox demonstration. Thus, the small pilot project was given the go-ahead, but the main Project Habbakuk was never put into action. The funds simply were not available due to other WWII projects.

Durability

Pykrete has a crush resistance of greater than 3,000 pounds per square inch (21 MPa) so a one-inch (25 mm) column could support the weight of a typical car. The wood pulp also makes the pykrete stable at higher temperatures. If a .303 Caliber bullet is fired at the pykrete, it will penetrate only 6.5 inches (16.5 cm).

For example:

[image][image]
The above image shows a 1 gallon milk jug filled with a 10% mixture (by weight using sawdust). The above image shows that same milk jug after being shot with a .243 rifle at approximately 100 meters. The Winchester catalog lists stats for a .243 bullet: 100 grain (6 g) bullet 1,945 ft·lbf (2637 J) energy.

[image][image]
The above image shows a one inch (25 mm) thick 50% mixture (by volume using shredded wood mulch) hit by a single 7.62 x 39 mm rifle round fired from 30 feet (10 m) which bounced off the surface. It took an additional 15 rounds of .223 fired from 15 feet to crack the block.The above image shows a two inch (50 mm) thick 50% mixture (by volume using shredded wood mulch) hit by a single 7.62 x 39 mm rifle round fired from 30 feet (10 m) which bounced off the surface. It took an additional 7 rounds of 7.62 x 39 mm fired from 15 feet (5 m) to penetrate the block.

Uses

Pykrete can be easily formed using water and common pulp, such as toilet paper or paper towels. Basically anything you can mold with this wet pulp will freeze and be extremely hard and cold.

External links

References