TENSEGRITY TENSILE DISMEMBERMENT DEVICE

NOTES ON THE

TENSEGRITY TENSILE DISMEMBERMENT DEVICE

The device presented here represents a new approach to machines of cruel and unusual punishment. Currently it is only a loose concept, however the elementary mechanics of its operation have been analysed and refined to a point where they can be deemed sound for circulation.

The device is essentially a machine for dismembering a human body. The machine generates a tensile force which can be applied to two points on a human body (envisaged to be the wrists and ankles). The body then has a gradually increasing axial load applied to it. This is eventually sufficient to separate the shoulder joints. The dismemberment will compromise the device’s structural integrity causing it to collapse.

The device is an assembly of three compression-loaded struts and nine tension-loaded tendons forming a static tensegrity structure. As with all tensegrity structures, each member is placed in pure tension or compression. As no bending moments act upon them, the chance of members buckling is minimised. The structure is thus extremely rigid and exceptionally light, the importance of which will become apparent shortly.

The tensile force that serves the device’s primary function is generated from the physical properties of the materials from which it is constructed. All substances (there are of course obvious exceptions) expand and contract as temperature rises and falls. When a piece of any solid material is fixed at two axially located points and heated it will be loaded in compression and in tension if it cools. This Device’s design revolves around harnessing the force generated by a material contracting as it cools and imparting this tensile load upon a human subject. This is achieved by using the body of the subject as a link between the main tendon material and the fixed point at the base of the adjacent strut. The material in the tendon is cooled causing it to contract, applying a tensile load to subject.

The generation of tensile force in this manner can be controlled by; the type of material, the length and the circumference of the tendon. One can predict how the tendon would behave if one can predict the change in temperature. The device is intended for outdoor installation where it responds to diurnal temperature variations. Specifically, its optimal performance is achieved with a diurnal temperature variation of 40°C, something found only in desert areas. The material selected for the tendon had to have a reasonably high coefficient of thermal expansion, however this is only a measure of a change in dimensions when expansion or contraction is unrestricted. To guarantee the generation of force through contraction, elasticity (indicated by Young’s Modulus) must be minimised as the tendon will potentially negate much of the contraction by elastic elongation. Polycarbonate plastic is used at this point. A 50m tendon with a diameter of 200mm would generate a maximal force of 150kN - sufficient for dismemberment.

The rest of the structure is designed in sympathy with this active tendon. Tensegrity structures tend to absorb forces globally. To prevent the cooling tension being dissipated, the struts and passive tendons need to be of materials exhibiting dramatically greater stiffness than polycarbonate. Secondly, thermal coefficient is a consideration in the strut material. Any contraction in these as the temperature drops reduces the tensile stress imparted on the subject. Finally, the entire structure must remain extremely light for a structure of this scale. The heavier the structure the greater the preload stress required for stiffness. If too high the preload stress alone would tear the subject apart immediately rather than the gradual tearing over time required of this device.

The struts are silicone carbide tubes. The ceramic material exhibits almost nil thermal contraction in concert with high a high Young’s modulus make it appropriate for this purpose. The passive tendons are single-walled carbon nanotube ropes. Carbon nanotubes offer the highest strength-to-weight ratio of any material known to man and a staggering Young’s modulus of 1TPa making them ideal for this purpose. This combination offers the most optimal combination of characteristics in currently available materials.